Effect of shade area on performance and welfare of ...

Effect of shade area on performance and welfare of short fed feedlot cattle M. L. Sullivan, A. J. Cawdell-Smith, T. L. Mader and J. B. Gaughan J ANIM SCI published online April 8, 2011

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Effect of shade area on welfare of cattle

Effect of shade area on performance and welfare of short fed feedlot cattle1 M. L. Sullivan*, A. J. Cawdell-Smith*, T. L. Mader†, and J. B. Gaughan*2 *School of Agriculture and Food Sciences, The University of Queensland, Gatton, Qld. Australia 4343 †

Haskell Agricultural Laboratory, University of Nebraska-Lincoln, 57905 866 Rd. Concord,

Nebraska, USA 68728

1

This study was funded by Meat & Livestock Australia P.L., Nth Sydney, NSW, Australia.

2

Corresponding author: School of Agriculture and Food Sciences, The University of Queensland, Gatton, Australia. [email protected]

1 Downloaded from jas.fass.org by guest June 17, 2012 Published Online First on April 8, 2011 ason doi:10.2527/jas.2010-3152

ABSTRACT: One hundred twenty-six Black Angus yearling heifers were used in a 119-d study to assess the effect of shade allocation (0 m2/animal, 2.0 m2/animal, 3.3 m2/animal, 4.7 m2/animal) on performance and welfare of feedlot cattle. Shade treatments were replicated 4 times and noshade was replicated twice. Shade was provided by 70 % solar block shade cloth, attached to a 4m high frame with north-south orientation. Cattle were randomly allocated to a pen (9/pen; 19.2 m2/animal) within treatment. Performance was assessed using DMI, G:F, ADG, HCW, dressing percentage and rump fat depth (P8). Climatic data (ambient and black globe temperature, solar radiation, wind speed, relative humidity and rainfall) were recorded. From these data the heat load index (HLI) was calculated. When the daily maximum heat load index (HLIMax) < 86, individual panting score (0 = no panting, and 4 = open mouth, tongue extended), animal location (eating, drinking, under shade), animal posture (standing or lying) were collected at 0600, 1200 and 1800 h. When HLIMax was ≥ 86 these data were collected every 2 h between 0600 and 1800 h. Feed intake was recorded weekly and water intake recorded daily on a pen basis. When HLIMax was ≥ 86 mean panting score (MPS: mean of animals within treatment) was greatest (1.02; P < 0.001) for unshaded cattle compared with shade treatments, which were similar (0.82; P = 0.81). During heat waves the MPS of unshaded cattle was greater (2.66; P < 0.001) than for shaded cattle. The MPS of 2.0-m2 cattle (2.43 ± 0.13) was greater (P < 0.001) than the 3.3- (2.11 ± 0.13) and 4.7-m2 cattle (2.03 ± 0.13). The MPS of the 3.3- and 4.7-m2 cattle were similar (P = 0.09). Number standing were similar (P = 0.98) between unshaded and the 2.0-m2 treatment at 4.75 and 4.76 animals/pen respectively. Fewer (P < 0.0001) were standing in the 3.3-m2 (4.19 animals/pen) and 4.7-m2 (4.06 animals/pen) treatments. Fewer (P = 0.004) cattle were under the 2.0-m2 shade (47.1%) compared with the 3.3- (53.7%) and 4.7-m2 (53.6%) shade. Unshaded cattle had the lowest (0.085 ± 0.006) G:F ratio (P = 0.01) followed by the 4.7-m2 cattle (0.104 ± 0.006; P ≤ 0.001). There was no difference (P = 0.12) between the 2.0- and 3.3-m2 treatments. There were no differences (P > 0.10) for final BW, HCW, dressing percentage and P8. Cattle with access to shade had lower panting scores, which suggests improved welfare, and had better feed efficiency. Shade reduced the intensity of heat load, but did not fully remove the impact. Key words: Shade area, Feedlot cattle, Heat stress

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INTRODUCTION Heat stress in feedlot cattle occurs when total body heat gain, which is the combined effects of environmental and metabolic heat, is in excess of the animals’ ability to dissipate body heat. The physiological responses to heat load are dynamic and complex. Individual animal responses are influenced by genotype, age, body condition, nutrition and health status. In order to cope with heat stress cattle exhibit changes in behavior, physiology and immune function (Mitlöhner et al., 2002). Respiration rate and body temperature increase, and feed intake generally decreases (Nienaber et al., 2003). Cattle will also alter their posture and seek shade when heat stressed (Robertshaw, 1985). Shade can provide immediate relief from the effects of solar radiation, improve performance (Blackshaw and Blackshaw, 1994; Mitlöhner et al., 2001; Gaughan et al., 2010a), and reduce mortality of feedlot cattle that are exposed to extreme heat load events (Busby and Loy, 1996; Entwistle et al., 2000). There are, however, inconsistencies in the performance outcomes attributed to shade between studies, for example Clarke and Kelly (1996) reported that access to shade did not improve cattle performance. Furthermore inconsistent DMI for cattle with or without access to shade have been reported (Mader et al., 1997; Brown-Brandl et al., 2005). The differences may be due to variations in nutrition, genotype, the type of shade material, shade structure and area of shade per animal. The effectiveness of various shade materials for stress reduction in beef cattle (Eigenberg et al., 2010), and shade area requirements (m2/animal) for dairy cows (Schütz et al., 2010) have been reported. However the optimal shade area for feedlot cattle has not been determined. The objective of this study was to investigate the effect of variations in shade area (m2/animal) on performance, carcass characteristics and welfare of feedlot cattle, housed in outside pens in a subtropical environment during summer.

MATERIALS AND METHODS One hundred twenty-six Black Angus yearling heifers (BW = 350 ± 45 kg) were used to determine the effect of 4 shade treatments on short fed (119 d on feed) feedlot cattle. The study was undertaken at The University of Queensland (UQ) research feedlot (Latitude: -27.54 S; Longitude: 152.34 E; 94 m AMSL) (Figure 1) and was approved by the UQ Animal Ethics 3 Downloaded from jas.fass.org by guest on June 17, 2012

Committee. The study commenced in mid summer (2 January) and finishing in the autumn (30 April). The summer climate is characterized by high temperature, high solar load and high humidity. The 30-yr means for the months January to March (BOM, 2010) are as follows. Mean maximum temperature = 30.8 oC, mean minimum temperature = 18.4 oC; mean rainfall = 349.9 mm; mean daily solar radiation (day light h) = 378 W/m2, and mean daily relative humidity = 54 %. On average (30-yr means) for the months January to March, 57 d will exceed 30 oC, and 9 d will exceed 35 oC. The 30-yr means for April (BOM, 2010) are: Mean maximum temperature = 27.4 oC, mean minimum temperature = 17.1 oC; mean rainfall = 57.3 mm; mean daily solar radiation = 399.5 W/m2, and mean daily relative humidity = 56.0 %. Hours of sunlight at the commencement of the study was approximately 13.5 h/d, and approximately 11.5 h/d by the end of the study. The average time of sunrise and sunset during the study were: January (0510 h and 1850 h), February (0535 h and 1830 h), March (0550 h and 1815 h) and April (0610 h and 1745 h). The shade treatments used were: (i) no shade, (ii) 2.0 m2/animal, (iii) 3.3 m2/animal, and (iv) 4.7 m2/animal (Figure 2). Each shade treatment was replicated 4 times and the no-shade was replicated twice. The no-shade was only replicated twice due to concerns about the welfare of the unshaded animals. Shade was provided by 70% solar block, black shade cloth (Darling Downs Tarpaulins, Toowoomba, Australia), attached to a 4.0 m high × 5.7 m wide × 7.5 m long steel frame (RPM Rural Products, Gatton, Australia) with a north-south orientation. Steel springs (140 mm × 25 mm) were attached to the longitudinal edges of the shade cloth at 1 m intervals. The end of the springs not attached to the shade cloth were attached to a 12-mm steel cable, which was attached to the top of the steel frame. The short end of the shade cloth was reinforced by a 30-mm wide steel rod and was bolted to the steel frame. For all shade areas the shade cloth was the same length (7.5 m) but varied in width to give the desired shade area. Cattle were randomly allocated to a pen (9/pen; 19.2 m2/animal) within a treatment and remained in the pen for 119 d. The pens were fixed for shade treatment. Pen maintenance was undertaken every 30 d. This included manure removal and repairs to the pen floor (i.e. filling in holes as required). The time taken for pen maintenance and pen floor repairs was recorded against each treatment pen. On induction into the feedlot (d 0) the cattle were weighed, ear tagged, treated against internal and external parasites (Cydectin; Fort Dodge Australia P/L, Baulkham Hills, NSW, Australia), vaccinated against clostridial disease (7 in 1; Pfizer Animal Health, West Ryde, NSW, 4 Downloaded from jas.fass.org by guest on June 17, 2012

Australia), bovine ephemeral fever (BEF) (Fort Dodge Australia P/L, Baulkham Hills, NSW, Australia) and trivalent tick fever (Tick Fever Centre, Wacol, Qld. Australia). The cattle were re-vaccinated for 7 in 1 and BEF on d 36.

Experimental data Climatic data. Climatic conditions (ambient temperature, °C (TA), relative humidity, % (rh), black globe temperature (in sun), °C (BG), black globe temperature (under 70% shade cloth), °C (BG) and wind speed, m/s (WS) were recorded at 10 min intervals from an automated weather station (Esidata MK-3; Environdata Australia P/L, Warwick, Qld., Australia). Rainfall data was collected daily at 0700 h. The weather station was located in a laneway close to the center of the feedlot. From these climatic data the heat load index (HLI) was calculated using the following equation (Gaughan et al., 2008): HLIBG>25 = 8.62 + (0.38 · rh) + (1.55 · BG) – (0.5 · WS) + [e(2.4 – WS)], and HLIBG 86.0. The AHL was divided into 4 heat load categories (Gaughan et al., 2008): (1) low heat load, when the AHL is < 10; (2) moderate heat load, when the AHL is 10.1 to 20; (3) high heat load, when AHL 20.1 to 50, and extreme heat load (4) when the AHL is >50. In addition, HLI and AHL were combined (HLI × AHL) to produce 4 risk categories, which were used to gain a better understanding of the relationship between climatic conditions, body heat content and panting. The following categories were: low risk (low: HLI < 70; AHL < 10), moderate risk (mod: HLI 70.1 to 77; AHL 10.1 to 20), high risk (high: HLI 77.1 to 86; AHL 20.1 5 Downloaded from jas.fass.org by guest on June 17, 2012

to 50) and extreme risk (ext: HLI > 86; AHL > 50). When exposed to an extreme risk event death of some unshaded cattle is likely to occur. Heat waves were considered as a separate category. For this study a heat wave was defined as 3 or more consecutive days where the mean HLI between 0800 h and 1800 h was ≥ 86, and AHL ≥ 40. Nutrition and feeding. Feed was provided ad-libitum from 2-t self feeders (Warwick Cattle Crush Company, Forest Hill, Qld., Australia), which were positioned to feed 2 replicate shade treatment pens (treatment pair). The feeders were separated internally along the longitudinal center line into 2 equal halves. The divider was a solid steel panel which was fixed to the floor of the feeder and was in contact with the lid of the feeder when the lid was closed. The feeder space (one side of the self feeder) was 1550 mm (166.7 mm/animal), which complied with the recommendation provided by the Australian Welfare Code for Cattle (SCAAHC, 1992), for cattle accessing a self feeder. The same type of feeders was used in the unshaded pens. The self feeders were filled each week (feed weighed into each half), and feed intake calculated on weekly basis for each treatment pen. Any feed removed from the feeders was weighed out. Feed samples (approximately 500 g) were collected at each feed delivery and then frozen at -20 °C for later dry matter and nutrient analysis. The diets used and their nutrient specifications are presented in Table 1. Prior to the commencement of the study DMI was estimated using the following equation: DMI = 4.54 + 0.0125 · initial BW (NRC, 1996). Based on this equation the expected mean DMI over the duration of the study was 8.92 kg/animal. Water was available ad libitum to the animals via 1,200-L plastic troughs (Rapid Plas 1200 L Pro Tub) located in each of the shaded pens (330 mm/animal). The cattle in each unshaded pen accessed a 1,500-L water trough (332 mm/animal). There was sufficient water trough space in each pen for all animals to access the water at the same time, however this could be reduced to 6 animals if dominant animals stood side on to the trough. Water meters were attached to each trough and water usage was recorded each day at 0700 h. Weighing. Cattle were weighed at the commencement of the study (d 1), 3 times during the study (d 36, 51 and 79) and the day before exiting the feedlot (d 119). It was initially planned that cattle would be weighed at 25-d intervals, however due to hot environmental conditions weighing was postponed a number of times. All weighing commenced at 0800 h. There was no feed or water curfew prior to weighing.


Animal data. A number of HLI thresholds have been determined for different cattle genotypes (Gaughan et al., 2008; 2010b). When cattle are above a specific threshold their ability to dissipate body heat is reduced, and there is a subsequent increase in body temperature. The HLI threshold for healthy Angus cattle, in a feedlot, without access to shade is 86. The frequency of data collection was determined on the basis of the predicted maximum HLI on a given day. The following animal data was collected. Individual panting score, number eating; defined as head in feeder or chewing feed at feeder, number drinking; defined as drinking or animal at water trough with water dripping from muzzle, number standing and lying under shade, and the number standing or lying in sun (but not eating or drinking). These data were collected at 0600, 1200 and 1800 h on days when the predicted maximum heat load index (HLIMax)1.2 high stress (Gaughan et al., 2008). All animal observations were made from outside of a pen so that the PS, behavior and animal location within pens was not altered by the presence of the observer. The cattle used in the study were accustomed to frequent human activity outside of the pens and rarely responded (apart from occasionally looking) to the presence of an observer outside of a pen. Individual animal health records were utilized to assess the cost for treatment of ill health within each treatment. Carcass measurement. At slaughter individual hot carcass weight (HCW) was obtained. Twenty-four hours after slaughter P8 fat depth was obtained. The P8 fat depth is obtained by 7 Downloaded from jas.fass.org by guest on June 17, 2012

measuring the amount of fat over the gluteus muscle on the rump. The site is located at the intersection of a line through the pin bone parallel to the chine and its perpendicular through the third sacral crest (Reverter et al., 2000). Dressing percentage was calculated using the final BW obtained on d 119 and HCW obtained on d 120. Light intensity and pen surface temperature. Light intensity (Lux) (Q-1400 Digital Lux Meter, Dick Smith Electrical, Sydney, NSW) and pen surface temperatures (Raynger MX, Raytek, Santa Cruz, California) were obtained under the shade and in the unshaded pens on 22 occasions. These occasions were determined on the basis of the maximum HLI (HLIMax) on a particular d. Data was collected on 10 occasions when HLIMax≥86, 10 occasions when HLIMax≤77, and on 2 occasions following rain. Pen surface temperature was measured on dry, wet, shaded and unshaded surfaces within the shaded pens; and dry, wet and unshaded surfaces within the unshaded pens. The surface temperature of a grassed area adjacent to the feedlot was also obtained on each occasion. Surface temperature was measured by holding the infrared sensor 1 m above and facing the ground. On each occasion measurements were made between 1200 h and 1400 h. Pen surface temperature was measured in each pen on each occasion and the mean of readings relating to each surface type were calculated.

Statistical Analysis The daily (day) HLI, AHL, HLI categories, AHL categories, and their interactions were used in the analysis of all data apart from DMI and water usage. Weekly means (week) of HLI, AHL, HLI categories and AHL categories were used in the analysis of DMI and water usage. All treatment effects (P < 0.05) were evaluated against a pen level variance term rather than an animal level sampling term. Dry matter intake and water usage were analyzed using a repeated measures model (PROC MIXED, SAS Inst., Inc., Cary, NC). The model included the effects of treatment (area of shade), week, and the interaction of week × treatment as fixed effects, with pen as a random effect. Location in pen (eating, drinking, in shade or in sun), posture (standing or lying), and MPS were analyzed using repeated measures (PROC MIXED) using REML estimation. The model included treatment (area of shade), time of day (0600, 0800, 1000, 1200, 1400, 1600, 1800 h), period (period 1: 0600 to 0900 h; period 2: 0901 to 1200 h; period 3: 1201 to 1500 h; 8 Downloaded from jas.fass.org by guest on June 17, 2012

period 4: 1501 to 1800 h), day, and the interaction of day × observation time as fixed effects, with animal included as a random effect. Least squares means were estimated for the various treatment effects. The same models was used to determine the impact of heat wave conditions on location in pen (eating, drinking, in shade or in sun), posture (standing or lying), and MPS. Carcass data (HCW, P8 fat depth and dressing percentage), ADG and G:F were analyzed with ANOVA procedures (PROC GLM) appropriate for a completely random design. Independent variables were shade treatment and final BW. Least squares means were estimated for treatment effects. In addition, estimates and SE were derived for the average change due to shade. When significance (P< 0.05) was indicated, the means were separated using Tukey’s Studentized range test.

RESULTS Animal health Three heifers in the unshaded treatment, 2 in the 2.0-m2 treatment and 1 in the 4.7 m2 were treated for bovine respiratory disease (BRD) complex. This was the only health problem encountered during the study. The cost of BRD treatment was allocated across treatments and the cost then proportionally allocated to each animal within a treatment. On an animal/treatment basis the cost (US$) of treating BRD were $3.30, $2.20 and $1.10 respectively for all animal within the unshaded, 2.0-m2 and 4.7-m2 treatments. Pen cleaning, maintenance and repair The pens were cleaned on d 30, d 62, d 100 and d 120 of the study. The final cleaning was undertaken after cattle had exited the feedlot. Maintenance and repair time was determined on a treatment basis. Because only 2 unshaded pens were used the time allocated to this treatment was doubled to allow an adequate comparison to be made to the shade treatments. The unshaded treatment and the 4.7-m2 treatment required the least amount of floor surface maintenance and repair time (6.3 h each) and the 2.0-m2 treatment the most (7.9 h). The 3.3-m2 treatment required 6.6 h of maintenance and repair. The greater time allocation to the 2.0-m2 and 3.3-m2 treatments was due to damage to the pen surface floor under the shade structure. Climatic data The HLI and AHL (unshaded cattle) are presented in Figure 3. A summary of the monthly climatic data over the duration of the study is presented in Table 2. Over the duration of 9 Downloaded from jas.fass.org by guest on June 17, 2012

the study rain occurred on 26 d (total rainfall = 175.5 mm). The majority of the rain occurred between d 0 and d 30 and was characterized by 2 storms which resulted in rain on d 25 (44.0 mm) and d 26 (31.8 mm). The maximum TA was greater than 35 oC on 18 d between d 0 and d 89. Between d 0 and d 31 maximum TA exceeded 35 oC on 13 d. The highest TA recorded during the study was 39.9 oC (d 29). Conditions were often overcast and mild between d 32 and d 59. The maximum TA recorded during this period was 34.7 oC. Between d 60 and d 89 maximum daily temperature exceeded 35 oC on 5 d, with the maximum of 38.8 oC being recorded on d 70. Over the duration of the study 4 heat waves were encountered; d 9 to d 12, d 19 to d 29, d 59 to d 62 and d 65 to d 69 (Figure 3). During the study period mean monthly maximums were slightly above the long term (95 y) averages (d 0 to d 31, +1.7 oC; d 32 to d 60, +1.4 oC; d 61 to d 91, +2.9 oC and d 92 to d 119, +2.1 oC). Accumulated heat load The maximum AHL for shaded cattle was 36.2 compared with 102.7 for unshaded cattle. The cattle with access to shade had an AHL > 30 once, in contrast the AHL for the unshaded cattle exceed 30 on 30 d of the study (Table 3). The 2nd heat wave (d 19 to d 29) was the most severe of the 4 heat waves encountered. High TA and humidity between d 19 and d 29 resulted in the maximum unshaded AHL recorded during the study (102.7 units). The period from d 25 to d 28 was a severe 4 d period for the unshaded cattle, and if it were not for a significant increase in wind speed (due to a frontal change) on the afternoon of d 27, and an 8 oC drop in TA (30.5 oC to 22.4 oC) over a 30-min period on the same day the study would have been terminated due to welfare concerns for the cattle. Pen Surface Temperature The intensity of sunlight reaching the ground under the shade at 1200 h was 77 % lower than that reaching the unshaded ground (182.0 ± 24 and 838.6 ± 95 Lux respectively). The mean ground surface temperature (measured using an infrared thermometer) in the unshaded pens was 56.7 ± 6.6 oC (range 43.8 to 64.2 oC). In the shaded pens the mean ground surface temperature in the sun was 55.9 ± 8.2 oC (range 39.0 to 62.5 oC). The ground surface temperature under the shade was 20 oC lower. The mean surface temperature under shade was 38.4 ± 3.9 oC (range 32.3 to 39.8 oC). The mean temperature in unshaded grassed areas (no cattle) was 44.5 ± 4.2 oC. When possible, wet ground under the shade and in the sun were also assessed. The mean 10 Downloaded from jas.fass.org by guest on June 17, 2012

temperature of the wet ground surface in the unshaded areas was 41.2 ± 5.3 oC (range 37.6 to 44.8 oC). Similar values were obtained for unshaded sections of the shaded pens. Wet areas under shade were approximately 6 oC lower than the dry surfaces. When HLIMax≤77 the fully exposed surface temperatures did not exceeded 35 oC (mean = 32.8 ± 1.9 oC). On days when rain fell or days immediately following a rain event the ground surface temperature was 30.2 ± 3.2 oC (range 28.1 to 33.4 oC). Relationship between MPS and HLI A MPS > 1.2 is indicative of excessive heat load and a high level of risk for the animal, and a MPS > 2.0 is indicative of an extreme level of risk for the animal. Over the duration of the study the MPS of the unshaded cattle (0.85 ± 0.02) was greater (P < 0.001) than for the shade treatments at 0.65 ± 0.01, 0.67 ± 0.01 and 0.65 ± 0.01 respectively for the 2.0-m2, 3.3-m2 and 4.7-m2 cattle. During the heat wave events the MPS of the unshaded cattle was 2.66 ± 0.18 which was greater (P < 0.001) than the MPS for cattle in the shade treatments. The MPS of the 2.0-m2 cattle (2.43 ± 0.13) was greater (P < 0.001) than for the 3.3- (2.11 ± 0.13) and 4.7-m2 cattle (2.03 ± 0.13). There were no differences (P = 0.09) between the 3.3- and 4.7-m2 treatments. Mean panting score increased in all treatments when the HLI category shifted from cool to moderate (Figure 4). There were small changes (P > 0.10) in MPS when conditions changed from moderate to hot, and larger increases (P < 0.01) when conditions changed from hot to very hot. The largest increase was observed for the unshaded cattle. Panting scores were similar (P > 0.05) between treatments under cool, moderate and hot conditions. It was only when conditions were classified as very hot or extreme (HLI >86) that differences were seen. Under very hot conditions the mean panting score was highest (1.02; P < 0.001) in the unshaded cattle. There were no differences (P > 0.81) between the shaded treatments. Relationship between MPS and HLI × AHL categories Greater panting scores (P ≤ 0.004) were observed for all treatments as the HLI × AHL risk categories shifted from low risk through to extreme risk. When HLI × AHL was categorized as extreme risk the MPS of the unshaded cattle was greater (1.72; P < 0.0001) than the shade treatments (Figure 5). The MPS of the shade treatments were similar (P ≥ 0.19) at 1.04, 1.09, and 1.03 respectively for the 2.0-, 3.3- and 4.7-m2 treatments. When the risk category was extreme, more (P < 0.01) of the unshaded group had an individual PS ≥ 3. Cattle with and individual PS = 11 Downloaded from jas.fass.org by guest on June 17, 2012

4 were observed 12 times during the first heat wave. Nine of the observations were made for unshaded cattle (6 animals). Within the 3.3-m2 treatment a single animal was observed 3 times with a PS of 4. The MPS of the cattle in the shade treatments did not exceed the high heat load or moderate risk category (MPS = 0.8 to 1.2) except during the heat waves. Dry matter intake There were DMI differences (P < 0.001) (weekly mean treatment intakes converted to an animal/d basis) between treatments. Daily DMI of all cattle was affected by climatic conditions. Over the duration of the study mean daily DMI was greatest (P < 0.001) for the unshaded cattle (11.0 ± 0.18 kg·steer-1), followed by the 4.7-m2 treatment (10.2 ± 0.13 kg·steer-1), the 3.3-m2 treatment (8.9 ± 0.13 kg·steer-1), and the 2.0-m2 treatment (8.7 ± 0.13 kg·steer-1). The largest climate induced reductions and fluctuations in daily DMI occurred with the unshaded cattle during the first 90 d of the study. In the unshaded group DMI reduced from 9.3 ± 0.23 kg·steer-1 to 4.8 ± 0.87 kg·steer-1 in weeks that included days classified as very hot (heat wave conditions). When conditions abated the unshaded cattle increased DMI to exceed their pre-heat wave intake within 4 d. During the post heat wave periods DMI of the unshaded cattle initially increased to 12.8 ± 0.98 kg·steer-1 and remained elevated for at least 7 d before returning to pre-heat wave intakes. Although reductions in the DMI of the shade treatments also occurred during the hot periods the effects were smaller (1.2 kg·steer-1; P = 0.02) compared with the unshaded treatment. The DMI of the shaded cattle returned to pre heat wave intakes within 2 d of the heat wave abating. Over the first 90 d of the study during which time the heat waves occurred, the DMI of the unshaded treatment (11.40 ± 0.32 kg·steer-1) was lower (P < 0.001) than the 4.7-m2 treatment (12.20 ± 0.22 kg·steer-1), but greater (P < 0.001) than the 2.0- and 3.3-m2 treatments at 8.95 ± 0.22 kg·steer-1 and 10.10 ± 0.22 kg·steer-1 respectively. Over the last 29 d when climatic conditions were milder, the DMI of the unshaded cattle were similar to the first 90 d but without the heat load induced fluctuations. Water intake During 2 rain events, 3 water troughs overflowed. During the first rain event, 2 troughs overflowed; 1 trough was in a 2.0-m2 treatment pen, and the second was in a 4.7-m2 treatment pen. During the second rain event, a trough in a 2.0-m2 treatment pen overflowed. On those occasions water usage for the affected pens could not be accurately determined. Water splashing was evident in all treatments but more so for the unshaded cattle when day was categorized as 12 Downloaded from jas.fass.org by guest on June 17, 2012

very hot. There were no differences (P > 0.05) in water usage between shade treatments during the study. When the day was categorized as cool there were no differences (P = 0.89) between shaded and unshaded cattle for water usage (22.1 ± 2.6 L·heifer-1). Under moderate and hot conditions water usage was greater (P = 0.02) for the unshaded cattle at 43 ± 5.3 L·heifer-1 compared with 38 ± 3.6 L·heifer-1for shaded cattle. When day was categorized as very hot, water usage increase to 54.0 ± 3.0 L·heifer-1 for the shaded cattle and was slightly lower (P = 0.09) at 49.0 ± 2.8 L·heifer-1 for unshaded cattle. Gain:feed, growth performance and carcass assessment The G:F was lowest (0.085 ± 0.006; P < 0.01) for the unshaded cattle. There were no differences (P = 0.85) between the 2.0- and 3.3-m2 treatments at 0.117 ± 0.006, 0.115 ± 0.006 respectively. The G:F obtained by the cattle in the 4.7-m2 treatment was lower compared with the other shade treatments (0.104 ± 0.006; P = 0.03). Over the duration of the study the unshaded cattle had the lowest ADG (0.93 ± 0.05 kg·d-1; P = 0.06). There were no differences (P > 0.25) in ADG between the shade treatments from d 0 to d 119. Over the first 90 d of the study the ADG of the unshaded cattle was lower (0.74 ± 0.05 kg·d-1; P < 0.0001) than the ADG of the shade treatments (Table 3). Over the same period the ADG of the 2.0-m2 treatment was numerically lower (1.03 ± 0.04 kg·d-1; P ≥ 0.20) than the ADG for the 3.3- and 4.7-m2 treatments at 1.12 ± 0.04 kg·d-1 and 1.11 ± 0.04 kg·d-1 respectively. However, for the period d 90 to d 119 the unshaded cattle had the highest weight gain (1.36 kg·d-1; P < 0.02). There were no treatment differences for HCW (P = 0.40), dressing percentage (P = 0.79) or P8 fat depth (P = 0.37) (Table 4). Animal location in pen, activity and posture The data in this section is presented on a mean (n/9) per pen (within treatment) basis, and as overall treatment percentages. Over the duration of the study the number of cattle standing were similar (P = 0.98) between unshaded and the 2.0-m2 treatment at 4.75 and 4.76 animals/pen respectively (Table 5). Fewer (P < 0.0001) cattle were standing in the 3.3-m2 (4.19 animals/pen) and 4.7-m2 (4.06 animals/pen) treatments. Within the shade treatments fewer (P = 0.004) cattle were standing and lying under the 2.0-m2 shade (47.1%) compared with the 3.3- and 4.7-m2 shade treatments. There were no differences (P = 0.81) for total number under shade between the 3.3-m2 and 4.7-m2 shade treatments at 53.7% and 53.6% respectively. More of the unshaded cattle (21.6%; P < 0.001) were observed eating compared with the shade treatments. Within the 13 Downloaded from jas.fass.org by guest on June 17, 2012

shade treatments more (19.9%; P = 0.06) of the 4.7-m2 treatment cattle were observed eating compared with the 2.0- and the 3.3-m2 treatments at 18.0 and 18.8% respectively. Similarly more of the unshaded cattle (0.65 animals/pen; P < 0.0001) were observed drinking compared with the shade treatments. Within the shade treatments the least number of animals (0.39 animals/pen; P < 0.001) were observed drinking in the 4.7-m2 treatment. There were no differences (P = 0.64) between the 2.0- and 3.3-m2 treatments. During the heat waves 85.1, 92.1 and 91.7% of cattle in the 2.0-, 3.3- and 4.7-m2 shade treatments respectively were observed under shade (Table 6). The total number standing was lowest (P = 0.66) in 4.7-m2 treatment (6.43 animals/pen) and highest in the 2.0-m2 treatment (6.99 animals/pen). Fewer of the unshaded cattle (1.00 animal/pen; P < 0.0001) were observed lying compared with the 3.3- and 4.7-m2 shaded treatments. Numerically more (1.42 animals/pen; P = 0.07) of the cattle in the 2.0-m2 treatment were observed lying compared with the unshaded cattle. There were no differences (P = 0.96) between treatments for number of cattle observed eating. However more of the unshaded cattle (1.67 animals/pen; P < 0.001) were observed drinking compared with the cattle that had access to shade at 0.17, 0.22 and 0.36 animals/pen respectively for the 2.0, 3.3- and 4.7-m2 treatments. Relative economic return for each treatment The relative financial return (all values are in US$) on each treatment were calculated by subtracting the cost of feed, yardage, health, carcass value, and pen maintenance from the carcass value (Table 7). Based on the price of shade cloth ($3.70 m2), the initial shade cloth cost associated for each shade area (on a per animal basis) were 2.0 m2 ($7.40), 3.3 m2 ($12.21) and 4.7 m2 ($17.39). The cost of the shade structural support plus incidentals will vary depending on required loading factors for wind and snow and also local government regulations. In the current study the cost of the shade structural support and fittings less the shade cloth was $52.35 per animal. Thus, for the 2.0-m2 treatment the total cost per animal shade area was $59.75 ($7.40 + $52.35), and for the 4.7-m2 treatment $69.74.

DISCUSSION Heat stress results in production losses and is a major welfare issue. Feedlot cattle may be exposed to extremes of weather and as a result productivity and welfare may be compromised. A number of management strategies can be implemented to minimize the effects of heat stress on 14 Downloaded from jas.fass.org by guest on June 17, 2012

the performance and welfare of feedlot cattle. One such strategy is the use of shade. It is well known that shade is an efficient means of providing relief from the direct effects of solar radiation and has been shown to improve production and welfare of cattle during extreme heat events (Beede and Collier, 1986; Mitlöhner et al., 2001; Gaughan et al., 2009; Gaughan et al., 2010a). However, little is known about the optimal area (m2/animal) of shade needed to improve welfare and performance of feedlot cattle when they are exposed to hot conditions. When exposed to high heat load cattle will generally decrease DMI (Yousef et al., 1968; Hahn et al., 1992; McGovern and Bruce, 2000) and in doing so will lower metabolic rate (Leonard et al., 2001; Hahn, 1999), which reduces metabolic heat load. As expected, DMI in the current study was affected by hot environmental conditions. The use of shade can reduce the effects of hot weather on cattle and can consequently reduce the impact of the hot conditions on DMI (Mitlöhner et al., 2001; Brown-Brandl et al., 2005; Gaughan et al., 2010a). During periods of high heat load daily DMI of the unshaded cattle decreased markedly (approximately 50%) compared with the shade treatments (10%). When hot conditions abated there was a period of compensatory intake in the unshaded cattle which DMI exceeded pre heat load intake by approximately 33%. Although compensatory growth following a heat stress event is likely, the differences between the shaded and unshaded cattle were unexpected and to our knowledge has not been previously reported. The compensatory gain of the unshaded cattle in the current study is contrary to Mitlöhner et al. (2001, 2002) and Gaughan et al. (2010a) who reported that unshaded animals exposed to heat stress did not show compensatory gain when the hot conditions abated. The differences between the Mitlöhner et al. (2001), the Gaughan et al. (2010a) studies and the current study may be due to the feeding methods used (bunk vs. self feeders). Generally water intake will increase as heat load increases (NRC, 1996). In addition drinking behavior may also change. An increase in the number of drinks taken by Bos taurus heifers increased from 60 drinks per d when ambient temperature was 20 °C to 90 drinks per d when ambient temperature was 30 °C (Yousef et al., 1968). In a chamber study Beatty et al. (2006) reported an increase in water consumption in Bos taurus heifers from 17 L/animal to 29 L/animal when wet bulb temperature rose from 26 oC to 32 oC. There may also be a change in time of drinking during periods of hot weather, with night water consumption increasing from 20 L at 20 °C to 70 L at 30 °C (Yousef et al., 1968). The effect of access to shade on the drinking 15 Downloaded from jas.fass.org by guest on June 17, 2012

behavior of feedlot cattle has not been quantified. In the current study water usage increased as heat load increased, but was greater for the shaded cattle, even though the unshaded cattle spent more time at the water troughs, especially during the heat waves. In contrast over a 120-d feeding period water consumption was greater for unshaded (66.8 L) vs. shaded feedlot cattle (56.8 L) (Gaughan et al., 2010a). However, Mitlöhner et al. (2001) reported that access to shade did not affect water intake, nor the percentage of cattle observed at the water trough. It is possible that greater increase in water usage in the shade treatments relative to the unshaded treatment is due to the greater DMI of the shaded cattle during the hot periods encountered relative to the unshaded cattle. Panting score is a useful method of assessing heat load status and consequently the welfare of feedlot cattle (Mader et al., 2006; Gaughan et al., 2010b). Similar responses to the MPS seen in the current study have been reported for Angus steers with and without access to shade (Gaughan et al., 2010b). A higher MPS of Bos taurus cattle without access to shade compared to those with access to shade has also been reported by Brown-Brandl et al. (2006a). In the current study, access to shade and an increased allocation of shade area reduced the impact, but did not fully eliminate the effects of heat wave conditions. It is likely that additional management strategies will be required to further reduce the impact of high heat load on cattle. In the current study, behavioral differences in terms of standing, lying, eating and drinking were evident between the unshaded cattle and cattle with access to shade. During the heat waves, cattle with access to shade had increased standing behavior relative to unshaded cattle. However, across all treatments more cattle were observed standing during the heat waves than during the non heat wave periods. Similar results were reported by Brown-Brandl et al. (2006b) who reported that standing behavior increased from 42.0% under thermonuetral conditions to 48.1% under heat stress conditions. In contrast, Mitlöhner et al. (2001) using a shade area of 2.4 m2/animal found no statistical differences in standing behavior between shaded and unshaded heifers, at 49.17 and 46.32% standing respectively when exposed to hot conditions. Although there are some inconsistencies between studies increased standing behavior of cattle may be a good indicator of increasing heat stress (Brown-Brandl et al., 2006b), especially when considered with other factors such as panting score. Shade is beneficial for feedlot cattle exposed to hot climatic conditions; however, in research conducted in Northeast Nebraska (Mader et al., 1999), positive benefits occurred only in 16 Downloaded from jas.fass.org by guest on June 17, 2012

the early portion of the feeding period and only in cattle with wind barriers provided. In this study, 3 summer-time trials were conducted over consecutive years. Shaded and unshaded cattle were fed in pens with or without wind protection provided. Performance was similar for shaded and unshaded cattle fed in the facility without wind barriers provided; some benefit to shade was found in facilities which had wind barriers provided. In general, the response to shade occurred within the first 56 d of the feeding period, even though shade use tended to increase with time cattle were on feed. This suggests that cattle must adapt to shade or social order around and under shade before optimum shade use occurs. Although no heat-related cattle deaths occurred in this study (Mader et al., 1999), these results suggest that shade improves performance in the summer when cattle are fed in facilities that restrict airflow and for cattle that have not become acclimated to hot conditions. Once cattle are acclimated or hot conditions subside, compensation by unshaded cattle offsets much of the benefits of providing shade. Benefits of using shade would most likely be found in areas having high ambient temperature and/or solar radiation (Hahn et al., 2001). Other factors such as humidity and wind speed also need to be considered (Livestock Conservation Institute, 1970; NOAA, 1976; Hubbard et al., 1999; Mader et al., 2006). More consistent benefits of using shade would likely occur the further south cattle are fed in the U.S. Mitlöhner et al. (2001, 2002), found excellent performance results to providing shade for cattle fed near Lubbock, TX. Adjustments for solar radiation must be considered when predicting heat stress or the impact of heat stress on cattle. Kelly et al. (1950), reported feedlot ground surface temperatures in excess of 65° C by 1400 h in Southern California. The ground surface temperatures reported in the current study are similar to Mitlöhner et al. (2002) who reported a maximum ground surface temperature of 56 oC (range 43 to 56 oC) in Texas. Similar surface temperatures can be found in most High Plains feedlots under dry conditions coupled with high levels of solar radiation. In the Mitlöhner et al. (2002) study the ground surface temperature under shade (solid steel roof) was approximately 24 oC lower than the unshaded surfaces. In the current study provision of shade (70% solar block) reduced ground surface temperature under the shade by 20 oC. Shading bare ground would appear to provide an area for cattle to dissipate body heat via conduction through the ground surface, and reduces solar load, thus allowing cattle to better adapt to environmental conditions. Results of the current study will aid in determining the effects of shade and allow thermal and predictive animal response adjustments to be made, based on area of shade available per animal. 17 Downloaded from jas.fass.org by guest on June 17, 2012

Relative financial returns of the cattle within the shade area options used in the current study are a useful financial indicator but need to be viewed with caution as they are dependent on a number of variables e.g. cost of feed, cattle purchase price, cattle performance, cattle sale price, and pen maintenance. Furthermore the load bearing requirements (snow and wind), and the life expectancy of shade materials and structures need to be considered when assessing the financial viability of shade. At the location of the current study installation of shade will improve the welfare and performance of cattle over the summer months. Whether or not shade is a financially viable management option will depend on the afore mentioned variables, weather conditions and the installation cost of shade. CONCLUSIONS Access to shade improved the welfare and performance of the cattle used in this study. Provision of a shade area greater than 2.0 m2/animal does not appear to provide any additional production benefits for short-fed cattle. However, the MPS and behavioral data, especially during the heat waves suggests that 2.0-m2 treatment did not produce the same welfare improvements as the 3.3- and 4.7-m2 treatments. The use of additional management strategies such as dietary manipulation may lead to further welfare and performance improvements during periods of high heat load. At the location of the current study, the installation of shade is financially viable. The financial viability of shade in other locations will largely depend on the number of high heat load days to which cattle are exposed over summer. However the welfare benefits of shade need to be considered, especially in regards to consumer demands for improved welfare of livestock. Further work is being undertaken to determine the shade requirements for heavier weight, longer fed cattle.

LITERATURE CITED Beatty, D. T., A. Barnes, E. Taylor, D. Pethick, M. McCarthy, and S. K. Maloney. 2006. Physiological responses of Bos taurus and Bos indicus cattle to prolonged, continuous heat and humidity. J. Anim. Sci. 84:972 – 985. Beede, D. K., and R. J. Collier. 1986. Potential nutritional strategies for intensively managed cattle during thermal stress. J. Anim. Sci. 62:543 – 554.


Blackshaw, A.W., and J. K. Blackshaw. 1994. Heat stress in cattle and the effect of shade on production and behaviour: A review. Aust. J. Exp. Agric. 34:285 – 295. BOM (Bureau of Meteorology). 2010. Monthly climate statistics – summary statistics University of Queensland Gatton. http://www.bom.gov.au/climate/averages/tables/cw_040082.shtml Accessed Jul. 28, 2010. Brown-Brandl, T. M., R. A. Eigenberg, and J. A. Nienaber. 2006a. Heat stress risk factors of feedlot heifers. Livest. Sci. 105:57 – 68. Brown-Brandl, T. M., J. A. Nienaber, R. A. Eigenberg, T. L. Mader, J. L. Morrow, and J. W. Daily. 2006b. Comparison of heat tolerance of feedlot heifers of different breeds. Livest. Sci. 105:19 – 26. Brown-Brandl, T. M., R. A. Eigenberg, J. A. Nienaber, and G. L. Hahn. 2005. Dynamic response indicators of heat stress in shaded and non-shaded feedlot cattle, Part 1: Analyses of indicators. J. Biosyst. Eng. 90:451– 462. Busby, D., and D. Loy. 1996. Heat stress in feedlot cattle: Producer survey results. Iowa Agric. Exp. Stn., A. S. Leaflet R1348. Iowa State Univ., Ames. Clarke, M. R., and A. M. Kelly. 1996. Some effects of shade on Hereford steers in a feedlot. Proc. Aust. Soc. Anim. Prod. 21:235 – 239. Eigenberg, R. A., T. M. Brown-Brandl, and J. A. Nienaber. 2010. Shade material evaluation using a cattle response model and meteorological instrumentation. Int. J Biometeorol. 54:509 – 515. Entwistle, K., M. Rose, and B. McKierran. 2000. Mortalities in feedlot cattle at Prime City Feedlot, Tabbita, NSW, 2000: A report to the Director General. NSW Agriculture, NSW Government, NSW, Australia. Gaughan, J. B., S. Bonner, I. Loxton, T. L. Mader, A. Lisle, and R. Lawrence. 2010a. Effect of shade on body temperature and performance of feedlot steers. J. Anim. Sci. 88:4056 – 4067. Gaughan, J. B., S. M. Holt, and R. H. Pritchard. 2009. Assessment of housing systems for feedlot cattle during summer. Prof. Anim. Sci. 25:633 – 639. Gaughan, J. B., T. L. Mader, S. M. Holt, and A. Lisle. 2008. A new heat load index for feedlot cattle. J. Anim. Sci. 86:226 – 234.


Gaughan, J. B., T. L. Mader, S. M. Holt, M. L. Sullivan, and G. L. Hahn. 2010b. Assessing the heat tolerance of 17 beef cattle genotypes. Int. J. Biometeorol. 54:617 – 627. Hahn, G. L. 1999. Dynamic responses of cattle to thermal heat loads. J. Anim. Sci. 77 (supp. 2):10 – 20. Hahn, G. L., Y. R. Chen, R. A. Nienaber, and A. M. Parkhurst. 1992. Characterising animal stress through fractual analysis of thermoregulatory responses. J. Therm. Biol. 17:115 – 120. Hahn, L., T. Mader, D. Spiers, J. Gaughan, J. Nienaber, R. Eigenberg, T. Brown-Brandl, Q Hu, D. Griffin, L. Hungerford, A. Parkhurst, M. Leonard, W. Adams, and L. Adams. 2001. Heat wave impacts on feedlot cattle: Considerations for improved environmental management. Pages 129 – 130 in Proc. 6th Intl. Livest. Environ. Symp., Louisville, KY. R. R. Stowell, R. Bucklin and R. W. Bottcher, eds. Am. Soc. Agric. Eng., St. Joseph, MI. Hubbard, K. G., D. E. Stooksbury, G. L. Hahn, and T. L. Mader. 1999. A climatological perspective on feedlot cattle performance and mortality related to the temperaturehumidity index. J. Prod. Agric. 12:650 – 653. Kelly, C. F., T. E. Bond, and N. R. Ittner. 1950. Thermal Design of Livestock Shades. Agric. Eng. 30:601 – 606. Leonard, M. J., D. E. Spiers, and G. L. Hahn. 2001. Adaptation of feedlot cattle to repeated sinusoidal heat challenge. Pages 119 – 128 in Proc. 7th Int. Livest. Environ. Symp., Beijing, China. Am. Soc. Agri. Eng. St. Joseph, MI. Livestock Conservation Institute. 1970. Patterns of transit losses. LCI, Omaha, NE. Mader, T. L., J. M. Dahlquist, G. L. Hahn, and J. B. Gaughan. 1999. Shade and wind barrier effects on summer-time feedlot cattle performance. J. Anim Sci. 77:2065 – 2072. Mader, T. L., L. R. Fell, and M. J. McPhee. 1997. Behavior response of non-Brahman cattle to shade in commercial feedlots. Pages 795 – 802 in Proc. 5th Int. Livest. Environ. Symp., Bloomington, MN. R. W. Bottcher and S. J. Hoff, ed. Am. Soc. Agri. Eng. St. Joseph, MI. Mader, T. L., M. S. Davis, and T. Brown-Brandl. 2006. Environmental factors influencing heat stress in feedlot cattle. J. Anim. Sci. 84:712 – 719. Mader, T. L., L. J. Johnson, and J. B. Gaughan. 2010. A comprehensive index for assessing environmental stress in cattle. J. Anim. Sci. 88:2153 – 2165. 20 Downloaded from jas.fass.org by guest on June 17, 2012

McGovern, R. E., and J. M. Bruce. 2000. A model of the thermal balance for cattle in hot conditions. J. Agric. Eng. Res. 77:81 – 92. Mitlöhner F. M., M. L. Gaylean, and J. J. McGlone. 2002. Shade effects on performance, carcass traits, physiology, and behaviour of heat-stressed feedlot heifers. J. Anim. Sci. 80:2043 – 2050. Mitlöhner F. M., J. L. Morrow, J. W. Dailey, S. C. Wilson, M. L. Gaylean, M. F. Miller, and J. J. McGlone. 2001. Shade and water misting effects on behaviour, physiology, performance, and carcass traits of heat-stressed feedlot cattle. J. Anim. Sci. 79:2327 – 2335. Nienaber, J. A., G. L. Hahn, T. M. Brown-Brandl, and R. A. Eigenberg. 2003. Heat stress climatic conditions and the physiological responses of cattle. Pages 255 – 262 in 5th Int. Dairy Hous. Proc. Soc. Eng. Agri., Food and Biol. Sys. Canada. NOAA. 1976. Livestock hot weather stress. Operations Manual Letter C-31-76. NOAA, Kansas City, MO. NRC. 1996. Nutrient Requirements of Beef Cattle. 7th rev. ed. Natl. Acad. Press, Washington, DC. Reverter, A., D. J. Johnston, H. U. Graser, M. L. Wolcott, and W. H. Upton. 2000. Genetic analyses of live-animal ultrasound and abattoir carcass traits in Australian Angus and Hereford cattle. J. Anim. Sci. 78:1786 – 1795. Robertshaw, D. 1985. Heat loss in cattle. Page 57 in Stress Physiology in Livestock. Vol. 1. M.K. Yousef, ed. CRC Press Inc. Florida. SCAAHC (Standing Committees on Agriculture, Animal Health Committee). 1992. Australian Model Code of Practice for the Welfare of Animals – Cattle. CSIRO Publications, East Melbourne, Victoria, Australia. Schütz, K. E., A. R. Rogers, Y. A. Poulouin, N. R. Cox, and C. B. Tucker. 2010. The amount of shade influences the behavior and physiology of dairy cattle. J. Dairy Sci. 93:125 – 133. Yousef, M. K., G. L. Hahn, and H. D. Johnson. 1968. Adaptation of cattle. Page 16 in Adaptation of Domestic Animals. E.S.E Hafez, ed. Lea & Febiger. Philadelphia.


Figure 1. Feedlot layout showing location of feeders, water troughs, shade and weather stations.



Figure 2. A. Cattle using the 4.7-m2/animal shade. B. Unshaded cattle



Figure 3. The heat load index (HLI; grey lines) and unshaded accumulated heat load (AHL; black line) at 30-min intervals from d -1 to d 119 of the study. The boxes indicate the 4 heat wave periods: d 9 to d 12; d 19 to d 29; d 59 to d 62; d 65 to d 69.


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Figure 4. Mean panting score (MPS) for cattle with no access to shade (0; light grey bar), access to 2.0 m2 of shade per animal (dark grey bar), access to 3.3 m2 of shade per animal (stripped bar) and access to 4.7 m2 of shade per animal (checked bar), when the heat load index (HLI) was classified as cool (HLI86; fourth bar)


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Figure 5. Mean panting score (MPS) for cattle with no access to shade (1), access to 2 m2/animal

(2), access to 3.3 m2/animal (3) or access to 4.7 m2/animal (4) on days when heat load index × accumulated heat load (HLI × AHL) were classified as low (low: HLI < 70; AHL < 10; first bar), moderate (mod: HLI 70.1 to 77; AHL 10.1 to 20; second bar), high (high: HLI 77.1 to 86; AHL 20.1 to 50; third bar) or extreme (ext: HLI > 86; AHL > 50; fourth bar). Bars without a common superscript differ (P < 0.05). The statistical comparison is made within each HLI × AHL category e.g. the first bar in each category are statistically compared with each other.


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4

Table 1. Composition of the diets fed during the study. Item Starter (d 1 to 28) Finisher (d 29 to 119) Ingredient, kg Wheat 139 300 Sorghum 749.7 225 Barley 430.7 Millrun 150 150 Legume hulls 150 150 Canola Meal 150 Molasses 30 30 Soybean hulls 180 Limestone 20 22 Urea 11 0 Salt 7.5 7.5 Potassium Chloride 1.0 3.0 Bentonite 60 30 Mineral/Vit supplement1 1.5 1.5 Rumensin 1002 0.3 0.3 Nutrient composition Dry matter,% 90.1 90.3 3 NEg , Mcal/kg 1.16 1.47 Ash, % 8.1 6.7 Crude fat, % 2.1 2.2 Crude protein, % 13.2 13.7 ADF, % 12.0 11.4 NDF, % 17.3 17.5 Na, % 0.29 0.25 K, % 0.64 0.70 P, % 0.38 0.36 Cl, % 0.51 0.50 S, % 0.15 0.16 Ca, % 0.74 0.79 1 Contained (on a DM basis): 3000 IU/g vitamin A; 250 IU/g vitamin D; 2500 mg/kg vitamin E; 5000 mg/kg copper; 50 mg/kg selenium; 250 mg/kg molybdenum; 1000 mg/kg cobalt; 250 mg/kg iodine; 7500 mg/kg iron; 25000 mg/kg zinc and 15000 mg/kg magnesium. 2 Contained 100g/kg monensin (Elanco Animal Health, West Ryde, Australia), provided 30 mg/kg monensin to the final diet. 3 On a DM basis.


Table 2. The mean (± SE), maximum (max) and minimum (min) monthly values for ambient temperature (TA, oC), black globe temperature (BG, oC), solar radiation (SR, W/m2), wind speed (WS, m/s), relative humidity (rh, %), and heat load index (HLI). Month 1 December January February March April o TA, C Mean 22.3 ± 0.19 25.7 ± 0.12 24.9 ± 0.13 24.7 ± 0.12 22.7 ± 0.12 Max 35.5 38.6 34.9 39.0 32.5 Min 13.6 15.9 15.4 13.0 9.7 o BG, C Mean 25.8 ± 0.32 29.2 ± 0.19 28.4 ± 0.21 28.0 ± 0.21 27.6 ± 0.22 Max 43.3 47.2 48.4 47.6 41.0 Min 13.8 15.8 15.4 13.1 9.2 2 2 SR , W/m Mean 391.5 ± 17.6 397.6 ± 11.1 410.8 ± 11.7 408.5 ± 12.2 398.5 ± 11.6 Max 1253.0 1306.1 1216.0 1113.6 1110.1 Min 0 0 0 0 0 WS, m/s Mean 1.26 ± 0.04 1.43 ± 0.03 4.53 ± 0.03 1.34 ± 0.03 1.32 ± 0.03 Max 4.69 8.11 6.94 6.77 6.28 Min 0 0 0 0 0 rh, % Mean 70.7 ± 0.75 68.9 ± 0.47 70.5 ± 0.49 71.1 ± 0.49 68.8 ± 0.48 Max 100.0 100.0 99.2 100.0 100.0 Min 25.0 8.2 31.5 16.8 14.0 3 HLI Mean 69.2 ± 0.54 75.8 ± 0.34 74.1 ± 0.36 74.2 ± 0.35 61.3 ± 0.33 Max 93.5 102.4 97.6 104.2 89.8 Min 55.4 53.9 53.6 51.4 49.0 1 The December data is provided to give an indication of the climatic conditions to which the cattle were exposed prior to the commencement of the study. 2 Only values > 0 were used to calculate mean SR. 3 The HLI consists of 2 parts based on a BG threshold of 25 oC: HLIBG>25 = 8.62 + (0.38 · rh) + (1.55 · BG) – (0.5 · WS) + [e(2.4 – WS)], and HLIBG90 0 5 1 Maximum AHL = 36.2; All shade treatments. 2 Maximum AHL = 102.7


Table 4. Mean BW (kg) and SE at d 0 (initial BW), d 90 (90 d BW), and d 119 (final BW); ADG (kg/d), for the period d 0 to d 90 (1ADG), for the period d 90 to d 119 (2ADG), and for the period d 0 to d 119 (3ADG); hot carcass weight (HCW, kg), dressing percentage (DR, %) and P84 fat depth (mm) at slaughter (d 120) for un-shaded cattle (0), and cattle with access to shade at 2.0, 3.3 or 4.7 m2/animal. Treatment Item 0 2.0 3.3 4.7 Initial BW, kg 352.6 ± 10.90 352.1 ± 6.44 344.1 ± 6.44 357.2 ± 6.44 90 d BW, kg 413.3 ± 11.88a 436.5 ± 8.20a,b 435.9 ± 8.20a,b 448.2 ± 8.20b Final BW, kg 463.6 ± 12.00 472.9 ± 8.50 466.3 ± 8.50 483.6 ± 8.50 1 a b b ADG , kg/d 0.74 ± 0.05 1.03 ± 0.04 1.12 ± 0.04 1.11 ± 0.04b ADG2, kg/d 1.36 ± 0.13a 0.98 ± 0.10b 0.82 ± 0.10b 0.96 ± 0.10b 3 a a,b a,b ADG , kg/d 0.93 ± 0.05 1.02 ± 0.04 1.03 ± 0.04 1.06 ± 0.04b G:F, kg:kg 0.085 ± 0.006a 0.117 ± 0.006b 0.115 ± 0.006b 0.104 ± 0.006c HCW, kg 270.4 ± 7.17 277.1 ± 5.07 272.0 ± 5.07 282.6 ± 5.07 DR, % 58.3 ± 0.75 58.7 ± 0.26 58.4 ± 0.26 58.4 ± 0.26 4 P8 , mm 14.6 ± 1.13 16.4 ± 0.79 15.1 ± 0.79 16.5 ± 0.79 1 ADG from d 0 to d 90. 2 ADG from d 90 to d 119. 3 ADG from d 0 to d 119. Cattle were slaughtered on d 120. 4 The P8 fat depth is obtained by measuring the amount of fat over the gluteus muscle on the rump. The site is located at the intersection of a line through the pin bone parallel to the chine and its perpendicular through the third sacral crest (Reverter et al., 2000). a,b Within a row, means without a common superscript differ (P < 0.05).


Table 5. The means ± SE for number and the percentage (in brackets) of cattle within the unshaded, 2.0-m2, 3.3-m2 and 4.7-m2 treatments that were standing (shade and no shade), total standing, lying (shade and no shade), total lying, eating and drinking within treatment, for the non heat wave days of the study (d 1 to d 8; d 13 to d 18; d 30 to d 58; d 61 to d 64; and d 70 to d 119). Shade treatments

0 Standing shade1

2.0

3.3

4.7

2.99 ± 0.06a 2.84 ± 0.06a,b 2.70 ± 0.06b (33.2) (31.6) (30.0) Standing no shade 4.75 ± 0.07a 1.77 ± 0.05b 1.35 ± 0.05c 1.36 ± 0.05c (52.8) (19.7) (15.0) (15.1) Total standing 4.75 ± 0.08a 4.76 ± 0.06a 4.19 ± 0.06b 4.06 ± 0.06b (52.8) (52.9) (46.6) (45.1) Lying shade 1.25 ± 0.05a 1.99 ± 0.05b 2.12 ± 0.05c (13.9) (22.1) (23.6) Lying no shade 1.66 ± 0.05a 0.86 ± 0.04b 0.69 ± 0.04c 0.61 ± 0.04c (18.4) (9.6) (7.7) (6.8) a b c Total lying 1.66 ± 0.08 2.11 ± 0.06 2.68 ± 0.06 2.73 ± 0.06c (18.4) (23.4) (29.8) (30.3) a b Total in shade 4.24 ± 0.08 4.83 ± 0.08 4.82 ± 0.08b (47.1) (53.6) (53.6) a b b Eating 1.94 ± 0.06 1.62 ± 0.03 1.69 ± 0.03 1.79 ± 0.03b (21.6) (18.0) (18.8) (19.9) a b b Drinking 0.65 ± 0.04 0.49 ± 0.02 0.45 ± 0.02 0.39 ± 0.02c (7.2) (5.4) (5.0) (4.3) 1 Observations (n = 595/pen) were made between 0600 h and 1800 h. The mean number of observations•pen d-1 over the 119 d of the study was 5. a,b,c Within a row, means without a common superscript differ (P < 0.05). -


Table 6. The means ± SE for number and the percentage (in brackets) of cattle within the unshaded, 2.0-m2, 3.3-m2 and 4.7-m2 treatments that were standing (shade and no shade), total standing, lying (shade and no shade), total lying, eating and drinking within treatment, during the heat waves1. Shade treatment

Standing shade2 Standing no shade Total standing

Lying shade Lying no shade

0

2.0

3.3

4.7

-

6.24 ± 0.61a (69.3) 0.75 ± 0.29b (8.3) 6.99 ± 0.46b (77.7) 1.42 ± 0.51a (15.8) 0b

6.63 ± 0.61b (73.7) 0.11 ± 0.29c (1.2) 6.74± 0.46b (74.9) 1.66 ± 0.51a,b (18.4) 0b

6.34 ± 0.61a,b (70.4) 0.09 ± 0.29c (1.0) 6.43± 0.46a,b (71.4) 1.91 ± 0.51b (21.2) 0b

6.00 ± 0.39a (66.7) 6.00 ± 0.65a (66.7) 1.00 ± 0.14a (11.1) 1.00 ± 0.62a (11.1) -

1.42 ± 0.43a,b 1.66 ± 0.43b,c 1.91 ± 0.43c (15.8) (18.4) (21.2) Total in shade 7.66 ± 0.76 8.29 ± 0.76 8.25 ± 0.76 (85.1) (92.1) (91.7) Eating 0.33 ± 0.66 0.42 ± 0.49 0.38 ± 0.49 0.30 ± 0.49 (3.7) (4.7) (4.2) (3.3) Drinking 1.67 ± 0.25a 0.17 ± 0.18b 0.22 ± 0.18b 0.36 ± 0.18c (18.6) (1.9) (2.4) (4.0) 1 The heat waves occurred on d 9 to d 12, d 19 to d 29, d 59 to d 62 and d 65 to d 69. 2 Observations (n = 168/pen) were made at 2 h intervals between 0600 and 1800 h. a,b,c Within a row, means without a common superscript differ (P < 0.05). Total lying


Table 7. The mean carcass value1 ($/animal), feed cost ($/animal), yardage fee ($/animal), health cost ($/animal), pen maintenance ($/animal), the animal value (carcass value less feed, yardage, health and pen maintenance; $/animal) and the relative difference ($/animal) between shade treatments (2.0 m2, 3.3 m2 and 4.7 m2/animal) and unshaded cattle (0 m2). Treatment Carcass Pen5 Animal Relative Feed Yardage4 Health 2 3 value maintenance value difference cost 0 893.39 261.80 47.60 18.30 565.69 2.0 915.53 207.06 47.60 17.20 1.35 642.57 +76.88 3.3 898.67 211.82 47.60 15.00 0.56 623.81 +58.12 4.7 933.70 242.76 47.60 16.10 627.54 +61.85 1 All monetary values are in US dollars. 2 $3.303/kg HCW ($150/CWT). 3 Feed costs = $200/tonne. 4 $0.40/d. 5 Additional cost above routine cleaning and maintenance cost of $5.23/animal (over 119 d).
