Effects of feeding canola screenings on apparent ...

Effects of feeding canola screenings on apparent digestibility, growth performance and carcass characteristics of feedlot lambs

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K. Stanford1, G. L. Wallins1, W. G. Smart2, and T. A. McAllister2 1Alberta Agriculture, Food and Rural Development, P. O. Bag 3014, Lethbridge, Alberta, Canada T1J 4C7 (e-mail: [email protected]); and 2Research Centre, Agriculture and Agri-Food Canada, P. O. Box 3000, Lethbridge, Alberta, Canada T1J 4B1. LRC contribution no. 3879852. Received 18 May 1999, accepted 3 December 1999.

Stanford, K., Wallins, G. L., Smart, W. G. and McAllister, T. A. 2000. Effects of feeding canola screenings on apparent digestibility, growth performance and carcass characteristics of feedlot lambs. Can. J. Anim. Sci. 80: 355–362. Commercial coarse canola screenings (CS) were substituted for barley grain, and the resulting experimental diets (0, 20, 45, 70 and 95% CS, as-fed) were evaluated in feedlot lambs, while the 0, 45 and 95% CS diets were evaluated in a digestibility study using Romanov × Suffolk lambs. The CS comprised 60% canola (as whole, broken and immature seeds), 25% weed seeds and 15% chaff/dust. The control diet (0% CS) contained 75% barley and 20% alfalfa (as a protein/fibre source). Dietary crude protein (CP) increased with inclusion of CS and was lowest for control and 20% CS diets (13%) and highest for the 95% CS diet (14.4%). Digestibilities of dry matter (DM), organic matter (OM), neutral detergent fibre (NDF) and acid detergent fibre (ADF) were reduced (P < 0.05) in the 95% diet as compared with the control diet. Nitrogen retention by lambs was three times higher in the control group than in the 95% CS group (P < 0.001). Growth and feed conversion efficiency in feedlot lambs were linearly reduced (P < 0.001) with increasing dietary CS, but so was saturation of carcass fat (P < 0.001), which may benefit human health. Reduced lamb performance with CS was likely related to its high contents of crude fat (9%, DM basis) and ash (14%, DM basis). Valuing CS at 86% of the cost of barley, incorporation of up to 45% CS in feeder lamb diets would be cost effective. Key words: Canola, by-product, screenings, lamb, growth, carcass Stanford, K., Wallins, G. L., Smart, W. G. et McAllister, T. A. 2000. Effets de l’utilisation des criblures de colza canola sur la digestibilité apparente, sur la croissance et sur les qualités de carcasse d’agneaux à l’engraissement. Can. J. Anim. Sci. 80: 355–362. Des aliments expérimentaux, constitués à 0, 20, 45, 70 et 95 % de criblures commerciales brutes de colza canola (cr.c.), en substitution partielle à l’orge, ont été évalués sur des agneaux en parc d’engraissement. Les aliments à 0, 45 et 95 % cr.c. étaient en outre évalués dans une épreuve de digestibilité sur des agneaux croisés Romanov x Suffolk. Les criblures consistaient à 60 % de graines de canola (entières, brisées et immatures), à 25 % de graines de mauvaises herbes et à 15 % de menue pailles et de poussières. Le régime témoin (0 % cr.c) contenait 75 % d’orge et 20 % de luzerne (comme source de protéine et de fibre). La teneur en PB augmentait avec la proportion de cr.c., atteignant son niveau le plus bas (13 %) dans l’aliment témoin et dans celui à 20 % cr.c. et son niveau le plus élevé (14,4 %) dans l’aliment à 95 % cr.c. Les coefficients de digestibilité de m.s., m.o., FDN et lignocellulose étaient significativement (P < 0,05) plus bas pour l’aliment à 95 % cr.c. que pour l’aliment témoin. Le niveau de rétention de l’azote chez les animaux était 3 fois plus élevé (P < 0,001) dans le groupe témoin que dans le groupe recevant l’aliment à 95 % cr.c. La croissance et l’efficacité alimentaire chez les agneaux à l’engraissement diminuaient (P < 0,001) en fonction linéaire inverse de la proportion de cr.c. dans l’aliment. L’accroissement de la proportion de CR.C. dans l’aliment produisait une baisse en fonction linéaire (P < 0,001) de la croissance et de l’efficacité alimentaire chez les animaux à l’engraissement, mais également, ce qui est peut-être bon pour la santé humaine, une baisse du taux de saturation des graisses de la carcasse. La baisse des performances zootechniques due à l’inclusion des cr.c. serait liée à leur forte teneur en graisse brute (9 % sur la m.s.) et en cendres (14 % sur la m.s.). Considérant le coût des cr.c. à 86 % de celui de l’orge l’inclusion de jusqu’à 45 % de criblures de canola dans l’aliment d’engraissement des agneaux serait rentable. Mots clés: colza canola, sous-produit, criblures, agneau, croissance, carcasse

If Canadian livestock are to remain globally competitive, low-cost by-products will likely become increasingly important feeds due to fluctuations in the value of cereal grains and other traditional feed ingredients. In western Canada, one of the more widely available by-product feeds is canola screenings, which are produced during seed cleaning, and consists of a mixture of canola, cereal grains, weed seeds, chaff and dust (Darroch et al. 1990). Canola screenings are commonly classified as either “fines” or “coarse screenings” as determined by their respective contents of CP and crude fat. Fines contain 17–21% CP, 15–25% crude fat, and 23–33% ADF (Beames et al. 1986). A number of stud-

ies on the use of fines in animal feeds have been reported (Bell and Shires 1980; Keith and Bell 1983; Beames et al. 1986; Tait et al. 1986; Darroch et al. 1990). Coarse CS contain less CP (10–16%) and crude fat (7–16%) than fines (S. Pylot, unpublished data). Studies evaluating CS for ruminant diets have been limited (Pylot et al. 1998). Generally, CS have been priced at approximately at 85 to 87% the cost Abbreviations: ADF, acid detergent fibre; CP, crude protein; CS, coarse canola screenings; DM, dry matter; NDF, neutral detergent fibre; OM, organic matter; SFA, saturated fatty acids 355

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Table 1. Comparison of the composition of canola screenings used in the present study and samples of canola screenings collected over a 12-mo period from the same plant Collected over a 12-mo period Analysis (%, DM basis) Present studyz


Organic matter Crude protein Crude fat Neutral detergent fibre Acid detergent fibre Calcium Phosphorus

86.0 15.3 8.6 44.9 30.8 NAy NA

Range 85.7 – 92.1 10.9 – 16.2 5.2 – 11.6 36.9 – 47.5 22.7 – 33.3 0.90 – 1.22 0.33 – 0.53

Mean (n = 14) 89.0 14.2 8.4 41.7 28.8 1.07 0.41

zConsisting

of 32.1% immature canola seed, 16.8% cracked canola seed, 15.1% coarse weed seeds, 15.0% chaff and dust, 11.1% whole canola seed, and 9.9% fine weed seeds (by weight). yNA, not available.

of barley. Thus, substituting CS into ruminant diets could be economically advantageous, provided that they did not impair animal performance or carcass quality. Although CS may represent a valuable feed resource, basic information on their feeding value (apparent digestibilities of DM, OM, ADF, NDF and N in diets containing varying proportions of CS) has not been reported. With appropriate vitamin and mineral supplementation, CS could meet the nutrient requirements of growing steers or lambs. Supplementing diets for lambs with up to 75% canola meal was found not to affect feed intake or apparent nutrient digestibility (Mustafa et al. 1997). However, elevated levels of fibre and crude fat in CS relative to canola meal, and the possibility of anti-nutritional factors in some constituents of CS, may reduce growth performance of ruminants fed CS. Tesfa (1993) determined that fibre digestion was impaired when 6.7% of dietary DM was provided as canola oil; consequently, the relatively high oil content of CS may affect fibre digestion, particularly if CS were to constitute a large proportion of the diet. However, other benefits may offset this potential for reduced fibre digestion. Adding 6.5% rapeseed to the diet was found to reduce the cholesterol content of lamb (Solomon et al. 1991), and canola seed added at 10% of dietary DM for cattle increased the longchain unsaturated fatty acid content in beef (Hussein et al. 1996), due to the high oleic acid (C18:1) content of rapeseed and canola. Mattson and Grundy (1985) reported a lower incidence of atherosclerosis associated with decreased dietary cholesterol and increased levels of long-chain unsaturated fatty acids. Thus, adding CS to ruminant diets may offer human health benefits. To complement recent findings with beef production (Pylot et al. 1998), and to further evaluate the use of coarse canola screenings in ruminant diets, the present study was conducted (1) to compare the apparent digestibilities of DM, OM, ADF, NDF and N in diets containing varying levels of CS against those of a standard alfalfa–barley diet for rapidly growing feedlot lambs; (2) to determine if lamb fat composition is altered by adding CS to diets; and (3) to estimate the economic feasibility of replacing barley with CS in diets for rapidly growing feedlot lambs.

MATERIALS AND METHODS All animals in this study were cared for according to the standards set by the Canadian Council on Animal Care (1993). Diets A representative 2-kg sample of loose CS was collected over a 12-mo period from a commercial canola-crushing plant in Lethbridge, AB, and manually sieved to determine composition (Table 1). The commercial plant supplied CS as a 10-mm pellet, prepared from screenings that had been hammermilled and passed through a 1-mm screen. Upon arrival at the Lethbridge Research Centre, the CS pellets used in this study were hammermilled again, and subjected to proximate analysis (Table 1) prior to incorporation into five completely pelleted experimental diets. A standard lamb grower diet for western Canada, containing 75% barley, 20% alfalfa (as a fibre/protein source), and 5% salt/mineral supplement, was used as the control diet. In the treatment diets, CS were incorporated at rates of 20, 45, 70 and 95% (as-fed basis), replacing all the alfalfa and progressively increased amounts of the barley (Table 2). Digestibility Trial Six Romanov–Suffolk ram lambs (initial weight 20.4 ± 0.1 kg) were used to evaluate voluntary feed intake and digestibility of the control, 45% CS and 95% CS diets. The study was designed as a replicated 3 × 3 Latin square, with three 21-d periods. Lambs were penned individually for the first 14 d of each period, then were moved to metabolism crates for the last 7 d. Water was available ad libitum throughout the trial. For the first 7 d of each period, lambs were allowed to adapt to the diets. Orts were removed and weighed on a daily basis, and each day 10% more feed was offered than was consumed the previous day. Ad libitum intake was then monitored for 5 d and the lambs fed at 95% of ad libitum intake for the last 9 d of the period. Total collections of faeces and urine were conducted daily for the last 7 d of each period. Acid (45 mL of 8 N H2SO4) was added each morning to the urine collection jugs to prevent volatization of ammonia from the urine. Faeces and urine were subsampled daily (10%), composited over each period and stored at –30°C until analysed. Individual Feeding Trial Fifty-four Romanov × Suffolk lambs were used to evaluate the five experimental diets (Table 2) in an individual feeding trial. The lambs (initial weight 22.9 ± 0.2 kg) were blocked by breed, sex and liveweight and randomly allocated to individual pens using a randomized block design. Lambs were adapted to experimental diets for 7d from a completely pelleted 19% CP post-weaning diet. Ad libitum access to water and pelleted diets was provided throughout the study. Lambs were fed once daily and orts were collected and weighed weekly. Lambs were weighed weekly and were shipped for slaughter after reaching 45 kg. At the abattoir, prior to slaughter, the maximum depth of the longissimus muscle (“B”) and subcutaneous fat depth perpendicular to B (“C”) were measured at the third lumbar

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Table 2. Ingredients (as-fed) and composition (DM basis) of experimental diets


Screenings content of diet (%) 0 (control)

20

750 0 200 13 5 10 16 2.5 4 0.25 0.13

750 200 0 13 5 10 16 2.5 4 0.25 0.13

Analysis Dry matter (%)

90.18

89.41

Organic matter Crude protein Crude fat Neutral detergent fibre Acid detergent fibre

90.53 13.00 2.81 37.18 18.27

91.01 13.04 3.47 30.47 11.98

Ingredients (kg t–1) Barley grain, whole Canola screenings Alfalfa Molasses, beet Canola oil Sheep mineralz Calcium carbonate Maxi-Pely Dicalcium phosphate Vitamin A, D, Ex Deccoxw

45

70

95

500 450 0 13 5 10 16 2.5 4 0.25 0.13

250 700 0 13 5 10 16 2.5 4 0.25 0.13

0 950 0 13 5 10 16 2.5 4 0.25 0.13

90.45 % (DM basis) 88.10 14.08 5.94 35.64 18.52

91.74

95.26

84.60 14.19 9.18 39.10 23.24

83.64 14.44 13.17 38.78 26.69

zContaining: 93.1% NaCl, 1.25% Mg, 0.9% Zn, 0.94% Mn, 0.13% Cu, 0.003% Se, 1.25% yFeed pellet binder (Mountain Minerals Ltd., Lethbridge, AB). xContaining 10 000 IU g–1 Vitamin A, 1250 IU g–1 Vitamin D, and 10 IU g–1 Vitamin E. wContaining 60 g kg–1 decoquinate (Rhône-Poulenc Canada, Mississauga, ON).

vertebra (Stanford et al. 1995) using an Aloka SSD model 500 SEM (Aloka Co. Ltd., Tokyo, Japan) real-time ultrasound scanner equipped with a 1.5 cm, 2-MHz probe. Carcass weight was measured 30 min after slaughter. Body wall thickness was measured at the grade rule site, 11 cm from carcass midline between the 12th and 13th ribs (Kirton and Johnson 1979). Samples of kidney fat and subcutaneous fat over the longissimus muscle were frozen in liquid nitrogen for subsequent fatty acid analysis. Chemical Analyses Feed and faecal samples were dried at 105°C for 24 h to determine DM, and ashed in a muffle furnace at 500°C for 5 h to determine OM. Faeces and feed were dried at 55°C for 48 h and either ground through a 1-mm screen for analysis of starch and NDF, or ground for 3 min in a Wig-L-Bug® Amalgamator (Crescent Dental Mfg. Co., Lyons, IL) prior to N analysis in a Carlo Erba® NA 1500 Carbon-Nitrogen elemental analyser (Carlo Erba Srumentazione, Rodano, Milan, Italy). Oil content of CS and the pelleted diets was determined by ether extraction (method 920.39, Association of Official Analytical Chemists 1990). The procedure of Van Soest et al. (1991) was used to determine NDF, with the modification of adding α-amylase to feed samples to solubilise starch and facilitate filtering. To prepare methyl esters of fatty acids, duplicate 15-g samples of kidney or subcutaneous fat were placed in tubes containing 4 mL of 35:45:20 (vol:vol:vol) boron trifluoride:methanol:hexane. The tubes were sealed and placed in a bath of boiling water for 1 h. After cooling, 2 mL of hexane and 3 mL of 1% (wt vol–1) sodium chloride solution were added to each tube, then they were mixed and allowed to

S, 1.25% K, 1.25% Fe.

settle. For analysis of the methyl esters, 25 µL of the hexane layer was diluted in 1 mL of hexane and injected onto a BPX 70 capillary column (0.25 mm × 25 mm; film thickness 0.25 µm; Rose Scientific, Edmonton, AB) on a Varian Model 3600 gas chromatograph equipped with a split port injector and a flame ionization detector. Statistical Analyses Data were analysed using the REG and GLM procedures and means were compared using the least-squares-mean linear hypothesis test (SAS Institute, Inc. 1993). To determine linear and quadratic effects orthoganol contrasts were made which adjusted for the level of CS in the diet. For the digestibility trial, the model included lamb, diet, period, and period × diet interaction. Data for the individual feeding experiment were analysed with sex, diet, and diet × sex interaction included in the model, and initial weight as a covariate. Carcass data were analysed both with and without carcass weight included as a covariate. Least-cost diets including CS were determined by setting the first derivative of a quadratic equation to 0 and solving for the proportion of CS (Steel and Torrie 1980). RESULTS AND DISCUSSION Composition of Canola Screenings The CS used in this study comprised 60% canola (as immature, cracked and whole seeds) and 25% weed seeds, with considerable ash (14%), presumably in the form of dirt or dust. Compared with canola/rapeseed fines evaluated in other studies, where weed seeds averaged 40% (Beames et al. 1986) and inorganic matter (soil and sand) was up to 40% of the

358


Table 3. Effect of level of canola screenings in diets on nutrient digestion and N metabolism in lambs Effect of level of screeningsz

Level of canola screenings in diet 0% (control)y


d–1)

DM Intake (g Digestibility (%) Dry matter Organic matter Acid detergent fibre Neutral detergent fibre N Intake (g d–1) Urinary N (g d-1) N digested (%) N digested (g d–1) N retained (g d–1) N retained (% of N intake) N retained (% of N digested) zL, linear effect. yControl diet contained (as-fed): 75% xSEM, standard error of the mean.

1366.7 68.7b 70.8b 30.7b 45.5b 28.2a 3.3 66.1b 19.3a 6.3b 23.3b 33.6b

45% 1577.7 69.1b 71.8b 32.2b 46.7b 35.5b 3.9 64.2ab 24.7b 8.3b 22.4b 32.1b

95% 1388.8 52.3a 57.5a 18.5a 36.7a 31.8ab 4.2 60.5a 16.7a 2.2a 7.1a 13.2a

SEMx

Linear

63.0

NS

0.5 0.6 2.0 1.3 1.4 0.4 1.7 1.0 0.7 2.3 2.9

*** *** *** *** NS ** * * ** ** **

barley grain + 20% alfalfa.

a–b within a row, diets followed by different letters differ (P < 0.05) *, **, ***: Significant at P < 0.05, P < 0.01 and P < 0.001, respectively; NS, not significant (P > 0.05).

screenings (Bell and Shires 1980), the CS used in the present study had less of such contaminants and were similar to those used by (Darroch et al. 1990) and (Keith and Bell 1983). The CP, crude fat and fibre contents of coarse canola screenings available from the commercial plant varied over the course of a year (Table 1), but such variability would not preclude utilisation of CS in diets for ruminants. Digestibility Trial Apparent digestibilities of NDF and ADF (Table 3) in the diets were reduced (P < 0.05) in the 95% CS diet as compared with control and the 45% diet. This was likely due to the increased fat content of the 95% diet (Table 2), although it is also possible that the NDF of CS is inherently less digestible than the NDF of barley. Crude fat content in the 45% and 95% CS diets was approximately four times that of the control diet. At levels approaching 10% of dietary DM, free canola oil has exerted toxic effects on protozoal and cellulolytic bacterial populations, resulting in depressed fibre digestion in cattle (Tesfa 1993). In contrast, Hussein et al. (1995) reported that whole or crushed canola seed included at 5% dietary DM as a fat source did not affect fibre digestion in steers fed high- or low-forage diets. Similarly, moderate levels of crude fat (6% of dietary DM) in the 45% CS diet did not affect fibre digestion appreciably in this study. This may have been due to binding of oil by canola seed even though the screenings were crushed in a hammermill prior to pelleting. Inhibition of fibre digestion by dietary fat is thought to be minimised by slow release of fat from the cellular structure of the seed (Murphy et al. 1987), as would be the case when canola is crushed or fed whole (Hussein et al. 1995). The 95% CS diet, however, likely had sufficient free canola oil to effect inhibition of ADF and NDF digestion. Levels of ADF and NDF were elevated in the 95% CS diet compared with the control and 45% CS diets, which may also have reduced ADF and NDF digestibilities.

Apparent digestibilities of DM, OM, ADF and NDF in the diets were linearly reduced (P < 0.001) with increasing CS content of the diet. All N retention measures were also linearly reduced (P < 0.01) with increasing CS content of the diet. Overall, N retention (as g d–1) in lambs fed 95% CS diet was approximately one-third of that observed in the control lambs, even though the control diet contained 1.4% less CP than the 95% CS diet. Reduced N retention by lambs fed the 95% CS diet was also reflected in low (115 ± 20 g d–1) weight gains over the 21-d period when they were fed the 95% CS diet, as compared with the mean growth rate for the same lambs in other periods (329 ± 14 g d–1). Although a diet with 14.4% CP should not have limited lamb growth, according to recommendations of the National Research Council (1985), N retention by lambs receiving the 95% CS diet was low, likely attributable to two factors: (1) lower digestibility (P < 0.05) of N in coarse canola screenings relative to barley and (2) impaired rumen microbial populations, due to the toxic effects of free canola oil. The presence of anti-nutritional factors may also have influenced N retention, but confirmation of this would require specific address in further studies. Canola has been selected to be low in glucosinolates, but the seeds of weeds such as stinkweed and wild mustard, which may be prevalent in CS (Keith and Bell 1983; Darroch et al. 1990), contain high levels of glucosinolates (7 to 8%, Beames et al. 1986). The variety of weed seeds present in CS (Bell and Shires 1980) increases the likelihood of other anti-nutritional factors, such as alkaloids, being present. Individual Feeding Trial The organic matter content of the CS in this study was 86.0% (Table 1). This is lower than OM values reported previously for high-quality canola meal (91.6%, McAllister et al. 1999; 94.6%, Bell and Keith 1991) and barley (96.4%, Galloway et al. 1993; 97.5%, Bakells et al. 1993), but is

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Table 4. Effect of level of canola screenings in feedlot diets for lambs on growth performance and carcass characteristics Effect of level of screeningsz

Level of canola screenings in diet (as-fed)


0% (control)y Number of lambs Initial wt (kg) Final wt (kg) Average daily gain (kg) Feed intake (g DM d–1) Feed conversion (feed gain–1) Ultrasound measurements (mm)w Fat thickness “C”v Ribeye depth “B” Adjusted fatu Adjusted ribeye depthu Carcass measurements Carcass weight (kg) GR (mm) Adjusted GR (mm)u

20%

70%

95%

SEMx

L

Q

11 22.9 50.5 388 1580 4.1

10 23.0 49.0 355 1413 4.1

10 23.2 47.6 376 1512 4.2

11 22.6 45.7 324 1466 4.6

11 23.5 45.3 300 1807 6.1

– 0.2 1.5 12 48 0.2

– NS *** *** ** ***

– NS NS NS *** ***

5.7 25.2 5.1 24.0

4.9 26.3 4.5 25.4

4.7 25.6 4.7 25.5

4.8 25.0 5.0 25.3

3.8 22.8 4.3 23.8

0.4 0.7 0.4 0.6

** ** NS NS

NS * NS **

25.4 16.1 15.0

25.0 14.5 13.7

23.8 13.0 16.3

23.1 12.8 13.0

22.0 9.9 10.8

0.7 1.0 1.0

*** *** **

NS * *

zL, linear effect; Q, quadratic effect. yControl diet contained 75% barley grain + 20% alfalfa. xSEM, standard error of the mean. wTaken at the third lumbar vertebra. vDepth of subcutaneous fat perpendicular to the maximum uAdjusted for carcass weight.

45%

depth of the ribeye.

*, **, ***: Significant at P < 0.05, P < 0.01 and P < 0.001, respectively; NS, not significant (P > 0.05).

similar to OM content of early bud alfalfa hay (85.9% OM, Canale et al. 1992). Substantial inorganic matter (dust and other impurities) in these CS reduced their OM content, which likely caused the linear (P < 0.01) and quadratic (P < 0.001) increases in feed intake and reductions in feed conversion efficiency (P < 0.001) observed with increasing dietary CS (Table 4). The previously discussed low N digestibility/retention and impaired fibre digestion with increasing CS in the diets may have also affected lamb growth performance. Although high levels of fat have been reported to reduce palatability (Rule et al. 1994), feed intake increased linearly (P < 0.01) with increasing content of CS in the diet. Palatability of the 95% CS diet was not reduced, but ADG decreased linearly (P < 0.001) with increasing dietary CS. In the individual feeding trial, the lambs receiving the 95% CS diet grew more rapidly than their counterparts in the digestibility trial, likely due to gradual adaptation by the ruminal microbes to the high fat content of the diet. The ability of ruminal microorganisms to adapt to other antinutritional factors, such as nitrites, has been previously recognised (Birnbreier and Hilliger 1993). Comparing growth rates of lambs in the initial 3 wk of the individual feeding trial against their growth rates after the third week illustrates this adaptation to CS. Over the first 3 wk of the trial, growth by lambs receiving 95% or 70% CS diets (263 ± 33 g d–1 and 276 ± 33 g d–1, respectively) was slow compared with lambs receiving 45% CS, 20% CS or control diets (408, 393 and 376 ± 33 g d–1, respectively). Beyond week 3, the growth rate of the control lambs changed little (+22 g d–1), whereas growth of lambs fed 20% and 45% CS diets was slower (by 46 and 42 g d–1, respectively) than in the initial period. In contrast, lambs receiving 70% and 95%

CS diets grew more quickly in the latter part of the trial (by 69 and 53 g d–1, respectively) than they did initially. Ultrasound measurements (Table 4) showed linear reductions (P < 0.01) in subcutaneous fat thickness over the ribeye and in ribeye depth, as dietary CS increased. However, when ultrasound data were adjusted for carcass weight, subcutaneous fat thickness had no relationship with CS content of the diet, although quadratic effects remained (P < 0.01) for ribeye depth. The grade rule measurement, which is an indicator of overall carcass fatness (Kirton and Johnson 1979), was linearly reduced (P < 0.01) with increasing dietary CS, with or without adjustment of measurements for carcass weight. Ribeye depth is a commonly used indicator of carcass muscling in lambs (Stanford et al. 1998). Consequently, the influence of CS on carcass muscling and fatness over and above their influence on carcass weight is likely related to the reduced digestibility of fibre and impaired N metabolism with increasing dietary levels of CS. Reduced fatness of lamb carcasses would be desirable from a consumer standpoint (Ward et al. 1995), although not when coupled with a reduction of carcass muscling. Fatty Acid Profiles Altering the composition of ruminant fat is difficult because of the hydrogenation of unsaturated fatty acids by ruminal microbes (Harfoot 1981). Consequently, in experiments in which diets were modified to include up to 18% canola seed (Solomon et al. 1991; Lough et al. 1992; Rule et al. 1994; McAllister et al. 1999), only minor changes in fatty acid profiles were achieved. By comparison, the dietary treatments in the present study were more extreme (e.g., 95% CS), and the lambs’ fatty acid composition was markedly influenced (Table 5). Saturated fatty acids (SFA) were

360


Table 5. Effects of level of canola screenings in feedlot diets for lambs on proportions of fatty acids (% of total fatty acids) in subcutaneous and kidney fat of lambs Effectz

Level of canola screenings in diet (as-fed) Tissue


Subcutaneous fat

Kidney fat

Fatty acid 14:0 15:0 16:0 16:1 17:0 18:0 18:1 18:2 18:3 20:0 20:1 SFAw MUFAw PUFAw Unknownw 14:0 15:0 16:0 16:1 17:0 18:0 18:1 18:2 18:3 20:0 20:1 SFA MUFA PUFA Unknown

0%

(control)y 3.52 2.98 23.06 2.05 6.20 11.53 34.00 3.21 0.52 0.12 0.18 47.42 36.24 3.74 8.62 2.79 0.82 22.42 0.96 3.40 27.20 28.45 4.16 0.67 0.08 0.22 56.71 29.60 4.83 3.40

20%

45%

70%

95%

SEMx

3.08 2.36 21.60 1.45 6.04 11.40 35.95 3.71 0.41 0.08 0.26 44.61 37.67 4.13 8.44 2.80 0.71 21.39 0.79 3.75 26.73 27.36 4.87 0.51 0.11 0.27 55.50 28.42 5.38 3.51

3.37 1.81 21.13 1.45 4.15 13.33 34.85 4.06 0.82 0.11 0.40 43.94 36.70 4.88 7.03 2.84 0.53 19.95 0.77 2.45 26.37 26.94 4.60 0.88 0.20 0.43 52.34 28.14 5.48 3.78

3.80 0.98 22.54 1.13 2.82 14.64 34.00 4.67 0.61 0.16 0.47 44.93 35.62 5.28 4.28 3.10 0.38 18.94 0.67 1.82 23.12 30.87 5.74 0.68 0.12 0.62 47.48 32.15 6.42 2.79

3.19 0.97 20.32 1.29 2.82 13.62 37.55 4.84 0.50 0.26 0.63 41.22 39.47 5.34 5.10 2.09 0.32 15.78 0.66 1.72 24.68 34.01 5.44 0.63 0.35 0.72 44.94 35.40 6.07 3.57

0.21 0.11 0.58 0.09 0.22 0.67 0.84 0.20 0.11 0.04 0.04 0.84 0.86 0.22 0.35 0.21 0.11 0.58 0.09 0.22 0.67 0.85 0.20 0.11 0.04 0.04 0.84 0.86 0.22 0.35

L

Q

NS *** * *** *** *** * *** NS ** *** *** NS *** *** NS *** *** *** *** *** *** *** NS *** *** *** *** *** NS

NS ** NS *** NS NS NS NS NS ** NS NS NS NS NS ** * NS NS NS NS *** NS NS NS NS NS *** NS NS

zL, linear effect; Q, quadratic effect. yControl diet contained 75% barley grain + 20% alfalfa. xSEM, standard error of the mean. wSFA, total saturated fatty acids; MUFA, total monounsaturated

fatty acids; PUFA, total polyunsaturated fatty acids; Unknown, total fatty acids of undetermined character. *, **, *** Significant at P < 0.05, P < 0.01 and P < 0.001, respectively; NS, not significant (P > 0.05).

reduced (P < 0.001) and polyunsaturated fatty acids were increased (P < 0.001) by increasing dietary CS, in both subcutaneous and kidney fat. The proportion of SFA in subcutaneous fat from lambs fed 95% CS was reduced by 11% compared with composite profiles for the subcutaneous fat of lambs fed high-concentrate diets (Jamora and Rhee 1998). Although 4 to 8% of the fatty acids in the present study were classed as unknown, a portion of these would be saturated; thus the reduction in SFA achieved in this study would still likely exceed that reported previously. Only linolenic (C18:3) acid in subcutaneous and kidney fat, and myristic (C14:0) acid in subcutaneous fat were unaffected by the level of CS in the lambs’ diet. The marked changes in fatty acid composition achieved in this study by adding CS to the lambs’ diets are in contrast to those reported by Solomon et al. (1991). In their study, adding 6.5% whole rapeseed to lamb diets increased the total level of SFA relative lambs fed a control soybean meal diet, although saturation of certain individual fatty acids was reduced. In the present study, SFA accounted for 41 to 47% of all fatty acids measured in subcutaneous fat (Table 5), which is higher than the 38 to 41% SFA proportion report-

ed by Solomon et al. (1991) for subcutaneous fat taken over the longissimus. The differences in fatty acid profiles between these two studies are likely due to a higher proportion of fat in a 95% CS compared with a 6.5% rapeseed diet. Additionally, Busboom et al. (1981) reported differences in fatty acid profiles due to breed and sex. In the present study, we used Romanov × Suffolk ram and ewe lambs, whereas Solomon et al. (1991) used Hampshire–Suffolk ram lambs. Oleic (C18:1) and linoleic (C18:2) acids have been linked to reduced serum cholesterol and subsequently lowered risk of heart disease (Mattson and Grundy 1985). These fatty acids were linearly increased in subcutaneous (P < 0.05) and kidney fat (P < 0.001) with increasing level of CS. Increasing dietary energy has been shown to elevate linoleic acid and reduce the proportion of linolenic (C18:3) acid in lamb fat (Field et al. 1978; Busboom et al. 1981), although reductions in linolenic from increased concentration of dietary crude fat were not apparent in the present study. The results of the present study demonstrate that the addition of high concentrations of canola screenings to lamb diets alters fatty acid composition, with potential benefits to human health. Further study is required to assess potential

STANFORD ET AL. — CANOLA SCREENINGS FOR FEEDLOT LAMBS Table 6. Cost of gain estimates for lamb feedlot diets in which rolled barley is replaced with canola screenings (CS), and predicted least-cost diets in two pricing scenarios CS in diet (%, as-fed)

Actual cost of gainz (CDN$ kg–1)


0 (control)x 0.554 20 0.548 45 0.536 70 0.558 95 0.702 Predicted least-cost diet (% CS) 43w

Predicted costs of gain (CDN$ kg–1) Scenario 1y Scenario 2y 0.430 0.396 0.391 0.412 0.525 36v

0.430 0.410 0.420 0.460 0.610 27u

zBased on actual values at the time of the study, CS = $115 t–1, $140 t–1. yScenario 1: The cost of CS is assumed to be 86% of the cost of

barley

barley grain. Barley = 100; alfalfa = 120; CS = 86. Scenario 2: The cost of CS is assumed to be equal to the cost of barley grain. Barley = 100; alfalfa = 120; CS = 100. xControl diet contained 75% barley grain + 20% alfalfa. wFrom first derivative of the equation: Cost kg gain–1 = 0.065 screenings2 + 5.704 barley, with barley = 100 – screenings, R2 = 0.96. vFrom first derivative of the equation: Cost kg gain–1 = 0.0004 screenings2 – 0.00298 screenings, R2 = 0.97. uFrom first derivative of the equation: Cost kg gain–1 = 0.0005 screenings2 – 0.00259 screenings, R2 = 0.98.

negative consequences of reduced saturation of lamb fat, such as increased softness or oiliness of fat (Busboom et al. 1981) or altered flavour of the meat (Jamora and Rhee 1998). Economics of Including Canola Screenings in Lamb Diets Traditionally, canola screenings are priced at 85 to 87% of the cost of barley. Using the feed conversion ratios of Table 4, regressions were performed using market price of CS at the time of the study and two hypothetical scenarios: (1) canola screenings valued at 86% of the cost of barley and (2) canola screenings equal in value to barley (Table 6). The maximum rates of inclusion of CS for the estimated lowest cost kg–1 gain were 43, 36 and 27%, with CS valued $115 t–1, and at 86% and 100% of the price of barley. In conclusion, canola screenings are a valuable Canadian feed resource, but the lowered digestibility of DM and fibre and impaired N retention and feed conversion by lambs, relative to those fed barley-based diets, precludes the inclusion of high levels of CS in feeder lamb diets unless a health-conscious market was to develop for lamb reduced in saturated fat. Assuming a CS price of 86% of the cost of barley, a feeder lamb diet of approximately one-third CS and twothirds barley would give the lowest estimated cost per gain. By necessity, such recommendations would need to be modified according to fluctuations in DM, OM, CP, fibre and the price of canola screenings, barley or alfalfa hay. ACKNOWLEDGEMENTS The authors gratefully acknowledge the financial assistance of Canodev Research Inc. and the Western Canadian Sheep Research Committee. We thank Canbra Foods Ltd. for supplying the canola screenings, and the Canada/Alberta Livestock Research Trust for provision of lambs and steers for the experiment. The usual excellent care of the lambs by Ray

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