Feed Intake and Apparent Digestibility of Hay ...

Feed intake and apparent digestibility of hay-supplemented brassica diets for lambs K. A. Cassida, B. A. Barton, R. L. Hough, M. H. Wiedenhoeft and K. Guillard J ANIM SCI 1994, 72:1623-1629.

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Feed Intake and Apparent Digestibility of Hay-Supplemented Brassica Diets for Lambs' K. A. Cassida*p2, B. A. Barton*v3, R. L. Hough", M. H. Wiedenhoeft'y4, and K. Guillardt Departments of "Animal, Veterinary, and Aquatic Sciences and +Plant, Soil, and Environmental Sciences, University of Maine, Orono 04469 and *Department of Plant Science, University of Connecticut, Storrs 06269

ABSTRACT: Animal performance on brassica diets often does not reflect laboratory estimates of the nutritive value of the herbage. Hay supplementation of brassica pastures should increase diet DM and fiber intake and dilute anti-quality factors. The optimal hay:brassica ratio needed to achieve desirable animal performance, however, has not been established. Effects of changing the hay:brassica ratio on feed and water intake, apparent digestibility of diets, thyroid status, and anemia were examined in five Dorset-cross wether spring lambs (initial BW 32.8 f 3.2 kg). The experimental design was a 5 x 5 Latin square with 21-d periods ( 7 d of adaptation, 6 d of intake measurement, and an 8-d digestion trial with jugular blood drawn on last day). Diets contained chopped grass hay and tyfon (turnip x Chinese cabbage

hybrid) at five hay:tyfon ratios (DM basis): 1OO:O; 75: 25; 5050; 25:75; and 0:lOO. As the proportion of tyfon in the diet increased, there were linear increases ( P < .05) in ad libitum DMI (922 to 1,359 g/d), total water intake (1.75 to 13.06 L/d), digestible DMI (401 to 952 g/d), and apparent digestibility of DM (55.9 to 86.3%), CP (52.9 to 84.5%), and neutral detergent solubles (57.2 to 88.5%). Hay plus tyfon diets exhibited negative associative effects for apparent digestibility of NDF, ADF, and cellulose. Plasma thyroxine and triiodothyronine, packed cell volume, red blood count, and hemoglobin concentration were not affected by diet. Tyfon influenced DMI and apparent digestibility of diets in a manner similar to that of a concentrate.

Key Words: Brassica, Hay, Forage, Digestibility, Lamb Feeding

J. h i m . Sci. 1994. 72:1623-1629

Introduction The turnip-Chinese cabbage hybrid tyfon ( Brassica campestris var. rapa L. x B. pekinensis [Lour.] Rupr.) is used to decrease costs of sheep production in the northeastern United States by extending the fall grazing season. Sheep pastured on tyfon can gain weight in excess of 150 g/d (Koch et al., 1987; Guillard et al., 1988; McCoy et al., 1990; Rule et al., 1991) but do not always perform to this level (Guillard et al., 1988). Lower than expected rates of gain in brassica-

'Publication no. 1773 of the Maine Agric. Exp. Sta. This research was funded by a grant from the USDA Low Input Sustainable Agriculture program. 'Present address: Dept. of Crop and Soil Sci., Michigan State Univ., East Lansing 48824. 3Present address: Purina Mills Dairy Research, Inc., St. Louis, MO 63166. 4To whom correspondence should be addressed. Received July 26, 1993. Accepted February 4, 1994.

fed sheep are often attributed to physical limitation of DMI by high forage water content, inadequate fiber intake for ruminal function (Lambert et al., 19871, or anti-quality compounds in the forage that result in thyroid dysfunction and anemia (Smith, 1980). Hay supplementation may alleviate these effects by increasing the DM and fiber content of the diet and diluting the intake of anti-quality compounds (Heinemann et al., 1981; Lambert et al., 1987). However, information is limited on the optimal hay: brassica ratio. Therefore, we quantified the effects of hay supplementation of tyfon-based diets on DMI, water intake, apparent digestibility of diet nutritive fractions, thyroid gland function, and anemia status in lambs.

Experimental Procedures

Design and Diets. Five Dorset-cross wether lambs, approximately 5 mo old, with an average initial weight of 32.8 k 3.2 kg, were shorn, treated with

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CASSIDA ET AL.

Table 1. Nutritive composition of hay:tyfon diets as consumed by lambs during the digestion trial phasea Hay:tyfon dry matter ratiobC Item

1oo:o

73:28

42:58

Dry matter

89.8

25.1

14.3

Neutral detergent fiber Acid detergent fiber Cellulose Hemicellulose Permanganate lignin Crude protein Ash Neutral detergent solubles

70.9 39.2 33.1 31.7 5.2 8.4 5.4 29.2

56.6 32.3 27.2 24.3 4.3 10.8 8.3 43.4

23:77

0:lOO

SEM

11.1

8.8

1.07

32.1 21.2 17.0 10.8 3.4 15.2 12.9 68.3

20.8 16.1 12.1 4.6 2.8 17.3 15.3 79.7

1.20 .67 .78 .65 .33 .53 .42 1.20

7L % of Dry matter

41.9 25.5 20.9 16.3 3.7 13.4 10.8 58.5

aLambs had free-choice access to a loose trace mineral salt premix !Lamb and Sheep Mineral Mix, Agway, Syracuse, NY) that contained 39% salt, 20% Ca, ,0067~Co, .46% Fe, .007%’I, .8% Mn, 1.6% Zn, and .009% Se. bDM, fiber, and CP concentrations in harvested tyfon during the five periods were 8.71 .63% DM, 21.29 ? 1.60% NDF, 16.21 ? 1.06% ADF, and 17.21 f .84%~CP. ‘DM, fiber, and CP concentrations in chopped grass hay during the five periods were 89.28 f 1.66% DM, 70.93 f .40% NDF, 39.52 ? .23% ADF, and 8.08 .225% CP.

*

+

.

ivermectin (Ivomec, Merck & Co., Rahway, N J ) to control parasites, and received approximately 50% tyfon in their diet for 7 d before the experiment. Lambs were housed in individual metabolism crates in a barn with a constant 16-h photoperiod and temperature maintained above 10°C. Treatment of the experimental lambs was in accordance with regulations of the University of Maine Animal Care and Use Committee. Experimental design was a 5 x 5 Latin square with 21-d periods. Periods included 7 d for adaptation to diets, followed by 6 d of ad libitum feed intake measurements. Hereafter, this 6-d period will be referred to as the intake ( I) phase of the experiment. The final 8 d of each period were the digestion ( D ) phase of the experiment. Dietary treatments consisted of the following hay: tyfon ratios (percentage, DM basis): 1OO:O; 75:25; 50: 50; 25:75; and 0:lOO. As-fed ratios were adjusted weekly based on DM analysis of hay and tyfon. Because feed bunks were not large enough to hold the entire daily allotment of feed for lambs on the bulky high-tyfon diets, each lamb’s feed allotment was weighed into a large container in the morning and feed bunks were refilled at intervals throughout the day until the entire allotment was fed. When feed was placed in bunks, whole tyfon leaves and chopped hay were layered alternately. Water and a mineral supplement that contained iodine (Lamb and Sheep Mineral Mix, Agway, Syracuse, NY) were available to lambs a t all times. Second-cut, mixed-mostly-grass hay was chopped to approximately a n 8-cm length in a single session before the experiment began. To minimize variation in hay quality during the experiment, chopped hay was mixed before it was stored in bags. Tyfon leaves were harvested by hand approximately 8 cm above ground

level from September 8 to December 22 ( 6 3 to 168 d after the tyfon was planted on July 7, 1989) and separated from senesced leaves and weeds. Initially tyfon was harvested each morning, but subsequent cool weather allowed a 2- to 3-d supply to be harvested. Tyfon nutritive composition was relatively stable over time (Table 1) and consistent with reported values for tyfon (Guillard and Allinson, 1988; Guillard et al., 1988). Nitrate nitrogen concentration of tyfon was low, averaging 600 m g k g of DM over the trial. The nutritive composition of the diets consumed by lambs during the digestion trial is presented in Table 1. Experimental Measurements. During the ad libitum intake phase, lambs were offered feed to ensure 10% refusal. Samples of hay and tyfon were taken daily and composited separately over the collection phase. Hay and tyfon in the orts were separated and weighed for lambs that were fed mixed diets, and a separate hay orts and tyfon orts composite sample was kept for each lamb and each collection phase. Composite hay and hay orts samples were stored in plastic bags at ambient temperature during the collection phase, whereas composite tyfon and tyfon orts samples were frozen. Dry matter intake was calculated on both a gramdday basis and as a percentage of BW.75 (metabolic BW) to allow more accurate comparison of feed intake among growing lambs. Water intake was measured as weight loss from buckets, and intake of water from the feed was calculated from feed intake data. During the D phase, lambs were offered feed restricted to 90% of their average ad libitum DMI. Feed and orts sampling and water intake measurement were performed as in the I phase. Feces and urine were collected daily for measurement of digestibility and water excretion, mixed thoroughly, subsampled, composited for each sheep, and stored at ambient


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DIGESTIBILITY OF BRASSICA/HAY DIETS FOR LAMBS

temperature until the end of the period. A 24-h lag time between feed consumption and fecal elimination was assumed (Schneider and Flatt, 1975). Before feeding on the last day of the digestion trial, jugular blood samples were taken by venipuncture into heparinized test tubes, and lambs were weighed. Between periods, lambs were allowed a 6-h exercise period in a group pen without access to feed and then switched abruptly to their new diets. Analyses. Feed, orts, and feces samples were dried a t 60°C immediately after each collection phase, ground to pass a l-mm screen, equilibrated to atmospheric humidity, and stored in plastic bags. Crude protein of feeds, orts, and feces was determined using a semiautomatic Kjeldahl method (AOAC, - ' 1984) on a Kjeltec Auto 1030 Analyzer (Tecator, Hoganas, Sweden). Nitrate concentration in feeds was determined using a colorimetric Cd-reduction method on a flow injection analyzer (Lachet, Milwaukee, WI) following aqueous extraction. Neutral detergent fiber, neutral detergent solubles ( NDS), acid detergent fiber, cellulose, hemicellulose, and permanganate lignin were determined sequentially in feed, orts, and feces using the procedures of Goering and Van Soest ( 1 9 7 0 ) as modified by Cherney et al. (1985). Apparent digestibility coefficients were calculated for DM, OM, NDF, ADF, cellulose, hemicellulose, CP, and NDS. Jugular blood samples were analyzed immediately after collection for packed-cell volume ( PCV) , red blood cell count ( RBC) , hemoglobin concentration ( Hb), and Heinz-Ehrlich bodies. Blood was drawn into capillary tubes and centrifuged, and PCV was read from a standard chart. A Hycel Counter 300 (Hycel, Houston, TX) was used to determine RBC and Hb. A blood smear was stained with new methylene blue N and examined under the microscope for the presence of Heinz-Ehrlich bodies. An aliquot of blood was centrifuged a t 740 x g for 20 min, and plasma was separated and frozen for later hormone analyses. Plasma thyroxine ( T 4) and triiodothyronine ( T 3) concentrations in plasma were determined using radioimmunoassay kits ( 1251 Thyroxine and 1251 Triiodothyronine, ICN Biomedical, Carson, CA). The sensitivity of the assays was .5 pgIdL for T4 and 1 ngl dL for T3. Statistical Analyses. Data were analyzed using the GLM procedures of SAS ( 1 9 8 5 ) with the model for the Latin-square design including terms for animal, period, dietary treatment, and residual. There were no missing data. Fisher's protected LSD ( P < . 0 5 ) test was used to separate treatment means. Because the proportion of tyfon actually consumed by lambs differed from the desired 25% treatment increments in both the intake and digestion trial phases, multiple linear regression (SAS, 1985) was employed instead of polynomial contrasts to relate treatment means for

'600

I

.U 0 0 LL

C C

A H #

600-

# @

,e*DMI-I

200

0 0 4 0 0

Y=930.49+4.50X

RZ =.99

0 DMI-D

Y=736.58+1 1.64X-.08X2

A DDMI

Y=448.30+5.52X

20

40

R' =.99

R2 z.96

60

80

I00

Tyfon, % of dietary DM

Figure 1. Dry matter intake during intake [DMI-I) and digestion trial (DMI-DJ phases and digestible DM intake [DDMI) during the digestion trial by lambs fed diets that differed in hay:tyfon ratio.

feed intake and apparent digestibility data to the proportion of tyfon in the diet. Treatment means were used in regression analyses.

Results

Feed Intake. During the I phase, DMI increased linearly ( P < .0001) as the percentage of tyfon in the diet increased (Figure 1 ) . Means for DMI as a percentage of metabolic BW (Table 2 ) revealed the same trend ( P < .05) among treatments as did DMI. During the D phase, DMI was least ( P < . 0 5 ) with the 1OO:O diet (Table 2 ) , and DMI fit a quadratic ( P < .05) regression model with peak intake a t approximately 25% hay in the diet (Figure 1 ) . However, during the D phase, digestible DMI (DDMI) increased linearly ( P < .01) with tyfon intake (Figure 1). Treatment did not affect ADG ( P < .16, Table 2 ) . Water Balance. Total water intake (Table 2 ) was a linear function ( P < ,011 of the proportion of tyfon in the diet in both the I and D phases. Regression equations were similar in both phases ( Y = .82 + .12X, R2 = .97 in the I phase; Y = .83 + .11X, R2 = .99 in the D phase, where Y = total water intake and X = percentage of tyfon consumed). Urinary water excretion increased in proportion to water intake (Table 2 ) ; however, urine production by lambs on diets containing 50% or higher of tyfon exceeded the handling capacity of the metabolism crates, resulting in underestimation of urinary output. Feces from lambs fed the 5050, 25:75 and 0:lOO diets had a paste-like consistency and contained more


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CASSIDA ET AL.

Table 2. Dry matter and water intake by lambs fed diets containing different hay:tyfon ratios Hay:tyfon dry matter ratio Itema

1oo:o

75:25

25:75

0:lOO

SEM

82.1 1,325d 9.ld

100.0 1,35gd 9.3d

23.0 130 .9

50:50

~~

Intake phase DM intake % Tyfon consumed g/d % of Metabolic BW, kg75 Water intake Imbibed, Ud In feed, Wd Total intake, U d Digestion trial phase DM intake 5% Tyfon consumed dd % of Metabolic BW, kg75 Digestible DMI, gld Water balance Imbibed, U d In feed, Ud Total intake, U d Urine, U d Fecal, Ud Fecal DM, % Average daily gain, gJd

0 922b 6.3b

1.66b .09b 1.75b

0 731b 5.0b 401a

34.3 1,09lbc 7.4b"

64.6 1,220'd 8.3Cd

.11' 3.53c 3.64'

7.65d 7.76d

28.0 1,019' 7.OC 650b

1.22b .87b 1.31b .45b .54b' 38.3b 35

.13' 3.06' 3.19' 1.93' .70Cd 34.9b 46

.ll' 10.40e 10.51e

.11'

.17' 12.8gf 13.06f

100.0 1,106' 7.6Cd 952d

77.0 1,181' 8.1d

57.5 1,117' 7.6'd 780bC

.15' 9.33e 9.48e 6.37e .78d 26.6' 163

.1oc 6.62d 6.72d 4.22d .79d 29.6' 110

.40 3.01 2.47

22.9 126 .8

4.4

.14' 11.36f 11.50f 8.65f .37b 28.5' 57

.29 2.66 2.47 1.96 .13 3.22 37.5

aEach value represents the mean of five observations. b,c,d,e,fMeanswithin a row that do not have common superscripts differ ( P < ,051.

water than feces from lambs fed the 1OO:O or 75:25 diets ( P < .05, Table 2). Total water excretion in feces on high-tyfon diets was low because of the small quantity of feces excreted and was numerically least for the all-tyfon ( 0 : l O O ) diet. Apparent Digestibility. Apparent digestibilities of dietary components are reported in Table 3. Altering the hay:tyfon ratio in the diet affected apparent digestibilities of all dietary fraction except hemicellulose. Digestibilities of DM ( P < .001), CP ( P < .Ol),

and NDS ( P < .05) were linear functions of the proportion of tyfon in the diet (Figure 2), as was OM digestibility ( P < .01). Digestibilities of NDF ( P < .lo), ADF ( P < .05), and cellulose ( P < .05) were quadratic functions of the proportion of tyfon in diets (Figure 3 ) . Blood Components. There were no differences among treatments for lamb plasma RBC, Hb, or concentration of T 4 and T 3 (Table 4 ) . However, PCV tended ( P < .06) t o be less with the 25:75 and 0 : l O O

Table 3. Apparent digestibility of dietary nutritive fractions in lambs fed diets that contained different hay:tyfon ratios Hay:tyfon dry matter ratio consumed Itema

1oo:o

72:28

4258

2337

Regression 0:lOO

SEM

Linear

P