绵羊食性

ANIMAL FEED SCIENCE AND TECHNOLOGY ELSEVIER Animal Feed Science and Technology 5 1 ( 1995 ) 73-90 Effect of ammonia treatment and carbohydrate supplementation on the intake and digestibility of barley straw diets by sheep C. Cast&lo, M. Fondevila*, J.A. Guada, A. de Vega Departamento de Produccibn Animal y Ciencia de 10s Alimentos, Universidad de Zaragoza, M. Serve& 177; 50013 Zaragoza, Spain Received 15 December 1993; accepted 17 May 1994 Abstract The changes in straw voluntary intake and apparent digestibility caused by the ammo- niation of straw and energy supplementation in diets fed to adult, non-productive sheep were studied in two experiments. In Experiment 1, untreated (US) or ammonia treated (TS) barley straw were given as the only feed to four ewes in a cross-over design. Ammo- niation increased straw dry matter (DM) intake from 30.2 to 50.6 g kg-’ LW”.75, organic matter digestibility (OMD) from 0.438 to 0.519 and digestible organic matter intake (DOMI) from 12.5 to 24.7 g kg-’ LW”.75, allowing energy maintenance requirements to be met. In Experiment 2, three groups of four ewes received US, with another three groups of four receiving TS, both supplemented with meadow grass hay (H) j rolled barley (B ) or sugar-beet pulp (P) in a 2 x 3 factorial design. Each supplement was given in amounts of 150, 300, 450 and 600 g day-‘, in a Latin-square design. The type of supplement did not significantly affect straw intake at any level of inclusion. The level of supplementation scarcely affected US intake, whereas DM intake of TS diminished linearly. Substitution rates were 0.49 + 0.088, 0.6 1+ 0.085 and 0.55 2 0.13 1 for TS-H, TS-B and TS-P diets, re- spectively (P> 0.05). Apparent digestibility of straw was not significantly affected by sup- plementation. Increases in total DOMI when the level of supplementation was augmented were lower in TS than in US diets, and with H than with B or P as supplements. To reach the DOMI obtained with TS as the only feed, US has to be supplemented with 420,272 or 269 g DM of H, B or P, respectively. Keys: Ammonia treatment; Barley straw; Carbohydrate; Digestibility, barley; Sheep, adult; Supplement feeding * Corresponding author. 0377-8401/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDI 0377-8401(95)00682-Y 14 C. Castrillo et al. /Animal Feed Science and Technology 5 l(1995) 73-90 1. Introduction The use of cereal straw for ruminant feeding is essentially constrained by its low digestibility and voluntary intake, so that energy requirements for mainte- nance are not satisfied when it is given as the only feed to animals (Castrillo et al., 199 1). Chemical treatment of straw, generally based on the use of alkalis, has been commonly used for improving both apparent digestibility and voluntary intake of straws (Chenost and Dulphy, 1987; Sundstol, 1988), but, when require- ments are above maintenance level, an energy supplement has to be included either in untreated or treated straw diets to meet those requirements. It has often been stated in the bibliography that the inclusion of supplements in roughage diets reduces both the intake and digestibility of straw, and that the extent of this depression depends on the quality of the basal roughage (Orr et al., 1985; Jarrige et al., 1986) and also on the source (Fahmy et al., 1984; Berge and Dulphy, 1985) and level (Garret et al., 1979; Henning et al., 1980) of supple- mentation. However, the minimum amount which causes the negative effects of supplements on straw intake and digestion to appear and the suitability of the combination of a certain type of feed at a given level of supplementation with either treated or untreated cereal straw to optimise its use in ruminants, is not yet totally clear. The present work studies the changes in the voluntary intake and apparent di- gestibility of cereal straw diets as a response to the treatment of straw with am- monia and its energy supplementation with different sources of carbohydrates. In this regard, two simultaneous experiments were designed using barley straw, either untreated or treated with anhydrous ammonia, offered ad libitum to adult sheep, as the only feed (Experiment 1 ), or supplemented with four increasing levels of grass hay, rolled barley or sugar-beet pulp (Experiment 2). The effects of the ammonia treatment of straw and the type and level of supplement on ru- men fermentation characteristics and feed degradation by sheep were studied in a complementary experiment (Fondevila et al., 1994). 2. Materials and methods 2. I. Animals and feeds Twenty-eight, 18-month-old Rasa Aragonesa, non-productive ewes, with ini- tial liveweights ranging between 40 and 49 kg (average 44.0? 0.45 kg) were penned individually, with free access to fresh water. The origin of the barley straw used experimentally, and the conditions for its treatment with anhydrous ammonia (30 g kg-‘), were the same as those de- scribed by Fondevila et al. ( 1994). Both untreated (US ) and ammonia-treated (TS) straws were chopped to 5-10 cm particle size. The daily ration of US was C. Castrillo et al. /Animal Feed Science and Technology Sl(l995) 73-90 75 Table 1 Chemical composition (g kg-’ DM) of feeds and their undegradable dry matter (uDM) and neutral detergent tibre (uNDF) content (g kg-’ DM) DM” OM N CF NDF ADF L N-ADF uDM uNDF Initial straw 914 949 4.2 451 830 520 85 1.9 - - Untreated straw (US) 689 943 15.7 440 814 495 82 2.0 390 337 Treated straw (TS) 867 940 17.0 439 778 493 78 2.9 266 212 Meadow hay (H) 863 896 23.1 302 609 339 51 - 205 160 Rolled barley ( B ) 872 973 19.3 14 309 96 17 - 60 51 Sugar-beet pulp (P) 870 948 15.7 214 514 250 38 - 52 52b a Grams per kilogram air-dry matter. b Assuming that all uDM was NDF, since there was not enough sample after rumen incubation to perform NDF analysis. Figures for DM, OM, N and NDF are average means of weekly samples of feeds (n = 19). Figures for CF, ADF, LP and N-ADF are average means of pooled samples of feeds ( n = 5 ) Declared mineral composition of vitamin-mineral complex (g kg-‘): P, 130; S, 30; Ca, 180; Mg, 40; Cl, 82; Na, 5.5; Mn, 3; Fe, 2.5; Zn, 3.9; Cu, 0.5; Co, 0.014; I, 0.076; Se, 0.006. Vitamin content (UI kg-’ ): vitamin A, 400 000; vitamin D,, 80 000. The added Na2S04 is not included in this relation. sprayed and mixed with 0.4 1 kg-’ straw of a urea solution (7.5 % w/v) before offering it, in order to increase its nitrogen content to a similar level to that of TS. The supplements used were a meadow grass hay (H), from the same batch as that used by Fondevila et al. ( 1994), chopped to the same size as the straws, and rolled barley grain (B ) and pelleted unmolassed sugar-beet pulp (P) of a differ- ent origin to that used by Fondevila et al. ( 1994). The chemical composition of the initial straw and the experimental straws and supplements is given in Table 1. 2.2. Experimental procedures Ewes were homogeneously allocated by weight into seven groups of four sheep. In Experiment 1, one group of four sheep was fed alternatively on US or TS as the only feed given in four experimental periods, i.e. two sheep per straw in each period. In a second experiment (Experiment 2 ), three of the remaining groups of ewes received US and the other three received TS, supplemented with either H, B or P, in a 2 x 3 factorial design. Supplements were given at four levels of inclu- sion ( 150, 300, 450 and 600 g day- ‘; air-dry basis) in a Latin square design (4x4). Straws were offered ad libitum, in three meals (at 09:00, 12:OO and 17:OO h), allowing for 15% refusals. Supplements were given separately, in a single meal at 09:OO h. Each sheep received daily 20 g of a commercial mineral-vitamin mix- ture (Pradial ovino, Nanta; Table 1)) enriched with Na2S04 at 50 g kg- ’ . In both experiments, each experimental period lasted 45 days, comprising 2 1 days for diet adaptation, 14 days for individual control of intake and 10 days for digestibility trial, three of these being for adaptation to the metabolic cages and seven for collection. To compensate the weight losses of the sheep fed on US as 16 C. Castrillo et al. /Animal Feed Science and Technology Sl(l995) 73-90 the sole feed (Experiment 1 ), these sheep received 300 g of rolled barley daily during the first week of the next adaptation period. The ewes were weighed at the beginning (Day 22) and at the end of the control of intake period (Day 35 ) and once the digestibility trial had concluded (Day 45). In order to determine the apparent digestibility of the supplements another balance was carried out at the end of the experiment with H or P as the only feed, each offered ad libitum to three sheep, after allowing 2 1 days for diet adaptation. Duplicated samples of feeds were incubated for 96 h in the rumen of three cannulated adult sheep fed on 900 g day-’ of alfalfa hay (Fondevila et al., 1993a) to determine the rumen undegradable dry matter fraction (uDM) of feeds and, once the bag residues from each feed were pooled, the undegradable neutral de- tergent fibre fraction ( uNDF, Table 1) . 2.3. Sampling and analyses The feeds were sampled daily and pooled and subsampled weekly to determine their dry matter (DM), organic matter (OM), Kjeldahl-N (Association of Ofti- cial Analytical Chemists (AOAC), 1980) and neutral detergent fibre (NDF) (Goering and Van Soest, 1975) content. Pooled feed samples for each latin square period were also analysed for crude fibre (CF) content (AOAC, 1980) and for acid detergent libre (ADF), permanganate lignin (L) and N linked to ADF (N- ADF, only for the straws) content (Goering and Van Soest, 1975). Analyses of US were performed after oven-drying samples at 45°C for 24 h, owing to their high moisture content after the addition of the urea solution. Refusals of feeds from the control of intake trial were analysed for their DM content. Faeces (after drying at 65°C for 48 h) and feed refusals from the balance of digestibility were analysed for their DM, OM, Kjeldahl-N and NDF content, following the above mentioned procedures. 2.4. Statistical analyses Statistical analyses were performed following the procedures described by Steel and Torrie ( 1980). Data from Experiment 1 were analysed by ANOVA as a cross- over design, comparing the effects of the type of straw (St) with the residual variance (8 d.f. ). In Experiment 2 the effects due to the factors St, type of sup- plement (Sp) and the interaction StxSp were contrasted with the variance be- tween animals ( 18 d.f. ), and the effect of the level of supplementation (Ls) and the interactions St x Ls, Spx Ls and St x Spx Ls were compared with the residual variance (5 1 d.f. ). The mean values of St and Sp were compared by Student’s t-test, and the means of Ls and its interactions were compared using Duncan’s multiple range test (PC 0.05 ). The nature of the response to the level of supplementation was stud- ied by orthogonal contrast analyses. The relationships between the variables were compared by simple or multiple regression analyses, removing the variance be- tween animals from the residual by a covariance analysis. Differences between C. Castrillo et al. /Animal Feed Science and Technology Sl(l995) 73-90 17 the regression coefficients of the linear equations were compared by homogeneity tests. 3. Results 3. I. Experiment I Table 2 presents the mean straw DM intake recorded in the control of intake period, together with the average DM intake of US and TS during the balance of digestibility and mean apparent DM, OM, NDF and CP digestibility coefficients (DMD, OMD, NDFD, CPD). In addition, Table 2 also shows the digestible OM intake (DOMI ), calculated for each sheep from its OM intake during the control of intake period and from the OMD obtained in the digestibility trial. The meta- bolic weight considered as the reference for intake parameters is derived from the liveweight at the beginning of the experiment (43.8 ? I .3 1 kg). In the control of intake period, the ewes which were fed on TS consumed 68% (P~O.001) more dry matter than those given US. Straw intake during the bal- ance of digestibility revealed the same trend as in the control of intake trial al- though the amount consumed was slightly reduced ( 8 and 19% lower for US and TS). Treatment improved DMD, OMD and NDFD by 2 1%, 18% and 24%, re- spectively (PC 0.001). By contrast, the apparent digestibility of CP was higher, though not significantly, in US than in TS. The improvements in both intake and OMD were reflected in a two-fold increase (PC 0.00 1) in DOMI. Table 2 Straw intake during the control of intake period, and straw intake and apparent digestibility coefti- cients obtained in the balance of digestibility, together with DOMI during the control of intake period, in sheep given untreated (US) or ammonia-treated (TS) straw as the sole feed (Experiment 1) us TS RSD” Control of intake period Straw (g DM day-’ ) 551a 858b 57.5 Straw (g DM kg-’ LW”.75) 30.2a 50.6b 3.05 Digestibility trial Straw intake (g DM day- ’ ) 471a 698b 81.8 DMD 0.416a 0.502b 0.029 OMD 0.438a 0.519b 0.029 NDFD 0.494a 0.61 lb 0.025 CPD 0.573 0.527 0.054 DOMIb (g kg-’ LW’.=) 12.5a 24.7b 1.64 a Residual standard deviation. b Calculated from total OM intake in the control of intake period and OMD from the digestibility trial. Different letters show statistical differences (PC 0.001). Ta bl e 3 (a ) A ve ra ge i ni tia l liv ew ei gh ts , su pp le m en t an d st ra w d ry m at te r in ta ke (D M I) an d pr op or tio n of s tra w co ns um ed (O /o ) o f un tre at ed (U S) or t re at ed (T S) s tra w d ie ts w ith 15 0- 60 0 g da y- ’ of h ay ( H ), ba rle y (B ) or s ug ar be et pu lp (P ) H B P 15 0 30 0 45 0 60 0 15 0 30 0 45 0 60 0 15 0 30 0 45 0 60 0 In iti al w ei gh t (k g) U S 44 .3 f0 .3 8 44 .5 40 .7 4 43 .8 kO .5 9 TS 43 .8 + 0. 50 44 .0 f0 .7 1 43 .8 + 0. 67 Su pp le m en t in ta ke U S 11 4d 23 1~ 34 7b 47 1a 13 1d 26 3~ 39 4b 52 2a 13 1d 26 0~ 39 3b 52 0a (g D M d ay -‘ ) TS 86 d 19 oc 21 6b 34 5a 13 1d 25 6~ 39 1b 52 2a 12 7d 26 2~ 39 1b 52 0a St ra w i nt ak e U S 52 7 49 3 49 4 45 3 57 6a 53 2a b 51 7a b 49 0b 56 8a b 60 6a 50 0b 55 8a b (g D M d ay -‘ ) TS 72 0a 64 4a b 59 8b 60 5b 85 0a 19 4a 68 8b 61 8b 71 7a 70 7a 58 8b 51 8b (g D M k g- ’ LW ’.“ ) U S 30 .6 28 .6 28 .7 26 .3 33 .4 a 30 .8 ab 30 .0 ab 28 .4 b 33 .5 ab 35 .7 a 29 .4 1, 32 .9 ab TS 42 .3 a 37 .8 ab 35 .2 b 35 .5 b 49 .la 46 .4 a 40 .2 b 36 .2 b 42 .5 a 41 .7 a 34 .5 b 30 .7 b (b ) Si gn ifi ca nt of s tra w t yp e, t yp e of s up pl em en t an d le ve l of s up pl em en ta tio n an d th ei r in te ra ct io ns St SP st xs p SD LS St xL s SP X LS St xS px Ls SD Su pp le m en t in ta ke H *Q er 31 .4 ** * N S tp 1 N S 23 .2 St ra w i nt ak e (g D M d ay -’ ) - N S N S 17 7. 6 - ** * N S N S 54 .3 (g D M k g- ’ Lv (I o. “) ** * N S N S 10 .0 - - N S N S 3. 2 Fo r ea ch t yp e of s tra w a nd s up pl em en t, di ff er en t le tte rs sh ow s ta tis tic al di ff er en ce s (P < 0. 05 ) . St , t yp e of s tra w ; Sp , t yp e of s up pl em en t; Ls , le ve l of s up pl em en ta tio n. N S, n ot s ig ni tic an t;Q P< :O .O 1; -P 0.05 ); *Pi 0.05; ***PC 0.00 1. 3.2. Experiment 2 Table 3 shows the mean values of supplement (g DM day- ’ ) and straw (g DM day- ’ and g DM kg- ’ LW”.75) consumed. Sheep given B or P consumed all the offered supplement in almost every case and hence intake differences between levels of both supplements were negligible and mainly caused by the variations in the DM content of feeds. By contrast, the H offered was not totally consumed, being refused to a greater extent when supplementing TS ( 3 1%) than US ( 12%)) but these proportions of refusals were not affected by its level of inclusion in the diet. The type of supplement did not significantly affect straw DM intake (average values of 567, 633 and 595 g DM day-’ for H, B and P diets), but, although StxSp interaction was not significant, the sheep which were fed the diet TS-B consumed about 100 g more straw DM daily than those given H (at levels of 150, 300 and 450) or P (at any level of supplementation). Ammonia treatment increased straw DM intake (P 0.05). Otherwise, although Spx Ls and StxSpx Ls interactions were not significant, diminution of TS intake was more noticeable when supplemented with B or P than with H. In order to estimate the substitution rates of US and TS by each supplement, linear regression equations were established between straw (y) and supplement (x) intake (g DM day-’ ). Intercepts, regression coefficients and statistics are shown in Table 4, obtained after having removed the variation due to the animal effect which accounted for an important proportion of total variation (64.5%, 80 C. Castrillo et al. /Animal Feed Science and Technology 51(1995) 73-90 22.4%, 34.6%, 82.8%, 78.0% and 33.0% for TS-H, TS-B, TS-P, US-H, US-B and US-P diets, respectively). The decrease in TS intake when increasing the supplement proportion followed a significant linear evolution for every supplement, but the linear decrease in US intake was only significant in B diets. The inclusion of a quadratic term did not improve the precision of any of the equations. Regression coefficients show the reduction in the amount of straw intake per unit of supplement ingested, i.e. the substitution rates of straw for each supplement. Substitution rates were 0.13 ? 0.090,0.2 12 0.069 or 0.11% 0.114 when H, B or P supplemented US, and 0.49 + 0.088,0.61? 0.085 or 0.55 + 0.13 1 with the same supplements in TS diets. These rates were lower in US than in TS in all cases, but there were no significant differences (P> 0.05) between supplements within straws