Oilseed meals or fortified cereal grain supplements for young sheep fed roughage diets.

Abstract

OILSEED MEALS OR FORTIFIED CEREAL GRAIN SUPPLEMENTS FOR YOUNG SHEEP FED ROUGHAGE DIETS a a R.M. DIXON , W. KARDA , B.J. HOSKINGab and A.R. EGAN a SUMMARY In Experiment 1 46 young crossbred sheep (18-24 kg liveweight (LW)) were fed OCR 63 days chcp@ barley straw or oat straw (a) alone (NI& or given supplements each third day of (b) barley grain + urea + Na.,SO, at 1.1% LW ww I (c) safflower meal at 1.8% LirJ (SAF) or (d) linseed'mea1 at 1.1% rJw (LIN) 0 Straw DM intake was similar for the two straws (11454261 g/'3 d), and was increased 17.33% (P(O.05) by each of the supplements. Rumen NH344 concentrations were on average 11 and 22 mg PJ/l for NIL treatments and were increased by all supplements. BAR supplement decreased rumen pH below 6.0 only briefly. Disappearance cf straw from nylon bags increased due to BAR supplement, and was further increased by SAF and LIL? supplements. Sheep given NIL supplements lost LW (-85 to -103 g/d), while each of the supplements resulted in approximate LW maintenance. In Experiment 2 46 young Merino sheep (26-32 kg LW) were fed for 42 days chopped pasture hay and the supplement treatments described in Experiment 1. Hay DM intake with NIL (2555 g/3 a> was decreased (P(O.05) by BAR supplement, but was not affected by SAF or LIN supplements. Sheep given NIL maintained LW (4 g/d); LW change tended to increase to i3 g/d with BAR, and increased (P(O.05) to 50-53 g/d with SAF and LIN supplements. Disappearance of supplement N from nylon bags indicated that both SAE' and LIN supplements provided rurnen degradable N rather than undegraded dietary protein. 'l`hese experiments indicated that when young sheep were fed cereal straws alone and were losing LW, supplements based on cereal grain + urea N + inorganic S could be as effective as oilseed meals high in true protein to maintain LW. However where the basal roughage was of sufficient quality for the sheep to maintain LW, the cereal grain + urea !-J + inorganic S supplement was much less efficient than oilseed meals to increase LkJ gain and wool growth. INT9ODUCTIOFJ When animals are fed roughage diets of low nitrogen (It) content and lcw digestibility, supplements high in ti and other essential nutrients often result in major increases in roughage intake and animal productivity. Despite numerous,published experiments the responses of animals in various physioltiical states and consuming various types of low N roughage to provision of the supplementary N as rurnen degradable f-J (EXDN), or as undegraded dietary protein (UDP), or various proportions of RDPJ to UDP are not clear. For example Kellaway and Leibholz (1981) concluded that roughage intake and liveweight (LW) gain responses obtained with supplementary RIM were often equal to those obtained with supplements high in UDP. Conversely other research groups (Hennessy, 1981; Preston and Leng, 1987) have concluded that productivity respnses to supplements of RDN were generally low compared with supplements containing substantial,proportions of UDP CL 'bypass protein'. Egan (1984) and Hunter (1988) have discussed the balance between supply and demand for abscrbed amino acids for various dietary situations and for animals in various physiological states, and likely animal res-ponses to additional absorbed amino acids. a. b. School of Agriculture and Forestry, The University of Melbourne, Parkville, Vic, 3052. Present address: Department of Agriculture, University of Reading, Earley Gate, E&ading RG2 6AT, United Kingdom. 15 tie foilowing studies were undertaken to further investigate responses of young sheep fed several types of roughage to supplements high in JY. Supplements examined were barley grain plus urea and inorganic sulpher, safflower seed meal known to contain a high proportion of fibre and with the protein readily fermented in the rumen, and linseed meal known to be low in fibre and with a protein less extensively fermented in the rumen. Roughages examined were low quality oat straw and barley straw, and a medium quality grass pasture hay. Supplements were given once each three days to simulate the infrequent feeding of supplements which is the usual management practice on cmrcial farms. MATERIALS AND METHODS Exueriment 1 Forty-six Merino x Romney cross lambs initially approximately 12 months of age and 21-31 kg liveweight (LW) were used in the experiment. The sheep were maintained in either single pens or in metabolism crates. The sheep were divided into six blocks on the basis of surgical modification and liveweight; blocks l-3 were rumen cannulated whereas blocks 4-6 were not cannulated. Eight dietary treatints were imposed for each of two periods of 63 days, and the sheep within each block were allocated at random to the eight diets. Blocks 1 -3 were held in the metabolism crates for the first 42 days of each period, and Blocks 4-6 were held in the metabolism crates from days 43-63. The diets consisted of two roughages (chopped barley straw or chopped oat straw and minerals) given ad libitum (approximately 20% excess of previous intake) alone (NIL) or supplemented each third day with 1.1% LW barley grain plus urea plus sodium sulphate (BAR), with 1.8% LW safflower meal (SAF) or with 1.1% LW linseed meal (LIP& The supplements were intended to provide approximately equal amounts of 1J. The BAR supplement was made by preparing an aqueous solution of 344 g urea and 67 g sodium sulphate per i, and on the day of providing supplements to the sheep mixing 200 ml of this solution with each kg airdry barley grain. Due to the difficulties of satisfactorily measuring roughage intake of the sheep when held in single pens, only the intake of roughage when the sheep were held in metabolism crates was considered reliable. Thus reported measurements of intake were made from day 25 to day 42 for Blocks l-3, and from day 46 to day 63 for Blocks 4-6. Total collection of faeces to determine digestibility was done from day 34 to day 42 for Blocks l-3, and from day 55 to day 63 for Biocks 4-6. Measurements of rumen digestion were made in the 24 cannulated sheep in Blocks l-3. Nylon bags (45 x 110 m, 44 p pore size cloth) containing approximately 2 g straw DM were inserted into the r:umen at the time of providing supplements, and duplicate bags removed after 24 h, 48 h and 72 h. Nylon bags containing straw were also inserted 24 h or 48 h after providing supplements and duplicate bags were removed after 24 h incubation and also in the former case 48 h incubation. During one 3 d feeding cycle samples of rumen fluid were obtained by gentle suction from nylon gauze covered probes in the rumen. pH was measured immediately using a glass electrode and 40 ml samples were acidified (0.5 ml, 10 N H2SO4) and stored for subsequent NH3-N analysis. Sheep were weighed at 6 day or 9 day intervals on day 1 of the feeding cycle and before feeding, and LW change calculated by linear regression of LW and time. Wool growth was measured by clipping midside patches (100 x 100 mn) on approximately day 21 and day 49 of each.period. Following the above feeding period all sheep were fed oat straw and respective supplement treatments. Sheep were killed with an overdose of sodium pentabarbitone 6 h, 23.5 or 71.5 h after offering supplements, and the reticula-rurnen contents weighed and smled. 16 Experiment 2 Forty-six Merino lambs initially approximately 15 months of age and 25-33 kg LW were used. The treatments imposed and measurements were similar to Experiment 1, the major difference being that the roughage consisted of grass pasture hay. The experimental design differed to the extent that measurements were made with the group of sheep not surgically modified during period 1, while the equivalent measurements with rumen cannulated sheep were made during period 2. Each period was 42 days. In addition to the measurements for Experiment 1 the rate of disappearance of supplement DM and N from nylon bags incubated in the rumen for 6, 24, 48 and 72 h was determined. Following these measurements the sheep were killed and reticula-rumen contents measured. RESULTS Experiment 1 The leaf/stem ratio of the barley straw was 0.88, but the straw also contained appreciable proportions of head (81 g/kg) and weed (72 g/kg) (Table 1). Grinding energy of barley stem (333 J/g) and head (392 J/g) were much higher than for barley leaf (134 J/g) and the weed (54 J/g). The leaf/stem ratio of the oat straw was 0.55, and the straw contained #only low proportions of head (36 g/kg) and of weed (8 g/kg). Grinding energy of oat stun (144 J/g) was higher than that of oat leaf (92 J/g), but both were much lower than the respective fractions of barley straw. Consequently the grinding energy of entire oat straw (113 J/g) was much lower than that of entire barley straw (193 J/g). Contents of N, NDF and ADF and IVOMD were similar for the two straws. TABLE 1. Experiment 1. Proportions of morphological components, proximal analysis (g/kg) and grinding energy of entire straw and straw components Barley straw Entire Leaf Stem Head Weed Proportion of components Grinding energy (J/g DM) Organic matter Nitrogen NDF ADF Lignin Silica q?oMD I 1000 193 954 4.3 839 497 52 10 467 396 134 933 5.4 782 491 34 29 650 452 333 966 2.5 895 553 ,70 8 303 81 392 72 54 Oat straw Entire Leaf Stem 1000 113 346 92 612 144 964 2.2 846 543 81 1 253 955 958 6.0 9.4 744 547 378 370 48 74 16. 1 562 364 961 966 4.0 4.6 833 819 417 440 61 41 1 3 446 608 Oat straw also contained 36 g/kg of head and 8 g/kg of weed. The N contents of the oilseed meal supplements were 37.0 g/kg for safflower meal and 47.1 g/kg for linseed meal. Barley grain contained 18.4 g N/kg, and the fortified barley grain 52.0 g N/kg. The safflower meal was extracted from safflower seeds without prior removal of the hull, and had high contents of NDF (634 g/kg), ADF (445 g/kg) and lignin (155 g/kg). 17 The intakes of the two straws when fed alone were similar (1261 and 1145 g/3 d for barley and oat respectively) (Table 2). Intakes of both straws were increased by the supplements by 17-33%, and there were no differences among supplements in straw intake. Grinding energy of straw refusals (264-277 J/g for barley, 135-142 J/g for oat) were similar to the respective stem fractions, indicating that sheep selectively consumed the leaf fraction. DM digestibility of oat straw (432 g/kg) was greater (PtO.05) than for barley straw (396 g/kg). DM digestibility was increased (P<O.OS) by the SAF supplement (to 458 and 467 g/kg) and further increased (P(O.05) by the BAR and LIN supplements to the range 503 to 524 g/kg. Digestible DM intakes were 495 and 499 g/3 d for the straws fed alone, and were increased to the range 856 to 949 g digestible DM/ 3 d for the supplemented diets. Sheep fed straw alone were losing LW at 85 to 103 g/d, while all supplements resulted in approximate LW maintenance. Clean wool growth was similarly increased from 33 mg per patch per day for the sheep fed straw alone to 47-58 mg per patch per day for the sheep receiving supplements. TABLE 2, Experiment 1. Intake, digestion and growth of lambs given straw ad libitum alone or with supplements each third day of fortified barley grain, safflower meal or linseed meal (n = 11 or 12) The rumen NH3-N concentration was low (11 and 22 mg N/l) in sheep fed straw alone (Table 3). When supplements were given NH -N concentration was increased on Day 1 of the feeding cycle, but by Day 3 aad decreased almost to the concentrations in sheep given the straw alone. Rumen pH was greater than about pH 6.2 for most of the feeding cycle. Rumen pH was depressed to pH 6.0 or less on Day 1 of the feeding cycle when BAR supplement was given, but this depression was brief, being observed at only one sampling time. Rate of disappearance of straw fram nylon bags over 24 h was increased markedly by all the supplements and particularly on Day 1 of the 3 day feeding cycle, and was increased more by the two oilseed meals than by the fortified barley grain. 18 TABLE 3. Experiment 1. Disappearance of DM from nylon bags incubated in the rumen, and rumen fluid pH and NH3-N of lambs given straw alone or supplemented with fortified barley grain, safflower meal or linseed meal (n = 6) Experiment 2 The pasture hay offered contained 16.1 g N, 692 g NDF, 400 g ADF and 45 g lignin per kg DM, The supplements were similar in composition to those used in Experiment 1. Intake of hay given alone was 2555 g DM/3 d, and intake was depressed (P<O.OS) by the BAR supplement with a substitution rate of 1.0 (Table 4). TABLE 4. Experiment 2. Intake, digestion and growth in young sheep given grass hay ad libitum alone or with supplements each third day of fortified barley, safflower meal or linseed meal (n = 10 or 12). 19 Hay intake was not significantly changed (P>O.OS) by the oilseed meal supplements, and substitution rates for both supplements were 0.4. DM digestibility was 1ittl.e affected by the supplements, and digestible DM intakes tended to increase by G% for the BAR supplement and 9-11% for the SAF and LIN supplements. Sheep given hay alone maintained LW (+ 4 g/d). BAR supplement tended to increase LW gain to 23 g/d, while the SAE' and LIN supplements increased (P<O.OS) LW gain to SO-53 g/d. Clean wool growth (83 mg/patch) was not affected by BAR supplement, tended to be increased by 7% by the SAF supplement and was increased (P<O.OS) by 22% by the LIN supplement. TABLE 5. Experiment 2. Disappearance of DM and N from nylon bags incubated in the rumen, rumen fluid pH and rumen fluid NH3-N concentration in young sheep given pasture hay ad libitum alone or with supplements each third day of fortified barley grain, safflower meal or linseed meal (n = 6). The rate of disappearance of supplement N from nylon bags indicates that both oilseed meals provided the majority of their N as RDN rather than as UDP, although linseed meal was less readily fermented than safflower meal. Following 24 h incubation 826 g/kg of safflower meal N and 762 g/kg of-linseed meal N had apparently disappeared from the nylon bags (Table S), Rumen pH was maintained when oilseed meal supplepnents were fed, but was depressed to pH 5.5 with BAR supplement. Rumen NH3-N concentration was elevated by all supplements on Day 1 of the feeding cycle, but was not different (P>O.OS) on Day 2 and Day 3. Hay 20 disappearance from nylon bags during 24 h on Day 1 of the feeding cycle was decreased (P<O.OS) by the BAR supplement, and was increased (P<O.OS) by both oilseed meal supplements. However by Day 2 of the feeding cycle only LIN supplement was associated with greater disappearance of hay DM from the nylon bags and by Day 3 there were no differences between dietary treatments. Reticula-rumen digesta at slaughter The amounts of wet and dry digesta present in the rumen at slaughter were similar for all treatments 23.5 and 71.5 h after offering supplements (Table 6). At 6 h after offering supplements the amount of digesta Dzvl was increased (P<O.OS) for all of the supplement treamnts. However the sheep accomodated the additional DM in the ingested supplant not by increasing the amount of wet digesta, but by increasing the DM content of that digesta; DM content increased from 11% for NIL sheep to 13.16% for the sheep consuming supplements. TABLE 6. Weights (g/kg fleece-free LW) of wet digesta and of dry digesta in the reticula-rumen of sheep measured by slaughter at various times after offering supplements to sheep (n = 4) DISCUSSION The oat straw and the barley straws were selected to provide two straws of low and high grinding energy, but similar contents of N, NDF, ADF and IVOMD, Oat straw is generally considered to be associated with higher voluntary intakes and to be of superior nutritive value to barley straw (McDonald et al. 1969; Mulholland et al. 1974). The grinding energies cf the two straws were similar to the highest and lowest values for a group of wheat straws within which voluntary intake by sheep of the straws increased from 303 g/d to 617 g/d as grinding energy decreased (Doyle et al. 1988). It would appear that if grinding energy is an important factor affecting voluntary intake of straws, separate relationships 'between grinding energy 21 and intake may leaf/stem ratio availability of In the present than of barley associated with occur for different species of straw. Parameters such as (apart from its effect on grinding energy) and nutrients in the straw to microbes may also be important. experiment the higher stem content of oat straw (612 g/kg.) straw (452 g/kg) may have negated any beneficial effects lower grinding energy of the oat straw. In Experiment 1 the intakes of the straws fed alone were about 20 g DM/kg LW, and the sheep were losing LW rapidly (-85 to -103 g/d) and producing only 2.4-2.6 g clean wool per day. The pasture hay used in Experiment 2 was higher in N and lower in NDF and ADF than the straws, and was associated with higher voluntary intake of about 26 g DM/'kg LW. Nevertheless these sheep were able only to maintain LW on this hay when fed alone. The rate of disappearance of oilseed meal M from the nylon bags of 63% and 44% at 6 h incubation and 83% and 76% at 24 h incubation for safflower meal and linseed meai respectively (Table 5) indicated that for both of these oilseed meals the majority of the N was fermented in the rumen to provide RDN rather than providing UDP for abserption from the small intestines. This disappearance from nylon bags is similar to previous measurements with samples o f those oilseed meals in our laboratories (Hosking ,et al. 1987). In Experiment 2 the 22% increase in wool production due to LIN supplement and the 9% increase due to SAF supplements also supported the concept that SAF provided little UDP and LIN a greater amount. The BAR supplement increased rate of digestion of the straw in the rumen, but was not as effective as the oilseed meals in this respect. BAR increased 24 h disappearance of barley straw by 61%, while LIU and SAF increased this disappearance by 85% and 92% respectively. The increases were less with oat straw, perhaps because 24 h disappearance of oat straw with NIL supplement (345 g/kg) was much greater than the equivalent disapparance of barley straw (232 g/kg) even though potential digestibilities, as reflected by the 72 h nylon bags with oilseed supplements, were similar. The increased straw digestion associated with the BAR supplement was probably primarily due to the urea N and Na SO in this supplement providing substrate for microbial activity. The r&d NH -N concentrations of 11 and 22 mg fJ/l when barley and oat straw respectively 3 were fed alone indicate that was a deficiency of NH -N substrate for rumen 3 microbial activity. The reasons for the greater straw fermentation with the oilseeds were not known, but may have been associated with an improved supply of peptides and amino acids as microbial substrates, changes in microbial populations present with the various supplements, or the short-term decrease in rumen pH associated with the BAR supplement. Rumen NH3-N supply in the rumen did not differ markedly between supplements (Table 3), but may have been less than optimal by Day 3 of the feeding cycle. Clearly 24 h disappearance of straw when supplements were fed was lower on Day 3 of the feeding cycle than on Day 1 and Day 2. The rate of rumen digestion of the pasture hay was increased by the two oilseed supplements, possibly because the NH3-N substrate availability (75-81 mg N/l) was less than that required for maximal rate of fermentation (Alvarez et al. 1983; Krebs et al. 1984) or due to provision of other microbial substrates such as peptides and amino acids. The decrease in the rate of rumen fermentation with the BAR supplement was probably due to changes in the microbial populations associated with starch ingestion (El-Shazly et al. 1961) and the depression in rumen pH (Mould and Orskov 1983/84; Dixon 1986). All of the supplements were associated with increases in intake of total DM by 42.64% over the 3 day feeding cycle, and most of this increase 22 occurred on Day 1 of the feeding cycle. However the similar amounts of wet and dry digesta DM in the rumen 23.5 and 71.5 h after providing supplements (Table 6) indicated that the 'rumen fill'` was similar for the NIL and the supplemented diets by this interval after offering supplements. A similar pattern occurred when the pasture hay was supplemented with the oilseeds. It would appear that an increased rate of fibre digestion allowed roughage intake to be maintained or increased. However a decreased rate of rumen digestion of hay and a decrease in hay intake were observed with the BAR supplement. Similar observations have been made by Orskov and Fraser (1975) where greatest depressions is roughage intake occurred when rate of rumen fibre fermentation was most severely reduced by pH depressions. The changes in rate of digestion of fibre in the rumen was probably an important factor contributing to the changes in roughage intakes which were observed. The greater amount of SAF supplement than of LI1J supplement and the higher content of indigestible fibre in SAF supplement did not affect the intake of either the straw or of the pasture hay, or the LW change of the sheep. When a basal diet of barley straw or oat straw was fed suppleinents which constituted 15.24% of total DM intake were able to change a severe LW loss to LW maintenance, and almost double wool growth. Most importantly the fortified barley grain supplement was almost as effective as the oilseed meal supplements to avoid the LW loss, and for practical feeding would be much lower in cost than oilseed meals. Possibly the physical form of the barley grain and urea were important. The wet mixture tended to be eaten slowly by the sheep and the grain was fed whole; -both of these factors would probably have contributed to slow fermentation of the barley grain in the rumen and the avoidance of severe depressions of rumen pH. A major practical disadvantage of the BAR supplement is that the mixture contained on a DM basis 7% urea. No cases of urea toxicity have been observed in our laboratories with this mixture, but obviously there is some risk of urea toxicity. However the results do indicate that where low levels of N supplements are given with cereal straw to achieve LW maintenance there is no advantage in including UDP rather than RDN in the supplement. Where the basal diet consisted of a medium quality pasture hay which could support LW maintenance and supplements were intended to increase productivity, there was a major advantage of the oilseed meal supplements over the BAR supplement to stimulate LW gain. Wool growth was not increased by the BAR supplement, and was increased most by the LIN supplement which had the highest UDP content. Coombe (1985) similarly observed substantial increases in intake, LW gain and wool growth when sunflower meal or rapeseed meal replaced a starch-urea mixture in oat straw based diets. The present experiment supports the concept that where LW gain or wool growth is required from young sheep fed roughage diets, supplements containing high levels of UDP are likely to have a substantial advantage and may well be more cost-effective than supplements containing high levels of RDN. ACKNOWLEDGEMENTS The authors wish to acknowledge the financial support for this work provided by the Australian Oilseeds Research Council and support from the International Development Program of Australian Universities and Colleges for a scholarship for W.K. REFERENCES ALVAREZ, F., DIXON, R.M. and PRESTON, T.R. (1983). In 'Recent Advances in Animal Nutritiorci in Australia 1983', p.9A, editors D.J. Farrell and Pran Vohra, (University of New England). 23 COOMBE, J.B. (1985) l Aust. J. Agric. Res. 36 : 717. In 'Ruminant Feeding Systems Utilizing Fibrous DIXON, R.M. ( Agricultural Residues - 1985', p.59, editor R.M. Dixon. (IDP : Canberra). 1986) l DOYLE, P.T.I CHANPONGSMJ, SoI WALES, W.J. and PEARCE, G.R. (1988). In 'Ruminant Feeding Systems, Utilizing Fibrous Agricultural Residues 1987', p.75, editor, R.M. Dixon. (IDP : Canberra). EGAN, A.R. (1984). In 'The Utilization of Fibrous Agricultural Residues as Animal Feeds', ~.25~ editor P.T. Doyle. (IDP : Canberra), EL-SHAZLY, KI DEHORITY, B.A. and JOHNSON, R.R. (1961). J. Anim. Sci. 20 : i 268. HENNESSY, D.W. (1981). In 'Recent Advances in Animal Nutrition in Australia 1981', p.74, editor D.J. Farrell. (University of New England). HOSKING, B.J.@ DIXON, R.M. and EGAN, A.R. (1987). In 'Herbivore Nutrition Research', p.205, editor M. Rose. (Aust. Soc. Anim. Prod.). Ai HUNTER, R.A. (1988). In 'Ruminant Feeding Systems Utilizing Fibrous Agricultural Residues - 1987', p.37, editor . R.M. Dixon. (IDP : Canberra). KELLAWAY, R.C. and LEIBHOLZ, J. (1981). In 'Recent Advances in Animal Nutrition in Australia 1981', p.66, editor D.J. Farrell.(University of New England). WEBS, G, and LENG, R.A. (1984). Proc. Aust. Soc. Anim. Prodn. 15 : 704. MCDONALD, P.# EDWARDS, R.A. and GREENHALGH, J.F.D. (1969). Animal Nutrition. (Oliver and Boyd : minburgh). mum, F.L. and ORSKOV, E.R. (1983/84). Anim. Feed Sci, Tech. 10 : 1. MULHOLLAND; J.G., COOMBE, J.B. and McMANUS, W.R. (1974). Aust. Jo Exp. Agric. Anim. Husb. 14 : 449. ORSKOV, E.R. and FRASER, C. (1975). Brit. J. Nub.' 34 : 493. = PRESTON, T.R. and LENG, R.A. (1987). Matching Ruminant Production Systems with Available Resources in the Tropics and Sub-tropics. (Penambul Books, Armidale). 24