NITROGEN AND ENERGY SUPPLEMENTS FOR LOW QUALITY ROUGHAGES INTRODUCTION JANE LEIBHOLZ*

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1 NITROGEN AND ENERGY SUPPLEMENTS FOR LOW QUALITY ROUGHAGES INTRODUCTION JANE LEIBHOLZ* Edibility and the digestible energy content of low quality roughages may be increased by:- (i) treatment of the forages by chemical and/or physical processes (ii) provision of supplementary nutrients. The two approaches often are complementary, as treatments which increase intake or digestibility may generate a need for additional nutrients to supply the needs of rumen bacteria as well as of the host animal. In these papers we have considered nitrogen (N) requirements of rumen bacteria and of the animal, in animals fed untreated and chemically-treated forages of low nutritive value. The reason for considering both bacterial and animal requirements is because all proteins contain rumen-degradable and by-pass fractions, the relative significance of which is likely to vary with the circumstances in which it is fed. Proteins also provide supplementary energy and minerals which may increase the edibility of roughages. Thus, effects of protein supplements may be attributed to one or more of the following factors:- (i) slow release of N in the rumen (ii) increase in the proportion of nutrients absorbed as essential amino acids (iii) supplementary energy, including gluconeogenesis (iv) stimulatory effects on intake. EFFECT OF NITROGEN SUPPLEMENTS ON INTAKE AND UTILIZATION OF LOW QUALITY FORAGES R.C. KELLAWAY* and JANE LEIBHOLZ* The N requirements for rumen bacteria can be supplied as protein and/or nonprotein nitrogen (NPN). -In vitro - studies indicate that the optimum value for NPN to amino acid N for microbial growth is 75:25 (Maeng et - al ). This suggests that amino acid N in the rumen could limit the synthesis of bacterial protein synthesis when ruminants are fed low protein diets supplemented with NPN. However, in three experiments (Table 1) it was found that the efficiency of bacterial protein synthesis with supplements of casein and HCHO-casein were no higher than with a supplement of urea. Hence, it may be concluded that the microbial N requirements can be supplied as urea in animals fed low quality roughages, and the pre-formed amino acids are probably supplied by endogenous (1977) calculated that microbial protein supplies 0.5 g N/MJ metabolizable energy (ME) which is sufficient to support growth rates of 0.5 kg/day in cattle of 200 kg live weight and 350 g/day in sheep of 40 kg live weight. Energy intakes from low quality roughages would mostly restrict growth rates below these levels, so that digestible by-pass protein should not be a factor limiting growth on these diets. The response to N supplements given in addition to urea was studied in six experiments (Table 2). The mean response to protein supplements was a 3.7% and non-significant increase in roughage intake. The conclusions from this work are that NPN and proteins are equally effect- * Department of Animal Husbandry, University of Sydney, Camden, N.S.W

2 ive in stimulating feed intake and supplying N for microbial protein synthesis in ruminants fed low quality roughages. When the supply of N for microbial protein synthesis is not limiting, protein supplements have a negligible effect on the intake of roughages. TABLE 1 Effect of supplements of urea (U), casein (C) and HCHO-casein (TC) on bacterial protein synthesis (g N/kg organic matter (OM) apparently digested in stomach) and the flow of N to the duodenum -t All animals received the same daily weight of supplements from either casein or corn starch. TABLE 2 Summary of response to protein supplements of urea (U), meat meal (M), casein (C), HCHO-casein (TC), cottonseed meal (CSM) and cracked barley (CB) given to cattle fed low quality roughages 62

3 TABLE 2 (continued) -f- See footnote Table 1 ROLE OF NUTRITIONAL SUPPLEMENTS IN THE UTILIZATION OF LOW QUALITY FEEDS BY RUMINANTS T.J. KEMPTON* The aim in developing production feeding systems for ruminants from low quality diets is to use judicious amounts of supplements to alleviate nutritional deficiencies in the basal diet, to maintain or increase intake of the basal diet, to increase the efficiency of utilization of nutrients, and to increase production. However, not all feeds added to a diet will act as a true supplement, since often the feed added will substitute part of the nutrient supply from the basal diet. Ideally a supplement should maintain or increase intake of the basal dietary material. The important distinction therefore, is whether the feed material has a supplementary effect or a substitution effect. SUPPLEMENTATION OF LOb7 PROTEn DIETS GIVEN TO SHEEP WITH NPN AND BY-PASS PROTEINS Feeding trials with lambs given low protein roughage based diets have shown there was a need to supplement the diet with (i) NPN to maximize the outflow of microbial protein from the rumen and (ii) a source of by-pass protein to augment the supply of amino acids from microbial protein and to meet the amino acid requirement of the animal for production. The increased production associated with these supplements was attributed to anincreasedintake of the basal dietary material (Kempton 1981). Since the digestibility of low quality roughages is not increased by by-pass protein supplementation (Kempton and Leng 1979) the animal must derive additional energy to support production either from an increased intake of basal material, or from catabolism of the supplement (Abidin and Kempton 1981). EFFICIENCY OF FOOD UTILIZATION FOR GROWTH From the relation between digestible dry matter intake (DDM) and live weight * Department of Biochemistry and Nutrition, The University of New England, Armidale, N.S.W.,

4 gain for lambs given a variety of diets (see Kempton 1981) it was evident that (i) the efficiency of utilization of DDM above maintenance was relatively constant for all diets and (ii) liveweight gain is a function of total digestible nutrient intake and that for animals on each diet there is a response in both food intake and liveweight gain to optimizing the balance of absorbed nutrients by supplementing that diet with NPN and a by-pass protein and (iii) for production to be increased above that in response to the NPN and by-pass protein supplements, the animal must further increase DDM intake. This may not be possible if the animal is consuming diets of low digestibility. FOFMJLATION OF FOOD SUPPLEMENTS TO MEET THE LIMITATIONS TO PRODUCTION ON LOW PROTEIN DIETS Feed supplements should be formulated according to the order in which nutritional factors will limit production. (i) Efficiency of microbial protein synthesis in the rumen There is a critical level of ammonia in rumen fluid (20-50 mg N/l) below which microbial growth may be impaired or efficiency reduced (Satter and Slyter 1972). Provision of readily soluble NPN supplements such as urea will increase rumen ammonia levels for a short period immediately post feeding, however, the ammonia levels may be below the critical level for a period of time until the next intake of supplement. Under these conditions the outflow of microbial protein may be considerably reduced (Helmer and Bartley 1971) and may contribute in part to the lack of response to urea in the majority of grazing studies (Leng et - al ). Studies have shown that the efficiency of utilization of NPN for microbial protein synthesis in sheep can be considerably increased by providing urea continuously in the rumen, as compared with providing the same quantity of urea in a single dose (Meggison et - al ). Formulation of supplements in which the rate of ammonia and carbohydrate release are synchronized with the rate of energy release in fermentation may give production responses where no previous response has been achieved to NPN supplements. Protein meals which are slowly degraded in the rumen may also act as slow release sources of ammonia. (ii) Protein requirements for production The protein requirements of ruminants varies with the physiological status of the animal such that during early growth, late pregnancy and lactation, the supply of amino acids from microbial protein will not meet the amino acid requirements of the animal (grskov 1977). In these cases, it is often necessary to augment the supply of protein of microbial origin with a source of by-pass protein, The need to supplement a diet with a by-pass protein must be assessed from the supply of microbial protein and dietary protein in relation to the protein requirement of the animal and can be calculated by the methods of Roy et - al. - (1977). The quantity of by-pass protein containing meal to be fed to meet a protein deficit can be determined from a knowledge of the protein content and rumen degradability of the protein meal. The ruminal degradability of protein meals can be determined from the loss of N from the meal in solvents (Craig and Broderick 1981), or from nylon bags suspended in the rumen of sheep or cattle (Mehrez and grskov 1977; Kempton 1980). (iii) ME requirement for production The energy requirements of ruminants for maintenance, or for a desired level of production, can be calculated with a degree of precision from the relationships outlined by the Ministry of Agriculture, Fisheries and Food (MAFF) (1975). These calculations, however, make no allowance for the effects of supplementary feeds. For instance, there are no allowances made for substitution or supplementary effects of feeds on food intake; nor are there allowances for the increased efficiency of utilization of energy for production

5 when the energy supplements are digested post-ruminally (Preston and Leng 1980). At present, therefore, it is necessary to calculate the ME requirements for production from methods such as outlined by MAFF (1975), and then to use the nutritional principles of supplementary feeding to formulate feeds which will increase ME intake to the extent required to support the desired level of production. The intake of low protein roughages with a low ME content (7 MJ ME/kg DM) can be maintained or increased by supplementation with NPN and a by-pass protein. However, the animal may be unable to consume sufficient DM to provide the required ME to achieve maximum production, unless the digestibility of the basal diet is increased, or the energy density increased by including an energy supplement in the diet. Digestibility of low quality roughages can be increased by grinding or pelleting, or treating the roughage with materials such as alkali (Jackson 1977). Although these techniques increase digestibility, ME intake and production, they have limited practical application to the grazing ruminant industry in Australia. Alternatively, the basal diet can be supplemented with NPN, a by-pass protein and a source of energy which is digested post-ruminally and does not inhibit intake of the basal material (see Kempton 1982). It may be concluded that the rate of production of ruminants from low protein diets is restricted by the low intake of digestible nutrients. Supplementation with a source of NPN and by-pass protein will increase amino acid supply to the animal and increase food intake. Intake of low quality diets is ultimately restricted by the physical size of the rumen such that the animals may be unable to consume sufficient DM to meet the energy requirements for maximum production. Since the efficiency of microbial protein synthesis in the rumen and the efficiency of nutrient utilization for growth is not increased by supplementation, ME intake must be increased by other means. Under these conditions ME intake can be increased by increasing the digestibility of the basal dietary material, or by supplementing with an energy form which does not suppress intake of the basal material. EFFECTS OF ENERGY SUPPLEMENTS ON THE INTAKE AND UTILIZATION OF LOW QUALITY ROUGHAGES JANE LEIBHOLZ and RX. KELLAWAY The first factor limiting the performance of ruminants fed low quality roughages is usually their low intake of digestible energy. Cereal grains often are used as sources of additional energy for roughages eaten -ad libitum. - Blaxter and Wilson (1963) and Campling and Murdoch (1966) showed that, in most cases, inconcentrates, However, intake of take of roughages was reduced by addition of low quality hay (energy digestibility 45.4%) and straw was increased by feeding small amounts of concentrates (Blaxter and Wilson 1963; Campling and Murdoch 1966; Crabtree and Williams 1971).This effect may h.ave been due to the N content of the concentrate. When N was not limiting, Mulholland -et al. - (1976) found that intake of ground oat straw was not increased by inclusion of 5-40% starch in the diets. In the present experiments, intake of paspalum hay (Paspalum dilatatum) was measured when sheep and cattle were given small amounts of energy supplements. MATERIALS AND METHODS Experiments 1 and 2 Paspalum hay (digestible dry matter (DMD) 44-47%) was chopped and sprayed with urea (28 g/kg) and minerals. It was offered -ad libitum- to six cannulated wethers (40 kg live weight) in a crossover design in each experiment. Feed intake was measured daily. Each of the experimental diets shown in Table 3 was fed for 21 days. In Experiment 1 and for Diet 2, Experiment 2, sucrose and starch were uniformly sprayed on the hay. Faeces and urine were collected 65

6 Digest- from day and abomasal and rumen samples were taken from days ion in the stomach was estimated by reference to lignin and Cr EDTA. TABLE 3 Intake of low quality roughages and supplements Experiment 3 Paspalum hay was chopped and offered ad libitum to 30 Hereford e- steers (200 kg live weight). All steers were given 400 g/day of meat meal. Cracked wheat grain was offered once daily to 20 of the steers as shown in Table 3. The duration of the experiment was 70 days. In all experiments the energy supplement provided about 10% of the intake of air dry feed or 20% of digestible energy intake. RESULTS AND DISCUSSION Total feed intake (Experiment 1) was increased by the supplement of starch or sucrose, and there was a significant increase in intake of hay with the sucrose supplement. The increased feed intake resulted in an increased flow of N to the abomasum and a greater retention of N. 66

7 In Experiment 2, results were similar to Experiment 1 when starch was continuously infused into the rumen or sprayed on the feed. However, intake of hay was not significantly increased when starch was given only once daily or infused into the abomasum. Infusion of casein into the abomasum gave similar results. When cattle were given wheat supplements once daily, there was no significant change in intake of hay (Experiment 3) which confirms findings in Experiment 2 that starch given once daily did not increase feed intake or N balance in wethers (Diet 5), but the continuous supply of starch increased feed intake (Diets 2 and 3). The treatment of barley grain with alkali results in a slower release of energy than feeding cracked grain once daily (Sriskandarajah et - al ) and this may also result in a greater intake of roughages. It may be concluded that small supplements of starch (10% of air dry feed) can increase the intake of paspalum hay if the supplement is fed continuously. This would agree with the observation of Blaxter and Wilson (1963), Crabtree and Williams (1971) and Lamb and Eadie (1979), and this response was not due to the N content of the supplement as urea or meat meal was given in addition to the energy supplements. SUPPLEMENTATION OF PREGNANT COWS WITH PROTECTED PROTEINS WHEN FED TROPICAL FORAGE DIETS J-A. LINDSAY*, G.W.J. MASON* and M.A. TOLEMAN** Native pastures in the dry tropics rapidly decline in digestibility and N content with the onset of the dry season. N supplementation is offered as a management strategy to overcome the dry season nutritional deficit. This deficit occurs despite an abundance of dry standing pasture and one of the susceptible groups of cattle is lactating cows. MATERIALS AND METHODS Twenty mature pregnant Brahman crossbred cows were allocated on the basis of foetal age and fasting live weight to one of four treatments. All cows had reared a calf the previous year. The treatments imposed were: chaffed native pasture hay (NP); NP plus a supplement of 55 g N as urea sulphur (US); NP plus US and 1 kg of protected protein (US+PP) - 80% formaldehyde cottonseed meal; 10% fish meal; 10% meat and bone meal; and NP plus 2.0 kg lucerne chaff (MS). The cows were individually fed in pens on a basal diet of m- ad libitum native pasture hay (predominantly Heteropogon contortus) containing 0.4% N. Urea was sprayed onto the hay in a water solution and the other supplements were fed in a separate trough. The experiment took place during the last 60 days of pregnancy and feed intake, cow live weights and calf birth weights were recorded. Data were anal.yzed by analysis of variante for a randomized block design. Dif'ferences between. treatment means were tested using the LSD procedure. RESULTS AND DISCUSSION The results for liveweight change and dry matter intake during a feeding period are presented in Table day One animal on the NP control treatment died from nutritional deprivation othemise health and calving were normal. * Department of Primary Indus ** Department of Primary Indus tries, tries, Swan's Lagoon, Millaroo, Qld P-0. Box 1085, Townsvill e, Qld

8 TABLE 4 Mean liveweight change (LWC), mean dry matter intake (DMI) and mean calf birth weights of cows fed native pasture diets with N supplementation for 60 days pre-calving Means within rows with dissimilar superscripts are significantly different (P < 0.01). The liveweight loss of the NP animals was dramatic, with a mean loss of 48.9 kg recorded. There was a significant reduction in liveweight loss (P < 0.01) when the US supplement was offered and the PP and MS supplements initiated a significant liveweight gain (P < 0.01). Much of the response in live weight appeared to be explained by a stimulus in roughage intake with N supplementation. Lee et - al. - (1980) working with lactating beef cows also observed that protected protein supplementation increased hay intake. There was a concomitant response in liveweight gain and milk yield. The significant increase in roughage intake (P < 0.01) when PP was added to the US supplement indicates a response to slowly degraded ruminal N supplement or to increased nutrient supply post-ruminally (Sriskandarajah et al. 1980). - - The calves of the NP control cows had a mean live weight of 22 kg and the calves from supplemented cows were on average 44% heavier. The supplements merely allowed the cows to produce a calf of normal birth weight (R.G. Holroyd, personal communication) and the NP diet limited nutrient supply sufficiently to influence foetal growth. A similar depression in calf birth weight was observed by Russell m- et al. (1979) when -pre partum - energy intake was severely restricted. These results indicate that the pregnant cows fed on the poor quality tropical forage diet used in this experiment required an increased supply of nutrients to reduce liveweight losses and ensure a normal calf birth weight. Supplementation with urea sulphur will meet this requirement. However, if the cows are in poor body condition it is likely that supplementation with protected protein or lucerne hay is necessary not only to minimize liveweight loss but also to enable an increase in live weight to occur. THE ROLE OF PROTEIN SUPPLEMENTS IN THE NUTRITION OF BEEF CATTLE GRAZING NATIVE PASTURES OF THE NORTH COAST OF NEW SOUTH WALES D.W. HENNESSY* The north coast of N.S.W. has a climate in which 60% of the annual rainfall (1000 mm) falls in the hot summer months, when the temperature range is C, and this favours the dominance of pastures by summer-growing grasses. However, by July, cattle are faced with a forage which has a digestibility as low as 43% and N as low as 0.4% (Cohen 1978). Cattle are unable to meet their maintenance require- * N.S.W. Department of Agriculture, Agricultural Research Station, Grafton, N.S.W

9 ments on these pastures and lose weight. It is the objective of this paper to discuss three grazing trials in which cattle were given supplements of protein. EXPERIMENTAL Experiment 1 Thirty-six Hereford steers were allocated to four treatment groups and set grazed a carpet grass-dominant pasture in 12 paddocks in the experiment reported by Hennessy et al. (1981). A group was offered for 140 days from June, either (i) a mineral supplement daily or (ii) 600 g/head/day of a pelleted protein or (iii) 2100 g/bead/3.5 days of the pelleted meals or (iv) 560 g/head/day of pelleted cracked sorghum grain. From late November, supplementation of group 3 continued until late March when the cattle were removed and set to graze on improved pasture for 12 months. Protein meal supplements significantly (P < 0.01) increased the live weight of young steers at the end of their first winter, and the summer following, with the advantage persisting for a further 12 months after steers were placed onto an improved pasture. Results are presented in Table 5. TABLE 5 Mean live weight (kg) of young steers at the end of three consecutive periods Experiment 2 One hundred and twenty-nine heifers were put in four groups. Half of each group was offered a supplement of linseed meal ( g/day) whilst all heifers grazed together on unfertilized carpet grass pasture. Heifers that were supplemented with linseed meal during the winter period of 3 years were significantly (P < 0.01) heavier and weaned more calves than unsupplemented heifers (Table 6). Experiment 3 Forty-four Hereford heifers (200 kg live weight) were divided into three groups and set to graze carpet grass pasture. From June, heifers were offered either (i) access to a mineral supplement or (ii) 2800 g of the pelleted protein meal mix (same as in Experiment 1) every 3.5 days or (iii) same supplement as for group 2. In November, bulls were placed with heifers of groups 1 and 2 for 9 weeks at the end of which supplementation ceased. In the following July supplementation for groups 1 and 3 recommenced as for the previous winter. Only heifers in group 2 which were pregnant were supplemented; the non-pregnant heifers being given access to a mineral supplement. Supplementation in group 2 was on the basis of 16 g pellet/kgom75 live weight. In November of the second year, all heifers were placed with bulls for mating. In the third year supplementation recommenced in July for pregnant cows on the basis of 16 g pellet/kg0'75 live weight, up to a maximum of 1.4 kg/head/day. Weaning was in March when calves were 200 days of age. 69

10 TABLE 6 Live weight of supplemented and non-supplemented heifers at joining, and proportion of heifers becoming pregnant Live weight of the heifers during the first winter was increasedsubstantially by supplements and this increased live weight enabled all heifers to be in oestrus during the joining period of the first year. In contrast, only 20% of unsupplemented heifers cycled during their first year and none became pregnant (Table 7). Protein supplements to lactating heifers improved the weaning weight of calves (Table 7) and the proportion of the group which went back into calf. TABLE 7 Iiveweight and proportion of heifers calving, and the weaning weight of their calves when offered a protein supplement during the winter of consecutive years? As a percentage of previously lactating heifers or cows These experiments have indicated the role of supplementary protein in the diet of young cattle grazing carpet grass pastures that are typical of much of the unimproved grazing lands of north coastal N.S.W. Live weight of steers and live weight and fertility of heifers have been improved by the additional protein. Protein meals contain a fraction of soluble protein and a fraction that is 70

11 insoluble but degradable in the rumen, thereby providing the rumen with ammonia precursors and dietary undegraded protein in the intestine. Linseed meal is relatively unprotected (Ferguson 1975) compared to the pelleted meal used in Experiment 1 and twice-a-week feeding of linseed may be a less efficient way of maintaining a raised rumen ammonia level and of providing dietary non-degraded protein to the intestine than by feeding the less degradable protein meal. The better growth responses in Experiment 1 than in Experiment 2 may be partly due to these features. SUMMARY JANE LEIBHOLZ Several conclusions can be drawn from the papers presented in this contract. 1. In animals fed low quality roughages, requirements for microbial protein synthesis in the rumen could be supplied entirely by NPN. 2. Supplements of both NPN and proteins stimulated the intake of roughages of low N content and increased live weights and joining percentages. 3. Protein supplements, in addition to NPN, did not stimulate the intake of roughage in steers, but increased the roughage intake of pregnant Brahman crossbred cows. 4. Energy supplements, 20% of digestible energy as starch or sucrose, increased roughage intakes by 8-23%. REFERENCES ABIDIN, Z., and KEMPTON, T-J. (1981). Anim. Feed Sci. Technol. = 6: 145. BLAXTER, K-L., and WILSON, R.S. (1963). Anim. Prod. 5: 27. CAMPLING, R-C., and MURDOCH, J-C. (1966). J. Dairy Rer. 33: 1. CRABTREE, J-R., and WILLIAMS, G.L. (1971). Anim. Prod. 13: 71. COHEN, R.D.H. (1978). Ph.D. Thesis. University of New England. CRAIG, W.M., and BRODERICK, G.A. (1981). J. Dairy Sci. 64: 769. FERGUSON, K-A. (1975). In "Digestion and Metabolism in t= Ruminant", p. 448, editors I.W. McDonald and A-C-1. Warner. (University of New England Publishing Unit: Armidale.) HELMER, L-G., and BARTLEY, E-E. (1971). J. Dairy Sci. 54: 25. HENNESSY, D-W., WILLIAMSON, P-J., LOWE, R.F., and BOIGENT7D.R. (1981). J. - Agric. Sci., Camb. 96: 205. JACKSON, M.G. (1977). Anim. Feed Sci. Technol. 2: 105. KEMPTON, T.J. (1980). Trop. Anim. Prod. 5: 107.= KEMPTON, T.J. (1981). In "Recent Advancesyn Animal Nutrition", p. 52, editor D.J. Farrell. (University of New England Publishing Unit: Armidale.) KEMPTON, T.J. (1982). Proc. Aust. Soc. Anim. Prod. 14: 649. KEMPTON, T.J., and LENG, R-A. (1979). Br. J. Nutr. 42: 289. LAMB, C-S., and EADIE, J. (1979). J. Agric. Sci., Gag. 92: 235. LEE, G.J., HENNESSY, D.W., and WILLIAMSON, P.J. (1980). Psc. Aust. Soc. Anim. Prod. 13: 483. LEIBHOLZ, JANE, a KELLAWAY, R.C. (1979). Ann. Rech. Vet. lo: 274. LENG, R-A., MURRAY, R-M., NOLAN, J-L., and NORTON, B.W. (1973) Aust. Meat Res. Comm. Rev. 15: 1. MAENG, W-J., VAN NEVETFC.J., BALDWIN, R.L., and MORRIS, J.G. (1976). J. Dairy Sci. 59: 68. MEHREZ, A-Z., anf@rskov, E.R. (1977). J. Agric. Sci., Camb. 88: 645. MEGGISON, P-A., McMENIMAN, N.P., and ARMSTRONG, D.G. (1979). Proc. Nutr. Soc. 30: 146A. 71

12 MINISTRY OF AGRICULTURE, FISHERIES AND FOOD (1975). "Energy Allowances and Feeding Systems for Ruminants". Tech. Bull. 33. (Her Majesty's Stationery Office: London.) MULHOLLAND, J-G., COOMBE, J-B., and McMANUS, W.R. (1976). Aust. J. Agric. Res. 27: 139. PRSKOV, E.R. (1977). In "Protein Metabolism and Nutrition", p. 110, E.A.A.P. Publ. No. 22. PRESTON, T-R., and LENG, R.A. (1980). In "Digestive Physiology and Metabolism in Ruminants", p. 621, editors Y. Ruckebusch and P. Thivend. (MTP Press: Lancaster.) REDMAN, R-G., KELLAWAY, R-C., and LEIBHOLZ, JANE (1980). Br. J. Nutr. 44: 343. ROY, J.H.B., BALCH, CC., MILLER, E-L., grskov, E.R., and SMITH, R.H. (l-7). In "Proceedings of the Second International Symposium on Protein Metabolism and Nutrition", p RUSSELL, A.J.F., PEART, J.N Anim. Prod. 28: SATTER, L-D., and SLYTET L 2. J., and WHITE, 1-R. 35: (1979). SRISKANDARAJAH, N., ASHWOOD 1%). J. Agric. Sci., Caxib. 95: 555. SRISKANDAGAH, N., KELLAWAY, RX., and LEIBHOLZ, JANE (1981). Br. J. Nutr. (in press). 72