Effects of dietary energy and protein supply on liveweight (LW) gain and gain of protein, fat and ash in the carcass, and weight and gain of non-carcass organs were determined in 118 weaned crossbred lambs from two nutritional histories at Camden, NSW in 1991. Half of the lambs were fed to achieve and maintain LW at 35 kg (LOW group) and half of the lambs were fed ad libitum until they attained 50 kg LW (HIGH group), during a preliminary period of 126 days. In the subsequent experimental period, lambs were allocated to treatments providing 500, 800, 1200 or 1500 g/day of pelleted diets (123 g crude protein, 10 MJ ME/kg dry matter). Diets at each intake contained either 0, 30, 60 or 90 g of formaldehyde-treated casein (rumen escape protein, REP). This resulted in an experiment comparing LOW and HIGH group lambs at four energy intakes, within which were four rates of inclusion of REP. During the 90-day experimental period, LOW group lambs had higher rates of gain of LW, carcass weight and all non-carcass components than did HIGH lambs (P<0·001). At any rate of carcass gain, LOW lambs contained a significantly lower proportion of fat in carcass gain than did HIGH lambs (P<0·05). After adjustment to a common carcass weight, the carcass of LOW lambs contained a significantly lower mass of fat than did that of HIGH lambs at slaughter (P<0·05).Carcass fat gain in the experimental period was not affected by LW at the start of that period or by nutritional history once initial LW was accounted for as a covariate. Data were consistent with fat deposition being principally controlled by energy intake over the immediate pre-slaughter period. In contrast, responses to energy intake in the rate of gain of carcass muscles, ash, liver, head and feet and gut tissue were significantly greater in lambs of LOW compared to HIGH nutritional history. A significant component of this effect of nutritional history was attributable to LW differences between LOW and HIGH lambs; however, nutritional history still had a significant effect on these parameters once initial LW was accounted for as a covariate. Nutritional history may also have modified carcass composition by changing the partial efficiency of use of available energy for protein deposition without changing the partial energetic efficiency of fat deposition.

1, The significance of blood urea-nitrogen transfer to the rumen was examined in sheep given alkali-treated wheat straw supplemented with 3.5 (diet A), 5.9 (diet B) and 11.6 (diet C) g urea-N/kg dry matter (DM).2. Mean voluntary intakes of DM (g/d) were 897, 1149 and 1225 for diets A, B and C respectively, indicating significant (P < 0.05) intake responses to urea supplementation. Digestion studies were conducted at 90% of voluntary intake. Dietary N intakes (g/d) were 7.1, 11.5 and 18.6 for diets A, B and C respectively. 3. Absorption of ammonia-N from the rumen (g/d) was 3.5, 6.7 and 8.9 for diets A, B and C respectively, with all dietary differences being significantly different (P < 0.05). 4.Non-ammonia-N (NAN) leaving the abomasum (g/d) was 9.6, 12.7 and 14.8 for diets A, B and C respectively. Microbial N leaving the abomdsum (g/d) was 6.8, 9.6 and 10.7 for diets A, B and C respectively.Hence, significantly (P < 0.05) more N was provided to the intestines with increased urea supplementation. Net efficiencies of microbial protein synthesis (g N/kg organic matter apparently digested in the rumen), estimated from 16N incorporation, were 24.2, 23.7 and 25.3 for diets A, B and C respectively, and were not significantly different (P > 0.05). . ~~~~ B and C respectively, reflecting the high proportion of total N as urea-N in the diets. Proportions of microbial N derived from blood urea-N were 0.31, 0.21 and 0.12 for diets A, B and C respectively, indicating a decreasing significance of blood urea as a source of microbial N as dietary urea increased ( P < 0.05). 6. Transfer of blood urea-N to the rumen (g/d) was 3.8, 4.7 and 2.6 for diets A, B and C respectively, being significantly (P < 0.05) lower on diet C. Using an estimate ,of the salivary contribution of urea-N to the rumen, it was concluded that there was a significant though not large transfer of blood urea-N across the rumen wall on all diets. 7. Net transfer of blood urea-N to the rumen was estimated from a two-pool model and was +0.4 g/d for diet A, though this was not significantly different from zero. Net transfers for diets B and C were -2.0 and -6.3 g N/d respectively.8. Significant intake responses to exogenous urea supplementation were observed because of a limited capacity to recycle N to the rumen under the conditions of low dietary N supply imposed.

A surgical preparation was developed to measure uptake of amino acids from the small intestine into the cranial mesenteric vein (CMV) of lambs. Results from this preparation were compared with those from the traditional hepatic portal vein (PV) preparation in the same lambs. Necropsy revealed that, in contrast to the PV preparation which included all portal-drained viscera, the CMV preparation drained primarily small intestine (0-84-0-92 small intestinal mass). The CMV preparation contributed 0-238 of blood flow from and 0-307 of oxygen consumption by the PV preparation. Venous-arterial differences for alpha-amino nitrogen (AAN), phenylalanine (Phe) and tyrosine (Tyr) were three-to fourfold greater in the CMV than in the PV preparation, indicating that the CMV preparation is more sensitive for measuring amino acid uptake. The ratio CMV/PV for uptake of AAN was 0-61 (P < 0001), but this ratio was much closer to unity (mean 0-84) for Phe and Tyr. Since the CMV preparation drains primarily the small intestine, through which all amino acid absorption occurs, it should prove to be extremely valuable for studying absorption from and metabolism within this organ using a combination of arteriovenous and isotopic tracer techniques.

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The effects of fuzzy whole cottonseed (WCS) on the performance and health of sheep were examined. Thirty 2-year-old Merino wethers were divided into 3 equal groups and offered maintenance rations for 138 days, with whole wheat grain to WCS ratios of 100:O (diet A), 75:25 (B) and 50:50 (C). Liveweight changes for diets A, B and C were -0.3, +4.4 and +3.0 kg respectively, and were significantly (P<0.05) greater on WCS diets. Wool growth rates were also significantly (P< 0.01) improved by the addition of WCS, with treatment means being 0.65 (diet A), 0.82 (B) and 0.88 mg/cm2.day (C). Digestibility of DM in diet C (677 g/kg) was significantly (P< 0.001) lower than in diets A (782) and B (777 g/kg), perhaps because of increased fibre and oil in the ration. Subclinical anaemia and muscle damage were evident in animals given WCS by days 43 and 127 respectively. Post mortems and histological examination revealed renal haemosiderosis in sheep given WCS, with increased severity at 50% inclusion in the ration. Despite the reduction in digestibility and the subclinical effects on health, at least 25% WCS can be safely included in a wheat-based maintenance ration for wethers and this ration has production advantages over wheat alone. Caution is advised in feeding higher levels of WCS or feeding such a ration for more than 5 months.