The effects of ammoniation of wheat straw with or without supplementation of protein sources of either high (casein) or relatively low (potato protein) rumen degradability on intake and digestion were studied with four sheep in a 4 x 4 Latin square design. Rations offered were: (1) untreated wheat straw (UWS), (2) ammoniated wheat straw (AWS), (3) AWS supplemented with 3-2 g caseinlkg live weight (W)O'" per d (AWSC) and (4) AWS supplemented with 3.9 g potato protein/kg W0'7s per d (AWSP). Straw was offered ad lib. and all rations were supplemented with sugarbeet pulp and a mineral mixture. NH, treatment increased intake and digestion. Supplementation of AWS with potato protein increased total digestible organic matter intake (DOMI) compared with AWS whereas supplementation with casein did not affect total DOMI. Protein supplementation of AWS significantly reduced rumen digestion of cellulose, and when the supplementation was with casein it reduced rumen digestion of neutral-detergent fibre and hemicellulose also. This lower rumen digestion was compensated by a higher proportion of digestion occurring in the hindgut for hemicellulose (P < 0.05 for AWSC, P > 0.05 for AWSP), but not for cellulose. Across all rations, rumen fluid volume increased with increasing cell-wall intake. The efficiencies of microbial protein synthesis were (average of three different methods of estimation) 23.3, 26.2, 34.8 and 31.7 g N/kg apparently-rumen-degraded organic matter for UWS, AWS, AWSC and AWSP respectively. The difference between UWS and AWS was not significant, but values for AWSC and AWSP were significantly higher than that for AWS. The rumen digestion of feed amino acid-N (AA-N) was significantly higher for AWSC than for the other rations. The apparent smallintestinal digestion of AA-N and N was significantly higher for AWSP than for the other rations. The true small-intestinal digestion values were 0.86, 0-84 and 0.68 for AA-N, N and non-protein-N respectively. Ileal endogenous losses of AA-N were approximately 6 mg/g duodenal non-protein drymatter flow. Linear relationships were observed between DOMI and N balance and truly absorbed AA-N, indicating that DOMI could have been limited by small-intestinal amino acid availability. Regression of N balance v. truly absorbed AA-N resulted in an estimate of net efficiency of utilization of truly absorbed AA-N of 054.Protein availability: Ammoniated wheat straw: N balance: Microbial protein synthesis.

The relationships of N input or protein status and the concentrations of serum insulin-like growth factor-1 (IGF-1), plasma fibronectin (FN) and total protein (TP) were examined in three experiments with steers and sheep nourished by intragastric infusion of nutrients. In Expt 1, three steers (340 kg live weight) were infused with three levels of volatile fatty acids (0,300 and 600 kJ/kg metabolic weight (w0'75) per d) and six levels of casein (0, 200, 400, 650, 1500 and 2500 mg N/kg W0'75 per d). Each N treatment was imposed for 5 d. In Expts 2 and 3, five groups of sheep (about 35 kg live weight) were infused with casein at 500 mg N/kg vv0.75 per d for 2 weeks followed by 1500,500 or 50 mg N/kg W0'75 per d in Expt 2, and in Expt 3, with 100 mg N/kg w0 75 per d for 6 weeks or 10 mg N/kg W0'75 per d for 4 weeks. Non-protein energy was maintained constant at 500 kJ/kg w0'75 per d throughout. Daily N balance and total body N content at the end were measured, and protein status was defined as a percentage of cumulative N accretion or depletion in relation to the total body N content at maintenance. It was found that IGF-1 and FN responded rapidly and substantially to altered N input, and that when daily N input was maintained constantly at sub-maintenance, their continuous declines were related closely to progressive protein depletion in the sheep. Plasma TP concentration was independent of N input when N input was altered acutely in the steers, but declined significantly and gradually with severe, chronic body protein depletion in the sheep. Plasma content of TP in the sheep however reduced acutely with a reduction in N input. Plasma volume fell substantially over the first 2 weeks of protein depletion, compensating for the declines in TP content and maintaining TP concentration plateau. The possible implications of the changes in TP concentration and content (concentration x volume) to body protein loss in sheep are discussed. IGF-1: Fibronectin: Protein status: RuminantsThe estimation of changes in total body N can be achieved using some advanced noninvasive laboratory techniques such as neutron activation analysis, tracer dilution methods and some instrument techniques (reviewed by Gibson, 1990 andEllis, 1992). However these techniques cannot easily be applied in practical situations. Several blood biochemical metabolites have therefore been studied as potential indicators of protein status in human subjects and animals (see reviews by Gibson, 1990;Young et al. 1990 central role in the regulation of whole-body protein metabolism by reconstituting absorbed and degraded tissue amino acids, removing N in the body by production of urea, using amino acids in gluconeogenesis, influencing protein synthesis via production of its insulinlike growth factor-1 (IGF-1) and producing and exporting plasma proteins to transport nutrients. It may, therefore, be possible to use the metabolic products which reflect liver function as an indicator of whole-body protein status. Plasma IGF-1 (Baxter, 1986) 1989). The present study ...