1. Digesta were collected from eleven preruminant calves fitted with re-entrant (four calves in Expt 1 and three in Expt 2) or single cannulas (four calves in Expt 1) in the terminal ileum. Collection periods lasted 24 h (Expt 1) or 96 h (Expt 2).2. Two milk-substitutes (fish and soya bean) and a control diet were given to the calves. In the control diet, protein was entirely provided by skim-milk powder. In the other two diets, protein was provided mainly by a partially hydrolysed white-fish protein concentrate or a soya-bean protein concentrate prepared by extracting soya-bean meal with hot aqueous ethanol.3. In Expt 1, flow rates of fresh matter, dry matter, nitrogen and ash exhibited two maxima between 6 and 8 h after the morning meal and between 4 and 6 h (control and soya-bean diets) or 6 and 8 h (fish diet) after the evening meal. Minimum pH values were observed at times of maximum flow rate. Variations observed in the flow rates and pH values were larger with fish and especially soya-bean diets than with the control diet.4. The apparent digestibility of the three diets in the terminal ileum was significantly higher in Expt 2 than in Expt 1 : for N, the values were 0.92, 0.83 and 0.75 (Expt l), and 0.94, 0.87 and 0.88 (Expt 2) with the control, fish and soya-bean diets respectively.5. The amount of N apparently absorbed in the terminal ileum represented 90-96% of the amount that disappeared from the whole digestive tract in Expt 1 and 95-99% in Expt 2.6. In Expt 1 the amino acid (AA) composition of digesta changed little with the flow rate when the calves were given the control diet (from 158 to 179 g glutamic acid/kg AA). With the fish and soya-bean diets the AA composition was similar to that observed with the control diet when the flow rate was minimum, but differences became apparent as the flow rate increased (281 and 161 g glutamic acid/kg AA for the soya-bean and control diets respectively with maximum flow rate). In Expt 2, the mean compositions of the digesta were very similar to the means obtained in Expt I.7. Different comparisons with dietary, endogenous and bacterial proteins indicated that for the three diets a common mixture containing approximately 65% endogenous and 35 % bacterial proteins reached the terminal ileum. The quantity of dietary protein added to this mixture appeared to be very low with the control diet, but it increased with the flow rate in the case of the fish and soya-bean diets.8. In Expt 2, the additional undigested protein in the small intestine was richer in glycine with the fish diet and in glutamic acid and aspartic acid with the soya-bean diet compared with the control diet. This undigested fraction probably originated mainly from the fish solubles and the glycinin of soya bean respectively. 9. With the control diet the apparent digestibility of threonine and cystine was always lower than the mean value for all AA while that of methionine was higher (0.92, 0.82 and 0.96 respectively). Digestibility of all AA was higher for the control diet than corresponding values ...

This study was performed to assess the effect of glucocorticoids (dexamethasone) on insulin-and IGF-I-regulated muscle protein metabolism in adult and old rats. Muscle atrophy occurred more rapidly in old rats, and recovery of muscle mass was impaired when compared with adults. Muscle wasting resulted mainly from increased protein breakdown in adult rat but from depressed protein synthesis in the aged animal. Glucocorticoid treatment significantly decreased the stimulatory effect of insulin and IGF-I on muscle protein synthesis in adult rats by 25·9 and 58·1% respectively. In old rats, this effect was even greater, being 49·3 and 100% respectively. With regard to muscle proteolysis, glucocorticoids blunted the anti-proteolytic action of insulin and IGF-I in both age groups. During the recovery period, adult rats reversed the glucocorticoidinduced resistance of muscle protein metabolism within 3 days, at which time old rats still exhibited the decrease in insulin-regulated proteolysis. In conclusion, the higher sensitivity of old rat muscle to glucocorticoids may in part result from the greater modification of the effects of insulin and IGF-I on muscle protein metabolism. These responses to glucocorticoids in old rats may be associated with the emergence of muscle atrophy with advancing age.

The yields and composition of milk from nursing mares were studied during the first two months of lactation in 11 mares of heavy breeds (784 kg). Daily yield increased from 21-7 to 24-6 kg between weeks 1 and 8 of lactation. Fat, protein, gross energy and Ca concentrations significantly decreased when lactose content increased during this period. Individual variations were higher for yield than for composition. Casein, whey protein and non-protein N (56, 34 and 10% of crude protein, respectively) and amino acid composition did not vary between weeks 1 and 8 of lactation.Information on the composition of milk from nursing mares is extensive: some 20 authors have studied the effects of lactation stage on milk fat and/or crude protein (Doreau & Boulot, 1989a). However, some components, such as those containing N, have seldom been studied in relation to lactation stage. Because of problems associated with the determination of milk production by lactating mares, simultaneous determinations of milk yield and composition are few. Moreover, some results are questionable because inaccurate methods were used (Doreau & Boulot, 19896). The most reliable are probably those of Oftedal et al. (1983).This trial was performed on a large number of mares managed individually under the same feeding scheme, in order to provide information on both milk yield and composition, and on nutrient output, and their variations according to individuals and to lactation stage. Special emphasis was placed on N fractions and amino acid composition. MATERIAL AND METHODS Animals and dietsEleven multiparous mares of heavy French breeds (Bretonnes, Comtoises), aged 5 to 16 years and weighing after foaling 784 + 39 kg, were managed indoors in individual boxes for the last month of pregnancy and for the first 2 months of lactation. All mares were in good condition at foaling. They were fed on a constant composition diet based on 85% natural grassland hay, first cut, and 15% concentrates containing 50% barley, 45% soyabean meal, 3 % molasses and 2% mineral premix. This diet was offered ad lib., with a mean of 10% hay refusals. The hay-concentrate ratio was adjusted daily. Hay was delivered 3 times/d and

Few investigations have studied protein metabolism in children and adolescent athletes which makes difficult the assessment of daily recommended dietary protein allowances in this population. The problematic in paediatric competitors is the determination of additional protein needs resulting from intensive physical training. The aim of this investigation was to determine protein requirement in 14-year-old male adolescent soccer players. Healthy male adolescent soccer players (N = 11, 13.8 +/- 0.1 year) participated in a short term repeated nitrogen balance study. Diets were designed to provide proteins at three levels: 1.4, 1.2 and 1.0 g protein per kg body weight (BW). Nutrient and energy intakes were assessed from 4 day food records corresponding to 4 day training periods during 3 weeks. Urine was collected during four consecutive days and analysed for nitrogen. The nitrogen balances were calculated from mean daily protein intake, mean urinary nitrogen excretion and estimated faecal and integumental nitrogen losses. Nitrogen balance increased with both protein intake and energy balance. At energy equilibrium, the daily protein intake needed to balance nitrogen losses was 1.04 g kg(-1) day(-1). This corresponds to an estimated average requirement (EAR) for protein of 1.20 g kg(-1) day(-1) and a recommended daily allowance (RDA) of 1.40 g kg(-1) day(-1) assuming a daily nitrogen deposition of 11 mg kg(-1). The results of the present study suggest that the protein requirements of 14-year-old male athletes are above the RDA for non-active male adolescents.

The digestive utilization of dietary proteins at different sites along the digestive tract and the effects of their ingestion on the function of the digestive tract (secretion of endogenous proteins, development of microflora) can be inferred from the proportions of dietary, endogenous or microbial proteins. A first approach was to examine the proportions of some characteristic amino acids. A more accurate interpretation could be made by studying the additional undigested protein provided by the ingestion of an ‘experimental’ diet whose composition was calculated, for example, with regard to the undigested protein obtained with a very digestible diet (milk in the calf). These interpretations were often insufficient and did not extract all of the possible information. Thus, more global methods with statistical criterions had to be used. Some allowed two proteins (correlation and linear regression, average relative difference, χ²) to be compared. Others made it possible to take many proteins into consideration (factorial correspondence analysis). Finally, examples were given to seek the respective proportions of many proteins in a complex mixture or to estimate the most probable amino acid composition of the ‘microbial + endogenous’ proteins which escaped digestion in the small intestine. These various approaches have been discussed, with examples taken from our experimental results obtained in the preruminant calf, to show their advantages and limitations. In any case, the quality of the interpretation depends on the quality of the available results on the amino acid composition of endogenous, microbial and undigested dietary proteins.