No abstract

Twelve Suffolk-Finn Dorset lambs were reared from 25 to 40 or 25 to 55 kg body weight on either pelleted dried grass or a ration of pelleted grass plus barley (ratio 1:1) in a comparative slaughter experiment designed to determine the amounts of total nitrogen and individual amino acids accreted in different body components during growth. Nitrogen (N) balance measurements were determined frequently during this growth phase and accumulated N retentions were compared with the total N accretion determined by comparative slaughter. Total N and individual amino acids accumulated in carcass, wool, skin, offal and blood, head and feet, gastro-intestinal tract and liver were linearly related to body weight in all cases other than for cysteine in carcass. At 25 kg live weight, proportionately 0·52 of total body N was in carcass components, 0·115 in wool, 0·08 in skin, 0·10 in offal and blood, 0·095 in head and feet, 0·06 in the gastro-intestinal tract and 0·02 in liver. However as the animals grew from 25 to 55 kg, 0·256 of the total N accretion was in wool, which was rich in cysteine (98 g/kg total amino acid). Carcass accretion represented only 0·449 of total body N accretion. The N balance technique overestimated net protein accretion by 0·24 (s.e. 0·036).

I. Three experiments wereconducted with sheep given spring-harvested dried grass (SHG) and autumn-harvested dried grass (AHG). The first was a calorimetric trial to determine the metabolizable energy (ME) content of each grass and the efficiency with which sheep utilize their extra ME intakes above the maintenance level of intake. The second examined the relative amounts of extra non-ammonia-nitrogen (NAN) and individual amino acids absorbed from the small intestine per unit extra ME intake as the level of feeding was raised from energy equilibrium (M) to approximately 1.5 M. The third was a further calorimetric trial to investigate the effect of an abomasal infusion of 30 g casein/d on the efficiency of utilization of AHG.2. The ME content of the SHG (11.8 MJ/kg dry matter (DM)) was higher than that of AHG (10.0 MJ/kg DM). The efficiency of utilization of ME for productive purposes (is. above the M level of intake; k,) was higher when given SHG (k, 0.54 between M and 2 M) than when given AHG (kf 0.43 between M and 2 M). Consideration is given to the possibility that the higher efficiency of utilization of ME in sheep given SHG may be related to the amounts of extra glucogenic amino acids absorbed from the small intestine which provide extra reducing equivalents (NADPH) and glycerol phosphate necessary for the conversion of acetate into fatty acids.

The kinetics of blood free amino acids (AA) transfer into milk casein were compared in goats (n 4) at 61 (SE . The I3C enrichments of blood free and casein-bound AA were fitted to a single exponential model to estimate isotopic plateaux and the fractional rate constant for milk casein labelling. Milk protein output and its contribution to whole-body flux was higher in Expt 1 (post-peak) than in Expt 2 (late lactation), but the kinetics of 13C labelling of the casein-bound AA were similar for all AA tracers in both experiments. At both stages of lactation the delay (6-8 h) between the attainment of isotopic plateau for the blood free AA and the corresponding attainment of plateau for the caseinbound AA indicated that the blood free pool was not the immediate precursor pool for milk casein biosynthesis. Plateau enrichments of casein-bound AA were generally higher than those for the corresponding blood free AA in both experiments. These results indicate that the relative contributions of different AA sources to the immediate precursor pool for milk casein biosynthesis are similar at different stages of lactation despite major changes in the partitioning of whole-body flux towards milk protein output. Non-milk protein fluxes were also similar in post-peak and late lactation.Milk protein: Amino acid kinetics: Casein: Lactating goats Lactation requires a major increase in the partitioning of amino acids (AA) towards the mammary gland for milk protein synthesis (3 1 4 6 % of whole-body protein flux compared with I-6% in dry, non-pregnant animals; Champredon et al. 1990;Baracos et al. 1991). However, milk protein output represents only a proportion (W609'0) of total protein synthesis in the lactating mammary gland (Oddy et al. Champredon et al. 1990;Baracos et al. 1991) and therefore approximately half of the synthesized protein must be degraded, assuming that there is no appreciable net gain by the mammary tissue protein pool. This may represent either general turnover of both constitutive and milk proteins, or a specific channelling of milk protein precursor AA through protein(s) which constitutes an intermediate mixing pool(s).The results of Oddy et al. (1988) would seem to indicate that the latter phenomenon exists, but their study involved only short-term infusions of a single AA tracer (leucine) which is known to be extensively metabolized by the gland. The present study involved the * For reprints.

We conclude that nicotine induces oxidative stress in pancreatic acinar cells and that these events trigger pathophysiological changes in the pancreas, leading to increased cell proliferation and injury.