Gerald B. Huntington

Glucose and lactate absorption and metabolic interrelationships in lambs switched from low to high concentrate diets.

Two experiments were conducted to measure glucose and lactate absorption and metabolic interrelationships in lambs either switched gradually (experiment 1) or abruptly (experiment 2) from hay to a high concentrate diet. In experiment 1, seven lambs were given primed, continuous, 3-hour infusions of 2-0[3H]glucose, U-[14C]L-lactate and para-aminohippuric acid (portal blood flow indicator) before and after switching from a pelleted hay to a pelleted, 85% concentrate diet. Blood samples were collected at 20-minute intervals during infusions. In experiment 2, four lambs were abruptly switched from a pelleted hay to an all-concentrate diet. Portal and arterial blood samples were collected before and up to 1 week after the diet switch. As a result of increased concentrate intake (experiment 1) net portal absorption and turnover of L-lactate and glucose increased. Percentage of glucose derived from L-lactate decreased. Net portal D-lactate absorption, L-lactate absorption as a percentage of turnover and conversion of L-lactate to glucose were not affected by diet. Lambs in experiment 2 did not become acutely acidotic. The insult to acid-base status peaked 12-16 hours after the diet switch, concurrent with maximum arterio-venous differences in plasma L-lactate and glucose. Arterio venous differences in plasma D-lactate were not significantly affected.

Net absorption from portal-drained viscera of nitrogenous compounds by beef heifers fed on diets differing in protein solubility or degradability in the rumen

The objective of the present study was to evaluate effects of in vitro rumen solubility or degradability of dietary protein on net absorption of nitrogenous compounds from portal-drained viscera of beef heifers. Four protein sources, casein, soya-bean meal, maize-gluten meal and blood meal provided about two-thirds of total dietary nitrogen in semi-purified diets given to four beef heifers in a 4 X 4 Latin square design. Although in vitro degradability of dietary N ranged from 842 (casein) to 310 (blood meal) g/kg total dietary N, net absorption of ammonia-N or alpha-amino-N was not significantly different (P greater than 0.10) among diets. However, net absorption of NH3-N tended to decrease and net absorption of alpha-amino-N tended to increase as intake of in vitro undegradable N increased. Net transfer of urea-N from plasma to portal-drained viscera was greater (P less than 0.10) when heifers were fed on soya-bean meal than when fed on maize-gluten meal or blood meal. The findings show with all diets that the non-protein-nitrogenous compounds, NH3 and urea, played a substantial role in absorption and transfer of N. Overall, net absorption of NH3-N was 61% of net absorption of alpha-amino-N, and transfer of urea-N from plasma to portal-drained viscera was 80% of net absorption of alpha-amino-N.