Ractopamine and age alter oxygen use and nitrogen metabolism in tissues of beef steers.

The objective was to quantify the effects of age and ractopamine (RAC) on whole body oxygen consumption and Leu flux, and oxygen flux and metabolism of nitrogenous compounds by the portal-drained viscera (PDV), liver, and hindquarters (HQ) of steers. Multicatheterized steers were fed a high energy diet every 2 h in 12 equal portions. Five younger steers (body weight, [BW] = 223 ± 10.

Physiological responses to known intake of ergot alkaloids by steers at environmental temperatures within or greater than their thermoneutral zone.

Two studies separated effects of dietary ergot alkaloids from effects of feed intake or ambient temperature on respiration rate (RR), heart rate (HR), surface temperature (ST), rectal temperature (RT), blood pressure (BP), serum hormone, and plasma metabolite concentrations in beef steers. The balanced, single reversal design for each experiment used 8 beef steers fed tall fescue seed [2.5 g/kg body weight (BW)] with (E+) or without (E-) ergot alkaloids as part of a 60:40 switchgrass hay: supplement diet.

Performance of lactating dairy cows fed varying levels of total mixed ration and pasture.

Two, 8-week experiments, each using 30 lactating Holstein cows, were conducted to examine performance of animals offered combinations of total mixed ration (TMR) and high-quality pasture. Experiment 1 was initiated in mid October 2004 and Experiment 2 was initiated in late March 2005. Cows were assigned to either a 100% TMR diet (100:00, no access to pasture) or one of the following three formulated partial mixed rations (PMR) targeted at (1) 85% TMR and 15% pasture, (2) 70% TMR and 30% pasture and (3) 55% TMR and 45% pasture.