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We conducted two experiments to determine the effects of various intake restriction strategies on performance and carcass characteristics of feedlot cattle. In Exp. 1, 104 steer calves (273 [+ or -] 12 kg BW) were allotted to 12 pens. During Period 1 (273 to 372 kg BW), steers were limit-fed according to net energy equations to achieve predicted gains of .91, 1.13, or 1.36 kg/d. Control steers were offered ad libitum access to feed during this period. During Period 2 (372 to 535 kg BW), all steers were offered ad libitum access to feed. In Period 1, steers limit-fed for predicted gains of .91, 1.13, and 1.36 kg/d gained 1.03, 1.22, and 1.40 kg/d, respectively. Control steers offered ad libitum access to feed gained 1.66 kg/d. Steers that were limit-fed in Period 1 were able to compensate in Period 2; for the total experiment, there were no differences (P > .10) among the four feeding strategies investigated for rate of gain, feed efficiency, total feed intake, and carcass characteristics. Experiment 2 used 107 steer calves (300 [+ or -] 11 kg BW). Four feeding strategies were compared: step-wise increases in intake to program for increasing rate of gain, stepwise decreases in intake to program for decreasing rate of gain, feeding to hold gain constant at 1.36 kg/d, or offering steers ad libitum access to feed throughout the experiment to allow for maximum gains. When averaged over the total experiment, growth rate and days on feed were not affected (P > .10) by feeding system. Steers fed to achieve a step-wise increase in growth rate throughout the experiment had the lowest (P < .09) daily intakes and the highest (P < .09) feed efficiencies. Steers fed for increasing gains required 109 kg/steer less (P < .09) total feed to reach market weight than those offered ad libitum access to feed throughout the experiment. Feeding strategy had little effect on carcass characteristics. We concluded that as intake is restricted to a greater extent, net energy equations are less accurate in predicting rate of gain. Programming intake during the feeding period can result in significant reductions in feed expenditures. Key Words: Restricted Feeding, Steers, Performance, Carcasses

Generalization occurs when an animal responds to novel stimuli in much the same way it has responded to similar, familiar stimuli. Our objective was to determine whether goats generalized foraging skills from older growth blackbrush (Coleogyne ramosissima) to shrub live oak (Quercus turbinella). Blackbrush (OGBB) has small leaves that are difficult to ingest without the twigs, whereas shrub live oak (SLO) has larger leaves that can be ingested easily without twigs. In Yr 1, 6-mo-old goats and in Yr 2 18-mo-old goats were given experience browsing with OGBB for 0, 10, 20, or 30 d. They were next tested for 5 min/d for 2 d on OGBB, and then tested in the same way on SLO. The number of bites and bite rate increased significantly as goats of both ages gained experience browsing OGBB. Likewise, goats with more experience browsing OGBB took more bites during a 5-min period when foraging on SLO. Thus, goats generalized foraging skills from OGBB to SLO. Plant life form also affected the response of goats. Total intake, intake rate, and bite size were significantly higher for SLO than for OGBB. There was an interaction between level of experience and plant life form. The interaction occurred because goats with no experience browsing OGBB took more bites per 5 min of SLO than of OGBB, whereas goats with increasing levels of experience browsing OBGG generally took more bites of OGBB than of SLO. Controls took more bites per 5 min of SLO than of OGBB, because SLO leaves could be ingested (harvested and chewed) more easily than OGBB twigs.

Metabolism of carbon-based nutrients in the portal-drained viscera and liver was assessed to determine the effect of growth hormone-releasing factor (GRF) on nutrient metabolism of crossbred steers. Increasing the food intake elevated blood flow and mobilization of most nutrients. On the other hand, GRF administration decreased liver clearance of amino acid and ammonia nitrogen and the release of urea nitrogen. Nitrogen retention over the net amino acid assimilation of the gastrointestinal tract increased with the administration of GRF.

Orexin is a hypothalamic neuropeptide that regulates feeding behavior in rats. Orexin-B has recently been cloned in pigs and was shown to stimulate food intake after intramuscular injection. This study was designed to determine whether intracerebroventricular (ICV) and intravenous injections of orexin could regulate appetite in sheep. Suffolk wethers were moved to indoor facilities, adapted to diets for 6 wk, and trained to stand in stanchions for 3 to 6 h each day for 2 wk before indwelling ICV cannulas were installed. These sheep were provided water and they consumed feed ad libitum. On the day before an experiment, each sheep was cannulated in a jugular vein. On the day of an experiment, sheep were placed in stanchions and allowed to stand for I h before use. Sheep were then monitored over a 2-h control period before i.v. injection with saline or porcine orexin-B (3 [micro]g/kg BW) or ICV injection with artificial cerebrospinal fluid (CSF), orexin (0.03, 0.3, or 3 [micro]g/kg BW) or in a second experiment with either orexin B (0.03, 0.3, 3 [micro]g/kg BW), neuropeptide-Y (NPY; 0.3 [micro]g/kg BW), or orexin plus NPY. Food intake was monitored for consecutive 2-h periods. The i.v. injections of orexin did not affect food intake or metabolite or hormone concentrations. In ICV sheep, orexin increased food intake at 2 (P [is less than] 0.04) and at 4 h (P [is less than] 0.02). Food intake was greatest with the 0.3 [micro]g/ kg BW dosage of orexin (P [is less than] 0.05). In the first 2 h after injection, orexin had an effect similar to that of NPY (0.23 kg for orexin and 0.2 kg for NPY). The combination of NPY and orexin had a greater effect on food intake (to 0.34 kg) than did either orexin (P [is less than] 0.05) or NPY (P [is less than] 0.008) alone. Differences were not apparent in the subsequent 2-h interval. No differences were noted in free fatty acid, glucose, growth hormone, luteinizing hormone, or insulin concentrations following orexin injection. There was an effect of ICV orexin treatment on plasma cortisol concentrations (P [is less than] 0.002). Cortisol was increased by orexin at the 0- to 2-h (P [is less than] 0.008) and in the 2- to 4-h (P [is less than] 0.009) intervals after orexin injection. These data indicate that central administration of orexin stimulates feed intake in sheep. Key Words: Appetite, Hydrocortisone, Hypothalamus, Sheep