Growth performance, serum hormones, and metabolite responses before and after weaning in lambs weaned at 42 days of age: effect of preweaning milk and postweaning alfalfa or grass hay diets.

Fourteen fall-born lambs were used to determine the effects of diet before and after weaning on intake, growth, serum hormones, and metabolite profiles. Before weaning, lambs were intensively sampled for 6 h at 35 and 42 d of age. Before sample collection, lambs were allowed to suckle, and milk intake was recorded. At 42 d of age, lambs were weaned and randomly allotted to ad libitum access to either alfalfa or grass hay. Blood samples were collected at 49 and 56 d of age for 6 h. Milk intake did not differ (P greater than .10) between groups. After weaning, lambs fed alfalfa hay consumed more (P less than .05) hay and had greater (P less than .05) ADG than lambs fed grass hay. Postweaning diet had no effect (P greater than .10) on serum insulin, growth hormone (GH), insulin:GH ratio, prolactin, cortisol, glucose, or nonesterified fatty acids (NE-FA) concentrations. Lambs consuming alfalfa had higher (P less than .05) serum urea nitrogen (SUN) at 49 and 56 d of age than lambs consuming grass. At 35 and 42 d of age, (P less than .05) serum insulin and insulin:GH ratio were higher (P less than .05) after milk intake than at 49 and 56 d of age after hay intake. Serum GH was higher (P less than .05) in lambs at 35 and 42 d of age for 2 h postfeeding, but by h 3 through 5, lambs consuming milk had lower (P less than .05) values than lambs consuming hay.(ABSTRACT TRUNCATED AT 250 WORDS)