INFLUENCE OF DIETARY BACKGROUND ON THE RESPONSE OF PIGS TO THE BETA-ADRENERGIC AGONIST BRL-47672

The level of protein in the diet both before and during treatment with beta-adrenergic agonist (BAA) was investigated with regard to its effect on growth performance and carcass characteristics of pigs. A total of 76 pigs were divided into two groups and given ad libitum access to diets containing either 12 or 18% crude protein (CP) during growth from 15 to 60 kg. At 60 kg, six pigs from each group were slaughtered and carcass composition was determined. For the test period (growth from 60 to 90 kg) the remainder of the pigs were divided into eight groups of eight pigs each. Half of the pigs from each of the two dietary pretreatment groups were switched to the other diet and half remained on the same diet. Of the four dietary groups, half were fed 0 mg/kg (controls) or 1 mg/kg of BRL 47672. During the test period, all pigs were fed at 90% of their calculated ad libitum DE intake. All pigs were slaughtered at 90 kg and carcass composition was determined. Addition of BRL 47672 to the diet resulted in an overall improvement (P < .05) in daily gain (.72 vs .64 kg) and gain/feed (.28 vs .26); the greatest improvement occurred with pigs fed the 18% CP diet (24 and 14% for daily gain and gain/feed, respectively). Pigs that had received BRL 47672 also had 12% less backfat, 10% less carcass lipid, 16% larger longissimus muscle area, and 5% more carcass protein (P < .05 for each), and the greatest changes occurred in pigs fed the 18% CP diet (-26, -16, +21, and +10%, respectively). However, comparing the two groups that had been fed the 18% CP diet, those pigs that had received the 12% CP diet before treatment responded less to BAA treatment than those that had received the 18% CP diet throughout the study. This suggests that pretreatment diet may influence subsequent response to BAA treatment.