No abstract

SUMMARYTwo trials involving 216 growing boars were conducted to study the effects of different levels of crude protein on daily gains, feed efficiency, feed intake and estimated carcass characteristics. The boars were fed either a 16, 18 or 20% crude protein ration from 23.8 to 55.8 kg (period 1). Upon completion of period 1, the protein level was reduced 2% for each treatment (14, 16 and 18%, respectively) from 55.8 to 99.6 kg (period 2).Average daily gain increased linearly (P<.01) and feed required per unit gain decreased quadratically (P<.05) as the percent protein in the diet increased from 16 to 20% in period 1 and 14 to 18% in period 2. Average daily feed intake was similar for boars on each treatment. Scanned backfat thickness decreased linearly (P<.01) and scanned longissimus muscle area increased linearly (P<.05) as protein in the diet increased.

Five trials involving 432 growing boars were utilized to study the effects of six levels of crude protein on gain, feed efficiency, feed intake, backfat thickness and longissimus muscle area. The boars were fed ad libitum either a 14, 16, 18, 20, 22 or 24% crude protein diet from about 24.6 to 54.4 kg (period 1). From 54.4 to 98.8 kg (period 2), the crude protein in each diet was reduced by 2%. During period 1, gain increased and feed to gain ratio decreased quadratically (P<.05)with increasing dietary crude protein in corn-soybean meal based diets and were maximum at protein levels of 20 to 22%. Feed intake was not affected by dietary protein level. During period 2, protein level did not significantly affect rate of gain, feed efficiency or feed intake. Overall, gain increased quadratically (P<.05)with increasing protein levels and was maximum for boars fed the 20/18% protein sequence during periods 1 .and 2, respectively. Feed to gain ratio decreased linearly (P<.05) with increasing dietary protein intake. Feed intake was not affected by dietary protein level. Scan backfat thickness and longissimus muscle area obtained at the end of the trial indicated that backfat decreased linearly (P<.05) with increasing protein intake, while longissimus muscle area increased quadratically (P<.05) as protein in the diet increased. These results indicate that small improvements in average daily gain, feed efficiency, longissimus