Carcass Quality Changes with the Broiler Chicken after Dietary Protein Restriction during the Growing Phase and Finishing Period Compensatory Growth

Abstract

Commercial source chicken broilers were placed sex-separate in floor pens and all birds received a 24% protein, 3100 kcal ME/kg ration during the first 2 weeks. Through the 2 to 5 week growing period, males received either a 24, 22, or 20% protein, 3100 kcal feed while females were fed a 24, 20, or 16% protein ration of the same calorie content (four pens of 100 for each protein level and sex). Finishing involved 5 to 7 weeks for the males, with all birds receiving the same 20% protein, 3200 kcal feed. Females were given a 16% protein, 3200 kcal ration from 5 to 8 weeks. Combinations of corn, soybean meal, and tallow were used in all instances. Males receiving the 22% protein feed during the growing period did not exhibit a body weight difference from those continued on the starting ration, but their feed conversion was poorer. Both gain and feed efficiency were reduced with cockerels offered the 20% protein ration. Compensatory growth during the subsequent 2 week finishing period was such that all males ended with comparable body weights and total feed conversion. Carcass grading at 5 weeks indicated substantial fat cover increases and fleshing decreases as grower protein was reduced. By 7 weeks, effects on fleshing were minimal but earlier finish changes continued to be readily apparent. Females presented a parallel pattern of results. However, reductions in fleshing were less and finish increases larger than observed with males. Percentage apparent carcass yield was not affected. The results show that consumer related alterations in carcass quality that are defined by the Canadian Grading System can readily occur as a consequence of earlier treatment and without changes in live performance parameters.