Effect of feeding restricted amounts of a medium and a high protein diet during the finishing period on growth, fat deposition and feed efficiency of male and female broilers

An experiment is described in which male and female broilers were fed either a 20 or a 23% crude protein diet, at 4 levels of intake— ad libitum and about 96, 92 and 87% of ad libitum —from 35 to 56 or 60 days of age. Males ate more, grew faster and converted food to body weight more efficiently than females. Male carcasses were significantly leaner than female carcasses at market age. On average, birds fed the high‐protein diet ate a similar amount of food, grew at a slightly slower rate and converted food to body weight significantly less efficiently than birds fed the medium‐protein diet. Carcass dry matter of birds fed the high‐protein diet contained only about two percentage points less ether extract than that of those fed the medium protein diet. Growth rate and feed efficiency in the 35‐ to 56‐day period decreased as the feed allowance was reduced. Groups fed the lowest level of food intake were kept until 60 days of age, when live weight was similar but carcasses were somewhat leaner than those of ad libitum groups at 56 days. In spite of the similarity in final live weight and lower body fat content, food conversion in the 35‐ to 60‐day period for birds fed the lowest level of food intake was less efficient than that for ad libitum groups in the shorter 35‐ to 56‐day period.