The Influence of Rearing Light Period and the Use of Broiler or Broiler Breeder Diets on Forty-Two-Day Body Weight, Fleshing, and Flock Uniformity in Broiler Stocks

Abstract

Feed restriction programs for rearing broiler breeders begin with a period of ad libitum feeding and long day lengths. It is not clear how much early growth rate is limited by light period or nutrient density. This trial was performed to determine the response of full-fed broiler males and females to 4-, 8-, 12-, or 16-h durations of light per day (after 3 d of age), and their responses to broiler or breeder diets. Body weight, feed consumption, mortality, corrected feed conversion ratio, BW uniformity, and carcass characteristics were measured weekly in Ross broiler chicks (800 males and 800 females). At 42 d, the 10 birds per pen closest to the mean BW (total = 320) were studied for external carcass morphometrics (shank length, chest girth and width, and keel length) and breast muscle and abdominal fat pad weights. Body weight uniformity was determined for the individual 42-d BW data.Males were heavier than females, and at 42 d had larger external measurements. However, females had a higher proportion of breast muscle at this time. The variability of 42-d BW of males (CV = 14.2%) was greater than that of females (CV = 12.8%). The 42-d BW of the birds fed the broiler diets was 2.16 kg, on average, compared with 1.79 kg for those fed the breeder diets. Surprisingly, the mean 42-d BW did not increase in direct relationship with light period. The 4-h light period was advantageous for growth and breast muscle yield, when the broiler diets were used. An 8-h light period reduced growth, when the breeder diets were used, while no change was observed with 8 h on the broiler diets. Broiler chicks exposed to 4 h of daylight early in rearing may be highly motivated to consume feed during the dark period. An 8-h light period can slow growth, particularly when breeder diets are used.