Effects of growth pattern and dietary protein level during rearing on feed intake, eating time, eating rate, behavior, plasma corticosterone concentration, and feather cover in broiler breeder females during the rearing and laying period

An experiment was conducted to evaluate the effect of growth patterns (GP) and dietary crude protein levels (CP) during rearing (2–22 weeks of age) on feed intake, eating time, eating rate, behavior, plasma corticosterone concentration, and feather cover in broiler breeder females during the rearing and laying period. A total of 768 day-old Ross 308 broiler breeder chicks, of which 288 hens were followed during the laying period, were allotted to 6 different treatments during the rearing period according to a 2 × 3 factorial design, with 8 replicates (pens) per treatment. Two growth patterns were followed by a restricted feeding regime up to a target body weight (BW) at 20 weeks of age of 2200 g (standard growth pattern = SGP) and 2400 g (high growth pattern = HGP) and 3 dietary protein levels (high = CPh, medium = CPm, and low = CPl). During lay, all birds were fed a standard breeder diet and followed a standard growth pattern. During rearing, HGP birds were fed on average 6.5% more feed than SGP birds. In HGP birds, eating time (min/day) during the rearing period increased by 17%, whereas eating rate (g feed/min) decreased by 8%, compared to SGP birds. This prolonged feeding behavior of HGP birds, but stereotypic object pecking and animal pecking was not reduced. Feather cover was not affected by growth pattern during the rearing and laying period. Only at 16 weeks of age a lower plasma corticosterone concentration was found for the HGP birds. HGP birds showed more feeding and sitting behavior, but less foraging behavior during the rearing period, while during the laying period only more walking behavior was observed. In order to maintain target weights, feed intake levels of CPm and CPl during rearing were set 4.6 and 10.0% higher than CPh, whereas eating time was increased by 22 and 63% and eating rate was decreased by 9 and 26%, respectively. A prolonged eating time during rearing for CPm and CPl birds resulted in more time spend feeding and resting and less stereotypic object pecking and animal pecking compared to CPh birds during rearing. In contrast to the rearing period, feed intake and eating time were not affected by CP level during rearing at 22 weeks of age, whereas eating rate was increased by 8 and 16% for CPm and CPl, respectively, compared to CPh. At 27 weeks of age the effect of CP level during rearing on eating rate had disappeared. Plasma corticosterone concentrations were not affected by dietary protein level during the rearing and laying period. Feather cover was inferior by lowering the dietary protein level, in particularly during the first 11 weeks of rearing. No effect of GP was found on feather cover. It is concluded that dietary protein levels positively affected some behavioral traits during the rearing period, whereas these traits were only slightly affected by growth patterns. However, the physiological parameter (plasma corticosterone concentration) was not affected.