Submitted to: Poultry Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/11/2006
Publication Date: 2/11/2006
Citation: Sun, J.M., Richards, M.P., Rosebrough, R.W., Ashwell, C.M., McMurtry, J.P., Coon, C.N. 2006. The relationship of body composition, feed intake and metabolic hormones for broiler breeder females. Poultry Science. 85:1173-1184. Interpretive Summary: Feed is a major cost to the producer growing broiler breeder hens for the reproduction market. Excess carcass fat produced as a part of the normal growth processes prior to reaching reproductive age can be a significant burden to producers. Likewise, some body fat is required for the breeder female to reach and maintain sexual maturity. Raising broiler breeder candidates under a feed restriction regimen reduced body fat without affecting reproductive performance. Stepwise regression indicated that T4 was the most important hormone for predicting the carcass fat in candidates. Thus, the hormone status of breeder pullets and hens as it relates to body composition and sexual maturity may be a key indicator that can be utilized as a management tool to predict the physiological readiness of pullets for photo stimulation or possibly the hormone status may be used as a selective tool by Primary Breeders for altering feed consumption in broiler progeny.
Technical Abstract: Three hundred and twenty Cobb 500 broiler breeder pullets, 21 wk of age, of a similar body weight (BW) were selected from a flock of 1000 pullets that had been fed according to Cobb Breeder Management Guide specifications. One hundred and sixty pullets at 21 wk of age were switched to ad libitum feeding while the remaining 160 pullets continued to be control fed according to Cobb guidelines. The pullets were photo-stimulated at 22 wk and maintained through a peak laying period with experiment being terminated when breeders were 36.5 wk. Breeder pullets were bled for plasma samples, BW determined, sacrificed, abdominal fat removed and weighed, and carcass homogenized for composition analysis at the following times: 1) 24 hr prior to photo-stimulation, 2) 2.5 wk after photo-stimulation, 3) Within 24 hr after first egg and 4) 36.5 wk following peak egg production. Compared with ad libitum breeders, the restricted breeders had 9.8, 9.0, 8.0, 7.4 % more carcass protein and 4.42, 13.33, 14.27, 7.88 % less carcass fat content at pre-stimulation, post-stimulation, first egg, and post-peak period, respectively. Total egg number was 14.9 higher and the percentage of abnormal eggs was 9.18 % lower for the feed restricted pullets compared with the ad libitum fed pullets at 36.5 wk. Carcass % fat content of ad libitum fed pullets was positively related with lucagon (P=0.045), IGF-? (P=0.0023), and 17ß-estradiol (P=0.0208) but negatively related with insulin (P=0.0004), insulin/glucagon ratio (P<.0001), IGF-? (P=0.0005), T4 (P<.0001) and T3 (P<.0001). Carcass % fat content of feed restricted pullets was negatively related with IGF-I (P<.0001), IGF-II (P=.0001), and T4 (P=.0003). Stepwise regression indicated that T4 was the most important hormone for predicting the carcass fat in ad libitum fed pullets (R2=0.2788, P<.0001) but IGF-I was the most important hormone for predicting carcass fat in feed restricted pullets (R2 =0.1632, P<.0001). A seven hormone index consisting of 4+insulin/glucagonatio+T3+IGF-I+IGF-II+17 -estradiol+glucagon produced an R2 of 0.5961 for predicting carcass fat in ad libitum fed pullets. A six hormone index consisting of IGF-I+T4+glucagon+IGF-II+insulin+insulin/glucagon ratio produced an R2 of 0.3084 for predicting carcass fat in feed restricted pullets. Feed consumption per metabolic BW for ad libitum fed pullets was positively related to insulin (P=0.0205), insulin/glucagon ratio (P=0.0397), leptin (P=0.0210), and T3 (P=0.0446) but negatively related to IGF-II (P=0.0102). The feed consumption per metabolic BW could be best predicted (R2 =0.1424; P=0.0059) for ad libitum fed pullets with a five variable index consisting of IGF-II+IGF-I+T4+glucose+leptin values. The hormone status of breeder pullets and hens as it relates to body composition and sexual maturity may be a key indicator that can be utilized as a management tool to predict the physiological readiness of pullets for photo stimulation or possibly the hormone status may be used as a selective tool by Primary Breeders for increasing feed consumption in broiler progeny.