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Title: An examination of the role of feeding regimens in regulating metabolism during the broiler breeder grower period 2. Plasma hormones and metabolites

item McMurtry, John
item Brocht, Donna

Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2007
Publication Date: 2/1/2008
Citation: DeBeer, M., McMurtry, J.P., Brocht D.M., Coon, C.N., 2008. An examination of the role of feeding regimens in regulating metabolism during the broiler breeder grower period 2. Plasma hormones and metabolites. Poultry Science. 87(2):264-275.

Interpretive Summary: Over the past several decades, broiler breeder pullets have undergone heavy genetic selection pressure for very rapid body growth rates. This has been achieved, but at a cost of overfeeding. This has resulted in several undesirable effects, such as obesity, poor reproductive performance, and skeletal problems. To overcome this problem, the industry utilizes feed restriction plans to reduce body weight, delay sexual maturity, and enhance livability during the laying period. The method for restricting feeding are variable, but usually involve some form of skip-a-day feeding program, which results in period when the birds are without feed. This can potentially influence endocrine and metabolic responses to feeding in these birds. This study was conducted to determine the effects of feeding regimens on plasma hormone and metabolites over time after feeding. The results clearly demonstrate that different feeding regimens do alter hormonal and metabolite profiles in spite of the fact that total feed consumption was equal. Furthermore, the data indicate that not unexpectedly, the hormone profiles from pullets reared on a feed restriction program exhibit signs of metabolic stress, despite that fact that feed is absent for only twenty-four hours. The results of this study provides information on the metabolic responses to feed restriction, and may be of assistance in developing the most effective and desirable feeding regimens. This information will be of interest to other scientists and the poultry industry.

Technical Abstract: A trial was conducted to determine the effects of different feeding regimens on plasma hormone and metabolite levels in 16 week old broiler breeder pullets. A flock of 350 Cobb 500 breeder pullets was divided in two at 4 weeks of age and fed either everyday (ED) or skip-a-day (SKIP) from 4 to 16 weeks of age. Total feed intake did not differ between the two groups. At 112 d, 52 randomly selected pullets from the larger flock of ED fed pullets, and 76 from the SKIP fed pullets were individually caged and fed a meal of 74 g (ED) or 148 g (SKIP), respectively. Blood samples were collected from 4 pullets in each group by cardiac puncture at intervals after feeding. Plasma was analyzed for insulin, glucagon, insulin-like growth factor-I and II, triiodothyronine (T3) and thyroxine (T4), corticosterone, leptin, glucose, non-esterified fatty acids (NEFA), triglycerides and uric acid. The rate of crop emptying was also noted. In ED birds the crop was empty by 12 hr and SKIP birds by 24 hr after feeding. The alterations in metabolic hormone and metabolite levels after feeding and during the subsequent fasting period were similar to those reported by several authors in true fasting and refeeding experiments. The physiological responses to fasting, such as increased glucagon and corticosterone, and reduced plasma triglyceride, occurred at times coincidental with crop emptying in both ED and SKIP birds. Overall mean IGF-I levels were higher in ED birds providing a further possible explanation for improved feed utilization in such birds. T3 was higher (P = 0.09) in SKIP birds, which may explain the observed elevations in hepatic lipogenesis reported elsewhere. Overall mean plasma corticosterone was two-fold higher in SKIP birds which may be related to the increased length of fasting periods, hunger and stress. Plasma leptin was consistently higher in ED fed birds which was indicative of their more consistent food supply and more stable energy status. In summary, the experiment reported here shows that different feeding regimens can alter hormone and metabolite profiles, in spite of total feed intakes being equal.