Submitted to: Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/17/2002
Publication Date: 3/1/2003
Citation: Richards, M.P., Poch, S.M., Coon, C.N., Rosebrough, R.W., Ashwell, C.M., McMurtry, J.P. 2003. Expression of selected genes related to lipid metabolism in broiler breeder chickens. Journal of Nutrition. 133:707-715. Interpretive Summary: Poultry producers have, over the years, intensively selected for lines of chickens and turkeys that grow faster and produce more meat than previous generations. Unfortunately, along with these improvements have come some unintended detrimental changes in feed intake and body composition. For example, modern commercial strains of broiler chickens tend to overeat when given free access to feed. This can lead to obesity, poor reproductive performance, skeletal abnormalities, and other health-related problems if the birds are not restricted in their access to feed. Therefore, it is important to understand the genetic regulatory mechanisms for controlling fat metabolism in poultry during rearing and breeding periods of production. This manuscript examined the effects of full feeding versus feed restriction of female broiler breeder chickens during egg production on the functioning of genes related to fat metabolism. By analyzing the expression of specific genes involved in the synthesis, transport, and storage of fat, as well as other metabolic pathways, it may be possible to assess the potential metabolic consequences of feed restriction and other management practices on growth, body composition and performance of broiler breeders. This information will be useful to researchers studying the control of fat metabolism and body weight in chickens and turkeys, as well as, producers in formulating new genetic selection and feeding strategies for commercial poultry flocks.
Technical Abstract: Cobb 500 broiler breeder pullets were fed according to Cobb Breeder Management Guide specifications until they reached 21 wks of age. At this time half the birds were switched to ad lib feeding (ad lib) while the remaining birds continued to be fed according to Cobb guidelines (restricted). At 22 wks all birds were photo-stimulated and maintained throughout a laying cycle ending at 36 wks. Samples of liver and abdominal fat pad were collected at the following times: 1) just prior to photo-stimulation, 2) after photo-stimulation at first egg, and 3) through peak egg production. Reverse transcription polymerase chain reaction in conjunction with capillary electrophoresis and laser-induced fluorescence detection (RT-PCR/CE-LIF) was used to quantify hepatic expression of specific genes relative to that of b-actin in total RNA samples. Expression of sterol regulatory element binding protein 1 (SREBP-1), ATP-citrate lyase (ACL), fatty acid synthase (FAS), malic enzyme (ME), acetyl-CoA carboxylase (ACC), and stearoyl-CoA (?9) desaturase 1 (SCD1) genes in ad lib birds declined from their highest levels just prior to photo-stimulation to reduced levels as the birds came into and maintained egg production. In contrast, the restricted birds displayed a dramatic increase in the expression of these genes following photo-stimulation at first egg with a subsequent decline in expression levels as they reached peak egg production. Hepatic expression of fatty acid binding protein (FABP), very low density apolipoprotein II (ApoVLDL-II) and apolipoprotein B (ApoB) genes increased in both ad lib and restricted breeders following photo-stimulation, whereas apolipoprotein A1 (ApoA1) gene expression declined in both groups. These changes are consistent with increased hepatic lipid transfer capacity toward yolk during egg production. Abdominal fat pad weights were significantly higher in the ad lib as compared to restricted birds following photo-stimulation and the expression of lipoprotein lipase (LPL) in this tissue showed a similar pattern of expression to that observed for the hepatic lipogenic enzyme genes. Hepatic leptin receptor gene expression did not differ significantly for ad lib as compared to restricted birds at any time. In conclusion, the ad lib and restricted feeding regimes produced significantly different effects on hepatic gene expression related to lipid metabolism in broiler breeders. By analyzing the expression of specific hepatic genes involved in lipogenesis and lipid transport as well as other metabolic pathways, it may be possible to assess the potential metabolic consequences of feed restriction and other management practices on growth, body composition and performance of broiler breeders.