Global Gene Expression of the Hen Ovary in Response to Different Feeding Conditions.

Abstract

Ovarian follicle selection and development in domestic hens is a highly ordered and efficient process. Optimum follicle development and subsequent egg production in hens depend on maintenance of the ovarian hierarchy with the largest follicle ovulating on each day and the penultimate follicle rising to primary position after each ovulation. Egg-laying strains of hens have been selected for precise and highly efficient ovulation rates resulting in strains that ovulate almost daily. In contrast, broiler strains are meat-producing birds that have been genetically selected to grow quickly and to efficiently accrue protein. As a consequence of genetic selection, reproductive performance has declined in broiler breeder hens. These hens have excessive follicle development, with multiple large follicles and a disordered hierarchy. Restriction of feed intake in the commercial setting has somewhat alleviated this reproductive inefficiency. A restricted diet results in a more ordered follicle development and enhances reproductive efficiency. The hormones or factors underlying the differential effect of feeding level on follicle development are unknown. To gain insight into this, we examined global gene expression in ovaries from broiler breeder hens which were either feed-restricted or fed ad libitum. Broiler breeder hens (Hubbard Farms, Walpole, NH) in the first year of lay were raised using conventional commercial practice except that one pen of hens was maintained on ad libitum feed (n=8) and one pen on restricted feed (87% of ad libitum diet; n=9) for one month prior to euthanasia. Hens on the restricted diet had a decreased ovarian weight, reduced number of large follicles and a well-ordered follicular hierarchy. Ovaries were collected and RNA extracted from the ovarian body of 3 hens from each group. The RNA was hybridized to GeneChip chicken genome arrays (Affymetrix, Santa Clara, CA) and scanned by the GeneChip scanner 3,000-7 G. This array contains 32,773 transcripts and represents over 28,000 genes in the Gallus gallus genome. Analysis was done at the Cornell University microarray core facility. Microarray results showed 243 significantly differentially expressed genes. Out of these, 137 transcripts were up-regulated and 106 were down-regulated in the restricted fed hens as compared to the ad libitum fed animals. Functional annotation analysis was subsequently carried out using DAVID Bioinformatics Resources (version 6.7) and revealed that the up-regulated transcripts were enriched for genes associated with cholesterol metabolism and biosynthesis and for DNA-binding proteins. These data provide insight into the ovarian changes associated with feeding level in hens and suggest targets for further study. This project was supported by National Research Initiative Competitive Grant no. 2008-35203-19097 from the USDA National Institute of Food and Agriculture. (poster)