Fetal and Postnatal Nutritional Programming of Reproductive Performance in Ruminants

Abstract Text: The influence of nutrition on reproductive function in females has been studied for decades.  In cows, early studies focused on the influence of nutritional status on the hypothalamic-pituitary-ovarian axis, demonstrating that in circumstances of extreme negative energy balance estrous cycles cease.  More recently, studies have focused on nutritional programming, and the hypothesis that differential feeding at key developmental stages can have long-term effects on physiology.  Anecdotal data reported impacts of drought on performance of the offspring of cows that were pregnant during the drought.  Subsequent controlled studies demonstrated that changes in intake during gestation altered reproductive performance and ovarian development of the female offspring.  During the peri-pubertal development period, decreasing nutrient intake decreased development costs and adapted heifers to perform better as cows when nutrient intake was limited.  In addition, there may be other advantages to developing heifers under reduced caloric intake.  In rodents, caloric restriction during the peri-pubertal period increased numbers of primordial follicle in the ovaries, prompting investigations into the influence of decreased caloric intake in developing replacement heifers on follicle numbers.  A review of the literature reveals that differences among studies are significant and emphasizes the need to understand the basic mechanisms that are being influenced by nutritional programming.  It is hypothesized that some of these programmed changes are due to epigenetic modification of the genome.  Differential methylation, histone modification, and changes in microRNA profiles have all been reported to alter the genomic response when nutritional status is altered in rodents, but these epigenetic modifications in response to nutritional programming in beef cows have not been reported to date.  This is partially due to the challenges of performing such research as controlled studies.  In practice, heifers are fed in groups, but for research purposes, either very large numbers of heifers are needed or heifers must be individually fed.  Depending on the experiment and the endpoints to be examined, such experiments can take anywhere between 4 mo and 6 yrs to complete, and this timeframe is increased dramatically if it is a multi-year study.  Thus, understanding the mechanisms in play will require a combination of in vivo and in vitro studies. If we can understand these mechanisms; however, then it may be possible to harness them and use targeted feeding to program heifers to their niche in the production system.  USDA is an equal opportunity provider and employer.

Keywords: Nutrition, epigenetics, reproduction