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United States Department of Agriculture

Agricultural Research Service

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Research Project: Strategies to Improve Heifer Selection and Heifer Development

Location: Nutrition and Environmental Management Research

Project Number: 5438-31000-093-00
Project Type: Appropriated

Start Date: Jul 31, 2012
End Date: Jul 30, 2017

Objective:
In Objective 1, we will determine genetic, nutritional, and physiological factors influencing development of the female reproductive tract from sexual differentiation through sexual maturity. Sub-objective 1.A focuses on developing methods to combine reproductive tract scoring and Lutalyse (prostaglandin F2'' to minimize labor while maximizing life time productivity and calf weaning weights in beef heifers. Sub-objective 1.B will validate the influence of polymorphisms in the glutamate receptor, ionitropic, AMPA 1 (GRIA1) gene on antral follicle counts in beef heifers. In Objective 2, we will examine the relationship between genes controlling carcass and production traits and reproductive function to identify biological pathways that mediate the genetic and phenotypic antagonism that exists between production traits and reproductive performance. We will do this by determining if polymorphisms in genes that influence carcass traits have a detrimental effect on reproductive traits (Sub-objective 2.A). In Objective 3, we will identify ovarian, embryonic, and uterine contributions to conception failure and apply them to increase lifetime productivity in beef cattle. We will do this by determining differences in uterine function between heifers with low and high antral follicle counts (Sub-objective 3.A). In sub-objective 3.B, we will combine analysis of ovarian vasculature and the vascular endothelial growth factor system with in vitro fertilization to determine if differences in ovarian vascularity contribute to the variation in oocyte quality in heifers differing in antral follicle counts.

Approach:
The overall objective of this project is to understand the factors controlling establishment of the ovarian reserve (i.e. the number of ovarian follicles that a heifer has at birth) and development of the female reproductive tract. The Reproduction Research Unit at the U.S. Meat Animal Research Center conducts research to identify highly fertile replacement females. Identifying these females early in life can improve overall production efficiency. For example, a replacement heifer must wean 3 to 5 calves to recoup her development costs or incur a net loss for the enterprise. The most practical method for evaluating reproductive capacity in beef heifers is palpation of the reproductive tract. This allows the palpator to identify heifers with small under-developed reproductive tracts. Adding ultrasonography to this process in the previous project demonstrated that antral follicle counts were also an indicator of heifer fertility. Limitations of palpation based evaluation of heifers are the number of animals that can be examined in a day and the age at which these exams can be performed. Understanding the physiological, genetic, and nutritional factors that influence development of the female reproductive tract will allow the implementation of novel technologies to aid in identifying replacement heifers at a very young age. Once they are identified, management strategies can be administered more efficiently to prepare them to conceive as early as possible in their first breeding season. Understanding the interaction of the genes controlling reproductive tract development with genes controlling production traits will determine the impacts of using genetic markers for production traits on reproductive performance in beef cows.

Last Modified: 8/21/2014
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