Impacts of Early Postpartum Metabolism on Follicular Development and Fertility

Abstract

High producing dairy cows often experience low rates of conception during the target breeding period of 60 to 120 d postpartum (Faust et al., 1988; Harrison et al., 1990). Low fertility is costly for dairy producers because of extra expenditures for semen and insemination and because of reduced income from excessive days open (Britt, 1985). Cows that fail to conceive to AI between 60 and 120 d postpartum often are bred to clean-up bulls of unknown genetic merit. This not only affects long-range potential income for producers, but it reduces the number of records available for AI progeny testing programs.

Review of experimental data and careful study of published papers reveal that not all high producing healthy cows experience low fertility during the breeding period (Butler and Smith, 1989; Fonseca et al.,1983; Helmer and Britt, 1986; Staples et al.,1990). On a within-herd basis, the association between level of production and fertility is often weak (Fonseca et al., 1983). This leads one to suspect that factors other than high production per se are responsible for low fertility. It is with this concept in mind that we have begun to examine various biological pathways that might account for differences in fertility in otherwise healthy high-producing cows.

This paper will focus on one potential pathway namely the latent effect of early postpartum metabolism on quality of follicles destined to ovulate during the breeding period. Such follicles influence fertility in two ways: 1) through the quality grade or viability of the ovulated oocytes, and 2) through the amount of progesterone secreted by corpora lutea (CL) formed from these follicles (Fonseca et al., 1983). This paper examines the possibility that quality of a follicle is dependent on the conditions under which it begins its initial development many weeks prior to ovulation.