Date of Award

12-2015

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Animal Science

Major Professor

F. Neal Schrick

Committee Members

Janice Lannett Edwards, Gina M. Pighetti, Brian K. Whitlock, Tulio M. Prado

Abstract

Reproductive performance of lactating dairy cows has decreased as milk production has increased as a result of genetic selection. Milk production alone is not the reason for decreased reproductive performance, as fertility issues are multifactorial and collaborative. Research chapters contained within have taken an applied approach focusing in two different areas of fertility. One approach was development of an evaluation system to identify lactating cows with decreased fertility prior to breeding; while another approach was to modify an ovulation synchronization protocol during periods of heat stress in order to improve fertility. The first focus was development and evaluation of a size and position score based on a one to three scale and assigned to lactating cows during a pre-breeding exam. This score was a reflection of the cervical and uterine horn diameter, and of the position of the reproductive tract in relation to the pelvis. Results indicated that cows with the largest reproductive tracts (score 3) had a 15% decrease in conception rates following artificial insemination compared to the smallest reproductive tracts (score 1). Score two reproductive tracts (intermediate) exhibited decreased conception rates compared to score one, but greater than score three. Identification of cows with lower potential fertility will allow producers to make the most economically, efficient decision when artificially inseminating lactating dairy cows. The second research focus modified an ovulation synchronization protocol by including an intravaginal progesterone releasing device (CIDR) nine days prior to artificial insemination during periods of heat stress. Use of a CIDR has shown to be beneficial with modest improvements in fertility in cool seasons, especially in anovular cows. This modification did not prove to be beneficial in improving conception rates during periods of heat stress. Lactating dairy cows with or without a progesterone releasing device had comparable conception rates. This research remains informative since use of a CIDR is expensive. This research exhibits this additional expense does not lead to positive results, thereby discouraging producers from incurring an unnecessary expense.

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