Date of Award


Degree Type


Degree Name

Master of Science


Animal Science

Major Professor

J. Lannett Edwards

Committee Members

F. Neal Schrick, Justin D. Rhinehart


The objective of this study was to compare fertility of sex-sorted semen in lactating cows using a voluntary waiting period (VWP) of approximately 55 days (VWP55) or 85 days (VWP85). At 21 days in milk (DIM), cows were randomly assigned to begin estrus synchronization at 55 or 85 DIM. Only cows confirmed cyclic by 55 DIM were synchronized. At 55 or 85 DIM, cows [VWP55 (n=44); VWP85 (n=45)] having a corpus luteum (CL) were administered PGF[two alpha]. Estrus was monitored continuously by the HeatWatch® [registered sign] system (HW) and by twice daily visual observation seven days following each PGF. Cows exhibiting estrus were artificially inseminated with sex-sorted Holstein semen using one of two different bulls having similar sire conception rates. After 14 days, PGF was administered to any cow that did not exhibit estrus. Cows not responding to either PGFadministration were administered GnRH and a controlled intravaginal drug releasing device (CIDR). Seven days later, CIDR was removed and PGF was administered. Pregnancy determination occurred 28 to 35 days after AI and was monitored at 60, 80, and 150 days. No difference in overall percentage of cows expressing estrus (79.55% and 77.78%, P = 0.8393), hours to estrus following either the first or all PGFadministrations (65.79 h and 72.65 h, P = 0.4908; 62.28 h and 73.00 h, P = 0.2218, respectively), number of mounts (9.05 and 10.54, P = 0.5246), average mount duration (4.59 s and 4.99 s, P = 0.2602), and total estrus length (8.16 h and 9.17 h, P = 0.6389) was observed between VWP55 and VWP85 cows. Conception rates 30 days after AI were significantly higher for VWP85 cows compared to VWP55 (51.43% vs. 22.86%, respectively; P = 0.0181). Conception rates were monitored at 60 (48.57% vs. 20.00%, respectively; P = 0.0166), 80 (42.86% vs. 20.00%, respectively; P = 0.0471), and 150 days after AI (42.86% vs. 20.00%, respectively; P = 0.0471) to monitor embryonic loss. Fertility of sex-sorted semen in lactating cows can be improved after a VWP of 85 days under specific management conditions.

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