19 BEEF CATTLE PREGNANCY RATES FOLLOWING INSEMINATION WITH AGED FROZEN ANGUS SEMEN

Abstract

Artificial insemination has proven to be a valuable asset to the cattle industry. It is assumed that once good quality semen is frozen in liquid nitrogen it should remain viable indefinitely; however, semen viability has not been systematically evaluated after being stored for several decades. In this experiment, frozen semen from 25 purebred Angus bulls processed during 3 time periods (1960-1975 = 5 bulls; 1976-1991 = 11; 1992-2002 = 9 bulls) was used to randomly inseminate purebred lactating Angus cows and heifers and lactating crossbred beef cows. In experiment 1, Angus cows (n = 24) and Angus heifers (n = 16) and in experiment 2, crossbred cattle (n = 88) of 5 breeds (Beefmaster, Romosinuano, Bons Mara, Brangus, Brangus F1) were artificially inseminated with frozen-thawed Angus bulls semen from the 3 time periods. All females were in good body condition and at least 45 days postpartum and were synchronized using the SelectSynch protocol. Briefly, on treatment Day 0, females received an Eazi-Breed CIDR (Pfizer Animal Health, New York, NY, USA) implant and were administered GnRH (Factryl, 100 μg im), on Day 7, prostaglandin (Lutalyse, 25 mg im, Pfizer Animal Health) was administered and the CIDR removed. Cattle not responding to synchronization were subjected an additional prostaglandin treatment 8 to 10 days later. Estrus detection was conducted using the HeatWatch™ system for the Angus females and with Estrotect™ patches for the crossbred females. Females fitted with HeatWatch transponders that were successfully mounted 4 times within a 6-h period were considered to be in standing estrus and were inseminated 12 to 14 h later. Females fitted with Estrotect patches were observed twice daily (morning and evening) to identify females whose patch was scratched. Females were inseminated by an experienced technician 12 to 14h after the patch were observed as being scratched a minimum of 50%. Response to synchronization in Angus cows and heifers was 76% (n = 40), whereas in the crossbred cattle the response was 74% (n = 88). Cows and heifers were confirmed pregnant via transrectal ultrasonography 45 days postinsemination. Pregnancy rates confirmed by chi-square analysis were not different for Angus cows and heifers (58% and 43%, respectively). Also, pregnancy rates for the Angus females were not different across time periods 1, 2, and 3 (58, 43, and 53%, respectively). Pregnancy rates for crossbred females were not different across time periods 1, 2, and 3 (35, 60, and 44%, respectively). Overall pregnancy rates (experiments 1 and 2) were 47, 52, and 40% across time periods 1, 2, and 3 respectively. It is concluded from this study that semen units processed and frozen from Angus bulls from time periods 1, 2, and 3 (from the 1960s through to 2002) are still viable and produce similar pregnancy rates in artificially inseminated beef females.

Thanks to Jared Pitchfordfor inseminating all of the cattle; Harvey Blackburn for providing the semen to make the project possible; and my advisors Dr. Gentry and Dr. Godkefor assisting throughout the entire project. I also thank all of the graduate students who have helped me throughout the project.