Date of Award

5-2010

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Animal and Veterinary Sciences

Advisor

Vernon, Kristine L

Committee Member

Bolt , Brian

Committee Member

Birrenkott , Glenn

Abstract

Sex selection is economically and genetically advantageous in cattle production. The only commercially available reliable sex selection technique is sexed semen; however, the technology is expensive and inefficient. Maternal manipulation could be beneficial to sway sex ratio. Frequent ultrasound coupled with rectal palpation has been shown to sway sex ratio towards female. In the preliminary study, cows with a corpus luteum (CL) ≥ 18 mm were randomly assigned to Treatment or Control (n=4 / group). Follicles > 5 mm were destroyed using ultrasound-guided ablation, a CIDR was inserted, and PGF2α (25 mg IM) was administered. Ovarian hyperstimulation began 48 h post-ablation and consisted of FSH administration (35 mg total IM) 2X/day for 4 days. Estrus detection began 24 h after CIDR removal (6th FSH injection) and was conducted every 4 h until standing estrus. At estrus, GnRH (100 µg IM) was given and cows were inseminated with 2 doses of frozen-thawed semen from a single bull 12 h later. 24 h after CIDR removal, Treated cows were subjected to trans-rectal ultrasound evaluation of their reproductive tracts with a 7.5 mHz probe every 4 h for 40 h. Controls were processed through the chute, but not subjected to ultrasound. Day 7 embryos were collected via trans-cervical uterine lavage. Sex determination was conducted by combined duplex PCR and dot blotting. The number of ovulations and transferable embryos collected were similar between Treated and Controls (13.0±3.3 vs. 11.8±1.1; 5.8±2.3 vs. 6.2±3.7, respectively). The female embryo percentage did not differ between groups or in comparison the expected 50:50 ratio. Experiment 2 followed the same protocol except heifers were used (n=7/group), cattle were administered FSH reduced to 30 mg total dose and control cattle were not subjected to chute processing. The number of ovulations and transferable embryos collected were similar between treated and controls (15.0±1.5 vs. 22.8±5.0; 5.7±2.2 vs. 6.8±2.5, respectively). The female embryo percentage did not differ between Treatment and Control; however, the Treatment and Control group combined (P=0.02) differed significantly from the expected value of 50:50.. Also, total embryos combined from the preliminary study and Experiment 2 differed from the expected value of 50:50 (P=0.02). This lead to Experiment 3 to determine if there was a timing of insemination effect. Cows were selected and hyperstimulated using the same protocol as the first two experiments, except FSH dosage was further reduced to 25 mg total dose and neither group was subjected to ultrasound. Cows ( n=6/group) were randomly assigned to either 0 hour insemination group (inseminated at onset of estrus) or 12 hour insemination group (inseminated 12 hours after the onset of estrus). The number of ovulations did not differ from each other (9.5±2.0 vs. 7.7±1.1). There was a trend for the total number of transferable embryos to differ from one another (0.5±0.5 vs. 4.5±1.8). The female sex ratio could not be statically analyzed between each other because of the low frequency but did not differ when compared to the expected value of 50:50. Frequent ultrasound and rectal palpation around timing of insemination did not effectively skew sex ratio.

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