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Dosing Bovine Semen by Progressively Motile Sperm: Impact on Pregnancy Rates in Dairy Cattle

Wednesday, May 12, 2010

Dosing Bovine Semen by Progressively Motile Sperm: Impact on Pregnancy Rates in Dairy Cattle

TO BE PRESENTED AT THE 2010 ANNUAL SOCIETY FOR THERIOGENOLOGY MEETING IN SEATTLE, WA JULY 27th-30th

Y. Zeron1, L. Rabinovitch2, U.Shalit2, M. Deutsch2.

1Sion A.I. Company, Israel, 2Medical Electronic Systems, Caesarea, Israel.

The objective of this field trial was to evaluate the impact on pregnancy rates in dairy cattle inseminated with frozen semen that was dosed by progressively motile sperm per AI dose post thaw (PMPT).

The trial was divided into two phases. Phase 1 established a post thaw progressive motility loss factor (PMLF) per bull enrolled in the trial, tested the accuracy of preparing AI straws by # of progressively motile cells/straw post thaw, and provided the AI straws for the second phase.  Phase 2 analyzed the impact on pregnancy rates when inseminating large numbers of dairy cattle with the AI straws prepared in the first phase. In phase 1 of the trial, a unique PMLF was established for each of four Holstein bulls enrolled in the trial. The PMLF represents the overall percent decrease in the number of progressively motile cells resulting from the freezing/thawing process. Both fresh and post thaw frozen semen was tested using an automated sperm quality analyzer for bulls, the SQA-Vb. AI doses were all prepared using B-Sperm™ dosing software (Medical Electronic Systems, Ltd., Israel). Once the PMLF was established for each bull, 10 ejaculates from each of the four bulls were collected and tested using the automated SQA-Vb. Each ejaculate was split into four aliquots and used to prepare four AI dose batches (A, B, C, D) following the B-Sperm™ dosing software instructions. Three aliquots (A, B, C) were dosed by the number of progressively motile sperm post thaw targeting 1.5, 3.5 and 7.0 million per dose respectively. One aliquot per ejaculate (D) was dosed by targeting 15.0 million total number of sperm/dose, representing the standard dose preparation procedure at the stud (SION AI Company, Israel) and served as the study control. Microsoft Excel™ was used for statistical evaluation of the trial results.

A complete semen analysis was performed on seventy-six post-thaw AI straws from each batch using the SQA-Vb to determine the actual PMPT. The mean values +/- SEM for PMPT by batch were: (A) 1.5 +/- 0.05; (B) 3.0 +/- 0.09 and (C) 6.2 +/- 0.18 million progressively motile spermatozoa per dose. The mean value +/- SEM for total sperm cells per AI dose in batch D (Control) was 13.6 +/- 0.15 million. These results were found to be acceptable and a total of approximately 8,000 AI doses (2,000 per group) were distributed into straws and frozen by the stud technicians (Sion AI Company, Israel). In the 2nd phase of the trial 6,494 Holstein cows residing in more than 500 farms were artificially inseminated with semen from batch A, B, C or D between January and April 2009. Manual palpation pregnancy testing was conducted by veterinarians at approximately 42 days post-insemination. The insemination procedure and the pregnancy testing were performed blindly.  Pregnancy rates (per cow per cycle) were found to be: (Group A Target: 1.5 M Progressively Motile Sperm/dose) 34.2%; (Group B Target 3.5 M Progressively Motile Sperm/dose) 39.3%; (Group C Target 7.0 Progressively Motile Sperm/dose) 43.2; (Group D Control Target 15.0 M Total Sperm/dose) 38.6%. Significant differences were found between groups A (1.5M Prog Mot) and D (15M Total), C (7.0M Prog Mot) and D (15M Total), A (1.5M Prog Mot) and C (7.0M Prog Mot). The relative differences in pregnancy rates in the experimental groups A, B and C vs. the control were: -11.4%, 1.8% and 11.9%, respectively. A high correlation between the pregnancy rates in groups A, B and C and the number of progressively motile spermatozoa per AI dose (r = 0.96) was found.


It can be concluded that it is possible to accurately produce AI straws of frozen bovine semen based on a targeted post thaw number of progressively motile sperm cells per dose in a commercial setting. It was also demonstrated that pregnancy rates highly correlate to the number of progressively motile sperm cells per AI dose as demonstrated by a favorable 11.9% increase in pregnancy rates using AI straws from the highest PMPT group (C=7.0M Prog Mot) vs. the control, and in contrast, a 11.4% decrease in pregnancy rates using AI straws from the lowest PMPT group (A=1.5M Prog Mot) vs. the control. 

Key words: Progressive motility; Pregnancy rate; SQA-Vb; Frozen bovine semen; B-Sperm


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