Evaluation of two seminal collection regimens for mature Holstein bulls

Variance component estimates for post-thaw sperm variables measured by computer assisted semen analyzer for inbred and non-inbred Hereford bulls

Inbreeding has been shown to have negative effects on animal reproductive performance. It, however, has not been documented as to the extent that inbreeding impacts sperm cell characteristics especially after cells have undergone cryopreservation. In the present study, therefore, there was evaluation of sperm motion and size characteristics from two inbred lines and non-inbred Hereford bulls using Computer Assisted Sperm Analysis (CASA). Pre-frozen semen samples were obtained from Line 1, Prospector, and a non-inbred Hereford bulls. Average inbreeding of each group was 27%, 45%, and 0%, for Line 1, Prospector, and non-inbred groups, respectively. For each bull, two straws (0.5 ml) were evaluated, within each straw two slides with ten fields per slide analyzed with the CASA. Cells were analyzed by mixed model analysis using a model that contained line as fixed effect and individual bull, straw, slide, and fields are random effects. No significant differences between lines of bulls were found for motility or progressive motility. For the head elongation (ELON), and head area (AREA) significant differences existed between lines. Mean separation indicated that Line 1 group had a larger head area and the heads were not as elongated as the Prospector and non-inbred group cells. The lack of significant differences for motility and progressive motility across lines was surprising and indicates there was no inbreeding depression for post-thaw semen characteristics. One explanation for this could be that indirect selection pressure was placed on these characteristics as inbreeding was increased.

Environmental, management, and genetic factors affecting semen production in Holstein bulls

The objective of this study was to evaluate the importance of environment, management, physiological status, and genetics on semen quality (volume of the ejaculate, sperm concentration, sperm motility, number of sperm, and number of motile spermatozoa per ejaculate) of Canadian Holstein bulls. For this purpose, semen production data from 198 bulls were analyzed using mixed linear models. Young bulls (up to 30 mo old) and mature bulls (between 4 and 6 yr old) were analyzed separately. Semen characteristics generally improved significantly with age of young bulls. Season significantly affected all semen traits in young bulls but did not significantly affect volume and sperm motility of mature bulls. Performance was better in winter than in summer. The highest numbers of motile spermatozoa per ejaculate were obtained with intervals of at least 4 to 5 d between collections. Although the bull handler and semen collector caused less than 10% of the variance, the collection team significantly affected semen volume, number of sperm, and number of motile sperm per ejaculate for both growing and mature bulls. Heritabilities for volume, concentration, sperm motility, number of sperm, and number of motile sperm per ejaculate were, respectively, 0.24, 0.52, 0.31, 0.38, and 0.49 for young bulls and 0.44, 0.36, 0.01, 0.54, and 0.64 for mature bulls. Repeatability of semen traits varied from 0.41 to 0.64. Genetics, management, and environmental factors clearly contribute to semen production in Holstein bulls.

Semen quality and behavior of Holstein bulls exposed to estradiol-treated bulls for mounts

The objectives were to test the effects of estradiol treatment of teaser bull mounts on sexual behavior and on quality and quantity of sperm obtained from sires managed as in large commercial AI breeding organizations. In a change-over design, the same teaser bulls were either untreated or treated with estradiol. Five semen-producing bulls were ejaculated twice per day on Tuesdays and Fridays after epididymal reserves were partially depleted. A 15-min period of continuous sexual preparation with three false mounts allowed was standard before each semen collection. All bulls were attracted to and licked the preputial area of the teaser bulls followed by the Flehmen response during the period of sexual preparation. Bulls usually completed the false mounts in < or = 15 min, and all thrusted vigorously with both hind feet moving forward synchronously at this time on 100% of the 80 semen collections. Major differences among bulls and between first and second ejaculates occurred in semen volume, semen concentration, and total sperm collected. An increase of 10% in total sperm output when bulls were exposed to treated teaser bulls could be of commercial benefit. The correlation between total time to first mount for the two ejaculates per bull each day and total sperm collected per bull per day was -.44. Thus, the shorter time to first mount may be useful as a low level predictor of higher sperm out-put per bull.