Masters Theses

Date of Award

12-1976

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

John D. Smalling

Committee Members

Patricia B. Coulson, J. B. McLaren

Abstract

Twelve Angus, 2 Hereford, and 1 Polled Hereford bull were used to determine the effects of extended semen collection, and subsequent semen incubation, on qualitative semen characteristics, as well as the possible effects of these semen characteristics on the reproductive efficiency of the bulls. All semen samples were obtained by electroejaculation. The semen characteristics evaluated were the percent of morpho-logically normal sperm cells with normal acrosomes (M) , the percent of morphologically normal sperm cells with abnormal acrosomes (NA), the percent of morphologically abnormal sperm cells with normal acrosomes (AN), the percent of morphologically abnormal sperm cells with abnormal acrosomes (AA), and the percent of live sperm cells. Correlations were obtained between the semen characteristics and the various factors of the collection and evaluation procedures that could have influenced the semen characteristics. Highly significant (P< .0001) positive correlations were found between sperm cells of the NN classi-fication and the percent of live spermatozoa, and between sperm cells of the NA classification and the percent of dead spermatozoa. A highly significant (P< .0001) negative correlation was found between sperm cells of the NN classification and those of the NA classification. Regression analysis revealed that collection day, bull, incubation time, and the percent of dead sperm cells were the factors explaining most of the variation in the semen characteristics evaluated. Fertility was defined as the calculated number of estrous cycles each female could have completed in the presence of a herd sire. All lactating females were computationally allowed 42 days of involution when calculating their possible number of estrous cycles. All estrous cycles were calculated in a manner to avoid penalizing a bull for a female's lack of conception in an estrous cycle that could have started prior to exposure to a bull and terminated in his presence. The effects of semen characteristics on fertility were analyzed by two methods. One was the regression of the percent of normal sperm cells with normal acrosomes and the percent of normal sperm cells with abnormal acrosomes on the calculated number of estrous cycles of only the females that calved as a result of exposure to a herd sire. The second analysis used the same semen characteristics regressed on the calculated number of estrous cycles of all females exposed to a bull. Based on their different rates of improvement in the semen charac-teristics, the bulls were divided into two groups. Group I (5 bulls) produced semen of higher quality than Group II (8 bulls). Regression analysis of fertility revealed that the semen charac-teristics in the NN and NA categories of Group I, for the overall in-cubation period, and after 8 hours of incubation, were significant (P <.05) in accounting for the greatest amount of variation in fertility within the Group I bulls. No significance was obtained in the analysis of Group II or of both groups combined. The results of the study indicate that improved techniques exist to aid in the characterization of bulls on sperm cell morphology and changing state of the acrosome. These techniques could be used to separate bulls of either increased or impaired fertility from bulls of average fertility. Separation of bulls with more subtle differences in fertility may be difficult to accomplish.

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