A Study of Some Factors That May Affect Semen Quantity and Quality as Well as Libido in Four Breeds of Dairy Bulls.
Artificial insemination, an important applied reproductive technology which is used worldwide in animal breeding has been used in Kenya since 1935. The Central Artificial Insemination Station (C.A.I.S), Kabete was established in 1946. There are about 100 dairy bulls at the station which have been selected based on milk yields of their dams and grand dams. Various factors, which include environment and the bull's anatomy may affect semen quantity and quality. Some work has been done to establish the factors that affect semen quantity and quality especially the effects of environment but scanty information is available about the associations between some reproductive organs of tropical dairy bulls and semen quantity and quality. This study was thus initiated with the aim of studying the interrelationships between age, body weight, scrotal circumference (SC), the size of seminal vesicles, length of cauda epididymis and testicular length on semen quality and quantity. In addition, this study attempted to establish the relationship between plasma testosterone concentrations and reaction time in the four dairy breeds, namely, Ayrshire, Friesian, Jersey and Guernsey kept at C.A.I.S. The study utilized a convenient sample of 98 bulls at the C.A.I.S. Nineteen of these bulls were less than 16 years of age and were not used for semen collection during the study period. Scrotal circumference, testicular length and length of the cauda epididymis were measured using a scrotal tape while the sizes of the seminal vesicles were estimated by rectal palpation. The semen samples were collected from the bulls twice a week using a standard artificial vagina. They were evaluated for volume, spermatozoa motility, concentration, morphology and viability. Blood samples for testosterone assays were collected by middle coccygeal venipuncture and the levels of testosterone in plasma were determined by radioimmunoassay. Statistical analyses of the gathered data involved computation of descriptive statistics, graphical, correlation and regression analysis as well as analysis of variance. XV There were no significant (p > 0.05) differences in ages of the bulls of the four breeds but there were significant (p < 0.05) differences in the body weights with Friesian bulls being the heaviest and Jerseys the lightest. Scrotal circumference,'seminal vesicle diameter, cauda epididymal length, testosterone concentration and reaction time did not differ among breeds (p > 0.05). However, significant differences were observed between breed-specific means of seminal vesicle lengths (p < 0.01) and also those of testicular lengths (p < 0.05) of some breeds. Differences observed in the means of the volumes of the ejaculates and the ones of the overall means of the percent spermatozoa motility between breeds were not significant (p > 0.05). Guernseys had the highest ejaculate volumes and Jerseys the lowest. However, these were not significantly different (p > 0.05). This seemed to be related to the sizes of the seminal vesicles which were longer in Guernseys and hence capable of holding more secretions than those of Jerseys. Guernseys had also the greatest testicular lengths and the Jerseys the shortest. In contrast, the mean spermatozoa concentration for Jerseys was significantly (p < 0.05) higher than those of the other breeds. In this study, the spermatozoa abnormalities found in the semen samples from all bulls irrespective of the breed were within the recommended ranges for normal fertile bulls. The most common head abnormality were detached heads (0.77 % in Ayrshires, 0.68 % in Friesians, 0.73 % in Guernseys and 0.96 % in Jerseys). For the midpiece, duplication were the most prevalent (0.21 % in Ayrshires, 0.13 % in Friesians, 0.05 % in Guernseys and 0.14 % in Jerseys). The predominant fail abnormalities were coiled tails in Ayrshires (1.47 %) and free tails, 1.36 % in Friesians, 1.15 % in Guernseys and 1.54 % in Jerseys. Non significant and negative correlations were observed between scrotal circumference and spermatozoa motility and primary as well as secondary Abnormalities. Ejaculate volume was positively correlated to scrotal circumference (r = 0.32), seminal vesicle length (r = 0.36) and diameter (r = 0-41) as well as cauda epididymal length (r = 0.29). The magnitudes and significance of coefficients between age or body eight and most of the
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