Effects of Bull Characteristics and Testicular Attributes on Semen Quality in Kenyan AI Station Bulls

Abstract

More than 24 million people in East Africa depend on the dairy industry, directly and indirectly through the dairy value chain. Within the sub-Saharan region, Kenya has the best dairy industry, which supports approximately 1.5 million smallholder farmers, with additional stakeholders in the dairy value chain. The dairy subsector contributes 4% to the gross domestic product (GDP) and 12% of the total agricultural GDP. The success in the dairy sector is attributed to the adoption of assisted reproduction technologies, especially artificial insemination, to improve the genetic makeup and subsequently increase milk production in dairy animals. Artificial insemination (AI) has dramatically enhanced milk production by disseminating improved genetic. However, despite the success in the dairy industry, several knowledge gaps on the selection of bulls for AI exist, necessitating the current study. The current study aimed at documenting the effects of bull signalment and testicular attributes on semen quality in bulls used for semen production in Kenya. The study was conducted at the Kenya animal genetic resources center. All healthy bulls aged above 16 months and in active collection were recruited. Prospective and retrospective data were collected. The prospective study was conducted on 96 bulls, and the collected data included the age, body weight, body condition score, breed, scrotal circumference (SC), semen volume, progressive motility, post-thaw motility, and concentration, which were determined and documented. On the other hand, the retrospective study included data on semen quality in 38 bulls aged above 84 months. xii Age and weight significantly affected the SC (p-value <0.0001). There was a significant variation in SC across the breeds (p-value <0.0001), where the Bos indicus had a greater SC than the Bos taurus. Furthermore, a logistic regression model revealed that testicular presence of hyperechoic lesions increased with age (p-value <0.001). The semen volume significantly increased with age (p-value <0.05), body weight (p-value <0.001), and SC (p-value <0.05). The body condition score negatively and significantly affected the post-thaw semen motility and sperm concentration (p-value<0.05). The breed significantly affected the progressive motility (p-value <0.01), post-thaw motility (p-value <0.05), and sperm concentration (p-value <0.001). The presence of hyperechoic lesions did not significantly affect semen quality in both studies (p-value >0.05), although semen volume was significantly higher in bulls with hyperechoic lesions in the prospective study (p-value <0.05). From the findings of this study, it is prudent to cull bulls based on semen quality rather than age, as there are old bulls consistently producing good-quality semen. Furthermore, over-conditioning bulls significantly affect sperm concentration and post-thaw motility. Finally, there is a need to substitute the use of an electro-ejaculator in the Bos indicus as their semen quality significantly varies from the Bos taurus, where an artificial vagina is used