The Influence of Breed and Non-genetic Factors on the Semen Quality of Exotic (Bos taurus) Bulls in Uganda
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Semen quality is one of the major factors that determine the success of Artificial Insemination (AI) in cattle. Hence, this study was aimed at identifying the effects of bull breed, age, season, time, year period of semen collection, and ejaculate number on semen quality of Entebbe bull stud. A total of 971 semen sample records for four cattle breeds: Holstein Friesian (n = 9), Jersey (n = 6), Ayrshire (n = 9), and Guernsey (n = 3) kept at National Animal Genetic Resource Centre and Data Bank (NAGRC&DB) over the period of 2009-2019 were used. Semen samples were analysed for physical characteristics to determine semen colour and ejaculate volume. Further microscopic analysis involved the use of Computer Assisted System Analysis (CASA) to determine progressive motility and sperm density in a Bovine Photometer. The results indicated that with exception of time of semen collection, the other fixed variables had a significant effect (p˂0.05) on ejaculate volume, sperm density and progressive motility. Semen colour differed significantly (p˂0.05) between breeds, year period and age group. All the ejaculates gave semen with in the standard range of semen quality. The best semen quality was recorded from the first ejaculates collected from mature (≥3 year old) Jersey bulls in the long rainy season. This can be attributed to their adaptability to the environmental conditions in the tropics and advancements in age. Therefore, multiple semen ejaculates (two or more ejaculates) can be collected from mature Jersey bulls (≥3 year old) at any time of collection (early-morning, mid-morning, afternoon and evening) in the long rainy season for the best semen quality.