Abstract:
A low calving rate (ranging from 20% to 40%) was recorded by state veterinary officials in 10 villages in the Moretele Local Municipal District in 2011. A previous study in the same area conducted in 2003 suggested that the probable cause of the low calving rate was bull infertility. However, only 13 bulls were examined in that study. The aim of the current study was to evaluate the fertility of a larger sample of communal bulls (n=50) to assess their fertility and the perceptions of farmers about bull fertility.
A participatory planning workshop was held to inform farmers from Moretele Municipal District about the project and 77 farmers agreed to participate in this study. The criteria for assessing bull fertility included testing for infectious diseases (brucella abortus, campylobacter fetus and trichomonas fetus), measuring scrotal circumference as well as scrotal and preputial tick damage. The electro-ejaculator method was used to collect semen from bulls throughout the study and the Computer Assisted Sperm Analysis system was used to measure total, progressive and non-progressive motility. Slides stained with eosin and nigrosin were examined microscopically for semen morphology. In herds studied, the number of cows and number of calves born over the study period (12 months) were recorded during farm visits, to calculate calving percentage. Data on farmer demographics and opinions were obtained using structured interviews.
Two bulls tested positive for brucellosis and ten others were excluded from the project due to various reasons. One was suspicious for T fetus. The average calving percentage of herds studied was 35.86%. The overall percentage motility of bull semen was 78.73 ± 25.34 %, but percentage progressive motility was very low, with an average of 27.39 ± 15.81 %. Percentage non-progressive motility was higher at 51.34 ± 19.92 %. Only 50.62 ± 35.80 % of the spermatozoa were morphologically normal. Tick damage to the scrotum and prepuce was observed in 92% of the bulls tested. Scrotal circumference showed an overall mean of 37.63 ± 3.42 cm and the overall mean age of the same bulls observed was 3.88 ± 0.99 years. About 13% of the bulls did not reach the minimum scrotal circumference threshold of 34 cm which is recommended at that specific age. Demographic data indicated that farmers were mostly interested in physical conformation of the bulls (n = 9)18.4% and their reproductive performance (n = 15, 30.6%). When purchasing a bull, no farmers asked for breeding soundness evaluation or proof that the bull was negative for B. abortus, T. fetus or C. fetus.
It was concluded that most of the bulls (92%) were infertile based on results showing that semen was of poor quality and lack of structural soundness, possibly due to tick damage. It is recommended that extension campaigns be aimed at disseminating information about pre-purchase examination of bulls, disease status and spot treatment of genital areas with an appropriate acaracides, to prevent tick damage to the scrotum and prepuce.
