Abstract

The success or failure of artificial insemination starts with the quality status of semen used, hence, this study aimed to investigate the effects of breed, season and year on bovine semen quality of the National Bull Stud of Rwanda kept at Masaka bull station, Rwanda. A total of 1475 semen samples were collected bi-weekly from nine bulls of Holstein Friesian (n = 3), Inyambo (n = 3) and Jersey (n = 3) breed using an artificial vagina. Semen volume, colour, concentration, mass motility, live sperm percentage and post-freeze motility were evaluated. Libido of the bulls at the time of semen collection was scored. Ejaculate volume, mass motility, individual motility, density and post freeze motility significantly differed (p < 0.05) among seasons of the year, bull breeds and age/year of collection. Friesian bulls had superior (p < 0.05) semen volume (5.76±0.08 ml) to that of Jersey (4.29±0.09 ml) and Inyambo (3.37±0.1 ml). However, Friesians had an inferior (p < 0.05) lighter coloured semen, with only 52.7% of Friesian samples having the preferred cream colour, as compared to 65.2% of Jersey and 64.9% of the Inyambo semen samples. Year of collection (2011 or 2012) and in essence age of the bull negatively affected (p < 0.05) all the parameters studied, with semen volume dropping from 5.16 to 5.10 ml, colour lightened from 62.8 to 54% of the samples being cream; mass motility fell from 2.98 to 2.65, while live sperm percentage in ejaculates dropped from 65 to 63%. Of the eight parameters studied, only post-freeze motility was not affected by passage of time. Semen collected during the October to December period had the best quality characteristics, though collections in the long rains (March to May) had comparable mass motility and post-freeze motility. Semen volume (4.61 ml per bull ejaculate) and post-freeze motility (39%) were poorest in the long dry season (January to February). In conclusion, the Friesian breed should be promoted at the bull station. Most semen should be collected during the rain season, particularly the short rains (October to November). Bulls below three years of age should be of focus.

Key words: Cattle, mortality, seasonality, semen evaluation, pedigree bulls.