SEMEN PRODUCTION AND PRODUCTIVE LIFE OF SAHIWAL BULLS: RELATIONSHIP WITH GENETIC WORTH

摘要

Objective of the present study was to document the semen producing ability, productive life and genetic ability for lactation milk yield of Sahiwal bulls used for artificial insemination (AI) in Punjab and to find the impact of AI bulls on the improvement of Sahiwal cattle. Data from Semen Production Unit (SPU), Qadirabad, Sahiwal, Pakistan were used for this purpose. A repeatability animal model was used for estimation of breeding values for lactation milk yield. Productive life of a bull was calculated as a difference between culling age and the age at first ejaculation. Number of bulls brought to SPU varied from 9 to 102 for any year. Average number of doses of semen produced by any bull for a year varied from 724 to 5745. On the average, 238 bulls produced 17143 +- 1164 semen doses during their average stay of 5.4 +-0.2 years. About 50% of the bulls stayed for less than four years at the SPU; with a maximum range of 14 years. Progeny tested bulls (n=90) produced 5000 and 10000 semen doses (Y) in three and four years of stay (X), respectively (Y = 24.8 + 2.3635 X - 0.0112 X~2). To produce 20,000 doses, it is predicted that bulls need to stay for six and a half years at the SPU. There was no association between breeding values for lactation milkyield estimated under a repeatability animal model (EBVs) and number of semen doses produced (r = 0.17) and EBVs and number of daughters. Lack of genetic superiority of bulls used indicated that AI did not bring desired genetic improvement in Sahiwal cattle in the present situation. Modifications for judicious utilization of bulls are suggested along with improvements in data recording.