Selection of herd sires for beef production
1992
Bosman, D.J. (Animal and Dairy Institute, Irene (South Africa))
The paper mainly dicusses traits to consider when choosing bulls. It states that it is a basic requirement that bulls that are selected must be adapted to the environment and production system concerned. The ideal is to purchase bulls that have been officially tested at central growth test centres or on the farms of owners, because the genetic potential of the bull is known, making a calculated selection possible. On completion of an official growth test, the following comparative indices are processed: weaning index, which evaluates the dam's milk production and the early growth of the calf; an index based on the growth potential of the bull during the post-weaning growth period; an index based on the ability to convert feed into beef and an index based on the mass per day of age. The shape of the frame is highly heritable, therefore, select for the type of frame that will be best adapted to the particular environment, taking into account that the bigger type of animal reaches sexual maturity later and require more food for normal body functions. Also the reproduction potential of a bull is reflected by the size and appearance of his scrotum. The srotum circumference is highly correlated with semen quality and that the use of a bull with a good scrotum circumference will result in sons and daughters with good reproduction characteristics. Once the bulls have been identified according to performance, it is necessary to make a visual evaluation with a view to abnormalities, muscling, skeleton, type, condition of the sheath and virility. The number of cows and heifers per bull will depend on age of the bull, length of the breeding season, grazing conditions and terrain. It is sound management policy to monitor the bulls with the cows and record mating dates. The use of breeding season is most advantageous because it simplifies management, cows calve during the most suitable time of the year and better care can be taken of the bulls. Herd bulls are critical for the success of the breeding programme, therefore the choice of a bull is an important decision
显示更多 [+] 显示较少 [-]