Advances in bovine theriogenology in New Zealand. 2. Breeding management and technologies for improved reproduction.
The importance of submission rates (SR) on conception patterns in dairy herds during a short artificial breeding (AB) programme was first reported in 1973. Subsequent research has focussed on achieving 3-week SRs of 90% through improved detection of oestrus utilising tailpainting and vasectomised bulls fitted with chin-ball harnesses. Despite nutritional limitations of spring pasture as a sole diet, conception rates to first insemination of 65% have been recorded in cycling cows in many trials. Anovulatory anoestrus (AA) has become a major factor compromising SRs as well as reducing average conception rates and herd in-calf rates by 4-7 weeks after the planned start of mating (PSM). Whole herd synchronisation programmes have been developed but not widely used on dairy cows and have had only limited use on dairy heifers, despite a focus on concentrated conception patterns. The related technologies have become most commonly used to increase the SR of AA cows. Extreme variation in the weekly demand for processed semen in seasonally-intensive AB programmes has been accommodated by the development of a unique semen diluent, Caprogen. Its use has allowed sperm to be temporarily stored without freezing and used at dose rates of 1 million sperm/insemination. Sire variation with this form of semen processing is lower than with deep frozen semen. The greater use of production genes derived from Holstein-Friesian sires of North American origin in most AB programmes has left progeny with reduced reproductive performance. This effect has been greater than that associated with the increased productivity of dairy cows achieved through continued use of semen from intensively selected groups of progeny tested sires.
Macmillan
K L
KL
University of Melbourne, Department of Veterinary Science, 250 Princes Highway, Werribee 3030, Victoria, Australia. k.macmillan@unimelb.edu.au