Agri Kultuur January / January 2018 - Page 28

Establish norms & standards for reproduction management Dr. Carel Muller Research Associate, Faculty of Animal Sciences, University of Stellenbosch A new milk production period starts at calving. The next reproduction phase also begins following the voluntary waiting period of about 40 days. Poor fertility in dairy cows, either through management or genetic merit, result in cows conceiving late or not at all. This may result in cows being culled reducing the income of a dairy herd. Culling cows is a direct loss because the value of cows is their future milk yield and not their current salvage value. An indirect cost of poor fertility is extending the lactation period when the daily milk yield of cows is lower than earlier in the lactation period. Although the milk yield per lactation increases, the average daily milk yield (and milk income) is reduced. Modeling has shown that extending the calving interval (CI) from 12 to 14 months results in a decrease in average daily milk yield of about 2 ℓ/day, reducing annual milk income by more than R3300 per cow. Overall, over the last 30 years, the fertility of dairy cows has decreased, i.e. extending CIs from 386 days in 1986 to 412 days in 2004. Poor fertility is attributed to a number of factors, i.e. increased milk yield per lactation, larger dairy herds, poor reproduction and housing management and possible changes in genetic merit. Breeding and selection programmes in dairy herds generally put little emphasis towards improving the genetic merit for fertility in dairy cows. Fertility is a complex trait affected by a number of factors, resulting in a low heritability. Therefore, to improve fertility genetically, change would be slow. At farm level, cows not becoming pregnant, are culled because of infertility. However, very few cows are inherently infertile. Poor AgriKultuur |AgriCulture management result in cows not becoming pregnant, i.e. cows may come on heat but because of poor heat detection, some cows are not inseminated. Poor insemination techniques also result in fewer conceptions. Overall, this results in management induced infertility. To improve fertility in a dairy herd, the level of reproduction management should be established to avoid culling cows incorrectly. The aim of this article is to provide ways indicating the level of reproduction management for a dairy herd. Norms and standard for reproduction management In South Africa norms and standards for reproduction management of dairy cows have not been established. This is because of a lack of a national database of service dates and derived fertility traits. Traditionally, calving interval (CI) and services per conception (SPC) are used as indicators of dairy cow fertility. Although important, both traits are not useful indicators of the standard of reproduction management. Cows not calving down again are not included in the estimation of herd CI. Inseminator skill affect mean SPC and is not an indication of dairy cow fertility. Fertility is defined as follows: the ability of cows to come on heat soon after calving, conceive from a minimum number of services while maintaining pregnancy to the next calving. An Australian survey suggested norms and standards using top performing and problem herds having to seek advice. This system uses four traits, i.e. 100-day-in-calf rate (the percentage of cows becoming pregnant within 28