The rate of genetic improvement in Ireland up until the mid-80’s waslow (approx. 0.5% per year) compared to North America where geneticmerit for milk production was increasing by 1.5% per year (Funk,1993). Since 1985 the rate of genetic improvement increasedmarkedly to about 1.5% per year in 1992 (Coffey, 1992). This highrate of genetic progress has mostly been achieved through theimportation of North American and European genetics. The relativemerit of these sires has been obtained from the performance of theirprogeny in systems of milk production which differ greatly from thoseoperated in Ireland.The term “high genetic index” (HGI) is used to describe a cow, whichas a result of selection, is generally predisposed to producesignificantly more milk than a cow of lower merit status. Studiesfrom New Zealand have shown that cows of high “genetic index” atpasture, produce more milk (20 to 40%), consume more herbage (5to 20%), were more efficient convertors of food into milk (10 to 15%)than lower merit cows (Holmes, 1988). However, these “high”genetic index cows would be considered “low” when compared topresent-day genetics. Recent results from Langhill (Veerkamp et al.,1994) have shown that increasing genetic index results in majorincreases in feed efficiency, reflecting increases in milk yield withcows fed indoors on silage/concentrate diets. There is littleinformation available on the performance of present-day HGI dairycows, on seasonal calving, grass-based systems of milk production
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