Estimation of genetic variation in the LH response to a GnRH challenge in pre-pubertal Holstein-Friesian heifers

摘要

Fertility of UK dairy cows is at an all time low (Royal et RAID., 2000). Genetic improvements through direct selection is minimal since parameters can only be measured in the mature female and generally have low heritability (h~2<0.1). It may be possible to overcome these genetic limitations with the use of an indirect selection criterion. Whilst commencement of luteal activity might prove a valuable genetic indicator of female fertility (Darwash et RAID., 1997), a major step forward would be the identification of a highly heritable trait in the male that is measurable in early life and genetically correlated to a measurement of female fertility. The physiological control of reproduction is by the same gonadotrophic hormones in both sexes (Land, 1973), and Haley et RAID. (1989) reported that the underlying variation in gonadotrophin response to GnRH is controlled by the same genes in both sexes. High heritabilities (0.4-0.55) for the response to GnRH have been reported in ram lambs (Haley et RAID., 1989) and beef bulls (Mackinnon et RAID., 1991). The objective of this study was to estimate the genetic variation in a number of parameters associated with the LH response to a GnRH challenge in pre-pubertal Holstein-Friesian (H/F) heifers.