Initial predictors of dairy bulls’ fertility proofs are currently limited to body condition score (BCS), milk yield and success of mating in the first 21 days (PM21) for their two-year-old lactating daughters. The first calving rate trait (CR42) is available after a cow has calved for a second time. Obtaining an earlier indication of fertility would be useful for genetic evaluation purposes. The aim of this study was to investigate the genetic and phenotypic control of heifer fertility in addition to investigating the relationship between heifer fertility and traits already included in the prediction ofthe fertility breeding value. Data were available on LIC’s Sire Proving Scheme animals born from 1989 to 2003 and included records on 244,453 animals. Using data on the first calving, planned start of calving was defined as the day within contemporary group when greater than 10% of animals had calved. A multivariategenetic analysis was undertaken with the traits PM21, CR42, BCS and 270-day milk yield recorded in lactating cows, in addition to a heifer fertility trait where success is defined as heifers that calve within21 days from the planned start of calving (CR21). The model fitted to these traits included contemporary group of the milking herd, breed proportions and age at first calving as linear and quadratic effects. The mean CR21 in this dataset was 71%. Heifers failing to calve within 21 days of the herd’s planned start of calving for heifers also had poorer fertility in first lactation, with a least-squares-mean of 75.5% (s.e. 0.2) versus 81.5% (0.1) for PM21 and 54.2% (0.22) and 62.4% (0.1) for CR42. The heritability estimate of CR21 was low (0.012), yet the genetic variation was comparable to other fertility measures. CR21 had a positive genetic correlation with CR42, indicating that CR21 may be a useful early indicator of fertility for use in genetic evaluations.
Proceedings of the New Zealand Society of Animal Production, Volume 67, Wanaka, 388-391, 2007
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