Abstract
Korean cattle breeders have shown interest in genetic improvement of milking ability because poor milking ability and short suckling period of Korean cattle is a hindrance to growth of calves. In this study, daily milk yields by period in Korean cattle were analyzed with an animal model. The milk yields were actually measured at sequential intervals from 1 to 4 months after calving: daily milk yields from delivery to 1 month (DMY1), from 1 to 2 months (DMY2), from 2 to 3 months (DMY3), and from 3 to 4 months (DMY4). Genetic variance estimates gradually increased by the periods while environmental variance estimates gradually decreased. This resulted in a dramatic increase in the heritability by periods: 0.02 for DMY1, 0.11 for DMY2, 0.16 for DMY3, and 0.42 for DMY4. In multi-trait analyses with daily milk yield and body weight of calf, genetic correlation estimates between milk yield and body weight were quite small (-0.08 to 0.02 for birth weight and -0.10 to 0.00 for weaning weight). The trends of the heritability estimated in this study showed that the genetic effects were more influential when the milking period was longer, suggesting genetic evaluations with daily milk yield collected at a longer period.
Highlights
The trends of the heritability estimated in this study showed that the genetic effects were more influential when the milking period was longer, suggesting genetic evaluations with daily milk yield collected at a longer period
There has been a great concern on milk production among Korean beef cattle breeders because the body weight and the milk production of beef cattle have been positively correlated (Freking and Marshall, 1992; Miller et al, 1999), and Korean cattle are known to have an inferior milking ability (Kim and Lee, 2000)
The estimates of variance components and heritabilities were obtained for the daily milk yield (Table 1)
Summary
There has been a great concern on milk production among Korean beef cattle breeders because the body weight and the milk production of beef cattle have been positively correlated (Freking and Marshall, 1992; Miller et al, 1999), and Korean cattle are known to have an inferior milking ability (Kim and Lee, 2000). Lee and Pollak (2002) estimated genetic and environmental correlations between body weight (birth weight, weaning weight, and yearling weight) of cow and daily milk yield at different periods in Korean cattle using a two-trait sire and maternal grandsire mixed model. They observed negative genetic correlation estimates between the body weight and the daily milk yield while environmental correlation estimates were positive. Further investigations of milk production in Korean cattle are in need to assess more accurate genetic ability of milking in Korean cattle
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