Effects of growth and dietary crude protein level until first insemination on milk production during first lactation in Holstein heifers

To decrease the age at first calving in Holsteins, the effects of average daily body weight gain (ADG) and crude protein (CP) level until first insemination on growth performance and milk production were examined. The MM group had a target ADG of 0.75kg and received a diet with a CP level of 14%. The HM and HH groups had a target ADG of 1kg; both these groups received a diet with CP levels 14% and 16%, respectively. The ADG in the HM and HH groups was 1.1kg, whereas in the MM group it was 0.97kg (P<0.01). The HM and HH groups showed no differences in withers height at body weight 350kg. The ages at first calving in MM, HM and HH groups were 23.1, 21.0 and 21.8months, respectively. The HM and HH groups had lower milk yield at day 305 than the MM group (P<0.01). These results suggest that growth performance until first insemination should be maintained at an ADG of 0.97kg or less with a CP level of approximately 14%, to shorten time until first insemination and prevent the decrease of milk yield.