Influência de diferentes taxas de crescimento de novilhas holandesas sobre a produção de leite e idade ao primeiro parto Influency of different Holstein heifers growth rates on milk production and age at first calving

The heifers raising has an important contribution in the total cost of milk production and management techniques adopted and can interfere with the expression of the productive and reproductive parameters of the animal. The objective of this work was to avaliate the correlations among the weight gain rate of heifers in pre-puberty, age at first birth and milk production in the first lactation. In the first phase of the study they were evaluated growth of 84 Holstein heifers from 6 to 12 months belonging to two farms. In the second phase, it was evaluated the age at first calving and milk production in the first lactation. The animals were weighed every 30 days from 6 to 12 months being registered the age at first calving. After the calving it was made the record of milk production daily. According to the weight gain from 6 to 12 months the animals were then allocated into three groups (treatments): T1 (n=28)- ADG of less than 0.70 kg/day; T2 (n=28)- ADG between 0.701 and 0.80 kg/day and T3 (n=28) - ADG more than 0.801 kg/day. From six month age until the calving the management adopted was similar between farms; however in farm 1 the lactating animals received a smaller amount of concentrate in diet. The data were submitted to the analysis of variance, using the statistical program SAS (2007) and the means were tested by the GLM procedure of the SAS program. There was no effect of treatment on milk production corrected to 305 days; however, there was effect of treatment on age at first birth. Due to management adopted in different properties at the stage of lactation, and also due to the genetic there was effect of farm in milk production. The high animal performance during the growth phase may be responsible for reducing the age at birth without therefore affecting the future milk production compared with the moderate growth.