The effect of growth intensity of heifers till 15 months of age on their milk production during first lactation

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The relative level of nutrition that induces differences in growth intensity of heifers during critical periods of mammary gland development can influence milk production during first lactation. However, even under the same nutritional and housing conditions, substantial individual variability in growth intensity exists (e.g. insufficient feeding places, variation in feeding among individuals). We hypothesized that such individual differences in the growth intensity during critical periods of growth could influence subsequent milk production as well. The aim of this work was to determine the effect of individual growth intensity of heifers in three growth periods (prepubertal, peripubertal, postpubertal) on milk production during first lactation. After weaning (day old), Holstein heifers were involved in the experiment. They were housed in free stall housing and fed at the same level of nutrition. The body weights of the heifers were measured at the age of 60 days (d), 90 d and then at 90 d intervals until 15 months (mo) of age. The data were evaluated using SAS 8.2 (one way ANOVA and Bonferroni t-test) programme. We have evaluated the effect of growth intensity in three periods of age on milk production during first lactation for the period of 90 d, 210 d and 270 d. First period represented prepubertal period from 3rd to 6th month (low growth intensity – less than 0.80 kg/d, middle - from 0.81 to 0.90 kg/d, high - over 0.9 kg/d), second period – around puberty occurrence was from 7th to 10th month (low – less than 0.70 kg/d, middle – from 0.71 to 0.85 kg/d, high - over 0.86 kg/day) and postpubertal period from 11th to 15th month (low – less than 0.64 kg/d, middle from 0.65 to 0.80 kg/d, high - over 0.81 kg/d). Variable growth intensity during prepubertal period did not influence the milk production in the different stages of lactation. Around the occurrence of puberty (from 7th to 10th month), we have observed a tendency of a negative relationship between growth intensity and milk production at all stages of lactation. The postpubertal relationship was the greatest at the middle of the growth intensity. In conclusion, different growth intensities of heifers before breeding, even under the same housing system and nutritional conditions, seem to influence their milk production during the first lactation. These effects tend to be inversely related in the peripubertal phase and exhibit a quadratic relationship postpubertally. However, it is necessary to evaluate more data to see the importance of the variability in the growth intensity of heifers in the critical periods of mammary development on milk production during first lactation.

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