ChileanJAR

Through differences in the nutritional plane, two homogeneous groups of 11 European Holstein heifers were reared up to differeIit calving bodyweights at a mean freshening age of 26.06 months. The bodyweights befare parturition were 463 Kg and 410 Kg, and after parturition were 527 Kg and 465 Kg for the heavy and light groups, respectively. After parturition the bodyweight faUs until day 42 andbegins to increase short before day 100. At the end of thefirst lactation the weight differences still remain (P < 0.01). These weight differences at second parturition are non-significant.
No significant differences (P > 0.05) at freshening pattem, ibreeding performance and milk production at 100 days and at the end of first lactation were obtained. However, a trend for higher weight to higher milk production was obtained. At 305 days in the second lactation, milk production for both groups was the same. The correlation coeficient for post-partum bodyweight and milk production was t = 0.394, which was significant (P < 0.01). The regression coeficient obtained was 6.13. To getthese coefficients therecordsof 18 additional heifers of the same ageand origin were included. Since their firstcalving ocurred at a mean age of 36 months, the records had to be age corrected.