Multiplicative factors of the adjustment of fat yield production in Gir breed for simultaneous effects of age at calving and calving season

The simultaneous effects of age at parturition and season parturition on fat production were estimated by maximum likelihood for two levels of herd production : (A) "high" (3098 Kg) and (B) "low" (2297 Kg). The data set group (B) included 3516 cows lactation of the Gir breed that calved between 1980 and 1992 in 15 herds, while that for group A consisted of 2040 lactations of the same breed and over the same period. The highest levels of fat production were attained between 99 and 110 months of age during the rainy season, independent of the level of herd production. During the dry season, from Abril to October, the maximum fat production was between 111 and 134 months age. The production during of fat was higher the dry season than during the rainy season. The fat mean production or groups A and B were 131 and 102 kg, respectively. The multiplicative age - season adjustement factors were obtained by the dividing the fat production estimates at the age of maximum production during the dry season, 99 to 104 months in group A and 123 to 134 months in group B by the classes of age at calving. These factors, estimated independently for each data Set, were used to adjust the fat production in the other data set and the simultaneous effects of age at calving and season parturition. The age - season reduction means squares, the F value and coefficient age - season regression on the fat production within the herd - year indicated that the multiplicative factors obtained from the low production herds serve for the adjustment of fat production in the high production herds. Multiplicative factors for adjusting milk production when tested for adjusting fat production in both groups, using the same procedures, were inadequate for adjusting the effects of age-season on fat production. This indicates that adjustment actors for milk production should not be used to correct age-season effects for fat production.