The effect of certain non-genetic factors, viz, season, period, age group and days open on the first lactation production and reproduction traits of Sahiwal cattle reared at organized farm under tropical condition was assessed. The records on first lactation production and reproduction performance of 961 Sahiwal cattle spread over a period of 47 years (1961-2007) were used for the study. The first lactation traits considered were age at first calving (AFC), first lactation 305-day or less milk yield (FL305DMY), first lactation length (FLL), first service period (FSP) and first dry period (FDP).The non-genetic factors incorporated in the model for AFC, FL305DMY, FLL, FSP and FDP accounted for 19.25, 21.25, 35.45, 07.09 and 21.12 per cent of total variation, respectively. Among the non-genetic factors, the period had highly significant effect on all the traits; while the age group had no effect on FL305DMY, FLL, FSP and FDP and the season had highly significant effect only on FDP. The days open had highly significant effect on FL305DMY, FLL and FDP. The overall least squares means for AFC, FL305DMY, FLL, FSP and FDP were 1117.02 days, 1759.86 kg, 303.46 days, 149.63 days and 163.75 days, respectively in Sahiwal cattle. It was concluded that the first lactation traits were highly influenced by the period of birth/ calving. It also reflected that the milch stock was maintained under comparatively favorable farm conditions and the fluctuations in extreme climatic conditions did not affect these traits in Sahiwal cattle.
