STUDY OF SOME PERFORMANCE TRAITS IN SAHIWAL COWS DURING DIFFERENT PERIODS

Data on some production performance traits of Sahiwal cows maintained at the Livestock Experiment Station, Bahadurnagar, Okara, Pakistan during three different periods i.e. period-1 (1973-1982), period-2 (1983-1992) and period-3 (1993-2002) were compared. Each period was spread over 10 years duration. The data set included 1895, 2123 and 1679 lactation records for the three periods, respectively. Five performance traits viz lactation milk yield, lactation length, dry period, service period and calving interval were included in the analysis. The least squares means for lactation milk yield for the periods 1, 2 and 3 were 1429 ± 21.27, 1632 ± 17.95 and 1527 ± 19.34 kg, respectively. The corresponding values for lactation length were 258 ± 2.51, 256 ± 2.13 and 267 ± 2.29 days, respectively. The means for dry period, service period and calving interval were 172 ± 3.70, 156 ± 4.03 and 437 ± 3.74 days, respectively in the period-1, 161 ± 3.19, 139 ± 3.45 and 420 ± 3.23 days, respectively for period-2. and 158 ± 3.55, 152 ± 3.86 and 429 ± 3.60 days, respectively for period-3. The analysis of variance showed that period of calving showed significant variation (P