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This study was carried out to investigate the effects of lactation number, service period and calving season on lactation milk yield and lactation curve parameters and to calculate the phenotypic correlations between lactation parameters of Holstein cows raised in a private farm. The data of the study were formed of daily milk yield records of477 lactations of 433 Holstein cows. In the analyses of lactation curve Wood equation (Yt=atb e-ct) was used.
In the study, least squares means were 9281.7 kg for lactation milk yield, 17.14 for a parameter. 0.265 kg for b parameter, 0.0042 for c parameter, 7.00 for persistency (S), 37.6 kg for maximum daily milk yield (Ymax), 66.7'hday for the day maximum milk yield (Tmax) was observed. The effects of lactation number, service period and calving season on lactation milk yield were found significant. It was observed that lactation milk yield increased with lactation number, the cows which were inseminated between 90-120th days had higher milk yield than the cows inseminated between 60-90"1 days and cows which calved in summer months had significant milk yield losses.
The cows which began lactation with high milk yield had higher results for peak milk yield (Ymax) and lactation milk yield. On the other hand the correlations between a parameter with b, c, Tmax and S parameters were found negative and significant. The correlation between the rising coefficient of the curve at the beginning of lactation (b) was not significant with Ymax; was significant and positive with c, Tmax and S was significant and negative with lactation milk yield. The lactation milk yields of cows reaching to peak milk yield faster were less and the decrease in daily milk yields of these cows after peak milk yield were faster.