The shape of the lactation curve for 475 Turkish Holsteins was estimated by fitting a gamma function to daily milk yields from monthly recording of 754 lactations. Lactation curve traits that were analyzed included a scaling factor associated with yield at the beginning of lactation, the inclining and declining slopes before and after peak yield, DIM at peak yield, and peak and lactation yields. Persistency of lactation yield was measured from 1) the gamma function, 2) the coefficient of variation for monthly test-day yields, and 3) the ratio of lactation yield to peak yield. The log-transformed gamma function explained 71% of variation in daily yield. Effects of farm operation, calving year, calving season, parity, and service period were significant for the various lactation curve traits. Peak and lactation yields were higher for cows that calved in fall and winter, and persistency was higher for cows that calved in summer and fall. Peak and lactation yields were lower, but persistency was higher during first lactation. Repeatability estimates were moderate for peak (0.26) and lactation (0.34) yields and lower (0.06 to 0.20) for other lactation curve traits.

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The objective of this study was to determine the relationships between milk yield and calving interval in first lactation and breeding efficiency, herd life and length of productive life of 1 293 Holstein cows maintained at Ceylanpinar State Farm in Southeast Anatolia from 1990 to 2002.The least-squares means of first lactation milk yield, lactation length and calving interval were 5 620.1 ± 76.6 kg, 315.5 ± 2.0 and 386.9 ± 2.6 days. The values for breeding efficiency, herd life and length of productive life were 94.9 %, 2 095.9 ± 34.7 and 1 257.2 ± 34.4 days. The year of first lactation had significant effect (P<0.05) on all traits except for calving interval and lactation length, and breeding efficiency was only affected by age at first insemination and age at first calving (P<0.05).Heritabilities were 0.27 ± 0.08 for milk yield, 0.02 ± 0.05 for lactation length, 0.06 ± 0.05 for calving interval, 0.05 ± 0.05 for breeding efficiency, 0.30 ± 0.08 for herd life and 0.29 ± 0.08 for length of productive life. Genetic and phenotypic correlations between different traits ranged from −0.49 to 0.99 and −0.37 to 0.99 respectively. Keywords

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