Authors: MUSTAFA TEKERLİ, MUSTAFA GÜNDOĞAN
Abstract: The present investigation was undertaken to study certain factors affecting production efficiency, milk production and reproduction and to estimate the repeatabilities and phenotypic correlations of these traits in Holsteins maintained at different farms in western Anatolia over 3 years (1990 - 1993). The data consisted of 506 first and 232 second lactations of 525 cows. Three production efficiency traits (milk yield per day of lactation length (MYPDLL), milk yield per day of calving interval (MYPDCI) and milk yield per day of age at second calving (MYPDASC)), one production trait (lactation yield (LY)), and one reproduction trait (calving interval (CI)) were studied. The means of MYPDLL, MYPDCI, MYPDASC, LY and CI were 19.04 kg, 15.44 kg, 4.91 kg, 6404.77 kg, and 418.86 days, respectively. The analyses of variance indicated that the effects of the region-year factor were significant (P < 0.05) for all traits, whereas none of the traits was influenced by the parity order. The calving months were significant (P < 0.05) for MYPDASC, LY and CI. Least-squares means illustrated that these traits were lower for summer calvers. Age also had an important effect (P < 0.05) on MYPDLL, MYPDCI and LY. The positive phenotypic correlation (0.55) between milk yield and calving interval suggested that the higher yielding cows had longer calving intervals. Fertility was also severely depressed when the lactation yield was higher than 7000 kg. The repeatabilities for MYPDLL (0.51), MYPDCI (0.41) and LY (0.43) were high, and low for calving interval (0.10).
Keywords: Milk production, production efficiency, reproduction, phenotypic correlation, repeatability, Holstein
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