Livestock Studies 2000, Vol 40, Num, 1     (Pages: 014-028)

Main Factors Affecting Milk Yield Traits of Holstein Cattle Bred under the Conditions of Different Operations, and Essential Parameters to Selection
II. Effects of Environment and Heredity on the Persistensi of Milk Production in Holsteins

Mustafa TEKERLİ 1

1 Afyon Kocatepe Üniversitesi, Veteriner Fakültesi Zootekni Anabilim Dalı -AFYON - Eleven measures of persistensi of milk yield were used to determine the effects of different environmental factors on this trait. Heritability and repeatability values were estimated and it was aimed to reveal the possibilities of using this trait in a selection.This investigation was based on 1130 lactation records of 670 Holstein cows being imported from Italy and born in Turkey in the scope of Turk-Anafi dairy cattle breeding development project. Persistensi was expressed as a ratio between maximum test day yield (peak yield) and mean test day yield, the ratio of total yield in 2X305 days to maximum test day yield, the standard deviation and coefficient of variation of the test day yields, the ratio between total test day yields in different part of lactation, the mean of the total of ratios of the mean yield of next test interval to mean yield of last test interval, and the ratio between different parts of lactation.

Analysis of variance indicated significant (P<0.05) effects of breeding region, calving year, calving season, parity, service period and age on the persistensi and milk production traits. The persistensi was higher, but the peak and 2X305 day milk yields were lower in the first lactations. Cows that conceived shortly after calving had lower persistensi.

The heritability estimates of different measures ranged from 0.063 to 0.145. The measures including whole or the last third of lactation were more heritable. Genetic corelations indicated that a genetic change toward greater persistensi would result in a higher 2X305 day milk yield. Keywords : Cattle, Holstein, milk, persistensi