Estimation of environmental effects of test day milk yield in White Maritza sheep

Petya Zhelyazkova, Doytcho Dimov

Abstract: The objective of this research was to estimate environmental effects of test day milk yield (TDMY) in White Maritza sheep breed. Test day milk yields were collected from 1992 to 2015 (24 years) and milk yield recordings were made in 18 flocks. We evaluated 8768 milk yield records in the test day. In the structuring the database, the following environmental effects were defined: animal; flock; year season of lambing effect (YS); parity effect (Par); litter size at birth (LS); age of ewe at lambing (AgeL); age of ewe at test day (AgeTD); suckling period (Suck); ewe test day (ETD); flock test day (FTD); flock-year-test day (FYTD); stage of lactation period (DIM); stage of lactation period defined
at 3-day intervals (DIM3). Average TDMY was 764.47 mL. The test day milk yield was highest (1074.34 mL) in the first test day of ewes, and gradually decreased in the last test day (233.33 mL). All mentioned environmental effects had influenced TDMY with high degree of probability p<0.001). The largest proportion in the total phenotypic variation had FYTD (44.96 %). Factors thatsignificantly influenced all of the studied traits varied: Animal (34.51%), AgeTD (34.24%), DIM (31.22%), DIM3 (30.08%), ETD (25.28%) and AgeL (24.24%). Considering the significant influence of the described environmental effects on the test day milk yield in the population of White Maritza sheep breed, they should be taken into account when estimating the genetic parameters, designing breeding programs
and for defining the best evaluation model.

Keywords: environmental effects; test day milk yield; White Maritza sheep breed

Date published: 2023-04-28