Covariance components by a repeatability model in Slovenian dairy sheep using test-day records

Abstract

ABSTRACT:The estimation of covariance components for daily milk yield, fat and protein content was performed in three Slovenian dairy sheep breeds (Bovec, Improved Bovec, and Istrian Pramenka). In the period 1994-2002, 38 983 test-day records of 3 068 ewes were collected according to ICAR regulations (method A4). All the available relationships between animals were considered. For that reason, information on 3 534 animals was included. Test-day records were analysed by a multiple-trait repeatability animal model. In its fixed part, the model contained breed and season of lambing as classes. Days after lambing, parity, and litter size were treated as covariates. Days after lambing were modelled with modified Ali-Schaeffer's lactation curve, parity with quadratic, and litter size with linear regression. The random part of the model consisted of flock-test month effect, additive genetic effect, permanent environment effect over lactations, and permanent environment effect within lactation. Covariance components were estimated using the restricted maximum likelihood method (REML). The estimated heritabilities were 0.11 for daily milk yield, 0.08 for fat content, and 0.10 for protein content. A relatively high variance ratio for all milk traits was explained by the flock-test month effect (from 0.27 for daily milk yield to 0.57 for protein content), while ratios explained by both permanent environment effects were lower (up to 0.13). Additive genetic correlations between daily milk yield and fat content, and daily milk yield and protein content were negative and similar (-0.36 and -0.37). A high and positive (0.67) additive genetic correlation between fat and protein content was found. Correlations for environmental effects showed a pattern similar to additive genetic correlations. Genetic parameters estimated in Slovenian dairy sheep showed that genetic progress in milk traits could be achieved using test-day milk records.

Genetic and environmental dispersion parameter estimationby test interval method in dairy sheep

“…Genetic evaluations of milk traits in dairy sheep are nowadays mainly performed by application of testday records (El-Saied et al, 1998a, Serrano et al, 2001, Oravcova et al, 2005, Komprej et al, 2009. Some advantages were found in such modelling of records (Ptak andSchaeffer, 1993, Serrano et al, 2001) in comparison to lactation yields (El-Saied et al, 1998a, El-Saied et al, 1998b, Portolano et al, 2001.…”

Recent developments in cattle, pig, sheep and horse breeding - a review

“…Heritabilities for dairy traits on a total lactation basis are low to moderate for milk, fat, and protein yields (Komprej et al 2009;Bauer et al 2012;Dimov 2013) and high for fat and protein percentages (Pelmus et al 2014). Duchemin et al (2012) showed that utilization of molecular markers can improve current selection methods.…”

Estimation of genetic parameters and evaluation of test-day milk production in sheep

“…Relationships between the milk production and the fecundity traits (litter size, number of weaned lambs) should be further analyzed by including a multi-trait approach. The milk-component effects could be used to optimize BV for milk product yield, as the dry matter content and the milk yield are negatively correlated (Othmane et al, 2002;Komprej et al, 2009), and product yield depends on both the parameters. When more records are available and the data have better connectedness, which can be facilitated by broader production recording, the random regression of days-in-milk should be tested as well.…”