Knowledge of milk traits in Slovak dairy sheep: a review

Abstract

The objective of this review is to summarize the knowledge of milk traits, lactation curves and genetic evaluation of dairy sheep in Slovakia. Thus, an emphasis was given on milk yield (daily and milking period yield), fat content and protein content. The special attention was drawn to modelling of lactation curves for these traits using the Ali and Schaeffer regression model. The following breeds: Tsigai, Improved Valachian i.e. breeds of local provenience providing low milk yields, and Lacaune (a specialized dairy breed providing high milk yield), were involved in the analyses. Various sources of information: test day records with daily milk yield, milking period yield, fat content and protein content incorporated in single-trait models and multitrait models were reviewed. Accordingly, the experience with estimations of genetic parameters and proportions of variance components for milk traits was covered. Approaches based on alternative strategies treating milk yield (fat and protein content) in individual months of lactation either as the same trait or as a different trait were documented (Tsigai chosen as a model breed). The review attempts to summarize the recent experience with description of milk traits (lactation curves and genetic evaluation) in dairy sheep in Slovakia.