Animal factors affecting fatty acid composition of cow milk fat: A review
The review summarizes literature dealing with the effects of animal factors (breed, cow individuality, parity and stage of lactation) on fatty acid (FA) composition of milk fat. Genetic parameters affecting the composition of the FAs in milk are reviewed and the possibilities for altering milk fat composition are discussed. Cow individuality and the stage of lactation appear to be the main animal factors affecting milk fat composition. Breed and parity affect the variability in FA composition to a limited extent. Some of these factors can be used effectively to alter milk fat composition. Polymorphism of the enzymes, stearoyl-CoA desaturase (SCD) and acyl-CoA-diacylglycerol acyltransferase (DGAT) can explain to some extent the variability among cows. The great individual differences, probably given by varying SCD activities, may be used in breeding programmes, supported by the heritability estimates determined for individual FAs. Effective results can also be achieved through the combined effect of several factors. For instance, the level of conjugated linoleic acid could be increased not only by feed factors, but also through thorough knowledge of rumen biohydrogenation or by cow selection using information on SCD and DGAT polymorphism. The animal factors that are discussed are closely related to milk yield, particularly fat content. Both parameters can change FA composition. Thus, it is necessary in breeding programmes to take these relationships into consideration, along with known genetic correlations.
Keywords: Breed, genetic correlations, heritability, milk and fat yield, parity, single nucleotide polymorphism, stage of lactation