Sources of variation of dairy production and milk composition in holstein cows, Jersey and Girolando

Abstract

The aim of this study was to quantify the effects of the genetic group, heat stress and somatic cell count (SCS) on the milk production and composition of Holstein, Jersey and Girolando genotypes cows in subtropical climates. Were used 14181 milk test-day records from a seven years period in a commercial farm. Cows were kept on pastures, with feed supplementation and shade access. Weather station data was used to determine the temperature and humidity index (THI). Year, lactation order, lactation period, THI and SCS as fixed covariate. The Holstein breed obtained higher productivity, except fat. In the Girolando breed, the production of milk and lactose did not differ from the Jersey breed, and the other parameters of production were lower than this breed. Concentrations of milk components were higher in Jersey milk, except for lactose content. The Holstein breed showed the lowest milk component contents except lactose. The increasing of SCS resulted in a decreasing of milk production, which totaled 26.3; 35.43 and 28.25% in the Girolando, Jersey and Holstein breeds, respectively. The increasing of THI had greater effects on the Holstein breed, in which the THI above 82 decreased 12.4% of fat concentration and 5.5% of total solids in milk. In conclusion, higher productivity was obtained with the Holstein and higher milk quality with the Jersey breed. SCS increasing above one unit decrease linearly milk yield in all breeds. Genotypes with a higher proportion of Holstein breed genes are more susceptible to heat stress effects.