Evaluation of milk yield traits of Holstein x Jersey crosses / Avaliação de características produtivas e de qualidade do leite em vacas do cruzamento Holandês x Jersey

ABSTRACT

The crossbreeding practice between specialized dairy breeds is an usual method for dairy producers and recently the Holstein x Jersey crosses has continuously increased in some regions of Brazil. Motivating factors of this practice include an interest in improving the milk solids content, somatic cell count (SCC), fertility, longevity and calving ease, in addition to reduce the problems of consanguinity. The aim of this paper was to evaluate the milk components and milk yield of Holstein x Jersey crosses. Data set comprised 59,331 monthly records of 6,429 pure Holstein (H) and Jersey (J) and ½ H x ½ J crossed cows calving from 1992 to 2010. The traits analyzed were test-day milk yields (MT), somatic cell score (SCS) and percentages of fat (%F) and protein (%P). Since the SCC is not normal distributed it was converted to a logarithmic scale in SCS, using the following equation, SCS = log2 (SCC/100) + 3. The variables MT, SCS, %F and %P were analyzed as dependent variables by least square method using GLM procedure. There were considered linear models containing the effects of breed (H, J and ½ H x ½ J or F1), herd, year and month of test as classificatory variables. Age at calving (AC) and days in milk (DM) were included as covariates (linear and quadratic effects) for all traits. The test-day milk yield was included as covariate for SCS model, %F and %P. All variables included

RESUMO

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