The objective was to estimate genetic correlations for persistency, milk yield and somatic cell score (SCS) in Holstein cattle in Brazil. A dataset with 190389 records of test-day milk and of test-day SCS from 21824 cows was used. Two-trait random regression model with a fourth order Legendre polynomial was used. Persistency (PS) was defined as the difference between estimated breeding values (EBV) along different days in milk using two formulae: and PS2=(EBV290–EBV90). Larger values for PS2 or lower ones for PS1 indicate higher persistency. Heritability was 0.24 for 305-day milk yield, 0.14 for SCS up to 305 days, 0.15 for PS1 and 0.14 for PS2. Genetic correlation between 305-day milk yield and SCS up to 305 days was –0.47. Genetic correlation of 305-day milk yield with PS1 and PS2 was –0.32 and 0.30, respectively. Genetic correlation of SCS up to 305 days was 0.25 with PS1 and –0.20 with PS2. The additive genetic correlations between milk yield, SCS and persistency showed that selection for higher persistency or for low somatic cell score will increase 305-day milk yield.

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Existem diversas opções de genética de ovinos para os sistemas de produção, desde recursos genéticos locais (geralmente adaptados as condições ambientais) até raças especializadas. O cruzamento é uma alternativa para explorar a heterose e complementariedade entre as raças. Este estudo avaliou oito grupos genéticos obtidos a partir do cruzamento entre Santa Inês (SI), Poll Dorset (PD), Dorper (DO), East Friesian (EF), Primera (PR), and White Dorper (WD). SI e PD foram usados com raças paternas e maternas, enquanto as demais foram usadas apenas como raças paternas. Quarenta e oito cordeiros foram avaliados para altura da cernelha, perímetro torácico, comprimento do corpo e da garupa e espessura da pele, bem como peso de carcaça fria e peso dos cortes comerciais como pescoço, fralda, paleta, pernil, costela e lombo. Os animais Santa Inês demoraram mais tempo para atingir o peso de abate (30 kg) que as cruzas com Dorper e Poll Dorset. Os animais 87PDSI, 75PDSI e DOPD apresentaram maior peso dos cortes comerciais e maior rendimento de carcaça. O uso da raça Santa Inês, uma raça localmente adaptada, como raça maternal em sistema de cruzamento apresentou resultados similares ao uso de Poll Dorset, uma raça especializada para produção de carne. Esses resultados destacam a utilidade dos recursos genéticos locais em sistema de produção intensivo. Poll Dorset é a raça paterna recomendada para o cruzamento com matrizes Santa Inês em sistema de produção intensivo.

The objective of this study was to estimate genetic parameters and genetic trends of different conformation and management traits regularly measured within the context of the National Dairy Gir Breeding Program (PNMGL). The estimation of genetic and residual variances for each trait was performed using average information restricted maximum likelihood (AI-REML) procedure in AIREMLF90 program software. The population was divided into three subpopulations constituted by measured females (with phenotype records), all females, and males. Linear regressions were applied for each trait, considering two periods of birth (1st period: 1938-1996; 2nd period: 1997-2012). The estimated heritability of conformation and management traits varied from 0.01 to 0.53, denoting a perspective of genetic improvement through selection and corrective matings for purebred Dairy Gir populations. The average genetic changes in conformation and management traits were, in general, variable and inexpressive, showing that the selection of Dairy Gir may have had been directed essentially to increase milk yield. The analysis of the two periods of birth indicated that some linear traits present progress (although inexpressive) in the 2nd period (more recent period).