Resumo

MENENDEZ-BUXADERA, Alberto  e  VERDE, Omar. (Co)variance components for milk production in a venezuelan buffalo herd analyzed by total lactation and test day models. Zootecnia Trop. [online]. 2014, vol.32, n.1, pp.65-75. ISSN 0798-7269.

Milk production was evaluated at 244 (L244) and 305 days (L305) for 9.814 births that occurred between 1991 and 2012 of 2.680 females in a buffaloes herd located in Apure, Venezuela, generated from daily (lt) production of 84.009 monthly records. Two procedures allowed to estimate the components of genetic (co)variance: one called total lactation (LT) for L244 and L305 and a random regression model known as Test Day (TD) on lt. L244 and L305 increased 750 kgs and 860 kgs respectively while lt increased 2 kgs/day. Number of calving exerted significant effect on the three traits. The highest daily production levels occur during the first 11 weeks. The LT model produced heritability (h2) of 0.29±0,08 and 0.26±0,06 for L244 and L305 respectively, while the genetic correlation (rg) for both traits was 0.95±0,16. The TD model results indicate that the (co)variance components and the h2 increase until week 15, with correlations higher than 0.9 in adjacent weeks. Principal component analysis for lt in different weeks of lactations showed that 89 and 9% of genetic variance is explained by the first and second vector, indicating the possibility of increasing lt and produce changes in the shape of the curve. Breeding values of animals for L244 estimated by models TD and LT manifest a significant variation and are highly correlated (r=0,869). It is concluded that TD models are highly recommended in this specie improvement programs.

Palavras-chave : dairy buffaloes; genetic parameters; comparison of models.

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