Resumen

PEREZ QUINTERO, Gilberto  y  GOMEZ GIL, Manuel. Genetic and environmental factors affecting productive performance in a brown swiss herd in the tropic: 2. Relationship between calving interval and milk yield. Rev. Cient. (Maracaibo) [online]. 2009, vol.19, n.1, pp.77-83. ISSN 0798-2259.

In order to evaluate genetic and environmental effects on calving interval (CI) and its relationship with 305-day milk yield (305L) in a Brown Swiss herd, data of 1343 calving intervals and 1890 lactations from 589 cows-years were collected on an intensive handling ranch located in Carabobo State (Venezuela) between 1995 and 2001. Mixed models and maximum likelihood (ML) analyses were carried out to evaluate environmental fixed effects. Models included: calving year (CY: 1995,…, 2001), calving month (CM: Ene.,…, Dic.), lactation number (LN: 1,…,7 or more) and age of dam at calving (DCA: 22,…,156). Univariate and bivariate animal models and Multiple Trait Derivate - Free Restricted Maximum Likelihood (DFREML) were used to estimate heritability (h²), to calculate repeteability (r_i) and to estimate correlations between CI and 305L. CY, CM, LN and DCA were important sources of variation (P<0.05). Adjusted mean was 418.7 ± 2.6 days. Estimates of h² (± standard error) and r_i were 0.05 ± 0.044 and 0.10, respectively. Estimates of genetic, environmental and phenotypic correlations between CI and 305L were 0.69, 0.004 and 0.09, respectively. These estimates indicate a positive association between both variables. Thus, the increase in the capacity of milk production of the cows will result in less reproductive efficiency.

Palabras clave : Calving interval; Brown Swiss; genetic parameters.