Genetic and phenotypic parameters of milk yield, milk composition and age at first kidding in Saanen goats from Mexico

A total of 4007 lactation records from 1520 Saanen goats kidding from 1999 to 2006 and obtained from 10 herds in Guanajuato, Mexico, were analyzed to estimate the heritabilities, repeatabilities, as well as genetic, environmental and phenotypic correlations for milk yield (MILK), fat yield (FAT), protein yield (PROT), fat content (VAT), protein content (%PROT) and age at fist kidding (AFK). A five-trait repeatability model was used to estimate (co)variances for milk traits, and a four-trait animal model for first lactation records was used to estimate (co) variances involving AFK. For MILK, FAT, PROT, VAT, %PROT and AFK, heritability estimates were 0.17 +/- 0.04, 0.19 +/- 0.05, 0.17 +/- 0.04, 0.32 +/- 0.06. 0.38 +/- 0.07 and 0.31 +/- 0.09, respectively. Repeatabilities for MILK, FAT, PROT, VAT and %PROT were 0.43 +/- 0.02, 0.42 +/- 0.02, 0.42 +/- 0.02, 0.64 +/- 0.02, and 0.63 +/- 0.02. respectively. The genetic correlations between MILK and FAT, and between MILK and PROT, were high and positive (0.72 +/- 0.08 and 0.87 +/- 0.04, respectively). Genetic correlations between MILK and VAT, between MILK and %PROT and between MILK and AFK, were - 0.24 +/- 0.16, - 0.30 +/- 0.15 and - 0.18 +/- 0.23, respectively. Genetic correlations between AFK and FAT and between AFK and PROT were - 0.09 0.24 and - 0.17 +/- 0.25, respectively; and genetic correlations between AFK and %FAT and between AFK and %PROT were 0.29 +/- 0.35 and 0.14 +/- 0.27. respectively. Selection for milk traits is possible using a repeatability animal model. Selection for milk production traits would probably not increase AFK. but more precise estimates of the genetic correlations are required. Selection to lower AFK is possible. These (co)variance estimates would make it possible to predict the selection responses from different economic indices in order to maximize the economic responses for the local markets. (C) 2009 Elsevier B.V. All rights reserved.