Phenotypic and genetic relationships between reproduction and milk production in dairy goats.

First lactations of 3286 Alpine, Nubian, Saanen, and Toggenburg does were used to assess consequences of correcting milk and fat yields for age and season of kidding and to estimate heritabilities and phenotypic and genetic relationships between milk production and reproductive traits. Does were classified into those that reproduced successfully during their first breeding year and those that did not and were held over to the following year before reproducing successfully. Heritabilities of milk and fat yield and fat percent adjusted for age-season were .68, .61, and .54 for Alpines, Saanens, and Toggenburgs and .35, .54, and 1.09 for Nubians. Phenotypic and genetic correlations between date of kidding and unadjusted milk and fat yield were negative but were close to zero for adjusted yields. Phenotypic correlations for age of kidding with unadjusted milk and fat yields were positive and with adjusted yields were near zero. Genetic correlations for age at kidding with unadjusted yields were positive but with adjusted yields were negative but small. Selection on unadjusted milk yield of first lactation would lead to fewer reproductive successes during the first breeding year and later ages at kidding, but selection on adjusted yields would result in little correlated change in reproductive performance.