Genetic relationships between reproduction and milk production in U.S. dairy goats
First lactation records on 3286 Alpine, Nubian, Saanen and Toggenburg does were used to examine genetic relationships between production and reproduction measures and to assess the consequences of correcting milk and fat production for age and season of kidding. Does were classified into two groups: 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. Age at kidding, date of kidding and breeding year (1st vs 2nd) seemed highly heritable. Breeding year was positively correlated genetically and phenotypically with unadjusted milk and fat yield, but correlations were close to zero after adjustment for age and season of kidding. Phenotypic correlations between date of kidding and both unadjusted and adjusted milk and fat yields were near zero, but genetic correlations between date of kidding and unadjusted yields were positive. For adjusted yields, genetic correlations with date of kidding were still positive but were smaller. Phenotypic correlations for age of kidding with unadjusted milk and fat yields were positive and with adjusted yields were near zero as expected. Genetic correlations for age at kidding with unadjusted yields were positive and with adjusted yields were negative but small. After adjustments for age and season of kidding, heritabilities of milk and fat yield were unchanged for Alpines, Saanens and Toggenburg but were increased slightly for Nubians. Selection on the basis of unadjusted milk or fat yield would lead to later ages and dates of kidding and fewer reproductive successes during the first breeding year, but selection on adjusted yields would result in little correlated change in reproductive performance
| Main Authors: | , , , , |
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| Format: | Texto biblioteca |
| Language: | eng |
| Published: |
Scottsdale, AZ (EUA)
1982
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