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ARTICLE |
1 Facultad de Agronomía, Universidad de la República, 12900 Montevideo, Uruguay
2 Department of Animal and Dairy Science, University of Georgia, Athens 30602-2771
* To whom correspondence should be addressed. E-mail: jurioste{at}fagro.edu.uy.
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Abstract |
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Calving records (n = 6,763) obtained from first, second, and third parities of 3,442 spring-calving Uruguayan Aberdeen Angus cows were used to estimate heritabilities and genetic correlations for the linear trait calving day (CD) and the binary trait calving success (CS), using models that considered CD and CS at 3 different calving opportunities as separate traits. Three approaches were defined to handle CD observations on animals that failed to calve: i) cows were assigned a penalty value of 21 d beyond the last observed CD record within contemporary group (PEN); ii) censored CD values were randomly obtained from a truncated normal distribution (CEN); and iii) CD records were treated as missing, and parameters estimated in a joint threshold- linear analysis including CS traits (TLMISS). The models included the effects of contemporary group (herd x year of calving x mating management), age at calving (3 levels), physiological status at mating (non-lactating or lactating), animal additive genetic effects, and residual. Estimates of heritability for CD traits in the PEN and CEN data sets ranged from 0.20 to 0.31, with higher values in the first calving opportunity. Genetic correlations were positive and medium to high in magnitude, 0.57 to 0.59 in the PEN data set and 0.38 to 0.91 in the CEN data set. In the TLMISS data set, heritabilities ranged from 0.19 to 0.23 for CD and 0.37 to 0.42 for CS. Genetic correlations between CD traits varied between 0.82 and 0.88; between CS traits, genetic correlations varied between 0.56 and 0.80. Negative (genetically favorable) medium to high genetic correlations (-0.54 to -0.91) were estimated between CD and CS traits, suggesting that CD could be used as an indicator trait for CS. Data recording must improve in quality for practical applications in genetic evaluation for fertility traits.
Key Words: beef cattle, calving day, calving success, censored records, genetic parameters, threshold-linear models
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