Factores genéticos y ambientales que afectan la preñez de vacas Brahman de primer servicio y primera lactancia
With the objective to determine the effects influencing the variation of the binary trait pregnancy of two year old first service and three year old lactating Brahman cows, the data base of the Genetic Section of the Veterinary Faculty of the Central University of Venezuela (UCV) was used. The data...
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| Published: |
2013
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| Online Access: | http://hdl.handle.net/10872/3271 |
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| Summary: | With the objective to determine the effects influencing the variation of the binary trait pregnancy of two year old first service and three year old lactating Brahman cows, the data base of the Genetic Section of the Veterinary Faculty of the Central University of Venezuela (UCV) was used. The data had been collected during 40 years within different research programs on private farms or experiment stations, which were in every case designed and executed by scientific personnel and supervised at the farm level by veterinarians and practical personnel. This study included the material of eight herds, six belonging to a genetic cooperative of Brahman cows, one is a university experiment station herd and the other a herd of a private cattle company which cooperated with the research group for many years. All herds had a limited breeding season between 3 to 4 months and there were basic management, sanitary and mineral-nutrition programs. The original base consisted of 12891 data. After eliminating 6266 data because of missing paternity or missing breeding bull identification, 6625 data were available for first service cows (heifers) and 3414 for first lactating cows in their second breeding season. When editing the data, pregnancy was coded to be success (100) or failure (0). After performing several preliminary analysis using the SAS statistical package the final models were constructed with the mixed models methodology using an animal model with the MTDFREML program. Fixed effects of the analysis of first service cows, were: herd (HE), birth year within herd BY(herd), birth month within herd BM(herd), the linear covariate of weight before the breeding season (24W) and the random effects of sire (S) and service bull (B). For first service cows the animal model included a fixed effects variable (HE-BY-BM). For the first lactating cows fixed effects on pregnancy were HE, BY(herd), lactation stage within herd LS(herd), sex of calf (SX) and the linear covariates 24 months weight and 205 day weaning weight and random effects of (S) and (B). Almost all included effects on pregnancy were highly significant . Mean non adjusted and adjusted pregnancy rates were 79.5 and 80.2 for first service cows and 42.4 and 39.2 for first lactation cows, respectively. Heritabilities for pregnancy of first service cows and first lactating cows were 0.08 ±0.02 and 0.06 ± 0.03, respectively. Genetic variances were for first service cows and first lactating cows 141.4 and 126.3, respectively. Genetic values of extreme bulls were 42 percentage points for the trait pregnancy of two year old first service and 29 percentage points for the trait pregnancy of three year old lactating Brahman cows. Although the variation among bulls for annual selection would be considerably less, there is a detectible genetic difference between bulls who transmit high and those who transmit low genetic potential for pregnancy rate, which should be considered in the selection program. |
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