Phenotypic analysis of pregnancy effect on milk, fat, and protein yields of Canadian Ayrshire, Jersey, Brown Swiss, and Guernsey breeds
| Autor: | J. Bohmanova, Janusz Jamrozik, L.R. Schaeffer, Filippo Miglior, S. Loker |
|---|---|
| Rok vydání: | 2009 |
| Předmět: |
Canada
Veterinary medicine Time Factors media_common.quotation_subject Breeding Biology Models Biological Fats 03 medical and health sciences Animal science Pregnancy Lactation Genetics medicine Animals Dairy cattle 030304 developmental biology media_common 0303 health sciences 0402 animal and dairy science 04 agricultural and veterinary sciences Milk Proteins medicine.disease 040201 dairy & animal science Regression Milk Phenotype medicine.anatomical_structure Milk fat Gestation Cattle Female Animal Science and Zoology Reproduction Brown Swiss Food Science |
| Zdroj: | Journal of Dairy Science. 92:1300-1312 |
| ISSN: | 0022-0302 |
| DOI: | 10.3168/jds.2008-1425 |
| Popis: | Pregnancy has a negative impact on milk production in dairy cattle. Estimates of the effects of pregnancy are required in genetic evaluation models. Test-day records of Ayrshire, Jersey, Brown Swiss, and Guernsey breeds were analyzed phenotypically for the effect of pregnancy using 4 different models. Milk, fat, and protein yields were analyzed separately. The first model used a fourth-order Legendre polynomial regression on days in milk within classes of 10 d open. The second model fitted stage of pregnancy within days open classes to investigate the possible interaction between lactation stage and gestation stage. The third model included a fourth-order Legendre polynomial regression on days pregnant. In the fourth model, test-day records were divided into stage of pregnancy classes. Given that the effect of pregnancy was significant for all models, and that the adjusted R-squared values were consistent across the models, implying that the models for each trait fitted equally well within breeds, models were therefore compared based on the practicality of the results. Analysis of the first model indicated that milk production for cows withor =180 d open tended to have low yields in the last part of lactation. Cows with longer days open, however, had proportionally higher milk yield throughout lactation, suggesting a possible confounding effect of production level with days open effects. Results from the analysis involving the second model illustrated that there was no apparent interaction between lactation stage and gestation stage. Results from the third and fourth models showed that milk and fat yields began to decline after about 4 mo of pregnancy for all breeds, and protein yield began to decline after about 2 mo of pregnancy for all breeds. A lack of records during the final 60 d of pregnancy (the typical dry period) severely limited the third model, as pregnancy effects could not be estimated accurately. This problem was lessened, however, with the fourth (stage of pregnancy) model, because test-day records for cowsor =210 d pregnant were grouped together, allowing for a moderate number of test-day records in the final class of days pregnant. Because the stage of pregnancy model showed a decline in production that increased as gestation progressed, and because there was not a lack of test-day records at the end of pregnancy, the fourth model provided the most realistic estimate of the effect of pregnancy on milk production. Further investigation is needed into the incorporation of stage of pregnancy effects into genetic evaluations. |
| Databáze: | OpenAIRE |
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