title: Effect of pregnancy on the genetic evaluation of dairy cattle.
abstract: We  investigated the effect of stage of pregnancy on estimates of breeding values  for milk yield and milk persistency in Gyr and Holstein dairy cattle in Brazil.  Test-day milk yield records were analyzed using random regression models with  or without the effect of pregnancy. Models were compared using residual  variances, heritabilities, rank correlations of estimated breeding values of  bulls and cows, and number of nonpregnant cows in the top 200 for milk yield  and milk persistency. The estimates of residual variance and heritabilities obtained  with the models with or without the effect of pregnancy were similar for the  two breeds. Inclusion of the effect of pregnancy in genetic evaluation models  for these populations did not affect the ranking of cows and sires based on  their predicted breeding values for 305-day cumulative milk yield. In contrast,  when we examined persistency of milk yield, lack of adjustment for the effect  of pregnancy overestimated breeding values of nonpregnant cows and cows with a  long days open period and underestimated breeding values of cows with a short  days open period. We recommend that models include the effect of days of  pregnancy for estimation of adjustment factors for the effect of pregnancy in  genetic evaluations of Dairy Gyr and Holstein cattle.
authors.affiliation: Departamento de Zootecnia, Faculdade de Ciências Agrárias e Veterinárias, Universidade Estadual Paulista Julio de Mesquita Filho, Jaboticabal, SP, Brasil. rodjunper@yahoo.com.br
authors.forename: R J
authors.initials: RJ
authors.lastname: Pereira
authors.forename: M L
authors.initials: ML
authors.lastname: Santana
authors.forename: A B
authors.initials: AB
authors.lastname: Bignardi
authors.forename: R S
authors.initials: RS
authors.lastname: Verneque
authors.forename: L
authors.initials: L
authors.lastname: El Faro
authors.forename: L G
authors.initials: LG
authors.lastname: Albuquerque
mesh_terms: D000818:Animals; D001947:Breeding / Q000379:methods*; D002417:Cattle / Q000235:genetics / Q000502:physiology*; D005260:Female; D007774:Lactation / Q000235:genetics*; D058751:Livestock; D008892:Milk / Q000378:metabolism*; D008894:Milk Proteins / Q000235:genetics; D011247:Pregnancy; D011270:Pregnancy, Animal; D013997:Time Factors
chemical_list: D008894:Milk Proteins