02135naa a2200217 a 450000100080000000500110000800800410001902200140006002400430007410000180011724501030013526000090023850000760024752014390032365300170176265300160177965300190179565300310181470000160184577300560186110128552019-10-03       2002    bl uuuu     u00u1 u    #d  a0022-03027 a10.3168/jds.S0022-0302(02)74396-82DOI1 aRAVAGNOLO, O.  aEffect of heat stress on nonreturn rate in holstein cowsbGenetic analyses.h[electronic resource]  c2002  aArticle history: Received August 13, 2001. / Accepted October 16, 2002.  aABSTRACT. The genetic component in heat tolerance for nonreturn rate in Holsteins was estimated using an animal linear model augmented by a random regression on a temperature-humidity index (THI). Data consisted of 18,059 nonreturn rates at 45, 60, and 90 d after insemination and 81,674 first-parity test-day milk yields from 78 herds in Florida. The THI on the day of insemination or test day was added to each record. Only first-insemination records were used. The model for nonreturn rate included the effects of herd-year-season, age, days in milk, milk yield, THI as a covariable, regular additive effect, and random regression on THI for heat-tolerance additive effect. With a single-trait model, heritability estimates for NR45, NR60, and NR90 at THI = 70 for first-lactation cows were 0.006, 0.014, and 0.053, respectively. Genetic correlation between regular NR90 and heat tolerance was -0.95. A bivariate analysis for NR90 and test-day milk production yielded a correlation between regular merit and heat tolerance for NR90 of -0.35, substantially lower than by the univariate model, indicating a bias in the univariate estimates caused by ignored selection. The regular genetic correlation between NR90 and milk yield was -0.41. Genetic correlation between heat tolerance for NR90 and heat tolerance for milk yield was -0.04, indicating the need to separate selection. © Copyright 2017 Elsevier B.V., All rights reserved.  aDairy cattle  aHeat stress  aNonreturn rate  aTemperature-humidity index1 aMISZTAL, I.  tJournal of Dairy Science, 2002, 85 (11): 3092-3100.