02375naa a2200277 a 450000100080000000500110000800800410001902200140006002400310007410000190010524501290012426000090025350000760026252015200033865000140185865000260187265300240189865300160192265300130193865300150195170000160196670000160198270000160199870000150201477300680202910128282019-06-18       2009    bl uuuu     u00u1 u    #d  a0022-03027 a10.3168/jds.2008-16262DOI1 aSÁNCHEZ, J.P.  aGenetic determination of the onset of heat stress on daily milk production in the US Holstein cattle.h[electronic resource]  c2009  aArticle history:  Received August 12, 2008. // Accepted March 18, 2009.  aABSTRACT. Existence of individual variation in the onset of heat stress for daily milk yield of dairy cows was assessed. Data included 353,376 test-day records of 38,383 first-parity Holsteins from a random sample of US herds. Three hierarchical models were investigated. Model 1 inferred the value of a temperature-humidity index (THI) at which mean yield began to decline as well as the extent of that decline. Model 2 assumed individual variation in yield decline beyond a common THI threshold. Model 3 additionally assumed individual variation for the onset of heat stress. Deviance information criteria indicated the superiority of model 3 over model 2. For model 2, genetic correlation between milk yield in the absence of heat stress and the THI threshold for heat stress was -0.4 (0.11) [marginal posterior mean (marginal posterior standard deviation)]. For model 3, genetic correlations were -0.53 (0.05) between milk yield and THI threshold and -0.62 (0.08) between milk yield and yield decay beyond the THI threshold. Total standard deviation (sum of additive genetic and permanent envi-ronmental standard deviations) for the THI threshold was 3.95 (0.06), and more than half of that variation had an additive genetic origin [56% (5%)]. Because of the high genetic correlation [0.95 (0.03)] between yield decay and THI threshold with model 3, using only one of them as a selection criterion for heat tolerance would modify the other in the desired direction.  © american Dairy Science association, 2009.  aLECHERÍA  aVARIABILIDAD GENETICA  aGENETIC VARIABILITY  aHEAT STRESS  aHOLSTEIN  aMILK YIELD1 aMISZTAL, I.1 aAGUILAR, I.1 aZUMBACH, B.1 aREKAYA, R.  tJournal of Dairy Science, 2009, 92 (8): 4035-4045. OPEN ACCESS.