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Multi-trait, multi-breed conception rate evaluations
Heifer and cow conception rates (HCR and CCR) were evaluated with multi-trait, multi-breed models including crossbred cows instead of the previous single-trait, single-breed models. Fertility traits benefit from multi-trait processing because of high genetic correlations and many missing observations, with 4 million HCR and 14 million CCR lactation records stored since 2003 vs. 66 million daughter pregnancy rate (DPR) records since 1960. Conception rates were previously modeled using multiple binary success records per parity (such as no, no, yes) that are now pre-adjusted for environmental effects and combined into lactation records for simpler multi-trait analysis with the continuous trait DPR. Genetic correlation estimates were 0.45 for HCR with CCR, 0.86 for CCR with DPR, and 0.36 for HCR with DPR. Inbreeding depression per 1% inbreeding was -0.21 for HCR, -0.10 for CCR, and -0.13 for DPR. Heterosis was 1.3 for HCR, 3.2 for CCR, and 1.4 for DPR. Crossbred cows get the combined effects of heterosis and no inbreeding compared to purebreds that may average 6%. Genetic differences among breeds were fairly consistent with phenotypic differences. Holsteins had the highest phenotypic and genetic averages for HCR, while Jerseys were highest for CCR. Evaluations from the new and previous models were correlated by >0.95 for both HCR and CCR for recent Holstein bulls with >50% reliability, but were less correlated in other breeds because of additional crossbred daughters and contemporaries. For Holstein sires with > 90% reliability, correlations between single-breed and multi-breed evaluations were 0.986 for HCR and 0.992 for CCR, indicating little change in rank when adding the other breeds. Genetic trend for CCR was more negative with multi-trait processing because of the correlation with DPR. Genetic trends were validated using Interbull tests 1 and 3. The genetic correlations with other countries estimated by Interbull changed little for Holsteins, averaging 0.02 higher for HCR and 0.02 lower for CCR, but were more variable for other breeds. The new model implemented in December 2013 combines data from all breeds and uses DPR as a correlated trait to improve HCR and CCR evaluations.
Keywords: conception evaluation multi-trait