International genetic evaluations for feed intake in dairy cattle
Feed represents a large proportion of the variable costs in dairy production systems. The omission of feed intake measures explicitly from national dairy cow breeding objectives is predominantly due to a lack of information on which to make selection decisions. Individual cow feed intake data are available in different countries, mostly from research or nucleus herds. None of these datasets are sufficiently large enough on their own to generate accurate genetic evaluations. Here we collate data from ten populations in nine countries. A total of 224,174 test-day records from parity one to five animals, as well as 1,784 records from growing heifers were available. Random regression models fitted to lactating cow test-day records were used to predict feed intake at 70 days post calving. Heritability estimates of predicted cow feed intake 70-days post-calving was 0.34 across the entire dataset and varied, within population, from 0.08 to 0.52. Repeatability of feed intake across lactations was 0.66. Heritability of feed intake in growing heifers was 0.20 to 0.34. The genetic correlation between feed intake in lactating cows and heifers was 0.67. A combined pedigree and genomic relationship matrix was used to improve linkages between populations for the estimation of genetic correlations between countries categorized as North America, Grazing, Other low input, and High input EU. Genetic correlation estimates between populations varied from 0.14 to 0.84 but was stronger (0.76 to 0.84) between the populations representative of high input production systems.
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