Genotype by environment interaction for female fertility traits under conventional and organic production systems in Danish Holsteins

摘要

Conventional and organic production systems mainlydiffer in feeding strategies, outdoor and pasture access,and the use of antibiotic treatments. These environmentaldifferences could lead to a genotype by environmentinteraction (G × E) and a requirement for including G× E in breeding decisions. The objectives of this studywere to estimate variance components and heritabilitiesfor conventional and organic production systems andinvestigate G × E under these 2 production systemsfor female fertility traits in Danish Holsteins. Theanalyzed traits included the interval from calving tofirst insemination (ICF), the interval from first to lastinsemination, number of inseminations per conception(NINS), and non-return rate within 56 d after the firstinsemination. Records of female fertility in heifers andthe first 3 lactations in cows as well as grass ratio offeed at herd level were collected during the period from2011 to 2016. The performances of a trait in heifersand cows (lactation 1 to 3) were considered as differenttraits. The (co)variance components and the resultingheritabilities and genetic correlations were estimatedusing 2 models. One was a bivariate model treatingperformances of a trait under organic and conventionalproduction systems as 2 different traits using a reduceddata set, and the other was a reaction norm model withrandom regression on the production system and thegrass ratio of feed using a full data set. The full data setcomprised records of 37,836 females from 112 organicherds and 513,599 females from 1,224 conventionalherds, whereas the reduced data set comprised recordsfrom all these 112 organic herds and 92,696 femalesfrom 185 convention herds extracted from the full dataset with grass ratio of feed lower than 0.20. All femalefertility performances of the organic production systemwere superior to those of the conventional productionsystem. Besides, heterogeneities in additive geneticvariances and heritabilities were observed betweenconventional and organic production systems for alltraits. Furthermore, genetic correlations between these2 production systems ranged from 0.607 to 1.000 estimatedfrom bivariate models and from 0.848 to 0.999estimated from reaction norm models. Statisticallysignificant G × E were observed for NINS in heifers,non-return rate within 56 d after the first inseminationin heifers, and ICF from the bivariate model, and forICF and NINS in cows from the reaction norm model.