title: Seasonality of fertility measured by physical activity traits in Holstein cows.
abstract: Seasonality of female fertility traits, including the interval from calving to first high activity (CFHA), duration of high activity episode (DHA), and strength of high activity episode (SHA) of first estrus, were studied. The physical activity traits were derived from electronic activity tags for 20,794 Holstein cows in 135 commercial Holstein herds in Denmark. Data were categorized in 3 ways: (1) into 4 seasons of calving: winter (January-March), spring (April-June), summer (July-September), and fall (October-December); (2) into 2 seasons: a cold season (October-March) and a warm season (April-September); and (3) into an increasing light season (IL; January-June), where daylight hours gradually increased, and a decreasing light season (DL; July-December), where daylight hours gradually decreased. At the phenotypic level, least squares means of CFHA were highest at 55d for cows calving in December and lowest at 31d for cows calving in September. The highest least squares means of DHA and SHA were recorded for cows calving in November and lowest for cows calving in May and June. Genetic parameters for all traits were estimated using average information-REML in a bivariate animal model that treated the same trait in different calving seasons as different traits. Heritability estimates for CFHA were highest for the winter season (0.13) and low for the other seasons (0.03-0.04), whereas heritability estimates for DHA and SHA were lowest for winter and highest for fall. Heritability estimates for CFHA for the cold season (0.17) was higher than that for the warm season (0.10). Heritability estimates of CFHA for the IL season (0.12) was higher than for the DL season (0.07), but the opposite pattern was found for DHA and SHA. Genetic correlations (rA) of CFHA between winter and summer (rA=0.34 ± 0.27), and winter and fall (rA=0.65 ± 0.20) were significantly lower than unity. The corresponding correlations of DHA and SHA between seasons were all close to unity, except for the correlation of SHA between winter and fall (rA=0.36 ± 0.34). When the year was split into only 2 seasons, the genetic correlation of CFHA between cold and warm seasons was only moderate (rA=0.46 ± 0.15) but was slightly stronger between IL and DL seasons (rA=0.63 ± 0.16); both significantly deviated from unity. These results indicate the existence of a genotype by environment interaction for CFHA regardless of calving season classification.
authors.affiliation: Department of Molecular Biology and Genetics, Center for Quantitative Genetics and Genomics, Aarhus University, PO Box 50, DK-8830 Tjele, Denmark; Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences, PO Box 7023, SE-750 07 Uppsala, Sweden. Electronic address: ahmed.ismael@mbg.au.dk.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Ismael
authors.affiliation: Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences, PO Box 7023, SE-750 07 Uppsala, Sweden.
authors.forename: Erling
authors.initials: E
authors.lastname: Strandberg
authors.affiliation: Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences, PO Box 7023, SE-750 07 Uppsala, Sweden.
authors.forename: Britt
authors.initials: B
authors.lastname: Berglund
authors.affiliation: Knowledge Center for Agriculture, DK-8200 Aarhus N, Skejby, Denmark.
authors.forename: Anders
authors.initials: A
authors.lastname: Fogh
authors.affiliation: Department of Molecular Biology and Genetics, Center for Quantitative Genetics and Genomics, Aarhus University, PO Box 50, DK-8830 Tjele, Denmark.
authors.forename: Peter
authors.initials: P
authors.lastname: Løvendahl
mesh_terms: D000818:Animals; D002417:Cattle / Q000235:genetics / Q000502:physiology*; D003718:Denmark; D004777:Environment; D004971:Estrus / Q000235:genetics; D005260:Female; D005298:Fertility / Q000235:genetics*; D005838:Genotype; D009043:Motor Activity / Q000502:physiology*; D010641:Phenotype; D012621:Seasons
keywords: female fertility; genotype by environment interaction; physical activity; seasonality