COMPARISON OF THE HEIFER REPRODUCTION TRAITS OF THE DAUGHTERS OF SEVERAL SIRE GROUPS

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Abstract
Ages at first heat and first conception, age and weight at first calving, number of services per conception, and incidence of difficult calving and retained placenta were obtained from 853 heifers of the National Cooperative Dairy Cattle Breeding project of the Research Branch of Agriculture Canada. Among these, 483 heifers were from Agriculture Canada Research Branch Holstein cows and by Research Branch, Canadian and U.S. Holstein sires (H line). The other heifers were from Research Branch Ayrshire cows and by Research Branch, Canadian, U.S. and Finnish Ayrshire as well as Brown Swiss and Norwegian Red sires (A line). The data were analyzed by least squares analysis of variance using a model containing fixed effects of station, year of birth, season of birth, line, sire groups within line, and sires within sire group within line. The effects of station and line were significant for most of the heifer reproduction traits studied while the effect of year of birth was only significant for age at first conception and weight at first calving. H line heifers on the average showed first heat 27 days earlier, were 11 days younger at first conception, were 13 days younger at first calving, were 33 kg heavier at first calving, had 30% more difficult calving and 9% fewer retained placenta than the A line heifers. Differences among the sire groups within the H line were small and nonsignificant while within the A line they were significant for age at first heat and weight at first calving. Key words: Heifer reproduction traits, dairy cattle