An analysis of the effect of nmnth of calving on length of subsequent calving interval was conducted, using 2,514 records for a 10-yr period from six Holstein herds of the North Carolina Institutional Breeding Program. The average calving interval ranged from 397 to 422 days for calvings in October to May, respectively. Differences in this interval were highly significant (P (0.01) for both among months in the same year and herd, and among herds, but not different among years for each herd. Monthly fluctuations in calving interval and air temperatures prevailing during 60 to 120 days post-partum were significantly correlated on a within-herd basis (0.30).
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Poston et al. (1962) studied this question.
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