Variation in the interservice intervals of dairy cows in the United Kingdom

An understanding of the normal estrous-cycle length of the cow is important when managing and monitoring dairy-herd fertility. Although the normal interovulatory interval is widely considered to be 21d, some studies have found alternative intervals to be more prevalent; previously, most of the varia...

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Bibliographic Details
Published in:Journal of dairy science 2015-02, Vol.98 (2), p.889-897
Main Authors: Remnant, J.G., Green, M.J., Huxley, J.N., Hudson, C.D.
Format: Article
Language:English
Subjects:
Animals
Cattle - physiology
estrous cycle
Estrus - physiology
Female
Fertility - physiology
interovulatory interval
interservice interval
Lactation - physiology
Milk - metabolism
Parity - physiology
Pregnancy
Regression Analysis
Time Factors
United Kingdom
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Summary:An understanding of the normal estrous-cycle length of the cow is important when managing and monitoring dairy-herd fertility. Although the normal interovulatory interval is widely considered to be 21d, some studies have found alternative intervals to be more prevalent; previously, most of the variation in interval length was expected to be between cows. The aim of this study was to assess the time between inseminations (interservice interval, ISI) in a large number of dairy cows and to explore possible associations between cow factors and estrous-cycle length. The study used ISI data from 42,252 cows in 159 herds across England and Wales. Univariate analysis of the subset of 114,572 intervals between 15 and 30d (a range covering the increased frequency of ISI occurring at the expected time of the first return to estrus) following an insemination revealed a modal ISI of 22d. Primiparous heifers had a modal ISI of 21d. Significant differences existed between the distribution of ISI for different yield groups, parity numbers, and the number of inseminations. Multilevel regression modeling was used to evaluate the associations between cow factors and ISI, while accounting for clustering at the herd and cow level. This revealed significant associations between predicted ISI and insemination number, days in milk, lactation 305-d milk yield, and month and year of insemination. Variance partition coefficients indicated that only 1% of variation in ISI was at the herd level, 12% at the animal level, and 87% at the insemination level, indicating that cycle length varies substantially more between cycles within a cow than between cows or herds. These findings suggest the normal range of ISI for modern UK dairy cows is longer than expected and cycle length has a large amount of unexplained variation within individual animals over time.
ISSN:0022-0302
1525-3198
DOI:10.3168/jds.2014-8366