Daylength Has Significant Impact on Summer Infertility

FRANCE - Seasonal infertility was impacted mostly by daylength (photoperiod), with high temperature being an exacerbating factor, according to a long-term field study soon to be published.
calendar icon 22 March 2010
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A group of researchers led by V. Auvigne have conducted a five-year field study to analyse the relative roles of heat stress and photoperiod in seasonal infertility in sows. Their paper is due to be published soon in the journal, Theriogenology.

The researchers explain that the objective of their study was to analyse the relative roles of high temperature and photoperiod as environmental factors of seasonal infertility in swine.

The results of five years (2003-2007) of ultrasound pregnancy diagnosis carried out in 266 indoor farms were analysed. For all farms, the data covered the entire study period. The farms were situated in four regions of France. The data of 22,773 batches and 610,117 sows were included.

Seasonal infertility was defined as the relative difference between the fertility rate in 'summer' (inseminations in weeks 25 to 42) and 'winter' (inseminations in weeks 1 to 18 of the same year).

In each region, two meteorological variables were defined, based on the data of a reference weather station: the number of hot days (maximum temperature >25 degrees C) and tropical days (maximum temperature >32 degrees C and minimum temperature >18 degrees C).

Mean fertility was 85 per cent. The median seasonal infertility was 2.8 per cent and more than 7.1 per cent for one-quarter of farms.

Seasonal infertility did not vary between areas and was not dependent on baseline fertility (defined for each studied farm as the average winter fertility over five years).

Seasonal infertility differed with the year (p<0.001). Seasonal infertility was significantly higher during 2003 than in the other four years, which did not differ from one another.

In the four regions, 2003 was the year with the highest number of hot days and 2007 with the least.

The study strengthens the hypothesis of a prominent role of photoperiod in seasonal infertility and of an additional role of heat stress the hottest years, conclude Auvigne and co-authors.


Auvigne V., P. Leneveu, C. Jehannin, O. Peltoniemi and E. Sallé. 2010. Seasonal infertility in sows: A five year field study to analyze the relative roles of heat stress and photoperiod. Theriogenology. 2010 Feb 26. [Epub ahead of print].

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