Meteorological effects on seasonal infertility in pigs

The presence of seasonal infertility has long been recognised, but its causes are much debated within the farming and scientific communities. Almost half of the UK breeding herd is kept outdoors and is therefore more likely to be susceptible to seasonal infertility.
Most research on the matter has been conducted on indoor sows, and so the aim of this thesis was to describe the effects of meteorological conditions on reproductive function in both outdoor sows and commercial boars. The data confirm that both sows and boars
suffer from seasonal reductions in reproductive output.

Reduced farrowing rates were the major manifestation of seasonality in sows. High temperatures and long days were associated with poor performance. A simulation model of
seasonal infertility was developed; with further re�nement this could potentially provide a tool for farmers, allowing them to make managerial adjustments to compensate for
low productivity in select months.

Seasonal effects on litter size were less apparent when assessed at herd level. However individual sows were found to be more or less susceptible to reductions from summer
services, suggesting a genetic predisposition to seasonal infertility.

Sow skin temperatures and respiration rates increased with external temperature humidity indices; these increases occurred at a lower threshold following cold conditions.
Together with observed thermoregulatory behaviour it appears that UK sows become acclimatised to cold weather and are therefore more susceptible to heat stress when it
becomes warmer.

Boar semen quality was reduced over the summer and early autumn months, with a higher proportion of abnormalities and lower sperm concentrations. However individual
boar and management parameters had a larger effect on semen quality than meteorological conditions.

More research into outdoor production systems is required and further links between boar and sow fertility should be made. Producers need to be aware that outdoor sows
may behave differently from those on indoor units.