Managing your Wean to Service Interval by Jemma Stephenson, Pig Nutritionist

7th June 2019

We are heading into the summer months, which means BBQ's, harvest, longer and brighter days and hopefully better pig prices. While the summer offers many opportunities it also brings some challenges, not least of which is reproductive performance.

When looking at the reproductive efficiency on a farm, one of the best indicators is non-productive days (NPD), the period when the sow is neither lactating or pregnant. Non-productive days have a significant effect on the biological and financial performance of a herd. One of the biggest contributors to NPD is the Weaning to Service Interval (WSI). Gilts and young sows, especially those rearing large litters are more susceptible to reduced appetite and loss of body condition during lactation and therefore increased WSI. The effect on WSI on subsequent reproductive performance is very pronounced, as demonstrated in the table below.

Farrowing Rate

Total Born

Wean to Service Interval - 4 days



Wean to Service Interval - 5 days



Figure 1 - Performance after service depending on the WSI. Aparicio et al, 2019

When trying to ensure a short WSI some of the factors that merit consideration include: season, lighting, temperature and body condition. The impact of season on fertility and prolificacy is well documented. During the summer months it is easy to forget the importance of lighting in our service and dry sow yards. Light is important to maintaining a normal WSI. The sow registers the reducing autumn daylight hours, increasing the production of the hormone, melatonin. Melatonin reduces fertility by preventing oestrus (heat) occurring (Teasasc, 2018). Light can be provided naturally and/or artificially. Good building design can often make great use of natural light through transparent areas in roofs and walls. Transparent areas of 15% are usually sufficient to give an adequate amount of natural light, as long as they are well maintained and kept clean. Buildings with large sources of natural light need to be well ventilated to counteract the increased heat build-up from solar gain through windows etc. A minimum of 16hours of light and 300lux should be maintained in the service, gilt, dry sow yard and farrowing rooms. Figure 2, demonstrates the benefit in additional light in the service area on reduced WSI during the autumn and winter.

Wean to Service Interval















Additional lighting installed






Figure 2 - Impacts of increasing service area light. Diaz et al, 2018

AHDB noted that the hot summer in 2018 saw a reduction in litters/sow/year, from 2.3 to 2.18. The sow struggles with high temperatures and can cause her thermal stress, which can lead to a reduction in hormonal activity that (a) triggers the onset of oestrus and (b) sustains embryo maturation. Not only does high temperatures cause a prolonged WSI but also a reduced farrowing rate, increased returns and compromises subsequent litter size. Ensuring ventilation is working during the summer months and keeping both dry and lactating sows cool, is very important. The ideal temperature for sows is between 16°C and 20°C. Higher temperatures can also have a negative impact on feed intakes during lactation (AHDB, 2018. Teagasc, 2016). It's critical to optimize nutrient intakes in the lactating sow to ensure both high levels of milk production but also support sow body condition. Body condition of sows at weaning and condition loss during lactation, has a significant impact on WSI and performance in subsequent pregnancies. Lactation is a physically demanding time for the sow, with higher numbers of piglets suckling, nutritional and energy requirements on the sow increase and diet must meet those demands. If feed intake in lactation falls consider increasing lactation diet spec.

To summarise, to minimise your non-productive days ensure correct thermal climates in your dry sow yard and farrowing rooms, as sows really struggle with excessive heat. Be sure to have sufficient light for at least 16 hours a day during the autumn/winter months. Clean light covers and windows to achieve 300lux light intensity all year round.

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