The demand of larger litter sizes pushes many sows into a negative energy balance. Body condition is falling too far and this affects fertility. And it is clear that sows are not producing enough milk to sustain maximum piglet growth. Meeting sow dietary requirements and ensuring feed intakes during gestation and
lactation periods are key. Preparation starts when sows are still gilts.
Modern highly prolific sows are producing larger litters. Sows striving to give the maximum quantity of colostrum and milk to their piglets often fall short of the demand. Individual piglet growth has not increased and often sow body conditions as well as fertility capacities are compromised.
Sow milk yield has risen over the years, but the amount of milk ingested per piglet has not. This is illustrated by a recent comparison of suckling piglets’ weight development in 1995 and 2012 on the same farm. Piglet weight gain was practically the same 16 years later. The increase in litter size that took place at this time has led to a decrease in the amount of milk ingested per piglet.
From several experiments it was concluded that suckling piglets have the potential to grow at double or triple the rate they typically achieve under practical farm conditions. It became clear that sows, however, are not producing sufficient amounts of milk to sustain maximum piglet growth.
As a rule of thumb, every extra piglet induces the sow to produce an extra 0.5 l of milk per day. Her daily milk yield can therefore exceed 12 l/ day. The high milk production puts a high demand on sow metabolism and feed intake. But her feed intake capacity is not sufficient to provide all the nutrients needed for this high milk production. Therefore, the sow gets into a negative energy balance. She has to mobilise fat and even protein from the tissues and minerals from the bones.
The larger litter sizes now typical on many units are clearly at the expense of the sow’s own body reserves. This is illustrated in a recent study by Dr Lia Hoving, at Wageningen University, the Netherlands. She showed that sows with a litter weight gain of 65 kg lost more weight during lactation than sows with a litter weight gain of 61 kg. Respective weight losses were 35 kg and 22 kg.
Effect on fertility
High demands on milk production call for careful nutrition as fertility will be affected in sows that lose too much body condition. This means that lactation feeding will have an impact on the next litter size.
Soon after farrowing and during lactation sows are experiencing a cascade of hormonal changes with ovaries and uterus preparing for the next gestation. Excessive mobilisation of body reserves of more than 10% will disturb these processes and will lead to lower fertility post-weaning and a longer farrowing to oestrus interval.
Poor conception rates are more likely too, along with a lower ovulation number, lower oocyte and embryo quality and reduced embryo survival. The consequence is a lower litter size at the next farrowing, as shown in Figure 2. This study also shows that first and second parity sows are more susceptible to weight loss, probably because their body reserves are relatively low and they are still developing. Older sows are more robust and seem to be better able to cope with high weight loss.
A recent experiment was carried out at Wageningen University looking at weight loss effects in first parity sows during their first lactation that were only mildly restricted in feed intake. After weaning, sows were divided into two weight loss classes: less than 14% weight loss and more than 14% weight loss. Sows were slaughtered at day 35 after insemination, and their uteri were examined. It appeared that the high weight loss sows had only 15 vital embryos in their uterus, whereas low weight loss sows had 17 vital embryos.
This was explained by a lower number of implantations and a lower embryonic survival in the high weight loss sows.
Prevent excessive weight loss
Based on the trial work mentioned and on current literature, weight loss in lactating sows should not exceed 10%. To establish the situation in this period, body condition records should be kept by weighing sows and measuring back fat thickness as they enter and leave the farrowing crate.
Lactation feed intake should be as high as possible and this starts with the feeding of gilts during rearing. Their feed should be not too concentrated and contain enough fibre to allow good stomach and intestine development which will increase their feed intake capacity.
Furthermore, the feeding regime during gestation is crucial and it should prevent sows building up too many body reserves. Sows that are too fat will have a lower appetite and eat less during lactation. Ideally, gestating sows should be fed individually following a ration that is based on their individual body condition. This will be a big challenge in group housing systems.
The gestation diet should also contain adequate fibre for gut development so that feed intakes are maximised during lactation. This dietary fibre content should remain in line with that in the lactation diet in order to maintain the fermentation processes in the hindgut.
After farrowing, the feed supply should be increased gradually by approximately 0.5 kg/day to a maximum at around day 12. Fresh drinking water should be easily accessible, and room temperature should not exceed 22oC. Lactation feeding determines to a large extent the next litter size.
Ensuring the modern highly prolific sow’s nutritional demands are met starts early – in her rearing phase. It is also necessary to review her diet through the gestation and lactation phases and keep appropriate records to ensure that excess body weight is not lost, that can easily lead to fertility problems in the longer term. Lactation losses should not exceed 10% in body weight and 4 mm for back fat thickness.
Boosting milk yields and preventing weight loss needs careful thought and there is still work to be done but inroads are being made into bridging the gaps and preventing performance dips. PP
Publication: The second parity sow
The subject discussed in this article is partly based on the recent PhD thesis by Lia Hoving, Wageningen University, the Netherlands, called ‘The second parity sow’. The publication, subtitled ‘Causes and consequences of variation in reproductive performance’, zooms in on second parity sows, representing on average 19% of the reproduction herd in the Netherlands. They often show reduced reproductive performance. Hoving received her degree on 11 May.