"How can we reduce piglet mortality?" asked Dr Emma Baxter at the start of her presentation.

Data from Pigplan-participating herds indicate that around two million piglets die in the UK each year. Total mortality has fluctuated around 18 per cent for the last 15 years or so and while live-born mortality has fallen from 14 per cent 20 years ago, it is now remaining stubbornly around the 12 per cent mark. At an average of 19.5 per cent, total mortality for indoor herds is slightly higher than the 16.2 per cent average for herds kept outside in an SAC survey.

Causes of Mortality

Crushing is usually thought to be the main cause of piglet mortality but mis-diagnosis appears to be quite common between stillbirths, crushing by the sow and other causes of death.

Differences between indoor and outdoor herds were noted in a study in 2000, when post-mortem examination found stillbirths to be the number one cause of mortality in indoor herds, and crushing to account for most of the mortalities in outdoor herds.

Factors Pre-Disposing Piglets to Stillbirth

Dr Baxter explained that there are essentially two types of stillbirth:

• Type I are those occurring prepartum of ante-mortem, often known as 'mummies' (mummified foetuses), which are caused by intrauterine infections, and
• Type II stillbirths, which occur during birth and have non-infectious aetiology.

Type II stillbirths are associated with prolonged farrowing in piglets later in the birth order and where the birth interval is prolonged. These factors, in addition to placental insufficiency, lead to perinatal asphyxia.

Dr Baxter described a case study in which she studied piglet survival in different environments: in farrowing crates indoors and on a commercial outdoor system.

The results show that a piglet is more likely to survive if it has a higher birthweight but it also emerged that also important were features of body conformation, including a higher ponderal index (birth weight ÷ crown-rump³), a higher body mass index (birth weight ÷ crown-rump²) and a larger abdominal circumference.

In summary, she said that stillborn piglets were disproportionately long and thin, which may be an indication of intra-uterine growth retardation.

Dr Baxter also proved that farrowing progression is important: stillborn piglets tend to be born later in the birth order.

How to reduce stillbirths

Providing optimum nutrition for the sow will contribute to improving the gestational environment for piglets, explained Dr Baxter, and improved farrowing progression can be achieved by avoiding sow stress by maintaining an ambient temperature no higher than 20ºC and providing materials for nesting. In the longer term, genetic selection may help to increase placental sufficiency, increase the physiological maturity of piglets at birth – a characteristic of the Meishan breed – and to select for optimum birthweight while decreasing within-litter variability.

Factors Pre-Disposing to Live-Born Mortality

The most important factors that pre-dispose piglets postnatal mortality in previous research were found to be chilling, starvation and overlying.

From Dr Baxter's own work from the case study, it appears that the most important physiological factors for survival are higher weight and body temperature at birth and 24 hours. A short time to find the teat and to suckle was also important for survival.

In their attempts to boost litter size, the breeders may inadvertently have increased the variation in birthweight within litters, a factor that has been found to be linked to an increased risk of mortality as the smaller piglets are unable to compete with their larger litter-mates.

Improving piglet birthweight

Dr Baxter identified optimum nutrition during gestation and lactation as the most important measure to help boost piglet birthweights. Maintaining high feed intake in lactation is known to increase both the growth and survival of the current litter as well as the subsequent one. In the longer term, genetic selection strategies could include the targets of optimum birthweight and reduced within-litter weight variability.

So what is an ideal birthweight? Dr Baxter cited previous research that shows the risk of mortality in live-born pigs falls for piglets weighing 1.4 kg or more, and total survival was optimum at a birthweight of 1.6kg.

Thermoregulation and piglet behaviour

Chilling is a major contributor to piglet mortality, and Dr Baxter demonstrated how a newborn piglet's temperature will fall rapidly if it is in an environment below its temperature of thermoneutrality (34°C) using thermal imaging.

Improving the microclimate around the piglet is one way to help, and improving sow nutrition in order to increase birthweight are ways to help improve the piglet's thermoregulation, Dr Baxter suggests. There may also be strategies for breeders to select for greater physiological maturity at birth and increased vitality.

Rooting behaviour in piglets was associated with a better chance of survival in Dr Baxter's research. Interestingly, this was not correlated with birthweight.

Improving sow behaviour by encouraging her to lie laterally for a prolonged period and decreasing farrowing time can positively influence the behaviour of her piglets.

Providing a better microclimate for the piglets can also help. Again using thermal imaging, Dr Baxter showed how providing some straw bedding in the farrowing pen can help thermoregulation.

It is important to achieve a balance between the temperature needs of the sow and her litter, so Dr Baxter recommended having the farrowing room at 20°C for farrowing, and drooping the temperature to 17°C by the end of the first week. In order to help the microclimate around the piglets, draughts through the slats should be minimised and straw should be provided before and for at least 24 hours after farrowing.

Maternal behaviour

Dr Baxter emphasised the importance of encouraging nesting behaviour in the sow before farrowing, and how prolonged periods of lateral lying and careful posture changes can help reduce crushing by the sow.

In practical terms, this means a minimum of stress during gestation by avoiding mixing during pregnancy, as well as providing bedding material and avoiding excessive temperatures during farrowing to prevent heat stress. In the longer term, it may be possible to select for better maternal behaviour: an initial study of the outdoor herd studies showed that where average mortality was 18 per cent, it was 12 per cent in the 'high survival' lines within just two generations.

Conclusions

It is important to diagnose accurately the causes of death among piglets in the herd because each cause is associated with different risk factors.

The risk factors of prenatal survival are similar for all farrowing systems, and these relate to piglet body conformation as well as to birth order and the duration of farrowing.

Risk factors for live-born mortality differ, however, depending on the farrowing system. For indoor systems using crates, the focus should be on the piglet – its birthweight, behaviour and vigour. For outdoor systems, it is maternal behaviour that has a great effect on piglet mortality.

"The sow, piglets and their environment all interact to influence piglet survival," concluded Dr Baxter, and so the solutions lie in provision of the correct environment in the short term. Biological improvements through genetic selection strategies may provide solutions in the longer term.

May 2009