Neonatal piglet mortality fits well with the PROHEALTH criteria for a production disease:

1. It is a persistent problem. Losses of piglets from stillbirth and early life mortality have averaged 15-25% of all piglets born for many decades in countries all round the world. The problem is not improving – data collected in the PROHEALTH project on a sample of farms in three different countries showed current levels averaging 20-30%.

2. It increases with intensity of production. As levels of sow productivity have increased, more piglets die in each litter. The emphasis on increased selection for prolificacy in recent years has resulted in a dramatic increase in average litter size of 2 piglets over the last 10 years. Data collected in the PROHEALTH project from a sample of 1575 farrowings in a UK herd illustrate how both the number of stillborn piglets and the number of piglets which die in early life are both increased in large litters (Figure 1).

Figure 1. The effect of litter size the number of piglets per litter which were born dead or died before first handling at 12-24h after birth (SM Matheson, G Walling, SA Edwards – unpublished data from PROHEALTH).

Traditionally farmers have attempted to reduce piglet mortality by improving the environment for the newborn piglet, using protective farrowing crates and supplementary heating, and by increasing the amount of stockperson supervision and care at the time of farrowing. However, work carried out in the PROHEALTH project has highlighted how attention to the welfare of the sow during pregnancy may be just as important in promoting good piglet survival. 

The French project partners at INRA set out to follow up a preliminary study which showed that sows housed during pregnancy in more enriched conditions had better piglet survival[1]. To understand the reasons for this, they replicated the housing treatments in an experiment in which detailed physiological and behavioural measurements were made on both the pregnant sows[2] and the newborn piglets[3]. Sows in the conventional system were housed throughout gestation on slatted floors, whilst the enriched system was on straw with 45% more space per sow. At 105 days of gestation, the sows from both systems were transferred into identical slatted farrowing pens and housed in crates. Sow feeding was similar in the two systems. Sows housed in the conventional gestation system had throughout pregnancy higher levels of the hormone cortisol, associated with a stress response. They also had higher levels of blood markers indicating oxidative stress (imbalance in the antioxidant system in the body, which can lead to cell and tissue damage). and immune system activation. Although there was no difference in the progress of farrowing, piglet mortality rates attributable to stillbirths and mortality in the first 72h were markedly lower in sows from enriched housing (12.8% v. 22.2 %). A detailed investigation of the piglets showed that sows housed in the more stressful environment during gestation tended to have more low birthweight piglets, with reduced energy stores in the muscle, lower temperature at 1h after birth, as well poorer expression of genes involved in muscular energy metabolism.  

The beneficial effects of the enriched gestation environment were attributed to less social aggression between sows and increased possibilities for foraging and exploration. To see whether a more commercially applicable enrichment regime in gestation could achieve the same effects, a second experiment was carried out to compare the same commercial control with a treatment in which the pen provided the same space allowance, but was enriched by providing pieces of oak hanging by a chain and straw pellets daily in a trough[4]. Once again, they were able to show that this treatment reduced the maternal cortisol level in pregnancy. Although there was no influence on piglet birth weight and markers of piglet metabolic status, the proportion of piglets that died at birth and within 12h of birth was again lower in litters from enriched sows (6.6% vs 11.1%).

Whilst these experiments focussed on long-term housing stress, another programme of work within the PROHEALTH project looked at more short-term interventions to reduce stress of sows prior to farrowing. As farming systems become larger and more automated, the level of contact between sows and their human caretakers is reduced. As a result, sows which only receive human contact during necessary, often unpleasant, treatments such as vaccination become fearful in the presence of humans. This can again raise stress hormone levels when they cannot escape proximity, such as when placed in a farrowing pen or crate. Work by SEGES, the Danish project partner, demonstrated that this fearfulness could be reduced by a relatively short period of positive handling[5] . Sows which experienced gentle scratching for 15 seconds per day in the period from transfer to the farrowing accommodation until giving birth showed reduced levels of fear, as indicated by their approach or withdrawal response to a human. In the same experiment, it was noted that playing music in the farrowing house also seemed to have a calming effect on the animals. To see if these fear reducing treatments could translate into improved piglet survival, a large-scale production experiment was carried out by Vedanko BVBA, a Belgian commercial partner in the project[6] . In a study involving more than a thousand sows, they found that the application of these two sow-calming treatments, gentle scratching and music, significantly reduced piglet mortality between birth and weaning by 3.4%.

What has been clearly shown by these different experiments in the PROHEALTH project (Figure 2) is that, as the challenges of prolificacy continue to increase in pig farms, paying attention to reducing sow stress during pregnancy will be an important part of future strategies to improve piglet survival.

Figure 2. The effect of improving sow welfare on total pre-weaning piglet mortality (including stillbirths) in three PROHEALTH studies

[1] Merlot E, Calvar C and Prunier A 2017. Influence of the housing environment during sow gestation on maternal health, and offspring immunity and survival. Animal Production Science 57: 1751–1758.

[2] Merlot E, Pastorelli H, Prunier A, Père M-C, Louveau I, Lefaucheur L, Perruchot M-H, Meunier-Salaün M-C, Robert F, Gondret F and Quesnel H 2019. Influence of sow environment during gestation: part I. Maternal physiology and lacteal secretions in relation with neonatal survival. Animal 13: 1432–1439

[3] Quesnel H, Père M-C, Louveau I, Lefaucheur L, Perruchot M-H, Prunier A, Pastorelli H, Meunier-Salaün M-C, Gardan-Salomon D, Gondret F and Merlot E 2019. Sow environment during gestation: part II. Influence on piglet physiology and tissue maturity at birth in relation with neonatal survival. Animal 13: 1440–1447

[4] Quesnel H, Peuteman B, Père M-C, Louveau I, Lefaucheur L, Perruchot M-H, Prunier A, Meunier-Salaün MC, Gardan-Salmon D, Gondret F, Merlot E. 2019. Effect of environmental enrichment with wood materials and straw pellets on the metabolic status of sows during gestation. Livestock Science 229: 43-48

[5] Moustsen VA, Johansson KP, Forkman B, Nielsen MBF, Andreasen SN. 2016. Impact of playing classical music and scratching on avoidance distance in loose housed farrowing sows. Proc. 50th Congress of International Society for Applied Ethology,  p. 276.

[6] Amalraj A, De Meyer D, Van Limbergen T, Fockedey M, Edwards SA, Moustsen VA, Chantziaras I, Maes D. 2020. Short Communication: effect of positive handling of sows on litter performance and pre-weaning piglet mortality. Animal, doi:10.1017/S1751731120000427