Too many piglets die in Danish pig production. Figures from the industry show that piglet mortality was approx. 23 % in 2020. This means that out of the 41.9 million piglets born in 2020, 9.7 million died.

Professor Lene Juul Pedersen, Department of Animal Science at Aarhus University (AU), points out that the continuous increase in litter sizes is the culprit creating the problems.

Large litters are a result of breeding goals

Increasing litter sizes are the result of a breeding strategy, according to which breeding animals are selected based on their genetic ability to give birth to large litters. However, already in the 2000’s it turned out that piglet mortality reached an unacceptable level.

Based on results from a research project accomplished in cooperation between Aarhus University (AU) and the Danish Pig Research Centre (now SEGES) and funded by the Danish Pig Levy Foundation, the Danish Pig Research Centre board decided to adjust the breeding goal of “as many piglets born as possible” to a goal of “as many living pigs as possible on day 5 after birth” (LG5). According to this goal, litter size at birth and number of living piglets at day 5 are given equal importance (an account of this is found in the report ”Pattegrisedødelighed i DK - Muligheder for reduktion af pattegrisedødeligheden i Danmark” (in Danish – “Piglet Mortality in Denmark – possibilities of reducing piglet mortality in Denmark”) prepared at a request from the Danish Veterinary and Food Administration).

Most piglets die during the first days after birth, and the new breeding goal was initially to combine the goals of increasing piglet survival rates and strengthen the fertility of Danish breeding animals at the same time.

More studies, e.g. an independent evaluation accomplished by Aarhus University in 2018 (commissioned by the Danish Veterinary and Food Administration), demonstrated that breeding according to the LG5 goal increased litter sizes and reduced piglet mortality in breeding herds until the middle of the 2010’s.

A certain delay exists when it comes to disseminating genetic results and information from breeding herds to production herds. Therefore, AU expected a minor decline in mortality in production herds up till now. However, recent years witnessed exactly the opposite in production herds, i.e. increasing mortality rates.

Large litters mean huge demands on management efforts

The problem is that increasing litter sizes  – and, as a consequence, lower birth weight –  increase the need for on-farm management strategies to care for excess and underweight piglets, to ensure their survival , says Professor Lene Juul Pedersen, Department of Animal Science at Aarhus University. In addition, individual piglet will receive less colostrum and thus less antibodies to protect against infection during the first weeks of life. These negative side effects of sows giving birth to large litters - often with more piglets than productive teats - means that managerial efforts should be increased, e.g. by means of farrowing surveillance and assistance, extra heat during farrowing, use of foster sows, and milk replacement as well as other intensive care initiatives for the smallest and weakest piglets. Otherwise, the mortality rates will be high as the sow is not capable of rearing all her piglets.

Lene Juul Pedersen further points out that the use of foster sows and the practice of moving piglets between pens partly constitutes a welfare problem both to the sow and the piglets; and partly contributes to reduced infection protection due to piglets/sows being moved between batches. This will further increase the risk of disease spreading and death.

In addition to being an animal welfare problem, Lene Juul Pedersen questions the economic profitability of large litters because of the ever increasing work efforts to save the last pigs. Moreover, we do not have sufficient knowledge neither on how the smallest and weakest piglets develop over time nor on the long-term consequences of the unstable social environment experienced by piglets being moved and mixed with foreign piglets when cross fostered or raised by a nurse sows.

Alternative to LG5

Senior Researcher Ole Fredslund Christensen, Center for Quantitative Genetics and Genomics (QGG) at Aarhus University, is one of the researchers studying the genetic possibilities to reduce piglet mortality.  

QGG was in charge of the LG5 evaluation, and in relation to this the researchers suggested that farmers should breed more directly to reduce mortality instead of achieving large litters. This might be accomplished by means of an alternative index to LG5, which includes a higher weighting of survival in relation to litter size than the implicit 1-1 weighting in LG5. The evaluation rendered it possible that this might result in a significantly higher reduction in mortality rather than breeding for LG5.

Breeding for survival until slaughter

Based on the increasing mortality, QGG initiated a new research project “Genetic improvement of pig survival”.

Within the framework of this project, researchers carry out genetic examinations of pig mortality in various periods from birth to slaughter. One aspect of this is to study genetic correlations to properties in the current breeding goals (growth, feed efficiency, LG5 etc.) in order to investigate whether we breed for properties that may indirectly have negative consequences for pig survival.

In the study, researchers will examine both the sow and the piglet’s own genetic contribution to survival, which is different from breeding for LG5.

- The superior purpose of the project is to examine the possibilities of breeding for reduced mortality in a longer period than to day 5. Breeding for survival until weaning is of special relevance, but breeding for survival until slaughter is also relevant, says Ole Fredslund Christensen says Ole Fredslund Christensen.