Pork meat is the most widely consumed meat around the world. In 2014, it amounted to 115.5 million tons (37% of the total amount of consumed meats), according to the Food and Agriculture Organization of the United Nations. The European Union (EU) is the second biggest producer of pork meat with 23,290 million tons produced in 2016, which is a record volume never earlier reported for the EU, behind China with 54,870 million tons (United States Department of Agriculture, 2016). The EU is also the second biggest consumer (20,974 million tons, 37 kg per capita in 2009), and in The Netherlands an average of 38 kg of pork meat per capita was consumed in 2015. The number of sows in the EU slightly declined from 12,300 to about 12,170 million heads from 2016 to 2017, but total slaughter increased by 1,050 million heads. This demonstrates that increased productivity of sows outbalances the lower sow numbers (United States Department of Agriculture, 2016). High productive and reproductive efficiencies contribute to the increase in productivity, and the largest contributing factor to this higher level of productivity is the increase in total number of piglets born per sow per year (Kridli et al. 2016). Modern dam line sows are characterized by a large litter size, with an ability to produce up to 30-35 piglets per sow per year (Schneider et al. 2014) with 2.4 to 2.5 litters per sow per year. In The Netherlands, there was an increase of approximately 3 piglets born alive and of 2 piglets weaned per litter from 2000 to 2013, with an average total number of piglets born of 16.2 and 14.6 piglets born alive in 2016 (Agrovision BV, 2017). In the United States, the total number of piglets born and the number of piglets born alive increased by approximately 2 piglets from 2000 to 2015, reaching 13.6 and 12.4 per litter, respectively (United States Department of Agriculture, National Agricultural Statistics Service 2015). In Denmark, genetic selection for total number of piglets born from 1992 to 2004 led to a total increase of 3.8 piglets per litter (calculated as the difference in estimated breeding values for total number of piglets born between 1992 and 2004) in Danish Landrace lines (Su et al. 2007), and in 2011 the number of piglets produced per sow per year was 37.5 with 2.4 litters born per sow per year (Franke et al. 2013). However, genetic selection for sows with the ability to farrow a high number of piglets has led to a decrease in average piglet birth weight (Quiniou et al. 2002), and for each additional piglet born in a litter there is a decrease of 30 to 35 grams in the average piglet birth weight (van der Lende and de Jager 1991; Quiniou et al. 2002; Quesnel et al. 2008; Beaulieu et al. 2010). Additionally, genetic selection for high litter size also increased the within litter piglet birth weight variation (Quiniou et al. 2002; Wolf et al. 2008). Measurements of the coefficient of variation (CV) of birth weights of small litters (< 10 to 12 piglets born) and large litters (> 15 piglets born) revealed an increase in ...