Intensive selection by breeding companies for prolificacy in their breeding programs has led to a significant increase of litter size. Recently, the financial benefit of improved bir th and weaning weight has resulted in them becoming important measured traits in the maternal line index.

Large litters result in more competition for teat space. Piglet viability, survival and growth is dependent on birth weight, colostrum access and milk intake.A sow’s capacity to produce milk varies during lactation. Milk production is a complex process; however it is a heritable trait. Hermitage farms in Ireland have weighed in excess of 6,000 litters and have demonstrated the high potential in milk output by measuring litter weight at weaning.Top weights recorded are 140Kgs litter weight at 27 days of age.

As a greater number of piglets are born alive, there is larger variation in birth weights.Variation in piglet weaning weight results in increased variation throughout the pig’s life. Recent work at Hermitage has shown a 1kg difference at weaning can result in a 5kg difference at slaughter giving an economic advantage of £2.50 per finished pig.

The results from this work have demonstrated that there is a significant variation in the weaning weight output of Maternal Line sows. Sows producing heavier litters at weaning are profitable for two reasons:

1. A heavier piglet at weaning is better prepared to deal with various challenges at weaning.These heavier weaned pigs achieve slaughter weight more efficiently and economically, producing the ‘Full Value’ pig.

2.Sows producing heavier pigs at weaning have an increased feed intake and better feed conversion ratio of feed intake to piglet gain, which creates a more economical and profitable lactating sow.


Litter weight at weaning is a means of selecting for high milk yield (a heritable trait); it has a heritability of approximately 20%.This means that when a sow has an advantage in their phenotype for litter weaning weight, approximately 20% of that difference is due to genetics and 80% due to non-genetic/environmental factors (days in lactation, no of pigs weaned, room temperature, nutrition, feeding system, management, health). Since January 2014 Hermitage Breeding Units have weighed more than 6,000 Landrace and Large White litters at weaning.This data is incorporated into the Hermitage BreedDirect BLUP system with a respective BreedingValue produced.This project led to Hermitage developing the MLI2; Litter Weight at Weaning. Hermitage clients can select Dam Line boars from the AI studs with high breeding value for milking ability. PIC-Hermitage Maternal Line MLI2 boars at AI are selected from high index, high milking, high litter weight dams.

PIC and Hermitage understand that some farms want to focus on improving litter size as a first priority, while other farms are now interested in the weaning weight of the litter as they are satisfied with the number born alive. PIC and Hermitage can facilitate this option for its customers by using the MLI 2 index with a higher emphasis on litter weaning weight.

Dr Patrick Varley, Ph.D. Hermitage Technical Expert