Are Larger Litters a Concern for Piglet Survival or An Effectively Manageable Trait?

Abstract

As sows continue to be selected for greater prolificacy, it is important to review problems that arise in larger litters, and whether these issues can be appropriately managed. Although a proportion of piglets in larger litters can be born underweight, proper supervision around farrowing and adequate colostrum intake has the potential to improve the survival of low-birth-weight piglets and their ongoing growth to weaning. As larger litters can impart greater stress and discomfort on sows, implementing a low-stress environment leading up to parturition may improve sow performance and subsequent survival of piglets. Additionally, treating sows with anti-inflammatory compounds, either dietary or pharmacologically, shows some promise for alleviating sow discomfort and improving piglet survival in larger litters. Understanding that selecting sows for larger litters not only affects piglet survival but the well-being of the sow, the decision to continue selecting for larger litters, regardless of management strategies, remains a topic of ethical concern.

Handling Associated with Drenching Does Not Impact Survival and General Health of Low Birth Weight Piglets

“…Given that the pigs in this study were considered less resilient because of their low body weight and younger age, this lower resilience did not seem to apply to a more profound stressor as drenching. Due to the LBW piglets’ low energy reserves [ 10 , 39 ] and smaller size, they are generally unable to compete against heavier littermates for the better, anterior teats, resulting in an insufficient colostrum intake [ 2 , 29 , 46 ]. This inadequate consumption of colostrum further depletes the LBW piglets’ energy reserves, which can explain why the animals were not able to struggle much during this experiment’s drenching moments and did not experience this as a significant stressor.…”

Salivary oxytocin co-varies with parturition and nursing behavior in domestic pigs (Sus scrofa domesticus)

“…During their domestication, the descendants of wild boars have undergone strong selection pressures for greater productivity [1,2], resulting in a doubling of average litter size at birth, from 5.4 (± 1.5) live born offspring in wild boars [3] to 11.7 (± 3.2) in domestic breeds [4], with the largest litters often containing more than piglets [5].…”

“…Less attention has been given to the potential impacts of these selection pressures on the welfare of sows and their offspring [2,5]. From an evolutionary perspective, producing larger litters is expected to exacerbate short-term fitness tradeoffs for mothers, between investing in more versus healthier offspring within a current litter, as well as long-term fitness trade-offs, between investing in current versus future litters [6].…”

“…This socio-biological perspective can help to explain the evidence that piglets from larger litters are more likely to die by starvation or infant-crushing [8], which are the two greatest risks to piglet survival, together accounting for up to 60% of pre-weaning mortality [9]. These two risks may be inter-related, since piglets who are not receiving milk may be too weak to avoid being overlain by mothers [5], and mothers may selectively direct crushing behavior at offspring who are not receiving milk [8]. High piglet mortalities represent not only a major economic loss but also an ethical problem, which may be addressed by balancing genetic selection for production with selection for additional traits that predict enhanced maternal care.…”

What is the current significance of low birthweight pigs on commercial farms in Northern Ireland in terms of impaired growth and mortality?

“…However, much of the existing literature comparing the performance of low birthweight pigs to heavier counterparts has been conducted on litter sizes of 11 pigs or less and a birthweight of over 1 kg, which is not reflective of current commercial practice ( Douglas et al, 2014 ). Although some recent studies have analyzed the performance and mortality of compromised pigs reared in large litters, this was not balanced with a comparison to heavier littermates ( Ward et al, 2020 ; Feldpausch et al, 2019 ). These studies were also conducted under controlled conditions, where animal responses may differ from those recorded in the field ( Magowan et al, 2007 ).…”