Increasing litter size has long been a goal of pig breeders and producers, and may have implications for pig (Sus scrofa domesticus) welfare. This paper reviews the scientific evidence on biological factors affecting sow and piglet welfare in relation to large litter size. It is concluded that, in a number of ways, large litter size is a risk factor for decreased animal welfare in pig production. Increased litter size is associated with increased piglet mortality, which is likely to be associated with significant negative animal welfare impacts. In surviving piglets, many of the causes of mortality can also occur in non-lethal forms that cause suffering. Intense teat competition may increase the likelihood that some piglets do not gain adequate access to milk, causing starvation in the short term and possibly long-term detriments to health. Also, increased litter size leads to more piglets with low birth weight which is associated with a variety of negative long-term effects. Finally, increased production pressure placed on sows bearing large litters may produce health and welfare concerns for the sow. However, possible biological approaches to mitigating health and welfare issues associated with large litters are being implemented. An important mitigation strategy is genetic selection encompassing traits that promote piglet survival, vitality and growth. Sow nutrition and the minimisation of stress during gestation could also contribute to improving outcomes in terms of piglet welfare. Awareness of the possible negative welfare consequences of large litter size in pigs should lead to further active measures being taken to mitigate the mentioned effects.
Increasing litter size has long been a goal of pig (Sus scrofa domesticus) breeders and producers in many countries. Whilst this has economic and environmental benefits for the pig industry, there are also implications for pig welfare. Certain management interventions are used when litter size routinely exceeds the ability of individual sows to successfully rear all the piglets (ie viable piglets outnumber functional teats). Such interventions include: tooth reduction; split suckling; cross-fostering; use of nurse sow systems and early weaning, including split weaning; and use of artificial rearing systems. These practices raise welfare questions for both the piglets and sow and are described and discussed in this review. In addition, possible management approaches which might mitigate health and welfare issues associated with large litters are identified. These include early intervention to provide increased care for vulnerable neonates and improvements to farrowing accommodation to mitigate negative effects, particularly for nurse sows. An important concept is that management at all stages of the reproductive cycle, not simply in the farrowing accommodation, can impact on piglet outcomes. For example, poor stockhandling at earlier stages of the reproductive cycle can create fearful animals with increased likelihood of showing poor maternal behaviour. Benefits of good sow and litter management, including positive human-animal relationships, are discussed. Such practices apply to all production situations, not just those involving large litters. However, given that interventions for large litters involve increased handling of piglets and increased interaction with sows, there are likely to be even greater benefits for management of hyper-prolific herds.
The aim of this study was to investigate the effects of individual physical characteristics on preweaning survival and growth of piglets born in a noncrate system. Data were collected from 3,402 neonatal piglets from 203 Landrace × Yorkshire sows housed in noncrate pens in a commercial Danish sow herd. Piglets were categorized into groups according to their survivability: surviving to weaning (SURV), stillborn (STILL), or dead between birth and weaning (DBW), which was subdivided into dead d 0 to 1 after farrowing (DEAD1) or dead d 2 to 26 after farrowing (DEAD26). Linear models were used to determine which physical characteristics affected survivability and growth of piglets. Results showed that characteristics related to the individual piglets had a greater degree of explanatory power in relation to survival than variables related to the sow. Survival of piglets increased if piglets were females (P < 0.001), had a greater body mass index (P < 0.001), and were born to sows of parity 3 or more (P = 0.017). Piglets with a greater birth weight were more likely to survive (P < 0.001), but birth weight was inferior to body mass index in explaining differences between SURV and DBW. Piglets that died 2 to 26 d after birth had a lower birth weight (P < 0.001), were born to sows of parity 1 or 2 (P = 0.014), and were born after a shorter gestation (P = 0.011) compared with SURV. Piglets that died on d 0 to 1 after birth had a lower body mass index (P < 0.001), displayed a greater degree of growth restriction (P = 0.004), and were born in large litters (P = 0.005). The gender of the piglets affected survivability at both d 0 to 1 (P < 0.001) and d 2 to 26 (P < 0.001). Piglets in DEAD1 differed from STILL by having a shorter crown to rump length (P < 0.001), a birth weight that deviated more from the mean weight of the litter (P = 0.001), and being more likely to be born before d 116 of gestation (P = 0.008). The only physical characteristic that was important for growth performance in the suckling period was birth weight (P < 0.001), yet using only birth weight as an indicator for survivability was too simplistic. The results of this study emphasize that individual characteristics of neonatal piglets could serve as indicators of survivability of piglets born in noncrate systems; however, the results suggest that the importance of characteristics differed in different periods of the preweaning period.
If loose-housed farrowing systems are to be an alternative to traditional farrowing crates, it is important that they can deliver the same production results as can be achieved in farrowing crates under commercial conditions. The aim of this study was to compare preweaning mortality in farrowing crates and free farrowing pens (FF-pens) within herds that had both systems. The study was conducted over 2 years in three commercial Danish herds that had FF-pens as well as traditional farrowing crates in their farrowing unit. Piglet mortality was analysed in two periods: before litter equalisation and after litter equalisation. Linear models were used to analyse effects of housing (crate or pen), herd (Herd A, B or C), parity (parities 1, 2, 3 to 4 or 5 to 8) as well as the effect of number of total born piglets on mortality before litter equalisation, and the effect of equalised litter size on piglet mortality after litter equalisation. All corresponding interactions were included in the models. Before litter equalisation piglet mortality was higher ( P < 0.001) in pens (13.7%) than in crates (11.8%). Similarly, piglet mortality after litter equalisation was higher in pens than in crates in all three herds, but the difference between pens and crates were dissimilar ( P < 0.05) in the different herds. In addition, piglet mortality, both before ( P < 0.001) and after litter equalisation ( P < 0.001), grew with increasing parity of the sows. Mortality before litter equalisation moreover increased with increasing number of total born piglets per litter ( P < 0.001), and mortality after equalisation increased when equalised litter size increased ( P < 0.001). No significant interactions were detected between housing and parity or housing and litter size for any of the analysed variables. In conclusion, there is knowledge how to design pens for free farrowing; but this study showed a higher preweaning mortality in the FF-pen. Nonetheless a noteworthy proportion of the sows in the FF-pens delivered results comparable to those farrowing in crates. This indicates that FF-pens are not yet a robust type of housing for farrowing sows.
To reduce mortality among suckling piglets, lactating sows are traditionally housed in farrowing crates. Alternatively, lactating sows can be housed in farrowing pens where the sow is loose to ensure more behavioural freedom and consequently a better welfare for the sow, although under commercial conditions, farrowing pens have been associated with increased piglet mortality. Most suckling piglets that die do so within the first week of life, so potentially lactating sows do not have to be restrained during the entire lactation period. Therefore, the aim of the current study was to investigate whether confinement of the sow for a limited number of days after farrowing would affect piglet mortality. A total of 210 sows (Danish Landrace × Danish Yorkshire) were farrowed in specially designed swing-aside combination farrowing pens measuring 2.6 m × 1.8 m (combi-pen), where the sows could be kept loose or in a crate. The sows were either: (a) loose during the entire experimental period, (b) crated from days 0 to 4 postpartum, (c) crated from days 0 to 7 postpartum or (d) crated from introduction to the farrowing pen to day 7 postpartum. The sows and their subsequent litters were studied from introduction to the combi-pen ∼1 week before expected farrowing and until 10 days postpartum. Confinement period of the sow failed to affect the number of stillborn piglets; however, sows that were crated after farrowing had fewer live-born mortality deaths (P < 0.001) compared with the sows that were loose during the experimental period. The increased piglet mortality among the loose sows was because of higher mortality in the first 4 days after farrowing. In conclusion, the current study demonstrated that crating the sow for 4 days postpartum was sufficient to reduce piglet mortality.
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