Sibling competition in suckling piglet from hyper-prolific sows: Effects of litter size, milk replacer and housing conditions on feeding behaviour and welfare

TY - GEN

T1 - Sibling competition in suckling piglet from hyper-prolific sows

T2 - Effects of litter size, milk replacer and housing conditions on feeding behaviour and welfare

AU - Kobek-Kjeldager, Cecilie

PY - 2020/10/9

Y1 - 2020/10/9

N2 - During the recent decades, intense selection for larger litters has resulted in the modern sow breeds giving birth to more piglets than there are teats on the sow. In turn, this has resulted in sibling competition for access to teats. Although the domestic conditions have removed the main threats to survival, such as predators and food limitations, piglet mortality is presently at 13–14% of the live-born while 6–7% of total born are stillborn or die immediately after birth. This mortality and its associated causes and consequences are subject to economic, animal welfare and ethical concerns, which in turn raises questions about the sustainability of the current production system. Several management actions have been taken to reduce mortality and to rear surplus piglets, including nurse sows and artificial rearing on milk replacer (e.g. Rescue Decks®). An alternative strategy increasingly being employed by pig producers using hyper-prolific sows is providing milk replacer as a supplement, using an automatic system inside the farrowing pen and letting the surplus piglets stay with their mother. The aim of this thesis was to investigate the behaviour and welfare of domestic suckling piglets from hyper-prolific sows under two housing conditions with the possibility of foraging on milk replacer. The hypotheses of this PhD project was that increasing litter size would increase sibling competition and compromise welfare and that these negative effects would be mitigated by access to milk replacer and improved udder access by loose housing. Yet, for this strategy to work, piglets need to forage and drink milk replacer at a much younger age than they would start to forage under natural conditions. The theory of optimal foraging from behavioural ecology states that a change in foraging strategy will occur if the benefit outweighs the cost. Based on this theoretical framework, it was hypothesised that the cost of suckling would increase with greater litter size and lower piglet body weight and that this in turn would cause more piglets to drink milk replacer. To study this, the PhD project consisted of one large experimental study wherein several measures related to sibling competition were recorded on days 7, 14, 21 and 28 after birth. The study was a 2×2×2 factorial design with the factors litter size day 1(LSD1), milk replacer (MILK) and housing (HOUSING). The LSD1 was either 14 (LS14, N = 49 litters) or 17 piglets (LS17, N = 49 litters), litters either had access to milk replacer in a cup from days 1 to 28 after birth (+MILK, N = 52) or did not have access to milk replacer (-MILK, N = 46 litters), and sows were either housed in crates (CRATE, N = 55 litters;) or loose housed (LOOSE, N = 43 litters). The study was conducted in three batches, and piglets below 700g at birth were not included. The results showed that increasing litter size day 1 from 14 to 17 piglets compromised piglet survival (P < 0.05), weaning weight (P < 0.05) and fat retention (P < 0.05). Increasing litter size on the given day in lactation was associated with more teat fighting (P < 0.05), snout abrasions (P < 0.05) and low suckling success (P < 0.05). Smaller piglets were especially compromised (P < 0.05). The compromised survival, weaning weight and competition at the udder could to some extent, but not fully, be mitigated by access to milk replacer (P < 0.05). Loose housing compromised piglet survival (P < 0.05), and as a tendency compromised total litter weaning weight (P = 0.07), but increased litter homogeneity (P < 0.05), reduced udder abrasions (P < 0.05) and tended to reduce udder massage (P = 0.07). Fifty-nine percent of the piglets with access to milk replacer (+MILK) were observed drinking at least once day 7, 65% on day 14 and 61% on day 21 (mean drinking frequency varied from 0.5 to 1.9 bouts per piglet/h across days). Piglets were categorised into four foraging strategies on each observation day: high suckling success (57–63% of piglets), high suckling success when frequently drinking milk replacer (22–25% of piglets), low suckling success when frequently drinking milk replacer (6–7% of piglets) and low suckling success (7–13% of piglets). Contrary to the expectation, larger piglets were more often drinking milk replacer (P < 0.05), and, in addition, they were successfully suckling. As a consequence, these had the highest growth rate (P < 0.05). The smallest piglets had the lowest suckling success where about half of these replaced suckling with drinking milk replacer. The small piglets replacing suckling with drinking milk replacer had a similar growth to successfully suckling piglets, likely due to changing suckling success during lactation. Nevertheless, piglets mainly drinking milk replacer on day 21 had a compromised body fat retention. The results of this PhD project confirm that large litters increase the competition at the udder and that especially the smaller piglets has a competitive disadvantage. Milk replacer was mainly used as a supplement to suckling and not as a replacement when a teat could not be accessed in the large litters. Overall, the results indicated that piglets, regardless of access to supplemental milk replacer, still tried to gain access to a teat at milk letdown. Milk replacer and loose housing could to some extent, but not fully, mitigate the compromised welfare. Similarly to the other management strategies of large litters (nurse sow and artificial rearing), sow rearing of large litters with milk replacer raises significant animal welfare concerns. If pig producers continue to develop this management strategy further, studies should focus on the content of the milk replacer and the design of the milk cup to best fit the motivation and need of suckling piglets. Combinations with early life intervention may also be necessary. As an alternative to such an elaborate management system, pig producers may as an alternative consider using less prolific breeds. Yet, the high production efficiency per animal is a main argument for modern pig production to be sustainable from an environmental and economic perspective. However, there is a need to outweigh and balance these criteria of sustainability in a broader perspective, also including social well-being and animal welfare.

AB - During the recent decades, intense selection for larger litters has resulted in the modern sow breeds giving birth to more piglets than there are teats on the sow. In turn, this has resulted in sibling competition for access to teats. Although the domestic conditions have removed the main threats to survival, such as predators and food limitations, piglet mortality is presently at 13–14% of the live-born while 6–7% of total born are stillborn or die immediately after birth. This mortality and its associated causes and consequences are subject to economic, animal welfare and ethical concerns, which in turn raises questions about the sustainability of the current production system. Several management actions have been taken to reduce mortality and to rear surplus piglets, including nurse sows and artificial rearing on milk replacer (e.g. Rescue Decks®). An alternative strategy increasingly being employed by pig producers using hyper-prolific sows is providing milk replacer as a supplement, using an automatic system inside the farrowing pen and letting the surplus piglets stay with their mother. The aim of this thesis was to investigate the behaviour and welfare of domestic suckling piglets from hyper-prolific sows under two housing conditions with the possibility of foraging on milk replacer. The hypotheses of this PhD project was that increasing litter size would increase sibling competition and compromise welfare and that these negative effects would be mitigated by access to milk replacer and improved udder access by loose housing. Yet, for this strategy to work, piglets need to forage and drink milk replacer at a much younger age than they would start to forage under natural conditions. The theory of optimal foraging from behavioural ecology states that a change in foraging strategy will occur if the benefit outweighs the cost. Based on this theoretical framework, it was hypothesised that the cost of suckling would increase with greater litter size and lower piglet body weight and that this in turn would cause more piglets to drink milk replacer. To study this, the PhD project consisted of one large experimental study wherein several measures related to sibling competition were recorded on days 7, 14, 21 and 28 after birth. The study was a 2×2×2 factorial design with the factors litter size day 1(LSD1), milk replacer (MILK) and housing (HOUSING). The LSD1 was either 14 (LS14, N = 49 litters) or 17 piglets (LS17, N = 49 litters), litters either had access to milk replacer in a cup from days 1 to 28 after birth (+MILK, N = 52) or did not have access to milk replacer (-MILK, N = 46 litters), and sows were either housed in crates (CRATE, N = 55 litters;) or loose housed (LOOSE, N = 43 litters). The study was conducted in three batches, and piglets below 700g at birth were not included. The results showed that increasing litter size day 1 from 14 to 17 piglets compromised piglet survival (P < 0.05), weaning weight (P < 0.05) and fat retention (P < 0.05). Increasing litter size on the given day in lactation was associated with more teat fighting (P < 0.05), snout abrasions (P < 0.05) and low suckling success (P < 0.05). Smaller piglets were especially compromised (P < 0.05). The compromised survival, weaning weight and competition at the udder could to some extent, but not fully, be mitigated by access to milk replacer (P < 0.05). Loose housing compromised piglet survival (P < 0.05), and as a tendency compromised total litter weaning weight (P = 0.07), but increased litter homogeneity (P < 0.05), reduced udder abrasions (P < 0.05) and tended to reduce udder massage (P = 0.07). Fifty-nine percent of the piglets with access to milk replacer (+MILK) were observed drinking at least once day 7, 65% on day 14 and 61% on day 21 (mean drinking frequency varied from 0.5 to 1.9 bouts per piglet/h across days). Piglets were categorised into four foraging strategies on each observation day: high suckling success (57–63% of piglets), high suckling success when frequently drinking milk replacer (22–25% of piglets), low suckling success when frequently drinking milk replacer (6–7% of piglets) and low suckling success (7–13% of piglets). Contrary to the expectation, larger piglets were more often drinking milk replacer (P < 0.05), and, in addition, they were successfully suckling. As a consequence, these had the highest growth rate (P < 0.05). The smallest piglets had the lowest suckling success where about half of these replaced suckling with drinking milk replacer. The small piglets replacing suckling with drinking milk replacer had a similar growth to successfully suckling piglets, likely due to changing suckling success during lactation. Nevertheless, piglets mainly drinking milk replacer on day 21 had a compromised body fat retention. The results of this PhD project confirm that large litters increase the competition at the udder and that especially the smaller piglets has a competitive disadvantage. Milk replacer was mainly used as a supplement to suckling and not as a replacement when a teat could not be accessed in the large litters. Overall, the results indicated that piglets, regardless of access to supplemental milk replacer, still tried to gain access to a teat at milk letdown. Milk replacer and loose housing could to some extent, but not fully, mitigate the compromised welfare. Similarly to the other management strategies of large litters (nurse sow and artificial rearing), sow rearing of large litters with milk replacer raises significant animal welfare concerns. If pig producers continue to develop this management strategy further, studies should focus on the content of the milk replacer and the design of the milk cup to best fit the motivation and need of suckling piglets. Combinations with early life intervention may also be necessary. As an alternative to such an elaborate management system, pig producers may as an alternative consider using less prolific breeds. Yet, the high production efficiency per animal is a main argument for modern pig production to be sustainable from an environmental and economic perspective. However, there is a need to outweigh and balance these criteria of sustainability in a broader perspective, also including social well-being and animal welfare.

M3 - PhD thesis

SN - 978-87-93148-63-5

T3 - PhD Theses - Department of Animal and Veterinary Sciences

PB - Aarhus Universitet

ER -