Cross-fostering Piglets on Commercial Sow Farms

Livestock Update, April 2001

Allen Harper, Extension Animal Scientist-Swine, Tidewater AREC

Fostering piglets from one sow to another within a farrowing group has been an established swine husbandry practice for many years. The purpose is simple, to reduce within-litter weight variation among piglets and to more evenly match the number of piglets with the sow's ability to nurse them. For example a first litter gilt may give birth to a large litter but, due to limited number of teats and milk production capacity, the gilt and her birth litter may perform better if a some of her pigs were fostered to a sow or sows with adequate teats and milk production.

A lot of what we know about cross-fostering piglets comes simply from the observations of experienced producers and farrowing barn managers. Interestingly, there has also been a substantial amount of practical research conducted on the behavior of suckling piglets and how cross-fostering can impact the sow and her litter. We know from research, for example, that piglets within a litter establish "teat fidelity" within 2 days after birth and each piglet within the litter will have a strong tendency to nurse the same teat throughout lactation. It is believed that the development of teat fidelity helps to prevent fighting and confusion among piglets during the 20 or more nursing periods that occur in each day throughout lactation.

With the increased use of segregated early weaning programs that place emphasis on weaning large numbers of heavy, uniform weight pigs at very young ages, there appears to be more frequent use of cross-fostering throughout the nursing period. Done properly, cross-fostering can be beneficial to sow and piglet performance. However, if done improperly or excessively, cross-fostering can have negative consequences. Swine researchers S. Robert from Quebec Province, Canada and G. P. Martineau from Toulouse, France reported on a study they conducted to assess the consequences of multiple cross-fostering of piglets throughout an 18 day nursing period (J. of Animal Science 79:88-93 [January 2001]). Their study teaches an important lesson about repeated cross-fostering and how it can affect both sows and litters.

In the study, litters produced from sows in farrowing crates were standardized within 26 hours of birth at 9 to 11 piglets per litter. There were 27 litters total, 13 litters designated as un-fostered controls and 14 litters further divided into 7 sow and litter pairs to be involved in cross-fostering treatments. On days 1, 4, 7, 10, 13, and 16 of lactation all piglets in the study were individually weighed within a 5-gram accuracy. After each weighing, three heavier weight pigs from the lightest litter in each sow and litter pair group were cross-fostered with three of the lighter weight pigs from the heaviest litter in the sow and litter pair. The researchers then carefully observed and recorded the behavior of all piglets in the study for 2 hours immediately after weighing and cross-fostering. Identifying marks were placed on the piglets to indicate if they were "resident" or "adopted" pigs in a cross-fostered litter. Pigs in the un-fostered litters were called "controls."

Some important and statistically significant observations in the study were as follows.

• During the 2-hour observation period after cross-fostering, the number of piglet fights were more frequent in the fostered litters than in the control litters on days 4, 7, 10, 13 and 16. On day 1 there was no statistical difference in fighting frequency between fostered and control litters. This effect was still present during an observed nursing period 21 to 27 hours after the piglets were cross-fostered on every day except days 1 and 16.
• At all ages of cross-fostering except day 1, fights at the udder were more frequent between resident piglets and adopted piglets than between two resident piglets or between two adopted piglets. At day 1 the frequency of fights between two resident piglets was similar to the frequency between a resident and adopted piglet, both of which were more frequent than between two adopted piglets.
• The number of piglets showing face and body lacerations 2 hours after adoption was significantly greater in cross-fostered litters than in control litters.
• During the 2-hour period after adoption, piglets vocalized more in the cross-fostered litters than in the control litters at all observation times except during day 1. Within the cross-fostered litters, adopted piglets vocalized more frequently than resident piglets.
• For the first two hours after cross-fostering, the percentage of nursing periods during which adopted pigs were present with a teat in the mouth was only 66%.
• Based on video recordings of the first 15 hours after adoption, the number of nonproductive nursing periods with no milk letdown was more frequent in cross-fostered litters than in control litters on all days except day 1. And the percentage of time that the sow spent laying on her side was 15 to 30% less for sows with cross-fostered piglets as compared to control sows.
• Sows with cross-fostered piglets snapped more frequently at piglets than did control sows on all days except day 1. And this aggression by the sow was directed more frequently toward adopted piglets than toward resident piglets.
• Adopted piglets were 13% lighter at days 13, 16 and at weaning on day 18 than control piglets. Resident piglets in cross-fostered litters were heavier than adopted piglets at days 16 and 18, but tended to be lighter than control piglets at weaning time. Therefor, in terms of weight gain during lactation, cross-fostered piglets were more negatively affected than resident piglets, but there was some negative affect of repeated cross-fostering among resident piglets as well.

In this study repeated cross-fostering of piglets after an initial cross-fostering act at day 1 of age had measurable negative impacts on piglets and sows. For piglets these negative impacts included negative behavior such as increased fighting resulting in more face and body lacerations, more vocalizations indicating distressed piglets and less effective nursing time for cross-fostered litters. Repeated cross-fostering translated into poorer growth during lactation for adopted piglets and, to a lesser extent, for resident piglets within cross-fostered litters. Negative effects for sows included more aggressive acts toward piglets, less time lying on her side to expose the udder and a greater frequency of nonproductive nursing periods.

Even on large swine breeding farms that practice early weaning systems, it appears that traditional rules of cross-fostering still apply. These include ensuring that piglets receive colostrum rich first milk from their birth sows before transferring. This may require leaving piglets with their birth sow for 4 to 6 hours before transferring. And transfer of piglets should occur before they are 24 to 48 hours old, preferably to a sow that has also recently given birth so that teat fidelity among piglets is not firmly established. Once transferred it is desirable for resident and adopted piglets within the litter to establish teat fidelity. And preferably the newly established litter would be kept intact without repeated cross-fostering until weaning time.

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