Effective cross-fostering maximises rearing capacity

John Richardson of the Garth Partnership discusses the use of cross-fostering to maximise pig output.

As litter size increases, the need for good cross-fostering skills and other alternative ways of rearing additional pigs become more important. Selecting gilts with a minimum of 14 functional teats is a prerequisite for highly prolific sows – and different breeds show a correlation between litter size and teat number. Even with 14 functional teats, there will be occasions in every batch of farrowed sows where the number of live born pigs exceeds teat numbers, or piglets start to fail – so fostering will be necessary.
In order to cross-foster successfully, it’s important to understand lactation and the suckling process – so working with, rather than against, a natural process.
Colostrum production commences a few days prior to farrowing; within 6-12 hours pre-farrowing, and certainly during farrowing colostrum can be readily expressed from the teats. Milk production results from a surge of the hormone prolactin, but milk can only be removed from the teat by the release of another hormone – oxytocin – stimulated by the sucking/nuzzling action of piglets.
Sows limit the amount of milk piglets can consume at each feed, helping prevent digestive upsets, hence she feeds them 20-30 times a day on a little-and-often basis. Sows alert the piglets by grunting and lying on her side to expose the udder; piglets then nuzzle the udder causing oxytocin release and milk ejection starts 25-30 seconds later, but only lasts for 15-20 seconds. They then continue to nuzzle the udder for several minutes, stimulating further prolactin output. Refilling of each milk gland is complete by 30-40 minutes after emptying, in readiness for the next feed.
The above suckling routine is established within 12 hours of farrowing; teats are adopted by piglets within hours of birth and are kept until weaned. Surplus teats that are not suckled do not get adopted by other piglets and so dry-off within three days. This means that successful cross-fostering will only be achieved by adding pigs onto non-suckled teats on day one of lactation. There may be limited success on day two, and no success on day three.

Colostrum
It’s vital that piglets take colostrum from their birth mother for six hours in order to gain specific dam-offspring protective cells; split suckling will ensure all piglets get a share of these vital cells and antibodies.
Thereafter, initial fostering must be done within the first 24 hours. Gilts are a priority and should have all 14 functional teats suckled in order to induce mammary development that will determine milk yield in successive lactations. Then count the number of spare teats available on other sows; choose sows with good teat placement, exposure and shape – thick, stubby or damaged teats are not suitable.
If there are surplus teats available, then transfer a piglet that’s slightly larger than the resident piglets to give it a better chance of adopting its own teat. This process needs to be done both am and pm on farrowing days.
If there are large numbers of small pigs (<0.9kg) then make up a litter of these pigs and foster them onto a gilt/parity-two sow with small teats that are well presented during suckling to optimise survival rates through reduced competition.
Subsequent fostering from day four onwards involves the early detection and action taken on pigs failing to thrive due to lack of milk intake. Failure to thrive may not be due to a lack of milk, but caused by lameness, infection or scours. These must be addressed first.
 Individual pigs can be moved to another litter if a teat becomes available due to a piglet death; if, however, there are a number of small or poor-doing pigs, then shunt-fostering is advised as detailed in Table 1 below.
It may be necessary to move the foster sow to a different farrowing room in order to maintain the same piglet age within the room assisting all-in/all-out management.
A potential disadvantage of the one-step system is that the large sudden reduction in milk output can result in sows showing oestrus during week five of lactation.  
Results from Danish trials comparing the one- or two-step nurse sows showed that the two-step approach resulted in more and heavier pigs being weaned as shown in Table 2 below.
Parity one and two sows were shown to be better foster mothers than higher-parity or cull sows; younger sows, however, do need feeding well to prevent loss of body condition and reduced fertility.
The time at which individual pigs are fostered onto an existing litter can also influence success. Either put the foster piglet onto the litter just as the sow ‘grunts-up’ the piglets and before actual feeding starts, or fasten the foster piglet in the creep area with the other piglets for 1.0-1.5 hours so that the foster pig smells the same as its new littermates, so reducing risk of rejection, also so they’re all eager to suckle when released. A small dose (0.5ml) of Oxytocin-S can also assist milk let-down for newly fostered pigs.

Rescue decks
Batch farrowing and all-in/all-out health programmes may mean that the use of foster sows is not possible, or alternatively there simply may not be enough spare teats for the extra piglets to suckle. In such cases rescue decks provide a good alternative.
Siting the rescue decks above the farrowing pens enables the pigs in these pens to benefit from the ‘grunting-up’ activity when the sow suckles her own pigs – this stimulates the deck pigs to feed as well. Pigs housed in the rescue decks must have received colostrum and preferably suckled for 2-3 days; it also helps if larger pigs are selected to be housed in the rescue decks – the result being that more pigs are weaned with a heavier total litter weight.
Alternative systems such as Nurtinger decks and piglet bowl drinkers using Primary Supp-le-milk are also well worth using to help sows rear increased weights of pigs at weaning.
Whatever form of fostering is utilised, to cope with larger litters timeliness is all important – the golden rule is foster the pigs when they need moving and not when you feel inclined to do it.

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