The appropriate use of fostering will help to minimise the numbers of piglets that die before weaning and also ensure good growth and development.

Modern 21st century prolific hybrid sows produce both higher numbers of viable piglets born alive and have the potential for up to twice the milk yield of breeding sows that served the industry some 30 or 40 years ago.

These so called hyper-prolific strains of breeding sows now make it possible for the suitably equipped producer, who possesses the necessary ability and skills, to achieve a consistent output of 32 pigs per sow per year.

Udder considerations

The modern sow’s udder is a resource that has the potential to feed 30 plus piglets per annum from a birth weight of around 1.4 kg to a weaning weight of 8 kg in the fourth week of life. This represents an annual piglet weight gain of about 200kg/sow to weaning and using a typical sow milk weight to piglet gain ration of 4:1 it equates to an annual yield of 800 kg of milk produced per sow and consumed by the 30 piglets weaned. 

In practice there will also be some contribution from high quality creep starter diets and liquid milk substitute feeds, but the majority of this growth will be milked directly from the sow’s udder.

The piglet is born with a powerful innate urge to get to the udder within minutes of birth and to take its first intake of essential colostrum. Practical observation and detailed scientifically controlled behavioural observation studies all illustrate that some piglets get to the udder, find and select a teat and commence suckling (unaided), within as little as three minutes of emerging from the womb.

However, there are also a good number that have still not suckled within 30 minutes or even after an hour or more. This delay can be due to the piglet not having the strength/energy to get to the required position on the udder and to get hold of a teat, or because there are too few teats available.

These piglets will suffer both from inadequate passive immunity through an inadequate intake of colostrum and probably be presented with the ‘availability’ of less productive teats. The fact is that as we produce larger litter sizes, we also need to maintain the average individual piglet birth weight and this can only be done by increasing the litter weight at birth.

This has been achieved, but there remains a typical variation in birth weight from <0.8kg to >1.8kg. The larger, stronger piglets thus have a better chance of suckling early and for taking in the essential >100 ml of colostrum necessary for a good start in life. Larger piglets will also fight over the favoured teats and this can delay their intake of colostrum. This is more likely in the larger litter where there may be less functional teats than piglets.

Fostering piglets onto sows that appear to have fewer piglets than functional teats at this early stage has been and remains an effective tool, as is split-suckling during the first hours of life. Care needs to be taken in ensuring that all piglets fostered from and into a litter take in sufficient quantities of colostrum prior to making the move, or are moved within a few hours of birth and obtain colostrum from the foster sow and must then also be within hours of birth.

Managing the fostering process requires a high degree of skill, combined with common sense, along with the use of previous individual sow records and a good understanding of piglet teat selection behaviour and its consequence for the piglet’s growth and development.

Before considering the fostering techniques being used on the increasing number of 30-plus top performing herds, it is worth considering some basic facts relating to how and why the piglets behave as they do and the implications for effective fostering procedures.

Udder behaviour

There have been relatively few studies of individual piglet behaviour from the moment of birth to weaning (and beyond). Such studies demand easy, clear and accurate identification of individual piglets and constant observation over at least the first 24 hours and for regular prolonged periods through to weaning. It was long the perceived wisdom that the larger stronger piglets at birth suckled the teat pairs nearer the head and the smaller/weaker born piglets were relegated to the poorer teats towards the sow’s rear.

Very detailed observational work carried out by Onderscheka in 1969 provided us with some valuable indicators of what actually takes place during the very short period after (and during) birth, when piglets select and maintain their place on a particular teat.

In this study the udder was numbered with the most forward teat position being numbered one and the rear teat pair as seven (the frequently present eighth pair was included under seven).

Individual piglet birth weights and individual weaning weights were allocated to the primary teat suckled. This is highly reliable because milk release (let down) during suckling occurs over a period lasting about 15 seconds and usually no more than 30 seconds, making it difficult for the individual piglet to effectively suckle two teats, but there are some (10%) that attempt it.

Figure 1 shows that by using an index to relate the birth weight to the weaning weight at each teat pair udder position yielded a couple of interesting tendencies.

It clearly illustrates that larger piglets do select the more forward teats (pairs one and two) and that the piglets on teat pairs three, four and five were significantly lighter at birth. However, it also clearly shows that the piglets that ‘chose’ the teat pairs furthest towards the rear (six and seven) were on average at least as heavy as those that chose the front teats.

However, the above average piglets that ‘chose’ to suckle from the sixth and seventh teat pairs suffered a considerable reduction in growth rate and actually had lower weaning weights (5% to 8% lower) than the lighter litter mates who selected teats in the middle. It is important to remember that when the sow turns over the teat positions change from top to bottom – the piglet follows its own teat and its suckling behaviour is not related to being on top or underneath.

The two trend lines in Figure 1 illustrate this distribution of birth weights across the udder in comparison to the virtually linear reduction in weaning weight from front to rear.

Teat popularity pattern

To this we must add that the front teat pairs are far more popular than those at the rear and detailed observation work we carried out over a five-year period with large teams of students and involving about 12 litters per annum (60 in all) in an attempt to verify the above pattern in sows (then weaning 23 pigs per annum), produced the teat popularity pattern shown in Figure 2.

The piglet birth weights and weaning weights related to the teat position selected and suckled over the five-year period in the 1980s produced a pattern almost identical to Onderscheka (1969). The first sow group used was weaned close to the fifth week of lactation with the pattern remaining the same, but with a more pronounced effect. The various trials also suggested that the heavier piglets at weaning had consumed more creep feed than the piglets on teats with poor milk output and that it appeared to be a factor in making the variation in weaning weights even greater than it was at 21 days. There was no apparent difference in variation in weight resulting from creep intake prior to 21 days.  Recent research also continues to suggest that supplementary feeding either a high quality dry starter diet or a milk supplement (i.e. whilst suckling) does not reduce variation in piglet weaning weights during the first four weeks of life. The benefit of creep feeding is principally the potential to improve overall growth rates after weaning.

Figure 3 illustrates that this pattern occurs even with a very small sample (11 litters) and this was repeated very closely with subsequent annual batches over a further four-year period.

The trial included recording individual birth order and status at birth. Every individual pig was ear marked in birth order, with weight, gender and general status being recorded. Each one was also clearly marked with its birth order number on its back for immediate and continuous identification.

The 11 litters in this study also included piglets that were both fostered into and from individual litters, as appropriate, in order to even up the numbers on each sow. Apart from the close observation and additional handling, e.g. taking regular weights, etc., the piglets were managed conventionally.

It is absolutely clear that the primary teat the piglet suckles and its position on the udder has a pronounced effect on its growth and development. The fact that some of the larger piglets tend to make the wrong choice and to choose to suckle a teat at the rear results in some reduction in the variation in weaning weight compared to birth weight is clearly illustrated in Figure 3. The larger piglets that suckled at teat pairs six and seven may have been influenced into making this territorial choice through fights and squabbles with their equally large siblings.

This fighting behaviour tends not to last much beyond eight hours following farrowing in healthy sows that are milking normally. We found that over 90% of piglets were locked onto their teat at every feed by the eight-hour stage. Their own adopted teat is defended vigorously and where there are more piglets than teats, then it is clear that we must intervene or accept high mortality rates.

Split-suckling and fostering techniques

Visiting pig farms already experiencing 30-plus performance, experiencing the techniques they adopt and discussing how and why they carry out certain procedures is probably the best approach to learning the best practices for achieving and even exceeding the 30 pigs per sow per year performance level. The following approaches are based on those being applied on farms in Denmark and Germany that are already at these exceptional levels of productivity.

All of these farms farrowed sows in large batches, some weekly and some based on a four- or even five-week batch cycle. The larger sow farrowing group facilitated by these batch farrowing systems provides for good fostering possibilities, with almost all of the piglets in the farrowing accommodation within a seven- to 10-day age range.

Split-suckling is a useful technique for the large individual litter and can help gain time before the excess piglets are fostered to even up and optimise the number of piglets on each sow. Split-suckling involves confining the first born and or large pigs in a heated box (crèche) and then allowing the smaller and later-born piglets to suckle without competition for about one hour and at the most two hours (it may be best to repeat this for two one-hour periods). Once all of the piglets have had at least four good suckling sessions to ensure a good colostrum intake, then they can be fostered as required.

Fostering for an ideal number

Fostering a piglet to provide the sow or gilt with the ideal number of piglets should ideally take place within the first 24 hours of life and before the end of the second day of life.  There are good reasons for this advice and it is clearly based on the fact that the selection of a teat occurs within hours of birth and a sow with a spare teat will no longer be able to produce milk from that teat after about three days.

Trials into fostering after the piglet is 3 days old show that the mortality rate and growth rates all deteriorate. In this case we need to be certain that a functional milking teat is available after the third day (perhaps when a piglet on the foster sow has been accidentally overlain) prior to attempting to foster after this stage.

However, there is some evidence to suggest that unused teats produce less milk in subsequent lactations and fostering will thus enhance a sow’s lifetime milk production.

Piglets that are to be fostered must be big enough and strong enough to adopt a teat in the new litter.

Fostering should be carried out to allocate the ‘ideal’ number based on previous individual sow records and for gilts to suckle 13 piglets. Extensive cross-fostering where piglets are allocated into evenly sized litters of almost equal weights does not lead to an overall reduction in the variation in piglet weight and will probably reduce the overall average weight at weaning. Some workers suggest that a more limited approach, where only the minimum number are fostered to allocate the ideal number per litter, will also produce higher numbers weaned.

Even though these top performing farms batch-farrow large numbers of sows in groups, they also continue to experience the problem of having more piglets than the total number of teats available. Where they operate a four- or five-week batch farrowing cycle (i.e. all sows farrow within a week every fourth or fifth week), they have fewer options than the farms where there is a weekly or fortnightly cycle and will need to resort to some artificial rearing using high quality piglet milk substitute.

Using first litter gilts

Where farrowings take place more regularly, a popular and effective approach in Denmark is to use first litter gilts for this purpose and to extend their lactation from the usual third week to the fourth or fifth week (i.e. up to 35 days).  The gilt’s own first litter is weaned at 21 days and the gilt takes the complete litter from a sow that farrowed five to seven days previously. The gilts are all given 13 large piglets to rear when they farrow and they can then usually take up to 13 piglets in their foster litter. The sow is then used to foster the excess newborn piglets.

The typical average weaning age is 25 to 28 days for sows and as a result of a good proportion of gilts being used as complete litter foster mothers, the average lactation length in gilts is 32 to 35 days. This longer lactation period for first litter gilts appears to be beneficial for their subsequent reproductive performance.

High density lactation diets with added fat are essential to achieve the required nutrient intake in the sows and gilts and these are best fed as a liquid diet to achieve the 10kg to 11kg of dry feed intake equivalent required by each sow in the latter half of lactation. The gilts must also be 160kg and nine months of age at first mating.

Litters are constantly assessed for the need to foster and appropriate measures taken to ensure that mortality rates are lowered.

A farm in Germany using a five-week batch farrowing cycle (i.e. farrowing every fifth week) is required to keep to a tight batch farrowing period (<7 days) and this makes the use of extended lactations in gilts or sows inappropriate (unless the sow is destined to be culled for reasons other than the number of pigs reared).

In this case the largest and oldest piglets (7 to 10 days of age) are weaned and reared using a highly effective sow milk substitute diet in a piglet crèche. The sow can then be used to foster on a complete litter made up from the strongest piglets from the later farrowing sows and gilts.

Both of these approaches involve the additional cost of either the extra time spent lactating (fewer litters per annum), or the cost of the specialist milk based emergency rearing diet and the crèche facilities. The opportunity cost of doing so needs to be monitored and considered based on the value of the additional piglets sold set against the cost of any special rearing procedures. Where this is carried out well, the results will invariably show a positive return for the effort invested. 

Fostering piglets successfully is the key to releasing the tremendous potential of the udder in the modern highly prolific sows that are now available to us.

Excellent observation skills have always been an integral part of what makes a good stockperson. Thus some people appear to have an innate ability to foster piglets effectively, whilst many of us have to learn to adopt effective procedures based on sound advice and training. Developing an understanding of what happens on the sow’s udder and how the piglets behave is an essential aspect of learning to foster and rear more piglets.

Making good use of the sow’s udder always has been and remains the key to rearing more piglets with good weaning weights.