If piglets are born overnight, they are often already eight hours old or more by the time the livestock handler starts work. In such cases, one can make use of their suckling behaviour by prioritising the transfer of piglets that do not have a fixed teat. If you are not entirely sure when selecting piglets, mark the piglets in question with a specific colour and observe them again at a later time (Fig. 3). Even after weaning, the piglets must still be kept under close observation to ensure success.¹⁴ However, if a small piglet in a large litter has a stable suckling position, it makes sense to leave it with its siblings.

If there are too many piglets per sow but no sows are (yet) available for litter balancing, one can, for example, in a litter of 17 to 18 piglets, confine the seven to nine largest piglets in the farrowing pen for about two hours on several occasions, whilst leaving the smaller piglets with their mother to bridge the gap. After several such intervals, the smaller piglets will also have had enough milk and will be more ‘confident’ compared to their littermates.^{12, 14}

However, alongside the many advantages of litter equalisation, there is also one major drawback: hygiene. Moving the piglets can also spread pathogens. In the worst-case scenario, this can lead to an infection spreading throughout the entire farrowing group. Nor should the potential stress on the piglets and sows be underestimated.

Whilst smaller piglets in particular benefit from litter equalisation, studies show that it is not necessarily advantageous for heavier piglets. These lose the advantage they have over lighter piglets in a mixed-weight litter, as they now have to compete with piglets of ‘equal strength’.^{15, 16} Furthermore, heavier piglets place greater demands on the lactating sow.

Some studies have also identified a link between litter equalisation and ear injuries¹⁷ or tail injuries/tail biting after weaning.^{18, 19} A further study by Calderón Díaz et al.²⁰ also found that litter equalisation influences pericarditis at the slaughterhouse. Another study classified frequent litter equalisation as a risk factor for the occurrence of PMWS (Post-Weaning Multisystemic Wasting Syndrome), the most common clinical condition resulting from a PCV2 (Porcine Circovirus 2) infection.²¹

Depending on when supplementary feeding of suckling piglets begins, it serves a different purpose. Early supplementary feeding of milk or milk replacer is primarily intended to keep very young piglets alive, for example, if the sow’s milk yield is insufficient or if small, weak piglets have less chance of securing a teat. Later supplementary feeding with prestarter, on the other hand, is intended to prepare the piglets for the upcoming change in diet at weaning and thus reduce the drop in weight gain following weaning.

The best feed for suckling piglets is sow’s milk. However, high numbers of piglets born per sow and litter require careful consideration of providing piglets with additional nutrients at an early stage. That said, this should not be started too early. All piglets should first consume colostrum, as the important protective substances cannot be artificially replaced.

It usually becomes clear within the first two to three days after birth whether piglets should be supplementary-fed. On farms with many live-born piglets, supplementary milk feeding is already standard practice.

It should be borne in mind that supplementary feeding may also result in overfeeding of strong piglets. In a study by Rohe and Hessel²², no benefits in terms of weight gain were observed in piglets with low birth weights following the use of milk cups (Fig. 4). From a birth weight of over 1.5 kg, the piglets benefited from the additional feed provided by the milk cups. The authors concluded that, contrary to expectations, it is not the lighter piglets that benefit from the cups, but the large, heavy ones.

From the first days of life up to the pre-starter phase, which begins around the third week of life, only liquid milk replacer should be used for piglet feeding.²³ After this, both liquid and dry feed mixtures can be provided. The composition of the supplementary feed must be tailored to the enzyme capacity of the piglet’s gut and therefore varies with the piglets’ age. In the first few days of life, the production of enzymes for digesting lactose predominates. The endogenous production of enzymes for other nutrients such as carbohydrates (e.g. starch), fats and proteins is very low at first and develops only slowly with increasing age. This also depends on the food available to the suckling piglet. Supplementary feeding of piglets, particularly from the 3rd or 4th week of life, therefore also serves as so-called ‘enzyme training’. A transition from milk powder to prestarter that is as gentle as possible can be achieved by blending the feed. In most cases, however, prestarter is offered as an additional option so that the piglet can choose. Further information can be found in the new DLG leaflets on piglet supplementary feeding.

DLG leaflet 485 "Stationary supplementary feeding systems for suckling piglets – Part 1"

DLG Fact Sheet 486 “Stationary supplementary feeding systems for suckling piglets – Part 2”

Another method of supplementary feeding involves the sow and piglets eating together from a trough or off the floor (Figs. 11 & 12). In this case, no special feed for suckling piglets is used, and the piglet eats the sow’s feed along with her. As a rule, they do not consume large quantities; the benefit for the piglet lies more in the fact that it learns to eat from its mother and its digestive tract is gradually prepared for solid feed.

Generally, one advantage of supplementary feeding with the sow’s own litter is that the reduced movement of piglets between litters and to foster sows reduces the horizontal and vertical transmission of diseases.

In addition to animal welfare considerations, the economic viability of supplementary feeding must not be overlooked. A key economic indicator for piglet production is the number of weaned piglets, which is determined by the sow’s high fertility and the reduction in suckling piglet losses up to weaning. The extent to which a supplementary feeding system is profitable depends on several operational factors as well as the cost basis used for the calculation. It is therefore not possible to make a general statement regarding the number of weaned piglets required for supplementary feeding to be economically viable. If simple supplementary feed troughs that are filled by hand are used, the investment costs are manageable, and running costs consist mainly of the milk replacer itself. However, the additional time required for manual supplementary feeding should not be underestimated. Mixing the milk replacer by hand and feeding, at best, small quantities several times a day takes a lot of time.

Full automation reduces the workload, but this comes at a price. The investment costs for the troughs, sensors, pipes and valves alone quickly amount to more than €160 per farrowing pen. Added to this are the costs for the mixing and distribution technology. Semi-automatic systems are slightly less expensive, with their technology limited to a timer-controlled pump and a bucket as a dosing container. A feeding system is available for around €650 including VAT.²⁴ Rohe and H²²essel concluded from their trial that automatic milk and prestarter supplementary feeding only breaks even if at least 0.65 more piglets per litter are weaned.

Natural foster sows are sows whose own piglets have already been weaned. They may therefore already be in their fourth or fifth week of lactation, meaning that the composition of their milk is no longer optimal for piglets in their first week of life. Young piglets may develop a deficiency in certain nutrients. Furthermore, the very high-fat milk can quickly cause diarrhoea. It is therefore essential that piglets consume colostrum before weaning so that they can absorb maternal antibodies and other important nutrients for a good start in life.

Even though piglets are not suckled by their own mother when reared by a foster sow, they can still be raised in a natural environment. Feeding on sow’s milk from a teat is the most natural behaviour. Other systems and the use of special piglet milk replacers always represent a compromise. As a further advantage alongside maternal care, foster piglets have the opportunity to learn behaviours such as drinking water from a bowl-type drinker from the sow.

Not only intensive litter balancing but also the transfer of piglets to foster sows can have a detrimental effect on animal health. Mixing piglets from different litters facilitates the spread of pathogens. Furthermore, the resulting stress has a negative impact on the immune system, making piglets more susceptible to disease.

However, piglets usually benefit from the use of a foster sow. Nevertheless, from the sow’s perspective, there are also disadvantages to consider. Even though the larger and stronger newborn piglets are generally placed with the foster sow, there is a clear discrepancy between the milk intake of the added piglets and the sow’s milk yield. The resulting milk pressure is painful for the sow and can lead to the new piglets not being accepted or even to the sow ceasing milk production entirely. Treatment with painkillers is therefore frequently administered.²⁶ Furthermore, there is a risk that the sow will be over-milked, leading to problems with rebreeding. The piglets’ live weight gain and the sows’ limited feed intake capacity often result in an energy deficit in the sows. To obtain additional energy for milk production, body tissue is therefore mobilised – accompanied by a loss of live weight in the sow.²⁷ In addition to regular monitoring of the foster sow’s body condition, the udder and teats should also be inspected, as the prolonged suckling period places considerable strain on the udder and teats.

If there is a surplus of piglets, if sows have insufficient milk, or if a sow dies and no foster sow is available, a two-stage foster system, as is common in Denmark, can be used.²⁹ In this system, the largest newborn piglets are reared by sows that have good milk production and have farrowed about a week earlier. The one-week-old litter is reared by sows that are currently being weaned (Fig. 15). A weekly cycle is therefore a prerequisite for this system.

However, it must not be forgotten that the lactation period for the foster sows is significantly extended. Therefore, the condition and milk yield of the foster sows should be checked regularly to ensure they are not overburdened.

Leave one or two of the sow’s own smallest piglets with her for up to 24 hours to help the new litter settle in. The presence of her own piglets is intended to have a calming effect on the sow, making it easier for the new piglets to bond with their foster mother.

A practical recommendation for cases where individual piglets rather than whole litters are to be transferred is to confine the two new piglets with the existing piglets in the farrowing pen for one hour. Beforehand, they can be rubbed against the foster sow’s vulva to help them adapt to her scent as quickly as possible.¹⁴

Staggered replacement is another way of positively influencing the acceptance of the new piglets. For this, the first half of the old litter is swapped for the new litter in the morning, and the second half in the evening.⁹ An oxytocin injection is also said to stimulate bonding with the new litter. However, the use of this hormone should always be discussed with the vet to avoid unnecessary hormone administration.

Foster sows must first become accustomed to the pen before they are given other sows’ piglets. Ideally, the sow should remain in the pen where she raised her own piglets. However, this means that the pens cannot be operated on a first-in, first-out basis.

For all-in/all-out pen allocation, a separate pen for foster sows can be set up, which, unlike standard pens, is usually occupied continuously. The sows serve as foster sows for as long as their milk production is sufficient. However, the foster sow should have the new piglets for approximately 8 to 24 hours before being moved to a new pen. New pens with unfamiliar odours due to cleaning and disinfection, combined with new piglets, can overwhelm even the most docile foster sows.¹⁴