Milk supplementation in the farrowing room: an alternative strategy with hyperprolific sows?

A key index for evaluating sow productivity is the number of piglets weaned per sow per year. Due to the physiological limitations of increasing the number of farrowings/year, in the last decade genetic progress has been oriented towards increasing litter size, selecting female lines considered "hyperprolific". However, the increase in prolificacy has created new challenges in the management of the sow and her litter. In this context, defining the optimal compromise between litter size and litter vigor remains a key point to ensuring piglet survival and consequently increasing the number of piglets weaned per sow per year.

It is known that litters of hyperprolific sows are associated with lower average birth weights and high variability of weights within the litter. This leads to non-homogeneous physiological development between siblings during the lactation phase, which makes post-weaning management complex. Ocepek et al. (2017) observed that piglets from large litters spend more time stimulating the udder, which leads to excessive energy expenditure that can significantly compromise neonatal vitality and their ability to survive in the lactation phase. This behavior is associated with a decrease in the functional teat to piglet ratio, which increases competition for teat access, causing frustration, which is a risk factor for piglet health, especially for piglets that are not dominant. The condition of frustration is not just associated with the risk of malnutrition; in fact, social stress can increase the secretion of glucocorticoid hormones with a negative impact on the physiological and immunological development of piglets, contributing to reduced pre- and post-weaning robustness.

To reduce the risk of malnutrition, as well as competition, strategies such as the provision of solid feed during lactation (creep feed) have been implemented; the formulation of the pre-starter feed, its physical characteristics and the design of the feeder, have received much attention (Van Hees et al., 2019; Wattanakula et al., 2005; Middelkoop et al., 2019; Van den Brand et al., 2014). However, the enormous variability in solid feed intake still represents the main limitation of this feeding strategy, especially if it is aimed at managing the problem of supernumerary piglets' competition for teat access (Bruininx et al., 2002).

An alternative strategy that is gaining popularity on intensive farms is the use of milk supplementation (MS) in addition to the sow's milk. In fact, as observed by Huting et al. (2021), during the first two weeks of lactation, almost 51% of the litter start ingesting MS compared to the 5% that approach solid feed. Recent evidence suggests the positive effect of MS on weight and ADG at weaning (Novotni-Dankó et al., 2015; Middelkoop et al., 2002) as well improved growth of lighter piglets (Douglas et al., 2014). Despite this, a recent study presented at the ASPA 2021 conference by Trevisi et al. found no differences in pre- or post-weaning performance, although it describes a favorable effect of MS supply distributed with automatic system for at least 12 hours per day, starting at 5 days of age and for two weeks, on mortality of pre-weaning piglets with respect to the same milk administered twice daily in containers fixed to the stall floor or to the sow's milk alone.

Although with different formulations of MS, Novotni-Dankó et al. (2015) have described a reduction in preweaning mortality using MS from 10 days of age to weaning. The authors hypothesize that constant access to MS may improve the nutritional status of the piglet, favoring vitality and reducing the risk of crushing during the first fifteen days of life. There are many differences among the various studies; as described in Table 1, MS can differ significantly in their nutritional profile and formulation; in fact, the products available on the market can be subdivided into two categories:

1. Powdered milk
2. Powdered milk-based complementary feed

*The percentages of sow's milk components are expressed as a percentage of total solids, equivalent to that of milk supplements with total solids of 86%.

In light of the data available in the scientific literature, the effect of the route and timing of administration, as well as the daily availability of MS, needs to be further investigated, although it seems that the effect is better when milk is offered from the first week of life until weaning, as the continuous availability of fresh MS would allow for a better nutritional status of the piglet.

On the other hand, there are almost no data on the effect of MS on the intestinal health of the piglet. Recently, Trevisi et al. (2021) have observed the ability of a reconstituted milk powder to maintain a higher intestinal microbial diversity compared to a milk-based complementary feed during the lactation phase. This is an aspect considered favorable for improving piglet resistance to colonization by pathogenic bacteria during post-weaning phase. Finally, the management of the MS and the equipment used to prepare and supply it is fundamental to controlling the risk of pathogenic bacteria proliferation in a substrate rich in protein and, many times, high in lactose. In this regard, there is no scientific data available, but experience has shown this risk linked to biosecurity within farms.