Phase feeding of sows in gestation

The objective of modern pig production is to maximise the quantity and quality of pig meat produced per sow per year – or per lifetime – at minimal cost. The first step is to ensure that the sow produces an adequate number of piglets per litter, per year or per lifetime. The nutrition and management of the sow during gestation is therefore critical in achieving these objectives.

During gestation the objectives are to feed the sow to ensure a litter size of at least 14 quality piglets, a specific gain in body weight and backfat thickness, as well as to attain a body condition score of 3.5 at farrowing (scale 1–5).

The amount of feed usually provided to sows during gestation is based on their energy requirement and the energy content of the diet (30 MJ ME/day provided by a diet containing 12.5 MJ ME/kg requires 2.5 kg feed/day). In terms of amino acids, it is assumed that lysine is the most limiting amino acid and if its requirement is known, as well as the quantity of feed provided, then the lysine content of the diet can be calculated (15 g SID lysine/day to be provided by 2.5 kg feed necessitates a diet containing 6 g SID lysine per kg). Most current amino acid requirements are based on standardised ileal digestibility (SID) values as these better reflect the amino acids available to the animal by taking into account the amino acids that are not available for digestion as well as the basal endogenous losses in the gastro-intestinal tract.

Energy and feed requirements

The priorities and requirements for nutrients change during gestation and this will influence the amount of feed to be provided. Figure 1 illustrates how the feed requirements change.

* Sow in ideal body condition (score 3.0-3.5) during gestation
Figure 1. Priorities for feeding the sow in gestation: 140 kg body weight at mating* (after Foxcroft, 2009)

In early gestation (Day 1–28) the objective is to ensure the maximum number of quality embryos, as well as to replace the body reserves of the sow lost during lactation and in the period between weaning and mating. For sows that have lost considerable body reserves and body condition, increasing the feed allocation may be beneficial. This is to attain and sustain the correct metabolic and endocrine status vital to successful embryo and foetal development and survival. For example, Hoving et al. (2011) showed that increasing the feed allocation from 2.5 to 3.25 kg/day in sows that had lost considerable body weight increased litter size from 13.2 to 15.2 piglets per litter. However, once these losses have been restored and body condition has been improved, then normal levels of feeding can be resumed.

In mid gestation (Day 29–84) there is a 2–3 MJ/day increase in energy requirements that can be met by a 0.15–0.20 kg/day increase in feed provided. Most of this increase is for maintenance and maternal body gain to ensure that the animal maintains the correct body condition.

In late gestation (Day 85–115), when most of the foetal and mammary growth occur, there is a significant increase in the nutritional needs of the sow and it is common to increase feed allocation by 0.5 kg/day or more, depending on the body condition of the sow and the environmental conditions. This also ensures that the sow does not become catabolic during this period, as this will influence foetal growth resulting in piglets of lower birth weight and a greater variation in birth weight of the litter.

Some idea of the change in nutrient requirements during early/mid and in late gestation is given in table 1 for sows of different parities, and hence body weight at mating, as well as differing rates of body gain. It is obvious that there is an increase in requirements as gestation progresses with the differences in estimates between the 2 sources primarily relating to differences in the body weight at mating and the weight gain of the animals.

Table 1. The energy and lysine requirements of sows of different body weight at mating
and body weight gain during gestation (a = GfE, 2006; b = NRC, 2012)

Amino acid requirements

If the lysine needs of the animals are known, then the requirements for the other essential amino acids can be based on the ‘ideal protein’ principle. In the past it has been assumed that this ratio remains constant during gestation. Most modern estimates of amino acid requirements are based on modelling principles and these show that the requirements not only change with the stage of gestation, but also the parity of the sow. For example, relative to lysine, there are large differences in the balance – and especially for threonine, tryptophan and methionine+cystine (table 2). This may be explained in that during early and mid-gestation the major requirement is for maintenance and maternal protein gain, whereas in late gestation the demands for foetal and mammary development increase and the amino acid balance may need fine-tuning. In addition, in older parity sows a greater proportion of the amino acid needs is for maintenance and this, too, alters the ideal protein ratio.

Table 2. Balance of essential amino acids in gestation: % relative to lysine (based on NRC, 2012)

The extent to which the balance of amino acids change has recently been reported for threonine by Professor Ron Ball and colleagues at the University of Alberta, Canada (Table 3) who commented that threonine, rather than lysine may be the first limiting amino acid for sows in late gestation. The pattern of other amino acids is currently being evaluated. The consequences of the changing amino acid requirement may call for different diets during gestation, though the effects on piglet growth and development need to be further assessed.

Table 3. Total lysine and threonine requirements of gestating sows (g/day)
(Samuel et al. 2010; Levesque et al. 2011; Moehn et al. 2012)

* Previously assumed to be 70-80%, irrespective of stage of gestation

Based on this recent information table 4 shows the changing lysine and threonine content of diets for sows of different parities and stages of gestation.

Table 4. Lysine and threonine content (g/kg) of diets during gestation*

* Based on values provided in Table 3 and normal feed intakes

Conclusions

The nutrient requirements of the sow change during gestation and the feed provision must meet this demand; hence the need for phase feeding. In terms of energy, a one diet-strategy may suffice (12.5 MJ ME/kg), with the levels increasing at day 85 of gestation. The amino acid requirements, too, increase, though there may also be a change in the balance of amino acids between early/mid and late gestation, as well as parity, and this may necessitate a diet of differing amino acid composition.

The practicality of feeding different diets should be possible in a computerised sow feeding station. Alternatively, a basic gestation diet may be fed with a ‘top-dressing’ supplement provided from day 84 of gestation. The question remains whether such a strategy will lead to improvements in sow reproductive performance and piglet quality and whether it is cost-effective. This needs to be tested in commercial production systems.