Few areas of animal production have matched the productivity gains observed in sows over the last 3 decades. Current sow genotypes are capable of weaning up to 40 pigs per year. However, this increase in productivity has come at a cost, as sow mortality has steadily increased. Does the current knowledge about exact mineral supplementation to gilts and sows need an upgrade?

Of the total mortality of sows in the United States alone, 28.8% is due to lameness and an additional 28% is due to prolapses (Figure 1). Therefore, more than 56% of all sow death losses is due to issues that are influenced by dietary concentrations of calcium and phosphorus, which represents a direct loss of more than US$500 million per year. These numbers, however, do not include the number of sows prematurely culled or removed from the herd due to lameness or locomotion issues. The total cost of lameness and locomotion issues is, therefore, greater than the above number.

The greater prolificacy of sows is a result of advances in genetics, breeding practices, and management strategies aimed at increasing productivity and efficiency in pork production. Highly prolific sows presumably require more calcium and phosphorus in both gestation and lactation compared to pigs of less prolific genetics due to greater litter size, which increases mineral requirements for fetal growth and milk production.

There has, however, not been a corresponding adjustment in recommendations for calcium and phosphorus in sow diets, and very limited research has been conducted on mineral requirements of modern sow genotypes. As a consequence, it is necessary to revisit the requirements for calcium and phosphorus in sow diets. The objective of this article is to describe current knowledge on the calcium and phosphorus nutritional requirements for developing gilts and gestating and lactating sows.

Requirements for developing gilts

Requirements for pigs for slaughter are well established. Compared with pigs for slaughter, developing gilts may need more standard total tract digestible (STTD) calcium and STTD phosphorus and a different ratio between the two minerals. As a consequence, it is believed that the calculated requirements for developing gilts will result in animals with maximum bone ash at the time of breeding (Table 1). The estimated requirement to maximise bone ash, which is expressed as the STTD calcium to STTD phosphorus ratio, increases with the body weight of pigs.

Requirements for gestating sows

The calcium and phosphorus requirements of gestating sows are the sum of the requirements for maintenance, and maternal, placental and fetal growth.

The requirement for maintenance can be estimated from the endogenous loss of calcium and phosphorus. Recent data indicates that sows lose around 1,000 mg calcium per kg dry matter intake and around 750 mg phosphorus per kg dry matter intake. Requirements for maternal growth were estimated under the assumption that sows would gain 25 kg per reproductive cycle, in addition to the gains associated with the conceptus. Current calcium and phosphorus requirements for placenta growth are low and are based on only 2 reports from the literature. Requirements for calcium and phosphorus for fetal growth increase throughout gestation with the requirement being minimal before day 70 and then gradually increasing towards parturition. As a consequence, the requirement is lower in diets before day 90 of gestation than during the period from day 90 to parturition.

Assuming gestating sows consume 2kg, 2.5kg or 3kg of feed per day, depending on dietary energy concentration, the total requirements for STTD calcium and STTD phosphorus for maintenance, maternal growth, placental gain, and fetal growth were estimated for each level of feed intake and expressed as a percentage of the diet (Table 2).

Requirements for lactating sows

The calcium and phosphorus requirements of lactating sows are primarily determined by maintenance needs and requirements for milk production (Table 3).

Maintenance requirements can be estimated from the basal endogenous losses of calcium and phosphorus with a correction for minimal urinary loss, as was also discussed for gestating sows. There are, however, very few reports about the endogenous loss of calcium and phosphorus in lactation, but the endogenous loss of calcium is assumed to be 1,000 mg per kg dry matter intake, whereas the endogenous loss of phosphorus is estimated at 500 mg per kg dry matter intake.

The requirements for calcium and phosphorus for milk production depend on daily milk yield and the assumed concentrations of calcium and phosphorus in the milk. The concentrations of calcium and phosphorus in colostrum and milk of lactating sows have been reported from numerous experiments, but there is a surprising variation among summarised values from previous experiments, with calcium in milk varying between 1.51 and 2.54 g/kg and phosphorus varying between 0.87 and 1.83 g/kg.

In summary…

When reviewing the literature on developing gilts, there is strong scientific evidence for the calculations of their requirements. For gestating sows and lactating sows, however, the calculations relied on various assumptions. There is, therefore, a need for validation of the calculated numbers. Given the importance of calcium and phosphorus for sows in reducing lameness, prolapses, and mortality, this is an area that needs increased focus.

References available upon request.

*This article is an approved summary of the 5th chapter of the recent book ‘Nutrition and Production Strategies for Today’s Sows’, published by and available at Novus International.