Phosphorus and bone: An alliance for sustainable mineral management in pig farming

Authors: Julien Heurtault, Guy Maïkoff, Patrick Schlegel and Marie-Pierre Létourneau-Montminy, Agroscope (Switzerland), Université Laval (Québec)

Article published in Porc Québec, June 2024, Volume 35, Page 45 and 45

In Quebec, the Agricultural Operations Regulation (REA) requires pig farmers to balance phosphorus levels on their farms, which can be a real headache in some regions. On the other side of the Atlantic, in Switzerland, it’s the same story: new rules aim to further balance the phosphorus balance in agriculture. A Swiss-Canadian research project is studying the subject.

Phosphorus is essential for pig health, but it can also be harmful to the environment, especially when there is too much of it in the fertilizers used on farms. In Switzerland, by 2030, surplus phosphorus in agriculture will have to be reduced by 20% compared to the average use between 2014 and 2016. This will have to be done directly on farms. That is why the pig industry is looking for ways to reduce surplus phosphorus. It can do this by reducing the quantities of phosphates imported for pig feed and by ensuring that the feed given to the animals contains just the right amount of phosphorus, not more, not less.

Phosphorus requirements of sows

In this project, an international team of researchers from Agroscope and Université Laval is looking at the phosphorus that sows need, the kind that is digestible. Basically, this phosphorus is necessary for everything from body structure, bone growth, to allowing the development of the young during gestation and lactation.

Currently, it is thought that the only way for sows to get this phosphorus is through their food. Is this really the case? To understand this, we need to take the example of energy. When a sow needs energy, she can draw on her food, but also on her body reserves, such as fat. Is it the same for phosphorus?

To gain a clearer picture, the researchers used a tool commonly used in human medicine to diagnose osteoporosis to scan the sows and see how their body reserves changed over time, particularly in terms of bones. At the Agroscope site in Posieux, a dual medical X-ray scanner was adapted to scan sows. The researchers followed 24 sows during lactation, followed by gestation. During lactation, they received different amounts of phosphorus in their feed, to simulate different levels of phosphorus deficiency. During gestation, they received feed providing nutrients according to the usual European recommendations.

Bones as a phosphorus sink

What they discovered is that during lactation, sows were able to draw phosphorus from their bones to provide enough phosphorus to their young through milk, even if they were only given half of what they normally would. At the beginning of the next pregnancy, when they needed less phosphorus, their bones were able to remineralize. With this type of feeding strategy during lactation, the researchers were able to reduce the use of phosphates, a non-renewable resource, by 75% and phosphorus discharge by 40%. This gives hope for reviewing how we calculate the phosphorus needs of sows and for issuing new recommendations. The researchers are continuing to work to confirm these results, to see if it also works with sows that have already had young and to verify the effects over several lactations.

Current research

Agroscope’s pig research group is investigating environmental issues related to phosphorus and nitrogen, while focusing on pig feeding. Researchers are conducting experiments to understand how sow feeding during the period before and after birth affects piglet development. For example, they are examining how fibre in the sow’s diet can influence the quality of the first milk, called colostrum. They are also looking at including more by-products or biscuit waste in pig and sow diets to reduce competition between animal feed and human food. These topics are also being studied by researchers at Université Laval in Quebec. This Swiss-Quebec collaboration will allow us to join forces.