Study sets calcium-to-phosphorus ratio for 11-22 kg pigs

Pig diets sometimes contain 0.22% more calcium, on average, than stated on product label.

The amount of calcium in pig diets must be calculated precisely, because too much can decrease phosphorus digestibility and feed intake, leading to lower weight gain in pigs, according to Hans H. Stein, professor in the University of Illinois department of animal sciences and the Division of Nutritional Sciences.

Stein and his graduate students have established the optimum ratio of calcium and phosphorus for most pig weight classes. In a recent Journal of Animal Science & Biotechnology article, they completed the picture with a recommendation for 11-22 kg pigs.

“We determined that if phosphorus is provided at the required level of 0.33%, the optimal ratio of calcium to phosphorus is 1.39:1 or 1.25:1 to maximize daily gain and gain-to-feed, respectively. To optimize bone ash, which is important for breeding sows, the ratio is 1.66:1,” Stein said. “This is in very good agreement with our previous data from other weight classes.”

Stein’s research team, led by doctoral student Vanessa Lagos, formulated 20 corn/soybean meal-based diets that varied in calcium and phosphorus concentration and fed them to 640 barrows (average weight of 11 kg) over 21 days. Diets were formulated to contain 0.16%, 0.33%, 0.44% or 0.50% standardized total tract digestible (STTD) phosphorus and 0.14%, 0.29%, 0.44%, 0.59% or 0.74% STTD calcium. These values represented 50-151% of the STTD phosphorus requirement and 30-170% of the total calcium requirement, according to the announcement from the University of Illinois.

By the end of the 21-day trial, at which time the pigs’ average weight was 22.4 kg, the researchers were able to determine pig growth performance. Specifically, they quantified final bodyweight, average daily gain, gain:feed ratio and incorporation of the minerals into bone.

The team also analyzed gene expression patterns and found more leakage of calcium out of the gut when the mineral was fed in excess, the university said.

“The bottom line is that it’s very important not to overfeed calcium. We have to know exactly how much calcium is in each ingredient and then formulate mixed diets to make sure we don’t get too much,” Stein said. “There are some calcium sources in the diet that feed companies may not necessarily be aware of, such as vitamin premixes that use calcium as a carrier. If you add it all up, you can get quite a bit too much.”

Stein added that a European study determined that pig diets contain 0.22% more calcium, on average, than stated on the product label. On the other hand, commercial diets are unlikely to provide excess phosphorus.

Phosphorus is not only one of the most expensive nutrients; it can also cause environmental harm when excreted in urine and manure, the university said.

Stein’s co-authors include Lagos, Su A. Lee, Guillermo Fondevila, Carrie Walk, Michael Murphy and Juan Loor. The research was supported by AB Vista.