Gestating sows do not digest calcium or phosphorus as well as growing pigs, study says

Courtesy of University of Illinois

URBANA, Ill. – Most values for digestibility of calcium and phosphorus are determined in growing pigs, with the long-held assumption that results can be applied to pigs at different life stages, including gestating and lactating sows. However, research is showing that sows may not absorb certain nutrients in the same way as growing pigs.

Many sows lost from commercial herds due to lameness may be attributed to lost minerals during gestation.

In a study published in the Canadian Journal of Animal Sciences, University of Illinois scientists reveal that gestating sows have reduced digestibility of calcium and phosphorus compared with growing pigs.

“The significance is that there are a lot of sows that are lost from commercial herds because of lameness, which can be related to calcium and phosphorus because they are the two most common minerals in bone,” says Hans H. Stein, professor in the Department of Animal Sciences at U of I and corresponding author on the study. “These results may have implications for longevity of sows in the herd. We need to do more work before we can conclude that, but this study was the first step in that direction.”

Stein and fellow U of I researchers Su A. Lee and Gloria A. Casas fed three diets to 48 gestating sows and 24 growing gilts. The diets included a standard corn-soybean meal diet; a diet with 60 percent corn-soybean meal and 40 percent full fat rice bran (FFRB); and a diet with 60 percent corn-soybean meal and 40 percent defatted rice bran (DFRB).

In the basal diet, 1.15 percent dicalcium phosphate and 0.8 percent limestone were included, whereas only limestone (1.64 percent) was included in the diets containing FFRB or DFRB. Analyzed calcium and phosphorus in the three diets totaled 0.65 and 0.6 percent, respectively, in the standard diet; 0.66 and 0.98 percent in the FFRB diet; and 1.16 and 1.09 percent in the DFRB diet. Microbial phytase was included in all diets, with analyzed values between 430 and 690 units phytase per kilogram complete diet.   

Because growing pigs are fed ad libitum while gestating sows are feed-restricted, Stein says it can be difficult to determine if nutrient digestibility differences are real or an artifact of feed intake. Therefore, sows were fed all three diets at 1.5 or 3.5 times the maintenance requirement for energy and gilts were fed at 3.5 times the maintenance requirement.

Feed intake level did not affect the apparent total tract digestibility (ATTD) of calcium or phosphorus in gestating sows, but ATTD of both minerals was reduced in sows compared with growing gilts.

“Phytate is a compound in cereal grains that binds phosphorus and calcium,” Stein explains. “We wanted to determine if there was a difference between high and low phytate in the two groups. Growing pigs were exactly as we expected: High phytate diets had lower digestibility than low phytate diets. But there wasn’t really a difference for sows between the low and high phytate diets. For both, digestibility values were much lower than what we saw in growing pigs.”

The study is the first to show a difference in digestibility of calcium and phosphorus in sows and growing pigs. Stein plans to determine why the difference exists and if it holds true throughout the entirety of gestation and into the lactation phase. Still, these initial results indicate that it may not be appropriate to apply results from growing pigs to gestating sows.

“It is possible that in the future we will need to use different digestibility values for Ca and P when we formulate diets for sows than we use for growing pigs,” Stein says. “This could improve accuracy of diet formulation, but we need more research before we can give recommendations on this.”

The article,was published in the Canadian Journal of Animal Science. Authors include Su Lee, Gloria Casas, and Hans Stein.