Calcium level and dEB affect the protein and mineral digestibility of lactating sows
Limestone (CaCO3) and sodium bicarbonate are included in pig diets to supply Ca and increase dietary electrolyte balance (dEB = Na + K – Cl, in mEq/kg diet), respectively. However, both ingredients increase the diet acid-binding capacity and may interfere with the phytate-protein and phytate-Zn complex in the digestive tract. The aim of this study was to assess if diets differing in Ca level and dEB may affect the whole-tract apparent digestibility in lactating sows fed on a typical European sow diet (25.0 % corn, 20.0 % barley, 20.0 % wheat, 18.3 % soy meal, 10.0 % wheat bran, 2 % rapeseed meal) containing a high phytic acid level (2.9 g phytic P/kg), and supplemented with an overdose of phytase (1260 FTU/kg). A total of 48 lactating sows (14th day of lactation) were distributed according to their parity number and number of piglets into six experimental diets (2 x 3 factorial) differing in the Ca level: 6 or 9 g/kg (lowCa or highCa, respectively), and dEB: 40, 176 or 235 mEq/kg (lEB, mEB or hEB, respectively). Calcium chloride (10 g/kg) was added to lEB diets. The rest of Ca was provided as CaCO3. Sodium bicarbonate was added (5 g/kg) to hEB diets. Titanium dioxide (3 g/kg) was used as indigestible marker. Diets were offered ad libitum for 7 days. Two fecal samples were obtained in two different times on day 21 of lactation for each sow and then pooled. Blood samples from sows fed highCa diets were individually collected on day 21 to measure acid-base status of the sows. Sows fed highCa diets showed higher (P < 0.05) digestibility of CP (87.4 %), Ca (21.4 %), P (45.2 %), and Zn (20.9 %) than sows fed lowCa diets (85.8, 14.3, 40.8 and 7.04 %, respectively). The use of sodium bicarbonate in lowCa diets (hEB) decreased (P < 0.05) DM digestibility as compared to the lowCa-mEB and the three highCa diets. The lBE diet reduced blood pH, bicarbonate and base excess values as compared with mBE and hBE (P < 0.05). In conclusion, the results showed that low Ca diets and sodium bicarbonate may reduce nutrient whole-tract digestibility in lactating sows fed on high phytic acid diets, even when phytase was overdosed.
calcium, dietary electrolyte balance, digestibility