In vitro and in vivo nutrient digestibility of a pig diet enriched with Yucca schidigera extract

Saponins are considered antinutritional factors which impair nutrient absorption. However, lately, it has been demonstrated that they improve performance and health status. In order to better understand their mechanism of action, an in vitro and an in vivo study were performed to assess the effects of a dietary Yucca schidigera extract (YE, 10.8% saponin richness) on the fermentations in the large intestine and the apparent total tract digestibility (ATTD) of nutrients (organic matter, OM; and crude protein, CP) in fattening male and female lean pigs. In the in vitro trial, three doses of inclusion of YE were tested (0, 150 and 300 mg/kg of feed). The feed was pre-digested performing a two-phase digestion, and then incubated to simulate the large intestine digestion. In the third phase four samples of cecal content, from two boars and two gilts of 115 kg of body weight (BW), were used as inoculums in 40 bottles (10 per inoculum, of which 3 bottles per treatment and one bottle used as blank). The gas produced (ml/g of incubated dry matter, DM) was measured through the first 10 h. For the in vivo trial, a total of 40 Pietrain x (Landrace x Large White) animals, with 76.1 ± 5.2 kg of BW, were allocated in 20 pens (2 pigs per pen) and randomly distributed in a factorial design 2 x 2, with two sexes (boars and gilts) and two diets (0 mg/kg and 300 mg/kg of YE). The study lasted 42 days and acid-insoluble ash (AIA) was used as internal marker for nutrient digestibility. In the in vitro trial YE reduced linearly the cecal pH in males (5.75 vs 5.85; P<0.05), but not the DM digestibility or the gas production (P>0.10). Also, female inoculum reduced the cecal DM digestibility (13.4 vs 23.8; P<0.05) and generated an earlier gas concentration peak than the male one (4 h vs. 6 h of fermentation, P<0.05), with no effect on total gas production. In the in vivo trial YE reduced the ATTD of OM (90.2 vs 92.1) and CP (87.7 vs 89.9; P<0.05). In addition, the ATTD of nutrients did not differ between the two sexes. In conclusion, in the in vitro trial, dietary YE increased the acidity in the male cecal contents but did not alter the fermentation process that occur in large intestine. However, in the in vivo trial, the YE diet reduced the ATTD of OM and CP. The sex affected the fermentation pattern in the in vitro study, and females showed a lower cecal DM digestibility, while the ATTD of nutrients resulting from the in vivo trial was similar in both sexes.