The combined use of triacylglycerols (TAGs) containing medium chain fatty acids (MCFAs) and exogenous lipolytic enzymes as an alternative to nutritional antibiotics in piglet nutrition: II. In vivo release of MCFAs in gastric cannulated and slaughtered piglets by endogenous and exogenous lipases; effects on the luminal gut flora and growth performance

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In a first experiment with gastric cannulated piglets, the simultaneous addition of 5% triacylglycerols (TAGs) containing medium chain fatty acids (MCFAs: coconut oil, MCTAG1 oil, butter oil) and two lipolytic enzymes (L2, L5: 1000 ppm) to piglet diets resulted in a physiological environment in the stomach which regulates and stabilizes the gastro-intestinal flora. It is striking that the amount of MCFAs released in the stomach parallels the degree of suppression ( P<0.05) of the bacterial load (total anaerobic count, Lactobacilli, Streptococci, E. coli) in the stomach. The most pronounced reduction in bacterial load in the stomach occurred with 1 g FFAs (free fatty acids) per 100 g fresh content (=60% fat hydrolysis) or 0.6 g MCFAs per 100 g with MCTAG1 oil+L5, followed by coconut oil+L5 with 0.8 g FFAs or 0.3 g MCFAs per 100 g and butter oil+L5 with 0.8 g FFAs or 0.06 g MCFAs per 100 g gastric content. In a second experiment under practical field conditions, four diets (A (control), 2.5% soybean oil; B, 2.5% MCTAG2 oil; C, 2.5% MCTAG2 oil+1000 ppm lipase L5; D, 2.5% soybean oil+1.5% organic acids), containing no antibiotics, were used in a zootechnical experiment lasting 21 days with 244 early weaned piglets, divided into four groups. Out of each treatment group, five piglets were sacrificed on day 18 after weaning and the contents of the proximal gut were sampled for bacteriological analysis and the analysis of the hydrolysis of the fat. Piglets performed better (overall daily weight gain, +10% ( P<0.10); feed conversion, −3%) on the diets containing MCTAG2 oil or MCTAG2 oil+lipase compared with the control (A) and the acid-supplemented diet (D). The results from the slaughter experiment indicated that with diet C, there was a correlation between the amount of released MCFAs (0.45 g per 100 g fresh content) in the stomach and duodenum and the inhibitory effect on the gastric and duodenal luminal flora (total count, Lactobacilli, E. coli), which decreased about 10-fold. These results are in line with previous in vitro experiments concerning the enzymatic release of MCFAs from specific TAGs and their antibacterial effects, showing that a minimal concentration of 0.35 g MCFAs per 100 g or 0.025 M in the medium (stomach, proximal gut) was necessary to obtain a significant (>10-fold) suppression of the luminal flora. This strong in vitro and vivo suppressive and stabilizing (non-caloric) effect of MCFAs on the pig proximal gut flora is essential to obtain a growth promotion comparable to that obtained with classic nutritional antibacterials, without the risks of the latter.