Feed physical form and formic acid addition to the feed affect the gastrointestinal ecology and growth performance of growing pigs

Abstract

The effect of feeding a coarsely ground meal (COARSE) and a finely ground pelleted diet with 1.8% (as-fed basis) added formic acid (ACID) was compared with feeding a standard finely ground pelleted diet (STD) on the gastrointestinal ecology of growing pigs at different intervals after feeding. One hundred five castrated male growing-finishing pigs (initial BW 27 kg) were used. At a BW of 63 kg, 60 pigs were killed 0.5, 2.5, 4.5, 6.5, and 8.5 h after feeding, and samples from the gastrointestinal tract (GIT) were obtained. The remaining 45 pigs were kept on the experimental diets to a BW of 99 kg. Feeding the three diets resulted in a similar pattern of gastric pH with time, (i.e., highest pH values 0.5 h after feeding and decreasing values at the following sampling times, to reach a value of 2.12 at 8.5 h after feeding). The pH of the gastric digesta of pigs fed the ACID diet was below 4 at all sampling times, whereas the digesta from the other two dietary groups had values above pH 4 at the first sampling times. Feeding the ACID diet decreased the counts of total anaerobes in the proximal GIT (P < or = 0.007), and of lactic acid bacteria (P < or = 0.001), enterobacteria (P < or = 0.02), and yeasts (P < or = 0.01) along the GIT compared with feeding the other two diets. Feeding the COARSE diet stimulated the growth of total anaerobes and lactic acid bacteria in the stomach and distal small intestine increased the microbial diversity mainly in the stomach (P = 0.001), compared with feeding the other two diets (P < or = 0.09), and decreased the number of enterobacteria in the cecum compared with the STD diet (P = 0.03), with the same tendency in the mid-colon (P = 0.07). The concentration of lactic acid in the stomach was highest in the pigs fed the COARSE diet compared with the other two groups (P < 0.05). The concentration of formic acid was highest in the stomach and all segments of the small intestine of the pigs fed the ACID diet compared with those fed the STD and COARSE diets (P < 0.05). The results from this study suggest that feeding a coarsely ground diet and a finely ground diet with added formic acid affect the gastrointestinal ecology of pigs mainly by changing the environment in the proximal GIT. The presence of organic acids in the proximal GIT is a crucial factor contributing to the decrease in the number of enterobacteria along the GIT. The time after feeding at which samples are taken to measure characteristics describing the gastrointestinal ecology affects the results from the stomach and small intestine.

Divergent modulation of swine ileal microbiota by formic acid and methionine hydroxy analogue-free acid

“…Differences in the diet composition, buffering capacity and farming practices make it difficult to compare results from different studies. However, in general, significant effects on performance and intestinal microbiota were observed in trials with higher than 0.5% inclusion level of FA (Bolduan et al, 1988;Partanen and Mroz, 1999;Canibe et al, 2005;Franco et al, 2005), whereas studies using less than 0.5% FA did not report significant effects (Gabert et al, 1995;Knarreborg et al, 2002). This, together with the observations made in the present investigation, strongly suggest that it is the inhibitory, rather than stimulatory, effect of FA that improves the animal performance.…”

“…This, however, would most likely reduce its value as a methionine source for the host. In studies with FA, a significant level of FA added in feed was found intact in the distal small intestine (Canibe et al, 2005). This explains why FA acted similarly both in in vitro and in vivo studies.…”

“…However, not only undissociated, but also neutralised acids inhibit microbial growth (Dijkhuizen and Harder, 1975;Pasricha et al, 1979). There are reports showing that OA applied in feed are not quantitatively absorbed in the proximal intestine, but are still found in ileum, and may thus account for the microbial modulation effects reported (Canibe et al, 2005;Malik et al, 2006).…”

“…Meta-analysis confirms that OA improve performance of weaned piglets, but the significance and magnitude of the effect appears to depend on the type and level of the OA used, as well as differences in feed composition and buffering (Partanen and Mroz, 1999;Partanen, 2001). Formic acid (FA, 90%) is one of the most commonly used OA, which have been shown to exert positive effects on animal performance and gastrointestinal health (Bolduan et al, 1988;Kirchgessner et al, 1992;Canibe et al, 2005;Franco et al, 2005;Partanen et al, 2007). The mode of action of OA still remains unclear, even though it is commonly accepted that after weaning OA help the piglets to maintain a low pH in the stomach, thus increasing proteolytic activity and feed digestion.…”

Effects of a dietary organic acid mixture and of dietary fibre levels on ileal and faecal nutrient apparent digestibility, bacterial nitrogen flow, microbial metabolite concentrations and rate of passage in the digestive tract of pigs

“…Because organic acids are antimicrobial agents, their effects on ileal apparent amino acid digestibilities can be mediated via microbes of the digestive tract. Several authors have reported changes in bacterial counts and microbial metabolite concentrations in gastric and intestinal digesta of pigs fed diets supplemented with formic acid (Roth et al, 1992;Canibe et al, 2005). Reduced bacterial protein synthesis may contribute to the improved ileal apparent protein and amino acid digestibilities seen with the diets supplemented with organic acids (Partanen et al, 2001).…”