Organic Acids in Diets for Entire Male Pigs

Liv Lønne Dille

The Storting (Norwegian parliament) has decided to ban the castration of pigs in Norway. The production of entire male pigs will be more efficient than raising castrates, but a considerable problem is the risk of a strong off-flavour/odour, the so-called boar taint. Boar taint is to a large degree linked to the compounds skatol and androstenon. In this study we have examined if the addition of organic acids to the feed could help to reduce the occurrence of boar taint.

In Norway, formic acid or formic acid salts are often added to feed for fattening pigs. Addition of organic acids to the feed has a beneficial antimicrobial effect in the intestine. Several studies have shown that feed regimes that reduce microbial activity in the digestive tract also lead to lowered concentrations of skatol and androstenon in pig faeces. However, none of these studies have included organic acids. Therefore, we wished to test if the addition of organic acids to the feed affects skatol production in boars. In this trial, we recorded the effect on weight gain, carcass quality, production of skatol and volatile fatty acids in the hind gut, as well as the hind-gut microflora. Skatol and androstenon levels in fatty tissue and blood were also studied.

Boars of the Noroc type were used for the trials. They were slaughtered at a live weight of about 113 kg. The trial feed contained either no additions of organic acids (control) or additions of one of the following organic acids: formic acid, benzoic acid, sorbic acid, Ca-coated butyric acid, or Ca-inulin-coated butyric acid. Each of the feed mixtures contained 0.85 % pure acid.

The results showed that feed with supplements of formic and sorbic acids gave improved growth rates and higher feed consumption (kg feed/kg growth) in the first half of the fattening period, but thereafter, there was no significant effect of organic acids on daily gain and feed intake. For the entire fattening period, there was however a tendency towards higher feed consumption by those pigs that were given feed containing formic acid, benzoic acid or propionic acid.

Skatol production in the hind gut considerably affects the amount of skatol that is deposited in fatty tissue. Low concentrations of skatol in the intestines result in low skatol levels in fatty tissue. An important part of our hypothesis was thus to study skatol production, production of volatile fatty acids and the microbial composition of the hind gut. The results showed that there was no significant effect of organic acids on the skatol concentrations in the contents of the colon, even if the lowest values for large intestinal skatol were found in pigs given feed containing sorbic acid or Ca-inulin-coated butyric acid. Regarding concentrations of volatile fatty acids (acetic acid, propionic acid and butyric acid) in the colon, butyric acid concentrations were highest in those pigs given feed with Ca-inulin-coated butyric acid, formic acid and Ca-coated butyric acid. Highest butyric acid concentrations were found in pigs given feed with sorbic acid.

Studies of the microbial composition of the hind gut showed that the addition of organic acids to the feed generally reduced the number of coliform bacteria, enterococci and lactic acid bacteria. Our study thus confirms that feed with supplements of organic acids has an antimicrobial effect.

The detected skatol values in backfat were generally low in the studied animals, and there was no significant effect of organic acids on the skatol concentrations in fatty tissue. Only two of a total of 58 pigs had skatol concentrations above the threshold value (0.2 µg/g fat). Feeding supplements of organic acids had a significant effect on skatol levels in the blood; pigs given feed with formic acid or benzoic acid showed the lowest values.

Of the 58 studied pigs, 31 had androstenon concentrations exceeding 1.0 µg/g backfat. Thus, 53 % of the pigs had unacceptable levels of androstenon. From earlier studies it is known that feed composition has very little effect on the contents of androstenon in pig fat, however, the feeding intensity may have a certain effect.

Our study concludes that feeding supplements of organic acids contributed to reducing the bacterial population in the digestive tract, whereas the levels of skatol in backfat or the colon were not affected. The reduction of intestinal bacteria is an interesting observation, as is the increased concentration of butyric acid in the hind gut when feeding supplements of formic acid, Ca-coated butyric acid and Ca-inulin-coated butyric acid. However, due to the low skatol values observed in our study, it is difficult to claim that feeding supplements of organic acids has a clear effect on boar taint and odour. The results of these trials with organic acids will be published in the journal Livestock Science (Øverland et al., 2007).

Published: 05.03.07
Updated: 14.05.09
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