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Report no. 488

Abstract
The effect of the growth promoter tylosin and the protein content in feed for growing-finishing pigs in the weight interval approx. 20-100 kg was studied in one herd.

The test was carried out as a factorial test and comprised the following test treatments:

· Tylosin (20 ppm) and 140 g digestible crude protein per FUp.
· No tylosin and 140 g digestible crude protein per FUp.
· Tylosin (20 ppm) and 125 g digestible crude protein per FUp.
· No tylosin and 125 g digestible crude protein per FUp.

There was good concordance between the calculated and analysed content of nutrients in the feed mixes.

Tylosin increased the microbial activity in the colon and increased the content of yeast in the stomach and the small intestine in growing-finishing pigs in the weight interval approx. 60-70 kg. Furthermore, tylosin in the feed caused pH to decrease in the small intestine and colon, and the composition of the organic acids was changed.

The protein level had no significant effect on the contents of bacteria and yeast nor on the concentration of organic acids in the gastro-intestinal tract in growing-finishing pigs in the weight interval 60-70 kg. At 140 g digestible crude protein per FUp the production (seen over time) of organic acids in the gastro-intestinal tract was higher, however, and pH in the colon was lower than at 125 g digestible crude protein per FUp. Especially the production of butyric acid was higher in the small intestine at 140 g digestible crude protein per FUp.

Tylosin had no effect on Salmonella prevalence. The prevalence of Salmonella was 1.2 times as high among pigs fed 140 g digestible crude protein per FUp as among pigs fed 125 g digestible crude protein per FUp. However, this difference was not significant.

Due to low prevalence of haemolytic spirochetes and Lawsonia intracellularis it is not possible from this study to establish the effect of protein level and tylosin on these pathogenic bacteria.

Removal of tylosin from the feed caused the production value to decrease significantly by 9% as a consequence of lower gain and poorer feed conversion. The protein level did not affect the production value.

The texture of the manure was thinner for growing-finishing pigs when tylosin was removed from the feed, however this did not increase the number of treatments for diarrhoea. It was possible to achieve a firmer manure texture by reducing the content of digestible crude protein from 140 to 125 g per FUp.

The changes in production value and manure texture by removing tylosin from the feed could not be explained from significant differences in the microbial ecosystem in the gastro-intestinal tract.

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