Effect of tannins and kafirins on the nitrogen and energy balance and performance of pigs

Context. Tannins are blamed for negatively affecting nutritive value of sorghum. Kafirins are sorghum storage proteins and may be associated with lower animal performance. They have been tested in poultry diets; however, information for pig diets is scarce. Aims. Our aim was to determine the role of kafirins and tannins in sorghum nutritive value for swine. Methods. Two experiments evaluated effects of sorghum tannin and kafirin levels on (1) nitrogen (N) and energy balance, and (2) performance of pigs. Two sorghum hybrids with low (LT) and high (HT) tannins were grown at two rates of N fertiliser to achieve low (LK) and high (HK) kafirins (i.e. four sorghum treatments: LTLK, LTHK, HTLK and HTHK) and added to soybean meal based diets. A fifth diet included maize instead of sorghum. Five pigs (48.8 +/- 0.4 kg) were used in a 5 x 5 Latin square design to measure N and energy balance, with 5 days of diet adaptation and 4 days of urine and faeces collection. The performance experiment included 60 pigs (54.0 +/- 12.4 kg, 30 barrows and 30 gilts, six of each per treatment) placed in individual pens with free access to water and feed. Key results. Energy balance showed a tannin x kafirin interaction (P < 0.05) for dry matter feed intake, which diminished with the LTHK diet and was unaffected with the HTHK diet. Dry matter digestibility was higher (P < 0.001) with maize, intermediate with LT, and lower with HT diets. Pigs fed maize retained more N (P < 0.05) and had higher energy digestibility (P < 0.001) than pigs fed sorghum. HT diets had lower (P < 0.01) energy digestibility than LT diets. In the finishing phase, average daily feed intake showed a tannin x kafirin interaction (P < 0.05); pigs fed the HTHK diet had lower average daily feed intake than other pigs. This lowered average daily liveweight gain and consequently final weight. Conclusions. Tannins negatively affected sorghum nutritive value; high kafirins worsened average daily feed intake and liveweight gain, and hence final weight. Implications. Management of kafirin content should be considered to avoid adverse performance effects in pigs fed sorghum.