Digestibility of proximate nutrients and standarized ileal digestibility of amino acids in pigs fed ensiled soaked cowpea (Vigna unguiculata) grains

Tropical native legumes are an alternative to cost-intensive conventional feedstuffs. However, the adverse climate in the tropics induces pest and diseases during storage, affecting the nutritional quality of the feedstuff. Ensiling can face this problem and moreover improve digestibility or reduce the content of anti-nutritional factors (ANF). This study inquired the effects of ensiling a mixture of soaked cowpea (CWP) and sorghum (SOR) grains on fermentation quality, contents of individual ANF, the apparent digestibility (AD) of proximate nutrients (PN) and the standardized ileal digestibility (SID) of selected amino acids (AA) in pigs.

Ripe CWP was soaked (24 h) at a grain:water ratio of 1:4 (w:v), drained, milled and mixed with coarsely ground SOR (4 mm mesh size). Molasses (4 %) and lactic acid bacteria inoculant (Lactabacillus plantarum, DSM 8862 and 8866, 3x10⁵ cfu) were applied as silage (SL) additives and the homogenized mixture was ensiled (60 d) in plastic tons (120 L). Furthermore, a not ensiled raw mixture (RM) of grains was prepared. Six castrated pigs were allotted in a 3 x 3 Latin square design, two animals per group with an initial bodyweight of 49 ± 2.1 kg. The AD of PN of RM and SL was determined in accordance to GfE (2005). Furthermore, eight adult castrated minipigs with end-to-end ileo-rectal anastomosis were placed in two 4 x 4 Latin square designs. The SID of RM and SL was determined by a regression method (GfE, 2005) restricting CWP inclusion to 0, 10, 20 and 30 % of dietary dry matter (DM).

Differences in the PN composition were only marginal, except for a remarkable reduction of starch from 620 (RM) to 312 (SL) g kg^-1 DM. Ensiling reduced condensed tannins (CT) from 0.24 to 0.15 % DM. Likewise trypsin inhibition activity (TIA) decreased from 39.6 to 31.1 mg trypsin inhibited g^-1 DM. Ensiling enhanced (P < 0.05) AD of crude ash, ether extract and acid detergent fibre, whereas AD of neutral detergent fibre decreased. AD of crude protein remained unaffected (P > 0.05). The SID of N and the majority of AA tended to be higher in SL than RM, except for lysine (P > 0.05). However, only SID of methionine was significantly (P < 0.05) increased from 56.5 % in RM to 70.3 % in SL.

Ensiling caused a remarkable increase in the digestibility of crude ash, whereas the digestibility of organic matter remained fairly unaffected.

The contradictory effect on the digestibility of fibers needs to be clarified further. The decrease of CT and TIA likely contributed in elevated (P < 0.05) SID of methionine. The present results indicate that ensiled CWP and SOR mixtures are a suitable pig feed.

Disclosure of Interest: None Declared.