Effects of herbage ingestion on the digestion site and nitrogen balance in heavy Iberian pigs fed on an acorn-based diet

Abstract

We conducted two experiments in heavy-weight Iberian pigs to determine: a) the effect of lysine or protein addition – the former as l-lysine·HCl, the latter by fresh cut herbage supplementation – on protein deposition when they were fed on holm-oak acorns; b) the digestibility of energy and nutrients in acorns and freshly cut, mixed herbage; and c) a possible change in the partition of digestion along the gastro-intestinal tract of the pigs fed on acorns with the inclusion of herbage. In Experiment 1, carried out in eight cannulated pigs, the daily intake of acorns reached 44.9 g DM/kg 0.75 BW and the addition of 0.58 g l-lysine/kg of whole acorns failed to alter N retention significantly ( P > 0.05). We obtained high coefficients for the apparent total-tract digestibility of dry matter (ApDM tt, 0.84) and organic matter (ApOM tt, 0.86) and of gross energy (ApGE tt, 0.84) in whole acorns. The corresponding ileal values were 0.71, 0.74 and 0.74. The N balance was on average − 1.08 g/day. In Experiment 2, fresh herbage containing principally legumes was offered to six cannulated Iberian pigs of 140 kg either as a single feed (13.7 g DM/kg 0.75 BW) or as a supplement to acorns (28.4 g DM/kg 0.75 BW; in this case the herbage accounted for 22% of the daily DM intake). The apparent ileal digestibilities of OM and GE for herbage accounted for 70 to 77% of the values observed at total-tract level (0.65 and 0.64 respectively). N retention reached 4.21 g/day. Average ApDM tt, ApOM tt and ApGE tt in the herbage/whole-acorn mixture were slightly above 0.74. The intake of freshly cut herbage as complementary feed to acorns resulted in a significant transference of digesta from the small intestine to the hind gut together with a substantial decrease in ileal digestibility of nutrients and energy ( P < 0.001) and a moderate decline in digestibility at throughout the whole tract ( P < 0.01– P < 0.001). On the other hand, the apparent digestibility of total N increased ( P < 0.001) and 31% of the N apparently digested was retained in the body of the pigs. We also observed a substantial decrease in the precaecal digestion of the DM ( P < 0.01), OM ( P < 0.01) and GE ( P < 0.05) in acorn kernels. We concluded that the main contribution of herbage to the overall nutrient supply to the grazing Iberian pig would rely upon the provision of amino acid N and also of available minerals, both present in low quantities in acorns.