Assessment of the nutritive value of whole crop peas and intercropped pea–wheat bi-crop forages harvested at different maturity stages for ruminants

This study measured the chemical composition, aerobic stability, feed intake, in vivo digestibility, nitrogen (N) balance and rumen degradability of spring-sown, whole crop peas (WCP) and intercropped pea–wheat bi-crop silages harvested at three stages of maturity. The WCP was harvested at the pod swell growth stage. The bi-crops were harvested after 14, 17 and 18 weeks of drilling, when the peas and wheat were respectively at the pod swell and early milk (cut 1), dry seed and early dough (cut 2) and early pod senescence and dough (cut 3) growth stages. The forages were conserved in 600 kg bales without additive treatment for 90 days and then analyzed for chemical composition, aerobic stability, rumen degradation, in vivo digestibility and N balance. The voluntary feed intake, in vivo digestibility and N balance of the bi-crops was measured using 6, 9 month-old, Suffolk cross wethers that were housed in separate metabolism crates. The WCP forage was similarly evaluated in a separate experiment. In situ degradation was measured in three ruminally-fistulated cows fed a perennial ryegrass silage diet without concentrate. The level of peas in the forages at harvest ranged from 90 to 170 g/kg dry matter (DM). The pH, DM and starch contents of the bi-crop silages increased (P<0.001), while their water-soluble carbohydrate (WSC) content and fermentation product concentrations decreased (P<0.01) with maturity. Crude protein content, DM intake, in vivo digestibility, N balance and rumen degradation were higher in WCP than in the bi-crops. Within the bi-crops, intakes of DM, organic matter (OM) and N were highest at cut 2, whereas digestibilities of DM, OM and N were highest at cut 1. Only the cut 1 bi-crop gave a positive N balance. The effective rumen degradability of DM and the N loss after 48 h were higher for cut 1 silages than for cut 2 and cut 3 silages. However, the starch loss after 48 h increased (P<0.05) with maturity. This study shows that the nutritive value of pea–wheat bi-crops is optimized after 14 weeks of harvest. Since the nutritive value of such low pea (<200 g/kg DM) bi-crops was considerably poorer than that for WCP, a complementary study is investigating the effect of sward pea content on the nutritive value of pea–wheat bi-crops.