The effect on voluntary feed intake, in vivo digestibility and nitrogen balance in sheep of feeding grass silage or pea–wheat intercrops differing in pea to wheat ratio and maturity

Abstract

This study determined the effect on the voluntary feed intake (VFI), in vivo digestibility and nitrogen (N) retention in sheep of feeding grass silage or pea–wheat bi-crop forages differing in maturity at harvest and pea to wheat ratio. Two bi-crops drilled at pea to wheat ratios of 25:75 (low pea; LP) or 75:25 (high pea; HP) on a dry matter (DM) basis were grown on each half of 6.5 and 3.5 ha fields and harvested after either 13 (cut 1; C1) or 15 (cut 2; C2) weeks of growth. The four resulting forages were ensiled in separate 40 t clamp silos and evaluated against a perennial ryegrass (PRG) silage, as a control, in an in vivo digestibility trial. Each forage was fed with 7 g of mineral/vitamin supplement daily to four Lleyns wether sheep for a 14-day adaptation period and a 10-day balance period. Daily forage intake and total faecal and urine output were measured and N balance was estimated. The mean DM contents at C1 and C2 were 301 and 333 g/kg while the mean proportions of peas in the LP and HP treatments were 402 and 729 g/kg DM, respectively. C2 bi-crops had higher crude protein (CP) ( P<0.05), starch ( P<0.001) and neutral detergent fibre (NDF; P<0.01) contents than C1 bi-crops while the HP treatment gave higher pea to wheat ratios at harvest ( P<0.001) in vivo digestibility values and CP contents ( P<0.01) than the LP treatment. Nevertheless, there were significant interactions between pea to wheat ratio and maturity. The LP C2 bi-crop silage had the highest ( P<0.05), DM, water-soluble carbohydrate (WSC), starch and NDF contents and metabolisable energy (ME) value and gave the highest, DM, digestible DM and ME intakes, N retention and N balance. Compared to the PRG silage which was moderate in quality, the bi-crops had higher ( P<0.05), CP, starch and WSC contents and gave higher DM, digestible DM and ME intakes, and better N retention and N balance. This study shows that the LP C2 had similar nutritive to the other bi-crops value but gave better animal performance. The work also suggests that pea–wheat bi-crops can be fed to livestock instead of average quality grass silage.