EFFECT OF CONDENSED TANNINS IN LOTUS-CORNICULATUS UPON LACTATION PERFORMANCE IN EWES

A grazing experiment was conducted for 8 weeks in the spring/summer of 1993 at Palmerston North, New Zealand, to study the effects of conden sed tannins (CT) in Lotus corniculatus (birdsfoot trefoil; cv. Grassla nds Goldie) upon the lactation performance of ewes rearing twin lambs. Effects of CT were evaluated by studying the responses of ewes to twi ce daily oral supplementation with polyethylene glycol (PEG; MW 3500), which binds and inactivates CT. A rotational grazing system with rest ricted feed allowance was used. Measurements were made of pre- and pos t-grazing herbage mass, the composition of the feed on offer and diet selected, voluntary feed intake (VFI), milk yield and composition, liv eweight gain and wool production. The concentration of metabolites in rumen fluid and in blood plasma was also measured. Lotus contained 35. 5 g total nitrogen and 44.5 g total CT/kg dry matter in the diet selec ted, with an in vitro digestibility of 73%. At peak lactation (weeks 3 and 4) milk yield and composition were similar for control (CT-acting ) and PEG-supplemented (CT-inactivated) ewes but, as lactation progres sed, the decline in milk production and in the secretion rates of prot ein and lactose were less for control than for PEG-supplemented ewes. In mid and late lactation (weeks 6-11), control ewes secreted more mil k (21%), more milk protein (14%) and more lactose (12%) than PEG-suppl emented ewes. Milk fat percentage was lower for control than for PEG-s upplemented ewes, but secretion rates of fat were similar for the two groups. VFI, liveweight gain and wool growth were similar for both gro ups. Plasma urea and glucose concentrations were lower for control tha n for PEG-supplemented ewes, but concentrations of non-esterified fatt y acids (NEFA), growth hormone and insulin were similar for the two gr oups. The concentrations of ammonia and molar proportions of iso-butyr ic, iso- and n-valeric acids in rumen fluid were lower for control tha n for PEG-supplemented ewes; molar proportions of acetic, propionic an d n-butyric acids were similar for the two groups. It was concluded th at for ewes rearing twin lambs grazing L. corniculatus, the action of CT increased milk yield and the secretion rates of protein and lactose without affecting VFI, thereby increasing the efficiency of milk prod uction. The increased milk production did not appear to be mediated by effects on plasma concentrations of growth hormone or insulin.