Use of Lotus corniculatus containing condensed tannins to increase reproductive efficiency in ewes under commercial dryland farming conditions

Two grazing experiments were conducted over 9.5-month periods of 2001 and 2002 at Massey University's Riverside dryland farm, in the Wairarapa, New Zealand. Dry conditions occur during the summer/autumn and were more severe in Experiment I than in Experiment 2. The experiments compared effects of grazing ewes on Lotus corniculatus L. (birdsfoot trefoil; cv. Grasslands Goldie) versus perennial ryegrass (Lolium perenne)/white clover (Trifolium repens) pasture for 9 weeks (Experiment 1) and 11 weeks (Experiment 2) during late summer/autumn, including the mating period. Experiment 2 also investigated the length of time (days) that ewes need to graze L. corniculatus before mating to maximise reproductive performance. In Experiment 1, shorn mixed age Romney ewes in light condition were rotationally grazed on L. corniculatus (n = 100) or pasture (n = 100) at a herbage allowance of 1.8 kg green DM/ewe/day for the first 3 weeks of feeding, increased to ad libitum (2.3 kg green DM/ewe/day) during the mating period for two cycles. In Experiment 2, groups of 75 ewes grazed L. corniculatus for 42, 2 1, 10 and 0 days before synchronised oestrous, with perennial ryegrass/white clover pasture being grazed for the balance of the 42 days. All L. corniculatus groups continued grazing L. corniculatus for a further 5 weeks. Feed allowance was initially 2.0 kg green DM/ewe/day, increased to 2.3 kg green DM/ewe/day during the mating period over two cycles. At the end of L. corniculatus feeding in both experiments the groups were joined and grazed on pasture until weaning. Total condensed tannin (CT) concentration in the diet selected was 18-29 g CT/kg DM for L. corniculatus, with only trace amounts in pasture. In vitro organic matter digestibility (OMD), digestible organic matter in dry matter (DOMD), and metabolisable energy concentration (ME) were higher for L. corniculatus than for pasture, whilst the concentration of neutral detergent fibre (NDF) was lower for L. corniculatus than in pasture, with these differences being greater in Experiment I than in Experiment 2. In Experiment I mating ewes on L. corniculatus increased lambs born and lambs weaned per ewe lambing by 16 and 32% units respectively (P < 0.05), due to more multiple and less single births (P = 0.06) and to reduced lamb mortality (P < 0.05). In Experiment 2, increased days of grazing L. corniculatus before ovulation (0, 10, 21 and 42 days) linearly increased ovulation rate (P < 0.05), number of lambs born and lamb weaned by up to 16% units, but had no effect upon lamb mortality. Mating ewes on L. corniculatus increased wool production (P < 0.01) and fibre length (P < 0.05) in Experiment I but not in Experiment 2. Grazing L. corniculatus had no effect on lamb birth weight and only small positive effects on weaning weight. It was concluded that under commercial dryland farming conditions, the use of L. corniculatus during the mating season in late summer/autumn can be used to increase reproductive efficiency and wool production, with the largest responses in years with exceptionally dry autumn periods. These effects are probably due to the higher digestibility and ME of L. corniculatus than pasture, and to the CT in L. corniculatus improving both protein digestion and absorption. Effects of forage CT upon the uterine microenvironment at the time of conception, implantation and early foetal growth, need to be investigated in future studies. (c) 2005 Elsevier B.V. All rights reserved.