The effect of condensed tannins in Lotus corniculatus upon reproductive efficiency and wool production in ewes during autumn

A grazing experiment, conducted for 81 days (from 13 February to 4 May) in the late summer/ autumn of 1999 at Massey University, Palmerston North, New Zealand, compared the reproductive efficiency and wool growth of ewes graz ing Lotus corniculatus (birdsfoot trefoil) or perennial ryegrass (Lolium pe renne)/white clover (Trifolium repens) pasture (referred to as pasture). Ha lf the ewes grazing L. corniculatus were given twice daily oral polyethylen e glycol (PEG: molecular weight 3500) supplementation to inactivate the con densed tannins (CTs) in lotus. A rotational grazing system with 225 mixed a ge ewes (53.2 +/- 3.78 kg per ewe) was used, with 75 ewes per treatment. The effect of forage species and PEG supplementation upon voluntary feed in take (VFI), concentration of plasma metabolites, reproductive efficiency, w ool production and wool length was measured during three synchronised oestr ous cycles. The ewes were restricted to maintenance feeding for the first 1 2 days of each oestrous cycle and then increased to ad libitum for the 5 da ys prior to and including ovulation. Lotus contained 18 a total CT/kg dry m atter in the feed offered. There were only trace amounts of total CT in pas ture. In vitro organic matter digestibility (OMD) of the diet selected was higher for lotus (0.82 versus 0.74) than for pasture, whilst the two forage s contained a similar nitrogen concentration. Mean ovulation rates (ORs) at cycle 3 for CT-acting and PEG sheep grazing l otus and for sheep grazing pasture were, respectively, 1.79, 1.58 and 1.48, with corresponding lambing percentages being 1.69, 1.39 and 1.22. Fecundit y (number of corpora lutea (CL) per ewe ovulating) at cycle 3 ovulation and lambs born per ewe lambing were greater for ewes grazing lotus than pastur e (P < 0.01), and for CT-acting than for PEG sheep grazing lotus (P < 0.05) . Increases in fecundity were due to a lower proportion of single ovulation s and a greater proportion of multiple ovulations. CT increased reproductiv e efficiency by increasing fecundity and by reducing embryonic loss. Rumen ammonia and blood plasma urea concentrations were lower for ewes graz ing lotus than pasture (P < 0.01), and were generally lower for CT-acting t han for PEG sheep grazing lotus. The nutritional treatments had little effe ct on plasma ammonia concentration. Organic matter intake (OMI) (P < 0.05), clean wool production (P < 0.01) an d staple length (P < 0.001) were significantly higher for ewes crazing lotu s than for pasture. Liveweight gain (LWG) was low, and lower for sheep graz ing lotus than pasture. There was no difference in OMI and LWG due to CT in lotus, but wool length (P < 0.01) and clean wool production (P = 0.07) wer e higher for CT-acting than for PEG supplemented ewes (CT not acting). It was concluded that grazing lotus during mating increased the efficiency of reproduction and clean wool production, with a component due to the acti on of CT. Possible mechanisms for CT increasing reproductive efficiency are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.