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

Abstract

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 grazing Lotus corniculatus (birdsfoot trefoil) or perennial ryegrass ( Lolium perenne)/white clover ( Trifolium repens) pasture (referred to as pasture). Half the ewes grazing L. corniculatus were given twice daily oral polyethylene glycol (PEG: molecular weight 3500) supplementation to inactivate the condensed tannins (CTs) in lotus. A rotational grazing system with 225 mixed age 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 intake (VFI), concentration of plasma metabolites, reproductive efficiency, wool production and wool length was measured during three synchronised oestrous cycles. The ewes were restricted to maintenance feeding for the first 12 days of each oestrous cycle and then increased to ad libitum for the 5 days prior to and including ovulation. Lotus contained 18 g total CT/kg dry matter in the feed offered. There were only trace amounts of total CT in pasture. 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 forages contained a similar nitrogen concentration. Mean ovulation rates (ORs) at cycle 3 for CT-acting and PEG sheep grazing lotus 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. Fecundity (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 pasture ( 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 ovulations and a greater proportion of multiple ovulations. CT increased reproductive efficiency by increasing fecundity and by reducing embryonic loss. Rumen ammonia and blood plasma urea concentrations were lower for ewes grazing lotus than pasture ( P<0.01), and were generally lower for CT-acting than for PEG sheep grazing lotus. The nutritional treatments had little effect on plasma ammonia concentration. Organic matter intake (OMI) ( P<0.05), clean wool production ( P<0.01) and staple length ( P<0.001) were significantly higher for ewes grazing lotus than for pasture. Liveweight gain (LWG) was low, and lower for sheep grazing 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) were 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 action of CT. Possible mechanisms for CT increasing reproductive efficiency are discussed.