A grazing experiment, conducted for 55 days (from 4 March to 29 April) in the late summer/autumn
of 1997, 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) dominant pasture (pasture). Half the ewes grazing
each forage were given daily oral polyethylene glycol (PEG: molecular weight 3500) supplementation
to inactivate the condensed tannins (CT) in lotus. A rotational grazing system with 200 mixed age
ewes (54·2±0·88 kg/ewe; 50 ewes/treatment) was used.
The effect of forage species and PEG supplementation upon voluntary feed intake (VFI),
concentration of plasma metabolites, reproductive efficiency, wool production and wool characteristics
was measured during two synchronized 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 6 days prior to and including ovulation. Lotus contained 17 g total CT/kg dry matter (DM) in
the diet selected. There were only trace amounts of total CT in pasture. In vitro organic matter
digestibility (OMD) was higher for lotus (0·82 v. 0·74) than for pasture, whilst lotus contained less
nitrogen (N; 37·8 v. 44·5 g/kg OM).
Mean ovulation rates (OR) for CT-acting and PEG sheep grazing pasture and lotus were
respectively 1·33 v. 1·35 and 1·78 v. 1·56, with corresponding lambing percentages being 1·36 v. 1·36
and 1·70 v. 1·42. Fecundity (number of corpora lutea/ewe ovulating) was greater for ewes grazing
lotus than pasture (P<0·01), and tended to be greater for CT-acting than for PEG sheep grazing
lotus (P=0·06). In unsupplemented sheep, ewes grazing lotus had increased plasma concentrations
of branched chain amino acids (BCAA; 57%) and essential amino acids (EAA; 52%) compared to
ewes grazing pasture.
In ewes grazing pasture, PEG administration had no effect on plasma concentrations of urea and
free amino acids, VFI, reproductive efficiency and wool production. However, in sheep grazing lotus,
plasma concentrations of urea were significantly lower and concentrations of most amino acids were
significantly higher for CT-acting than for PEG supplemented ewes (CT not acting); there was no
difference in VFI between these two groups. Compared to ewes grazing pasture, ewes grazing lotus
had similar VFI but produced more wool with longer staples and thicker fibre diameter, with there
being no effect of PEG supplementation.
It was concluded that feeding lotus increased the efficiency of both reproduction and wool
production without an increase in VFI, and that a possible cause was the action of CT in increasing
plasma EAA and especially BCAA concentration.