The use of blood equol values in devising grazing management strategies for red clover-based pastures

Abstract

Feeding and grazing trials were carried out to establish relationships between formononetin intakes and blood equol levels, and to characterise the build-up and clearance of free and conjugated equal in the blood of sheep feeding on either high (Grasslands Pawera) or low (G27) formononetin red clovers. In the feeding trials, blood equol levels were positively correlated with formononetin intakes, and levels peaked at 2-4 hours after feeding. In the grazing trial, groups of 10 sheep grazed either Pawera or G27 red clover pastures for l-, 2-, or 3-week periods while a control group was on grass-dominant pasture. Analysis of blood equal showed differences in the rates of accumulation and in the mean blood concentrations. Free equol was present in the blood of sheep after one day of grazing on Pawera whereas it was not detected in blood of sheep on G27 until 5 days after grazing began. Blood equal rose to equilibrium levels and remained thus until sheep were removed from the red clovers. The concentrations of equol in Pawera ewes were approximately three times those in G27 ewes. Free equoal was rapidly cleared from the blood and was below the limit of detection by day 2 after transfer to a ryegrass pasture. The 4-day lag between start of grazing and the appearance of free equal in the blood of ewes on G27 offered scope for devising grazing management strategies which might enable use of G27 for flushing without an adverse effect on fertility. Results of trials in 1995 and 1996, in which ewes grazed alternately for 3.5 or 3 days on G27 and then for 3.5 or 4 days on grass pastures (per week) for 4 weeks before and during a 4-week mating period showed that the reproductive performance of ewes was unaffected. Such on/off systems of grazing management, therefore, enable G27 to be grazed safely by ewes around the time of mating. Keywords: equol, ewe fertility, flushing, formononetin, grazing management, oestrogenic compounds, Trifolium pratense