Live-weight gains on leucaena and native grass pastures after dosing cattle with rumen bacteria capable of degrading DHP, a ruminal metabolite from leucaena

Abstract

Summary The effect on live-weight gain from dosing cattle with rumen bacteria capable of degrading 3-hydroxy-4(l H)-pyridone (DHP) was measured on cattle grazing leucaena and native grass pastures in south-east Queensland. Dosing increased the growth rate of cattle grazing only leucaena pasture: from 0·52 kg/head per day when not dosed, to 1·03 kg/head per day when dosed, in the period 6·19 weeks after treatment. Dosing did not affect the growth rate of cattle either grazing leucaena with native pasture, or grazing only native pasture. The introduced bacteria spread naturally to untreated cattle after 19 weeks post-dosing. The response to dosing occurred when untreated cattle grazing only leucaena pasture had high urinary concentrations of DHP (maximum 0·28%) and low concentrations of serum thyroxine (< 30 nmol/1). The results show that DHP-induced depressions in growth rate may occur in this environment when cattle graze mainly on leucaena-based pasture. Dosing with DHP-degrading bacteria will overcome this problem.