Effect of avoparcin on the yield and composition of milk and on bloat in pasture-fed dairy cows

Abstract

The effect of avoparcin on the yield and composition of milk was assessed in two trials. Trial 1 involved 60 Friesian cows with half of the cows untreated as controls and half drenched daily with 125 mg avoparcin/cow for 14 weeks. Trial 2 involved 10 mixed-breed twin pairs. One member of each pair was untreated and the other was drenched daily with 150 mg avoparcin/cow for 12 weeks. In each trial the treatment period was preceded by a 2-week uniformity period. The cows grazed pastures containing rye grass and white clover. Yields of milk and milk solids were significantly increased by avoparcin treatment in Trial 2 but not in Trial 1. There was no difference between the treatment groups in changes in Iiveweight or condition score over the treatment period. The effect of avoparcin on bloat was assessed in Trial 3. Three groups of 10 cows of high susceptibility to bloat were untreated (controls) or

Bloat in cattle: 48. Effect of copper in a bloat drench on rumen by‐pass in cattle

“…A range of Cu, zinc, and sodium salts were evaluated in that study, but Clunies-Ross concluded that passage to the abomasum was determined more by the period over which the animal had been deprived of water than by the nature of the fluid given. Similar results were reported in cattle by Wester (1930), so that fasting may have been largely responsible for the by-pass of liquid reported by Carruthers (1992).…”

“…The use of mineralised bloat drenches has renewed interest in this controversy because of a widely held but probably incorrect view that copper (Cu) salts elicite an oesophageal groove closure in cattle, so that the drench would by-pass the rumen. This speculation has been linked to work which showed several mineral solutions were able to by-pass the rumen in some fasted cows before slaughter (Carruthers 1992).…”