Effect of bloat on the milk production and grazing time of dairy cows

Abstract

Twenty cows previously shown to be susceptible to bloat were selected to study the effects of bloat on milk production and grazing time in mid-lactation. The cows were either treated with a bloat prophylactic so that no bloat occurred, or were left untreated. They grazed irrigated red clover (Trifolium pratense) pasture, receiving a fresh strip of pasture each morning. Over a period of 184 cow days, there were 116 observed cases of bloat; 16 of these were classified as severe. Milk yield was reduced by 0.14 kg for each hour of bloat (P< 0.01), but there was no significant difference in yield between those cows that suffered mild bloat, and those that suffered severe bloat, despite the obvious acute stress in the latter cases. There was also a loss of 20 minutes of total daily grazing time for each hour of bloat, whether mild or severe. A major part of this loss occurred whilst the cows were bloated. Under the system of management used, it is unlikely that bloat prevention could be justified by the increase in milk production. The only criterion for bloat prevention in these circumstances should be to prevent deaths.