Short communication: Effects of monensin on 3-methylhistidine excretion intransition dairy cows

Urinary 3 methyl-histidine excretion was measured in high yielding dairy co ws between 10 and 3 d precalving and between 3 and 9 d postcalving. Cows re ceived a sodium monensin controlled-release capsule or a placebo 3 wk befor e calving. Monensin did not affect urinary 3 methyl-histidine. Average urin ary 3 methyl-histidine excretion was significantly higher postcalving (4.11 mmol d(-1)) than precalving (2.48 mmol d(-1)). This increase is assumed to be predominantly due to the negative nitrogen balance in the postcalving p eriod caused by insufficient nutrient intake to meet nutrient requirements, which necessitates catabolism of mainly myofibrillar protein.