The effect of monensin in lactating beef cows in poor body condition receiving low levels of energy

Abstract

Two studies were conducted to determine if reproductive patterns or blood constituents could be altered by feeding monensin. In the first study the effects of monensin on weight gain, body condition and reproductive performance were studied in 78 mature Angus and Brahman X English crossbred cows in thin body condition. Cows were allotted 162 to 168 days after breeding by expected calving date, age, breed and body condition score (cows scored 2, 3 and 4 on a subjective scoring system of 1 to 9 with 1 being a thin cow) to a control group and a group receiving 200 mg monensin/head/day. Cows were fed both concentrate and hay portions of the rations in individual feeders prior to calving. Postcalving they received Coastal Bermudagrass hay ad libitum and were fed the concentrate portion of the ration in individual feeders. Weights, heart girth measurements and body condition scores were obtained every 28 days. Rumen fluid samples were obtained at three separate times during the trial and were analyzed for volatile fatty acid composition. Following calving, cows were observed twice daily for estrus. Cows were inseminated 12 to 18 hr after estrus and were examined for pregnancy 35 to 42 days later. Total volatile fatty acid concentration in the rumen was essentially the same in control and monensin-fed cows; however, ruminal propionate was increased by an average of 24% (P < .05) with monensin treatment..