Graduate Thesis Or Dissertation
 

The effect of monensin on efficiency and production of a brood cow herd

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  • Ninety-six mature pregnant Hereford cows were allotted to three replications with four treatments. Pregnancy was determined by rectal palpation prior to the initiation of the study. The cows were artificially inseminated the previous spring, beginning the end of May, over a period of 42 days to a single Angus sire. Hereford cleanup bulls followed for 21 days. The cows were stratified by breeding date, weight, condition score and the previous year's adjusted weaning weights and randomly assigned to treatments. Replications were by calving date. Monensin treatments consisted of 0, 50, 200 and 300 mg/hd/day and was provided in ground barley. Controls received .45 kg of barley/ head/day with the monensin treatments receiving their doses in like amounts of barley. The basic feed was native meadow hay containing 9.5% crude protein. Hay was weighed in daily and refusals out weekly. Throughout the study hay was adjusted to maintain equal weight gain or loss between treatments. Initially the control cows were fed hay free choice and consumed 13.4 kg/head/day. The initial monensin treatment levels were 95% of the control's diet for the 50 mg level and 90% each for the 200 and 300 mg groups. Hay consumption for the entire confinement period was 92, 89 and 90% of the control group's diet for the 50, 200 and 300 mg groups respectively. Rumen samples were taken twice during the study, once prior to calving and another postpartum. An esophageal hose connected to a vacuum pump was utilized on four cows per pen for a total of 48 samples. On the morning samples were taken the cows were fed at one-half hour intervals to allow ample time for sampling. All cows were sampled three to four hours after supplemental feeding. Volatile fatty acid concentration results show rumen acetic acid production was reduced and propionic increased with the 200 and 300 mg levels. Cow weights were obtained every 28 days prior to calving and were used to adjust hay intake. Cows and calves were also weighed 24 hours postpartum, treatment termination and weaning. Initial cow weights for the control, 50, 200 and 300 mg treatments were 455, 447, 456 and 457 kg, respectively, with prepartum gains of .34, .38, .38 and .37 kg. Weight loss during the calving and postpartum periods were similar with the exception of the 300 mg group, which lost more weight. At or near time of calving cows were removed from their pens and taken to a calving shed. Hay fed was adjusted accordingly so the cows remaining in the pens received the proper level. Cows that lost calves or had health problems were eliminated from subsequent data.
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