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C. N. Hemphill, T. A. Wickersham, J. E. Sawyer, H. C. Freetly, K. E. Hales, 082 The Effects of Feeding Monensin to Bred Heifers Fed in a Drylot on Nutrient and Energy Balance, Journal of Animal Science, Volume 95, Issue suppl_1, December 2016, Page 41, https://doi.org/10.2527/ssasas2017.082
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Abstract
Intensification of beef cow systems may be a viable production method when forage availability is limited. Confined cows receiving limit-fed diets containing monensin may benefit from decreased methane production, increased feed efficiency, and greater nutrient utilization. The objective of this study was to evaluate the effect of monensin on duration and magnitude of methane reduction and digestible and metabolizable energy intake. Sixteen pregnant MARC III (1/4 Angus, 1/4 Hereford, 1/4 Red Poll, 1/4 Pinzgauer) composite heifers (482 ± 7 kg initial BW) were used in a 161-d completely randomized design. Heifers were randomly assigned to 1 of 2 treatments, 250 mg monensin per d (MON) or no monensin (CON). Diets consisted of corn stalks (80%), corn silage (10%), and wet distillers' grains with solubles (7%). Monensin was delivered in a pelleted supplement that was top-dressed at 3% of the diet. Pellets not containing monensin were fed to CON at 3% of the diet. Heifers were limit-fed 100% of estimated MEm requirements, with amounts recalculated for the first, second, and third trimesters. Total fecal and urine collections were conducted over 96 h to determine digestion and energy metabolism. Collection periods occurred on d 14, 42, and 161 of feeding monensin, corresponding to the first, second, and third trimesters of gestation. Gas exchange was measured on d 0, 3, 14, 28, 42, and 161 using portable headbox calorimeters designed on the concepts of open-circuit calorimetry. Individual heifer oxygen consumption, carbon dioxide production, and methane production were determined over a 24 h period. There were no significant differences (P > 0.05) in DM intake as a result of feeding monensin (6.60 kg/d vs. 6.61 ± 0.09 kg/d; CON and MON, respectively). Diet digestion did not differ (P > 0.05) between treatments, averaging 44%. On d 42 there was a tendency (P = 0.09) for MON heifers to consume 1.12 ± 0.64 Mcal/d more DE and 1.19 ± 0.63 Mcal/d more ME (P = 0.06) compared to CON heifers. Monensin resulted in a significant reduction (P < 0.01) in methane production from 1.58 L/kg MBW for CON to 1.47 ± 0.03 L/kg MBW for MON. The magnitude of methane reduction was consistent across time, suggesting monensin is a viable production option for reducing methanogenesis long-term.
