Effect of Monensin and Forage Source on Digestion and Energy Metabolism in Limit-Fed Beef Cows
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Date
2017-07-25
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Abstract
As beef demand increases and available land resources are diminished, innovative approaches to livestock production are required to meet global demand for food. One such strategy is the intensification of cow-calf systems, which allow for greater dietary control during times of limited forage availability. Monensin, an ionophore feed additive, may have value in intensified cow-calf operations by increasing feed utilization and energy efficiency. Furthermore, forage source may affect digestion and ruminal fermentation of limit-fed diets. Three experiments were designed to determine the effect of monensin on energy and nitrogen balance in nutrient-restricted bred heifers and to evaluate the effect of differing forage sources in a limit-fed total mixed ration (TMR) as well as consequences of limit feeding on voluntary intake and ruminal fill. Monensin had no effect on intake (P > 0.94) or digestion (P > 0.52) in limit-fed bred heifers. There were also no differences (P > 0.16) observed in fecal, urinary, methane, or heat energy losses due to monensin inclusion, and thus, monensin also had no effect (P = 0.36) on RE. Nitrogen balance did not differ (P > 0.13) between control and monensin heifers. In assessing the inclusion of varying forage sources in a limit-fed TMR, DE intake was greater (P < 0.03) for bermudagrass than alfalfa with milo stalks being intermediate. Dry matter digestion (DMD) was greater (P < 0.02) for wheat straw and bermudagrass than milo stalks, and there was a tendency (P = 0.06) for alfalfa DMD to be lower than wheat straw DMD. Organic matter, NDF, and ADF digestion were greater (P < 0.02) for wheat straw than alfalfa or milo stalks. Ruminal DM fill was not different (P = 0.18) between treatments and averaged 4.90 kg; however, liquid fill was greater (P < 0.02) for alfalfa and milo stalk treatments than bermudagrass with a tendency (P = 0.06) for wheat straw to also be greater than bermudagrass. Ruminal solid passage rate was greatest (P < 0.01) for steers consuming wheat straw diets and not different between bermudagrass, alfalfa, and milo stalk diets. Dry matter intake and ruminal DM fill following feed restriction remained lower (P < 0.04) than pre-trial levels, while ruminal liquid fill returned to pre-trial levels by d 10 of refeeding. Results of these experiments suggest that adding monensin to limit-fed, corn stalk-based diets has little effect on the energy and nitrogen balance of confined heifers. Additionally, there does not seem to be a clear advantage of feeding one forage over another when considering limit-fed TMR, and voluntary intake and ruminal fill are not restricted following a prolonged period of limit feeding.
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Beef cows, Digestion, Energy balance, Forage, Limit feeding, Monensin