Effects of monensin and dietary energy intake on maintenance requirements in beef cows.
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abstract
A decrease in land availability and inventory of the cow herd has created a concern for the sustainability of beef cattle production. Intensifying production by feeding cows in a controlled environment (i.e. drylot) that allows for dietary manipulation could improve system efficiency, although logistical issues of feed delivery need to be solved. Subsequent trials were designed as 2 2 factorials to determine if limit-feeding an ionophore diet to cows during mid-gestation could reduce maintenance energy requirements. Both projects were designed to feed one diet at either 120% (H) or 80% (L) of NRC requirements with either 0 or 200 mghd-1d-1 of monensin. Forty cows were fed for 56 d to determine performance, while sixteen ruminally cannulated steers were used for intake and digestion. To aid in feed delivery, bulk density and void space were calculated for common feed ingredients to determine mix-ability and maximum payloads. Steers fed L had greater (P < 0.01) DM digestion, OM, ADF and GE than H, while monensin did not significantly affect digestion (P > 0.15). Passage rate was slower for L than H (P < 0.01) and 200 than 0 (P < 0.03). Acetate:propionate was lower in 200 than 0 (P < 0.01) while rumen pH was increased (P < 0.05). Cows gained more BW when fed at H versus L (P < 0.01) with no effect of monensin (P = 0.97). Retained energy per EBW0.75 was greater for H than L (P < 0.01) although heat production was also greater (P < 0.01). Monensin had no effect on either RE (P = 0.94) or HE (P = 0.53). Monensin did not alter feed required for maintenance or fasting heat production. However, FHP was estimated to be 62.85 kcalEBW-0.75d-1, a decrease of 26.1% from NRC requirements. Roughages had lower (P <0.01) bulk density and greater void space (P < 0.01) than concentrates. Accurate predictions of maximum payload of multiple ingredients were able to be made from these calculations. Overall, it appears limit-feeding diets can increase production efficiency of cow-calf systems. Use of bulk density and void space data may allow optimization of mixing and reduce delivery costs of high-roughage diets to large numbers of cattle in confinement systems.
