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Effects of Ammoniated Bermudagrass Hay and Monensin Supplementation on Heifer Postweaning Growth

Louisiana State University Agricultural Center^,5, Baton Rouge 70893

Abstract

Ammoniation of bermudagrass hay (HAY) and supplemental monensin (200 mg/head/ d; M) were evaluated for interactive effects on feed intake and digestibilities, VFA and N components of rumen fluid and postweaning growth of heifers. Fall-weaned Angus (16) and Brangus heifers (24) were assigned to four postweaning dietary treatments (106 d): HAY, HAY + M, HAY treated with anhydrous ammonia at 3% of DM (AHAY) and AHAY + M. Each heifer received 2.27 kg/d of a concentrate supplement. A 28-d intake trial, composed of a 7-d adaptation period and a 21-d intake period, was initiated on d 64 of the feeding trial. Ruminal fluid was obtained on d 99 of the feeding trial, 4 h after supplement consumption. Concentrate was completely consumed by all heifers each day and concentrate intake was unaffected by dietary treatment. Hay DM intake was similar between HAY and AHAY (P = .36). Ammoniation increased CP and ADF content of treated hay, which subsequently increased daily intake of hay CP (P < .05) and ADF (P < .05). Monensin supplementation decreased daily intake of hay DM (P < .05), x M (P < .05), CP (P < .05) and fiber components (P < .05). An ammoniation x M interaction affected 106-d daily gain (P = .13). Daily gain was .31, .43, .50 and .52 kg/d for HAY, HAY + M, AHAY and AHAY + M. Monensin decreased rumen NH₃ N concentrations (P < .01) and acetate:propionate ratio (P < .05) for the heifers fed HAY but not for those fed AHAY. Hay ammoniation and monensin supplementation were concluded to not be fully additive in their effects on postweaning growth by heifers.

¹ Iberia Res. Sta., Jeanerette 70544; to whom requests for reprints should be addressed.

² Dept. of Anim. Sci.

³ Present address: Cargill Res. Farm, P.O. Box 301, Elk River, MN.

⁴ Present address: USDA-ARS, Coastal Plain Exp. Sta., Tifton, GA.

⁵ Approved for publication by the director of the Louisiana Agric. Exp. Sta. as manuscript 88-70-2411.