Ammoniation or Cane Molasses Supplementation of Tropical Grass Hay

Abstract

Molasses-urea mixtures are often fed with low-quality hay or stockpiled grass pasture to wintering beef cattle (Bos spp.). Chemical treatment of low-quality forage may improve fiber digestibility and animal performance more than energy supplementation of the untreated forage. Laboratory, digestion, and growth studies evaluated the effects of anhydrous ammonia treatment or molasses supplementation on the feeding value of mature stargrass (Cynodon nlemfuënsis Vanderyst) hay. Ammoniation reduced (P < 0.003) neutral detergent fiber (NDF) concentration (89.5 vs. 83.3%) and increased (P < 0.01) in vitro organic matter (OM) digestion (38.6 vs. 51.2%) of the hay. Molasses supplementation (25% of the dietary dry matter) of untreated hay increased (P < 0.05) in vivo OM digestibility by cattle (51.1 vs. 56.8%), but NDF digestibility of untreated hay was reduced (P < 0.05) by molasses supplementation (59.6 vs. 54.6%). Ammoniation increased (P < 0.05) OM (61.6%) and NDF (73.2%) digestibilities compared to untreated hay fed alone or supplemented with molasses. Gestating Brahman crossbred (Bos spp.) first-calf heifers (800 lb) were placed on bahiagrass (Paspalum notatum Fluegge) pasture during the winter and fed (i) untreated hay plus a 16% crude protein molasses-urea supplement, or (ii) ammoniated hay alone. First-calf heifers fed ammoniated hay consumed more (P < 0.05) hay (18.5 vs. 23.5 lb), lost less (P < 0.05) weight during lactation and weaned heavier calves (P < 0.05) than those fed untreated hay plus molasses-urea. Milk production measured from approximately 60 to 150 d postpartum from first-calf heifers fed ammoniated hay remained constant (P > 0.10; 11.4 lb/d), while milk production from first-calf heifers fed untreated hay plus molasses-urea declined (P < 0.05; 14.0 to 5.2 lb/d) during lactation. No toxic effects of ammoniated hay were observed in first-calf heifers or their calves. Ammoniation improves the feeding value of stargrass hay, and offers an option to traditional winter feeding programs of untreated forage plus molasses-urea.