Comparison of eastern gamagrass grain and cottonseed meal as supplements for sheep fed mature eastern gamagrass hay

Eastern gamagrass (Tripsacum dactyloides (L.) L.) is a highly palatable warm season grass that has the potential to become a perennial grain crop with a high protein content (29% crude protein). Twelve wether lambs were used to evaluate eastern gamagrass grain and cottonseed meal as protein supplements for mature eastern gamagrass hay in a conventional digestion and nitrogen balance trial. Voluntary intake of organic matter (OM), neutral detergent fiber (NDF) digestibility, and nitrogen balance were determined for hay alone (CONTROL), hay plus eastern gamagrass grain (GGG), and hay plus cottonseed meal (CSM) treatments. Organic matter intake of supplemented lambs (25.7 g/kg BW) was higher (p<0.001) than lambs fed only hay (20.6 g/kg BW). There was no difference (p=0.22) in OM intake between GGG and CSM supplement treatments. Total tract digestibility of OM differed (p<0.001) among the GGG (61.8%), CSM (58.6%), and CONTROL (54.9%) treatments. However, differences in digestibility may be the result of addition of highly digestible protein and carbohydrate supplements, rather than an increase in digestibility of the hay. Digestibility of NDF was greater (p=0.01) for supplemented lambs (58.4%) than unsupplemented lambs (57.4%) and differed (p=0.04) between the CSM (59.1%) and GGG (57.7%) treatments. Addition of the supplements improved (p<0.001) the digestible (DE) and metabolizable energy (ME) of the total diet. The diet with GGG had more (p<0.001) favorable DE and ME values than the CSM supplemented ration. Nitrogen balance was more favorable (p<0.001) for supplemented (+5.7 g N/day) than for unsupplemented lambs (+1.7 g N/day). Lambs supplemented with GGG (+6.3 g N/day) retained more (p=0.01) nitrogen than lambs supplemented with CSM (+5.0 g N/day) even though nitrogen intake was similar (p=0.98). The difference in the nitrogen retention between the supplement treatments was the result of higher (p=0.01) urinary nitrogen excretion from the CSM as compared to the GGG treatment, while fecal nitrogen excretion was similar (p=0.63) for both supplement treatments. Eastern gamagrass grain was comparable to CSM as a protein supplement for moderate to low quality hay.