Impacts of graded dietary fiber levels on feed efficiency and carbon footprint of two beef breeds

•Low fiber diet enhanced feed efficiency while reducing carbon footprint in Bonsmara and Nguni steers.•Bonsmara steers emitted less carbon footprint over Nguni steers, irrespective of the dietary fiber level.•Nguni steers had better feed conversion ratio over Bonsmara steers across all experimental treatments.•Nguni steers emitted 1% less of consumed moderate fiber diet as methane compared to low fiber diet. An experiment was conducted to evaluate the impacts of graded dietary fiber levels on feed efficiency and carbon footprint in 9 Bonsmara (225 ± 10.0 kg live weight) and 9 Nguni (215 ± 10.0 kg live weight) steers. The steers were aged between 8 and 9 months. Three treatment diets had graded neutral detergent fiber (NDF) levels of 64.3% (high fiber) for Diet 1, 40.4% (moderate fiber) for Diet 2 and 29.9% (low fiber) for Diet 3. Steers were fed respective experimental diets for 90 days and housed in feedlot individual pens. Body weight gain was measured fortnightly to monitor feed efficiency. Methane emissions were measured to ascertain carbon footprint, using a LaserMethane Mini (LMm). Feed intake was enhanced and carbon footprint was reduced in both breeds by a low fiber diet. When methane emissions were expressed as the percentage of feed intake, 17%, 8% and 6% were observed for Bonsmara steers receiving high, moderate and low fiber diets, respectively. On the contrary, Nguni steers emitted 25%, 12% and 13% of consumed feed as methane for high, moderate and low fiber diets, respectively. Nguni steers in all three treatments had better feed conversion ratio than the Bonsmara steers. Additionally, Nguni steers emitted 1% less of consumed moderate fiber diet as methane compared to low fiber diet. Feeding a low fiber diet can be used to reduce carbon footprint while improving feed efficiency of beef steers.