Fat supplements differing in physical form improve performance but divergently influence methane emissions of grazing beef cattle

Abstract

The objective of this experiment was to determine how physical form of fat supplements affect forage intake, ADG, and enteric CH4 emissions from steers grazing tallgrass-prairie in late summer. Steers (n = 20; BW = 269 ± 35 kg) were acclimated to a portable, automated head-chamber system (AHCS; GreenFeed; C-Lock Inc., Rapid City, SD), and were randomly assigned to one of four treatments, either no supplement (CON), whole cottonseed (WCS), a supplement with bypass fat (BYP; Megalac, Arm and Hammer Animal Nutrition, Princeton, NJ), or a supplement containing soybean oil (SBO). Control steers gained less (P < 0.01) average daily gain (ADG; kg/d) than those that were supplemented. This was a result of improved performance by the SBO and BYP treatments, as BYP had similar (P = 0.13) performance to WCS and SBO, but WCS had significantly lower (P = 0.05) ADG than SBO. Supplemented steers had greater DMI than the CON (P = 0.04) due to the additional supplement, which did not reduce forage intake (P = 0.08). The WCS treatment reduced ADF digestibility (P = 0.02) compared to the other treatments, but aNDF digestibility was not affected by supplementation (P = 0.11). The supplements containing rumen available fat had similar (P = 0.88) CH4 emissions and were lower than BYP and CON (P < 0.01). Bypass supplemented steers and CON had similar (P = 0.75) CH4 emissions. Supplements reduced emission intensity (g CH4/kg ADG) compared to the CON (P ≤ 0.03). However, SBO had lower (P = 0.05) emission intensity than WCS. Across all treatments, increases in forage intake and ADF digestibility increased CH4 emissions (P < 0.05), but aNDF digestibility had a negative relationship (P = 0.03). Both rumen available fat supplements reduced daily CH4 emissions (P < 0.01); however, WCS had less (P = 0.05) ADG compared to SBO. Hence, SBO had a lower (P = 0.05) CH4 emission intensity than WCS. WCS reduced ADF digestibility compared to the other treatments and greater ADF digestibility increased CH4 emissions, therefore it is safe to say that this is the mechanism for CH4 reductions by WCS. The mechanism for SBO is less apparent but may be related to shifts in microbial populations. All supplements improved the sustainability of the tall-grass prairie system, albeit by different mechanisms.