PSIII-9 - Protein supplementation on low-quality forage: impact on enteric emissions from beef heifers

Abstract: In recent years, there have been numerous experiments both across the U.S. and abroad examining methods to reduce enteric methane emissions. However, baselining enteric methane emissions and common supplementation strategies have not been extensively researched and little work has been done in collaboration with beef cattle producers. The objective of this project was to quantify the impact of two supplementation strategies on enteric emissions of lactating beef heifers grazing low-quality native forage: 1) Hand-fed supplement (HDF) and 2) Self-fed protein block (SPB; 20% CP). The HDF treatment was a meal-based supplement (31% CP) fed at 0.91 kg/hd/d offered 3-d per week. Enteric CH₄ production was measured using a GreenFeed emission measurement system (AHCS; C-Lock Inc., Rapid City, SD) equipped with CO₂ and CH₄ gas analyzers. Before the experiment started, 120 heifers (initial BW = 371 kg) were acclimated to the AHCS system for approximately 21-d. During this period, heifers were grazing stockpiled pasture prior to movement into treatment pastures and body weight collection. Heifers were selected for use based on pre-trial AHCS utilized and sorted into treatment groups (40 hd per treatment) and moved to dormant native range pastures of approximately 40 ha per pasture for a 50-d enteric gas measurement period. Initial and final body weights were similar across the two treatment groups. Tub consumption over the project period averaged 0.58 kg/hd/d for the SPB treatment. For enteric CH₄emissions, there was a significant difference between the two treatments (P = 0.04), where the HDF treatment (152 CH₄ g/d) had lower enteric CH₄ than the SPB (169 CH₄ g/d) treatment. Carbon dioxide emissions followed a similar numeric trend to enteric CH₄ emission rates but no difference was detected between treatments (P = 0.18). These results would indicate that the HDF supplement likely encouraged partial substitution of the pasture as forage quality (< 4% CP) was not sufficient to meet heifer maintenance and energy requirements alone, and the HDF had an improved overall plane of nutrition resulting in lower emissions.