This study evaluated enteric methane (CH₄) emissions, dry matter intake (DMI), and performance in rearing beef heifers fed either a Guinea-grass-only diet (0WCS) or Guinea grass supplemented with whole cottonseed (WCS) at 0.5% of body weight (BW). Twenty-four Braford heifers were randomly allocated into four pens (three animals per pen) per treatment over two experimental periods. Methane emissions were measured using the SF₆ tracer technique. Heifers receiving WCS supplementation produced 29% less CH₄ (120.64 vs. 169.54 g/day for 0.5WCS and 0WCS, respectively; p = 0.02) and showed a 22% reduction in CH₄ yield (7.30% vs. 9.41% of gross energy intake; p = 0.02). Methane intensity was 33% lower in supplemented heifers (0.37 vs. 0.55 g CH₄/kg BW; p = 0.01). However, WCS supplementation significantly reduced total DMI and forage DMI (p = 0.01 and p < 0.01, respectively). In terms of performance, heifers in the 0.5WCS group gained 0.28 kg/day, while those in the 0WCS group lost 0.10 kg/day. These results indicate that WCS supplementation mitigates CH₄ emissions while improving weight gain in beef heifers fed low-quality forage diets, making it a promising strategy for enhancing the sustainability of beef cattle production systems.

This study evaluated enteric methane (CH₄) emissions, dry matter intake (DMI), and performance in rearing beef heifers fed either a guinea grass-only diet (0WCS) or guinea grass supplemented with whole cottonseed (WCS) at 0.5% of body weight (BW). Twenty-four Braford heifers were randomly allocated into four pens (three animals per pen) per treatment over two experimental periods. Methane emissions were measured using the SF₆ tracer technique. Heifers receiving WCS supplementation produced 29% less CH₄ (120.64 vs. 169.54 g/day for 0.5WCS and 0WCS, respectively; p = 0.02) and showed a 22% reduction in CH₄ yield (7.30% vs. 9.41% of gross energy intake; p = 0.02). Methane intensity was 33% lower in supplemented heifers (0.37 vs. 0.55 g CH₄/kg BW; p = 0.01). However, WCS supplementation significantly reduced total DMI and forage DMI (p = 0.01 and p < 0.01, respectively). In terms of performance, heifers in the 0.5WCS group gained 0.24 kg/day, while those in the 0WCS group lost 0.10 kg/day. These results indicate that WCS supplementation mitigates CH₄ emissions while improving weight gain in beef heifers fed low-quality forage diets, making it a promising strategy for enhancing the sustainability of beef cattle production systems.

Enteric methane (CH₄) emissions from ruminants are one of the major contributors to greenhouse gas emissions (GHG) from agriculture. We hypothesized that increasing levels of whole cottonseed (WCS) in diets decreases CH₄ production in ruminants fed low-quality forages without compromising feed digestibility. Dietary lipid supplementation, particularly with oilseeds such as WCS, has the potential to reduce enteric CH₄ production by altering rumen fermentation pathways. This study aimed to evaluate the effects of WCS inclusion in a tropical forage-based diet on in vitro gas and CH₄ production, fermentation characteristics, and in vitro dry matter digestibility (IVDMD). Five treatments were tested using guinea grass hay (GG) supplemented with 0, 12.5, 25, 37.5, and 50% of WCS (DM basis). Results after 48 h of incubation showed a quadratic response of total gas production with increasing WCS inclusion (p < 0.01), with the highest values observed at 12.5% and 25% WCS. Methane production from digested DM significantly reduced at 50% WCS inclusion (−10.66% respect to control; p = 0.02), suggesting a mitigation effect without detrimental impacts on IVDMD (p = 0.16), which remained unaffected across all treatments. No effects were found in initial or final pH (p = 0.98 and p = 0.89, respectively) or total protozoa count among treatments (p = 0.99). However, levels of 50% WCS inclusion exceed the recommended limit of fat in ruminant diets (>6% DM). Further in vivo validation trials are recommended to confirm these in vitro results and evaluate long-term impacts on animal performance and CH₄ emissions. This article is a revised and expanded version of Whole cottonseed as an alternative to mitigate in vitro methane emissions on low-quality forage-based diets. Presented at the International Research Symposium on Agricultural Greenhouse Gas Mitigation. From Research to Implementation. 21–24 October 2024, Berlin, Germany.