By-product feeds from cocoa, coconut and rice could cut methane in ruminant diets

Commercial concentrate feed has become a financial burden for many ruminant farmers in Trinidad and Tobago, and a new open-access study suggests that supplemental feeds built from locally available crop by-products could offer a workable alternative. Researchers at the University of the West Indies formulated two alternative supplemental feeds from agriculture by-products that are actually obtainable on the islands, including cocoa hulls and pods, coconut meal, powdered bean, rice bran, rice hulls and corn stover, and then tested how they behaved in an artificial rumen compared with a popular commercial concentrate.

The study was motivated by economics as much as by nutrition. In the Caribbean, feed expenses account for roughly 25 to 50 percent of the variable costs of ruminant livestock production, and traditional high-quality feedstuffs such as corn and soybean are limited or absent in Trinidad and Tobago, so the ingredients for commercial feeds must be imported at high cost. Recent global crises have disrupted trade and reduced the availability of these feedstuffs, pushing prices further upward. The research team, led by Mikeilah Daniella Elizabeth Scott, Eden Natalia John and Kegan Romelle Jones, set out to determine whether feeds formulated from small-scale, seasonally available by-products could serve as a viable nutritional substitute for conventional grain-based concentrates.

Both experimental feeds were designed to be iso-nitrogenous and iso-caloric, meaning they contained similar protein and energy levels, with a metabolizable energy target of 10 megajoules per kilogram of dry matter and a minimum crude protein content of 120 grams per kilogram of dry matter. One formulation, called Supp.-CM, excluded coconut meal, while the other, called Supp.-CS, excluded corn stover, because those two ingredients are the most limiting and are mainly available in contrasting seasons. Corn stover is abundant during the dry season from February to June, whereas coconut meal appears in larger quantities during the wet season from July to December. The feeds were formulated with WINFEED 2.8 software using a stochastic model, and a commercial concentrate made from corn, wheat by-products and soybean meal, the most popular concentrate among sheep and goat farmers in the country, was included as a positive control.

To test the feeds, the researchers used the reading pressure technique, an in vitro method in which approximately one gram of each sample was placed into 125-millilitre glass serum bottles with 100 millilitres of buffered rumen fluid. The fluid consisted of 90 millilitres of buffer solution and 10 millilitres of rumen inoculum, which was collected at the University of the West Indies Abattoir from a five-month-old West African sheep of roughly 35 kilograms that had been fasted for about 12 hours before slaughter. Headspace gas pressure was measured with a pressure transducer at 2, 4, 6, 8, 10, 12, 18, 24, 36, 48 and 72 hours after incubation began, and the pressure readings were converted to gas volumes using a site-specific linear equation with an R-squared value of 0.951. Each treatment had five replicates, and the data were analyzed by one-way ANOVA with Tukey multiple comparison at a significance level of 0.05.

The gas production data were fitted to the non-linear Orskov and McDonald model to extract fermentation kinetics. This model separates gas produced from the immediately soluble fraction of the feed, designated fraction a, from gas produced from the insoluble but fermentable fraction, designated fraction b, and estimates the rate constant for the insoluble fraction, designated c, as well as the lag time before microbial activity begins. The commercial concentrate produced significantly more gas from the immediately soluble fraction and showed higher potential degradability than either alternative feed. The rate constant for the insoluble fraction, the lag phase, ruminal pH and the partitioning factor, a measure of fermentation efficiency, did not differ between feed types.

The timing of peak gas production differed markedly between the feed types. Gas production rate peaked six hours after incubation in the commercial feed, while the alternative supplemental feeds reached their peak rate between 12 and 18 hours after incubation. Both alternative feeds also recorded negative gas production and negative rates of gas production shortly after incubation began, an anomaly the authors found surprising. They suggest that, barring procedural error, the cause is unclear, but they note that cocoa by-products were included in both alternative feeds and may contain toxic levels of phytochemicals such as theobromine, the principal methylxanthine accumulated in cocoa hulls and pods, which exerts deleterious effects on animal production. Some countries have placed restrictions on the inclusion of cocoa by-products in animal feed for this reason.

The concentrations of cocoa pods and hulls in the alternative feeds were below the previously reported optimum inclusion level of around 5 percent of dietary dry matter, suggesting that a combination of factors may be responsible for the negative early gas values. The authors propose that any deleterious effect of theobromine from the cocoa pod inclusion may be short-lived, since only fermentation of the immediately soluble fraction was affected, and volatile fatty acid production usually peaks within three hours after feeding. They also speculate that adaptation of the rumen microbiome to cocoa pods through consistent dietary inclusion of minimum levels could mitigate this short-term adverse effect, though this remains a hypothesis rather than a demonstrated outcome of the study.

Estimated methane production, calculated from total gas production using a published prediction equation, was significantly lower for the alternative feeds than for the commercial concentrate. The commercial concentrate was estimated to produce 49.1 millilitres of methane per gram of dry matter, compared with 40.5 millilitres per gram for Supp.-CM and 41.5 millilitres per gram for Supp.-CS. The authors caution that the lower estimated methane in the alternative feeds suggests lower fiber digestibility and cumulative gas production, which could affect the balance between acid production and utilization in the rumen. Organic matter digestibility after 48 hours was highest in the commercial feed at 586 grams per kilogram, and the observed pH values fell within the lower limits of the normal ruminal pH range, close to the threshold for subacute ruminal acidosis, despite the buffered inoculum.

The chemical composition of the feeds also shaped the interpretation. All three feeds contained similar dry matter, organic matter and metabolizable energy contents, but crude protein was highest while neutral detergent fiber, acid detergent fiber and lignin were lowest in the commercial concentrate. The crude protein content of 120 grams per kilogram of dry matter in the alternative feeds is considered low for supplemental feeds, and the authors note that good quality forages, including grass, legumes, high-protein trees or shrubs, would be needed to ensure adequate dietary protein for highly productive animals. The high lignin contents of the alternative feeds are also a concern because lignin negatively affects digestibility and intake, and since grass forages are the main feedstuffs for small ruminants in Trinidad and Tobago, the overall lignin content of diets containing the alternative feeds could suppress digestibility and intake.

The authors conclude that supplemental feeds from available agriculture by-products have potential to be used as alternatives to commercial concentrate feeds for ruminants in Trinidad and Tobago, owing to comparable fermentation efficiency, comparable fermentation of the insoluble fraction and reduced estimated methane production. However, they emphasize that the potential deleterious effects of Supp.-CM and Supp.-CS at the onset of ruminal fermentation are concerning and may require further investigation. The study also has clear limitations: in vitro fermentation does not fully replicate in vivo digestion, so animal trials are necessary to confirm the nutritional benefits, and the seasonal availability of agro-by-products may affect feed consistency. Future research, the authors suggest, should focus on in vivo feeding trials to assess growth performance and health effects in small ruminants, along with the economic feasibility of large-scale production and optimization of protein content in the alternative feeds.

Subject of Research: In vitro ruminal fermentation kinetics of supplemental feeds formulated from agriculture by-products in Trinidad and Tobago

Article Title: In vitro ruminal fermentation kinetics of alternative supplemental feeds formulated with by-products from food crops

Article References: Scott, M. D. E., John, E. N., & Jones, K. R. (2025). In vitro ruminal fermentation kinetics of alternative supplemental feeds formulated with by-products from food crops. Dairy Science and Management, 2(1), Article 5. https://doi.org/10.1186/s44363-025-00006-w

Image Credits: AI Generated

DOI: 10.1186/s44363-025-00006-w

Keywords: ruminal fermentation, in vitro, agriculture by-products, Trinidad and Tobago, methane, ruminant nutrition, cocoa hulls, coconut meal, rice bran, corn stover, commercial concentrate, feed formulation