Can feedlot cattle increase productivity and decrease methane emissions by lowering the straw particle size?

Abstract

The objective of this study was to assess the effect of using ground and pelleted straw, instead of straw in the long form, on feed utilization by and methane production from feedlot cattle. Eighteen Montbéliarde cross bred male beef calves (358 ± 3,8 kg and 251 ± 0,5 days) were assigned to two treatments (9 animals per treatment) in a Randomized Complete Block Design: large straw (LS), and ground (6 mm sieve) and pelleted (8 mm granule diameter) straw (PS), both offered ad libitum. All animals were fitted in the dorsal sac of the rumen with a 15 mm internal diameter permanent cannula, and consumed the same concentrate ad libitum. Average daily gain, and intake of straw and concentrate, were recorded through a sixteen-week period. Digestibility was estimated using chromic oxide as marker, and rumen liquid and gas samples were obtained at different times of the day in two occasions during the experimental period to characterize rumen fermentation. Abundance of total bacteria, methanogens, protozoa and anaerobic fungi was also analysed. All animals were slaughtered at a target LW of 500 kg, and dressing percentage and carcass classification were obtained from the slaughterhouse. All data were analysed using the PROC MIXED of SAS. The results showed that the particle size of straw had not a significant effect (P > 0.05) on final live weight (LW), average daily gain, carcass dressing percentage, intake of straw, concentrate, dry matter or digestible organic matter, digestibility values, production of methane (CH₄) and carbon dioxide (CO₂), and abundance of microorganisms in the rumen. However, animals fed pelleted straw had lower rumen pH (5.97 vs 6.43, P = 0,0423), and tended to have lower rumen protozoal concentration (P = 0.0826), suggesting a higher risk of experiencing rumen acidosis than those fed long straw. In conclusion, reducing the particle size of straw does not seem a suitable strategy to reduce methane production or prevent rumen acidosis in feedlot cattle.