EFFECTS OF SUPPLEMENTING METABOLITES ON RUMEN FERMENTATION AND MILK PRODUCTION IN DAIRY COWS

Abstract

Microbial fermentation provides essential precursors necessary for milk formation in dairy animals. Archaeal methanogens use some of the available energy to form methane gas. Several nutritional additives have been suggested to change the pattern of ruminal fermentation in ways that could decrease methane emissions or improve efficiency. For example, red algae can directly inhibit methanogens, probiotics may shift fermentation to certain pathways, and metabolites like sulfite and acetate may change metabolic pathways. This study investigated the influence of the combination of such factors on rumen fermentation and milk production and feed intake of dairy cattle. In Chapter 2, an in vitro batch culture system with timothy hay substrate was used to test the effects of Lactobacillus plantarum and red algae (Asparogopsis taxiformis), alone or combined, on gas production dynamics. Red algae consistently reduced methane fraction and cumulative methane production from 0 to 72 h, while increasing hydrogen accumulation and initially suppressing total gas production before it exceeded the control at later incubation times; carbon dioxide parameters were unaffected, indicating strong anti-methanogenic potential that warrants further study of hydrogen redirection in alternative sinks. In Chapter 3, an in vitro dose-response experiment investigated four levels of sodium sulfite (0 - 0.4 mM) on fermentation of timothy hay. The highest sulfite concentration reduced total gas production and methane at early time points (4 - 8 h), increased net hydrogen production at 4 h, and temporarily depressed volatile fatty acid (VFA) concentrations, however, fermentation recovered by 24 h, suggesting delayed but not permanently affecting fermentation in vitro. In Chapter 4, 32 multiparous Holstein cows in a replicated 4 × 4 Latin square received diets containing three levels of sodium sulfite (0, 0.45, 0.9% of DM) with or without 1% sodium acetate to evaluate effects on intake, body weight, and milk production and composition. The treatments were mixed up in the corn based total mixed ration (TMR). Cows fed 0.45% sulfite had the greatest body weight, whereas 0.9% sulfite reduced milk yield and both sulfite levels lowered dry matter intake compared with the control. Sodium acetate did not affect milk yield, energy‑corrected milk, or milk composition, and neither additive altered fat, protein, or fatty acid percentages, contrary to the original hypothesis that sulfite would improve milk yield via increased propionate and that acetate would enhance milk fat. Chapter 5 focused on rumen gas composition, VFA, pH, and redox potential (Eh) in cannulated cows using an unreplicated 4 × 4 Latin square design. The cows were fed one of four diets: bicarbonate, bicarbonate + sulfite, acetate, or acetate + sulfite. Ruminal samples were collected on Days 0, 3, 7, 14, 17, and 20 of each period, with additional samples collected on Day 17 at 0, 4, and 8 hours after feeding. Sodium sulfite and acetate, alone or in combination, did not affect mean rumen H₂, CH₄, CO₂ fractions, CH₄/CO₂ ratio, VFA concentrations, acetate:propionate ratio, or diurnal patterns of fermentation variables, whereas substantial variation was associated with period and sampling time, including lower pH and less negative Eh at 8 h post‑feeding (p<0.05). This study suggested that the sulfite dose used in this trial did not affect the anti-methanogenic or VFA shifts in lactating cows. Therefore, further investigation was needed to explore the adaptability of ruminal micro-organism under such dietary conditions. Finally, Chapter 6 used rumen fluid from cows previously exposed to dietary sulfite as donor inoculum for a 24‑h in vitro batch culture to evaluate microbial adaptation. Donor diet had no effects on total gas production and VFA profiles, but in vitro sulfite addition again reduced gas and methane production, increased hydrogen accumulation, and tended to decrease acetate concentration and the acetate:propionate ratio. These findings indicate that, even after several weeks of exposure to dietary sulfite, the rumen microbiota did not fully adapt to eliminate the anti-methanogenic response, as sulfite infusion in vitro showed alteration on gas dynamics and VFA patterns. Collectively, these studies show that red algae and sulfite effectively suppressed methane and altered hydrogen dynamics in vitro. In contrast, under the conditions of the in vivo study, sulfite inclusion did not produce clear or consistent effects on rumen fermentation, rumen gas profiles, or performance in high-producing dairy cows. The limited replication and challenges associated with high-air rumen gas samples may have reduced the ability to detect treatment differences. Therefore, further work is needed to optimize dose, sampling methodology, and co-substrates to better evaluate the practical potential of sulfite for methane mitigation.