As temperatures rise during the summer months, dairy farmers often observe a decline in milk production and overall herd health. While heat stress is a known factor, another less visible culprit—ruminal acidosis—can significantly impact dairy cattle, particularly in high-producing herds.

What is Ruminal Acidosis?

Ruminal acidosis is a metabolic disorder characterised by a decrease in rumen pH due to the accumulation of volatile fatty acids (VFAS) and lactic acid. This condition arises when cattle consume large amounts of rapidly fermentable carbohydrates, leading to an imbalance in rumen fermentation.

There are two primary forms:

• Acute Ruminal Acidosis: A sudden drop in rumen pH below 5.0, often resulting in severe clinical signs and potentially fatal outcomes.
• Subacute Ruminal Acidosis (SARA): A more insidious form where rumen pH ranges between 5.5 and 5.8 for extended periods. SARA is particularly prevalent in high-yielding dairy cows and can lead to decreased feed intake, reduced milk fat, and increased risk of laminitis (1).

Why is SARA More Common in Summer?

Several factors contribute to the increased incidence of SARA during warmer months:

1. Reduced Forage Intake: Heat-stressed cows often consume less forage, leading to a higher concentrate-to-forage ratio in the diet.
2. Altered Feeding Behaviour: Cattle may eat fewer but larger meals during cooler parts of the day, resulting in rapid fermentation and acid accumulation.
3. Dehydration: High temperatures can lead to dehydration, reducing saliva production, which is essential for buffering rumen pH (2).

Prevention and Management Strategies

Effective management of ruminal acidosis involves a combination of dietary adjustments, monitoring, and supportive interventions:

• Dietary Management: Ensure a balanced diet with adequate fibre to promote chewing and saliva production. Gradually introduce dietary changes to allow rumen microbes to adapt. Maintain consistent feeding schedules to prevent large fluctuations in rumen fermentation.
• Monitoring: Regularly assess rumen pH levels, especially during diet transitions. Observe cows for signs of SARA, such as reduced milk fat, loose faeces, and decreased feed intake.
• Supportive Interventions: Incorporate feed additives that stabilise rumen pH and support microbial balance. Research indicates that certain dietary supplements, such as live yeast cultures and probiotics, can enhance rumen function, improve fibre digestion, and mitigate the effects of SARA (3)(4). Functional additives like mannan oligosaccharides (MOS) and beta-glucans are also gaining attention for their role in modulating gut health and immune responses in ruminants, indirectly supporting recovery from digestive upsets (5).

Conclusion

Ruminal acidosis, particularly SARA, poses a significant challenge to dairy production, especially during the summer months. By understanding its causes and implementing proactive management strategies, farmers can safeguard herd health and maintain optimal productivity. For more insights into effective rumen health management, consider exploring this resource.

References:

1. Plaizier, J. C., Krause, D. O., Gozho, G. N., & McBride, B. W. (2008). Subacute ruminal acidosis in dairy cows: The physiological causes, incidence and consequences. The Veterinary Journal, 176(1), 21–31. https://doi.org/10.1016/j.tvjl.2007.12.016
2. Gressley, T. F., Hall, M. B., & Armentano, L. E. (2011). Ruminant nutrition symposium: Productivity, digestion, and health responses to hindgut acidosis in ruminants. Journal of Animal Science, 89(4), 1120–1130. https://doi.org/10.2527/jas.2010-3301
3. Liu, Q., Wang, C., Yang, W. Z., Guo, G., Huo, W. J., Yan, T., & Zhang, S. L. (2014). Effects of Saccharomyces cerevisiae on rumen fermentation and performance of dairy cows during heat exposure. Animal Feed Science and Technology, 198, 61–71. https://doi.org/10.1016/j.anifeedsci.2014.10.008
4. Mao, S., Zhang, R., Wang, D., & Zhu, W. (2013). The diversity of live yeasts in the rumen of dairy cows under different diets. FEMS Microbiology Ecology, 83(2), 313–322. https://doi.org/10.1111/1574-6941.12067
5. Malmuthuge, N., Liang, G., & Guan, L. L. (2019). Understanding the gut microbiome of dairy calves: Opportunities to improve early-life gut health. Journal of Dairy Science, 102(7), 5996–6005. https://doi.org/10.3168/jds.2018-16005