Improving Fibre Digestion In Dairy Cows During Periods Of Heat Stress

Additionally, heat stress can cause changes in the rumen microbiome. There is often a decrease in the population of cellulolytic (fibre-digesting) bacteria such as Fibrobacter and Ruminococcus which are crucial for breaking down fibre (Kim et al., 2022). Conversely, there may be an increase in lactate-producing bacteria like Streptococcus and Enterobacteriaceae which can lead to a drop in rumen pH and potentially cause acidosis. All these events lead to the reduced ability of the rumen to break down fibre. Since the rate of fibre degradation in the rumen controls the rumen bypass rate, this leads to reduced feed intake during heat stress. 

Improving fibre digestion during heat stress helps maintain a stable rumen environment and increases feed intake which is essential for effective digestion, nutrient absorption, and milk production. 

Supplementing dairy cow diets with an exogenous enzyme complex rich in xylanase helps break down hemicellulose, a major component of plant cell walls, into simpler sugars. This process provides more available cellulose to the rumen cellulolytic bacteria for rapid colonisation and fermentation into volatile fatty acids (VFAs), enhancing the digestibility of fibre in the ration and allowing for better nutrient absorption and utilisation. Efficient digestion of fibre reduces the metabolic heat produced in the rumen during fermentation and helps lower the overall heat load on the cow, making it easier for them to cope with high temperatures.

For a xylanase-based enzymatic complex to work efficiently in the rumen, it needs to be:

• effective at the high pH (above 6) found in the rumen
• effective at the temperature of the rumen
• resistant to rumen bacteria proteolysis

Hostazym® X is ideally adapted to the rumen conditions of the dairy cow.

Several in vitro studies showed a significant increase in dry matter and neutral detergent fibre (NDF) rumen digestibility when Hostazym X was added at the optimal dose (Alejandro et al., 2024; Catalina et al., 2024). This was also seen in increased in vitro gas production, a marker for higher rumen fermentation. 

In an in vivo study conducted in Mexico (Higalgo et al., 2025) under heat stress conditions, Hostazym X was supplemented to treated animals at a rate of 9000 EPU/kg DMI (dry matter intake). The dairy cows were fed a typical total mixed ration (TMR) based on corn silage, corn grain and soybean meal between June and October, with total heat allowance (THA) reaching above 75 during the study. Hostazym X helped improve feed efficiency, feed intake, milk production, and milk fat during the trial (Table 1). 

Table 1. Effect of Hostazym® X on performance in dairy cows. Within rows, least square means with different superscripts (a,b) are significantly different (p < 0.01)

The lactation curve of both groups was modelled over 450 days in milk using the spline regression mixed statistical model (Figure 1). 

Figure 1. Lactation curve model over 450 days in milk for cows fed a control ration or the same ration supplemented with Hostazym® X

Conclusion 

During periods of heat stress, dairy cows have reduced feed intake and rumen fermentation, including lower fibre digestion. The addition of the exogenous NSP enzymatic complex Hostazym X shows improvements in rumen dry matter and fibre digestion, supporting higher feed intake levels and better feed efficiency. This leads to increased milk production and higher milk fat content.