Heat stress: watch out for oxidative stress

As summer is hitting our hemisphere, there is a higher risk of heat stress for dairy cows and beef cattle. It has recently been shown that heat stress impacts, in fact, the animal full life cycle, even before its birth! Producers can experience losses of performance and welfare issues linked to high temperature-humidity index in all ruminant types.

Thus, it is crucial to reduce heat stress impact in all stages of production, including dry cows. In this context, antioxidant supplementation is a valuable tool for heat stress management.

When heat stress becomes oxidative stress

Heat stress is known to affect the animal oxidative status: it generally increases the production of free radicals, leading to oxidative stress :

• In dairy cows, oxidative stress has a negative impact on immune and reproductive functions: increased mastitis frequency and higher somatic cells counts in milk, decreased fertility, increased embryo mortality, post-partum retained placenta, and early calving.
• In beef, in addition to animal health and immune status, oxidative stress can indirectly impact meat quality before slaughtering. Indeed, oxidizing agents present in the meat affect tissue integrity, inducing water loss by fat and muscle cells, and impacting meat color.

Benefits of antioxidant supplementation

It is important to ensure optimal antioxidant supplementation in order to limit some of these long-term consequences of heat stress.  For example :

• Supplementing cow diet with bioavailable organic selenium source Selenium-enriched yeast (Alkosel) shows increased dairy cows total antioxidant status (TAS) and results in higher selenium level in milk.
• In beef, a trial performed from April to November on Charolais (Cozzi et al., 2011) also shows significant improvement of the TAS (Figure 1), as well as the selenium meat content and meat organoleptic quality (color) at slaughter.

Reminder: practical recommendations

Altogether, heat stress is a costly issue for both performance and health of dairy and beef that affects the whole life cycle of the ruminants. Some nutritional recommendations to help manage heat stress comprises:

• Produce high quality, stable forage, using good silage management practices and adapted silage inoculants to optimize aerobic stability.
• Increase the energy density of the diet to make up for the reduced feed intake. More starch or added fat can be useful. Fat is not fermented in the rumen, hence does not release heat during digestion.
• High-quality fiber sources in the diet are essential for optimal rumen efficiency and rumination, especially for high-producing herds receiving high starch diets.
• Take care of the mineral electrolytes balance since excessive sudation, or panting, leads to losses of sodium and potassium.
• Consider live yeast cerevisiae CNCM I-1077 supplementation to optimize rumen function and pH and maintain feed intake.
• Adapt the feeding strategy. Go from once to twice-a-day feeding. Consider feeding less in the day and more at night, when it is cooler.

And, don’t forget antioxidant supplementation!