ISSUE FOCUS 32 FEED & ADDITIVE MAGAZINE June 2022 As a result, the average daily gain (ADG) was improved by 50 g /day, and the carcass weight by 5 kg over the fattening period (70 days) with a poorly acidogenic diet. Another study conducted in Italy on a commercial farm (Consortio Agrario del Nordeste) on Charolais breed cattle showed similar results: + 5% ADG (Firgure 1) with an average thermal index THI around 70, and allowed a further understanding of the mechanisms involved. By supplementing the animals with a bolus system, which allows measurement of the ruminal pH in real time (SMAXTEC), this trial indicate that: • Rumen pH decreases in conditions of heat stress, linked in particular to the strong variations of feed intake and loss of saliva buffering capacity (panting). • The live yeast helps stabilizes the rumen pH, especially as the animal is in a heat stress condition (Figure 2). • Thus, ruminal pH is indirectly affected by climate conditions and the use of a ruminant specific live yeast, known for to helps stabilize ruminal pH (rumen modifier), allows the consequences of heat stress on feed intake and growth performance to be minimized. ANTIOXIDANT SUPPLEMENTATION IS KEY During heat stress periods, animals face decrease in antioxidant status. For example, level of superoxide dismutase enzyme (SOD) can decrease and pro-oxidant and stress indicator, such as Malondialdehyde (MDA) can more than double (Fike and Saker, 2005). This is why, ensuring an adequate level of antioxidant solution is important. Nutritionists can choose and combine different sources of antioxidants, either primary or secondary antioxidant. Providing primary antioxidants such as Selenium yeast (such as Alkosel) and natural source of super oxide dismutase (such as Melofeed) helps maintain weight gain of meat type ruminants during heat stress and helps preserve the antioxidant status of animals. A study conducted on a commercial farm in France, during high temperature and humidity period (July with maximum THI of 80) on Charolais breed cattle shows that animals fed a combination of organic selenium source, ALKOSEL, and SOD source MELOFEED shows a higher body weight (+5.8 kg) compared to control group after 28 days of trial (Figure 3). In conclusion, heat stress could be underestimated in beef cattle. However, it does represent a challenging period for the animals, affecting feed intake and consequently rumen conditions and efficiency. Heat stress will have short-term consequences, afFigure 1: Effect of Levucell SC on Charolais daily weight gain (Period 3 correspond to heat stress) (Consortio Agrario del Nordeste, Italy, 2015) Figure 2: Top: Effect of LEVUCELL SC on rumen pH variations. Bottom: Variations of the temperature-humidity index (THI) for the same period (Consortio Agrario del Nordeste, Italy, 2015).
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