ISSUE FOCUS FEED & ADDITIVE MAGAZINE November 2023 23 In a nutshell, there are two parameters to ensure proper rumen function development: a beneficial microbiota and a beneficial diet to allow these microbiota to thrive. Practical tips: How to assess proper rumen development on the farm - Calf starter intake is an important indicator. The target for early weaned calves (~6 weeks) is 0.9-1.4 kg of starter grain per head per day for 3 consecutive days before weaning. This goes up to 1.8-2.3 kg/head/ day for calves weaned at 8 weeks (DCHA, 2016). WEANING: A STRESSFUL EVENT FOR THE CALF AND ITS DIGESTIVE TRACT During early life, while immunity is still weak, calves experience a lot of external stressors (transportation, transition from liquid to solid feed, dehorning, etc.). All these stressors increase the risk of morbidity and mortality by making the immune system more vulnerable. This can lead to visible signs of poor immune defenses such as digestive and respiratory diseases. The major causes of mortality and morbidity are digestive challenges (32% and 51%, respectively) (Urie et al., 2018). In addition, weaning is a challenge for the animal, the rumen and its microbiota. Ruminal diversity decreases due to increased starter intake and decreased rumen pH. The microbial composition changes dramatically at weaning (Figure 1). HOW TO SUPPORT CALVES AT THE WEANING TRANSITION THROUGH NUTRITIONAL STRATEGIES First, the objective will be to strengthen gut immunity to secure the fragile digestive system and limit diarrhea and respiratory diseases. The gut plays an important role in the immune defense system as innate and acquired immunity are concentrated within the gastrointestinal lymphoid tissue (GALT). GALT gathers up to 70% of the body’s white blood cells. Using nutritional additives to support a balanced immune response can be a winning strategy to improve calf health and performance around weaning. In U.S. dairy calf operations, economic consequences of long-term diarrhea outbreaks are estimated to be around 71.15$ per calf (USDA, 2014). “Research has shown a positive correlation between the number of bacterial strains in the rumen and the length of rumen papillae, as well as the thickness of the rumen wall and weight of the rumen, all linked to optimal rumen function and efficiency.” Figure 1. Pre- and post-weaning major rumen bacterial populations (Adapted from Meale et al., 2016).
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