SPECIAL STORY 60 FEED & ADDITIVE MAGAZINE April 2023 During the first month of life, baby calves will experience lot of changes in addition to extensive immunity and gut maturation. Moreover, it is well described that the first two months of life of calves are critical for future performance (Abuelo et al. 2021; Buczinski et al. 2021). This article provides a better understanding of immune system maturation and function and its link with gut maturation to design successful calves management nutrition. THE IMMUNITY WINDOW At birth, before developing its own immune system, the calf is protected thanks to the maternal antibodies (Y) from colostrum: this is known as passive or innate immunity, which is why colostrum intake is key in the first hours and days of life and it should be correctly managed. This is particularly challenging for male dairy calves which are of less value and eventually transported long distances at only a few weeks of age. It is not before two weeks of age that the calf starts to acquire its own immunity, called adaptative or active, with the production of antibodies by B-cells. In between, there is a gap called the immunity window or sensitive window, where the calf’s natural defenses are particularly low and critical (Figure 1). A CHALLENGING PERIOD THAT CAN HAVE GREAT ECONOMIC CONSEQUENCES During the first month of life, while immunity is still weak, the calves experience a lot of external stressors (birth, 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 first opportunistic disease to appear is enteric disease during the first three weeks - E. Coli, C. Perfringens, Salmonella -, followed by pneumonia from the second week until adult age. Urie et al. described a morbidity around 34% with a mortality of 5% in 1 month old calves. The major causes of mortality and morbidity are digestive troubles (32% and 51% respectively). In US dairy calves operations, economic consequences of long-term diarrhea outbreaks have been evaluated to almost 71.15$ per calf (USDA, 2014). IMMUNITY AND GUT ARE CLOSELY LINKED Immune defenses have three main components: ENSURING CALVES IMMUNITY, ROLE OF GUT MATURATION AND NUTRITION Marie-Valentine Glica Global Ruminant Marketing Manager Lallemand Animal Nutrition
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