This research reflection examines the physiological links between redox balance, skeletal health and gastrointestinal functionality in dairy cows. With the increase in demand of animal products caused by the growth in human population, the dairy industry needs to develop and implement innovative strategies which are profitable, sustainable and cow friendly. Redox balance, skeletal heath and gastrointestinal functionality are three key physiological systems that are often seen as independent entities. In this research reflection we intend to stress that the antioxidant system, bone health and the microbiome are intimately intertwined. Antioxidants are crucial for the maintenance of redox homeostasis and optimal immune function. Optimal gastrointestinal functionality is important to maintain animal performance, health and welfare. In particular, the intestinal microbiome is increasingly seen as a driver of health and disease. Vitamin D metabolism is pivotal not only for optimal skeletal health, but in light of all the extra-skeletal effect of vitamin D, it is the foundation for optimal productive life. It makes sense to ask the question ‘how are redox balance and the microbiome involved in the modulation of bone health and immune function?’ In other words, are bugs and bones connected in dairy cows! The existing data available in the literature suggests that this might be the case. The characterization of the interactions between redox balance, skeletal health and the microbiome, will allow the development of a multisystem biological approach to refine nutritional interventions to improve dairy cattle health, welfare and productive longevity.

Diet and physical exercise concur in the determination of skeletal mass at the end of adolescence and in the conservation of it during adult life. The functional demand imposed on bone is a major determinant of its structural characteristics. Stress applied to a skeletal segment affects the geometry of the bone, the microarchitecture and the composition of the matrix. The stimulatory effect occurs when the skeleton is subjected to strains exceeding habitual skeletal loads, and the intensity of load is more important than the duration of the stimulus.

Physical activity leads to greater bone density in children and adolescents and, to a minor extent, in adults. Weight bearing activities, such as walking, have a greater effect than non weight bearing activities, such as cycling and swimming. Reduction of loads as in bed resting or in space flights leads to bone loss. Intense training may cause damage, promptly repaired, as in stress fractures observed in army recruits. Female athletes may experience oligo-amenorrhea, though they still have a positive bone balance.

There is an important interaction between the mechanical demands and the availability of nutrients to manufacture bone tissue. The increase in bone density in post-menopausal women is positively related to calcium intake when calcium supplementation is accompanied by exercise. When mechanical demands are low, such as during immobilisation, the intestinal calcium absorption is reduced. Calcium intake should also be analysed in the light of other dietary factors affecting the balance between absorption and excretion, and in combination with a number of other minerals, trace elements and bioactive substances with an impact on bone metabolism.