Recent advances in the understanding of subacute ruminal acidosis (SARA) in goats, with focus on the link to feeding behaviour
Résumé
Sub-acute ruminal acidosis (SARA) is a major nutritional disease occurring in intensive ruminant nutrition due to the allowance of diets rich in highly fermentable ingredients necessary to meet the requirements of the animals. It has been widely described in dairy cows, but less in goats. It is quite difficult to study because, on a given diet, animals are not impacted at the same moment and with a similar severity. The understanding of acidosis has improved recently by measuring simultaneously, in dairy goats fed different diets, feeding behaviour, rumen parameters, blood and plasma parameters, milk yield and composition. Thus, it was possible to study the interrelationships between these variables and to analyse the inter-animal variability to better understand the between-animal differences in SARA susceptibility. Several mechanisms are involved in the multifactorial aetiology of SARA. The first is feeding behaviour. It has been shown that pH evolution is highly related to intake rate and level of intake. Further, chewing and sorting behaviours are modified when animals are given a high concentrate diet. The second mechanism concerns microbial rumen digestion: goats show different susceptibilities to a sudden increase in the percentage of concentrate in the diet. This can be due to differences in initial rumen parameters or to differences in absorption of volatile fatty acids and ammonia across the ruminal epithelium. A third mechanism concerns the metabolism of the animal, and especially the electrolytic balance. Within and between days modelling approaches are helpful to better understand the aetiology and consequences of acidosis in dairy goats. Consideration of these different mechanisms has improved the knowledge about acidosis, and it is expected that the application of automated monitoring technologies together with omics methods will further enhance the understanding of SARA.