From a healthy calf to a performing cow: a case-control study

Objectives: As well as for any enterprise, the main target of the bovine dairy industry is economic sustainability. In other words, the core objective of a dairy operation is to reach an amount of milk production that helps to meet its goals. A dairy herd must be considered as an integrated, productive unit. Starting from newborn calves to milking cows, the health status of the animals is pivotal at obtaining satisfactory economic results. Neonatal calf diarrhoea (NCD) is considered the primary pathology involving newborn calves. Conversely, respiratory disease is the leading cause of losses after 60 days of life. This study aimed to assess the impact of NCDs on health, growth and milk productivity in a selected population of dairy cattle. Materials & Methods: A case-control study was carried out in 300 newborn calves from 5 large dairy cow operations located in the Po Valley (Italy). The animals were split out in two groups: group A (cases) included 150 animals experiencing severe (needing antibiotic therapy) neonatal diarrhoea and group B (controls) included 150 calves without a clinical sign of neonatal enteritis. Weight at the born, 6 and 15 months of life besides the amount of milk during the whole lactation were collected. Also, the mortality rate and prevalence of respiratory disease episodes, involving single animals and requiring antiinflammatory- antibiotic treatments, were recorded. Results: The comparison of group A (cases) with group B (controls) showed: mean weight at the born 47.6±4.2 vs 47.2±3.8kg; at six months of life 182.5±32 vs 198.5±23kg, at 15 months 360.82±32.4 vs 379.4±21kg and average milk production of 11,720±425 vs 12,480±346kg. Group A suffered a mean loss of 760kg of milk per cow, equivalent to about €350- 450, depending on the milk productive destination. The calculation did not take into account losses from mortality and costs for therapy of respiratory disease episodes. Besides, the mortality rate and prevalence of respiratory disease were respectively 9% and 31% in group A vs 5% and 21% in group B. In particular, 45% vs 21% of respiratory disease cases showed relapsing character. Conclusion: The complex of obtained data supports the thesis that neonatal enteritis harms the weight gain during grow period and on milk production too. Regarding the pathogenesis of NCD, failure of passive transfer (FPT) plays an important role in favouring viral, bacteria and parasite infections and related pathogenic effect. A concentration of IgG <1000 mg/100 ml of blood serum collected from calves 3-10 days of life is considered the index of FPT status. The phenomenon is widespread in dairy cattle. A previous study carried out on newborn calves serum samples from 254 Italian Friesian herds with high milk production (≥11000kg/cow/lactation), pointed out an FPT mean prevalence of 28%. Colostrum samples from animals of the same herds showed a 17% prevalence of low-quality colostrum. Parity did not significantly affect colostrum quality. In this study, animals with previous diarrhoea showed a higher prevalence of the respiratory disease in their lifetime. Impairment of enteric barrier triggers a microbial (mainly bacteria) translocation from gut to the bloodstream and then to different organs, lung included. Isolation of E. coli enteropathogenic strains from the lung of calves experienced neonatal diarrhoea credits of value that pathogenetic hypothesis. Furthermore, the anatomy of the bovine lung (8 lobes, absence of interalveolar pores and presence of interlobular septs) hampers the microbial clearance, promoting the persistence of silent foci of infection that can reactivate long life causing relapsing respiratory episodes. If severe, NCD affects health, growth and production of dairy cattle, the control of the disease is the first step to support the sustainability of the business. Following the mantra “is better to prevent than cure”, vaccination of dam during the dry period is included in the protocols to cope with neonatal enteric disorders. If an FPT status persists, even in the presence of active maternal immunization, prevalence and seriousness of the disease often persist as well. To avoid that, it’s pivotal to detect the origin of FPT in the herd, setting up possible solutions.