CORRELATION BETWEEN INADEQUATE TRANSFER OF PASSIVE IMMUNITY AND NEONATAL CALF DIARRHEA: DIAGNOSTIC, PROGNOSTIC AND TREATMENT ASPECTS

Calves at birth have a naïve immunity system and their immune protection is almost exclusively ensured by the maternal immunity transferred by the ingestion of colostrum in the first hours of life2. Inadequate transfer of passive immunity (ITPI) has been related to increased morbidity and mortality in calves3. Furthermore, calves with ITPI have a 24 times greater risk of developing. Neonatal Calf Diarrhea (NCD) and are more likely to be bacteremic. NCD is a multifactorial disease that causes severe economic losses due to mortality, treatment cost, and poor growth. The clinical presentation of NCD is characterized by liquid feces, dehydration, metabolic acidosis, alterations in posture, behavior and hypovolemic shock. This first study of this research project aims to compare serum total protein (sTP) and gamma-glutamyl-transferase (GGT) activity in calves affected by NCD to discriminate calves with or without adequate transfer of passive immunity (ITPI). Forty-three Holstein Friesian calves admitted to the Clinic for Ruminant and Swine (CTS)-Veterinary Teaching Hospital of the University of Milan for neonatal calf diarrhea (NCD) were enrolled from May 2018 to May 2019. For each calf, age, dehydration degree, hematocrit, sTP, GGT activity and immunoglobulin G (IgG) were measured and recorded. The results underline the influence of the dehydration degree (p 0.02) on sTP concentration and the association between age and GGT activity concentration (p 0.01). The ROC curve analysis, considering the influence of dehydration degree and age of calves, showed different cut-off points for sTP in normohydrated calves (52 g/L) and dehydrated animals (56 g/L), with high sensibility (1 and 0.8 respectively), but low sensitivity (0.6 and 0.58 respectively). The cut-off points of GGT activity, based on the age of the calves, resulted from 295 UI/L in calves with 5 days or more and 100,5 UI/L in calves oldest than 5 days, with high sensitivity (1 and 0.85 respectively) and good sensibility (0.75 and 0.77 respectively). GGT is an interesting test to use in the case of NCD because the variability of results appears to be associated only with the age of the animals and not with the effects of diarrhea. Therefore, the results suggest that the GGT activity is a more accurate test for detecting ITPI in calves affected by NCD compared to the sTP. The second aim of this research project was to identify the major risk factors associated with case fatality in diarrheic calves undergoing a standard therapeutic protocol. Clinical and laboratory findings were reviewed in 225 Holstein Friesian diarrheic calves over a 2 year period. Calves were treated according to a fluid therapy protocol using an oral electrolyte solution or an IV infusion. After therapy, 159 calves were discharged in a healthy state, whereas 66 calves died. Logistic regression analysis showed that serum total protein (STP) concentration (odds ratio, OR, 0.51; 95% confidence interval, CI 0.31–0.84; P < 0.01) and the strength of suckle reflex (OR 4.83; CI 1.17–19.88; P < 0.05) were the major risk factors associated with case fatality in diarrheic calves. These results could help to distinguish between diarrheic calves with a good prognosis and those with a major risk of treatment failure. During NCD, the aim of the treatment is to correct hydration and acid-base imbalance with fluid therapy. Antibiotic treatment is commonly recommended regardless of the pathogen involved, but the real efficacy of its use is controversial. The third study of this research project investigates the efficiency of antibiotics during NCD and their influence on gut microbiota, considering the immunity status of the calf. Forty-two Holstein Friesian calves with NCD, aged from 1 to 28 days were enrolled, excluding those with other concurrent neonatal diseases. Upon admission, dehydration was estimated as body weight percentage and the acid-base imbalance was assessed by venous blood-gas analysis. Furthermore, the immunity status was investigated using serum total protein and the calves were then split into two groups depending on the presence, absence or inadequate transfer of passive immunity (ITPI). For each group, calves were randomly assigned to the antibiotic group (Group A) or to the antibiotic-free group (Group FA). The 4 groups obtained were group A1 (NCD calves with antibiotic administration), group FA1 (NCD calves without antibiotic administration), group A2 (NCD calves with ITPI and treated with antibiotics), group FA2 (NCD calves with ITPI and treated without antibiotics). Group A1 and A2 received ampicillin (10 mg/kg IV q12h for 5 days), a wide spectrum antibiotic as the antibiogram results were delayed. Group A2 and FA2 received hyperimmune plasma as a treatment for ITPI. Each calf was monitored for 28 days. Calf Health Scoring Chart (CHSC), average daily gain and sepsis score were recorded daily. Calves of both groups whose general conditions deteriorated (sepsis score > 60%) were given an antibiotic based on antibiotic susceptibility tests. Furthermore, the microbiota analysis was performed. The results showed no statistical difference for mortality rate, failure of treatment, average daily gain and days with diarrhea between the groups treated with or without antibiotics, regardless of presence or absence of ITPI. Furthermore, the antibiotic treatment was found to be associated with a worsening of the fecal score and scleral vessels. The microbiota analysis showed that the microbiota of calves treated without antibiotics was re-established earlier than calves treated with antibiotics. Our data suggest antibiotic treatment should be omitted in cases of NCD. The last study in this research project was focused on the long-term effects of NCD on reproductive and production outcomes during the first lactation. We also analyzed the effect of the severity of the largest clinicopathologic abnormalities observed during NCD on subsequent first production and reproductive performance. Clinical and laboratory findings were reviewed in 88 Holstein Friesian diarrheic calves over a 4-year period. Calves were treated according to a fluid therapy protocol and then discharged from the hospital in a healthy state. For each animal, days in milk (DIM), 305-day milk yield, milk fat and protein production, and age of first calving (AFC) were recorded. For the control group, we examined non-hospitalized heifers (n=85) of the same age and from the same herd without a clinical history of NCD. The general linear model analysis showed that there were no significant differences between the two groups concerning DIM (P=0.740), 305-d milk yield (P=0.883), fat (P=0.660) and protein (P=0.582) production, and AFC (P=0.879). No effect of the severity of NCD on the first performance was found. These findings suggest that treated NCD had no effect on AFC and first lactation production. This would ensure suitable reproductive and production standards during the first lactation even in calves that have had severe NCD. The present project improves the knowledge of the relation between ITPI and NCD. In particular, the results of this study add to our knowledge in diagnostic, prognostic, therapy and long-term effects regarding the correlation of these two diseases. Based on the results obtained in this project, the recommendations emerged are to prefer GGT as a diagnostic method to identify ITPI calves during NCD, to omit antibiotic treatments during NCD, and to give more importance to fluid therapy. Fluid therapy alone could be sufficient to cure NCD and is also likely to not cause any damage in the long term. The sTP concentration results can be representative of the fatality risk during NCD and administration of hyperimmune plasma seems to be efficient in controlling mortality rates.