Passive immunity and association with morbidity and mortality of dairy calves reared in large-scale Estonian dairy herds

Abstract

Calves are born immunologically naive, thus they achieve passive immunity via colostrum intake and absorption. If the transfer of colostral antibodies is insufficient, the calf has failure of passive transfer of immunity (FPTI), which predisposes the calf on diseases and increases the risk of mortality. The aim of this study was to analyze the prevalence of FPTI and association with morbidity and mortality risk of dairy calves reared in large Estonian dairy herds. In total, the number of calves were 372 (number of herds = 30) for the mortality analysis and 209 (n = 20 herds) for the morbidity analysis (bovine respiratory disease (BRD) and diarrhea). Blood samples from jugular vein were collected from 2-7-day-old calves. Serum total protein (TP) concentration was measured by using a refractometer, a TP cut-off point of 5.2 g/dl was used to discriminate poor and good passive immunity groups. The calflevel follow-up period was 6 months. Survival analysis was used for data analysis. Prevalence of FPTI was 47.0% (175 calves out of total 372 calves). According to the mixed-effect Cox regression model, mortality hazard for calves that acquired poor immunity was on average 3.3 times higher compared to mortality risk of those calves that had good passive immunity (p = 0.007). In poor passive immunity group there was on average 33% higher chance for a calf to develop diarrhea and on average 3% higher change for a calf to develop BRD compared to good passive immunity group. These differences were statistically insignificant (p = 0.263, p = 0.929, respectively). In conclusion, roughly half of the studied calves were identified having FPTI indicating that colostrum feeding practices should be improved in large-scale Estonian dairy herds. Although morbidity was not significantly affected by low serum TP levels, calves with FPTI had considerably increased risk for mortality during the first six months of age. Further studies are motivated to analyze the reasons for FPTI in Estonian dairy herds.

Vasikad sünnivad immunoloogiliselt naiivsetena, seega saavad nad passiivse immuunsuse ternespiimas olevate antikehade imendumise kaudu. Kui antikehade ülekanne ternespiimaga on ebapiisav, ebaõnnestub vasikal passiivse immuunsuse ülekanne (ingl k failure of passive transfer of immunity - FPTI), mis soodustab tal haiguste tekke- ja suremusriski. Käesoleva töö eesmärgiks oli analüüsida Eesti suurtes piimakarjades peetavate piimavasikate FPTI levimust ning seost haigestumis- ja suremusriskiga. Kokku oli vasikate arv suremusanalüüsis 372 (karjade arv = 30) ja haigestumusanalüüsis (veiste hingamisteede haigus (ingl k bovine respiratory disease – (BRD) ja kõhulahtisus) 209 (n = 20 karja). Vereproovid koguti 2–7- päeva vanustelt vasikatelt kägiveenist. Seerumi üldvalgu (ingl k total protein - TP) kontsentratsiooni mõõdeti refraktomeetriga, halva ja hea passiivse immuunsusega rühmade eristamiseks kasutati TP piirväärtust 5,2 g/dl. Vasikate jälgimisperiood oli 6 esimest elukuud. Andmete analüüsiks kasutati elumusanalüüsi. FPTI levimus oli 47,0% (175 vasikal kokku 372 vasikast). Segamõjulise Cox regressioonimudeli järgi oli ebapiisava passiivse immuunsuse omandanud vasikate suremusrisk keskmiselt 3,3 korda kõrgem võrreldes nende vasikate suremusriskiga, kellel oli hea passiivne immuunsus (p = 0,007). Halva passiivse immuunsusega vasikate rühmas oli kõhulahtisuse tekkerisk keskmiselt 33% suurem ja BRDsse haigestumise risk keskmiselt 3% suurem võrreldes piisava passiivse immuunsuse omandanud vasikate rühmaga. Need erinevused olid statistiliselt ebaolulised (vastavalt p = 0,263 ja p = 0,929). Kokkuvõttes tuvastati ligikaudu pooltel uuritud vasikatel FPTI, mis näitab, et ternespiima jootmise praktikaid tuleks Eesti suurtes piimakarjades parandada. Kuigi haigestumisriski seerumi madal TP tase oluliselt ei mõjutanud, oli FPTI-ga vasikatel esimese kuue elukuu jooksul märkimisväärselt suurem risk surra. Edasistes uuringutes oleks vajalik analüüsida Eesti suurtes piimakarjades peetavate vasikate FPTI põhjuseid.