Milk Fever and Subclinical Hypocalcaemia - An evaluation of parameters on incidence risk, diagnosis, risk factors and biological effects as input fora decision support system for disease control

The present review analyses the documentation on incidence, diagnosis, risk factors and effects of milk fever and subclinical hypocalcaemia. It is her eby evaluated whether the existing documentation seems sufficient for furth er modelling in a decision support system for selection of a control strate gy. Several studies have been carried out revealing an incidence of milk fe ver most often in the level of 5-10%. Few studies indicate that the inciden ce of subclinical hypocalcaemia is several times higher than milk fever. Th e diagnosis based on clinical or laboratory methods or based on presence of risk factors is outlined. The clinical symptoms of milk fever are highly s pecific and the disease level may thus be determined from recording of trea tments. Diagnosis of subclinical hypocalcaemia needs to include laboratory examinations or it may be determined by multiplying the incidence of milk f ever by a certain factor. From the documentation on risk factors, it is ver y complex to predict the incidence from the exposure level of the risk fact ors. Due to uncertainty, sensitivity analyses over a wide range of values f or each parameter are needed. The documentation of cow characteristics, nut rition, environment and management as risk factors are described. Among cow characteristics, parity or age, body condition and production level were f ound to be important. Risk factors associated with nutrition included most importantly dietary cation-anion difference and calcium level whereas the i mportance of general feeding related factors like type of feed stuff and fe eding level were less clear. Environment and management included season, cl imate, housing, pasturing, exercise, length of dry period and prepartum mil king. Several of the parameters on environment and management were confound ed among each other and therefore firm conclusions on the importance were d ifficult. The documentation of the effect of milk fever includes the downer cows, reproductive disorders, occurrence of other diseases and the effect on milk production, body weight and culling. The reproductive disorders inc luded most importantly dystocia, uterine prolapse, retained placenta, metri tis and repeat breeding, and occurrence of other diseases included ketosis, displaced abomasum and mastitis. The documentation was substantial and oft en quantifiable within certain limits. Overall it is concluded that the pre sent documentation on milk fever concerning incidence, diagnosis, risk fact ors and effects seems sufficient for a systematic inclusion in a decision s upport system. A model on milk fever should take into consideration the var iation in biological data and individual herd characteristics. The inclusio n of subclinical hypocalcaemia would be more uncertain and probably should await further documentation on possibilities of determining the herd level incidence and also the effect of this condition on production.