[Management of the dry and transition periods of dairy cattle in free stall housing systems in Lower Saxony. - Part 2: Risk factores for subclinical ketosis, hypocalcaemia and increased lipomobilisation].

OBJECTIVE: Determination of the frequency of subclinical hypocalcaemia, increased lipomobilisation and subclinical ketosis as problems in dairy herds and identification of possible risk factors.

MATERIAL AND METHODS: Information was obtained from 51 dairy farms on husbandry, feeding, management of the cows and heifers, animal health and prophylactic treatments using a questionnaire. Blood samples from 20% of the cows and 30% of the heifers of each farm (= herd sample) were collected in the week ante partum (a. p.) for determination of serum calcium (Ca), magnesium (Mg), phosphorus (P) and non-esterified fatty acids (NEFA) concentrations and in the week post partum (p. p.) for measurement of serum β-hydroxybutyrate (BHB) concentration. For evaluation of the herd sample results, the percentage of animals with a laboratory value above a determined threshold value for the various parameters was calculated. When the percentage exceeded a certain threshold (alert) level, a herd problem was assumed. Alert levels from the literature and adapted levels were used.

RESULTS: For minerals, an adapted alert level of 10% was taken as a basis. In cows, the alert level for Ca, Mg, P (too low) and P (too high) was exceeded in 13.7%, 13.7%, 25.7% and 7.8% of the herd samples, respectively. NEFA (a. p.) and BHB (p. p.) had an adapted alert level of 30%. For NEFA, the alert level was exceeded by cows and heifers on 47.1 % and 51.0% of the farms, respectively. For BHB, the alert level was exceeded by cows and heifers on 33.3% and 13.7% of the farms, respectively. As risk factors, a too large group size for the transition cows (Ca, Mg), pasturing (Ca, BHB), one phasic feeding of dry cows (Mg, BHB) and a lack of a separated dry cow area (BHB) were identi fied. Risk factors for the heifers were no pasturing of the young stock (NEFA) and a low frequency of pushing up the diet in the feed bunk (BHB).

CONCLUSION AND CLINICAL RELEVANCE: Subclinical ketosis in cows and an increased lipomobilisation in heifers were frequent herd problems in the dairy herds studied and were asso ciated with husbandry, feeding and management. Therefore, these herd problems should be handled intensively in veterinary herd health programs with the aim to establish effective preventive measures.