Sjukdomsfrekvens och utslagningsorsaker hos kor med 12 respektive 15 månaders kalvningsintervall

Abstract: The incidence of many of the most common diseases in dairy cattle has been proven to be highest during the time closest to calving. It is possible that the current breeding strategy with 12 month calving intervals increases the risk for disease in dairy cattle, which is problematic concerning both animal welfare and for economic reasons. The economic incentives behind a calving interval of 12 to 13 months have mainly been based on milk- and feed- costs and no costs due to diseases or fertility disturbances have been included.The aim of this study was to see if a lengthening of the calving interval would result in lower disease frequency. The hypothesis is that cows with a planned calving interval of 15 months have a lower disease incidence than cows with a calving interval of 12 months due to less number of calvings. Therefore the difference in disease frequency should be larger when compared over a long period of time, such as over lifetime, since cows with a longer calving interval experience fewer calvings.The study was performed between August 17th, 1994, and January 24th, 2007. The material was collected from Jälla where the Department for Animal Breeding and Genetics until recently had a research herd with approximately 90 dairy cows of the SRB (Swedish Red) and SLB (Swedish Holstein) breeds. The cows were randomly assigned to planned calving intervals of 12 or 15 months with first inseminations 50 and 140 days after calving, respectively. The given calving interval was followed until the cow was culled or till the end of the study. Concern was taken to distribute the breeds equally between the groups. The study included 508 cows in total; 273 with a calving interval of 12 months and 235 cows with a calving interval of 15 months. The study included 1160 lactations and a total of 1523 diagnoses. All diagnoses performed by veterinarians were included. This lead to a diagnose frequency somewhat higher than the disease incidence owing to the fact that a veterinarian may treat the same cow several times during the same period of disease. The most common diagnoses were described separately while the diagnoses with lower frequency were grouped. In total eleven groups of diagnosis were formed.The frequency of diagnoses per year in the study was 1.34 in the group with a calving interval of 12 months and 1.17 in the group with a 15 month calving interval. No difference was seen between the different calving intervals in number of diagnoses per lactation. The main reasons for culling were clinical and subclinical mastitis and decreased fertility; together they accounted for 50 % of the culling. Culling caused by decreased fertility was higher in the shorter calving interval (23% vs 16 %; p < 0.08). The SLB cows in the 15 month calving interval had shorter survival than those in the 12 month calving interval, the reason for this is yet to be investigated. Cows with 12 month calving interval tended to be culled because of decreased fertility more often than cows with longer calving intervals. A tendency towards higher disease frequency in the 12 month group was observed for the tree most common diagnoses; mastitis, paresis and leg- and hoof disease. The results from this study suggest that a longer calving interval may reduce the disease incidence which would entail less animal suffering and decrease the need for treatments using antibiotics and hormones.