Occurrence of cystic ovaries in dairy cows in Sweden

The occurrence of cystic ovaries in dairy cows in Sweden was investigated using data on almost 390 000 individuals. Logistic regression analysis was used to assess relationships between cystic ovaries and explanatory variables. Cows of the Swedish Red and White breed (SRB) had twice as many diagnosed cystic ovaries as did Swedish Friesians (SLB), and first-parity cows had half as many cystic ovaries as older cows. The odds for cystic ovaries increased with increasing parity for SRB cows, even after second parity, but not for SLB cows. The diagnosis appeared to be made earlier during lactation in SRB and in high-parity cows. Twin calving in the present lactation and cysts in the previous lactation increased the odds. Cows calving either during months with subsequent risk periods during pasturing or during months with increasing daylight had lower odds for cystic ovaries. The odds increased with increasing milk yield in the present lactation (estimated conditionally on yield in the previous lactation), but decreased with increasing production in the previous lactation (estimated conditionally on yield in the present lactation). In SRB cows, the odds decreased with increasing herd production level.