Milk progesterone in Finnish dairy cows: a field study on the control of artificial insemination and early pregnancy

Seasonal progesterone levels were determined by radioimmunoassays in defatted and whole milk samples from about 10 000 Finnish dairy cows on the day of AI (day 0) and 22 to 23 days later to develop a technique for monitoring fertility status in cows in the field.Fluctuations in milk progesterone levels were seen both on day 0 and day 22/ 23. Mean progesterone concentration on day 0 was 0·7 nmol/l in defatted and 5·6 nmol/l in whole milk. The seasonal variation was positively correlated with the number of luteal phase inseminations during different months (mean 4·6%, June to September about 3%, other months 4 to 8%). Mean progesterone concentration on day 22/23 was 8·7 nmol/l in defatted and 51·9 nmol/l in whole milk. The seasonal variation correlated positively with the non-return rates during different months (January to May 42 to 48%, June to November 53 to 72%).The Finnish breed cows had lower 0-day and higher 22/23-day progesterone levels than the Ayrshire and Friesian cows. These differences correlated positively with the non-return rates, which were 73, 57 and 62% in summer for the Finnish, Ayrshire and Friesian breeds, respectively.The overall accuracy of the defatted milk pregnancy diagnoses was 88% compared with rectal palpation data and 85% compared with non-return rates. Respective figures for the whole milk pregnancy diagnoses were 89 and 85%. The breed and seasonal differences were not considered to significantly affect the accuracy of the milk progesterone pregnancy test.Based on this field study, the Finnish Co-operative Dairies' Association has offered this oestrus monitoring and pregnancy diagnosis service to the farmers in eastern Finland.