Use of milk progesterone and prostaglandin F2 alpha in a scheduled artificial insemination program

We tested the efficacy of monitoring progesterone in dairy cows using a commercially available milk progesterone test as a determinant for administration of PGF2 alpha to induce estrus in cows before first AI. Holstein cows milked twice daily were assigned randomly for AI at their first estrus after d 42 postpartum (control) or to receive PGF2 alpha after a milk progesterone test. Milk progesterone was assessed in samples from the Monday morning milking in both groups of cows, but only those in the treatment received PGF2 alpha when milk progesterone tested high. Blood was collected before injection of PGF2 alpha on Monday afternoon to verify retrospectively the accuracy of the milk progesterone test. Agreement of serum concentrations of progesterone was 87% for high milk progesterone tests and 63% for low tests. Use of milk progesterone plus PGF2 alpha reduced days to first AI, calving intervals, rate of reproductive culling, and cost per pregnancy and increased the proportion of cows inseminated within 21 d of the beginning of breeding. As a management tool in an AI program, PGF2 alpha use is warranted and cost effective. However, the milk progesterone test is not justifiable unless the cost is significantly lower than the cost of a weekly injection of PGF2 alpha.