Serum progesterone levels in post-partum dairy cows after repeated application of the prostaglandin F-2 alpha analogue D (+) cloprostenol sodium

Reproductive management programmes based on strategic use of prostaglandin F-2 alpha (PGF(2 alpha)) to induce and synchronize oestrus in post-partum d airy cows are widespread. Repeated shortening of the oestrous cycle during early lactation in high-yielding dairy cows, however, could impair corpus l uteum function and thus decrease fertility. The objective of this study was to analyse the effect of repeated treatments with the prostaglandin F-2 al pha analogue D (+) cloprostenol sodium on progesterone concentrations indic ative of a functional corpus luteum in post-partum dairy cows. Furthermore, the influence of milk production, parity and endometritis on progesterone concentrations under these circumstances were studied. Eighty-four cows of a commercial dairy operation were treated three to four times with D (+) cl oprostenol sodium (Preloban(R); Hoechst Roussel Vet, Wiesbaden, Germany) at 14-day intervals, starting 22-28 days postpartum. Blood samples were colle cted prior to treatment 1 (sample 1) and 14 days after treatments 1, 2 and 3 (samples 2-4) and serum progesterone (P4) levels were determined. The per centage of cows with P4 levels < 1 ng/ml decreased from 51 % in sample 1 to 23 % in samples 3 and 4. More primiparous cows had low P4 levels 14 days a fter the second treatment than older cows (P < 0.05). Cows with low progest erone levels in sample 3 or 4 had lower protein contents in milk on the sec ond milk test day postpartum and in their cumulative milk yield of the firs t 100 days of lactation. Clinical endometritis at postpartum examination di d not influence progesterone levels after treatment with PGF(2 alpha). Repe ated application of PGF(2 alpha) (more than twice) in the post-partum perio d does not influence serum progesterone levels 14 days after treatment. Fai lure to develop luteal tissue after treatment contributed to the conception failures after first service.