A new intravaginal progesterone releasing device for cattle (CIDR-B) for oestrous synchronisation, increasing pregnancy rates and the treatment of post-partum anoestrus

Abstract

New intravaginal (CIDR) devices have been developed for the controlled administration of progesterone to livestock. A series of trials associated with the evaluation of the CIDR-B device for use in cattle showed that the amount of hormone released during a 15 day treatment period was highly repeatable and depended on initial progesterone content. In spite of this predictable hormone loss, individual treated animals showed wide variations in plasma progesterone concentrations. The effect which supplemental progesterone had on the inter-oestrous interval depended on the stage of the cycle at insertion, the duration of treatment and interactions with other compounds administered at device insertion (oestradiol benzoate) or removal (prostaglandin F 2α). There were significant differences in the distribution of post-treatment intervals to oestrus among synchrony treatments, and among herds within a treatment. Synchrony was more precise with insertion periods of 14 days or more, but pregnancy rates were reduced. The results highlight the desirability of producing treatment regimes which are of short duration (10 days or less) and which combine synchronised luteolysis with synchronised ovarian follicle wave patterns. Pregnancy rates to first insemination were increased if a CIDR device was inserted 6–8 days after insemination. Although this effect was not demonstrated if the device was inserted after mid-cycle, returns to service were synchronised, resulting in fewer missed oestrous events and fewer 6 week return intervals. Progesterone treatment combined with an injection of pregnant mares' serum gonadotrophin (PMSG) at device removal produced oestrus with ovulation in 68% of 855 dairy cows which had a prolonged period of post-partum anoestrum without ovulation. Another 14% of cows ovulated without being detected in oestrus and 18% did not ovulate. This response pattern varied significantly between herds, possibly because of differences in the degree of under-nutrition in early lactation. The results from these comprehensive series of trials demonstrated that the controlled administration of progesterone using a CIDR device can facilitate studies designed to investigate factors which may affect the metabolism of this hormone, or which may influence ovarian activity and pregnancy rate. The likely outcome is that the use of progesterone supplementation, either alone or in combination with other hormones, will be extended beyond the objective of oestrous synchrony to include effective cycle stimulation, return-to-service regulation and pregnancy enhancement.