EFFECTS OF ADMINISTERING PROGESTERONE AT SELECTED INTERVALS AFTER INSEMINATION OF SYNCHRONIZED HEIFERS ON PREGNANCY RATES AND RESYNCHRONIZATION OF RETURNS TO SERVICE

In 3 separate trials at 2 locations, dairy heifers (n = 396) were trea ted with a Controlled Internal Drug Release (CIDR) progesterone device (4) for 9 d. On Day 7 of CIDR treatment, all heifers were injected wit h PGF(2 alpha)(5). Synchronized estruses were detected using a tailpai nt and chalk (TPC) scoring system. An animal's tailhead was painted at device insertion, and this strip was covered with a contrasting color of chalk at device removal. Over all trials, 85.1% of the heifers wer e detected in estrus and were inseminated at 48 or 72 hours after CIDR removal. These synchronized and inseminated heifers were divided into the following treatment groups: 1) untreated controls, receiving no f urther treatment (n = 138); 2) post-insemination progesterone suppleme ntation with a new (n = 59) or used (n = 29) CIDR device for Days 1 to 8 or 2 to 9, respectively, following insemination; or 3) resynchroniz ation of return to service with a used CIDR device for Days 17 to 22 a fter insemination (n = 112). The pregnancy rate to first insemination in the control and resynchronized groups (Groups 1 and 3) was 45.4 %, but decreased to 18.2 % with the post-insemination progesterone supple mentation. Resynchronization of returns to service (estrus detected 1 to 4 d following removal of second CIDR) occurred in 58.9 % of all non pregnant heifers in Group 3. In summary, CIDR devices used in conjunct ion with PGF(2 alpha) effectively synchronize estrus in dairy heifers. Progesterone supplementation within 2 d of first insemination for 7 d suppressed fertility. Used CIDR devices inserted for Days 17 to 22 af ter first insemination resynchronized heifers not pregnant to first in semination.