Reproductive efficiency is the primary factor affecting productivity in buffaloes, but is greatly hindered by weak estrus symptoms, long postpartum anoestrus and subsequent calving interval. The use of controlled internal drug release (CTDR) devices for the synchronization of estrus in cattle is now well accepted throughout the world. The use of CIDR devices has permitted the opportunity to synchronize estrus in buffaloes efficiently during the low breeding season. The objective of the present study was to determine the effect of once used CIDR and FSH on estrus expression and pregnancy rate (PR) during low breeding season in Nili-Ravi buffaloes. Two experiments were conducted during June-August, 2008. In experiment 1, buffaloes received either a used CIDR (UCIDR, n 26) or a new CIDR (NCTDR, n = 24) for 7 d and PGF2a on d 6. During the experiment, two CIDRs were lost in used CIDR group. At the end of the experiment 48 buffaloes were under observation; UCIDR (n = 22) and NCIDR (n = 26). Estrus detection was done twice daily. Buffaloes were inseminated, 12 and 24 hr after the onset of estrus. Pregnancy diagnosis was performed 45 days post insemination using ultrasonography. Estrus expression was similar (P>0.05) between UCIDR (84.6 1%) and NCIDR (95.45%) buffaloes. The mean interval to estrus from PGF2x in UCIDR was 64.5 1.2 h compared to 68 ± 2.5 h in NCIDR (P>0.05). The pregnancy rate did not differ (P>0.05) due to treatment (34.61% in UCIDR vs. 36.36% in NCIDR). In experiment 2, buffaloes at unknown stages of estrous cycle received CIDRs on d 0 and PGF2a on d 6. Animals were either treated with two injections of FSH (5 I.U. i/rn at 12 hr interval; n = 10) starting at CIDR removal on d 7 or remaind untreated (Control, n 10). At the end
19 buffaloes were under observation because of lost of one CIDR from FSH group. Estrus detection, insemination and pregnancy diagnosis was similar as in experiment 1. FSH treatment did not affect the proportion of buffaloes expressing estrus, mean interval from PGF2a administration to estrus and. ovulation, size of ovulatory follicle or pregnancy rate (P>0.05; overall estrus expression rate (84.2%), interval to estrus from PGF2a (62.8 ± 3.3h) and interval to ovulation from estrus (35 ± 5.6h), ovulatory follicle size (10.55 ± 0.55 mm), pregnancy rate (26.3%). In conclusion, a) compared to NCJDR devices, previously UCIDR devices are equally effective to induce estrus and ovulation synchronization with comparable pregnancy rate in buffaloes during low breeding season and b) low dose FSH treatment at CIDR removal did not improve estrus expression or