The Effect of Season on Estrous Cycle and Timing of LH Surge and Ovulation Following Hormonal Induction in Desert Goat

Abstract

This study was conducted to determine whether south Darfurdesert goats are seasonal breeders ornot. Furthermore, the ovulation time and LH surge were correlated with estrous onset. Three experiments were conducted. Experiment 1 was designed to determine whether or not there is a true seasonal pattern of ovarian cyclicity in the female desert goats. Fifteen female desert goats were used in this experiment. Ovarian cyclicity was monitored by measuring plasma progesterone concentration twice per weekfor one year. The results indicated that does were cycling during all the seasons of the year with a slight decrease in summer and winter. Experiment 2 was conducted to study the chronological relationships between estrus onset, time of LHsurge and ovulation time in does synchronized with chronogest or CIDR. Forty six desert goats were divided into 2 groups; they were assigned for estrous induction using intravaginal spongeor CIDR. At time of sponge or CIDR removal, the animals were injected with 300IU pregnant mare serum gonadotrophin (PMSG). Observations for estrous to detect the onset and duration was carried out every 4 hours after sponge or CIDR removal. Blood samples for LH assay were collected at 0, 24, 28, 30, and 32 hours post sponge or CIDR removal. The ovaries were observed for x ovulation at 48, 50, 52 and 54 hours post sponge or CIDR removal. The results indicated that there was no significant difference in the estrus onset, estrous duration, ovulation time and time of LH surge in does synchronized with either chronogest or CIDR. Ovulation was detected 54 hours post sponges or CIDR removal. LH surge occurred 28 hours post removal ofsponge or CIDR. No significant difference was detected with regard to the time taken from oestrus onset to ovulation time in does synchronized with chronogest and CIDR (25.4 and 23.5 hours respectively). Also, there was no significant difference in the time taken from LHsurge to ovulation time in does synchronized with chronogest and CIDR (25.6 and 25.3 hours respectively). This finding of estrous onset, time of ovulation and the time of onset of the LH peak could be of great help in timing AI or mating for maximum conception in goat breeding programs when CIDR or sponges were usedwith 300IU PMSG. Experiment three was designed to study the Effect of PMSG dose rate on estrous phase, LH pattern and ovulation time in does with estrous induced using chronogest. A total of 90 desert goats were used in this experiment. All does were treated with impregnated vaginal sponge containing 45 mg chronogest. At sponge removal, animals were divided randomly into 3 groups (A, B, and C) and assigned to differentPMSG doses (groupA, 300 IU, group B, 500 IU and group C, 700 IU). The interval betweenthe withdrawal of the sponges and estrus was 28.9, 28.8 and28.2 hours, respectively. Estrus xi duration was 36.0, 42.0 and 42.0 hours, respectively. There were no significant differences (P>0.05) between the treatment groups for the onset of estrus or estrus duration. The results ofthis experiment showed that ovulation was occurred 54 hours postremoval (HPR) in does synchronized using chronogest with 300 IU PMSG and 48 HPR in experimental desert goats synchronized using chronogest with 500 and 700 IU PMSG. LH surge reached 28 hours post removal, irrespective of the treatment. The chronological relationships between ovulation and estrous onset was significantly longer in does receiving 300IU PMSG(25.7 hours) compared with those injected with 500 or 700IU PMSG (19.2 and 19.4 hours, respectively). There was no significant difference in the time taken from estrous onset to ovulation time in does injected with 500 compared with 700IU PMSG. The time taken from LH surge to ovulation was significantly longer indoes receiving 300IU PMSG (25.5 hours) compared with those injected with 500 or 700IU PMSG (19.7 and 19.8 hours, respectively). There was no significant difference in the time taken from LH surge to ovulation indoes injected with 500 compared with 700IU PMSG. The results imply that the increasing doses of PMSG, following a 12-day treatment with intravaginal sponges, significantly affect the ovulation time and chronological data in desert goats