Effects Of Feeding Castor Beans On Oestrous Cycle And Subsequent Fertility Of The Sudan Desert Ewes (Hamari)

Abstract

This study was carried out to determine the length of the oestrous cycle and progesterone (P4) profile during the oestrous cycle of the Sudan Desert ewes (Hamari) and to investigate effects of feeding castor beans on the oestrous cycle and subsequentfertility of the treated ewes. Experiment 1was conducted to determine the length of the oestrous cycle and P4profile during the cycle. Ten cyclic Hamari ewes were monitored throughout two natural oestrous cycles, using teaser rams. Blood samples were collected from the jugular veins at 48 hr intervals, starting from the onset of oestrus as detected by the teaser rams, 9 samples were collected from each ewe during each cycle. Blood serum was removed and stored at-20°C until assayed for the P4concentrations. Results of this experiment showed that the mean length of the oestrous cycle in the Hamari ewes was 16.5 ± 1.4 days, with a duration of oestrus of about 25 hr. The mean P4concentration in the peripheral serum of the ewes was lowest on day 0 (0.11 ± 0.01 ng/ml), with a small increase occurring through day 4 (0.35 ± 0.03 ng/ml). The P4levels continued to increase from day 6 (1.39 ± 0.07 ng/ml) to day 8 (1.62 ± 0.04 ng/ml). Then a pronounced rise on day 10 (2.59 ± 0.04 ng/ml), with a peak value on day 12 (2.63 ± 0.04 ng/ml). This high level was maintained for few days, before declining rapidly on day 14 (1.20 ± 0.09 ng/ml) to reach a basal level on day 16 (0.29 ± 0.1 ng/ml) of the cycle. The shape of the P4 profile can be divided into: an initial sigmoid rise, a plateau and a precipitous decline. Experiment 2was conducted to determine a probable luteolytic effect and the effective dose of the whole beans of castor plant. Thirty cyclic Hamari ewes were used. Twenty ewes were randomly assigned between ix two equal treatment groups (A and B). The remaining 10 ewes, whose natural oestrous cycles were monitored in experiment 1,were used as a control group (C). Oestrus was synchronized in the treatment groups with 2 intramuscular injections of PGF2α(125µg), 9 days apart. Group A was fed 2-4 gm/ewe (55-110 mg/kg bwt) whole castor beans on day 9 of the oestrous cycle (T1) and group B was fed 6-8 gm/ewe (165-220 mg/kg bwt) whole castor beans on day 9 also (T2). Thereafter the ewes were monitored for oestrus response using the teaser rams. Nine blood samples were collected from eachewe, at 48 hr intervals starting from the onset of the synchronized oestrus. Blood serum was removed and deep frozen. The serum P4concentrations were assayed in these samples to determine the effects of the treatments on the luteal function. Results of this experiment showedthat both castor beans treatments induced luteolysis 72 hr after the treatment, in 8 out of 10 of the treatment 1 group and in all of the treatment2 group, with highly significant difference (P<0.001) in the P4concentrations between the control and each treatment group. The P4profile of each treatment group corresponded with that of the control group until day 10 of the cycle. Luteolysis encountered on day 12 as evident by the sharp drop of the profile. Thereafter the treatment profileassumed a reversed trend to that of the control through day 16 of the cycle. Experiment 3was conducted to investigate the location of the active ingredient in the beans of castor plant. Ten ewes from the previous treatment groups were randomly assigned between two treatments after the elapse of 2 natural oestrous cycles from the last treatment. The castor beans were decorticated and the husks obtained from 8 gm castor beans were fed to each of 5 ewes (T3) and the remaining decorticated seeds obtained from 8 gm castor beans werefed to each of the other 5 ewes (T4). These treatments were done on day 9 of the oestrous cycle. Oestrus x was detected using the teaser rams. Three out of five ewes fed castor bean husks showed apparent oestrus 72 hr after the treatment, whereas those fed the decorticated beans did not express oestrus during the following five days of the treatment. Experiment 4was conducted to test the possibility of synchronizing oestrus by feeding castor beans.The remaining 10 ewes from the previous treatment groups (T1and T2) after the elapse of 2 natural heats from the last treatment, were used in this experiment. Each ewe was fed 8 gm (220 mg/kg bwt) whole castor beans as a single meal (T5) irrespective of the stage of the cycle. The oestrus was monitored using the teaser rams. Eighty percent of the ewes responded with oestrus occurring after 48 to 72 hr of the treatment. Experiment 5was carried out to compare the synchronizing potency of castor beans with that of PGF2αin the Hamari ewe. Oestrus in the treatment groups was already synchronized with PGF2αor castor beans. Consequently, comparison was madeutilizing the available data. The level of synchronization produced by feeding castor beans (80%) was similar (P>0.05) to that obtained for the 9-day PGF2αregime (n=10). Experiment 6was designed to investigate the effects of castor beans’ treatment on the subsequent fertility of the treated ewes. All the ewes, which have been treated with castor beans in the above experiments, were monitored for the oestrus detection. Thereafter they were mated with two fertile rams. The fertility of the ewes was assessed by noting pregnancy and lambing rates. The pregnancy rate (95%) and the lambing rate (111%) of the castor beans fed ewes were comparable (P>0.05) to that of the control group. In conclusion, the average length ofthe oestrous cycle and the heat duration found in this study agree with the previous information on other ecotypes of the Sudan Desert sheep. The P4 profile during the oestrous xi cycle follows the general trend of the P4profile of cyclic ewes shown in previous studies in other breeds of sheep. Feeding castor beans to cyclic ewes induces luteolysis of the corpusluteum. Furthermore, castor beans can synchronize oestrus without decreasing fertility. Therefore, the presented method could be used asan alternative for effective synchronization of oestrus in ewes