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Deslorelin acetate for induction of ovulation
Deslorelin acetate for induction of ovulation
Reports from The 1997 Equine Nutrition and Physiology Symposium. May 28-31, 1997 Fort Worth, Texas
A study at Colorado State University by K. C. Nickerson and coworkers compared two dosages of the GnRH analogue deslorelin acetate on induction of ovulation in seasonally anestrous mares. A report was made at the 1997 Equine Nutrition and Physiology Society Symposium, in Fort Worth, Texas. Based on the results of this study, administration of deslorelin acetate implants every 3 days to seasonally anestrous mares will induce ovulation in a limited percentage of mares. The development of large follicles that subsequently regressed in several GnRH-treated mares may indicate that LH concentrations were not sufficient to induce final follicular maturation and ovulation. Therefore, the researchers suggested that additional stimulation, such as hCG, may be required in conjunction with the GnRH treatment to induce ovulation in these mares. They noted that immediately following implantation, LH levels increased significantly, but dropped by the third day after GnRH administration. They thought it possible that administration of GnRH implants every two days may result in levels of LH that are maintained at a more constant elevated level and that higher ovulation rates may subsequently occur. They recommended further studies on dosages and administration frequency of deslorelin acetate and the potential benefit of GnRH plus hCG.
Prolactin There is currently little information on how prolactin functions in horses, according to B. S. Leise, speaking at the 1997 ENPS Meeting. Besides its involvement in lactation, prolactin has been implicated in such processes as reproduction, hair shedding, fat metabolism, and immune responses in other species. In horses, there is one report of increased follicular growth in anestrous mares administered prolactin. There have been reports that prolactin enhances immune responses in chickens, and rats. One report showed that prolactin increased after a meal in mares and stallions. A study was conducted at Louisiana State University to determine how the lack of prolactin effects horses. Horses were immunized against prolactin so that antibodies would neutralize prolactin. There was no effect of immunization against prolactin on the onset of estrus or hair shedding. There was no difference in response to feeding between the two groups; thus, even though prolactin increases after feeding, it does not appear to have any direct effect on plasma insulin, nonesterified fatty acids, or glucose responses. There was a greater immune response in immunized mares, which is contrary to that found in other species. Affects of melatonin administration on prolactin concentrations
According to S.E. Wheeler and B.P. Fitzgerald, there is general agreement that the administration of melatonin in mammals is associated with a suppression of PRL secretion, yet while pinealectomy or ablation of the suprachiasmatic nuclei may disrupt endogenous melatonin secretion, a seasonal rhythm of prolactin
306
JOURNAL OF EQUINE VETERINARY SCIENCE
Reports from The 1997 Equine Nutrition and Physiology Symposium. May 28-31, 1997 Fort Worth, Texas
A study at Colorado State University by K. C. Nickerson and coworkers compared two dosages of the GnRH analogue deslorelin acetate on induction of ovulation in seasonally anestrous mares. A report was made at the 1997 Equine Nutrition and Physiology Society Symposium, in Fort Worth, Texas. Based on the results of this study, administration of deslorelin acetate implants every 3 days to seasonally anestrous mares will induce ovulation in a limited percentage of mares. The development of large follicles that subsequently regressed in several GnRH-treated mares may indicate that LH concentrations were not sufficient to induce final follicular maturation and ovulation. Therefore, the researchers suggested that additional stimulation, such as hCG, may be required in conjunction with the GnRH treatment to induce ovulation in these mares. They noted that immediately following implantation, LH levels increased significantly, but dropped by the third day after GnRH administration. They thought it possible that administration of GnRH implants every two days may result in levels of LH that are maintained at a more constant elevated level and that higher ovulation rates may subsequently occur. They recommended further studies on dosages and administration frequency of deslorelin acetate and the potential benefit of GnRH plus hCG.
Prolactin There is currently little information on how prolactin functions in horses, according to B. S. Leise, speaking at the 1997 ENPS Meeting. Besides its involvement in lactation, prolactin has been implicated in such processes as reproduction, hair shedding, fat metabolism, and immune responses in other species. In horses, there is one report of increased follicular growth in anestrous mares administered prolactin. There have been reports that prolactin enhances immune responses in chickens, and rats. One report showed that prolactin increased after a meal in mares and stallions. A study was conducted at Louisiana State University to determine how the lack of prolactin effects horses. Horses were immunized against prolactin so that antibodies would neutralize prolactin. There was no effect of immunization against prolactin on the onset of estrus or hair shedding. There was no difference in response to feeding between the two groups; thus, even though prolactin increases after feeding, it does not appear to have any direct effect on plasma insulin, nonesterified fatty acids, or glucose responses. There was a greater immune response in immunized mares, which is contrary to that found in other species. Affects of melatonin administration on prolactin concentrations
According to S.E. Wheeler and B.P. Fitzgerald, there is general agreement that the administration of melatonin in mammals is associated with a suppression of PRL secretion, yet while pinealectomy or ablation of the suprachiasmatic nuclei may disrupt endogenous melatonin secretion, a seasonal rhythm of prolactin
306
JOURNAL OF EQUINE VETERINARY SCIENCE