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Society For Theriogenology
SOCIETY FOR THERIOGENOLOGY The Annual Meeting of the Society for Theriogenology was held August 25-27, 1994, at Kansas City, Missouri. Several papers related to the equine were presented, as well as some general information regarding genetics and reproduction in livestock.
Gene Maps Dr. Joe W. Templeton discussed the significance ofgene maps, pointing out that while more than 10,410 genes have been mapped in the human, maps for other mammals have many less gene locations described. Because mice are traditional genetic research animals, over 2,222 genes have been mapped in this species. While he did not mention how many have been mapped in the horse, he said that over 590 have been mapped in cattle. Most mammals have about 50,000 genes; therefore, much work lies ahead to locate them all on the various chromosomes. A gene map is just that; a description of the linear location on a particular chromosome. The domestic horse has 66 chromosomes of various sizes, with an approximate average number of 750 genes per chromosome. Templeton said, "Our experience has been that gene mapping is crucial to our discovery and characterization of genes controlling resistance to infectious diseases. The relationship of our genetic studies with reproductive biology is essential in that we need to artificially propagate our large families other than by natural matings in order to economically produce sufficiently
538
large genetically informative families. If we are able to identify cattle that possess the genes for natural resistance to brucellosis and tuberculosis, the rapid introduction of these genes into the population will be by artificial insemination and embryo transfer technology. Lastly, there are genes which also have an effect on reproduction. The discovery and characterization of these genes will be facilitated by a gene map."
Faulty Uterine Clearance in Endometritis Dr. Michelle M. LeBlanc said that it is exciting that we may be getting closer to identifying the pathophysiology of recurrent endometritis. She suggested that a delay in physical clearance of intrauterine products during estrus may be the inciting cause and pointed out that the use of oxytocin to enhance clearance is a preferred treatment. "Until recently, oxytocin was not considered to be an appropriate treatment of endometritis," LeBlanc said. "Veterinarians were taught that oxytocin induced strong uterine contractions in mares only after foaling, and then only within the first 24-48 hours." But she described how oxytocin enhances uterine clearance of radiocolloid infused into the uterine lumen in mares resistant and susceptible to endometritis during estrus and 48 hours after ovulation. "Administration of 20 IU of oxytocin IV to susceptible mares results in clearance of more than 85% of the radiocolloid within 15 minutes of intrauterine infusion," she reported. "The same mares clear negligible amounts ofradiocolloid within 4 hours when no drug was given."
She provided the following advice for examining mares for infertility: "Veterinarians must always examine diligently any mare referred for reproductive consult. Racing or performance careers and reproductive histories must be recorded. Conformational defects need to be noted and corrected surgically if deemed appropriate. Examination of the vagina and uterus must be performed as aseptically as possible, as iatrogenic infections may be caused. Ultrasonographic examination of the reproductive tract should be conducted if equipment is available to determine if fluid is accumulating within the uterine lumen. A uterine biopsy may be warranted and, if taken, particular attention should be paid to the presence of lymphatic lacunae."
Estrous Cycles in the Winter While most mares move into diestrus during the winter, a small percentage exhibit estrous cycles during the non-breeding season, according to Dr. B. P. Fitzgerald, University of Kentucky. He believes that elucidation of the factors underlying this interruption of reproductive quiescence may offer new approaches to the manipulation of seasonal reproductive patterns in mares and, in addition, enhance our understanding of the importance of environmental factors, particularly photoperiod, in the control of seasonal breeding in mares. Studies have shown that maintenance of a fixed, long-day photoperiod, beginning at the longest day or summer solstice, caused some but not all mares to cycle during the winter months. It has become c o m m o n practice to abruptly change the day length for open mares beginning at a time when the day
JOURNALOF EQUINEVETERINARYSCIENCE
is shortest. It is evident that most mares are responsive to increasing daylength but not decreasing daylength. Fitzgerald asked the question, "What factors are involved in the termination of the breeding season, and which Steps fail to occur in mares which continue to exhibit estrous cycles during the non-breeding season?" He provided ideas which are a starting place for an answer to this question. "It is likely that the mare employs photoperiod to regulate the timing of the onset and cessation of the breeding season in one of three ways," Fitzgerald said. "First, a critical daylength may be used to initiate and terminate seasonal reproductive activity. Second, the annual reproductive cycle could be driven by an endogenous rhythm, with photoperiod acting to time the rhythm. Third, a critical daylength could be employed to initiate or terminate the breeding season, but not both, with the length of the breeding season or non-breeding season controlled by an endogenous rhythm. Unfortunately, a clear solution regarding which strategy is employed by mares is not forthcoming, although current evidence might favor the second." Fitzgerald said that preliminary studies suggest that estrous cycles may occur during the non-breeding season as a consequence of reduced responsiveness to the photoperiodic signal relayed by the pattern of secretion of melatonin. However, an alternative interpretation could be that melatonin plays little, if any role, in the cessation of the breeding season, he added. He concluded, "While enormous strides have been made in our understanding of the factors controlling seasonal breeding in mares, further research is required to fully understand this fascinating biological process. Along this path, new information will undoubtedly result in improved methods for the manipulation of reproductive activity. Such developments may provide breeders and practitioners with
Volume 14, Number 10, 1994
a mare for all seasons." Colostrum Calcium Carbonate Content Predicts Parturition Dr. William B. Ley, Virginia Polytechnic Institute & State University, reviewed the usefulness of the calcium carbonate test of colostrum in predicting the time of foaling. The colostral content of various electrolytes changes prior to foaling. The calcium carbonate content, especially, correlates with fetal maturity. Ley described the usefulness of a quantitative, colorimetric test kit designed to measure calcium carbonate content of water samples for pre-foaling mammary secretions. He said tests have shown this kit to be both sensitive and specific, with useful positive and negative predictive values, when attempting to evaluate the mare's approaching readiness for birth. He advised, "Pre-foaling mammary secretions should be collected once daily in the morning, as soon as mammary development is noted and mammary secretions can be obtained. Samples should be milked into clean plastic vials that have been previously rinsed with double-distilled water and allowed to air dry prior to use. The minimum sample quantity desired is 1.0 to 1.5 ml (0.5 to 0.75 ml per udder half). The test is based on the reaction of calcium with the zinc salt of ethylene glycol-bisN,N,N'-N'-tetraacetic acid (EGTA) in the presence of the indicator, zincon. The zinc is liberated from the EGTA salt by calcium and the endpoint is signaled by the blue color of the resulting zinc-zincon complex. Sample analysis should be performed within 1 hour of collection; if this is not possible, refrigeration of the sample is recommended to prevent, spoilage until testing. A dilution of the pre-foaling mammary secrttion is made in a ratio of 1 part mammary secretion to 6 parts distilled water. One drop of the indicator dye solution, that is provided in the test kit, is added to the diluted sample. Small
quantifies of the diluted sample are then aspirated into the evacuated chamber of the test vial, called a Titrettor. The initial color of the solution should be orange to reddish-orange. The solution should be mixed prior to each aspiration to observe for the solution to change color to blue, the end-point of the reaction. A direct reading of the printed scale on the chamber provides the amount of calcium carbonate (ppm) in the diluted sample tested. The result is not converted to reflect the calcium carbonate of the raw sample. As the mare progresses towards her expected foaling date, and calcium carbonate values increase above 120 ppm, twice per day sampling is advised." Ley has set the threshold value indicating the mare's approaching readiness for birth at 200 ppm from previous experience using this, and other test kits.
539
Gene Maps Dr. Joe W. Templeton discussed the significance ofgene maps, pointing out that while more than 10,410 genes have been mapped in the human, maps for other mammals have many less gene locations described. Because mice are traditional genetic research animals, over 2,222 genes have been mapped in this species. While he did not mention how many have been mapped in the horse, he said that over 590 have been mapped in cattle. Most mammals have about 50,000 genes; therefore, much work lies ahead to locate them all on the various chromosomes. A gene map is just that; a description of the linear location on a particular chromosome. The domestic horse has 66 chromosomes of various sizes, with an approximate average number of 750 genes per chromosome. Templeton said, "Our experience has been that gene mapping is crucial to our discovery and characterization of genes controlling resistance to infectious diseases. The relationship of our genetic studies with reproductive biology is essential in that we need to artificially propagate our large families other than by natural matings in order to economically produce sufficiently
538
large genetically informative families. If we are able to identify cattle that possess the genes for natural resistance to brucellosis and tuberculosis, the rapid introduction of these genes into the population will be by artificial insemination and embryo transfer technology. Lastly, there are genes which also have an effect on reproduction. The discovery and characterization of these genes will be facilitated by a gene map."
Faulty Uterine Clearance in Endometritis Dr. Michelle M. LeBlanc said that it is exciting that we may be getting closer to identifying the pathophysiology of recurrent endometritis. She suggested that a delay in physical clearance of intrauterine products during estrus may be the inciting cause and pointed out that the use of oxytocin to enhance clearance is a preferred treatment. "Until recently, oxytocin was not considered to be an appropriate treatment of endometritis," LeBlanc said. "Veterinarians were taught that oxytocin induced strong uterine contractions in mares only after foaling, and then only within the first 24-48 hours." But she described how oxytocin enhances uterine clearance of radiocolloid infused into the uterine lumen in mares resistant and susceptible to endometritis during estrus and 48 hours after ovulation. "Administration of 20 IU of oxytocin IV to susceptible mares results in clearance of more than 85% of the radiocolloid within 15 minutes of intrauterine infusion," she reported. "The same mares clear negligible amounts ofradiocolloid within 4 hours when no drug was given."
She provided the following advice for examining mares for infertility: "Veterinarians must always examine diligently any mare referred for reproductive consult. Racing or performance careers and reproductive histories must be recorded. Conformational defects need to be noted and corrected surgically if deemed appropriate. Examination of the vagina and uterus must be performed as aseptically as possible, as iatrogenic infections may be caused. Ultrasonographic examination of the reproductive tract should be conducted if equipment is available to determine if fluid is accumulating within the uterine lumen. A uterine biopsy may be warranted and, if taken, particular attention should be paid to the presence of lymphatic lacunae."
Estrous Cycles in the Winter While most mares move into diestrus during the winter, a small percentage exhibit estrous cycles during the non-breeding season, according to Dr. B. P. Fitzgerald, University of Kentucky. He believes that elucidation of the factors underlying this interruption of reproductive quiescence may offer new approaches to the manipulation of seasonal reproductive patterns in mares and, in addition, enhance our understanding of the importance of environmental factors, particularly photoperiod, in the control of seasonal breeding in mares. Studies have shown that maintenance of a fixed, long-day photoperiod, beginning at the longest day or summer solstice, caused some but not all mares to cycle during the winter months. It has become c o m m o n practice to abruptly change the day length for open mares beginning at a time when the day
JOURNALOF EQUINEVETERINARYSCIENCE
is shortest. It is evident that most mares are responsive to increasing daylength but not decreasing daylength. Fitzgerald asked the question, "What factors are involved in the termination of the breeding season, and which Steps fail to occur in mares which continue to exhibit estrous cycles during the non-breeding season?" He provided ideas which are a starting place for an answer to this question. "It is likely that the mare employs photoperiod to regulate the timing of the onset and cessation of the breeding season in one of three ways," Fitzgerald said. "First, a critical daylength may be used to initiate and terminate seasonal reproductive activity. Second, the annual reproductive cycle could be driven by an endogenous rhythm, with photoperiod acting to time the rhythm. Third, a critical daylength could be employed to initiate or terminate the breeding season, but not both, with the length of the breeding season or non-breeding season controlled by an endogenous rhythm. Unfortunately, a clear solution regarding which strategy is employed by mares is not forthcoming, although current evidence might favor the second." Fitzgerald said that preliminary studies suggest that estrous cycles may occur during the non-breeding season as a consequence of reduced responsiveness to the photoperiodic signal relayed by the pattern of secretion of melatonin. However, an alternative interpretation could be that melatonin plays little, if any role, in the cessation of the breeding season, he added. He concluded, "While enormous strides have been made in our understanding of the factors controlling seasonal breeding in mares, further research is required to fully understand this fascinating biological process. Along this path, new information will undoubtedly result in improved methods for the manipulation of reproductive activity. Such developments may provide breeders and practitioners with
Volume 14, Number 10, 1994
a mare for all seasons." Colostrum Calcium Carbonate Content Predicts Parturition Dr. William B. Ley, Virginia Polytechnic Institute & State University, reviewed the usefulness of the calcium carbonate test of colostrum in predicting the time of foaling. The colostral content of various electrolytes changes prior to foaling. The calcium carbonate content, especially, correlates with fetal maturity. Ley described the usefulness of a quantitative, colorimetric test kit designed to measure calcium carbonate content of water samples for pre-foaling mammary secretions. He said tests have shown this kit to be both sensitive and specific, with useful positive and negative predictive values, when attempting to evaluate the mare's approaching readiness for birth. He advised, "Pre-foaling mammary secretions should be collected once daily in the morning, as soon as mammary development is noted and mammary secretions can be obtained. Samples should be milked into clean plastic vials that have been previously rinsed with double-distilled water and allowed to air dry prior to use. The minimum sample quantity desired is 1.0 to 1.5 ml (0.5 to 0.75 ml per udder half). The test is based on the reaction of calcium with the zinc salt of ethylene glycol-bisN,N,N'-N'-tetraacetic acid (EGTA) in the presence of the indicator, zincon. The zinc is liberated from the EGTA salt by calcium and the endpoint is signaled by the blue color of the resulting zinc-zincon complex. Sample analysis should be performed within 1 hour of collection; if this is not possible, refrigeration of the sample is recommended to prevent, spoilage until testing. A dilution of the pre-foaling mammary secrttion is made in a ratio of 1 part mammary secretion to 6 parts distilled water. One drop of the indicator dye solution, that is provided in the test kit, is added to the diluted sample. Small
quantifies of the diluted sample are then aspirated into the evacuated chamber of the test vial, called a Titrettor. The initial color of the solution should be orange to reddish-orange. The solution should be mixed prior to each aspiration to observe for the solution to change color to blue, the end-point of the reaction. A direct reading of the printed scale on the chamber provides the amount of calcium carbonate (ppm) in the diluted sample tested. The result is not converted to reflect the calcium carbonate of the raw sample. As the mare progresses towards her expected foaling date, and calcium carbonate values increase above 120 ppm, twice per day sampling is advised." Ley has set the threshold value indicating the mare's approaching readiness for birth at 200 ppm from previous experience using this, and other test kits.
539