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J. E. Aurich, I. Dobrinski, H.-O. Hoppen and E. Grunert

Summary. Plasma concentrations of β-endorphin and met-enkephalin were measured, with appropriate radioimmunoassays, in cows during gestation and at parturition and in newborn calves. During pregnancy β-endorphin immunoreactivity (IR) concentration increased, but values during the last month of gestation were not different from those at parturition. Highest met-enkephalin IR levels were obtained in cows during calving. A term Caesarean section caused an increase in plasma β-endorphin and metenkephalin IR concentrations, but no such increase occurred in cases of a preterm Caesarean section. In calves β-endorphin IR values were lower before umbilical cord rupture than immediately after birth. Values decreased continuously thereafter. This was also the case for met-enkephalin IR concentrations in calves born at term. In preterm calves met-enkephalin IR values were low immediately after delivery and increased during the first hour of life. A significant correlation existed between the degree of acidosis and plasma levels of both opioid peptides in the calves. We conclude that a direct stimulation of peripheral β-endorphin release by the pain or stress associated with calving does not seem to exist in cattle, whereas met-enkephalin seems to be more directly related to parturition. In calves the change to the extrauterine environment causes an immediate, increased release of both opioids.

Keywords: β-endorphin; met-enkephalin; cattle; parturition; neonate

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R Rathi, A Honaramooz, W Zeng, R Turner and I Dobrinski

Grafting of testis tissue from immature animals to immunodeficient mice results in complete spermatogenesis, albeit with varying efficiency in different species. The objectives of this study were to investigate if grafting of horse testis tissue would result in spermatogenesis, and to assess the effect of exogenous gonadotropins on xenograft development. Small fragments of testis tissue from 7 colts (2 week to 4 years of age) were grafted under the back skin of castrated male immunodeficient mice. For 2 donor animals, half of the mice were treated with gonadotropins. Xenografts were analyzed at 4 and 8 months post-transplantation. Spermatogenic differentiation following grafting ranged from no differentiation to progression through meiosis with appearance of haploid cells. Administration of exogenous gonadotropins appeared to support post-meiotic differentiation. For more mature donor testis samples where spermatogenesis had progressed into or through meiosis, after grafting an initial loss of differentiated germ cells was observed followed by a resurgence of spermatogenesis. However, if haploid cells had been present prior to grafting, spermatogenesis did not progress beyond meiotic division. In all host mice with spermatogenic differentiation in grafts, increased weight of the seminal vesicles compared to castrated mice showed that xenografts were releasing testosterone. These results indicate that horse spermatogenesis occurs in a mouse host albeit with low efficiency. In most cases, spermatogenesis arrested at meiosis. The underlying mechanisms of this spermatogenic arrest require further investigation.

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J. E. Aurich, I. Dobrinski, H-O. Hoppen and E. Grunert

Concentrations of β-endorphin and oxytocin were measured in plasma of cows before, during and after parturition. The effect of the PGF analogue cloprostenol on β-endorphin and oxytocin release was investigated. During parturition, there were marked, parallel increases in β-endorphin and oxytocin concentrations. Both hormones were released in an episodic manner in conjunction with uterine and abdominal contractions. It is therefore likely that factors stimulating oxytocin release also enhance β-endorphin secretion. This suggests a role of labour or labour-associated hormones in stimulating peripheral β-endorphin release. Cloprostenol caused an immediate, pronounced increase in plasma β-endorphin and oxytocin concentrations.

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I. Dobrinski, H. P. A. Hughes and A. D. Barth

The techniques of Feulgen staining, acridine orange staining, and a sperm chromatin structure assay using acridine orange and flow cytometry were compared for selective examination of bovine sperm nuclei. Twenty frozen semen samples were simultaneously analysed by all three methods. The prevalence of abnormally condensed DNA and its relationship to other semen traits were determined in ejaculates from 70 bulls presented for routine examination for breeding soundness and in frozen semen from 348 bulls evaluated over five years. A breeding trial with 118 beef heifers using semen from six bulls with different degrees of nuclear abnormalities was performed to assess the importance of the defects with respect to fertility. The results indicate that few spermatozoa with abnormal DNA condensation are found in normal semen, but the incidence increases with disturbance of spermatogenesis. However, high numbers of abnormally condensed nuclei were found in the absence of an increase in other defects. This nuclear defect might be at least partially of epididymal origin; it can lower fertility and can be compensated for by increasing the numbers of normal spermatozoa in the insemination dose. The percentage of abnormally condensed sperm nuclei as detected by Feulgen staining was significantly correlated with that detected by microscopy after acridine orange staining and by the sperm chromatin structure assay. We therefore consider the Feulgen technique to be a valuable tool for assessing the nuclear integrity of bovine spermatozoa.