Reproductive considerations: mare and stallion.

Functional alterations within the reproductive system and in other supporting systems may limit the reproductive capacity of geriatric patients; however, the age of onset and degree of compromise show wide individual variation. Aging of the hypothalamopituitary-ovarian axis in the mare manifests as delayed entry to the breeding season, prolonged follicular phases, reduced response to ovulation induction, irregular cycles, oocyte defects, increased early embryonic death, and, eventually, persistent anestrus. Aging of the reproductive tract may increase her susceptibility to endometritis, compromise placental formation with long-term effects on the fetus and viability of the resulting foal, increase her risk of ascending placentitis, alter gestation length, and make her more prone to catastrophic rupture of the uterine arteries at the time of parturition. Effects on the stallion are less well documented but include a reduction in sperm output associated with progressive testicular degeneration and potential compromise of libido and mating ability that is often associated with degenerative conditions of the musculoskeletal system.     

Reproductive behavior of the stallion

The reproductive behavior of semi-wild and feral horses is described briefly in order to provide a background on the reproductive patterns and the specific behavioral elements comprising courtship and mating in the horse. The reproductive behavior of the domestic stallion is discussed at length as are various breeding conditions and normal breeding performance. Finally, sexual behavior problems are considered.     

The anatomy and physiology of the avian endocrine system.

The endocrine system of birds is comparable to that of mammals, although there are many unique aspects to consider when studying the anatomy, physiology, and biochemistry. Avian endocrinology is a field of veterinary medicine that is unfamiliar to many practitioners; however, it is important to have a comprehensive understanding when evaluating companion birds in clinical practice. This article covers the anatomy and physiology of the normal avian, and readers are referred to other articles for a more detailed explanation of altered physiology and pathology.     

Avian reproductive anatomy, physiology and endocrinology.

Although many environmental cues influence reproductive activity, the seasonal breeder responds most strongly to long day length. THE MALE BIRD: Testicular interstitial cells secrete testosterone, which influences reproductive behavior such as territorial aggression and song. Other changes observed in seasonal breeders include testicular hypertrophy and enlargement of the ductus deferens and seminal glomus. THE FEMALE BIRD: Early changes associated with rising estrogen levels in the hen include osteomyelosclerosis and hypercalcemia. Ovulation is then induced by LH, which is followed by eggshell calcification, which is under the control of progesterone. Sources of calcium for shell production include intestinal absorption from the diet, renal control of calcium levels, and mobilization of bone calcium stores. During oviposition, PGF2 alpha and vasotocin stimulate powerful uterine contractions [32] in the presence of calcium. Incubation is associated with falling LH levels and rising prolactin levels. If the hen actually enters reproductive quiescence at this time, then molt will follow. Molt is associated with the total regression of the reproductive tract.     

Reproductive physiology of the nonpregnant mare. An overview and update

This article reviews the reproductive events in the nonpregnant mare with emphasis on recent advances. The discussion is restricted to the salient features of puberty (prenatal and prepubertal events), seasonality (gonadotropins, photoperiod, and other modifying factors), and the estrous cycle (hormones, estrus, diestrus, and the control of cyclicity) in the nonpregnant mare.     

The anatomy, physiology, and diseases of the avian proventriculus and ventriculus.

Diseases affecting the proventriculus and ventriculus often present with similar clinical signs. It is important for the avian practitioner to be familiar with these diseases, their prevalence, and the species most commonly affected to judiciously prioritize the appropriate diagnostic techniques. A basic understanding of the anatomy and physiology of the proventriculus and ventriculus is useful in integrating the pathophysiology and clinical signs associated with variable disease processes. It is also essential to evaluate radiographs and endoscopic images, perform diagnostic techniques, make a diagnosis, and provide appropriate therapy.     

The anatomy and physiology of the bovine respiratory system relating to pulmonary disease.

Bovine respiratory anatomy and physiology were reviewed and considered in relationship to the pathogenesis of pulmonary disease. Factors which may predispose cattle to respiratory disease included a small physiological gaseous exchange capacity, greater basal ventilatory activity, and greater anatomical compartmentalization of the lung as compared with other mammals, a low level and atypical bioactivity of bovine lysozyme, and low numbers of macrophages within the alveolar lumen.     

Adrenal-testis interaction in the stallion.

The authors describe the short and long term effects of synthetic adrenocorticotrophin and of cortisol on peripheral plasma testosterone concentrations in 2 stallions. A single injection of either hormone temporarily raised plasma testosterone concentrations but repeated injection (twice daily for 5 days) depressed plasma testosterone concentrations. Cessation of treatment was followed by a rise in plasma testosterone to concentrations higher than those in the pretreatment period. These findings are briefly discussed.     

Cryopreservation of stallion semen: Effect of adding antioxidants to the freezing medium on sperm physiology

Cryopreservation of stallion semen has not reached the level of efficiency and positive results described in other species. This is mainly due to the greater sensitivity of stallion sperm to the freezing process, showing higher rates of oxidative stress and plasma membrane damage, which trigger the activation of several cell damage pathways that ultimately culminate in DNA fragmentation and cell death. Therefore, finding molecules that improve the efficiency of this technique in stallion by preventing oxidative stress and cell damage is required. Thus, the aim of the present study was to evaluate the effect of adding three antioxidants (MnTBAP, NAC and FeTPPS) to the freezing medium on the quality and functional parameters of stallion sperm. Semen samples from three stallions frozen with the antioxidants were evaluated in two conditions: (a) adding the antioxidants before freezing, and (b) before and after freezing. Plasma membrane integrity, mitochondrial membrane potential, lipid peroxidation, intracellular ROS levels, membrane lipid disorder, DNA damage, sperm motility and binding to the zona pellucida were assessed. The results showed that MnTBAP was the antioxidant treatment that best controlled the oxidative stress process and post-thaw cell damage, showing higher plasma membrane integrity, mitochondrial membrane potential, sperm motility, number of spermatozoa bound to the zona pellucida of bovine oocytes and lower lipid disorder. Additionally, it was determined that a second post-thaw application of antioxidants is detrimental since induced higher cell damage and lower sperm motility, without showing any beneficial effect on the spermatozoa.     

Evaluation of stallion semen.

This article outlines a basic method for conducting a stallion semen evaluation. After the removal of the gel fraction of the ejaculate, semen gel-free volume is determined, and any abnormality in appearance is noted. Concentration of sperm cells in semen can be determined with the use of either a hemacytometer or spectrophotometer after appropriate dilution of raw semen. The percentage of progressively motile sperm is evaluated promptly after collection of semen with the use of a phase-contrast microscope. The total numbers of sperm and progressively motile sperm in the ejaculate are calculated. The determination of seminal pH and the classification of sperm morphologic features are additional seminal characteristics evaluated during a semen evaluation. Sperm motion characteristics can be further evaluated with the use of computerized sperm image analysis systems and may add additional information concerning the quality of ejaculated sperm. Unfortunately, no single seminal characteristic has in itself been shown to be highly correlated with fertility, although various seminal characteristics are known to affect fertility. Therefore, to properly interpret the fertility of a semen sample, a complete and thorough semen evaluation must be performed.