Liquid storage of stallion spermatozoa - Past, present and future.

The ability to store stallion spermatozoa between the events of semen collection and insemination has facilitated improved rates of gain in selective breeding programs by enabling the transport of spermatozoa. While cryopreservation is the only viable means of storing spermatozoa for long intervals, the higher costs and reduced fertility of cryopreserved spermatozoa have led to most breeders opting to use liquid stored spermatozoa. Stallion spermatozoa is commonly cooled during liquid storage (approximately 4-5 °C), and there has been an enormous body of research dedicated to development of protocols and media to facilitate sperm survival including identification of energy sources, antioxidants, pH buffers and toxic metabolite scavengers, along with membrane-stabilising components to reduce deleterious effects of cold shock. Despite these efforts, the upper time limit for cooled sperm storage is ∼ 72 h and there are many stallions whose spermatozoa cannot tolerate the process of cooling. As such, media have been developed to allow spermatozoa to be liquid stored at higher temperatures (15 - 22 °C), and these efforts have led to development of a medium that can effectively store stallion spermatozoa for at least 7 d with no appreciable loss of fertilising capacity. Furthermore, there is an increasing body of research aimed at providing substrates that allow spermatozoa to repair and regenerate during storage, thereby challenging the paradigm that post-ejaculatory sperm damage is irreversible. This review aims to summarize stallion sperm liquid storage strategies and the developments that led to the technologies available today.

Supplemental Nicotinic Acid Elevates NAD+ Precursors in the Follicular Fluid of Mares.

A deficiency in NAD+ has previously been linked with increased occurrences of congenital abnormalities and embryonic death in humans and mice. Early embryonic death is a major factor involved in pregnancy loss in mares, and very little is known regarding the NAD+ requirements for optimum reproductive function in horses. The aim of this study was to determine the effect of supplementing the diet of mares with nicotinic acid (NA) on the composition of NAD+ metabolites in the blood and follicular fluid. Vehicle alone or NA (3 g per os) were administered to seven mares over a minimum of 3 consecutive days during the follicular phase of the oestrous cycle. Blood samples were collected immediately prior to supplemental feeding and follicular fluid aspiration. Follicular fluid was collected from the dominant follicle through transvaginal ultrasound-guided aspiration. Blood and follicular fluid samples were processed and analysed by mass spectrometry. The concentration of nicotinamide mononucleotide (NMN) in the follicular fluid of NA-fed mares was 4-fold greater than that in the corresponding plasma and 10-fold greater than that in the follicular fluid of vehicle-fed mares. The concentrations of NA, nicotinamide (NAM) and nicotinuric acid (NUR) tended to be greater in the follicular fluid of NA-supplemented mares than in the corresponding plasma. The results show that NA supplementation increased the bioavailability of NAD+ precursors in the follicular fluid of the dominant follicle, which is proposed to better promote the maturation of good quality oocytes, especially in older mares.