Sexual Activity Influences the Secretion of Reproductive Hormones in the Stallion

Semen Quality of the First and Second Ejaculates Collected from Breeding Inactive Stallions after Cooling and Freezing

This study aimed to assess the semen quality after the cooling and freezing of the first and second ejaculates of the season, which were collected 1 h apart. After collection (n = 40 ejaculates), the gel-free semen volume, concentration, total number of sperm, and sperm morphology were determined. An aliquot of each ejaculate was extended and cooled for 48 h; a second aliquot was cushion-centrifuged and cooled for 48 h; and a third aliquot was processed and then frozen. The total motility (TM) and progressive motility (PM), plasma membrane integrity (PMI), and high mitochondrial membrane potential (HMMP) were assessed pre-(0 h), 24 h, and 48 h post-cooling and before and after freezing. The second ejaculate had a lower gel-free semen volume (p = 0.026). The sperm concentration was greater in the first than in the second ejaculate (p < 0.001). The sperm morphology was similar between the ejaculates (p > 0.05). Cushion-centrifugation prevented a reduction in the TM, PM, and PMI over time (p < 0.05). The TM, PM, and PMI decreased after freezing but not between the ejaculates (p > 0.05). The first and second ejaculates of the season, which were collected 1 h apart, varied in quantity but not in quality after cooling and freezing.

Aspects of Breeding Stallion Management with Specific Focus on Animal Welfare

Risk prevention is often counterproductive to stallions' living conditions when assessed under welfare aspects. In the wild, stallions live in social groups, but under domestic conditions, the majority of breeding stallions live in individual boxes with limited social contact. This stimulates aggressiveness and the incidence of stereotypic behavior. While racehorse stallions start their breeding career after having finished their performance career, riding horse stallions are often simultaneously used for breeding and performance. Training, performance, and the associated stress are unlikely to impair semen characteristics, but performing stallions may benefit from more opportunities for social contact. With regard to accommodation of stallions in single boxes, changes in the construction of the partition between them may help to improve social contact from merely visual to much more physical. This will help to reduce social isolation but requires careful observation if neighbors tend to either sympathize or fight with each other. Careful organization of the barn is thus of great importance. Under certain conditions, even keeping adult stallions in groups on spacious pastures is possible. Interestingly, the frequency of agonistic interactions usually decreases quickly and remains low after successful group integration. General changes in the husbandry of young stallions and at their transfer into the future career may help to produce stallions with better social skills and facilitate accommodation under improved welfare conditions.

Season does not have a deleterious effect on proportions of stallion seminal plasma proteins

The mechanism by which the content of the major groups of seminal plasma proteins in stallion semen changes between the breeding and non-breeding seasons remains unknown. Here, we investigated the proportions of non-heparin-binding, phosphorylcholine-binding, and heparin-binding proteins in seminal plasma with the aim of relating them to sperm quality and testosterone levels in good and bad freezer stallions. Only minor variations in the major protein groups were found between the breeding and non-breeding seasons. In the non-breeding season, a higher content of a subset of non-heparin binding proteins as well as of heparin-binding proteins was found. Analysis of semen characteristics revealed a somewhat contrasting picture. While only minor variations in sperm kinematics and sperm morphology were found between seasons, the flow-cytometric measurements of mitochondrial membrane potential and also, to some extent, reactive oxygen species production indicated lower sperm quality in the breeding season. Chromatin integrity and testosterone levels were unchanged between seasons. The results suggest that stallion ejaculates could be used year-round for freezing, since only minor differences in protein composition exist between the breeding and non-breeding seasons, as well as between good and bad freezers. In addition, sperm quality is not impaired during the non-breeding season.

Ejaculate Characteristics Depend on Social Environment in the Horse (Equus caballus)

Sperm competition theory predicts semen characteristics to be affected by the social environment. We used the polygamous horse (Equus caballus) to experimentally study within-subject plasticity in response to different social environments. Stallions were sequentially exposed, over a period of 8 weeks each, to other stallions and then singly to mares, or vice versa (in adjacent boxes separated by grills). Ejaculates were collected to determine semen characteristics. Highest sperm numbers were found in stallions that were first exposed to other stallions and then to mares, while lowest sperm numbers were observed in stallions that had been exposed to mares but not yet to other stallions. One of three sperm velocity measures (curvilinear velocity) was consistently elevated in stallions that were first exposed to stallions and then to mares. Sperm number after exposure to mares and curvilinear sperm velocity after exposure to stallions were both positively correlated to average blood testosterone levels during the corresponding period of exposure. We conclude that ejaculate characteristics are plastic traits affected by the social environment in horses.