Exposing dairy bulls to high temperature-humidity index during spermatogenesis compromises subsequent embryo development in vitro.

The possible impact of natural heat stress on animal fertility is currently a major concern for breeding companies. Here, we aimed to address this concern by determining the effects of natural heat stress on the fertility of Holstein bulls located in the Netherlands. Semen samples were collected from six bulls at two locations in March 2016 (low temperature-humidity index (THI) group; maximum THI of 51.8 and 55 at their respective locations) or August (high THI group; maximum THI of 77.9 and 80.5 during meiotic and spermiogenic stages of spermatogenesis, 42 to 14 days prior to semen collection). The effect of heat stress on semen quality was assessed by sperm morphology, motility, reactive oxygen species production, lipid peroxidation, viability, and DNA fragmentation. Moreover, we evaluated the development of embryos generated in vitro by low and high THI semen, and determined inner cell mass/trophectoderm ratio, apoptotic cell ratio, and embryonic gene expression in day-8 blastocysts. An increase in cell death (propidium iodide-positive cells; P = 0.039) was observed in the high THI group (31.5%) compared to the low THI group (27.6%). Moreover, a decrease (P < 0.001) was observed in the total blastocyst rates at day 7 post-insemination (15.3 vs 20.9%) and day 8 (23.2 vs 29.6%) in the high THI compared to the low THI group, respectively. There were no differences in the relative abundance of candidate transcripts examined. In conclusion, sperm samples from dairy bulls obtained during a period with higher THI had reduced viability and led to a decrease in blastocyst development and delayed hatching, compared to semen collected during a period with low THI.

Carnosine as malondialdehyde scavenger in stallion seminal plasma and its role in sperm function and oxidative status.

Semen biotechniques may impair sperm quality due to excessive production of reactive oxygen species (ROS). Additionally, products of the oxidative reaction, especially involving lipids (e.g., malondialdehyde - MDA), may be even more harmful to sperm. Carnosine, previously reported to be present in seminal plasma of several species, may be a key factor on sperm tolerance to biotechniques by counterattacking the deleterious influence of MDA. Therefore, the aim of this study was to measure the levels of carnosine present in equine seminal plasma and relate these findings with sperm function and oxidative status during cooling and cryopreservation. Thus, semen samples were collected from 40 stallions in duplicate (N = 80) and then submitted to cooling and cryopreservation. Samples were then allocated into groups of high and low tolerance to refrigeration and cryopreservation (bad cooler and good cooler/bad freezer and good freezer, respectively), and in groups of different concentrations of carnosine (High, Medium-high, Medium-low and Low carnosine). Samples were evaluated for sperm kinetics patterns, function of sperm structures and oxidative status. In good cooler samples, it was observed higher concentrations of carnosine (Good cooler: 224.98 ±â€¯19.16 ng/mL; Bad cooler: 159.72 ±â€¯15.99 ng/mL; p = 0.0056), ROS production (Good cooler: 26.40 ±â€¯18.33%; Bad cooler: 18.33 ±â€¯1.84%; p = 0.001) and lipid peroxidation rates (Good cooler: 193.23 ±â€¯18.22 ng/mL; Bad cooler: 131.92 ±â€¯12.25; p = 0.0064). Groups of samples with higher carnosine concentrations had lower levels of malondialdehyde (High: 79.33 ±â€¯6.72 ng/mL; Medium-high: 140.45 ±â€¯11.70 ng/mL; Medium-low: 202.57 ±â€¯16.30 ng/mL and Low: 231.02 ±â€¯32.35 ng/mL; p < 0.05), demonstrating that carnosine was effective in removing lipid peroxidation products. Due to the removal of seminal plasma during the cryopreservation process, no differences occurred in carnosine levels between bad and good freezer groups. In this context, this study provides relevant data for future therapies using carnosine during cryopreservation, aiming to replace the levels lost due to the necessary removal of seminal plasma.