# In Vitro Effect of Elevated Ammonia and Urea Levels on Post-Thawed Bull Semen Sperm Characteristics

## TL;DR

This study shows that high ammonia levels harm bull sperm function, especially mitochondrial activity and movement, more than urea.

## Contribution

The study is the first to evaluate ammonia and urea effects on bull sperm at physiologically relevant concentrations.

## Key findings

- High ammonia significantly reduced mitochondrial activity and sperm motility.
- Ammonia decreased sperm viability within one hour of incubation.
- Urea had a smaller impact on motility and did not affect DNA integrity or oxidative stress.

## Abstract

This study investigated the effects of ammonia and urea, at levels found in cattle fed high-nitrogen diets, on bull sperm quality. Thawed semen was incubated with low and high concentrations of each compound, and sperm motility, viability, DNA integrity, mitochondrial function, and oxidative stress were measured. High ammonia significantly reduced mitochondrial activity and sperm movement. High urea also decreased mitochondrial activity, but had less impact on motility. Ammonia reduced sperm viability at one hour. Neither compound affected DNA integrity or oxidative stress. These results suggest that ammonia, in particular, negatively impacts sperm function, which is crucial for fertilization.

Elevated ammonia and urea, common byproducts of nitrogen metabolism, are increasingly found in dairy cows and may negatively impact reproductive function. However, their effects on bull sperm remain unclear. This study aimed to assess the impact of ammonia and urea at physiologically relevant concentrations on key sperm characteristics. Thawed bull semen was incubated under five treatment conditions: control (no added ammonia or urea), low urea (LU), high urea (HU), low ammonia (LA), and high ammonia (HA). Sperm motility and kinematics were assessed using Computer-Assisted Semen Analysis (CASA), and sperm viability, DNA integrity, mitochondrial membrane potential (MMP), and oxidative stress markers were evaluated using flow cytometry. HA significantly reduced MMP (p = 0.008) and several motility parameters, including progressive motility and velocity (VCL, VSL, ALH), compared to LA and control groups. A decrease in sperm viability was observed in the HA group compared to LA at the beginning of incubation. While HU reduced MMP (p = 0.002), sperm motility was not significantly affected compared to LU. No significant differences were found in DNA fragmentation or oxidative stress biomarkers between groups. These results highlight the impact of ammonia, specifically, on sperm mitochondrial function and motility, which are crucial for successful fertilization.