Reproduction Abstracts

Seedstock bulls in Australia are commonly fed high-energy supplements prior to sale. These supplements contain readily fermentable carbohydrates, which may precipitate ruminal acidosis. We hypothesise that a single transient acidotic SARA event would decrease semen production sufficient to preclude bulls from BBSE thresholds and thereby sale.

Santa Gertrudis bulls (n=10, age 20±6 months) were fed in yards on ad lib hay with daily individual grain feeding prior to acidosis challenge. Semen was collected fortnightly prior to challenge with sperm parameters and blood hormone parameters determined. Ruminal acidosis challenge treatments consisted of either a single oral dose of oligofructose (6.5 g/kg LW) or an equivalent dose of water in bulls that had achieved a stable spermiogram. Rectal and scrotal temperature, heart rate, rumen pH and tone, were monitored during challenge with concomitant ruminal fluid collection. Ejaculates and blood were collected every 3rd day for a period of 7 weeks, then once weekly until 3 months post-challenge.

Oligofructose treatment decreased rumen pH from 2 to 16 h post treatment (P≤0.006) with associated increases in individual VFAs, D-lactate, ammonia and respiration rate. Measures of sperm quality decreased in oligofructose treated bulls from 18 days post treatment and remained significantly lower upon completion of the study at 90 days post challenge (P=0.02). This was associated with increased cortisol and decreased FSH and testosterone in these bulls (P≤0.05).

This is the first study to show that a transient acidosis event is sufficient to induce effects upon sperm production in bulls for up to 3 months, thereby supporting our hypothesis. Oligofructose was shown to be effective in inducing a SARA event where a compact dosing form is required in unhandled range bulls. In the collected ejaculates, as anticipated, there was a transition through the recognised sequence of sperm abnormalities, according to stage of spermatogenic cycle or position in tract, when the acidotic event occurred.