An investigation into factors influencing the success of ovine artificial insemination programs

Abstract

Variation in pregnancy rates following laparoscopic artificial insemination (LAI) in sheep has resulted in reduced adoption of reproductive technologies and genetic gain. The study aimed to determine the impact of male and female factors on the probability of pregnancy following LAI. Data from Merino ewes (N=30,254) including age, uterine tone (1; flaccid-5; turgid), intra-abdominal fat (1; little present-5; high fat), time of LAI and sire (N=388), were recorded at AI. Semen was assessed for volume, concentration, motility and morphology 0hr post-thaw. Motility (CASA), viability, acrosome integrity (FITC-PNA/PI), membrane fluidity (M540/Yo-Pro), mitochondrial superoxide production (Mitosox Red/Sytox Green), lipid peroxidation (Bodipy C11), level of ROS (H2DCFDA) and DNA fragmentation (Acridine Orange) were assessed at 0, 3 and 6h post-thaw. A binomial logistic regression analysis and odds ratios evaluated the impact of factors on pregnancy. New validation data was collected (per above) and run through the model to predict pregnancy probability. Predicted outcomes were evaluated against ultrasound results using discrimination and calibration statistics. The concentration at which sperm was frozen (P<0.001), a CASA PCA (0h; P=0.03), percent of viable, acrosome-intact sperm (6h; P=0.02), percent of abnormal sperm (P<0.001), uterine tone (P<0.001), and intra-abdominal fat (P=0.03) of ewes affected the likelihood of pregnancy post-LAI. The model demonstrated high accuracy (74%), excellent precision (96%), lower specificity (33%), strong recall (76%), and AUC (0.62). There was no difference in pregnancies predicted versus ultrasound detected (P=0.184). Thresholds for each predictor (freezing concentration; 680.85×106 sperm/mL, CASA PCA; 18.34, %viable; 6.31 and %abnormal; 15.5) were calculated, returning a cumulative 64.3% chance of pregnancy. These findings offer a practical means for screening semen and ewes before AI to maximise the LAI success for the sheep industry.