Variation in pregnancy rates following laparoscopic artificial insemination (LAI) in sheep has resulted in reduced adoption of this reproductive technology, limiting genetic gain for the industry. This study aimed to determine the contribution of various male and female factors on the probability of pregnancy following LAI.
Data from Merino ewes (N=30,254) including age, uterine tone (1; pale/flaccid-5; turgid/pink), intra-abdominal fat (1; no/little fat present-5; high fat), time of insemination and semen sire (N=388), were recorded during AI. Semen used for AI was assessed for volume, concentration, subjective motility and morphology immediately post-thaw, while 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 intracellular reactive oxygen species (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 and interplay of factors on pregnancy. New validation data was collected (as described 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 influenced 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 the number of pregnancies predicted versus ultrasound detected (p=0.184). Thresholds for each predictor (freezing concentration; 680.85x106 spm/mL, CASA PCA; 18.34, %viable; 6.31 and %abnormal; 15.5) were calculated, returning a cumulative 64.3% chance of pregnancy.
These findings enable a practical means of screening semen and ewes before AI to maximise the success of artificial insemination for the sheep industry.