Model* Effect tested AIC X2 d.f. p σ2 (% of total) a) Control   d + s   199.3         d Sire 198.5 1.1 1 0.28 0.03 (8.0) s Dam 217.0 19.7 1 <0.001 0.21 (52.5) b) TSB   d + s   211.5         d Sire 215.7 6.2 1 0.01 0.09 (23.7) s Dam 214.7 5.2 1 0.02 0.10 (26.3) c) S.ferax   d + s   305.2         d Sire 303.2 0.0 1 1.0 0.0 (0.0) s Dam 326.0 22.8 1 <0.001 0.17 (47.2) *d = dam, s = sire

Table 2: Likelihood ratio tests on mixed model logistic regressions on embryo mortality within the three treatments. Different models are compared to determine whether sire and dam (random factors) cause significant variance in embryo mortality (binary response variable). The Akaikes information criterion (AIC) indicates the quality of fit of a model. P-values were obtained from comparisons between a model and the respective reference model (s+d) within each treatment.