Table 2. Odds ratios of the variables included in the final logistic regression model for factors affecting the twin pregnancy rate in high-producing dairy cows.
Factor | Class | n | Twinning rate % | Odds ratio | 95% Confidence interval | P |
Herd | 1 | 94/636 | 14.8 | Reference | ||
2 | 19/332 | 5.7 | 0.3 | 0.2–0.5 | <0.001 | |
3 | 24/168 | 14.3 | 1.1 | 0.7–1.7 | 0.5 | |
4 | 153/922 | 16.6 | 1.0 | 0.8–1.4 | 0.5 | |
Treatment* × parity | Control × primiparous | 68/561 | 12.1 | Reference | ||
Control × multiparous | 184/997 | 18.5 | 1.5 | 1.4–2.0 | 0.005 | |
PEG × primiparous | 17/161 | 10.6 | 0.7 | 0.4–1.3 | 0.4 | |
PEG × multiparous | 21/339 | 6.2 | 0.4 | 0.2–0.7 | 0.001 |
P=0.0001. R2 Nagelkerke=0.11. *Treatment: control = natural estrus; PEG = prostaglandin F2α and eCG given on the day of sub-estrous diagnosis (presence of a corpus luteum), GnRH given 48 h later and FTAI conducted 24 h after GnRH treatment.