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. 2013 May 23;59(4):393–397. doi: 10.1262/jrd.2013-017

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 F 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.