Too Many Twins
Dr. Ken McMillan
The genetics for twinning, mildly heritable, are most likely in the cow side of the herd. Regarding your herd bulls, they have no effect on twinning. Most twins occur when the cow ovulates two eggs, which are then fertilized, producing fraternal twins. When one egg is fertilized and splits, we see identical twins. Multiple ovulation is a slightly heritable trait, so the genetics for twinning is most likely in your cow herd.