A study of variation in twin cattle: II. Fertility

Results from a uniformity trial with fifteen pairs each of one-egg and two-egg twins and pairs of half-sibs are described. 2. Intra-pair variance in age at the first observed heat was less for the one-egg than for the other pairs but not significantly so. The slowest growing pairs showed delay in onset of heat. 3. 71·8% of the intervals between heats shown by unserved heifers were 17–27 days in length. No genetic variation and no individuality could be detected in either this character or the number of services per conception. 4. The variance in the gestation period was less within the one-egg than within the other pairs but not significantly so.