Animal Production: Volume 12, part 1, pp. 55–62: A number of arithmetical errors have been found in the paper entitled: The incidence, Repeatability and effect on dam performance of twinning in british friesian cattle

An estimate of the frequency of twin calvings was obtained from the analysis of over 38 000 calvings of Friesian cows in M.M.B, milkrecorded herds. The incidence of twinning increased from 0·54% in the first parity to 3·37 % in the fifth parity. A significant excess of cows above expected produced either more than one set of twins or no twins at all. Repeatability ranged from 0·028 for cows with three calvings to 0·063 for cows with five calvings.

Data on lactation yield and duration, butterfat percentage and calving interval showed some significant effects of twinning. Consistent trends were noted showing that dams which calve twins have longer subsequent lactations, higher whole lactation yields and lower fat percentages than contemporary dams with single calves. The possible causes for these trends are discussed and are considered to be the lower breeding efficiency and longer calving intervals of dams of twins.