An attempt has been made to ascertain the best interval between calvings, so that the cow's average weekly yield over a long period may be at a maximum. It was only possible to consider the case of the “average cow,” but it is claimed that the general principle has been established, that cows should calve at intervals of not less than a year, and not more than thirteen months; this optimum will probably be subject to a slight variation in particular cases. This is approximately the state of affairs in practice—though Norfolk farmers appear to err on the side of serving too early in the lactation, rather than too late.