There appears to be a west to east cline in the four north Wales counties in: (i) the proportion of calves sold during the autumn months September to December; (ii) the proportion of December milk sales in relation to the September sales; (iii) the proportion of the dairy and breeding herd in milk during the winter; (iv) the quarterly rates of conception in heifers during the period 4 December to 4 March. There does not appear to be any relation between percentage winter milk production and percentage tillage area in this region. It is postulated that the west to east cline is dependent mainly upon factors other than husbandry and that climatic conditions, particularly the hours of bright sunshine during the winter months, have a marked influence upon the breeding performance of cows and heifers during the period December to March.

This investigation has formed part of the survey of animal health and production in Wales, and thanks are due to the scientific branch of Messrs Cooper, McDougall and Robertson, Berkhamsted, for financial support. Grateful acknowledgement is made to the Ministry of Food, Colwyn Bay, for readiness in providing data and helpful advice; to Messrs Pritchard, Auctioneers, Bangor, and Messrs Beardmore, Auctioneers, Abergele, for permission to examine their records; to the Milk Marketing Board for providing the data on milk sales; to Profs. A. N. Worden and E. G. Bowen for the interest they have taken in the work.