1 UDDER MORPHOLOGY AND EFFECTS ON MILK PRODUCTION AND EASE OF MILKING IN DAIRY SHEEP Maristela Rovai 1 , David L. Thomas 2 , Yves Berger 3 , and Gerardo Caja 4 1 Physiology Weihenstephan, Technical University Munich, D-85350 Freising, Germany 2 Department of Animal Science and 3 Spooner Agricultural Research Station, University of Wisconsin-Madison, 53706 Madison, USA 4 Grup de Recerca en Remugants, Unitat de Producció Animal, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain Summary Mammary morphology is generally accepted as a key factor for machine milkability, and its inclusion in dairy sheep improvement programs has been widely recommended. The anatomical and morphological characteristics of the mammary gland and their relation with milk production, machine milkability and manageability in dairy sheep have become of greater interest from farmers to researchers. The sheep udder is an exocrine epithelial gland mainly constituted by tubulo-alveolar parenchyma with alveoli and well differentiated cisterns. Two anatomical compartments are considered for milk storage: alveolar and cisternal; the large-cisterned animals being more efficient milk producers. The evaluation of external morphology by using udder typology, objective udder measurements and linear scores in practice is also discussed. Recent methodology using ultrasonography has been applied for the study of the mammary gland, providing a satisfactory non-invasive method for determination of milk storage characteristics in dairy species. Machine milkability is evaluated by milk fractioning and milk emission curves during milking. Both criteria are discussed and analyzed in sheep breeds of different milk yield. Relationship between morphological and productive traits in dairy sheep is analyzed as a result of anatomical and physiological characteristics. Phenotypic and genetic correlations indicate that selection for milk yield will produce worse udder morphology, resulting in udders which are inadequate for machine milking, especially in highly selected flocks. Teat and cistern characteristics appear to be the most limiting factors in machine milkability. Some selection pressure on udder traits in long-term breeding programs needs to be considered and the use of linear udder traits is recommended in practice to improve udder morphology and milkability. Knowledge of the relationship of udder morphology traits with milk production and milking time in U.S. dairy ewes is needed to provide producers with recommendations for culling strategies based on ewe udder traits. The effectiveness of the European scoring systems for dairy-meat breeds cross ewes in U.S. dairy sheep farms is discussed.