Udder Morphology and Machine Milking Ability in Dairy Sheep

This paper describes the particularities of the anatomy and morphology of the dairy sheep udder and the current implications on machine milkability. The sheep mammary gland is an exocrine epithelial gland mainly constituted of tubulo-alveolar parenchyma with alveoli and well differentiated cisterns. Two anatomical compartments are used for milk storage: alveolar and cisternal, the large-cisterned animals being more efficient milk producers. New methodologies are available for the study of the mammary gland ultrastructure and for the use of non invasive or dynamic measures. A detailed description of alveolar and ductal changes in the ewe udder occurring during lactation is presented. The study of external morphology by using udder typology, objective udder measurements, and linear scores in practice is also discussed. 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. Relationships between morphological and productive traits in dairy sheep are analyzed as a result of anatomical and physiological characteristics. Phenotypic and genetic correlations indicate that selection for milk yield will produce a worse udder morphology, resulting in udders which are inadequate for machine milking. 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.