The influence of delayed breeding on the fertility of beef heifers

Abstract

(1) Twenty-five beef heifers were subjected to delayed breeding up to ages varying from four years to five years eight months. (2) Observations on body-weights, age of sexual maturity, the periodicity and duration of oestrus and the results of mating are recorded. (3) Seven heifers bred successfully, while the remainder showed extensive disturbances in sexual activity. (4) The changes occurring in the genital tract during the normal sexual cycle and during pregnancy are described. (5) Profound functional and structural changes were observed in the genitalia of the majority of animals, leading to abortion, functional sterility, nymphomania and anaphrodisia. (6) Correlative macroscopical and histological changes were observed in the anterior pituitary, thyroid and adrenals of normal and affected animals. (7) The genesis of sterility in relation to delayed breeding in the light of the structural and physiological alterations observed, is discussed.