Prolonged oestrus as a cause of infertility in dairy cattle – A review

Prolonged oestrus is one of the conditions associated with perturbed follicular dynamics that culminates into substantial economic losses to dairy industries through low success rate of artificial insemination, increased inter-calving period, reducing total milk yield, lowering calf production, shortening reproductive life of the animals, lowering fertilisation rate and abnormal embryonic development. Prolonged oestrus is characterized by the exhibition of extended duration of oestrus in various breeds of cattle. Cows having prolonged oestrus need to be examined at frequent intervals for determining the correct time of artificial insemination. This makes it challenging to inseminate the animals at the correct time, which is a major inconvenience for the field veterinarians and farmers. Since the follicular dynamics in cows is intricate to comprehend, the disorders in which also often go unnoticed and not treated/managed wisely in the field conditions. Therefore, it is of paramount importance to understand the aetiology of prolonged oestrus so that strategies to improve fertility could be designed. Alterations in hypothalamohypophyseal-gonadal axis, which is also influenced by some other extrinsic factors like stress, nutrition, age, parity, breed etc., apart from the endocrine alterations could cause the prolonged dominance of follicle. The presence of suprabasal progesterone and luteal insufficiency are considered as the main cause of this condition among cattle. In this review, we attempted to analyse the prior art on the topic and to delineate the possible causes, and to suggest managemental strategies to mitigate the prolonged oestrus condition in dairy cows