The Effect of Stress on Reproduction and Reproductive Technologies in Beef Cattle—A Review

SIMPLE SUMMARY: The economic sustainability of beef herds relies on achieving a reliable percentage of weaned calves. Efforts to lift reproductive efficiency of beef herds have traditionally focused on physical health and nutrition aspects, by extrapolating knowledge from dairy herds. However, animal welfare and stress on beef farms is of outstanding importance. Stress affects the economic sustainability of the farm directly by reducing productive and reproductive performance, as well as indirectly by pushing away customers, who demand farming practices that ensure better animal welfare and lower stress. Despite its relevance and the increasing efforts made by the industry, the detailed ways in which stress influences reproduction of beef herds are still not well understood. Trying to contribute to clarity and reviewing the huge advances made in this topic, we describe the major factors contributing to stress in beef cattle and the effects of that stress on their reproductive performance. We highlight main stressors in beef, such as cattle management, handling stress while passing through the chutes, social hierarchy or weaning effects, besides the nutritional and climate stress and include the acclimatization, acclimation and temperament. We pay attention to the beef bull. And finally, we point out strategies demonstrated to alleviate stressful situations, improving reproductive performance. ABSTRACT: Researchers have contributed by increasing our understanding of the factors affecting reproduction in beef, mainly physical health and nutrition aspects, which have been main concerns during decades. Animal welfare is of outmost relevance in all animal production systems and it is strongly associated to stress. Stress responses involve endocrine, paracrine and neural systems and the consequences of this stress on the reproductive efficiency of specifically, beef cattle and bulls, need to be highlighted. We, therefore, describe the fundamentals of stress and its quantification, focusing in beef herds, reviewing the highly valuable pieces of research, already implemented in this field. We examine major factors (stressors) contributing to stress in beef cattle and their effects on the animals, their reproductive performance and the success of reproductive biotechnologies. We include terms such as acclimatization, acclimation or temperament, very relevant in beef systems. We examine specifically the management stress due to handling, social environment and hierarchy or weaning effects; nutritional stress; and thermal stress (not only heat stress) and also review the influence of these stressors on reproductive performance and effectiveness of reproductive biotechnologies in beef herds. A final message on the attention that should be devoted to these factors is highlighted.