Reproduction during lactation of dairy cattle: Integrating nutritional aspects of reproductive control in a systems research approach

Abstract

Reproductive success in any mammalian species, including highly selected dairy cattle, is a result of dynamic, interacting genetic and environmental factors. These include the genetic background or genome of the animal and the nutrient composition, and intake; a complex of interaction between hormonal and neural processes; and environmental factors such housing, temperature, and season of year. Although few would argue with this generic summary, it is a primary premise of this review that to improve dairy cattle reproductive success, the research and application communities including university scientists, breeding organizations, bull studs, nutrition companies, and pharmaceutical firms must fully accept the complexity of the process and adapt accordingly. That said, we have had a tremendous increase in both basic and applied, “on-farm” knowledge about reproductive management. Because of the increase in basic knowledge and improved method to apply it practically, attitudes about research funding and practical management are changing rapidly. There is in the past few years a significant increase in more complex (systems biology) approaches to reproductive improvement and recognition that this is truly the only way to move forward. We hope to encapsulate recent research findings that demonstrate the complexity of the situation and provide one or two examples of how the dairy science research and application communities are moving forward, which should speed improvement in reproductive success. The primary goal is to stimulate an increase in coordinated, systems-based research and analysis in the animal agriculture community worldwide. This is meant to be a general review, not an in-depth reiteration of detail, which can be found in the references. In addition, the primary goal is to stimulate discussion and thought from, perhaps, a little different perspective compared with traditional approaches and also to encourage the audience of younger scientists and students to pursue new approaches in their careers. As an example of a systems approach in describing complex biological relationships, in the decision process for a title of this paper, the phrase “how lactation competes with resources for subsequent reproduction” was suggested. Additionally, phrases such as “negative energy balance reduces reproduction” or “high-producing cows are less fertile,” or “genetics does not affect reproduction” have been used many times in teaching and in research reviews. However, in fact, these are all simplifications that can be misleading, especially to students. Thus, in this review we hope to encapsulate recent research findings that demonstrate the complexity of the situation and provide one or two examples of how the dairy science research communities, both basic and applied, are moving forward and can speed improvement in reproductive success. Hopefully, we can seize opportunities to solve what in effect is actually a quite simple problem: how to feed everyone in the world a highly nutritious diet that includes animal products. Our call and challenge as animal scientists is no less than this: how do we ensure a safe and sustainable high quality protein food supply worldwide for future generations?