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* Dexcel, Private Bag 3221, Hamilton, New Zealand
Liggins Institute, University of Auckland, Private Bag 92019, Auckland 1003, New Zealand
The School of Animal Biology, University of Western Australia, 37 Stirling Highway, Crawley, 6009, Australia
Division of Animal Sciences, University of Missouri, Columbia 65211
# 21 Scotsman Valley Road, Hamilton, New Zealand
|| University of Tasmania, PO Box 3523, Burnie, Tasmania, Australia 7320
¶ Department of Animal Sciences, University of Florida, Gainesville 32610
** University of Nottingham, Division of Agriculture and Environmental Sciences, School of Biosciences, Loughborough, Leicestershire, LE12 5RD, United Kingdom
2 Corresponding author: lucia.chagas{at}dexcel.co.nz
Management, nutrition, production, and genetics are the main reasons for the decline in fertility in the modern dairy cow. Selection for the single trait of milk production with little consideration for traits associated with reproduction in the modern dairy cow has produced an antagonistic relationship between milk yield and reproductive performance. The outcome is a multi-factorial syndrome of subfertility during lactation; thus, to achieve a better understanding and derive a solution, it is necessary to integrate a range of disciplines, including genetics, nutrition, immunology, molecular biology, endocrinology, metabolic and reproductive physiology, and animal welfare. The common theme underlying the process is a link between nutritional and metabolic inputs that support complex interactions between the gonadotropic and somatotropic axes. Multiple hormonal and metabolic signals from the liver, pancreas, muscle, and adipose tissues act on brain centers regulating feed intake, energy balance, and metabolism. Among these signals, glucose, fatty acids, insulin-like growth factor-I, insulin, growth hormone, ghrelin, leptin, and perhaps myostatin appear to play key roles. Many of these factors are affected by changes in the somatotropic axis that are a consequence of, or are needed to support, high milk production. Ovarian tissues also respond directly to metabolic inputs, with consequences for folliculogenesis, steroidogenesis, and the development of the oocyte and embryo. Little doubt exists that appropriate nutritional management before and after calving is essential for successful reproduction. Changes in body composition are related to the processes that lead to ovulation, estrus, and conception. However, better indicators of body composition and measures of critical metabolites are required to form precise nutritional management guidelines to optimize reproductive outcomes.
The eventual solution to the reduction in fertility will be a new strategic direction for genetic selection that includes fertility-related traits. However, this will take time to be effective, so, in the short term, we need to gain a greater understanding of the interactions between nutrition and fertility to better manage the issue. A greater understanding of the phenomenon will also provide markers for more targeted genetic selection. This review highlights many fruitful directions for research, aimed at the development of strategies for nutritional management of reproduction in the high-producing subfertile dairy cow.
Key Words: subfertility • high-producing dairy cow
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