Effects of excess dietary protein on fertility in the beef herd

It has been well documented that a negative relationship exists between blood, plasma, or milk urea nitrogen and fertility in dairy cattle, with increased concentrations of plasma urea nitrogen (PUN; > 19 mg/dL) and milk urea nitrogen (MUN; > 15.4 mg/dL) being associated with suppressed fertility. Although this relationship is not fully understood, likely contributing factors have been suggested including altered sperm transport, impaired oocyte competence, and uterine environment. In the beef industry, while largely unfounded, it has been widely accepted that a similar negative relationship between plasma or blood urea nitrogen and fertility exists. While definitive cause-and-effect relationships are sparse, recent research indicates that excess dietary protein may have no negative impact on reproductive processes and fertility in beef cows.