The reproductive performance of a dairy herd can be affected by three nutritional issues. There can be: 1. an inadequate supply of nutrients (e.g. energy) 2. an excess supply of nutrients (e.g. protein) 3. unplanned anti-nutritional dietary components (e.g. toxins, pathogens, etc.)

Each of these potential conditions should be examined when evaluating poor reproductive performance.

While a serious lack of most nutrients, including energy, protein, minerals and vitamins, will negatively affect reproductive performance, a shortage of energy is the most common reason for cows not breeding back in a timely manner. After freshening, cows will experience negative energy balance where the demand for energy to produce milk exceeds energy intake, and will strip body condition to meet those energy demands.

The greater the loss of body condition, the longer time before a cow will begin to ovulate and be ready to breed. This situation is characterized by University of Wisconsin research showing that 1/3 of cows with a body condition score (BCS) = 2.25 are not ovulating (i.e. anovular), while 1/5 of cows with a BCS = 3.0 are anovular. Anovular cows have almost 40 percent lower first-service conception rates than ovulating cows. Lower first-service conception rates will often lead to longer intervals between breedings and greater days open.

To combat the negative energy balance due to intake limitations in early lactation, we often increase nutrient density in the cow’s diet, which can lead to an excess supply of nutrients. The most common example of this issue is increased crude protein (CP) concentrations to support high milk production. However, protein, often rumen-degradable (RDP), supplied in excess of requirements, will be converted to ammonia, and this ammonia must be converted to urea in liver.


The urea returns to the bloodstream resulting in elevated blood urea nitrogen (BUN) and milk urea nitrogen (MUN) levels. Elevated BUN levels do not affect when cows will begin to ovulate after freshening, but have been implicated in altering the uterine environment and reducing embryo development after conception. This reduced fertility is often exhibited in cows with a MUN level above 16 mg/dL.

Outside of diet formulation, there can be anti-nutritional issues that show up unexpectedly and affect herd reproductive performance. The most commonly described issue is the presence of mycotoxins in forages and grains. Given the wet fall of 2009, we are seeing increased reports of mycotoxins in both high-moisture and dry corn. Zearalenone (ZEA) is the mycotoxin often identified as affecting reproductive performance, with scientific studies showing reduced fertility and anovulation with levels of 400 ppb. The treatment strategies for mycotoxin contamination include removal of contaminated feed, dilution of contaminated feed in the diet or use of binders.

We should remember that nutritional status is only one of many factors that can affect reproduction, and when investigating nutrition as a possible cause for poor reproductive performance, consider three aspects: undersupply of nutrients, oversupply of nutrients and unexpected presence of anti-nutritional factors. PD

References omitted due to space but are available upon request by sending an email to .

— Excerpts from Penn State Dairy Focus, Vol. 11, No. 1

Ken Griswold