Excess Dietary Protein in Dairy Rations Can Impair Reproduction

Excess Dietary Protein in Dairy Rations Can Impair Reproduction Excess Dietary Protein in Dairy Rations Can Impair Reproduction

Dr. Allen Young
USU Extension Dairy Specialist

For many years it has been known that high levels of protein in the ration can lead to reproductive impairment. At the 1st Intermountain Nutrition Conference held in Salt Lake City, Utah, Dr. Charles Staples, from the University of Florida, gave an excellent paper on Dietary Fat and Protein Effects on Fertility of Lactating Dairy Cows. In his paper he outlined possible reasons why protein can reduce fertility. I have listed those reasons below and ranked them in importance (my ranking, not Dr. Staples).

Energy costs for detoxifying ammonia into urea (waste product resulting from excess protein) may aggravate an existing energy shortage resulting in reduced ovarian activity. This means that excess protein requires extra energy to remove it from the body. If cows are in a negative energy balance and are losing weight, they will lose even more weight because of the excessively high protein. Cows that lose excessive weight have a harder time re-breeding and probably won’t until their weight begins to come back.
A cow may not be able to utilize available nutrients too fully because excess urea may impair the liver’s ability to convert propionic acid to glucose. In addition, the cow’s ability to utilize available glucose is reduced. This could lead to more of a cow’s body reserves being used than necessary. Again, ovarian activity is reduced. The development of fatty livers in early postpartum cows can reduce the liver’s ability to detoxify ammonia by converting it to urea.
Excess levels of urea can alter the uterine environment and cause the development of a “hostile” environment for the development of the embryo, leading to death of the fertilized embryo. Much work has been done in this area, but as yet, this relationship is not well supported.
Excess dietary protein can depress the immune system by some unknown mechanism. An example is that cows fed higher protein diets took longer to become pregnant when they had health problems compared to healthy cows.

So what do you do to keep reproduction and nutrition optimal? I suggest the following:

Make sure your ration is correctly balanced. Never feed a ration that has 20% CP or more; even 18% is too high in most instances. Especially make sure the rumen degradable protein (RDP) fraction is not excessive (no more than 65% of the total protein) and is balanced with the soluble carbohydrate fraction.
Monitor excess protein levels by consistently having all cows in your herd tested for Milk Urea Nitrogen (MUN) each month. This will help make sure the protein and carbohydrate fractions are balanced.
Make sure that your reproductive technique is optimal. Poor technique cannot be replaced by balanced rations.
Monitor body condition scores (BCS) as a way to determine if excess body weight is being lost.
Consider feeding fat in the ration to overcome some of the negative energy problems.

Optimal reproduction is very closely tied with optimal nutrition. Early lactation diets are critical to successful reproduction and monitoring is important. For additional information on Dr. Staples’ article, contact me at (435) 797-3763 or by e-mail at alleny@ext.usu.edu. Proceedings from the Nutrition Conference are can be obtained for $12 by contacting Karma Wood at (435) 797-2145.