Cow Camp Chatter: The Postpartum Anestrus Period

Ron Torell, Long-Standing Educator and Advocate of Agriculture

        The structure and function of a cow’s uterus is fascinating. It accepts the calf, a substance that is completely foreign to it, while blocking the body’s normal defense mechanism designed to destroy foreign invaders.  The uterus nourishes, protects, and sustains the developing calf while growing up to 24 inches or more in diameter. When the time is right, the uterus receives a signal from the calf and transforms itself into a delivery system forcibly expelling the calf. It then begins the amazing process of  preparing itself for a repeat of the whole cycle.  The recovery process for a cow between calving and her next pregnancy is critical to a profitable beef enterprise and is quite frequently misunderstood.          

   The stage of reproductive inactivity in a cow between the breeding cycle which immediately follows calving is known as the anestrus period. The amount of time that the cow remains in anestrus until her first estrus cycle is the postpartum interval. The rate of  involution, a term that encompasses uterine shrinkage, fluid loss, and tissue repair following calving,  is largely determined by nutrition, lactation rate, age, health and flesh condition of the cow. During the anestrus period the cow’s reproductive abilities are put on hold while uterine involution occurs and her body builds up enough energy reserves to allow her to become reproductively active again.   

            Reducing the length of the postpartum anestrus period is the first basic principal of reproductive management. This can be accomplished by incorporating better management practices.                 

            The postpartum anestrus period is the highest nutrient demanding phase of the cow. By banking fat reserves during the lower nutritional demanding stages of her biological cycle, the cow then has a nutrient source of energy to draw from during the higher energy demanding periods in both the last trimester and the anestrus period.   

             Nutritional and body reserve deficiencies are the first place to look when non-cycling cows are encountered as a result of an extended postpartum anestrus period. Chances are it could take months for a cow to rebreed if she is in poor condition and lactating.   If she is a two or three year old cow, large-framed or heavy-milking, she may not breed back at all. It is important to note that reproductive diseases and bull fertility may also play a role in open cows. 

  
            If the goal is to have a cow calve at the same time next year, the postpartum anestrus period should not exceed 83 days.  In order for this to happen, management of the anestrus period needs to be a twelve-month effort. This can be done by managing the body condition of the cow. 

            Adequately addressing the nutritional needs of the cow and using body condition score (BCS) as a management tool will help the cow prevail over anestrus. Consider BCS management to monitor the condition of cattle particularly in the fall after weaning and a few months before calving. Generally scores from one to nine are assigned to cows with the thinnest possible score being one and the fleshiest possible being nine.  Having a BCS of five is considered to be the optimum breeding condition for mature cows while a BCS of a five or six is suggested for first-calf heifers.  If you do not have these body reserves at the minimal level your cows may not reproduce. 

            Evaluating body condition is not enough. You need to take action on your assessment.   On dry years and as body condition is reduced below a five, management changes must be made such as supplementation, weaning, or moving cattle to better feed. If you do not act on a group of cattle that are low in body condition they will continue to lose weight.  It is easier and cheaper to preserve body condition than it is to bring a thin cow back into condition.   

            Cows that experience difficulty during calving often have more difficulty overcoming the effects of anestrus and take longer to rebreed.  The cervix acts as a valve that seals the uterine interior from the outside environment and opens wide at calving to allow the calf to pass. This open valve may lead to a contaminated uterus when human assistance is required at the time of calving by admitting whatever bugs are in the neighborhood. Subsequently the cow may develop a uterine infection. Minimizing calving difficulty and employing sanitary practices when assisting births in a timely manner may help to save more calves and attain higher rebreeding rates the following breeding season.  

            Additional management practices that may help reduce the anestrus period include calving heifers prior to the mature cows, utilizing certain estrus synchronization protocols, employing teaser bulls during the anestrus period, implementing strategic weaning methods, grazing or winter feeding classes of cattle separately,  and feeding energy pre- and post-partum. When all is said and done, never underestimate the power of genetics.  Selecting bulls for high reproductive efficiency and those who are of moderate frame and milk is an additional long-term aid to decreasing the anestrus period.    

                That’s enough for this month. A special thanks to my wife Jackie for her part in writing Cow Camp Chatter.  As always, if you would like to discuss this article or simply want to talk cows, do not hesitate to contact me at 775-385-7665 or rtbulls@frontier.com.