This article was written by Kalyn Waters, former SDSU Extension Cow-Calf Field Specialist.
The state of South Dakota ranks fifth within the United States in total cow/calf production. There are approximately 29.9 million cows in the United States cattle herd, with 1.61 million of those beef cows in the state of South Dakota. While 73% of these cattle are managed in a spring calving program, the remaining producers utilize a fall calving program. With all beef producer facing extreme challenges during a time of drought, those calving in the fall, following a summer of record breaking temperatures and rainfall values well below average, face a unique set of challenges that warrant addition management considerations.
Body Condition Score
Body condition scoring (BCS) is a tool that can be used to estimate the energy reserves of cattle. In the beef industry a 9-point scale is used, with 1 being emaciated and 9 being obese. Using BCS, producers can estimate the energy balance of their herd. Research has revealed that the BCS prior to calving has a greater impact on subsequent reproductive performance of a female, than BCS following calving, regardless of BCS or weight gained following calving. It is recommended that cows calve in a BCS of 5 to 5.5 for optimal reproductive efficiency.
With the nutrition value of range forage being less then optimal during a drought, BCS must be closely monitored to ensure that fall calving cows do not enter into a negative energy balance and begin to loose BCS prior to calving. This will have a detrimental impact on subsequent pregnancy rates. In addition, cows that are thin (BCS ≤ 4.5) or in a negative energy balance are at a higher risk of experiencing calving difficulties, which not only puts the cow and calf at risk during birth, but also may reduce the reproductive performance for the following breeding season.
Birth Weights and Gestation Length
Uterine blood flow is critical not only for the development of the placenta, but also for the continued growth of the fetus. In times of heat stress, thermal regulation mechanisms are activated to maintain homeostasis and normal body temperatures within the animal. One of the main mechanisms mitigating heat stress is the direction of blood flow. During periods of high temperatures, blood flow is directed away from the core of the body, to the surface for cooling. Nutrients are delivered to the fetus via the maternal blood, therefore this cooling processes results in a reduction of nutrients available for placental and fetal growth. Research has shown that reduced uterine blood flow resulted in a reduction of cotyledonary mass, reducing the total surface area for maternal to fetal nutrient exchange. Therefore with the reduction of nutrients available for growth, it is common to experience reduced birth weights following a period of heat stress during gestation. In addition to lower birth weights, calving dates may be earlier than expected. While in most cases calves will not be born early enough to have serious consequences, producers should still be prepared.
Extensive research has been conducted on the effects of heat stress in the lactating dairy cow; little has been done to examine heat stresses impact on the beef cow’s lactation. While beef and dairy cattle have very distinct lactation curves, peaking at different times, with different amplitudes, the general means in which lactation is regulated does not differ. Therefore, the research does carry over. Thus, heat stressed beef cows will possibly experience reductions in milk yields. This may be seen not only in the volume of colostrum and or milk being produced, but also its nutrient quality. This is compounded by the fact that many of these heat stressed beef cows are grazing suboptimal forage; therefore supplementation of nutrients may be needed. Therefore close monitoring of calf health and growth will be needed.
Practices such as BCS and forage testing are tools that can be used to aid in managing a drought stressed fall calving herd. While producers calving in the fall, following a drought stricken summer, will experience several obstacles that are not traditionally expected in a fall calving system, with good management and preparedness, a successful calving season is still attainable.