Drought: Commodities

Beef Cattle — Drought, heat and reproduction

As summer approaches we can conclude two simple facts; it will get hot and we need more rain.  Realizing this, we expect that elevated temperatures will cause our electric bills to rise, but we may overlook the fact that heat stress can impact reproduction and profitability in our cow-calf operation. 

Scientists from South Dakota State University reported that heat stress resulting from excessive exposure to high temperatures and humidity may cause physiological changes to occur in cattle (Table 1).

Table 1.

Physiological Changes that May Occur Due to Heat Stress

Increased respiration rate Increased rectal temperature Increased water consumption Decreased weight gain Decreased activity Decreased fertility

(Source: South Dakota State University)

 

Cow-calf operations that are managed on a year-round breeding season may need to aggressively address heat stress. Since many cattle on this type of breeding program may calve and breed during the hottest months of the year, heat stress may impact production goals.

Reproductive efficiency is the most critical factor affecting profitability of a cow-calf operation. Aside from the fact that calves born during summer months typically weigh less than their counterparts born during fall and spring at weaning, their dams may have difficulty rebreeding. Research has demonstrated that elevated daytime temperatures can result in increased rectal temperatures, thereby causing reduced pregnancy rates (Table 2; Biggers, 1986).

Table 2.

Effects of Imposed Heat Stress on Reproduction in Beef Cows *
	Control	Mild	Severe
Day Temp (F)	71	97	98
Night Temp (F)	71	91	91
R. Hum. (%)	43	27	38
Rectal Temp	38.9	39.2	39.8
Pregnancy (%)	83	64	50

(Original Source of data: Biggers, 1986; OSU)
(*Table from Cow-Calf Corner "Heat Stress Can Reduce Pregnancy Rates," Dr. Glen Selk, OSU)

 

Researchers from Oklahoma State University have demonstrated that bulls experiencing heat stress (elevated body temperatures) due to elevated air temperature, percent motile sperm decrease from 75 – 80% to less than 50% in some cases. Bulls that undergo breeding soundness exams are required to maintain a sperm motility rate above 70% to receive a satisfactory classification. Failure to do so would result in the bull failing a breeding soundness exam.

To prevent reduced conception rates, producers who breed during summer months may want to consider moving the breeding season to a different time of the year. However, careful consideration should be given to align marketing options with operation goals.

Producers who plan to continue breeding during summer months can help reduce effects of heat stress and overall stress by providing adequate shade, water and an effective internal and external parasite control strategy.

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