Managing weather-stressed cattle for reproductive success

Extreme heat and drought conditions this summer have taken a heavy toll on beef producers and cow herds throughout the South. Now that summer has come and gone, cow/calf producers will need to guard against a false sense of relief brought on by cooler temperatures. For livestock that have experienced heat and nutritional stress over an extended period of time, the recovery period will take time and careful management this fall and winter. 

"The focal point for producers now should be on returning breeding animals to an adequate body condition to support productivity and health," said John M. Davidson, DVM, professional services veterinarian, Novartis Animal Health. "Nutritional management including vitamin and mineral supplementation is critical to restore and maintain body condition scores, particularly in pregnant cows and heifers. Don't forget that adequately conditioned animals can still have hidden nutritional deficiencies that can impact production."

Heat and nutritional stress can have profound effects on reproductive performance and significantly reduce pregnancy rates. Drought-stressed pastures or forages are often lower quality and deficient in the key vitamins and trace minerals necessary to support optimal reproduction. With feed challenges, nutritional deficiencies and heat stress, cows are much less likely to conceive and bulls can have a sharp drop in semen quality 60 – 90 days after a period of environmental stress.   

"Pregnancy checking is probably more important this year than it's ever been," said Davidson. "Given the rising costs to feed and maintain females with limited pasture resources, ranchers really need to work with their veterinarian to preg-check and cull nonproducing females." 

Davidson added that producers who keep more cows than can be fed properly could end up paying in more ways than one. "Certainly there's an unwanted cost associated with feeding open cows," he said. "But if those animals aren't fed in a manner that improves body condition in time for breeding, producers will be faced with an extended calving season and lightweight calves at weaning time."

The optimum body condition score (BCS) at calving is 5 (on a 9 point scale) for cows and 6 for heifers.  Missing the mark here will have an impact down the line.  A quick review of the bovine gestation period reminds us that for a cow to calve every 12 months, she must settle by her 80th day postcalving.  Studies have shown that nearly half of the cattle that calve at a BCS of 4 or less won't be cycling by the 80th day.  This delays conception and shifts that cow's calving to later in the season which results in a lighter calf at weaning.     

Nutritional Stress and Immunity

Nutritional deficiencies brought on by the lack of high-quality forage also place a huge burden on the cow's immune system, leaving her and ultimately her calf more vulnerable to disease.

"Pregnant cows have a pretty tall order and they can't do it all if they're short on nutritional resources," Davidson explained. "First, she has to maintain her pregnancy and build her own immune system. Then she has to take what's left and make it available to her calf through colostrum."

Passive transfer of immunity to calves is dependent on both the quality of the colostrum (concentration) and the proper timing of ingestion.  If the concentration of antibodies in colostrum is low, protection against viral and bacterial infections won't last nearly as long as it should. "This is where producers need to think about the herd health calendar and how proper timing of vaccinations can help support colostrum quality and early calf health," added Davidson. 

"Producers who typically vaccinate only for blackleg or clostridial diseases at branding may want to consider vaccinating for viral diseases like BVD, IBR, BRSV and Lepto hardjo-bovis at branding this year to make sure those calves have early protection." 

Vaccinating calves as young as four weeks of age has proven to be an effective approach to disease prevention. In a 2010 challenge study conducted by Novartis Animal Health, calves were vaccinated with Vira Shield® 6+VL5 HB at four weeks of age and received a booster at eight weeks of age. Results of the study showed those calves were protected from both kidney and reproductive tract colonization of Lepto hardjo-bovis following a severe challenge 12 months after vaccination.

 A key conclusion of the study was that despite a severe challenge, starting a vaccination program with Vira Shield HB in calves as young as four weeks old may significantly reduce the risk of chronically infected animals.

"The most important thing for cow/calf producers with herds coming off heat stress is to preg-check cows and continue to monitor body condition throughout gestation to ensure cows are gaining ground," said Davidson. "By working with their veterinarian and nutritionist, producers can have a positive impact on the future productivity of their herd, not only from a reproductive standpoint, but also from an immunological and herd health standpoint as well."