Severity Of Winter And Impact On Calf Birth Weights

Dr. Glenn Selk, Oklahoma State University Emeritus Extension Animal Scientist, offers herd health advice as part of the weekly series known as the "Cow Calf Corner" published electronically by Dr. Peel and Dr. Glenn Selk. Today,

Dr. Selk offers research he has found as to whether or not the severity (coldness or mildness) of the winter has an impact on spring-born calf birth weights.

 

"Does the severity (coldness or mildness) of the winter have an impact on spring-born calf birth weights? Ranchers have asked that question during many springs and veterinarians have speculated for years. The debate rages on! This is obviously a difficult subject to research because you cannot have a "control" group of cows to compare to a "treatment" group that is exposed to a cold winter while still running on the same pasture. Therefore research data on this subject is limited. 

 

"University of Nebraska researchers have done the next best thing. They have monitored the birth weights of genetically similar calves across three different winters and have related average winter temperatures to birth weights. A 3-year study was conducted to evaluate effects of high and low air temperatures and wind chills during winter months on subsequent calf birth weights and calving difficulty of spring-born calves. Records on approximately 400 2-year-old heifers and their calves were used. Heifer and calf genetics were the same each year. Heifers were fed similar quality hay free-choice each year before calving. High temperatures during the 1994-95 winter were 9 degrees higher than during the 1992-93 winter. The low temperatures were five degrees higher for 1994-95 compared to 1992-93. The greatest differences in monthly temperatures between years were found during December, January and February. Average temperatures for these three months increased 11 degrees F over the three years. Average calf birth weights decreased 11 pounds (81 to 70) from 1993 to 1995. A 1:1 ratio was observed. Although calving difficulty was high due to the research design, it also decreased from 57% to 35% from 1993 to 1995. Results indicate that cold temperatures influenced calf birth weight. Weather cannot be controlled; however, when we have below average winter temperatures, larger birth weight calves and more calving difficulty may be expected in the spring. (Source: Colburn, et al. 1996 Nebraska Beef Cattle Report.) So far in 2019, 30 of 49 days have been below normal in daily maximum temperature in Central Oklahoma.