December 14, 2015

Selecting efficient cows for a changing environment


By Samantha Kneeskern

December 14, 2015 – The weather has been quite variable the past few years in the United States and for some beef producers, their herds are still trying to recover from the 2012 drought. However, other beef producers in the Western U.S. are continuing to experience drought and have not had any relief. The global surface temperature has steadily increased during the past decade and the forecast for the coming decade shows little promise for decreased global temperatures.

Concomitantly, beef producers are selecting for enhanced growth characteristics. Therefore, cow size has also been increasing. Furthermore, larger cows require more forage and nutrients to meet maintenance requirements. Beef cattle producers may need to consider how to adapt to more persistent drought conditions and learn how to match cow type with environment to maximize cow efficiency. But how should producers do this?

To answer that question, researchers at the University of Wyoming have been collecting data during the past 4 years on 80 Angus × Gelbvieh cows and their calves (310 total calves in 4 years) in a semiarid rangeland production environment.

In comparison to the precipitation average over the last 50 years at the beef research station in Wyoming, 2011 brought slightly below average rainfall, 2012 saw the most severe drought in 50 years, 2013 was wetter than average, and 2014 was one of the wettest years on record.

Regardless of cow size, the lightest calf weaning weights (WW) were recorded in 2012, the same year as the severe drought. The greatest calf WW were in 2013 and 2014, with above average rainfall. Cow size also influenced calf WW, but was dependent on weather conditions. In 2012, the largest cows weaned the largest calves. However, during the wettest year, the smallest cows weaned the heaviest calves. During an average year (2011), intermediate sized cows weaned the largest calves.

The smallest cows had the greatest change in calf weaning weight, from 426 pounds per calf in 2012 to 608 pounds in 2014. Furthermore, another objective of the study was to determine cow efficiency. The authors observed that regardless of precipitation, the smallest cows had higher efficiency ratios compared to the largest cows each of the 4 years. Actually, they were the only group to wean 50% of their body weights.

Additionally, they found that small cows required 17 pounds of forage for every 2.2 pounds of calf weaned, while the largest cows required 21 pounds of forage.

“Even though small cows weaned smaller calves in the drought year, smaller cows had higher biological efficiency, suggesting that per unit of production, smaller cows are more efficient and WW may not always reflect that advantage,” the authors write.

The researchers hope that regionally specific models relating cow size to WW and efficiency can be developed to help producers match their cows to their environment. They believe that producers could be more cautious when selecting for larger growth potential, especially in semiarid rangelands.

The article, “Drought effect on weaning weight and efficiency relative to cow size in semiarid rangeland,” can be found in the December issue of the Journal of Animal Science. To access it, click here.

Photo: Sam Cox, formerly with ARS