Drought effect on weaning weight and efficiency relative to cow size in semiarid rangeland1

Abstract

Cow size has been suggested to be an important consideration for selecting cattle to match their production environment. Over the last several decades, the trend in genetic selection for maximum growth has led to gradual increases in beef cow size. An unrelated trend during this same period in the western United States has been an increase in temperature, drought frequency, and drought severity. Due to the potential influence of the increasing cow size trend on nutritional maintenance costs and production, we assessed the effect of cow size on weaning weight and efficiency in relation to drought on a semiarid high-elevation ranch in Wyoming. This study addresses a lack of empirical studies on the interaction between cow size and drought. We measured calf weaning weights of 80 Angus × Gelbvieh cows from 2011 to 2014 and assessed how drought affected weaning weights, efficiency (considered as calf weight relative to cow weight), intake requirements, and potential herd sizes relative to cow size. We stratified cows into 5 weight classes (453, 498, 544, 589, and 634 kg) as a proxy for cow size and adjusted weaning weights to a 210-d calf sex adjusted value. Cow size was a significant factor every year, with different cow sizes having advantages or disadvantages different years relative to weaning weight. However, efficiency for the smallest cows (453 kg) was always greater than efficiency for largest cows (634 kg; < 0.001). Efficiency for the smallest cows was greater in the driest year (0.41 ± 0.02) than efficiency of the largest cows in the wettest years (0.37 ± 0.01). The change in efficiency (ΔE) between wet and dry years was 0.18 for the smallest cow size and 0.02 for the largest cow size, and ΔE decreased as cow size increased. This is an indication of the ability of smaller cows to lower maintenance requirements in response to changes in the production environment but with optimal upside potential when conditions are favorable. These results indicate large cows (589 to 634 kg) do not maximize genetic potential in this production environment when conditions are optimum or provide any advantage over small or moderate size cows (453 to 544 kg) across the drought gradient.

Effect of mature body weight and stocking rate on cow and calf performance, cow herd efficiency, and economics in the southeastern United States1

“…But other measures of productivity (pregnancy rates and net returns) were comparable with LGHT cow productivity, even though measures of weaning efficiency (kg of calf BW weaned per 100 kg cow BW) were reduced in HVY cows. Scasta et al (2015) reported that large cows are not able to meet genetic production potential in a semiarid high-elevation rangeland production environment in Wyoming and, similar to the current research, smaller cows had greater weaning efficiency ratios than larger cows.…”

Can We Predict Forage Nutritive Value With Weather Parameters?

“…The total pounds weaned ranges from 50,000 lb for 1,000 lb cows to 35,500 lb for 1,400 lb cows if larger cows offer no advantage in calf weaning weight (Table 1). Finally, the only cow size capable of weaning 50% of her body weight would be the smallest 1,000 lb cows; a result that is also supported by ranch level data in Scasta et al 16 (Table 1). Thus, because smaller cows require less forage, more individual cows can be placed on the same pasture and more total calf crop weight produced if the growth potential of larger cows is constrained by the environment.…”

“…15 Contradictory results from a semi-arid rangeland environment in Wyoming recently indicated however that smaller cows weaned calves as heavy as the largest cows and may have an advantage over large cows due to their ability to reduce forage inputs while simultaneously increasing total output measured in annual total weaned weight of calves. 16 Using this general result for the cow size*rangeland environment interaction, we developed a hypothetical modeling scenario presented in Table 1 that we suggest for western rangelands. We used a formula assuming that forage dry matter intake (DMI) is 2.2% of a lactating cow's body weight on low quality forage 17 for five cow sizes (Table 1, Fig.…”

“…20 The provision of shade and water offers y Assuming an average 500 lb weaned calf across all cow sizes and across the drought gradient. 16 Calculated as calf weight:cow weight with a common target of a cow weaning 50% of her body weight or an efficiency ratio of 0.5.…”

Drought Consequences for Cow-Calf Production in Wyoming: 2011—2014

“…20 The provision of shade and water offers 17 y Assuming an average 500 lb weaned calf across all cow sizes and across the drought gradient. 16 Calculated as calf weight:cow weight with a common target of a cow weaning 50% of her body weight or an efficiency ratio of 0.5.…”