The influence of RFI classification and cow age on body weight and body condition change, supplement intake, and grazing behavior of beef cattle winter grazing mixed-grass rangelands

Providing adequate nutrition for animals is the greatest operating cost for cow–calf producers where supplemental feed can account for 65% of the annual expenses to maintain a cow–calf operation (Arthur et al., 2004; Van der Westhuizen et al., 2004; Meyer et al., 2008). In addition, the USDA Economic Research Service estimated that feed-associated costs comprised greater than 55% of all nonfixed costs of U.S. cow–calf operations (USDA-ERS, 2005). Traditionally, selection pressure has been placed on production traits associated with increasing outputs, which can also result in increased inputs to meet animal production potential. Since feed costs constitute the greatest proportion of total inputs, selection pressure for efficient animals that have lower feed intake but maintain production could have a great impact on cow–calf profitability (Meyer et al., 2008). It is estimated that two-thirds of feed energy is required for body maintenance (Ferrell and Jenkins 1984, 1988; Montaño-Bermudez et al. 1990), and substantial animal-to-animal variations, independent of body size and growth, exists in maintenance requirements of cattle (Arthur et al., 2001; Nkrumah et al., 2006; Crowley et al., 2010). Thus, improving feed efficiency through genetic selection holds significant opportunity for the beef industry. Residual feed intake (RFI) is currently being used as a selection tool for purchasing and retaining heifers and for selecting bulls and semen. However, the use and relevance of RFI as a selection tool for the cow–calf industry in the western United States needs additional research. Little if any research supports selection for beef cows that fit western rangeland beef cattle systems using RFI values obtained in post-weaning studies. Most RFI studies have included energy-dense diets and rations focusing on feedlot performance (Lawrence et al., 2014). Research pertaining to RFI in cattle offered forage-based diets is limited (Arthur et al., 2005), with even fewer data available that relate to beef cows (Basarab et al., 2007; Meyer et al., 2008; Sprinkle et al., 2020). As a result, more research is needed to evaluate the utility of RFI estimates on the lifetime production of beef cattle in extensive forage base systems (Manafiazar et al., 2015; Sprinkle et al., 2020). Therefore, the objectives of this study are to evaluate the influence of cow RFI classification and cow age on weight and body condition change, as well as supplement intake and grazing behavior of winter grazing beef cattle. We hypothesized that there is no difference between cow RFI classification and cow age on production, supplement intake, nor grazing behavior.

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