Using Growth Implants in Bos indicus Cattle Compared to Bos taurus Cattle Reganne Briggs, Caleb Reichhardt, Kara Thornton-Kurth, Matthew Garcia, and Laura Motsinger Climate changes present many challenges for beef producers, including fluctuations in temperature, drought, and quantity and quality of available feed (Capper & Hayes, 2012). Improving beef production efficiency can mitigate the negative impacts of these challenges. One way to improve efficiency is altering breed type (i.e., Bos indicus vs. Bos taurus) or crossbreeding to maximize heterosis. This process requires evaluating breed complementarity. Breed complementarity is vital in crossbreeding schemes as different breed types are known to vary in production traits (Frisch & Vercoe, 1977), and the hybrid offspring are usually better performing in specific production traits when compared to straightbred cattle (Figure 1). Introducing Bos indicus genetics may improve efficiency of production as these cattle are better adapted to nutritional stress, can carry a higher parasite load, are more heat tolerant, and have increased longevity compared to Bos taurus cattle (Forbes et al., 1998). However, only 8% of U.S. cattle inventory is Bos indicus influenced (Cundiff et al., 2012), possibly because these animals are more excitable and possess less desirable carcass traits, such as lower-quality grade and tenderness (Behrends et al., 2009; Voisinet et al., 1997). Crossbreeding Bos indicus cattle with Bos taurus cattle can minimize these traits. For example, Santa Gertrudis cattle are a cross between Brahman (3/8) and Shorthorn (5/8) (see Figure 1C). Beef producers use growth implants, also known as anabolic hormone implants, to increase cattle production efficiency and growth (Behrends et al., 2009; Cundiff et al., 2012; Voisinet et al., 1997). Growth or anabolic implants can be natural or synthetic 1
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Figure 1. (A) Angus (Bos taurus), (B) Brahman (Bos indicus), and (C) Santa Gertrudis Cattle in Feedlot Settings