This article was written by Ben Holland, former SDSU Extension Beef Feedlot Specialist.
Feeding cull cows is an option that many cow/calf operations consider each year, and cull cows may provide profit potential to cattle feeders. There are several reasons to consider feeding cull cows, such as changing the market timing to receive price premiums and increasing cow grade. However, like many feeding enterprises the goal of feeding cull cows is to put on the most weight with the least cost. Several growth promoting technologies are available and should be used when feeding cull cows.
Cull cows typically have very high dry matter intake (2.25 to 2.6% of body weight), and often have poor feed efficiency. Cull cows, especially those grown in feedlots on high-concentrate diets, should be fed an ionophore according to label directions. Ionophores, such as Rumensin® or Bovatech®, can improve feed efficiency and reduce the risk of digestive upset. Another feed additive that should be included in cull cow diets to improve efficiency is melengestrol acetate (MGA). Cows will not cycle when fed MGA, resulting less riding behavior during estrus, and improved efficiency.
Similar to younger growing and finishing cattle, implanting cows can improve average daily gain, feed efficiency, and hot carcass weight. In general, implants that are labeled for heifers can be used for cull cows. Positive responses have not been observed when implanting cull cows with some classes of implants. Implants with lower potency, and those that are either only estrogenic or androgenic do not result in positive growth responses in cull cows. However, combination implants that have both estrogenic and androgenic activity result in improvements in feedlot performance, carcass weight, ribeye area, and yield grade of cull cows. In younger cattle, we know that aggressive implant strategies can negatively impact marbling, but this is not as large a concern in cull cows where marbling is not emphasized as much.
In recent years, β-agonist have found wide acceptance in feedlots to improve feed efficiency, carcass weight, and dressing percentage of growing cattle. Currently, two β-agonists are labeled for use in beef cattle, ractopamine (Optaflexx) and zilpaterol (Zilmax). Either product can be fed according to label directions during the last 28 (Optaflexx) or 20 (Zilmax) days prior to slaughter to improve performance of implanted cows.
With current high feed costs and the inefficient nature of cows in a feedlot, every option should be taken to improve feed efficiency to increase profit potential. This includes using ionophores, aggressive implant programs with estradiol and trenbalone acetate, and possibly a β-agonist when feeding cull cows.