Effects of ruminally-protected lysine and Megasphaera elsdenii on performance and carcass characteristics of finishing cattle

Abstract

Ractopamine hydrochloride is a β-adrenergic agonist (BAA) commonly added to cattle finishing diets that redirects nutrients from fat deposition to protein synthesis and muscle growth. Physiological conditions established by BAA suggests that cattle fed diets containing BAA would have greater requirements for dietary protein to sustain BAA-induced accretion of lean tissue. Three hundred and eighty-four crossbred steers (413 ± 29.2 kg initial body weight) were used in a finishing trial to evaluate effects of ruminally-protected lysine (RPL) supplementation on performance and carcass characteristics of beef steers. Treatments were (2 × 4 factorial) 0, 20, 40, or 60 g/animal daily of SafeGain (i.e., approximately 0, 0.6, 1.2, or 1.8 g of lysine/kg diet dry matter based on an assumed daily feed intake of 10 kg per animal) in conjunction with a BAA (33 mg/kg diet dry matter basis) during the last 42 days on feed (112 days finishing period); and two step-up regimens: traditional 21-day step-up or an accelerated 12-day step-up with an oral dose of Megasphaera elsdenii probiotic (M.e.). Steers were blocked by weight; randomly assigned to treatments; implanted with 200 mg trenbolone acetate, 20 mg estradiol USP, and 29 mg tylosin; and allocated within blocks to 64 concrete-surfaced pens containing 6 steers per pen. A basal diet (dry matter basis) of 688.7 g/kg steam-flaked corn, 200 g/kg corn gluten feed, 70 g/kg alfalfa hay, and 19.1 g/kg vitamin and mineral supplement was fed ad libitum once daily. Ruminally-protected lysine was supplemented only during the BAA administration period, which comprised the last 42 days on feed. At the end of the finishing period, pens of cattle were weighed and then transported to a commercial abattoir. Harvest order, hot carcass weight, and liver abscess incidence and severity were evaluated the day of harvest. Longissimus muscle area, back fat, marbling score, USDA Yield Grade and USDA Quality Grade data were collected following a 36-hour refrigeration period. There were no effects of RPL supplementation or M.e. on average daily gain (P > 0.63), dry matter intake (P > 0.45), or feed efficiency (P > 0.81) of finishing steers; but liver abscess incidence was increased with RPL supplementation (P < 0.05; 28.3, 39.0, 46.9 and 39.4 % for cattle fed 0, 20, 40 and 60 g/animal daily of RPL, respectively). An interaction between RPL and M.e. was observed for hot carcass weight (P = 0.01). Dosing cattle with M.e. with an accelerated transition period decreased marbling score (P = 0.03) and yielded a lower percentage of carcasses grading Choice (P = 0.03) than those traditionally adapted. No other effects of M.e. or RPL were observed for carcass characteristics (P> 0.10). Thus, supplementation of RPL in conjunction with ractopamine hydrochloride yielded no benefits during feedlot finishing; however, an accelerated step-up program with M.e. yielded finishing performance comparable to that of traditionally-adapted cattle.