An evaluation of bunk space requirements for limit-fed growing heifers and feeding strategies for beef × dairy steers

Abstract

Two experiments were conducted to evaluate the effects of bunk management strategy and restrictive feeding regimen on receiving cattle growth, performance, liver abscess (LA) prevalence, and feedlot performance. One option when feeding newly arrived light-weight cattle is to limit- or program-feed energy-dense diets. Previous research demonstrated that limit feeding a high-energy diet during the receiving period improved feed efficiency, illness detection, and diet digestibility when compared with feeding high-roughage diets for ad libitum intake. When limit feeding, cattle feeders have questioned the need to increase bunk allotment per calf when compared with cattle fed for ad libitum intake. Previous research on bunk allotment for limit-fed cattle fed once daily has been conducted in small pen studies containing 4 to 14 cattle per pen. In Exp. 1, a total of 332 crossbred beef heifers were used in a randomized complete block design. Heifers were blocked by origin and then stratified by weight to pens containing 18 to 28 heifers per pen. Pens within block were randomly assigned 1 of 4 treatments, providing 15.2, 25.4, 35.6, or 45.7 cm of linear bunk per heifer, with 4 pens per treatment. Heifers were limit-fed once daily at 2.0% (dry matter basis) of body weight (BW) for 56 days. Bunk allotment did not affect (P ≥ 0.09) final BW, average daily gain (ADG), dry matter intake, or gain to feed (G:F) among treatments. However, a quadratic effect (P = 0.05) was observed on the standard deviation of ADG within pen, with heifers allotted 35.6 cm of bunk space having a greater standard deviation than those allotted 15.2 or 45.7 cm of bunk space per heifer. In Exp. 2, program feeding strategy and roughage and tylosin phosphate inclusion were evaluated in beef × dairy (B × D) crossbred steers for growth performance, LA prevalence, and subsequent feedlot and carcass performance. A total of 529 B × D growing steers were used in a randomized complete block design. Steers were blocked by weight and stratified to pens within block by individual arrival weight. Pens were randomly assigned to 1 of 5 treatments, with 8 pens/treatment. Treatments included diets formulated to provide 1.1 Mcal of NEg/kg DM fed for a targeted gain of 0.91 kg/d (HR), 1.32 Mcal of NEg/kg DM fed for a targeted gain of 0.91 or 1.36 kg/d (MRL and MRH, respectively), or a diet formulated to provide 1.41 Mcal of NEg/kg DM fed for ad libitum intake with or without tylosin phosphate (ALT and ALNT, respectively). Steers were fed once daily for 126 d, and at the conclusion steers were weighed by pen, and ultrasounded for LA. Steers were then shipped to a commercial feedyard and finished on a common diet in 1 of 5 pens, based on treatment, for 179 ± 12 d. Finally, steers were sent to a commercial packing plant where carcass data and LA prevalence and severity were collected. Growing phase final BW and ADG were greatest (P ≤ 0.04) for ALNT and ALT, intermediate (P ≤ 0.04) for MRH, and least (P < 0.01) for HR and MRL. Steers fed MRL and MRH had similar (P ≥ 0.20) G:F compared with ALNT and ALT. Feeding MRH reduced (P ≤ 0.02) LA prevalence by 62% compared with feeding ALNT and ALT. Liver abscess prevalence did not differ (P = 0.80) between ALNT and ALT at the end of the growing period. Steers fed HR, MRL, and MRH had greater ADG and G:F during the finishing period compared with ALNT and ALT. At the conclusion of the finishing phase, LA prevalence did not differ (P = 0.28) among treatments, but MRH tended (P ≥ 0.06) to have a higher proportion of A+ adhered LA when compared with all other treatments. Overall, program feeding a moderately energetic diet resulted in similar feed efficiency during the growing period and improved performance and efficiency during the finishing period compared with feeding a high-energy diet for ad libitum intake. Programmed-fed steers had less LA prevalence at the end of the growing period but LA prevalence at harvest did not differ among treatments. In addition, feeding tylosin phosphate did not reduce LA prevalence at the end of the growing period or at harvest. Overall, these data demonstrate the performance benefits to restrictively feeding cattle as well as possible mitigation strategy to LA development in the growing phase. Additionally, producers do not need to increase bunk space to implement these restrictive intake strategies in existing growing systems without compromising performance or animal health.