Investigating thin beef cull cow realimentation strategies

Date

2019-12

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Abstract

A trio of experiments were conducted to identify methods to improve red meat yield of cull cows targeted for a lean market. In the first study, a set of thin beef cull cows (n = 144; initial BW = 465.8 ± 56.9 kg, initial BCS = 2.13 ± 0.68) were serially harvest (28, 42 and 56 d on feed; DOF) with the aim of modeling compositional changes, to benchmark the timeline of compensatory growth. Furthermore, half of the cows were top dressed 400 mg∙animal-1∙d-1 of ractopamine hydrochloride (RH; Actogain 45; Zoetis, Parsippany, NJ) to evaluate the efficacy of the β-agonist and explore its relationship with compensatory growth. No DOF x RH interactions were detected for any parameter (P ≥ 0.11) impying that the compensatory state did not affect the magnitude of the RH response. Extending DOF generated a linear increase in DMI (P <0.01) yet a decline in carcass ADG (P <0.01). Furthermore, kidney weights tended to decrease (P = 0.07), while several % fabricated cuts linearly declined (eye round, P =0.04) or tended to decline (inside round, P =0.09; sirloin top butt, P =0.10; tender loin, P =0.06). Collectively, implying a majority of compensatory gain occurred in the first 28 d. Compared to controls, RH incited improvements in feedlot performance, improving ADG by 13.7% (P = 0.04) and carcass ADG by 16.9% (P = 0.02). Although, inclusion of RH in the finishing diet increased HCW by 4.5% (P = 0.05; 12.9 kg) it did not alter red meat yield (P ≥ 0.16). In experiment II, thin, beef cull cows (n = 144, BCS= 2.10 ± 0.61; BW = 456 ± 47 kg) were studied to evaluate methods to accelerate dietary step up to exploit the narrow timeline of compensatory gain. Cattle were organized into a 2x2 factorial arrangement of treatments, to measure the effect of finishing diet roughage level and oral drenching of Megasphaera elsdenii NCIMB 41125 (Lactipro; Lactipro Advance; MS Biotec Inc., Wamego, KS). Cattle were finished over a 42-d realimentation period, and aggressively stepped up over a 10-d period to either a high roughage finisher (25% roughage) or a low roughage finisher (10% roughage). Additionally, cattle were drenched with either 0 or 100 mL of Lactipro (M. elsdenii NCIMB 41125, 2 x 108 cfu/mL) on d 0. Decreasing finishing roughage level tended to improve average daily gain by 9.7% (0.26 kg, P = 0.08), while decreasing dry matter intake (DMI) by 1.11 kg (P = 0.09), provoking a 19.7% enhancement of feed efficiency (0.036 units, P < 0.01). However, a significant improvement between treatments was only detected during the final interim period, suggesting increasing caloric density may help offset the performance regression typically observed following compensatory gain. Overall, oral drenching of Lactipro tended to augment ADG (0.26 kg, P = 0.08) and tended to improve carcass ADG (0.20 kg, P = 0.10); implying Lactipro was effective at alleviating the elevated acidosis risk prompted by the rapid step-up period employed in the trial. In the final trial, beef cull cows were (n= 45, BW = 503 ± 58 kg; BCS = 2.1 ± 0.6) challenged with a 0-d step up in order to quantify the effect of Lactipro on ruminal health parameters. Cattle were randomized into two treatments (0 versus 100 mL of Lactipro) and fed exclusively an aggressive 90% concentrate finisher over a 35 d realimentation period. Daily rumination was monitored with a wireless rumination tag (Allfex Flex Tag; SCR Engineers, Ltd., Netanya, Israel). Rumen morphometrics were recorded on the harvest floor, with further papillae analysis conducted in the lab. Lactipro-drenched cattle registered a 13.3% increase in rumination time (39.27 minutes/d, P = 0.03) during the first wk of the trial. Lactipro-drenched cattle posted superior absorptive surface area (P =0.01) and a greater ratio of papillae area of absorptive surface area (P = 0.05). Generally, a precursor of enhanced VFA absorption, rapid papillae surface area growth may help explain the uncharacteristically high ADG (2.41 kg) observed in experiment III. Collectively, it is apparent that Lactipro is favorably bolstering ruminal ecology via promoting papillae growth and safeguarding sensitive microflora from lactate-driven pH drops.

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Keywords

Cull cow, Megashaera elsdenii, Realimentation, Beta-adrenergic agonist

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