Effects of ractopamine hydrochloride on growth performance, carcass characteristics, and physiological response to different handling techniques.

Feedlot cattle ( = 128; BW = 549 ± 60 kg) were used to evaluate the effects of ractopamine hydrochloride (RAC) on growth performance, physiological response to handling, and mobility during shipment for slaughter in a study utilizing a split-plot design with a 2 × 2 factorial arrangement of treatments: 1) diet (CON [no ß-adrenergic agonist] vs. RAC [400 mg·animal·d ractopamine hydrochloride for 28 d]) and 2) handling intensity (HI; low-stress handling [LSH; cattle moved at a walking pace with no electric prod use] vs. high-stress handling [HSH; cattle moved at a minimum of a trot and an electric prod applied while in the alley for posthandling restraint and during loading for shipment to the abattoir]). Cattle fed RAC tended to have greater ADG and G:F ( = 0.06), and had greater HCW and LM area ( = 0.04). The HI treatments were applied on the day after the 28-d growth performance period. Blood samples were collected before HI treatment (baseline), after HI treatments (POSTHAND), after transport to the abattoir (POSTTRANS), and during exsanguination at slaughter. A diet × HI interaction ( = 0.01) was observed in the change in cortisol from baseline to POSTTRANS, and there tended ( ≤ 0.07) to be diet × HI interactions for the change in epinephrine from baseline to POSTHAND and for the change in creatine kinase (CK) from baseline to POSTTRANS. Feeding RAC and HSH both increased the change from baseline to POSTHAND in norepinephrine and pH ( ≤ 0.05). The HSH cattle also had greater changes from baseline to POSTHAND in blood HCO, base excess, partial pressure of CO, lactate, cortisol, and glucose ( ≤ 0.01). Ractopamine and HSH both produced greater increases in CK concentrations from baseline to slaughter ( < 0.01). Mobility was not affected by RAC at the feedlot or following an average 6-h lairage ( ≥ 0.43). This study confirms RAC improves growth performance and suggests metabolic acidosis, a precursor to fatigued cattle syndrome, develops in cattle allowed to trot without the use of a lead rider regardless of RAC administration. Cattle fed RAC displayed altered hormonal responses to handling and transport stress, and the overall proportion of cattle with compromised mobility appears to increase later in the marketing channel. These findings warrant additional research aimed at better understanding the physiological response to stress and protect the welfare of cattle during shipment for slaughter.

Effect of handling intensity at the time of transport for slaughter on physiological response and carcass characteristics in beef cattle fed ractopamine hydrochloride.

The effects of handling intensity on the physiological response and carcass characteristics of feedlot cattle fed ractopamine hydrochloride were evaluated at the time of transport to slaughter. Eighty steers (BW = 668 ± 36 kg) representing 10 lots of similar breed, frame size, and degree of finish were blocked by lot, stratified by weight, and randomly assigned to 1 of 2 handling intensities (HI) over a 1,600 m dirt alley course: 1) low-stress handling (LSH) or 2) high-stress handling (HSH). For the LSH treatment, 4 penmates were kept at a walk with the use of a lead rider. For the HSH treatment, 4 penmates were kept at a minimum of a trot and received 2 applications of an electric prod (approximately 1 s per impulse) at 2 separate instances: first in the alley before post-handling sampling, and again during loading for transportation to the abattoir. Behavioral observations and physical indicators of stress were recorded a minimum of 1 h before handling (baseline), immediately after handling (POSTHAND), and while in lairage after a 200 km transport to the abattoir. Vital parameters were recorded at baseline and POSTHAND. Venous blood samples were collected via jugular venipuncture at baseline and POSTHAND, and mixed arterial and venous blood samples were collected during exsanguination at slaughter. Muscle tremors tended to be more prevalent in HSH cattle at POSTHAND ( = 0.10). The HSH cattle tended to have greater POSTHAND heart rate ( = 0.08); however, there was no effect of HI on POSTHAND respiration rate or rectal temperature ( 0.34). The HSH cattle had greater lactate, epinephrine, norepinephrine, cortisol, and glucose concentrations at POSTHAND ( ≤ 0.02). Additionally, HSH cattle had lower POSTHAND blood pH, bicarbonate, base excess, and partial pressure carbon dioxide ( < 0.0001). Bicarbonate concentrations were greater in HSH cattle at slaughter ( = 0.05); however, there were no differences between HI treatments for the remaining blood variables ( 0.11). Concentrations of stress hormones and CK were significantly greater at slaughter relative to baseline and POSTHAND for both LSH and HSH cattle ( < 0.001). These findings suggest cattle trotted without a lead rider develop metabolic acidosis, and illustrate the importance of low-stress handling at the time of transport for slaughter. Further research is warranted to develop strategies to mitigate stress at the time of transport and ensure the welfare of beef cattle presented to abattoirs.

Effect of shade on animal welfare, growth performance, and carcass characteristics in large pens of beef cattle fed a beta agonist in a commercial feedlot.

Feedlot cattle ( = 1,395; BW = 568 ± 43 kg) were used to evaluate the effects of shade on animal welfare, growth performance, and carcass quality during the summer of 2013 in a Kansas commercial feedlot. Seven lots of predominately black steers and heifers (4 and 3, respectively) visually determined to be approaching the final mo on feed were identified, randomly gate-sorted, and allocated to pens located across the feed alley from each other to receive 1 of 2 treatments: 1) Shade (mean shade area = 1.5 m/ animal) or 2) No shade. Shade was provided using a 13-ounce polyethylene fabric and pens were oriented northwest to southeast. The mean starting date was June 13 and the mean days on feed for lots while on the study was 38 d. Cattle were fed a 77.67% DM steam-flaked corn-based diet and had ad libitum access to water throughout the duration of the trial. Zilpaterol hydrochloride (ZIL) was included in the finishing ration at an inclusion rate of 8.3 mg/kg of DM for the last 20 d on feed with a 3 d withdrawal period. Pen floor temperatures (PFT) were measured using an infrared thermometer and prevalence of cattle open-mouth breathing (OMB) was recorded on a pen basis. In addition to shade treatment, the effect of temperature humidity index (THI) on PFT and OMB was analyzed by classifying days as either "Alert" (THI < 79) or "Danger" (THI > 79). On the day of slaughter, pens within a replicate were kept separate through all stages of the marketing channel from loading at the feedlot until stunning at the plant. Pen served as the experimental unit for all measurements. There was a THI × shade treatment interaction for PFT and OMB ( < 0.001) where days classified as "Danger" increased PFT and prevalence of OMB compared to "Alert" days in unshaded but not shaded cattle. Shaded cattle had greater DMI ( = 0.01); however, unshaded cattle had greater G:F ( = 0.05) and therefore no differences were observed in ADG ( = 0.39). Shaded cattle had greater dressing percentage ( = 0.01), although HCW, LM area, fat thickness, marbling score, and quality grade did not differ between treatments ( > 0.05). Heat stress, a significant animal welfare concern and cause of reduced performance in feedlot cattle during the final phase of the feeding period, was alleviated in shaded cattle and illustrates the importance of shade provision as 1 tool to protect the welfare and increase feed consumption in large pens of feedlot cattle during hot summer months.