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 β-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.

The effect of days on feed and zilpaterol hydrochloride supplementation on feeding behavior and live growth performance of Holstein steers

This experiment was designed to study the effect of days on feed (d 225-533) and zilpaterol hydrochloride (ZH) supplementation on Holstein steer ( = 110) performance and feeding behavior as part of a serial slaughter trial. Steers were randomly assigned to 1 of 11 harvest groups with 10 steers ( = 5 control and = 5 ZH; ZH at 8.33 mg/kg diet) harvested each 28 d. Steers were weighed every 28 d (d 225, 253, 281, 309, 337, 365, 393, 421, 449, 477, 505, and 533); individual daily meal consumption data for each steer were recorded using GrowSafe technology. In the pretreatment period, dry matter intake expressed a negative quadratic relationship with days on feed (DOF) {DMI = -5.7120 + (0.08370 x DOF)- (0.00011 x DOF); Adj. = 0.2574; RMSE = 0.25 75; 0.01}. A linear increase in BW ( < 0.01) occurred during the pretreatment 308 d period from 466 to 844 kg, {BWend = 137.61 + (1.4740 x DOF); Adj. = 0.8819; RMSE = 37.06; < 0.01}, whereas ADG and G:F decreased linearly. Dry matter intake per meal exhibited a quadratic relationship over days on feed and peaked ( < 0.01) during d 365 to 392 at 1.065 kg coinciding with the highest numerical daily DMI (11.19 kg). Daily consumption visit duration differed ( < 0.01) during the 308 d period, with a low of 52.29 min (d 337-364) and a high of 55.59 min (d 365-392). Consumption rate peaked at 714 g/min (d 337-364) and exhibited a quadratic relationship to DOF. The difference ( < 0.04) in DMI between control and ZH treated cattle across all 11 harvest groups averaged 0.575 kg. Moreover, ZH treatment resulted in decreased ( 0.01) DMI per meal event of 0.093 kg. Gain to feed tended to improve ( = 0.06) with ZH treatment by 0.017 kg gain per kg feed relative to the control cattle. Daily bunk, consumption, and meal visit durations were influenced by ZH during the 20 d treatment period ( = 0.01); the average difference between control and ZH supplemented cattle over the 308 d trial was 9.09, 8.71, and 11.39 min per d, respectively. The data collected in this trial indicate live growth performance and feeding behavior were impacted by both DOF and ZH supplementation.

Effects of dietary urea concentration and zilpaterol hydrochloride on performance and carcass characteristics of finishing steers

Cattle receiving zilpaterol hydrochloride () may recycle less N and require a greater supply of RDP. This study evaluated effects of ZH on performance and carcass characteristics of steers fed diets with increasing dietary RDP concentrations supplied as urea. Steers (429 animals; BW = 423 ± 4.5 kg) were sorted into 3 blocks according to BW and assigned to 1 of 6 treatments (6 pens per treatment) in a randomized complete block design. Treatments were a 2 × 3 factorial arrangement of either no ZH or ZH (75 mg ZH per steer daily) supplemented to finishing diets containing 0, 0.5, or 1.0% urea of dietary DM. Pen weights were recorded before treatment initiation; urea was fed for 27 d, and ZH treatments were fed for 24 d with a 3-d withdrawal period. Pen weights were recorded before transporting steers to a commercial abattoir. Continuous response variables were analyzed using the MIXED procedure and categorical data were analyzed using the GLIMMIX procedure of SAS. No ZH × dietary urea interactions ( ≥ 0.14) occurred for all performance and carcass response variables. Feeding ZH for the last 27 d (included a 3-d withdrawal period) of the finishing period increased ( < 0.01) ADG, decreased ( < 0.01) DMI, and increased ( < 0.01) G:F compared with no ZH. In addition, ZH increased HCW ( < 0.01), dressing percentage ( < 0.01), LM area ( < 0.01), and decreased ( = 0.01) yield grade. Increasing dietary urea linearly decreased ( = 0.01) ADG and DMI. A tendency for a linear decrease ( = 0.10) in HCW, and a tendency for a quadratic increase ( = 0.07) in marbling score were observed as urea increased in the diet. Results indicate that cattle supplemented with ZH do not require additional RDP in the diet, and that performance and carcass characteristics were negatively affected when urea was increased in the diet.

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.

Zilpaterol hydrochloride improves feed efficiency and changes body composition in nonimplanted Nellore heifers

This research aimed to evaluate the effects of zilpaterol hydrochloride (ZH; MSD Animal Health, São Paulo, SP, Brazil) on the performance, carcass traits, serum metabolites, body composition, and gain composition of nonimplanted Nellore heifers. Nellore heifers ( = 72; average BW = 267 ± 16 kg; average 18 mo of age) were maintained in a feedlot system for 118 d. Heifers were separated into 2 groups: Control and ZH. The ZH group received ZH (8.3 mg/kg diet DM) for 30 d with 3 d of withdrawal before slaughter. Heifers were allotted to 18 pens, 9 pens per treatment, and assigned to a randomized block design. The animals were weighed, blood samples were collected, and subgroups of heifers were slaughtered at the beginning of supplementation and after 20 and 33 d to evaluate performance, blood metabolites, empty BW (EBW), and EBW composition. Hot carcass and kidney-pelvic fat weights were recorded at slaughter. At 24 h postmortem, carcasses were fabricated and the 9-10-11th rib (HH) section was removed from the primal rib to analyze moisture, protein, ash, and ether extract (EE) content in empty body (EB) and gain composition. Heifers fed ZH had gains in HCW that were 19.7 kg greater than controls, reflecting the 30% increase ( < 0.01) in ADG. There was no change in DMI, resulting in a 20% greater G:F ratio ( < 0.01) for heifers fed ZH. Heifers supplemented with ZH had carcass dressing percentages that were 3% greater than controls ( < 0.01), and there was also a 19% reduction in kidney-pelvic fat ( = 0.05) in ZH-treated heifers. Zilpaterol increased serum creatinine ( < 0.01), tended to increase ( = 0.06) serum triacylglycerol, decreased serum NEFA ( = 0.04), and tended to decrease ( = 0.06) serum glucose. The EBW composition was changed after 20 d of ZH supplementation ( = 0.02), with ZH increasing the moisture, ash, and protein contents, whereas carcass fat was decreased by ZH by 14%. Consequently, the carcass CP:EE ratio after 20 d was increased ( = 0.03) by 24% with ZH supplementation. There was no change on EBW composition after 30 d of ZH supplementation ( = 0.17). Regarding carcass gain composition, ZH increased EBW gain ( = 0.02) by 842 g/d from d 0 to d 30, EB protein gain by 221 g/d ( = 0.05) from d 0 to d 20, and by 180 g/d ( = 0.01) from d 0 to d 33. In conclusion, ZH supplementation in nonimplanted Nellore heifers altered the composition of body weight gain, promoting greater lean tissue deposition and improving feed efficiency.

Beef cattle welfare in the USA: identification of priorities for future research

This review identifies priorities for beef cattle welfare research in the USA. Based on our professional expertise and synthesis of existing literature, we identify two themes in intensive aspects of beef production: areas where policy-based actions are needed and those where additional research is required. For some topics, considerable research informs best practice, yet gaps remain between scientific knowledge and implementation. For example, many of the risk factors and management strategies to prevent respiratory disease are understood, but only used by a relatively small portion of the industry. This is an animal health issue that will require leadership and discussion to gain widespread adoption of practices that benefit cattle welfare. There is evidence of success when such actions are taken, as illustrated by the recent improvements in handling at US slaughter facilities. Our highest priorities for additional empirical evidence are: the effect of technologies used to either promote growth or manage cattle in feedlots, identification of management risk factors for disease in feedlots, and management decisions about transport (rest stops, feed/water deprivation, climatic conditions, stocking density). Additional research is needed to inform science-based recommendations about environmental features such as dry lying areas (mounds), shade, water and feed, as well as trailer design.