Forty-eight Pelibuey×Katahdin male intact lambs (23.87±2.84 kg) were used in an 84-d feeding trial, with six pens per treatment in a 2×2 factorial design arrangement. The aim of the study was to evaluate the interaction of two dietary energy levels (3.05 and 2.83 Mcal/kg ME) and two dietary protein levels (17.5% and 14.5%) on growth performance, dietary energetics and carcass traits. The dietary treatments used were: i) High protein-high energy (HP-HE); ii) High protein-low energy (HP-LE); iii) Low protein-high energy (LP-HE), and iv) Low protein-low energy (LP-LE). With a high-energy level, dry matter intake (DMI) values were 6.1% lower in the low-protein diets, while with low-energy, the DMI values did not differ between the dietary protein levels. Energy levels did not influence the final weight and average daily gain (ADG), but resulted in lower DMI values and higher gain efficiencies. No effects of protein level were detected on growth performance. The observed dietary net energy (NE) ratio and observed DMI were closer than expected in all treatments and were not affected by the different treatments. There was an interaction (p2.80 Mcal/kg ME). Providing a level of protein above 14.5% does not improves growth-performance, dietary energetics or carcass dressing percentage.

To determine the effect of adding β2 agonist zilpaterol hydrochloride during different periods on growth performance, dietary energetic, carcass traits and fatty acid profile, forty male lambs Pelibuey × Katahdin (37.70 ± 0.83 kg) were blocked by body weight and randomly assigned to pens. Treatments consisted in: 1) control, no zilpaterol supplementation, 2) zilpaterol supplementation for 20 d (ZIL20), 3) zilpaterol supplementation for 30 d (ZIL30), and 4) zilpaterol supplementation for 40 d (ZIL40). Compared with control treatment, zilpaterol supplementation increased final live weight (FLW) (3.5 %; P = 0.0563), average daily gain (ADG, 14.8 %; P = 0.0598) and gain:feed ratio (10.3 %; P = 0.0324). As well as hot carcass weight (6.1 %; P = 0.0064), dress out percentage (2.6 %; P = 0.0139) and Longissimus dorsi muscle area (13.7 %; P = 0.0015). Compared to control group, zilpaterol increased (P = 0.0413) observed vs. expected dietary of NEm (net energy requirements for maintenance) and NEg (net energy requirements for growth) (5.7 and 8.1 %, respectively). Twenty days of zilpaterol treatment improved FLW (4.4 %, P = 0.0566) and tended to improve ADG (17.4 %, P = 0.0718) when compared to control group. Only intramuscular fat showed a positive linear effect (P = 0.0006) in stearic fatty acids proportion and negative linear effect (P = 0.0585) in araquidonic fatty acid proportion. We conclude that zilpaterol hydrochloride improved variables of growth performance, energy retention and carcass traits with noticeable effects from 20 d of zilpaterol supplementation.

Bruises threaten the welfare of cattle because they cause pain, suffering, and stress during the pre-slaughter stage. Thus, we used meta-analyses to estimate the prevalence of carcass bruising in cattle from the American continent, determined the characteristics of the bruises, and calculated the odds ratio (OR) of risk factor categories associated with bruising. We searched electronic databases to retrieve primary studies conducted in the American continent, which reported cattle carcass bruising, analyzed the size, location, shape, and age of the bruises, and assessed risk factors for bruising. We included 46 studies from nine countries comprising 928 447 cattle carcasses with an overall prevalence of 59.5 % (95 % CI: 51.9 – 66-9) and 2.9 (range 3.4 – 7.4) bruises per carcass in average. The prevalence doubled from 30.7 % during 1991 – 2000 to 64.2 % during 2011 – 2020. Fresh, small-sized bruises of the lowest severity and located mainly in the hindquarter were highly prevalent (37.5 – 66.4 %). The removed meat due to bruising ranged 0.11 – 1.12 kg/carcass with an accumulated weight of condemned meat between 15.6 – 647 kg. Among intrinsic factors, older cattle, dairy cattle, and female cattle had greater odds of bruising (OR=1.57 – 1.98). For extrinsic factors, the odds for bruising increased 1.4 – 2.2 in cattle sourced from auction markets and exposed to poor handling, suboptimal transportation conditions, and deficient facilities. In cattle from America, bruises are a concern because their prevalence is growing and 60 % of cattle assessed in the studies suffered a bruise. Improving facilities and transportation conditions together with proper training of the personnel during the handling and transportation of the cattle will reduce bruising incidence.

This study evaluated the impact of supplementing ZH in combination with D3 on the growth performance, energy efficiency, carcass traits, and meat quality of feedlot lambs. Thirty-two Dorper × Katahdin cross lambs (37.3 ± 5.72 kg) were utilized in a 29 d experiment in a completely randomized block design with a 2 × 2 factorial structure consisting of two levels of ZH for 26 d (0 and 0.20 mg/kg PV⁻¹) and two levels of D3 for 7 d (0 and 1.5 × 10⁶ IU/d⁻¹). ZH improved (p ≤ 0.05) the average daily gain (ADG) and feed efficiency by 9.9% and 17.8%, respectively, as well as hot carcass weight (HCW) and dressing carcass by 4.3% and 2.6%, respectively. (p ≤ 0.03). However, ZH increased (p < 0.01) muscle pH and Warner–Bratzler shear force (WBSF) (2.5 and 23.0%, respectively). D3 supplementation negatively affected (p ≤ 0.02) dry matter intake (DMI) (last 7 d) and ADG by 15.7% and 18.1%. On the other hand, D3 improved the pH of the longissimus thoracis muscle by 1.7% (p = 0.03) without affecting WBSF. When D3 was supplemented in combination with ZH, it was observed that meat quality was improved by reducing muscle pH compared to lambs treated only with ZH. However, D3 did not improve the meat tenderness negatively affected by ZH supplementation.

The objective of this study was to evaluate the effects of zilpaterol hydrochloride supplementation strategies on growth performance, dietary energetics, carcass traits, and meat quality in feedlot finishing lambs. Twenty-four Dorper × Katahdin crossbred male lambs (45.5 ± 4.53 kg, mean ± SD) were used in a 27 d feeding trial. The zilpaterol supplementation strategies were: (1) control, no zilpaterol supplementation (CON); (2) zilpaterol administered once daily as a full dose in the morning feeding (ZMOR); (3) zilpaterol incorporated into the total mixed ration and continuously available throughout the day (ZMIX); and (4) intermittent zilpaterol supplementation applied in a daily alternating pattern, one day on, one day off (ZINT). A target dose of 0.20 mg/kg live weight of zilpaterol hydrochloride per administration was used for all supplemented treatments, with daily administration in ZMOR and ZMIX and alternate-day administration in ZINT. Compared to the CON, zilpaterol supplementation through the ZMOR + ZMIX strategies improved average daily gain (ADG) and feed efficiency (FE) by 28.6% and 18.5%, respectively. Additionally, dressing percentage and longissimus thoracis muscle area increased by 3.2% and 17.0%, respectively. The ZINT strategy also enhanced ADG by 20.9% and FE by 15.4%. However, ZINT did not improve hot carcass weight or dressing percentage. All zilpaterol supplementation strategies increased meat toughness by up to 39.2%. Results indicate that both the ZMOR and ZMIX strategies optimize the response to zilpaterol, with no evidence that ZMOR supplementation results in a diminished response.

The study evaluated the impact of supplementing ZH in combination with D3 on growth performance, energy efficiency, carcass traits, and meat quality of feedlot lambs. Thirty-two Dorper x Katahdin cross lambs (37.3±5.72 kg) were utilized in a 29 d experiment in a complete randomized block design with a 2x2 factorial structure consisting of two levels of ZH for 26 d (0 and 0.20 mg /kg PV-1) and two levels of D3 for 7 d (0 and 1.5x106 IU/d-1). ZH improved (P≤0.05) average daily gain (ADG) and feed efficiency by 9.9% and 17.8%, respectively, as well as hot carcass weight (HCW) and dressing carcass by 4.3% and 2.6%, respectively. (p≤0.03). However, ZH increased (p<0.01) muscle pH and Warner-Bratzler shear force (WBSF) (2.5 and 23.0%, respectively). D3 supplementation negatively affected (P≤0.02) dry matter intake (DMI) (last 7 d) and ADG by 15.7% and 18.1%. On the other hand, D3 improved the pH of the longissimus muscle (LM) by 1.7% (p=0.03) without affecting WBSF. When D3 was supplemented in combination with ZH, it was observed that meat quality was improved by reducing muscle pH compared to lambs treated only with ZH. However, D3 did not improve meat tenderness produced by ZH supplementation.