The study was carried out at the National Beef Cattle Research Center of the Brazilian Corporation of Agricultural Research (Embrapa Beef Cattle), Campo Grande, MS, Brazil (20°26'42''S, 54°43'22''O). Over a 2-year study period (Year 1 = 2013 to 2014 and Year 2 = 2014 to 2015), crossbred steers (n = 49 and 56 for Years 1 and 2, respectively) and heifers (n = 52 and 48 for Years 1 and 2, respectively) were submitted to different nutritional strategies during the postweaning period, which was undertaken in grazing systems, following a single strategy for finishing in the feedlot.
Cattle were produced from matting Nellore and crossbred spring-caving cows (½ Nellore x ½ Angus and ½ Nellore x ½ Caracu) with tropically adapted sires (Braford, Charbray, and Caracu), using fixed-time artificial insemination, and weaned at 8 to 10 mo of age in June 2013 (Year 1) and June 2014 (Year 2). Then, cattle were allocated to eight paddocks, blocked by sex and balanced by genetic group. Paddocks were 8 ha on average, composed of Brachiaria brizantha cv. Marandu (marandu-grass) and received nitrogen fertilization in February 2014 and 2015 (100 kg urea ha− 1). Forage availability was evaluated every 56 days by harvesting and weighing the forage mass in 40 random plots per paddock. Composite samples were dried (55°C, 72 h) to calculate forage availability on a dry basis. A subsample was divided into leaf, stem, and dead material to calculate the leaf-to-stem ratio. Leaves were dried and ground (1-mm sieve), and their chemical composition was estimated using Near-infrared spectroscopy with standard curves calibrated for the genus Brachiaria, according to Marten et al. (1989).
Cattle were maintained in pastures for 12 months and submitted to different treatments during the whole phase before being enrolled in a feedlot for finishing. Treatments were composed of different nutritional strategies with focus on the use of VM (Eskalin, Phibro, Guarulhos, Brazil) as a growth promotor, provided to cattle through a protein supplement in the dry season (June to October) and a mineral supplement in the following rainy season (November to May) (Table 1). The VM was included in the supplements to provide a daily VM intake of 45 mg/100 kg BW, and the expected daily supplement intake was 0.25 and 1.0 g kg/BW for mineral and protein supplements, respectively. In Year 1, all paddocks received protein supplements (P-D, 35% crude protein) during the dry season (106 days) and mineral supplements during the rainy season (M-R, 203 days). However, VM was included in the supplements of four paddocks (two paddocks per sex), and the other four paddocks received no VM (Control). In Year 2, the lengths of the dry and rainy seasons were 125 and 213 days, respectively, and the same treatments as those in Year 1 were applied, except that the control group received a second protein-energy supplement (PE-R, 25% crude protein) without VM in the rainy season, replacing the mineral supplement (Table 2). The supplements were offered ad libitum in sheltered feeding bunks, and daily supplement intake was measured by weighing orts weekly.
Table 1
Supplements and feedlot diet composition.
Item | Supplements |
Year 1 | | Year 2 |
P-D | M-R | | P-D | M-R | PE-R |
CP, g/kg | 350.0 | - | | 350.0 | - | 250 |
NPN (max), g/kg | 297.0 | - | | 297.0 | - | 150 |
Ca (min), g/kg | 60.0 | 60.0 | | 60.0 | 60.0 | 30 |
Ca (max), g/kg | 68.0 | 180.0 | | 68.0 | 180.0 | 40 |
P (min), g/kg | 18.0 | 40.0 | | 18.0 | 40.0 | 25 |
S (min), g/kg | 8.0 | 9.0 | | 8.0 | 9.0 | 15 |
Na (min), g/kg | 47.0 | 42.0 | | 47.0 | 42.0 | 45 |
Mg (min), g/kg | | 5.0 | | | 5.0 | 6.0 |
Co (min), mg/kg | 0.0023 | 46 | | 0.0023 | 46 | 20 |
Cu (min), mg/kg | 0.2 | 615 | | 0.2 | 615 | 260 |
Fe (min), mg/kg | 0.15 | - | | 0.15 | - | |
I (min), mg/kg | 0.01 | 36 | | 0.01 | 36 | 100 |
Mn (min), mg/kg | 0.4 | 440 | | 0.4 | 440 | 310 |
Se (min), mg/kg | 0.002 | 14 | | 0.002 | 14 | 10 |
Zn (min), mg/kg | 1.0 | 1950 | | 1.0 | 1950 | 720 |
F (max), mg/kg | 0.18 | 600 | | 0.18 | 600 | 250 |
TDN (min), mg/kg | | | | | | 400 |
Ingredients | Feedlot TMR (Years 1 and 2) Dry basis (g kg -1) |
Sorghum silage | 35 |
Corn, dry ground | 49,8 |
Soybean hulls | 9 |
Soybean meal 45% CP | 3.6 |
Urea | 1.1 |
Mineral premix | 1.5 |
Nutrients | Year 1 | Year 2 |
DM | 989.4 | 936.0 |
CP | 117.6 | 114.1 |
EE | 23.9 | 36.6 |
NDF | 381.3 | 352.7 |
ADF | 155.1 | 224.4 |
ADL | 15.5 | 20.6 |
TDN | 736.4 | 737.1 |
P-D = protein supplement in the dry season; M-R = mineral supplement in the rainy season; PE-R = protein-energy supplement in the rainy season; TMR = total mixed ration; CP = crude protein (g/kg DM); NPN = non-protein nitrogen; DM = dry matter (g/kg DM); EE = ether extract; NDF = neutral detergent fiber (g/kg DM); ADF = acid detergent fiber (g/kg MS); ADL = Acid detergent lignin (g/kg MS); TDN = total digestible nutrients (Weiss et al., 1999). |
Table 2
Scheme of experimental arrangements and summary representation of supplementation strategies during the post-weaning phase in grazing cattle.
Season | Year 1 | | Year 2 |
Dry | P | Pvm | | P | Pvm |
Rainy | M | Mvm | | PE | Mvm |
Contrast | P-D/M-R | Pvm-D/Mvm-R | | P-D/PE-R | Pvm-D/Mvm-R |
n = 50 | n = 51 | | n = 52 | n = 52 |
P = protein supplement; M = mineral supplement; PE = protein-energy supplement; Pvm = protein supplement with virginiamycin; M = mineral supplement with virginiamycin; P-D/M-R = supplementation strategy with protein supplement in the dry season and mineral supplement in the rainy season; Pvm-D/Mvm-R = addition of virginiamycin both in the protein and mineral supplements; P-D/PE-R = supplementation strategy with protein supplement in the dry season and protein-energy supplement in the rainy season. |
During this phase, cattle were subjected to protocols for deworming (doramectin 1%, Vallé, Brazil) as well as tick and fly (cypermethrin) control (June to October), and steers were castrated (November). Weighing was carried out after a 16-hour fasting period every 56 days, and carcass traits were evaluated by ultrasound on four occasions throughout the last 5 months of the growing period. Cattle were scanned using a real-time Piemedical, Scanner 200 VET (Pie Medical, Inc., Maastricht, The Netherlands) ultrasound equipment unit equipped with an 18-cm, 3.5-MHz linear array transducer and a coupled acoustic guide. Vegetable oil was used for acoustic coupling. Ultrasound images of the longissimus thoracis muscle (LT) between the 12th and 13th ribs were used to determine the ultrasound rib eye area (UREA) and subcutaneous backfat thickness (UBFT), and images of the biceps femoris muscle were used to obtain ultrasound rump fat thickness (URFT).
Following the growing period, cattle were housed in individual soil-surfaced pens (2 x 19 m) with water fountains and sheltered feed bunks and enrolled in a feeding trial, receiving a total mixed ration (TMR, 2.69 Mcal ME/kg, and 14.3%CP on a dry matter basis, Table 3). A single TMR was offered to animals from both treatments and both years such that the effects of the previous nutritional regime could be evaluated. Cattle were allowed to adapt to the diet and feeding procedures for 25 days when sorghum silage was offered ad libitum and gradually substituted for concentrate to meet the final TMR. After the adaptation period, the TMR was offered ad libitum, at 8:00 h and 15:00 h, to allow for 5% refusal, and orts were weighed daily before the morning feed delivery to calculate the daily dry matter intake (DMI). The TMR samples were collected weekly for determining the DM concentration and chemical composition. Feed samples were dried at 55ºC for 72 h and ground to pass a 1-mm screen. Dry matter, ash, crude protein (micro-Kjeldahl method), and ether extract contents were determined according to the AOAC (1990), and neutral and acid detergent fiber was measured according to Van Soest et al. (1991). Total nutrient digestibility was estimated according to Weiss (1999).
Table 3
Forage characteristics during the postweaning phase.
Item | Sampling days | MSE1 | P-value² |
Year 1 |
| Oct-13 | Nov-13 | Jan-14 | Mar-14 | Jun-14 | | |
FM | 16.13a | 10.88b | 14.82a | 14.72a | 16.10a | 0.43 | < 0.0001 |
GFM | 5.33bc | 4.67c | 7.91a | 8.13a | 6.87ab | 0.28 | < 0.0001 |
LM | 2.29d | 2.65cd | 4.69a | 3.83ab | 3.43bc | 0.17 | < 0.0001 |
L:S | 0.79c | 1.23b | 1.61a | 0.94bc | 1.13b | 0.06 | < 0.0001 |
SR | 0.76d | 0.84cd | 0.95bc | 1.09ab | 1.23a | 0.03 | < 0.0001 |
OM | 910.1a | 894.7c | 908.8ab | 905.2ab | 903.0b | 1.12 | < 0.0001 |
CP | 70.2c | 71.2c | 66.2c | 78.9b | 86.5a | 1.32 | < 0.0001 |
NDF | 732.2a | 735.2a | 737.9a | 706.4b | 694.7b | 3.15 | < 0.0001 |
ADF | 366.9b | 382.5a | 377.4ab | 352.7c | 342.2c | 2.76 | < 0.0001 |
ADL | 29.1ab | 29.2a | 29.3a | 26.6ab | 26.3b | 0.37 | < 0.0001 |
OMIVD | 523.2c | 528.5c | 517.1c | 558.6b | 598.9a | 5.54 | < 0.0001 |
| Year 2 | |
Aug-14 | Oct-14 | Jan-15 | Mar-15 | May-15 |
FM | 14.59a | 11.65b | 10.52b | 11.16b | 13.22a | 0.28 | < 0.0001 |
GFM | 5.94b | 4.40c | 5.93b | 7.55a | 7.90a | 0.27 | < 0.0001 |
LM | 3.10cd | 2.43d | 3.56bc | 4.27a | 3.84ab | 0.13 | < 0.0001 |
L:S | 1.11b | 1.26b | 1.50a | 1.31b | 0.94b | 0.05 | < 0.0001 |
SR | 0.81c | 0.86bc | 1.02b | 1.18a | 1.30a | 0.03 | < 0.0001 |
OM | 904.6c | 907.8bc | 903.4c | 912.0ab | 916.3a | 0.98 | < 0.0001 |
CP | 84.5a | 79.2a | 67.9b | 83.6a | 83.0a | 1.25 | < 0.0001 |
NDF | 722.7ab | 668.9d | 734.9a | 690.6c | 716.6b | 4.04 | < 0.0001 |
ADF | 356.2b | 315.4d | 371.5a | 341.3c | 340.0c | 3.11 | < 0.0001 |
ADL | 28.8a | 21.6d | 26.3b | 24.6bc | 23.4cd | 0.47 | < 0.0001 |
OMIVD | 562.4c | 628.2a | 530.0d | 589.0b | 556.8c | 5.73 | < 0.0001 |
FM = forage mass (t DM/ha); GFM = green forage mass (t DM/ha); GLM = leaf mass (t DM/ha); L:S = leaf: stem ratio; SR = stocking rate (animal units/ha); OM = organic matter (g/kg DM); CP = crude protein (g/kg DM); NDF = neutral detergent fiber (g/kg DM); ADF = acid detergent fiber (g/kg MS); ADL = acid detergent lignin (g/kg MS); OMIVD = organic matter in vitro digestibility (g/kg DM). Means followed by different letters differ significantly (P < 0.05). |
¹ Mean standard error. ² Probability of error type I. |
The finishing period length was 83 and 84 days for heifers and 119 and 98 days for steers in Years 1 and 2, respectively. At the end of the finishing period, cattle were slaughtered at a commercial abattoir (Naturafrig, Rochedo, Brazil), following humane slaughter guidelines as required by Brazilian laws. Carcass processing followed the common industry practices adopted in Brazil. Animals were desensitized by a captive bolt pistol and bleeding through incisions of the jugular veins and carotid arteries. Liver weight and pooled kidney, pelvic, and inguinal fat mass weight (KPI) were recorded. Carcasses were longitudinally half divided, weighed (HCW), washed, and immediately chilled at 0–2°C. After a 24-h postmortem period, carcass pH was measured on the LT muscle. The LT section between the 12th and 13th ribs was exposed, and the marbling score (MAR), rib eye area (REA), and backfat thickness (BFT) were measured. Two 2.5-cm-thick and one 0.5-cm-thick (~ 30 g) steaks were obtained from the exposed LT for Warner-Bratzler shear force and fat content analyses. Steaks were allowed to bloom for 20 minutes, and light reflectance scores for lightness (L*), redness (a*), and yellowness (b*) were obtained using a MiniScan XE colorimeter (HunterLabs, Reston, VA). Samples were also classified into different groups of the marbling score according to Gomes et al. (2021), from practically devoid to abundant, according to a photographic scale (100 = practically devoid and 900 = abundant), by qualified university personnel. The samples were either packed in polyethylene bags and immediately frozen at -20°C or vacuum-packed, aged for 7 d at 3 to 4°C, and frozen at -20°C until analyses.
The 2.5-cm-thick steaks were thawed in a refrigerator with an internal temperature set at 4°C for 24 h. Samples were cooked in an electric oven with upper and lower heating elements, set to 180°C, until the sample internal temperature reached 71°C (AMSA, 2016), as measured by digital thermometers. Subsequently, steaks were wrapped in plastic film and chilled overnight at 4°C. Eight 1.27-cm cores were removed parallel to the muscle fiber with a mechanical coring device. Cores were sheared in a Warner-Bratzler meat shear apparatus, and the shear force values were averaged to determine the Warner-Bratzler shear force (WBSF).
Data were analyzed in a randomized complete block design by applying the Mixed procedure of SAS (SAS Inst. Inc., Cary, NC), with paddock as the experimental unit for the measurements of supplement intake, body weight, and average daily gain in the postweaning period and animal as the experimental unit for all other traits. The mixed model included the fixed effect of treatment (with or without VM during the postweaning regime) and random effects of sex and genetic group. The least-square means statement was used to calculate the adjusted means for treatments. All data were checked to fit a normal distribution by the Shapiro-Wilk test, using the UNIVARIATE procedure of SAS. Significant effects were considered when P < 0.05.