Local and treatments characterization
All procedures and protocols in this experiment were approved by the Committee of Ethics on Animal Use (CEAU) of the Universidade Tecnológica Federal do Paraná (CEAU number 2016-002), located at 25°44'S and 53°04'W.
The experimental design used was completely randomized, with three treatments (supplements) and three replicates (paddocks). The treatments were: mineral salt supplementation (mineral salt), energetic-protein supplementation formulated for ingestion of 1.5 g/kg body weight (low-intake), and 4.0 g/kg body weight (medium-intake). These supplements were composed of corn meal, soybean meal, mineral salt, common salt, feed grade urea, and calcitic limestone (Table 1). The supplements were provided ad libitum once a week, we estimated the orts at 10% of voluntary intake, which was monitored weekly by weighing the offered supplements and orts. The animals had free access to water.
Table 1
Dry matter composition of supplements and ingredients of the diet of steers receiving self-fed supplements on Aruana grass pasture.
Items | Supplements | Corn meal | Soybean meal |
Salt Mineral1 | Low intake2 | Medium intake3 |
Corn meal§§ | -- | 493 | 670 | -- | -- |
Soybean meal§§ | -- | 164 | 138 | -- | -- |
Mineral salt*§§ | 1000 | 133 | 67.8 | -- | -- |
Common salt | -- | 166 | 79.1 | -- | -- |
Feed grade urea§§ | -- | 33.1 | 33.9 | -- | -- |
Calcitic limestone §§ | -- | 11.1 | 11.3 | -- | -- |
Dry matter§ | 1000 | 960 | 939 | 859 | 874 |
Ash§§ | 1000 | 336 | 170 | 13.7 | 67.1 |
Crude protein§§ | - | 243 | 284 | 99.2 | 468 |
Neutral detergent fiber§§ | - | 148 | 199 | 102 | 124 |
Non-fibrous carbohydrates§§ | - | 252 | 322 | 756 | 315 |
§g/kg of fresh material; §§g/kg of dry matter; 1mineral salt supplementation; 2energetic-protein supplementation formulated for intake of 1.5 g/kg body weight; 3energetic-protein supplementation formulated for intake of 4.0 g/kg body weight. Manufacturer’s warranty levels (g/kg): calcium, 170; phosphorus, 60; sodium, 136; manganese, 5.0; zinc, 2.52; iron, 1.2; cobalt, 0.02; copper, 0.06; iodine, 0.07; selenium, 0.02; fluorine, 0.45; and sulphur, 0.1. |
The experimental area had 4.5 ha of Panicum maximum Jacq ‘Aruana’ in a soil classified as clay Latosol, divided into nine paddocks (0.5 ha). The seeding of the Aruana grass (September 2015) occurred in the interweaving of a corn crop for silage, by no-tillage, using 15 kg/ha of seeds. The base fertilization (300 kg/ha) was applied during the planting with a formulated fertilizer 10-20-10 (N, P2O5, KCl). After harvesting the corn for ensiling, the area was left for pasture growth. The nitrogen was applied as urea (150 kg N/ha) divided into three applications (12/16/2016, 02/03/2017, and 03/14/2017).
The grazing started in mid-October and the experimental period started in 12/04/2016. The grazing cycle lasted 120 days (+ 15 days for adaptation), until 04/18/2017. We used 36 steers during the grazing cycle. From this total, 24 steers of the Aberdeen Angus breed were the testers animals, and they remained on the pasture throughout the experimental period. The animals came from the same herd and calving season, they were 15 months of age and had 364.8 ± 21.7 kg of body weight (BW). At the beginning of the experiment, all animals were submitted to endo and ectoparasites control.
The pasture was managed to maintain between 40 and 50 cm height, and it was measured weekly in 25 spots of each paddock. The pasture was managed under a continuous stocking rate, with the put-and-take adjustment method (Mott and Lucas 1952) and 15 days of intervals. Three tester animals were used in each paddock, except in one paddock of each treatment that we used two tester animals. The forage allowance was calculated as described by Sollenberger et al. (2005), according to the equation: FA = (FMmean) / (kg LW/ha), where: FA: Forage allowance; FM: forage mass, calculated as ((FMcut 1+FMcut 2)/2); and LW: live weight. The stocking rate (SR) was calculated as the sum of the tester animals’ body weight, corrected by the area size added to the weight of the grazing-height regulator animals, taking into account the number of days that the regulators remained in each paddock.
Forage mass (FM) was estimated every 31 days (Barthram 1985) in three sites (1 m2). The daily forage accumulation rate (DFAR) was measured using three grazing exclusion cages per paddock. All samples were cut at ground level. The forage samples for chemical analysis were obtained by manual grazing simulation. The pasture samples were dried in a forced air oven at 55°C for 72 h.
For chemical analysis, all samples were ground in a Wiley-type mill fitted with a 1-mm-sieve. We determined the contents of dry matter (DM), ash, organic matter (OM), crude fat (CF), and crude protein (CP) by the AOAC (1993); the neutral detergent fiber was determined by Van Soest et al. (1991) method adapted by the ANKOM 2000 methodology (ANKOM 2000 Fiber Analyzer, ANKOM Technology Corporation, Fairport, NY, USA). The non-fibrous carbohydrates (NFC) content was determined according to Sniffen et al. (1992): NFC (g/ kg) = 1000 - (CP + EE + ash + NDF).
The animal behavior assessments were conducted during daytime periods of 13 hours (5 am to 7 pm), totaling two evaluations with 60 days of interval. We observed two animals per paddock, and their rumination time, grazing time, and other activities were evaluated. The grazing time was obtained by the direct observation (Penning and Rutter 2004), recording the most frequent activity at the end of each 10 min interval, including the time spent in rumination and idleness. Other activities such as rest, supplement intake, drinking, and social behaviors were grouped.
The time spent by the animal to perform 20 bites was evaluated to calculate the bite rate (Hodgson 1982). The ingestive and rumination behaviors, and displacement pattern were measured six times a day - three times in the morning and three in the afternoon. The observed variables were: time spent to complete 10 feeding stations, number of steps between stations, number of chews per bolus, and rumination time per bolus. Displacement rate (steps/min) and daytime number of feeding stations were estimated from these data. The number of bites per station was calculated by the ratio between the number of daytime bites and feeding stations. The number of bites per day was obtained by multiplying the bite rate and grazing time. The number of stations per minute was calculated by dividing the number of daytime stations by grazing time.
The average daily gain (ADG) during the entire grazing period was evaluated by two weighings, one at the beginning and one at the end of the experimental period. The animals fasted for 14 hours before the weighings. The ADG was calculated as the difference between the initial (IBW) and final weight (FBW) divided by the number of days in grazing. At the time of the initial and final weighings, the tester steers were evaluated for subcutaneous fat thickness (SFT) between the 11th and 12th ribs by an ultrasound device (Pie Medical – Scanner 200 VET, model 51B04UM02). The subcutaneous fat thickness gain (SFTG) was calculated as the difference between the initial and final SFT divided by the number of days in grazing. The average weight gain per area (AWG) was obtained as the product of the testers’ daily gain and the evaluation days (Euclides et al., 2016), added to the gain of the regulators corrected by the time in the paddock.
We used a Latin square design with three Aberdeen Angus steers for the evaluation of the intake and diet digestibility, the animals were 15 months of age and had 296.5 ± 8 kg of body weight. They were managed together with the other animals of the experiment, being also submitted to endo and ectoparasites control at the beginning of the experimental period, and their effects on the SR were considered. The dry matter intake (DMI) was determined by: Intake (kg/day) = fecal production (kg DM/day)/1-diet DM digestibility. The forage intake was determined by the difference between the total intake and supplement intake.
Titanium dioxide (TiO2) was used as an external marker to estimate fecal production. TiO2 was supplied in the daily amount of 10 g/steer (4 pm) for 12 days. The fecal collection occurred directly from the animals' rectum, twice a day (12 pm and 4 pm) as proposed by Penning and Rutter (2004). In each evaluation period (19 days) the animals had seven days for adaptation to the supplements. After each evaluation period, a composite feces sample per animal was obtained and the TiO2 concentration was determined by uv-vis spectrophotometry (Myers et al., 2004). Fecal production (FP, kg of DM/day) was determined as: FP = intake TiO2/fecal TiO2. The apparent digestibility (AD, g/kg of DM) was determined as: AD = (nutrient intake - nutrient excreted)/nutrient intake.
A completely randomized design was used for the evaluation of animal performance, ingestive behavior, and forage characteristics. For the evaluation of intake and forage digestibility, we used a 3 x 3 double Latin square (3 treatments and 3 periods). The data were analyzed using a mixed model methodology (Littell et al., 2006) incorporating the fixed effect (treatment) and random effects (for the Latin square, we considered animal, period, and the treatment*period interaction as random effects) into the model. We used the Tukey-Kramer test for comparison between means (α = 0.05). The model used for variables that followed the completely randomized design was represented by:
Yijk = µ + Ti + β1Xij + eijk,
In which Yijk is the dependent variable, µ is a constant, Ti is the effect of diets, β1Xij = is the effect of the covariates (IBW and SFT), and eijk is the residual experimental error.
For the Latin square design, the model was represented by:
Yijk = µ + Ti + Pj + Ak + TPij + eijk,
In which Yijk is the dependent variable, µ is a constant, Ti is the effect of diets, Pj is the effect of period, Ak is the animal effect, TPij is the effect of interaction between treatment and period, eijk is the residual experimental error.