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In Uruguay, during the summer, fattening cattle grazing natural fields or planted grass, or both, register a marked decrease in their productivity with respect to what they achieve in spring (Simeone 2000). This could be associated with the high temperature and humidity index (THI) and the low production and quality of grasses in summer.
The supplementation on seasonal grasses during summer (Montossi et al. 2017), restriction of access time to grass, associated with confinement with artificial shade and water, in cattle that graze permanent grasses (Beretta et al. 2013) and seasonal grasses (Rovira 2012), as well as free access to natural shade in forest areas by cattle grazing natural fields (Simeone et al. 2010), have been strategies used interchangeably in Uruguay to improve productivity during summer and try to reduce the adverse effects of heat stress. However, the productive responses have been very mixed.
Forage sorghum improves the forage base due to its adaptability to the environment and high volumes of forage (Moyano et al. 2021 y Zavala-Borrego et al. 2021). However, the low level of protein and high fiber content (Ríos Moyano et al.2021) could limit the productivity of developing cattle. Supplementation with a source of energy and protein could reduce these grass nutritional limitations.
Dried distillery grains with solubles (DDGS) are non-starchy protein-energy supplements (30.9 % CP, 13.4 ME MJ/kg) (BCNRM 2016 and Pancini et al.2021), which contain three times the concentration of nutrients of the grain that gave rise to it (Trujillo et al. 2017 and Iram et al. 2020). The DDGS have a high content of ether extract (10.7 %) (BCNRM 2016), which is why they are considered a food with high energy density and low heat increase (De Boever et al. 2014). This resource, associated with day confinement with shade and water, could help reduce the risk of heat stress and improve productivity and efficiency in the use of food by cattle grazing forage sorghum. However, there are few studies evaluating this by-product under pastoral conditions and in animals that graze forage sorghum with day confinement, shade and water, during the summer period.
The objective of this study was to evaluate the effect of DDGS supplementation and day confinement with artificial shade on the productive performance of Hereford steers grazing forage sorghum (Sorghum spp.).
Materials and Methods
The study was carried out in the West Coast of Uruguay (Lat: 32.5º S, Long: 58º W), from January 16, 2019 to March 6, 2019 (49 d) in 6 ha of forage sorghum (hybrid ADV 2800), sown on December 1, 2018, at a rate of 25 kg/ha with 60 kg/ha of formula 18-46-0 and fertilized with urea after the first grazing (100 kg/ha).
Animals, treatments and experimental design. A total of forty-eight Hereford steers (267 ± 29.5 kg) were randomly assigned to four treatments in a 2x2 factorial arrangement. The main factors were the management of supplementation with DDGS (without supplement, vs with supplement; 1 kg of DM/100 kg of LW) and grazing management (free grazing, vs day confinement; 10: 00 a.m. to 4:00 p.m.). The treatments consisted of free grazing without supplement, free grazing with supplement, day confinement without supplement and day confinement with supplement.
Experimental management. As a supplement, mixed DDGS (40 % corn, 60 % wheat) were used, from the local alcohol production factory in Uruguay (ALUR, Paysandú). They were obtained in a single batch and stored in silo bags for use during the experimental period. The supplementation was carried out at 7:00 a.m., at a rate of 1 kg DM/100 kg LW (1 % LW), offered in group feeders per repetition in the plot. The quantity supplied was fitted every 14 days, according to the DM content and the last LW.
Between 10:00 a.m. and 4:00 p.m., the animals with day confinement were removed from the grass and moved to an area adjacent to the paddock area, divided into four pens delimited by electrical fencing (1 per experimental unit), provided with water and artificial shade (80 % interception mesh, 2.75 m height, 3.5 m2/ animal, East-West orientation).
It was grazed in weekly strips with an 8 kg DM/100 kg LW animal grazing allocation. The grazing area was delimited by electric fencing. It was weekly fitted, by varying the offered grass area according to the biomass of DM available and the last LW, without considering the projection of mean daily gain (MDG) or the growth rate of sorghum. The strip change was always carried out in the morning, after supplementation.
Sampling, measurements in the grass and supplement. The LW was recorded every 14 days, with a previous fast of 12-16 h. The biomass of available and remaining grass was weekly determined by means of the double sampling technique (Haydock and Shaw 1975) with marking of a three-point scale and two repetitions. The grass was evaluated at 100 random points per plot. The scale samples were weekly collected, by cutting the biomass at soil level in a 0.3 x 0.3 m square. They were subsequently placed in a forced air oven (60 ºC until reaching constant weight) for the determination of the dry weight and its conservation for later analysis. The height of the available and remaining grass was measured with a ruler at five points on the diagonal of each square, by recording the point of contact with the highest unextended living leaf.
Supplement intake was daily recorded as the difference between the quantity offered and the quantity rejected. The samples of the offered and rejected supplement were weekly collected and dried at 60 ºC. They were kept for later chemical analysis.
The records of day performance were taken from four steers per plot, randomly chosen through direct observation, by recording the activity carried out every 20 min during daylight hours (7:00 a.m. to 7:00 p.m.): grazing (effective plus search), rumination, rest, access to feeders and water intake. The probability of occurrence of each activity was estimated (Forbes 1988). The bite rate was determined as the number of bites in one minute (Gregorini et al. 2007 and Gregorini et al. 2009) at two moments: first grazing session in the morning (7:00 a.m) and first grazing session at the exit from the confinement (4:00 p.m.).
Respiratory rate was measured as the number of flank movements, recorded in one minute (resp/min) during three consecutive days per week, at two times of the day (7:00 a.m. and 4:00 p.m.) and in the same animals studied for the observation of grazing performance.
Temperature and humidity index. The records of the historical series 2002-2019 and the daily records of air temperature (°C), relative humidity (%), wind speed (m/s) and solar radiation (W/m2) during the experimental period were taken from the automatic meteorological station (Model Vantage Pro 2, Davis Instruments, CA, 2007), belonging to Mario A Cassinoni Experimental Station.
The THI was calculated, according to Mader et al. (2006):
Where: T, air temperature, Rh; relative humidity
The risk of heat stress was categorized as normal (THI ≤ 74), alert (THI ˃ 74 ≤ 78), danger (THI ˃ 78 ≤ 84) and emergency (THI> 84), according to the climatic safety indicator for beef cattle (Livestock Weather Safety Index) (Eigenberg et al. 2005).
THI fits were made by wind speed (WS) and solar radiation (SR):
Vernon spheres(BG) temperature fits were also made (Mader et al. 2006):
For the latter, four Vernon spheres were placed: two in the shade and two in the sun, at a height of 1.5 m (Berbigier 1988). The temperature was recorded on the spheres every 30 min. using Kooltrak sensors (iButtons-TMEX model DS1921, Dallas Semiconductors, Dallas, TX).
The DM intake of grass was estimated for each experimental unit using the Beef Cattle Nutrient Requirement Model (BCNRM 2016). As input for the model, the information collected during the experimental period was used: animal LW (start and end), grazing days, available biomass and used area, intake supplement and meteorological information. As food information, what was referred by the food library of the model was used. The contribution of ash, protein, ether extract and NDF of forage sorghum and DDGS was corrected with analytical information. The intake was calculated for each grazing plot, by executing the calculation function of the model (empirical solution) and fitting by successive approximations the grass intake necessary to achieve the respective weight gain. The contribution of ME in each diet was obtained from the model.
Grass use and supplement conversion efficiency. The forage use (FU) was calculated from the available biomass (AB) and remaining biomass (RB):
The conversion efficiency (CE) was estimated as the amount of intake supplement (DMI) per unit of weight gain (WG) (Beretta et al. 2006):
Chemical analysis. The supplement samples and the dry samples of the scales corresponding to the determination of the offered biomass were milled to 2 mm in diameter in a WILEY mill and combined into a single sample, composed of food for the experimental period, where each sampling date contributed equal weight.
The composite samples of available grass by sampling date were made up by weighting the contribution of each point on the scale, according to the frequency of appearance in the grass.
The content of dry matter (DM, method 934.01), organic matter (OM, method 942.05), crude protein (CP, N × 6.25; method 984.13) and ether extract (EE, method 920.39) were determined according to AOAC (1990) and AOAC (2007).
To calculate the content of insoluble N in acid detergent and NDF, α-amylase was used and it was corrected for contamination with ash (aNDFmo) and ADF, according to Goering and van Soest (1970).
Statistical analysis. Linear models of the SAS statistical package, version 9.4 (SAS Institute, Cary, NC 2012) were used.
General model:
Yijk - response variable
μ- general mean
Ei grazing management (i = confinement, free grazing)
Sj supplementation management (j= control, supplemented)
Eij- experimental error
For the determination of the LW, DMG and conversion efficiency of the supplement, the GLM model was used. The DM intake (grass, supplement and total), bite rate and respiratory rate were analyzed as repeated measures in time with the MIXED model.
For the bite rate and respiratory rate, the sampling time was considered as a fixed effect. The grazing behavior was analyzed as repeated measures in time, assuming a binomial distribution using the GLIMMIX procedure.
To determine the predicted temperature value of the Vernom spheres (BG) in sun and shade, the statistical program ARIMA (Auto Regressive Integrated Moving Average) was used. Hourly data were used and the ARIMA seasonal model was fitted until the predicted value and standard error were obtained at each hour and means were compared using the bilateral t test.
Results and Discussion
Table 1 shows the average records of temperature, relative humidity, wind speed and solar radiation, taken from the meteorological station and Vernon spheres, as well as the average of the biometeorological indices (THI and THI fitted) for the historical series (2002-2018) and experimental period (2019).
Table 1 Climatological record and biometeorological indices corresponding to the experimental period and the historical series 2002-2018
| Year 2019 (January 16 to March 6) | Year 2002-2018 (January 16 to March) | |||||||
|---|---|---|---|---|---|---|---|---|
| Mean | SD | Maximum | Minimum | Mean | SD | Maximum | Minimum | |
| Temperature, °C | 23.3 | 3.4 | 28.9 | 16.7 | 24.0 | 2.8 | 33.1 | 15.2 |
| Relative humidity, % | 76.5 | 10.2 | 94.8 | 60.0 | 69.2 | 13.5 | 100.1 | 24.6 |
| Winds speed, m/s | 3.3 | 3.4 | 16.4 | 0.0 | 2.7 | 1.8 | 13.9 | 0.0 |
| Radiation, W/m2 | 251.6 | 80.3 | 354.7 | 52.8 | 267.8 | 95.3 | 307.5 | 0.0 |
| THI | 71.5 | 5.2 | 80.8 | 61.0 | 72.0 | 3.9 | 83.7 | 59.1 |
| THI, fitted | 68.4 | 13.5 | 84.3 | 19.6 | 70.6 | 7.2 | 86.1 | 31.0 |
SD: standard deviation
The values of temperature, humidity, and THI index were located within ± 1 deviation of the historical average value, and the year was located in an average year. The experimental period showed maximum temperature and humidity lower than the historical record and higher wind speed and solar radiation, which resulted in lower THI and THIfitted maximum. The average values of temperature were in the limits of the thermoneutral zone (0 to 25 ºC), reported for taurid-type animals. The relative humidity was above the value that is considered acceptable (70 %), when the temperature is in the thermoneutral zone (Rondán et al. 2019).
The experimental period showed a lower percentage of days with normal THI (62.0 vs 67.2 %, THI ≤ 74) compared to the historical series. This involved a higher percentage of days with THI in the alert category (34.0 vs 30.4 %, THI > 74 ≤ 78) and danger (38.0 vs 2.8 %; THI > 78 ≤ 84), according to the climatic safety indicator for cattle (Eigenberg et al. 2005).
When analyzing the hourly distribution of the THI, in approximately 52 % of hours, the THI was between the values considered normal (THI ≤ 74), as 54 % corresponded to the night phase (21:00 to 7:00 h) and 46 % to the day phase (7:00 to 20:00 h).
The 95.3 % of the hours in which the THI indicator was in alert values (THI > 74 ≤ 78) corresponded to the day phase, while the hourly distribution in emergency values (THI> 84) occurred between 11:00 and 18:00 h, which coincides with the time when the cattle remained in day confinement (10:00 - 16:00 h) and the two hours after their leave.
The BGTHI was lower in the shade than in the sun (73.2 vs 76.9 ± 1.1, P<0.05). The greatest differences were between 12:00 and 20:00h. In the shade as in the sun, the BGTHI was higher than 74 from 9:00 a.m. to 8:00 p.m. Reyes et al. (2018) stated that the access to shade reduces the impact of the heat load received by radiation. In this study, free-grazing animals received a higher incidence of solar radiation, thus increasing their head load throughout the day. Meanwhile, the treatment with day confinement carried out the last grazing section when the temperature was still high.
The respiratory rate (average daily value) of the animals with supplement did not depend on the grazing management carried out (P = 0.696). However, in the animals with supplement increased 24 % with respect to the animals without supplement (51.76 vs 67.90±1.7 resp/min; P = 0.003). While the day confinement improved the respiratory rate 30 % with respect to free grazing (66.20 vs 53.46 ± 1.7 resp/ min; P = 0.006). The reduction in the respiratory rate due to the confinement was higher in steers without supplement (78 vs 52 resp/min) with respect to those with supplementation (98 vs 78 resp/min).
Even though DDGS has a high content of ether extract, which contributes to the low heat increase (De Boever et al. 2014 and BCNRM 2016), the intake of energy foods and solar radiation continue to be the main causes of heat production (Brosh et al. 1998 and Rondán et al. 2019). Therefore, the activation of heat dissipation mechanisms by animals would be necessary, as it is the respiratory frequency (Amamou et.al 2019).
Table 2 and 3 show the effect of grazing management and the supplementation for the variables describing the grass condition and its use.
Table 2 Effect of grazing management and supplementation in the biomass of available grass and entrance height.
| Indicator | Available biomass, kg/ha | Entrance height, cm |
|---|---|---|
| Animals in confinement, without supplement | 8758.5ab | 104.5ab |
| Animals in confinement, with supplement | 9709.2a | 117.7a |
| Animals in free grazing, without supplement | 8696.6ab | 107ab |
| Animals in free grazing, with supplement | 8173.5b | 99.6b |
| SE ± | 298.6 | 3.7 |
| Significance | 0.0296 | 0.0143 |
Different letters in rows show statistical difference to P < 0.05)
Table 3 Effect of grass management and the supplementation on the remaining biomass and the grass use
| Rejected biomass, kg/ha | Exit height, cm | Grass use, % | |
|---|---|---|---|
| Animals in confinement | 3018.25 | 33.88 | 66.75 |
| Animals in free grazing | 3624.00 | 44.44 | 53.88 |
| SE ± | 182.10 | 1.90 | 3.50 |
| Significance | 0.0783 | 0.0012 | 0.0600 |
| Animals without supplement | 2747.81 | 33.56 | 66.19 |
| Animals with supplement | 3894.44 | 44.75 | 54.44 |
| SE ± | 182.10 | 1.90 | 3.50 |
| Significance | 0.0112 | 0.0007 | 0.0765 |
The biomass and average height of the grass at the entrance to the grazing plot was 8834.5 ± 1383.8 kg/ha and 107.3 ± 18.4 cm in height, with the available grass being higher in the treatments with confinement with respect to those of free grazing, a response that depended on supplementation (P<0.05)
The rejected biomass and its height were lower in the supplemented treatments, regardless of grazing management. There were not differences between treatments with the use of grass (P> 0.05) (table 3).
The grass accumulation rate was 105.4 ± 40.3 kg DM/d, which resulted in an effective grass allocation of 8.1 % LW. According to (Berreta et al. 2006), grazing with a grass allocation higher than 6 % does not restrict grass intake. In this study it seems that the available grass was not a limitation for intake, but it was for the grass quality (table 4), mainly due to its low protein content (8.9 % CP). Fernández et al. (2011) reported 16.52 % of crude protein for the first year of evaluation and 12.91 % for the second year in brown veined sorghum (BMR).
Table 4 Chemical composition of DDGS, forage sorghum and resulting diets in each treatment
| Chemical composition, % on dry basis | Available grass | DDGS | Diet without supplement | Diet with supplement | Diet with day confinement | Diet free grazing |
|---|---|---|---|---|---|---|
| DM | 18.9 | 94.1 | 18.9 | 50.1 | 35.0 | 35.0 |
| OM, ashes | 13.0 | 4.7 | 13.0 | 9.6 | 11.1 | 11.1 |
| CP | 8.9 | 36.0 | 8.9 | 20.1 | 14.7 | 14.7 |
| NDF | 62.6 | 62.7 | 62.2 | 62.6 | 62.2 | 62.2 |
| Ether extract | 2.2* | 6.6 | 2.2 | 4.0 | 3.1 | 3.1 |
| NDT* | 62.1 | 89.0 | 62.1 | 73.3 | 67.5 | 67.5 |
| ME*, MJ/kg) | 9.41 | 13.43 | 9.41 | 11.09 | 10.21 | 10.21 |
The diet was estimated from the proportion of the grazed biomass and supplement intake in the total diet.
* Values obtained from BCNRM (2016) table
In the analyzed variables, the response to DDGS supplementation did not depend on grazing management aimed at reducing heat stress in steers grazing forage sorghum (P> 0.05) (table 5).
The supplementation with DDGS at 1% of the LW increased the DMG 2.9 times with respect to the control. Even when grass intake decreased, total DM intake increased (0.9 kg/animal/d) and the daily contribution of metabolizable energy (ME 36 %) and metabolizable protein (MP 168 %) increased in relation to the control treatment.
Table 5 Effect of supplementation man agement and grazing management on dry matter intake, weight gain and supplement conversion efficiency
| Confinement | Free grazing | SE | Significance | Without suplementation | With suplementation | SE | Significance | |
|---|---|---|---|---|---|---|---|---|
| DM intake of the grass, kg/a/d | 5.06 | 5.07 | 0.16 | 0.97 | 6.05 | 4.09 | 0.16 | 0.001 |
| DM intake of the supplement, kg/a/d | 1.40 | 1.40 | 1.44 | 0.91 | - | 2.90 | 0.01 | <0.001 |
| DM intake of the total, kg/a/d | 6.50 | 6.51 | 0.17 | 0.97 | 6.05 | 6.99 | 0.17 | 0.01 |
| ME intake, MJ/d | 16.01 | 16.02 | 0.39 | 0.97 | 13.6 | 18.4 | 0.39 | 0.001 |
| Metabolizable protein intake , g/d | 639.0 | 639.4 | 11.5 | 0.98 | 347.5 | 931.0 | 11.5 | <0.0001 |
| LW start, kg | 261.7 | 265.0 | 1.84 | 0.07 | 263.7 | 263.0 | 1.84 | 0.59 |
| LW end, kg | 311.8 | 308.2 | 6.76 | 0.36 | 287.2 | 332.8 | 5.02 | <0.0001 |
| DMG, kg/a | 0.92 | 0.93 | 0.05 | 0.74 | 0.46 | 1.39 | 0.05 | <0.0001 |
| Conversion efficiency of the supplement | - | - | - | - | - | 3.1 | 0.13 | 0.53 |
The steers without supplement registered intake equivalent to 2.5 % of the LW. The estimation of the potential intake for Hereford steers according to CSIRO (2007), depending on their age and weight, would be in the order of 11 kg DM/d. However, the real predicted intake, when considering the availability and quality of the grass base used, would be limited to 37 %, due to the restriction imposed by the grass quality (0.63 potential intake value) and, to a lesser extent, due to the harvesting capacity associated with availability (estimated at 0.9 of potential intake), which yielded a value of 6.9 kg, similar to that estimated for steers without supplementation.
The substitution of grass for the supplement would have been in the order of 0.68 ± 0.09, which shows the substitution-addition effect of the supplement. This substitution rate value would be lower than that reported by CSIRO (2007), according to the quantity and quality of the grass base and the supplement, which would be 0.81.
In steers- with supplement, a higher DM intake, associated with a higher concentration of protein in the diet with respect to the control (20.1 vs. 8.9), allowed to lift the restriction in the contribution of the diagnosed MP for the control, also increasing the contribution of ME (2.65 vs. 2.25) and with it, the daily gain. The nutritional evaluation of the BCNRM (2016) diet shows that, in the case of animals supplemented with DDGS, the maximum gain achieved was limited by the contribution of ME. Meanwhile, the contribution of MP exceeded by 60.4 % the requirements for the observed DMG.
The response to supplementation was 0.928 kg/d with supplement conversion efficiency of 3.1: 1, which was not affected by grazing management (table 3). This value represents an improvement with respect to that reported for this category on permanent grass, supplemented with corn grain at 1 % of LW (6: 1, 9: 1 and 45: 1) (Simeone and Beretta 2004 and Simeone and Beretta 2008) or on seasonal grasses (sorghum and sudan) and supplemented at 0.5 % of LW with soy expeller (conversion efficiency of 13: 1) or sunflower expeller (33: 1) (Montossi et al. 2017).
Low values of food conversion efficiency are explained by the high response in the LW gain in relation to the control without supplemented. This would be, to a large extent, the result of the increase in the intake of DM (15.5 %) and ME (36.6 %) estimated for steers. High LW gains, such as those achieved by supplementing, although they may have a higher energy cost per kilogram of LW gained, by increasing the proportion of fat in the gain in relation to the control (NRC 2000), they also contribute to dilute the relative weight of the maintenance expense, improving all growth efficiency (CSIRO 2007 and Larson et al. 2019).
The grazing management (table 6) did not affect the productive variables (LW, DMG, and CE) or DM intake (P> 0.05) (table 5), despite that, the environmental conditions would have been predisposing to heat stress. The effect of shade on weight gain has varied in feedlot animals (Mader et al. 1999 and Reyes et al. 2018), as well as in grazing animals. In Uruguay , for cattle that graze in natural fields with free access to shade, Simeone et al. (2010) reported a response around 0.250 kg/d. In confinement meadows with shade and water, Berreta et al. (2013) found improvement of 14 %. However, Rovira (2012) did not found significant effect of shade availability on beef cattle grazing Sudan grass; neither Saravia (2009) in dairy cows (Holando and Jersey) that graze sorghum.
Table 6 Effect of grazing management and supplementation on grazing, rumination, rest activity and bite rate
| Activity | Day confinement | Free grazing | Significance | Whithout supplement | With supplement | Significance |
|---|---|---|---|---|---|---|
| Grazing | 38.0 ± 0.01 | 42.9 ± 0.01 | 0.0911 | 46.9 ± 0.01 | 34.3 ± 0.01 | 0.0043 |
| Rumination | 23.1 ± 0.01 | 12.5 ± 0.008 | 0.0012 | 22.1 ± 0.01 | 13.1 ± 0.008 | 0.0023 |
| Rest | 31.9 ± 0.01 | 35.6 ± 0.01 | 0.0671 | 26.2 ± 0.009 | 42.0 ± 0.01 | 0.0004 |
| Bite rate | 12.7 ± 0.37 | 12.5 ± 0.37 | 0.7294 | 13.2 ± 0.37 | 12.0 ± 0.37 | 0.0261 |
Taking into account that the high temperatures in Uruguay start from December (Cruz and Saravia 2008 and Rovira 2012), from the beginning of the season (summer) until the beginning of the experimental period (12/21/2018 - 1/15/2019), the average temperature recorded was 23.7 ± 4.1 °C, with 80.3 ± 12.4 % of humidity, estimating an average THI of 72.5. According to Bianca (1959), cattle begin to acclimatize in a period of two to seven weeks of exposure to heat, when temperatures vary from 28 °C to 45 °C. Therefore, it is possible that acclimatization has contributed to attenuate the stress of grazing cattle and reduce the productive response with regard to grazing management and access to shade.
The grazing performance, evaluated through the probability of finding animals that graze or are ruminating or resting during the observation period, was affected by the supplementation (P <0.05). The grazing and rumination activities were higher in animals without supplement with respect to those supplemented (P <0.05), they also had less resting time (P <0.05), without affecting the average bite rate (P >0.05).
It is possible that the animals with supplement have decreased energy expenditure, due to lower grazing and rumination activity, with no differences in the bite rate with respect to the control. Di Marco and Aello (2001) reported an increase in energy expenditure associated with the grass harvest (kJ/hour/LW0.75), which, depending on the grass conditions, could vary between 16 and 52 %.
Grazing management affected only rumination (P <0.05). It was observed that animals in confinement remained more time ruminating than those that were in free grazing, respectively (table 6). The bite rate was not affected by grazing management (P> 0.05) or by the time in which the measurement was made (7:00 a.m; 4:00 p.m).
The distribution of animal behavior activities varied throughout the day. In the first three hours of the morning, the animals without supplement increased grazing activity with respect to those supplemented (0.7 ± 0.04 vs 0.5 ± 0.04; P = 0.02), which remained longer at rest (0.1 ± 0.02 vs 0.3 ± 0.03; P = 0.01) with no differences in rumination (0.2 ± 0.03 vs 0.1 ± 0.02; P = 0.08). Then, in the late afternoon, the animals without supplement continued with higher grazing activity with respect to the supplemented animals (0.9 ± 0.02 vs 0.8 ± 0.03; P = 0.01).
The grazing management had no effect on grazing, rumination or rest activity in the first morning session (P >0.05). However, at the exit of the confinement, the steers in confinement compensated the shorter access time to the grass with higher grazing activity compared to the steers in free grazing (0.9 ± 0.02 vs 0.6 ± 0.02; P < 0.0001), without verify differences in the remaining activities (P> 0.05). The increased time spent grazing is the main mechanism by which cattle respond to restrictions on access time to grass during the next time available for grazing (Gregorini et al. 2009 and Mattiauda et al. 2013). It occurs mainly in the early morning and during the afternoon around to get dark, being longer and more intense at dark (Gregorini et al. 2007).
The day confinement of the animals between 10:00 a.m and 4:00 p.m did not affect the daily grass intake. However, it modified the grazing pattern during the time of access to the grass with respect to what was observed in animals in free grazing. These results agree with those reported by Gregorini et al. (2009) and Beretta et al. (2013), who did not report differences in intake, but did report higher grazing activity in animals with grazing restriction.
Conclusions
Hereford steers, grazing forage sorghum with an 8 % LW supply, show limited growth due to the daily contribution of metabolizable protein. Supplementation with DDGS at 1 % LW improves productive performance with an increase of 2.9 times the DMG and efficiency of 3.1 kg of supplement for each kg of LW. This response is independent of grazing management and access to shade.
The confinement with shade and water, between 10 and 16 h, improves the heat comfort of steers that graze forage sorghum. This management does not affect the daily grass intake and an increase in grazing activity is observed at the exit of confinement, which compensates for the shorter access time to the grass with respect to what is recorded in animals in free grazing, without access to shadow.
