Diurnal ingestive behaviour of steers grazing Alexander grass with various levels of nitrogen and feed supplements

Copyright resides with the authors in terms of the Creative Commons Attribution 4.0 South African License. See: http://creativecommons.org/licenses/by/4.0/za Condition of use: The user may copy, distribute, transmit and adapt the work, but must recognize the authors and the South African Journal of Animal Science ______________________________________________________________________________________ Abstract Given the increasing availability of new cultivars with high yield potential, the use of annual tropical forages to improve cattle production systems is increasing and therefore warrants more research. The objective of this study was to quantify the influence of feed supplementation and nitrogen fertilization on the diurnal ingestive behaviour of crossbred steers (zebu x taurine), maintained on a pasture of Alexander grass (Urochloa plantaginea). The treatments included the application of nitrogen fertilizer at 100 kg/ha; at 100 kg/ha + supplemented feed of wheat bran (0.5% of bodyweight); and at 200 kg/ha. The study used a completely randomized design with three replications. The paddock size was 0.7 ha. Data were analysed by fitting mixed models. The times spent resting, ruminating and consuming water were not different among treatments. However, time spent grazing significantly differed. On average, steers given supplemented feed spent less time grazing (297 min/day) than steers without the supplemented feed (345 min/day). Steers in the pasture with supplementation showed a significantly greater number of daytime bites (2029 bites) than steers in the 200 kg nitrogen treatment (1715 bites). Supplementation reduced grazing time without altering other behaviour variables. The number of daily bites was lower on the pasture with the higher nitrogen level. ______________________________________________________________________________________


Introduction
The increased availability of new cultivars with high forage-mass production potential has led to the widely promoted use of annual tropical grasses.Benefits include reduction of production costs and of length of production cycle in growing and finishing cattle.Millet (Pennisetum americanum) and Alexander grass (Urochloa plantaginea) present satisfactory results in the finishing of beef cattle in Mexico when used as forage and are no longer considered invasive plants (Sánchez-Ken, 2011).These authors reclassified Alexander grass in the genus Urochloa.
Among the factors that influence animal performance, ingestive behaviour has been used as an important tool for understanding variations in the productivity of animals.Behavioural changes are due to environmental, genetic and dietary factors and are dynamic and sensitive to variations in processes in the physical environment and in social stimuli (Snell-Rood, 2013).
Animals' grazing behaviour is influenced by pasture characteristics such as structure, forage, leaf to stem ratio and bromatological characteristics.Variations in the food structure can have positive or negative effects on food consumption by influencing the size of the bite and bite rate and, consequently, the time spent grazing (Glienke et al., 2016).Grazing activity typically ranges from 4 to 12 hours per day on lowenergy diets (Burger et al., 2000) and resting time, without rumination, lasts approximately 10 hours a day.
High-roughage diets tend to increase rumination, resulting in reduced particle size and greater surface area of particles (Campos et al., 2006).This allows for greater exposure to the rumen bacteria involved in digestion and eventually a greater total digestibility of the feedstuff.Thus, increased fibre intake amplifies rumination time (Weckerly, 2013), whereas food consumption without concentrated supplementation tends to reduce it (Van Soest, 1994).Consequently, increasing the level of concentrate in the diet changes the food intake.However, the level of supplemental feed consumption needed to maintain energy is not known.Furthermore, the quality of grass in fertilized pastures is higher than that in non-fertilized pastures, thus offering increased nutrition to meet the demands of the animals and contributing to reduced food intake (Burger et al., 2000).
Evaluating behaviour is an important tool in nutritional rating because it provides an understanding of the relationships that determine animal performance and suggests strategies for improving productivity.Thus, the aim of the study was to evaluate the influence of energy supplementation and nitrogen fertilization (N) on the ingestive behaviour of crossbred steers (zebu x taurine), kept on a pasture of Alexander grass.

Materials and Methods
The study was conducted at the Teaching and Research Unit of Beef Cattle, Federal Technological University of Paraná (UTFPR), Campus Dois Vizinhos, from January to March 2013.The experimental area is located at 25°42′52″ S and 53º03′94″ W, and 519 m above sea level.The soil of the region is characterized as typic alfisol distroferric (Brazilian Agricultural Research Corporation, 2006), with an average slope of 5%.The climate in the area is classified as mesothermal humid subtropical, according to the Köppen classification.The average temperatures during the days of the behavioural evaluation, recorded in the meteorological station of Dois Vizinhos-Paraná, Brazil, varied between 20 ºC and 25 °C.The minimum and maximum temperatures of the experimental period were 14 ºC and 32.8 ºC, respectively.The relative humidity of the air ranged from 58% to 93.6%.The historical rainfall of the period (January to March) for the region is 526 mm (Possenti et al., 2007).However, during the experiment the rainfall was 796 mm, with the highest intensity in March (358 mm).
After a period of grazing on the oat/ryegrass/vetch pasture in the area, and a rest period in October and November 2012, fertilizer and pasture residue were incorporated into the soil by harrowing.The Alexander grass (Brachiaria plantaginea, synonym Urochloa plantaginea) was established by natural reseeding from the previous year's seed bank.
The experimental area consisted of nine 0.7 ha paddocks, totalizing 6.3 ha.There were three treatments in a completely randomized design experiment with three replications.The treatments were N100 (low N; 100 kg N/ha), N100S (low N plus wheat bran supplemental feed; 0.5 kg/100 kg of bodyweight), and N200 (high N; 200 kg/N/ha).On 5 October 2012, 250 kg/ha of 5-20-10 (N-P-K) were applied to all pastures.Urea (45% N) to meet the N treatment application level was applied in four split applications at the start of each trial period (every 21 days).
Twenty-seven tester animals were used, three in each repetition, with a variable number of regulators, through the put-and-take technique (Mott & Lucas, 1952), with an herbage allowance of 10 kg dry matter (DM) of forage for every 100 kg BW for all treatments.There were three 10-month-old non-castrated crossbred Nellore (zebu) x Braford (taurine), weighing an average of 276 ± 41 kg, in each paddock.The animals were used in accordance with the Animal Utilization Protocol approved by the UTFPR, based on guidelines set by Olfert et al. (1993) in the Canadian Council on Animal Care.The standard housing procedure on the pasture was applied, as in standard meat production, so the bioethical commission agreement was not needed.
Animals were placed on the experimental paddocks on 13 December 2012.After a 23-day adaptation period, data were collected for four 21-day periods.The forage mass was determined at the beginning of both the adaptation period and the first period, and at the end of each period, at 21-day intervals, using the double-sampling technique developed by Wilm et al. (1944).A subsample of the double sampling was used to determine DM.The determination of the accumulation rate of DM was performed according to the methodology described by Klingman et al. (1943).Herbage had a mean mass of 3007 kg of DM/ha, the daily herbage allowance was 9.87 kg DM/100 kg of body weight (BW) and the leaf : stem ratio was 0.46, without significant differences between the treatments.Further details of the results of treatments on grazing and animal performance are presented in Venturini et al. (2017).
Chemical composition analysis (Table 1) was performed at the Laboratory of Bromatology UTFPR-DV, based on their botanical separation.Samples were collected to determine their total DM, ash, and crude protein (CP) by the micro Kjeldahl method (AOAC, 1990).Neutral detergent fibre (NDF) and acid detergent fibre (ADF) were calculated according to the method in Van Soest et al. (1991) and in vitro digestibility of organic matter was calculated according to Tilley & Terry (1963), as modified by Goering & Van Soest (1970).
Two evaluations per trial were performed, and each evaluation included eight 12-hour (07:00 until 19:00) direct behavioural assessments of the animals.In 2013, observations of grazing time, the number of cud and chewing, and the number of bites and feeding stations were made on 17 and 23 January (first period), 7 and 13 February (second period), 28 February and 6 March (third period), and 21 and 25 March (fourth period).The dates were chosen at random as long as typical climatic conditions (excess rain or wind) did not occur.During the observation, every 10 min.the animal was classified into the following activities: grazing, ruminating, taking in water, taking in supplement and idling.The activities of each animal were recorded in an exclusive and unique way by evaluators with experience in these evaluations.Each evaluator observed three paddocks.The animal testers had been previously identified with numbering in the thoracic region, according to the methodology described by (Thurow et al., 2009).Grazing time was recorded as the time spent selecting and seizing forage, including the time spent moving around for diet selection.The rumination time was identified as the end of grazing and the onset of mastication and rumination.The period in which the animal came to the water cooler or to the troughs with supplement (treatment N100S) was classified as consumption of water and/or supplement.An idle period was when the animal remained at rest (Forbes, 1988).The activities were expressed as total time in min/day.
The time spent for the animal to perform 20 bites was evaluated to calculate the rate of bites minute-1 (Hodgson, 1982).The intake behaviour was measured six times per day: three times each in the morning and afternoon.Observed variables were time spent to complete 10 food stations and the number of footsteps between stations.A feeding station was regarded as the space corresponding to grazing without moving the front legs (Laca et al., 1992).A footstep was defined as every movement of the front legs.Displacement rate (footsteps minute-1) and daytime number of feeding stations were estimated from these data.The number of bites per station was calculated by dividing the number of daytime bites by the feeding station's daytime number.The number of stations per minute was calculated by dividing the number of daytime stations by grazing time.
A completely randomized design was employed with three treatments (N100, N100S and N200) and three replications (paddocks).Data were tested for normality using the Shapiro-Wilk test, and compared by the PROC MIXED procedure, with fixed effects for the treatments and the random residual error.Analysis was performed with the MIXED procedure of SAS 8.2 (SAS Institute Inc., Cary, NC, USA, 2000).The data for day grazing time from the observation days (Day 1 and Day 2) were included in the model as a fixed effect, significance was declared at P ≤0.05.

Results
The steers spent a mean of 5 hours and 29 min grazing, 4 hours and 34 min in idleness, 1 hour and 49 min ruminating, 52 min chewing the bolus, 1 hours and 27 min taking 20 bites and 13 min ingesting water (Table 2).Supplemented animals spent an average of 23 min at the trough.Grazing activity was lower in the supplemented animals than for cattle in the other treatments.This difference was caused by the amount of time the animals spent feeding on the concentrate.Therefore, the mass and forage allowance did not vary among treatments.Idle time did not differ among treatments (P >0.05).Similarly, offering a low amount of supplement did not negatively influence idle time.The number of chews per bolus and time for daylight rumination, idleness, chewing and taking 20 bites were similar (P >0.05) among treatments (Table 3).Times for chewing and for taking 20 bites were not negatively influenced by the treatments because forage availability and supply were similar in the homogenous pastures.Bites per station, bites per minute, stations per minute and steps per minute were similar (P >0.05) among treatments, with average values of 6.9, 15.4, 2.3 and 6.3, respectively.The number of bites was greater (P ≤0.05) for the supplementation treatment and for the pasture-only treatment than it was for the treatment with N fertilization (2029.9, 1863.6 and 1715.7, respectively).The number of chews per bolus, number of chews per min/day, number of chewed bolus/day, and the number of stations/day were not influenced by the treatments (P >0.05).

Discussion
The daytime grazing behaviour showed that these results were within the range observed in experiments with tropical forage species (Brâncio et al., 2003;Sbrissia et al., 2004;Palhano et al., 2006).Grazing activity was lower in the supplemented animals than in the other treatments.This difference was caused by the amount of time the animals spent feeding on the concentrate.Therefore, the mass and forage allowance did not vary among treatments.The supplement was a filler that caused rumen satiety and contributed to the energy demands of the animals, thereby reducing grazing activity.Sheahan et al. (2011), in New Zealand, concluded that cows reduced grazing time by 12 min for every 1 kg DM of concentrate supplement consumed.According to Carvalho et al. (2007), the time taken for grazing daily (24-hour evaluation) ranges from 6 to 12 hours and is rarely above or below these values.In the current daytime study, the total time spent grazing averaged 5 hours and 29 min.This value can be considered high because it belonged only to daytime data.However, the average temperature during the experimental period was moderate and did not cause extreme heat stress.Therefore, animals were able to graze rather than seek shaded areas.In addition, the crossbred animals used in this study are more heat tolerant than European breeds.
Idle time did not differ among treatments.In general, supplemented animals spend less time ruminating after reduced forage intake, and consequently their intake of neutral detergent fibre decreases.Van Soest et al. (1991) reported that ruminating time was influenced by the type of diet and the bulky cell wall content and was thereby directly proportional to increased supplement amounts.However, in the present work, this activity showed no difference, probably because of the low level of energy supplement ingested by the animals.Similarly, the idle time was not influenced negatively by this low amount of supplement, but more studies should be conducted to determine the level that will bring changes, as idle time usually increases with an increase in the amount of dietary concentrate (Valente et al., 2013).
The amount of time spent in rumination, idleness and chewing, chews per bolus and the time required for 20 bites were similar among treatments.The timing of the evaluation period for grazing behaviour in the middle period may have been one of the factors that resulted in no significant differences between the pasture-only treatment and the pasture and supplementation treatment because rumination occurs mainly at night, and idleness is a daytime activity (Bremm et al., 2005).Non-assessment during the 24 hours of the day may have been a limitation of the current study.
The number of chews per bolus and the times for chewing, bolus formation, and taking 20 bites were not influenced by the treatments because forage availability and supply were similar in the homogenous pastures.According to Gregorini et al. (2013), the number of bites per feeding station, the total number of bites, the number of feeding stations and the rate of displacement per minute are considered functional responses of grazing animals to the forage supply.
The lowest bite rate was observed in N200, and may be because of the greater accumulation rate (Venturini et al., 2017), mainly from the emergence of new leaves at the top of the plant, which could be consumed more easily.According to Teixeira et al. (2011), in pastures where there is a greater availability of forage, the bite rate is reduced because the animal can increase the depth and volume of the bite, thereby resulting in a lower bite rate.Supplementation did not affect chewing time, probably because of the low fibre content in the supplements and the type of supplement, which had low starch content.Valente et al. (2013), in Brazil, found a reduction in chewing activity in young bulls finished in a feedlot that were fed various levels of concentrate.However, the amount of supplementation was greater than that provided in this study, supporting the idea that the level used here was not sufficient to cause a change in this behaviour.
It is important to highlight the use the Alexander grass as a pasture grass because, in addition to having spontaneous summer reseeding (especially in areas used for crop-livestock integration), it has high forage potential for animal production.Future research should address higher supplementation levels and doses of N in grasslands.These increased levels may result in greater productivity gains in the pasture and the animals, contribute to behaviour all changes in the animals, and indicate the economic viability of the system better.
Energy supplementation proved to be an important pasture management tool, since it was able to alter the grazing behaviour of the animals, reducing grazing time and increasing the number of bites.Result not found with increase in nitrogen level.

Table 1
Mean nutritive values (%) during experimental period for Alexander grass (Urochloa plantaginea) grown with additional nitrogen or supplementation

Table 2
Mean values of diurnal ingestive behaviour variables for cattle given energy supplementation and grazed on Alexander grass (Urochloa plantaginea) with nitrogen addition

Table 3
Mean values of daytime behaviours for cattle given energy supplementation and grazed on Alexander grass (Urochloa plantaginea) with added nitrogen a,b Row means with different superscripts differ significantly at P ≤0.05 SEM: standard error of mean 1 100 kg/ha of N + 0.5 kg/100 kg BW from wheat bran; 2 200 kg/ha of N; 3 100 kg/ha of N N: nitrogen