Supplementation level increasing dry matter intake of beef cattle grazing low herbage height

ABSTRACT

To evaluate the foraging behaviour of yearling bulls grazing on Marandu grass, we conducted two experiments. In the first experiment (Exp. 1), three grazing heights of 15, 25, and 35 cm were evaluated, with bulls receiving 0.3% of body weight (BW) of supplement (161 g kg^–1 crude protein (CP) and 20.1 MJ kg^–1 gross energy (GE)); in the second experiment (Exp. 2), supplementation levels were decreased as grazing height increased: (1) low height (15 cm) and high supplementation (0.6% BW: 142 g kg^–1 CP and 18.9 MJ kg^–1 GE (LH-HS)); (2) moderate height (25 cm) and moderate supplementation (0.3% BW: 161 g kg^–1 CP and 20.1 MJ kg^–1 GE (MH-MS)) or (3) high height (35 cm) without supplementation (HH-WS). Ingestive behaviour was evaluated by direct visual observations, and intake using markers. It was used 9 paddocks each experiment. The experimental design was completely randomized, analysing effects by polynomial orthogonal contrasts (Exp. 1) and Tukey test (Exp. 2). In Exp. 1, a linear decreasing response to daily grazing time (P < 0.01) was observed, whereas a linear increasing response to herbage intake (P < 0.01) was observed with increased grazing height. In Exp. 2, LH-HS bulls had lower herbage intake (P < 0.01) than their counterparts. Bulls from both experiments showed increased grazing activity after 12 PM (P < 0.05). The herbage intake substitution effect of supplements can be explored as a production strategy, as the adjustment of supplementation levels can promote high dry matter intake as well as performance in beef cattle, in conditions of low grazing height or low forage allowance, even with a high stocking rate.

KEYWORDS:

• Bite rate
• herbage intake
• supplements
• tropical grasslands

Introduction

Beef cattle production in Brazil is predominantly based on pasture and grassland. According to Da Silva et al. (2013), herbage intake is one of the most important factors influencing animal performance and is dependent on mechanisms such as grazing time and bite rate. Cattle can adapt these mechanisms according to variations in morphological structure or herbage allowance (Mezzalira et al. 2014).

Supplementation strategies can also change behavioural intake mechanisms of grazing cattle by influencing ruminal fermentation (Moore et al. 1999). Understanding grazing behaviour and intake mechanisms are critical when developing supplementation and grazing management strategies through optimization of supplementation and herbage intake (Casagrande et al. 2011). Therefore, the factors influencing feeding behaviour for allowing efficient herbage utilization are becoming more important (Carvalho 2013).

Decreasing grazing height, as well as increasing the supplement dose, tend to reduce forage intake. However, this may not be detrimental if the combination of decreasing grass height with increasing doses of supplementation leads to an increase in nutrient intake, intensifying beef production per unit area, and allowing for high stocking rates with the maintenance of high animal performance.

In this study, we tested the hypothesis that different combinations of Marandu grass grazing height and supplementation levels may modify the ingestive behaviour and herbage intake of yearling bulls The objective of this study was to evaluate if the ingestive behaviour and herbage intake by yearling bulls is altered by Marandu grass at different grazing heights and supplementation level combinations.

Materials and methods

Experimental area

Two experiments were conducted simultaneously at the Forages and Grasslands division of São Paulo State University ‘Julio de Mesquita Filho’ (UNESP), in Jaboticabal, SP, Brazil (21°15′22″ S latitude, 48°18′58″ 77 W longitude and 595 m elevation). The typical climate is humid subtropical, mild with dry winters, and hot wet summers. The pastures used as the study site were established in 2001 using Brachiaria brizantha (Hochst ex A. Rich) Stapf ‘Marandu,’ divided into 18 individual paddocks. Experiments were conducted during the wet season of 2012/2013. Grazing heights were established from 26 November 2012 to 11 January 2013, animal adaptation from 12 January to 26 January 2013 (14 days) and 84 days of evaluations (January to April).

Animals and treatments

Experiment 1

The experiment consisted of three treatments, with three replicates per treatment, totalling 9 experimental paddocks with a fully randomized design. Sixty Nellore yearling bulls with an initial body weight (BW) of 334.9 ± 6.3 kg were used. Bulls were identified, weighed, and randomly distributed in groups of six bulls per paddock. The remaining bulls were used as flexible grazers to maintain a pre-established grazing height, using put-and-take methodology (Mott and Lucas 1952). Pasture management and animal performance evaluation were performed as previously described in (Barbero et al. 2015). The protocol from ethic council for animal use was 022368/12 (UNESP).

Grazing heights used in this study were 15, 25, and 35 cm and were based on the range of recommendations by Da Silva et al. (2013) for Marandu grass. Paddocks were managed under continuous stocking and areas were 0.7, 1.0, and 1.3 (hectare) ha for 15, 25, and 35 cm, respectively. The variation in paddock size was established to maintain the same number of bulls per paddock for the different sward heights evaluated. Bulls received 0.3% BW of supplement (161 g kg^–1 crude protein (CP) and 20.1 MJ kg^–1 gross energy (GE)), which was formulated based on the herbage allowance and nutritive value content previously analysed, aiming to achieve 1.0 kg day^–1 average daily gain (ADG) according to NRC (1996). Supplementation was delivered once a day at 11h00 m for all bulls in each paddock and access to water was ad libitum.

Experiment 2

Sixty Nellore yearling bulls with an initial BW of 336.4 ± 5.7 kg were used. Bulls were identified, weighed, and randomly distributed in groups of 6 bulls per paddock. The experiment consisted of three treatments and three replications (paddock), totalling nine experimental paddocks (n = 9). The remaining bulls were used to maintain a pre-established grazing height, using the put-and-take methodology (Mott and Lucas 1952). Supplementation and grazing strategies were: (1) low grazing height (15 cm) and high supplementation (0.6% BW: 142 g kg^–1 CP and 18.9 MJ kg^–1 GE) (LH-HS); (2) moderate grazing height (25 cm) and moderate supplementation (0.3% BW: 161 g kg^–1 CP and 20.1 MJ kg^–1 GE) (MH-MS); or (3) high grazing height (35 cm) without supplementation (HH-WS). The supplements were formulated based on the herbage allowance and nutritive value content previously analysed, aiming to achieve a 1.0 kg day^–1 ADG (NRC 1996), with the exception of HH-WS without additional supplementation. Supplementation was offered in the same manner as in Experiment 1. Paddock area varied so as to maintain the same number of bulls per paddock, as described in Experiment 1.

Herbage characteristics

To maintain grazing heights, swards were measured weekly at 80 random points (‘hits’) ha^–1 to estimate average paddock height. To estimate herbage mass, 8 samples per paddock were collected from a 0.25 m² area (5 cm residual height) every 28 d (January to April 2013), separated into dead material, stem + leaf sheath, and green leaves, then dried at 55 ± 5°C to constant weight to estimate dry matter (DM) ha^–1. To estimate herbage nutritive value, samples were hand-picked every 28 d (20 average sward height in each paddock), dried at 55 ± 5°C to constant weight, then sieved through a 1 mm screen in a shear mill (Thomas-Wiley Laboratory Mill Model 4, H. Thomas Co., Swedesboro, New Jersey, USA) for analyses. In vitro DM digestibility (IVDMD) was estimated using the ANKOM^®, Daisy (Ankom technologies, Macedon, New York, USA) methodology. Crude protein was estimated using LECO® FP 528 (Leco corporation, St. Joseph, Michigan, USA). Neutral detergent fibre (NDF) and acid detergent fibre (ADF) were analysed with polyester filter bags and ANKOM® equipment (Ankom technologies).

Behaviour observation

Ingestive behaviour was evaluated by direct visual observations (Hughes and Reid 1951) undertaken every 10 min (Martín and Bateson 1986). Three consecutive days were employed for observations during the experimental periods, which occurred every 28 d. Average temperature was 23°C, with no precipitation. Average daily photoperiod was 12 h with 12 continuous hours of observation per day from 06h00m to 18h00m. Every bull was marked with a number painted on their flank. The bite rate was assessed by direct visual observations on one focal bull per paddock, totalling three bulls per treatment. The number of bites in 20 s intervals (Forbes and Hodgson 1985) were considered during three periods on each observation day: 08h00m to 10h00m, 12h00m to 14h00m, and 16h00m to 18h00m, three times (grazing cycles) per interval.

Intake estimations

In the half of the experimental period, three markers were used to estimate faecal excretion. The external marker for isolated lignin, purified and enriched from Eucalyptus grandis (500 mg), was orally administered daily for 6 d, with 3 d of adaptation to stabilize to faecal excretion of the marker, and 3 d for sample collection every 12 h (Santos et al. 2011). To estimate dry matter intake (DMI) of the supplement, an external marker made of titanium dioxide (TiO₂) was added to the supplement at 10 g of TiO₂ per animal for 9 d, with 6 d of adaptation to stabilize faecal excretion of the marker, and 3 d for sample collection every 12 h (Titgemeyer et al. 2001). Faecal samples were dried at 55 ± 5°C for 72 h to constant weight, then ground. The lignin marker concentration was quantified using the infrared spectroscopy method (Saliba et al. 2013), and the TiO₂ concentration was quantified through a spectrophotometry read at 410 nm (Myers et al. 2004). Herbage DMI was estimated using undigested NDF as an internal marker, estimated by ruminal incubation (Nocek and English 1986) for 240 h (Casali et al. 2008). Herbage DMI was estimated from the faecal output of the internal marker corrected for the supplement contribution as follows (Equation 1):(1) $\mathrm{Herbage}\mathrm{DMI}=(\mathrm{FE}\times [\mathrm{iMF}]-\mathrm{DMIS}\times [\mathrm{iMS}])/[iMH]$(1) where FE = faecal excretion, DMIS = DMI of supplement, [iMF], [iMS] and [iMH] are the concentrations of the internal marker in faeces, supplement, and herbage, respectively. Total DMI was obtained by addition of herbage and supplement DMI.

Statistical analyses

Means of each data type collected were calculated for each paddock. The experimental design was completely randomized. The statistical analyses accounted for three treatments with three replications (paddocks) per treatment. Assumptions for analysis of variance were tested using procedures of SAS® (SAS Institute Inc. 2008). Exp. 1: the day hour effect (each 3 h) per treatment was evaluated by Tukey test (P < 0.05), and the grazing height effects were analysed by polynomial orthogonal contrasts, using the PROC MIXED of SAS® (SAS Institute Inc. 2008). Exp. 2: assuming that all variables could be influenced by the association between grazing height and supplement levels, treatment effects were analysed using Tukey test (P < .05), by PROC MIXED of SAS® (SAS Institute Inc. 2008). The following mathematic model was used (Equation 2):(2) $Yij=\mu +TRi+\epsilon ij$(2) where Yij = dependent variable, μ = general average effect, TRi = treatment, effect ‘i,’ ‘j’ = replication effect, and εij = random error.

Results

Experiment 1

Green leaf mass (15 cm = 2595 kg DM ha^–1; 25 cm = 3166 kg DM ha^–1 and 35 cm = 4238 kg DM ha^–1) exhibited a linear increase (P < .01) as grazing height increased. In contrast, IVDMD responded with a linear decrease (15 cm = 683 g kg^–1 DM; 25 cm = 669 g kg^–1 DM and 35 cm = 646 g kg^–1 DM; P < .01) with increased grazing height. Crude protein (141 ± 5.6 g kg^–1 DM), NDF (590 ± 9.3 g kg^–1 DM), and ADF (292 ± 2.4 g kg^–1 DM) were not affected by treatments (P = .19, P = .07 and P = .44, respectively). All bulls observed, independent of the treatment group, exhibited increased grazing activities after 12 PM (P ≤ .05; Figure 1). Total daily grazing time and bite rate decreased linearly (P < .01; Table 1) with increasing grazing height. A negative linear response was observed on total daily rumination time (P = .03). All other daily activities (such as vocalization, social interactions with physical contact, etc.) were not affected by treatments (P = .34). Herbage DM intake showed a positive linear response to grazing heights (P < .01; Figure 2).

Figure 1. Daily grazing distribution (in minutes) by yearling bulls on Marandu grass on different grazing heights (Experiment 1). Different letters on the same colour bars are significantly different by Tukey test (P < .05).

Figure 2. Herbage dry matter intake (DMI) in percent of body weight (BW) by yearling bulls on Marandu grass grazing on different heights (Experiment 1).

Table 1. Total daily grazing time, rumination, bite rate, and others activities by yearling bulls on Marandu grass on different grazing heights (Experiment 1).

Activity	Grazing height (cm)			SEM	Effect	P-value
	15	25	35
Grazing	428	350	302	43.7	Linear	<.01
Rumination	192	230	296	9.8	Linear	.03
Bite rate	43	32	30	3.82	Quadratic	<.01
Others	100	140	122	36.5	ns	.34

Note: Grazing, rumination and others are shown in minutes/day (6–18 h) and bite rate in bites/minute, standard error of mean (SEM) and non-significant (ns).

Experiment 2

Green leaf mass was highest for HH-WS (4197 kg DM ha^–1), intermediary for MH-MS (3166 kg DM ha^–1), and lowest for LH-HS (2554 kg DM ha^–1; P < 0.01). In vitro DM digestibility was highest for LH-HS (677 g kg^–1 DM) and MH-MS (669 g kg^–1 DM), and HH-WS having the lowest (649 g kg^–1 DM; P = 0.04). Crude protein content (139 ± 0.4 g kg^–1 DM), NDF (592 ± 4.4 g kg^–1 DM), and ADF (296 ± 2.2 g kg^–1 DM) were not affected by treatments (P = .18, P = .45 and P = .61, respectively). As in Exp. 1, bulls from all different treatments showed increased grazing activity after 12 PM (P < .05; Figure 3). Bulls in the LH-HS treatment had highest total daily grazing time (P < .01) and lowest total daily rumination time (P = .02), total other daily activities (P = .04) and bite rate (P < .01; Table 2). Herbage DM intake was affected by treatments (P < .01), with LH-HS treatment exhibiting the lowest intake, MH-MS treatment intermediary intake, and the highest intake for HH-WS (Figure 4).

Figure 3. Daily grazing distribution (in minutes) by yearling bulls on Marandu grass grazing different heights and supplementation levels (Experiment 2). Treatments: short grazing height with high supplementation (LH-HS), moderate height with moderate supplementation (MH-MS) and tall height without supplementation (HH-WS). Different letters on the same colour bars are significantly different by Tukey test (P < .05).

Figure 4. Herbage dry matter intake (DMI) in percent of body weight (BW) by yearling bulls on Marandu grass on different grazing heights and supplementation levels (Experiment 2): short grazing height with high supplementation (LH-HS), moderate height with moderate supplementation (MH-MS) and tall height without supplementation (HH-WS). Means with different letters on the same colour bar are significantly different by Tukey test (P < .01).

Table 2. Total daily grazing time, rumination, bite rate, and others activities by yearling bulls on Marandu grass grazing different heights and supplementation levels (Experiment 2).

Activity	Treatment			SEM	P-value
	LH-HS	MH-MS	HH-WS
Grazing	436^a	348^b	320^b	29.4	<.01
Rumination	188^b	220^a	220^a	23.7	.02
Bite rate	41.0^a	32.0^b	30.0^b	3.35	<.01
Others	96.0^b	152^a	180^a	15.5	.04

Notes: Treatments: short grazing height with high supplementation (LH-HS), moderate height with moderate supplementation (MH-MS) and tall height without supplementation (HH-WS). Grazing, rumination and others are shown in minutes/day (6–18 h) and bite rate in bites/minute. Standard error of mean (SEM). Means with different letters on the same row are significantly different by Tukey test (P < .05).

Discussion

Foraging behaviour and herbage intake by cattle can be altered by factors such as grazing intensity (Estell et al. 2012) and supplementation (Moore et al. 1999). Time of day, amount, and type of supplementation can influence cattle grazing times and herbage intake (Casagrande et al. 2011). The observed results in both experiments can provide important information on management strategies. Grazing activity increased after 12 PM, and that should be the time limit for supplementation provision so as to not interfere with afternoon grazing activities.

Bircham and Hodgson (1983) discuss changes in feeding behaviour as changes in herbage supply and sward structure occur, where bulls with a limited herbage supply tend to increase time spent grazing to offset the lower intake of herbage. This same pattern of response was observed in both experiments, especially in treatments with lower grazing height, and the herbage mass estimated factor in grazing time. Consequently, bulls kept in pastures with greater grazing heights spent more time on other activities, such as leisure and social interactions.

In both experiments, bulls maintained in pastures with managed greater grazing heights showed an increase in rumination time. Grazing cattle tend to be selective, consuming plant fractions of higher nutritional value, such as green leaves, regardless of grazing heights (Barbero et al. 2012). Nonetheless, pastures with greater grazing heights tend to have increased fibrous tissues because of advanced maturity of plant tissues (Bircham and Hodgson 1983), which also agrees with the observed IVDMD in both experiments. Ultimately, the increased fibrous forage and decreased digestibility may increase rumination time.

Barbero et al. (2014) evaluated tropical grazing intensities and found that grazing height can affect canopy structure, chemical composition and consequently affecting animal performance. The increased bite rate of bulls kept in pastures with a lower grazing height can be interpreted as an adaptation mechanism to compensate for the limited availability of the herbage mass (Da Silva et al. 2013). This observation, together with the increase in time spent grazing, is an indication that the bulls spent more time grazing trying to compensate for a likely lower hourly intake rate.

Although we observed an increase in grazing time and bite rate in conditions of low grazing height, herbage intake was influenced by grazing height in both experiments. Lower intake by animals was observed in treatments with lower forage allowance. According to Moore et al. (1999), herbage intake can be replaced by supplements. In Exp. 2, we found that herbage intake decreased with reduced grazing height and high supplementation amount, which may be caused by a negative substitutive effect in herbage intake.

Advances in ruminant nutrition are dependent on the search for new information regarding the numerous factors that influence animal performance (Poppi and McLennan 2010). Increase in the docility of supplemented bulls compared to non-supplemented bulls, due to human presence, can have a positive effect on production systems, which may facilitate future management and also provide greater security to managers. The results of our study showed that Marandu grass grazing height, associated with supplementation levels, can change some behavioural aspects in beef cattle, but that grazing intensity has a great influence on their ingestive behaviour.

Dry matter, protein and energy intake in both experiments is compatible with the recommended performance of about 1.0 kg/bull/day (NRC 1996). The substitutive effect of starch-containing supplements on forage intake is usually shown as a negative factor because of increased production costs. However, it can be explored as a production strategy in systems with high stocking rates by adjusting the supplementation levels to grazing heights. Supplementation would promote increases in dry matter intake and consequently in animal performance by beef cattle, even with low grazing heights or in conditions of low forage allowance.

Grazing activity increased after 12 PM, illustrating the need for supplementation delivery to occur prior to this time to avoid reducing the influence of supplementation on grazing activity. The decrease in grazing height resulted in an increase in the bite rate and in daily grazing time and reduced herbage intake. Although herbage intake was reduced under these conditions, intake of the additional dry matter of the supplement promoted an increase in the total intake of dry matter (forage + supplements). This strategy of adjusting supplementation levels according to the grazing height can be used to improve beef production efficiency, allowing increases in stocking rate without compromising the nutrient intake.

Implications

Forage management and supplementation strategy in this study affected the grazing behaviour and herbage intake. The decrease in grazing height lead to increased bite rate, daily grazing time and reduced herbage intake. Supplementation level needs to be adjusted according to grazing intensity, which can promote an increase in dry matter intake even while beef cattle are foraging on low grazing height.

Statement of animal rights

The procedures described above were approved by the Institutional Animal Care and Use Committee (number 022368/12, November 8, 2012), from São Paulo State University ‘Julio de Mesquita Filho’ (UNESP).

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Rondineli Pavezzi Barbero http://orcid.org/0000-0002-1577-395X

Additional information

Funding

The authors would like to thank the ‘São Paulo Research Foundation’ [Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) grant numbers 2012/14956-6 and 2012/20264-0] and ‘Trouw Nutrition Brasil’ for their financial support.