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This article in CS

  1. Vol. 51 No. 4, p. 1815-1823
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    Received: June 28, 2010
    Published: July, 2011


    * Corresponding author(s): gscaglia@agcenter.lsu.edu
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doi:10.2135/cropsci2010.06.0375

Grazing Behavior and Diet Preference of Beef Steers Grazing Adjacent Monocultures of Tall Fescue and Alfalfa: II. The Role of Novelty

  1. Holly T. Bolanda,
  2. Guillermo Scaglia *b,
  3. David R. Notterc,
  4. Andrew J. Rookd,
  5. William S. Sweckere and
  6. Azenegashe O. Abayef
  1. a Mississippi State Univ., Prairie Research Unit, 10223 Hwy. 382, Prairie, MS 39756
    b LSU AgCenter, Iberia Research Station, 603 LSU Bridge Rd., Jeanerette, LA 70544
    c Dep. of Animal and Poultry Sciences (0306), Virginia Tech, Blacksburg, VA 24061
    d formerly of IGER, Devon, EX20 2SB, UK
    e Large Animal Clinical Sciences, VA-MD Regional College of Veterinary Medicine, Blacksburg, VA 24061
    f Dep. of Crop and Soil Sciences (0404), Virginia Tech, Blacksburg, VA 24061

Abstract

Domestic ruminants select a mixed diet when grazing heterogeneous pastures. Adjacent monocultures allow diet preference to be evaluated without certain constraints that could influence diet selection; however, few forage species have been evaluated. Adjacent monocultures of tall fescue (Festuca arundinacea Schreb.) and alfalfa (Medicago sativa L. ssp. sativa) were used to test the theories that selection of mixed diets is influenced by a plant's “novelty,” and that regardless of forage species, cattle will have a partial preference for legumes over grasses. Cattle without previous experience eating alfalfa spent 78% of total grazing time eating alfalfa, whereas after having experience grazing alfalfa they spent less (P = 0.04) time grazing alfalfa (72%). Overall, proportion of the day spent grazing was less (P = 0.001) when alfalfa was novel (40%) than when steers were experienced with both forages (46%). Proportion of the day spent idling was greater (P < 0.001) when alfalfa was novel (35%) than when both forages were familiar (26%). The proportion of grazing time in alfalfa was greater (P = 0.02) in the afternoon (76.8%) than in the morning (72.1%), differing from previous studies that reported a decline in legume preference over the day with an increased grass preference in the afternoon. Application of adjacent monocultures in production systems would benefit from additional research on performance of cattle grazing in this paddock arrangement.


Abbreviations

    ADF, acid detergent fiber; BW, body weight; CP, crude protein; NDF, neutral detergent fiber; TNC, total nonstructural carbohydrates; TOD, time of day; Yr 1, Year 1—2006; Yr 2, Year 2—2007

Cattle exhibit a partial preference for white clover (Trifolium repens L.) over perennial ryegrass (Lolium perenne L.) of around 70% when given a choice between the two forages as adjacent monocultures (Rutter et al., 1999, 2004a, 2004b, 2005). There are a number of theories as to why domestic ruminants consume a mixed diet in these proportions. One theory suggests that the “novelty” of a forage plays a role in diet selection in short-term experiments (Rutter, 2006). Effect of previous diet has been evaluated in sheep grazing different allotments of perennial ryegrass and white clover. Sheep were observed to have a greater preference for the forage that was lacking in their most recent diet (Parsons et al., 1994). Those sheep had prior experience grazing both forages, so while the forage was novel in the sense that it had been absent from the diet in the previous few weeks, neither of the forages studied was unfamiliar to them. Other views on response to novelty have been reported. For example, Villalba (2007) stated that animals will prefer familiar over unfamiliar foods, which they will regard with caution, while Illius and Gordon (1990) suggested that grazing animals may need to sample plants or areas that are unfamiliar to learn about them and determine whether they are a viable food source. Others reported that an animal will readily consume a novel food because the food is new or rare (Ganskopp and Cruz, 1999; Baumont et al., 2000).

Tall fescue (Festuca arundinacea Schreb.) and alfalfa are relatively new forages in the area of adjacent monoculture research. Therefore, the effect that novelty might play in diet preference of these two forages was of interest. The objectives of this experiment were to evaluate (i) diet preference, (ii) diurnal pattern of preference, and (iii) overall grazing behavior of beef steers grazing adjacent monocultures of tall fescue and alfalfa when alfalfa was a novel forage compared to behavior when steers have previously grazed both forage species.


MATERIALS AND METHODS

Treatments and Management

The procedures used in this experiment were approved by the Virginia Tech Institutional Animal Care and Use Committee. This experiment was conducted at Kentland Farm (37°11′ N, 80°35′ W), Blacksburg, VA, during August of 2006 (Year 1 [Yr 1]) and 2007 (Year 2 [Yr 2]). The first treatment (Novelty) was used to evaluate animal response to grazing endophyte-free tall fescue and alfalfa in equal proportions of ground area when steers had prior experience grazing only tall fescue. The second treatment (Experience) was used to evaluate animal response to grazing these two forages when steers had prior experience with both tall fescue and alfalfa. The same steers were used in both treatments within each year, with the Novelty period conducted from 11 to 15 August in Yr 1 and 3 to 5 August in Yr 2. The Experience period was conducted from 26 to 30 August in Yr 1 and 16 to 20 August in Yr 2. Site description and pasture establishment have been described in Boland et al. (2011).

Eighteen Angus-crossbred steers (9 steers yr−1, 16 mo old, Yr 1 initial body weight [BW] = 392 ± 8 kg, Yr 2 initial BW = 323 ± 9 kg) were used. Before the study, steers had no experience eating alfalfa and had grazed pastures of predominantly endophyte-infected tall fescue. Steers grazed endophyte-free tall fescue for several months before the study. Steers were blocked by initial BW and then steers within blocks were randomly allotted to paddocks with three steers in each paddock, and three paddocks total. Paddocks were 0.22 ha of tall fescue monoculture adjacent to 0.22 ha of alfalfa monoculture. Each paddock was subdivided into three subpaddocks with electric poly-tape. One subpaddock was used for the Novelty period, the second was grazed between periods, and the third was used for the Experience period. Within each paddock the steers could move freely between each forage type. Water troughs and mineral blocks with poloxalene as an antibloat agent (Bloat Guard Pressed Block, Sweetlix Livestock Supplement System, Mankato, MN) were provided ad libitum and located at the midpoint of the paddock where the two forage types converged. This ensured that the steer's need to drink and consume mineral did not influence into which forage monoculture the steer would travel.

Behavioral Sampling

Behavior data recorders (Rutter et al., 1997) were used to monitor grazing behavior. This device consists of a halter-mounted data logger and jaw sensor. The jaw sensor was a carbon-packed tube serving as an electrical transducer converting movements of the jaw to electronic signals. The data from the sensor were recorded on a Compact Flash memory card (Pretec USA, Fremont, CA) in the data logger and analyzed by GRAZE software (version 0.801, Rutter, 2000). Activities reported were time spent grazing, ruminating, and idling (defined as not grazing or ruminating), as well as numbers of bites and ruminating mastications. Bites were recorded as the severing of plant material from the sward during grazing. Mastications were recorded as the chewing activity during rumination. All steers were trained to wear these devices before the experiment. Training began 2 wk before the experiment by fitting a nonfunctional version of the recorders on each steer for a period of 4 h on first day of training and increasing the length of time by 4 to 8 h each day until steers were acclimated and could wear the device continuously for 4 d. Training versions were of similar size and weight and fitted to the same halter steers would wear during the trial. Steers were brought to the working facility between 0700 and 0800 on Day 1 of the Novelty and Experience periods and were fitted with the behavior data recorders. Steers were put in their respective paddocks between 0800 and 0900, remained there for 48 h, and were then brought back to the working facility where batteries and memory cards were exchanged in the data recorders. Steers were then returned to the paddocks for an additional 48-h period.

Video surveillance cameras in weatherproof enclosures (DCS-5300 in DCS-70, D-Link, Fountain Valley, CA) were mounted 6 m above the ground on poles in each paddock to monitor steers. Color video containing date and time stamps were recorded digitally during daylight hours onto a computer hard drive and were later reviewed using a digital media player (Windows Media Player, Microsoft Corp., Redmond, WA). Steers within paddocks were identified by a unique color neckband and fluorescent livestock marking paint (Mark-Her, H and W Products, Salem, OH). Instantaneous scan sampling (Altmann, 1974) was performed during video review and steer behavior documented at 10-min intervals. Steers were considered to be exhibiting that behavior for the entire 10-min period. At each observation, three variables were recorded: body position (standing or lying); jaw activity (grazing, ruminating, idling); and field location (alfalfa, tall fescue, or on the boundary line between the monocultures). Standing was recorded if the steer was in an upright position and lying was recorded if the steer was in a recumbent position. Grazing was recorded if the steer was observed consuming or searching for forage. Ruminating was recorded if the steer was observed masticating (not grazing and could be standing or lying). Idling was recorded if the steer was not grazing or ruminating (could be standing or lying). Field location was identified by colored posts located along the boundary line between the two forage areas. Water troughs and mineral feeders were also clearly visible.

Data collected from the behavior data recorders and video recordings were combined and analyzed by matching the time stamp of the recorded data from one device to the data collected on the other devices. Proportion of time for behaviors spent on the boundary line between the two forage monocultures was divided and half the value added to the proportion of time that behavior was recorded in each forage type. Bite rate while grazing in alfalfa or tall fescue was calculated on a focal steer in each replicate paddock at three times in the morning and three times in the afternoon on Days 1 and 3. This was performed using the combined data from the behavior recorder and video surveillance analyses.

Forage Sampling and Analyses

Hand-plucked forage samples were taken for nutritive value analysis on the day before and the day after each experimental period. Samples were collected while walking along a cross section of the paddock and grabbing a sample every 10 steps from the top 7 to 10 cm of the sward. Separate samples from each paddock of each forage type were collected between 0730 and 0830 h in the morning and between 1700 and 1800 h in the afternoon. Forage samples were collected from morning and afternoon time-of-day (TOD) intervals to determine diurnal changes in carbohydrate concentrations, which have been shown to influence diet selection (Ciavarella et al., 2000; Mayland et al., 2000b). Samples were packed on ice directly after collection, placed in a freezer, and later freeze-dried (25L Genesis SQ EL-85, VirTis, Gardiner, NY). Samples were then ground through a 1-mm screen using a Wiley mill (Laboratory Mill Model 4, Arthur H. Thomas Co., Swedesboro, NJ), and analyzed for chemical composition by near-infrared spectroscopy (Foss NIRSystems 6500, Foss Tecator, Eden Prairie, MN; AOAC, 2000) at a commercial laboratory (DairyOne, Ithaca, NY). Tall fescue subsamples were further ground to 0.5 mm (Cyclotec 1093 Sample Mill, Foss Tecator, Eden Prairie, MN) and analyzed for alkaloid concentration by enzyme-linked immunosorbent assay (Agrinostics Ltd. Co., Watkinsville, GA) to ensure they had the anticipated low alkaloid levels. Mean alkaloid level of tall fescue pastures in Yr 1 was 111 ng g−1 and in Yr 2 was 51 ng g−1.

Forage mass and sward height measurements were taken on the day before and the day after each experimental period. Six quadrants of 0.25 m2 were selected from each adjacent monoculture of tall fescue and alfalfa (three in each forage type, six per treatment area). Sixty measurements of sward height were taken with a ruler within each paddock to characterize sward conditions. Clippings were collected at 2.5 cm above ground level and forage was placed in cloth bags and dried in a forced draft oven at 60°C for 48 h to determine dry matter (%) and forage mass.

Statistical Analyses

Data were analyzed using SAS (version 9.1.3, SAS Institute, Cary, NC). The experimental unit for all analyses was the paddock of three steers (Rook and Penning, 1991). Behavior recorder output and surveillance video data were combined to obtain the proportion of time spent in alfalfa and tall fescue during daylight observations. Angular transformation of proportions was conducted to stabilize variance (Parsons et al., 1994). The angular-transformed percentage of the total time a behavior was observed on each forage type was used to determine preference for that behavior to occur on a specific forage. Diurnal patterns of preference and bite rate were analyzed using the MIXED procedure with a model that included fixed effects of treatment, TOD (morning or afternoon), and their interaction. The model for bite rate also included effects of forage type. Behavior data were analyzed using the MIXED procedure and the compound symmetry covariance structure. The repeated measure was day for all variables. The model for behavior data (grazing, ruminating, idling, standing, and lying, number of prehensions and mastications) included fixed effects of year, treatment, day, and their interaction. Repeated measure was day within year. Forage nutritive value and sward measurement data were analyzed using the MIXED procedure using a model that included fixed effects of year, forage type (alfalfa or tall fescue), treatment (Novelty or Experience), sampling phase (pre- or postgrazing), and interactions. The model for nutritive value parameters which have diurnal changes (i.e., carbohydrates) included fixed effects of year, forage type, sampling TOD (morning or afternoon), and interactions. The experimental unit was the paddock within period. Paddock (within year) was considered a random effect. Least squares means are reported for all variables with means separated by Tukey's adjustment. A significance level of α ≤ 0.05 was set for all analyses, with trends defined as 0.10 > α > 0.05.


RESULTS AND DISCUSSION

Forage and Sward Measurements

Alfalfa neutral detergent fiber (NDF) (333 ± 20 g kg−1), acid detergent fiber (ADF) (247 ± 7 g kg−1), and crude protein (CP) (250 ± 12 g kg−1) concentrations did not differ (P ≥ 0.10) by year or treatment. Lignin concentrations in alfalfa tended (P = 0.06) to be greater in the Novelty treatment period than during the Experience period (71 and 65 ± 2 g kg−1, respectively). This could be due to appearance of new growth in the paddocks of the Experience periods. Year effects (P ≤ 0.04) were observed for both CP and lignin in tall fescue, with decreased CP (150 and 178 ± 6 g kg−1) and greater lignin (53 and 48 ± 2 g kg−1) in Yr 2 than in Yr 1, respectively. Tall fescue NDF (515 ± 8 g kg−1) and ADF (303 ± 5 g kg−1) did not differ between years (P ≥ 0.13).

There was an effect of forage type (P ≤ 0.0007) on nutritive value, with alfalfa having less NDF and ADF, and greater lignin and CP concentration (Table 1). Forage nutritive values declined (P ≤ 0.009) between pre- and postgrazing samples. There was no effect of year (P ≥ 0.18) on overall CP, NDF, or lignin of the pastures, while ADF tended (P = 0.07) to be greater in Yr 1 than in Yr 2 (284 and 266 ± 5 g kg−1, respectively).


View Full Table | Close Full ViewTable 1.

Nutritive value of forages being offered to beef steers as adjacent monocultures.

 
Forage Sampling phase† NDF‡ ADF Lignin CP
g kg −1 dry matter
Alfalfa Pre 315c§ 235c 64b 257a
Post 350b 260b 71a 240a
Tall fescue Pre 504a 299a 53c 171b
Post 520a 306a 49c 160b
SEM 15.2 6.7 1.9 10.7
Pre = pregrazing samples taken 1 d before grazing; Post = postgrazing samples taken 1 d after grazing.
NDF = neutral detergent fiber; ADF = acid detergent fiber; CP = crude protein.
§Within columns, means followed by the same letters are not different at P < 0.05.

Forage mass was greater (P = 0.02) in Yr 1 than Yr 2 (2717 and 2250 ± 127 kg ha−1, respectively). Forage mass did not differ by treatment or forage type (2484 ± 125 kg ha−1, P ≥ 0.21). Pregrazing forage mass tended (P = 0.07) to be greater than postgrazing mass (2574 and 2393 ± 103 kg ha−1, respectively). There was no interaction of treatment × forage × sampling phase observed (Table 2, P = 0.27).


View Full Table | Close Full ViewTable 2.

Forage mass (kg of dry matter ha−1) and forage height (cm) of alfalfa and tall fescue when paddocks were offered as adjacent monocultures when alfalfa was a novel forage (Novelty) and when steers had experience grazing both forages (Experience).

 
Treatment
Novelty
Experience
Measurement Forage Pre† Post Pre Post
Mass‡ Alfalfa 2633 2573 2873 2322
Tall fescue 2309 2380 2482 2296
Height§ Alfalfa 31a¶x# 22c 26bx 20c
Tall fescue 23ay 22ab 20by 17c
Pre = pregrazing samples taken 1 d before grazing; Post = postgrazing samples taken 1 d after grazing.
Forage mass SEM = 206.
§Forage height SEM = 1.4.
Within rows, means followed by the same letters are not different at P ≤ 0.05.
#Within columns, means followed by the same letters are not different at P < 0.05.

All main effects for sward height were significant, as was the treatment × forage × period interaction (P ≤ 0.01, Table 2). Sward height was taller in Yr 2 than Yr 1 (26 and 19 ± 2 cm, respectively). Given that forage mass was less in Yr 2, these data help to characterize the general structure of the sward: the alfalfa was taller in Yr 2 than Yr 1 (28 and 21 ± 2 cm, respectively) but not as leafy. This difference was likely due to an infestation of leafhoppers (Empoasca fabae L.) before the trial. Alfalfa was taller than tall fescue (25 and 21 ± 1 cm, respectively) and pregrazing height was greater than postgrazing (25 and 20 ± 1 cm, respectively).

Diet Preference

Steers spent more of their time grazing alfalfa in the Novelty period (77.5%) than in the Experience period (72.1%, P = 0.04; Table 3). Consequently, steers spent less time grazing the familiar tall fescue forage in the Novelty period (22.5%) than in the Experience period (27.9%). Results of previous studies of animal responses to novel vs. familiar foods varied among studies. Phillips and Youssef (2003a) conditioned ewes and lambs to one of four different forages. Sheep were then offered pastures containing all four forages. The sheep spent more time grazing the familiar forage, regardless of its species. Some studies have reported that animals will avoid or only eat small quantities of novel foods (Provenza and Balph, 1987; Burritt and Provenza, 1989; Provenza et al., 1995; Villalba, 2007), but others report that animals will prefer foods that are novel, rare, or previously were lacking in their diet (Tuttle et al., 1990; Newman et al., 1992; Parsons et al., 1994). The preference for novelty may be a hedonic behavior, and a novel forage item may be interpreted as a reward by the animal (Baumont et al., 2000). The preference for rarity in the present case, however, could be discounted because Boland et al. (2011) offered steers different proportions (25:75, 50:50, and 75:25) of tall fescue and alfalfa. If steers prefer the “rare” forage, then they would have been expected to show a greater preference for tall fescue when it was only 25% of the forage being offered, but instead grazed on alfalfa 65% of the time. Preference for alfalfa over endophyte-free tall fescue is not likely to be attributed to any negative association with tall fescue related to endophyte-infected tall fescue (containing ergot alkaloids) that the steers consumed earlier in life. These steers had experience grazing both types of tall fescue, and ruminants have been shown to be able to differentiate endophyte-free from endophyte-infected forages (Jones et al., 2000; Cosgrove et al., 2002).


View Full Table | Close Full ViewTable 3.

Proportion of beef steer behaviors† spent in paddocks of alfalfa and tall fescue as adjacent monocultures when alfalfa was novel forage (Novelty) and when steers had experience grazing both forages (Experience).

 
Treatment
Novelty
Experience
Forage Grazing Ruminating Idling Grazing Ruminating Idling
Alfalfa 77.5a‡ 47.2a 16.6a 72.1b 25.6b 14.6b
Tall fescue 22.5b 52.8b 83.4b 27.9a 74.4a 85.4a
Standing Lying Standing Lying
Alfalfa 50.1a 8.6 45.7b 8.0
Tall fescue 49.9b 91.4 54.3a 92.0
SEM
Grazing Ruminating Idling Standing Lying
2.2 3.5 1.1 1.6 0.9
Data reported as percentage of time the animals exhibited the behavior while in one forage or the other.
Between treatment within behavior and forage type, means followed by the same letters are not different at P ≤ 0.05.

Pattern of preference was also affected by day (P = 0.0003), with preference for alfalfa decreasing and preference for tall fescue increasing from Day 1 to Day 4 (Fig. 1). This may be due to depletion of the most preferred leaves of the alfalfa sward over the course of the trial. Forage mass of alfalfa did not differ between pre- and postgrazing (Table 2); however, growth rate of the forage was not calculated and might account for the lack of difference between pre- and postgrazing forage mass. An interaction of treatment × day (P < 0.0001) was observed in the pattern of grazing preference (Fig. 2). From Day 1 to 2 the steers’ preference for alfalfa increased in the Novelty treatment period and by Day 4 had returned to a similar proportion as that observed on Day 1. Because these paddocks were unfamiliar to the steers, as was the alfalfa, the steers may have been sampling the new forage and exploring their new surroundings during the first 24 h. Introducing animals to novel foods in unfamiliar environments may cause animals to reject the novel food in favor of a familiar food (Burritt and Provenza, 1997). However, if animals are introduced to new pastures with companion animals or if the area is similar to familiar areas (as they were here), they are more likely to explore their new paddocks as opposed to exhibiting neophobia (Launchbaugh and Howery, 2005). Ganskopp and Cruz (1999) reported that cattle introduced to novel forages will show dietary preferences similar to that of experienced cattle within minutes of being offered the new forages. On Days 2 and 3, the steers increased their grazing time on alfalfa and perhaps were still determining what their preferred or optimal legume:grass ratio was going to be, then returned to a decreased proportion of time grazing alfalfa on Day 4. During the Experience treatment period, steers grazed more alfalfa on Day 1 than any other day (Fig. 2). Parsons et al. (1994) showed a similar pattern in ewes grazing 50:50 adjacent monocultures of perennial ryegrass and white clover with preference for clover being as follows: Day 1 = 81.2%, Day 3 = 68.0%, and Day 6 = 70.9%. Even though steers in the present study were grazing adjacent monocultures of tall fescue and alfalfa before the start of the Experience treatment period, the stimulus of being given a new allotment of fresh forage, along with their previously observed partial preference for alfalfa, likely led to this greater grazing time on Day 1 in alfalfa. Sheep have been shown to consume a greater proportion of ryegrass if their previous diet was white clover, and more white clover was consumed if their previous diet was perennial ryegrass (Parsons et al., 1994). While alfalfa was not absent from the area the steers grazed before they entered the Experience treatment paddocks, the most desirable leaves of the alfalfa may have been consumed from the sward by the time they were moved to the new paddocks and may have influenced their grazing pattern on Day 1.

Figure 1.

Proportion of time beef steers spent grazing forages in paddocks of alfalfa and tall fescue as adjacent monocultures. Within-forage means followed by the same lowercase letters are not different at P < 0.05.

 
Figure 2.

Proportion of time beef steers spent grazing forages in paddocks of alfalfa and tall fescue as adjacent monocultures when alfalfa was a novel forage (Novelty) and when steers had experience grazing both forages (Experience). Within treatment and forage, means followed by the same lowercase letters are not different at P < 0.05.

 

An effect of year (P = 0.02, SEM = 4.6) was observed for time spent grazing in each forage with grazing time in alfalfa being greater in Yr 2 (86.1%) than Yr 1 (62.8%) and, conversely, grazing time in tall fescue was greater in Yr 1 (37.2%) than Yr 2 (13.9%). This result may be due to differences in climate between years. Air temperatures in Yr 2 were hotter (Table 4) and year-to-date rainfall was less (479 vs. 443 mm) than in Yr 1. Sward conditions may have also influenced grazing time. Even though forage mass of tall fescue did not differ from Yr 1 to Yr 2 (2448 and 2286 ± 180 kg ha−1, respectively), the tall fescue in Yr 2 was observed to contain more dry and dead material, which may have made it less palatable than in Yr 1. Consequently, steers spent more time grazing alfalfa, which is more tolerant of drought conditions (Sheaffer and Evers, 2003). Crude protein of tall fescue in Yr 2 was less than in Yr 1 (150 and 178 ± 6 g kg−1, respectively) and may have impacted diet selection, particularly if animals were trying to maintain a particular ratio of C:N, which has been suggested as a factor influencing the selection of mixed diets in domestic ruminants (Rutter, 2006). A mixed diet of legumes and grasses will enable the animal to adjust the balance of energy to soluble protein and thus regulate ammonia accumulation in the rumen (Hill et al., 2009). Animals are likely able to balance their diets based on feedback from nutrients after eating particular foods (Provenza, 1995; Villalba and Provenza, 1999). Because of differences in the nutritive value of tall fescue between years (due to drought in Yr 2), the steers in Yr 2 may have been receiving a more positive postingestive feedback when eating alfalfa and thus preferred a greater proportion of alfalfa in their diet.


View Full Table | Close Full ViewTable 4.

Meteorological conditions during the experimental periods.

 
Air temperature
Morning
Afternoon
Treatment Day Precipitation Max. Min. Max. Min.
mm °C
Novelty
 Year 1 1 8 21 20 21 18
2 9 18 17 21 15
3 0 21 14 27 17
4 0 26 15 28 19
 Year 2 1 0 27 16 31 20
2 0 28 16 31 21
3 0 26 18 29 22
4 0 29 19 30 22
Experience
 Year 1 1 0 26 15 31 18
2 0 25 14 30 20
3 0 28 17 32 21
4 0 28 20 29 20
 Year 2 1 0 29 15 36 23
2 1 28 19 31 18
3 0 25 16 29 15
4 0 26 11 34 19

Diurnal Pattern of Behavior

Across treatments, the proportion of grazing time in alfalfa was greater (P = 0.02, SEM = 3.3) in the afternoon (76.8%) than in the morning (72.1%) and, conversely, proportion of grazing time in tall fescue was greater in the morning (27.9%) than in the afternoon (23.2%). No interaction of treatment × time of day (P = 0.60) was observed for the proportion of time spent grazing within each forage type; both morning and afternoon grazing times were similar between Novelty and Experience treatments (Table 5). Within treatments, proportions of time spent grazing in morning and afternoon periods of the day also did not differ (Table 5). Sheep and cattle grazing perennial ryegrass and white clover adjacent monocultures were reported to have a diurnal pattern of preference, with greater preference for white clover in the morning than in the afternoon (Parsons et al., 1994; Rutter et al., 2004a, 2004b). Boland et al. (2011) evaluated different spatial allocations of tall fescue and alfalfa and had similar results to the present experiment, with no decrease in preference for alfalfa over the course of the day and no increase in preference for tall fescue in the afternoon, both of which are contrary to past studies. Parsons et al. (1994) reported that ewes differing in physiological state (dry or lactating) and background diet (ryegrass/white clover adjacent monoculture, ryegrass only, or white clover only) showed a decrease in preference for white clover from morning to afternoon. In that study, the greater proportion of clover in the diet would return again the following morning. Observations of greater rumination time after eating ryegrass compared with white clover in previous research (Penning et al., 1991) leads to an explanation of why ruminants have been observed to graze more ryegrass in the afternoon (Parsons et al., 1994). If rumination time is less after eating white clover, this means the animal will start grazing again sooner than it would after eating and ruminating ryegrass. Domestic ruminants generally have longer periods of rumination at night when it does not interfere with major periods of intake during the day (Parsons et al., 1994). Being less active at night also puts the animal at less risk of predation (Gluesing et al., 1980). The slower passage and greater time needed to ruminate after eating grass is due to its greater fiber concentration (Rutter, 2006). Steers in the present study did not appear to utilize this strategy because fiber was greater in tall fescue than in alfalfa (Table 1).


View Full Table | Close Full ViewTable 5.

Proportion of time† in the morning (AM) and afternoon (PM) spent grazing in alfalfa and tall fescue when forages were offered as adjacent monocultures.

 
Treatment
Novelty
Experience
Forage AM PM AM PM
Alfalfa 75.3ab‡ 78.6a 68.9b 74.9ab
Tall fescue 24.7ab 21.4b 31.1a 25.1ab
SEM = 4.8
Within rows, means followed by the same letters are not different at P < 0.05.

Carbohydrate concentrations increase over the course of a day due to net photosynthesis, respiration, and translocation in the plant (Mayland et al., 2005). Concentration of total nonstructural carbohydrates (TNC) has also been shown to influence diet preference of cattle and sheep. Most notable has been the greater preference for tall fescue and alfalfa hays cut in the afternoon (containing greater TNC) compared with hays cut in the morning (Fisher et al., 1999, 2002; Mayland et al., 2000b). Greater concentration of water-soluble carbohydrates (WSC) have been linked to greater preference in grazed forages as well (Ciavarella et al., 2000). In the present study, however, WSC did not differ between forage species at either time of day (Table 6) and thus would presumably not influence preference. Nonfiber carbohydrates (NFC) were calculated in this study (TNC + organic acids and soluble fiber) and were greater in alfalfa at both times of day, so organic acids and/or soluble fiber may be influencing the greater preference for alfalfa. However, Mayland et al. (2000a) reported that organic acid concentration was not related to diet preference of cattle among eight tall fescue cultivars.


View Full Table | Close Full ViewTable 6

Carbohydrate fractions of forages being grazed by beef steers as adjacent monocultures.

 
Forage Time-of-day interval† NFC‡ WSC ESC Starch
g kg −1 dry matter
Alfalfa Morning 318b§ 83b 67b 16
Afternoon 360a 105a 90a 21
Tall fescue Morning 221d 85b 61b 12
Afternoon 258c 114a 93a 18
SEM 8.2 4.9 3.3 2.6
Morning, 0730 to 0830 h; Afternoon, 1700 and 1800 h.
NFC = nonfiber carbohydrates (simple sugars, fructans, soluble fiber, organic acids); WSC = water-soluble carbohydrates (simple sugars, fructans); ESC = ethanol-soluble carbohydrates (simple sugars).
§Within columns, means followed by the same letters are not different at P < 0.05.

Steers’ bite rate was greater (P = 0.0002, SEM = 1.5) while grazing alfalfa (66 bites min−1) compared with tall fescue (63 bites min−1). Bite rate during the time when alfalfa was a novel forage was less (P < 0.0001, SEM = 1.5; 62 bites min−1) than during the Experience treatment period (66 bites min−1). Increase in bite rate with experience has also been previously reported. Phillips and Youssef (2003b) reported that lambs had lower bite rates on forage they were not experienced with, and then bite rates increased after they became experienced with the forage. Bite rate was not affected by TOD (P = 0.48, 64 ± 1.6 bites min−1) and no interactions were significant (P ≥ 0.30).

Standing and Lying Behavior

No effect of year (P = 0.53) on the amount of time spent standing in either forage type was observed. An effect of treatment (P = 0.001) was observed, with steers standing in the alfalfa more during the Novelty than in the Experience treatment period, but neither proportion was different (P ≥ 0.12) from 50% (the proportion of forage offered) so animals did not show a clear preference for where they stand (Table 3). An effect of day (P = 0.002, SEM = 1.7) was observed as the percentage of time standing in alfalfa decreased from 51% on Day 1 to 45% on Day 4. Steers spent a disproportionate amount of time lying in the tall fescue in both the Novelty and Experience treatment periods (Table 3). The percentage of time spent lying in tall fescue was greater in Yr 1 than Yr 2 (95 and 88%, respectively; P = 0.002, SEM = 1.5). The proportion of time spent lying in tall fescue was greater (P < 0.0001) than the 50% of tall fescue area available, so this result indicates that steers had a partial preference to lie on tall fescue rather than alfalfa. This preference may have arisen because the alfalfa was taller and had a lower proportion of leaf mass than tall fescue, perhaps making the alfalfa area less comfortable to the steers. Cattle generally prefer to lie on areas that provide more cushion to their body (Drissler et al., 2005).

Overall Grazing Behavior

The proportion of the day spent grazing (overall on both forages) was less (P = 0.0001, Fig. 3) during the Novelty treatment period (39.7%) than in the Experience (46.1%). This difference also created a difference in time spent idling, with greater (P < 0.0001) idling time in the Novelty treatment period (35.3%) than in the Experience (26.2%). Movement to unfamiliar pastures may cause short-term (1 to 2 d) changes in behavior, such as increased walking along the fence-line or idling; however, cattle have been shown to adapt quickly to new surroundings (McIlvain and Shoop, 1971). Lambs with previous experience grazing perennial ryegrass were shown to graze more than lambs that were inexperienced (496 vs. 447 min d−1, respectively; Phillips and Youssef, 2003b). Conversely, Ganskopp and Cruz (1999) reported that steers offered novel forages had longer grazing sessions than steers experienced with all forages being evaluated; however, the difference was not significant (39 and 35 min, respectively; P = 0.17). Steers were observed to graze predominantly in the alfalfa within the first 24 h of the Novelty treatment period, indicating that they readily adapted to this new forage.

Figure 3.

Proportion of day beef steers spent grazing, ruminating, and idling when grazing paddocks of alfalfa and tall fescue as adjacent monocultures when alfalfa was a novel forage (Novelty) and when steers had experience grazing both forages (Experience). SEM: grazing = 1.0, ruminating = 1.9, idling = 1.5. Within-behavior means followed by the same lowercase letters are not different at P < 0.05.

 

A year effect was observed for time spent grazing (P = 0.02, SEM = 1.0) and idling (P = 0.03, SEM = 1.8). Overall grazing time per day in Yr 2 was less than in Yr 1 (40.1 and 45.7%, respectively), while idling time in Yr 2 was more than in Yr 1 (34.6 and 26.8%, respectively). Increased afternoon temperatures in Yr 2 may have contributed to the decrease in grazing time (Table 4). Bos taurus cattle begin to decrease feed intake as air temperature approaches 28°C, and cease intake completely at 41°C (Findlay, 1958).

No effect of year or day on number of prehensions was observed (34,754 ± 2303 prehensions d−1, P ≥ 0.12); however, the number of prehensions did differ by treatment (P < 0.0001). Daily number of prehensions was greater during the Experience treatment period (39,482) than during the Novelty treatment period (30,026). This difference is probably due to the greater proportion of the day spent grazing by steers in the Experience treatment period (Fig. 3). No effect of year (26.4 ± 2.4%, P = 0.52) on time spent ruminating per day was observed, with trends for day (P = 0.07) and treatment (P = 0.09; Fig. 3). Similarly, no effect of year, day, or treatment (33,133 ± 3737 mastications d−1, P ≥ 0.37) on number of mastications by steers was found. Daily numbers of mastications during the Novelty and Experience treatment periods were 32,050 and 34,215 ± 2895, respectively.


CONCLUSIONS

Forage novelty did have an effect on the grazing behavior of steers in this experiment. Steers spent more time grazing the novel forage alfalfa than grazing tall fescue. Cattle without previous experience eating alfalfa spent more of their grazing time eating alfalfa than after having had experience grazing alfalfa. However, a partial preference for alfalfa was observed regardless of whether cattle were naïve or experienced with alfalfa. These results are consistent with those of Boland et al. (2011), supporting the theory that domestic ruminants have a partial preference for legumes over grasses. The partial preference for alfalfa in the present study is within the range of values reported for preference of other legumes offered as 50:50 adjacent monocultures with ryegrass. Differences in weather and sward conditions may have led to partial preference variations from one year to another, but still indicate preference for legume. The present study also showed that previously observed diurnal patterns of preference (increased preference for grass in the afternoon) may not always occur. The exact mechanisms that determine overall and diurnal patterns of preference remain elusive; however, this new information may help to narrow down future areas of evaluation. Additional studies on diet composition and grazing management of tall fescue and alfalfa (and other forage combinations) as adjacent monocultures over an extended period is needed to observe if partial preference varies over longer periods of time and changing sward conditions. Such research would help in determining the strategies being used by the animal that drive diet selection.

 

References

Footnotes


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