Cattle generalise visual cues from the pen to the field to select initial feeding patches

Applied Animal Behaviour Science 109 (2008) 128–140 www.elsevier.com/locate/applanim

Cattle generalise visual cues from the pen to the field to select initial feeding patches Wilma J. Renken a,*, Larry D. Howery a, George B. Ruyle a, R. Mark Enns b a

School of Natural Resources, The University of Arizona, 325 Biological Sciences East, Tucson, AZ 85721, USA b Colorado State University, Department of Animal Sciences, Ft. Collins, CO 85023, USA Accepted 27 March 2007 Available online 9 May 2007

Abstract Free-grazing ruminants forage in environments containing multiple levels of complexity; the forage selection process operates at the landscape scale, when selecting feeding sites, and at the plant part level when selecting actual bites. Pen trials have shown that livestock associate visual cues with feeding sites, however, no field study has shown that animals generalise from training with visual cues in pens in order to choose feeding sites in the field. Our study tested nine beef heifers’ ability to generalise a learned visual cue association to select feeding sites in a rangeland setting offering a novel forage, Lehmann lovegrass (LL). Initially, animals were trained to associate high quality feed with a visual cue during pen trials. We then tested animal response to the cue before and after they gained 14-day grazing experience with LL. Two identical field experiments (i.e., novel, before animals had experienced foraging LL versus familiar, after the animals had 14-day grazing experience with LL) were conducted over 3-day periods. Each experiment consisted of 27, 10-min trials. Animals were tested in plots containing high quality (HQ) and low quality (LQ) LL patches. For each trial, one of three randomly selected scenarios was presented: (1) the visual cue was placed in the HQ patch, (2) the visual cue was placed in the LQ patch, or (3) no visual cue was placed in either patch. Dependent variables were first patch-type chosen, bite rate in each patch, and number of observations of grazing in each patch. Cue presence influenced initial patch choice, bite rate, and grazing tallies within patch type. Heifers took 212 more HQ bites than LQ bites when the cue was placed in the HQ patch (P < 0.04), but took only 45 more HQ bites than LQ bites when the cue was placed in the LQ patch (P < 0.02). Heifers took 135 more bites from the HQ patch than the LQ patch when no cue was present (P < 0.02). Heifers clearly preferred HQ patches over LQ patches regardless of cue presence or absence, but grazed more in HQ and LQ patches when the cue was placed in those patches. The number of grazing tallies was directly related to bite rate within a patch. Animals grazed more in HQ than LQ patches when no cue

* Corresponding author. Present address: USDA-NRCS Willcox Field Office, 656 N. Bisbee Avenue, Willcox, AZ 85643, USA. Tel.: +1 520 384 2229x117; fax: +1 520 384 3571. E-mail address: [email protected] (W.J. Renken). 0168-1591/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.applanim.2007.03.014

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was present. Visual cue placement altered this pattern; animals increased grazing in cued patches regardless of quality. Grazing experience did not influence observed grazing behaviour or the influence of the visual cue. # 2007 Elsevier B.V. All rights reserved. Keywords: Cattle; Generalisation; Visual cues; Patch selection; Foraging behaviour; Rangelands

1. Introduction Free-grazing livestock use all of their senses to evaluate abiotic and biotic factors when selecting feeding sites (Howery et al., 2000). Both abiotic and biotic factors influence animal distribution patterns across rangelands, however, the process influencing selection at the patch and feeding site level of the foraging hierarchy is poorly understood (Senft et al., 1987). Bailey (2005) proposed a conceptual model that described how animals rate individual feeding sites based on abiotic and biotic factors. According to this model, animals rank good, intermediate and poor feeding sites, and use spatial memory to select sites that maximize nutrient intake, minimize travel effort, and maintain comfort (e.g., thermoneutrality, predator avoidance). Finding and exploiting forage resources on rangelands requires animals to locate positions on the landscape to focus feeding efforts (within four levels of a spatial hierarchy decreasing from feeding site, patch, feeding station, to bite). A feeding site is a landscape-scale area in which freegrazing animals spend up to 4 h feeding within various patches (plant community scale). Feeding stations are positions where bites are taken within these patches (Bailey et al., 1996). Selection of an individual patch may depend upon visual cues indicative of forage quality or quantity (Bazely, 1990; Renken et al., 1998; WallisDeVries et al., 1999) and the size of the patch itself. WallisDeVries et al. (1999) found that steers feeding in an irrigated pasture with experimentally controlled short, high-quality patches exhibited non-random foraging patterns with animals seeking and selecting course-grained (5 m  5 m) high-quality patches but smaller (2 m  2 m) patches were not differentiated from the whole sward. Free-grazing cattle on Lehmann lovegrass (LL) dominated rangelands rigidly maintained patches of shorter, higher quality vegetal shoots by concentrating grazing efforts on previously grazed patches (Ruyle et al., 1988), apparently exhibiting adaptive behaviour to maintain nutrient and digestible energy intake per unit of time (Demment and Greenwood, 1988). Generalisation, the tendency of animals to respond similarly to like stimuli within different environmental contexts (Barker, 1997), may help ruminants adapt to new foraging challenges across the scales of foraging hierarchy (Senft et al., 1987). Livestock use flavour generalisation and post-ingestive feedback to select nutrients, avoid phytotoxins, and accept novel foods (Launchbaugh and Provenza, 1994; Launchbaugh et al., 1997; Villalba and Provenza, 2000). At the patch level, animals may use visual cue generalisation to select and return to preferred foraging sites (Senft et al., 1987), and to avoid painful stimuli (electric shock) (Cibils et al., 2004). In controlled studies, visual cues helped large ungulates select preferred forages and feeding areas (Edwards et al., 1997; Renken et al., 1998; Howery et al., 2000) and avoid electric shock (Cibils et al., 2004). However, no research has been conducted on how visual cues may influence cattle foraging behaviour under field conditions. Increasing our understanding of how livestock use visual cues during grazing bouts may lead to additional insights on what controls livestock distribution. Further, the development of management techniques to increase utilisation

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of low quality forage while alleviating patch grazing or other problems associated with uneven livestock distribution (Howery et al., 2000). The objective of this field study was to assess whether cattle could generalise training with visual cues in pens to using those same cues to help choose high quality (HQ) and low quality (LQ) feeding sites in a rangeland pasture dominated by a monoculture of Lehmann lovegrass (Eragrostis lehmanniana, Nees), a warm season perennial bunchgrass from South Africa. Two hypotheses were tested: (1) heifers trained to associate a visual cue with a HQ food in pens will generalise the cue to select feeding patches on rangeland and (2) heifers naı¨ve to LL will forage less efficiently than experienced heifers, as indicated by lower bite rates and grazing times. Justification for hypothesis 2 comes from previous research indicating that, as free-ranging cattle gain experience with LL and other forage plants, they increasingly concentrate their grazing efforts on previously grazed patches (Demment and Greenwood, 1988; Ruyle et al., 1988). 2. Methods and materials 2.1. Animals and training procedures Ten heifers, four Angus (281  13 kg, 14 mo of age) and six Hereford (446  9 kg, 18 mo of age) were used as study animals. Most ranches in the western United States of America operate multiple breed cow-calf herds. We used heifers of two common breeds to simulate the practice of introducing replacement heifers to a novel grazing environment. Prior to this study, all heifers were naı¨ve to LL but had previous experience grazing native bunchgrass pastures in Arizona, USA. Heifers were separated by liveweight and housed in two adjacent holding pens (five animals/pen). Because Angus heifers weighed less than Hereford heifers, the lightest weight Hereford was housed with the four Angus heifers. A 30-day conditioning phase was conducted at the University of Arizona’s West Campus Agricultural Center, Tucson, Arizona, USA. During the 30-day conditioning phase, individual heifers were trained to associate an orange traffic cone (66 cm height  16.5 cm basal diam., 5 cm top diam.) with a protein supplement (15% protein) in a training pen located out of sight (about 100 m) from the holding pens. We selected a traffic cone as the visual cue because it was a novel object for the study animals and not found on rangelands. The training pen contained two feeding tubs (24.5 cm diam., 10.2 cm depth) placed about 4 m apart. The visual cue was placed beside one feed tub that contained 0.5 kg protein supplement. The other tub with no visual cue contained no food. The location of the container that held the food and the visual cue were randomly altered each day so that animals learned the visual cue was always associated with food irrespective of cue location. Training allowed the individual heifers to associate the location of HQ feed with a visual cue and to become tractable by becoming accustomed to being removed from penmates. Each heifer was exposed to the cue twice daily, once in the morning and once in the afternoon, for 30-day. Daily morning and afternoon training sessions were conducted about 6 h apart. An individual training session ended after a heifer had completely consumed the protein supplement, or after 15 min, whichever came first. Animals almost always completely consumed the protein supplement before the 15-min trial ended. Heifers were fed alfalfa hay (total 9 kg/head/day) in their holding pens after the afternoon training session was complete. 2.2. Field site The field site consisted of semi-desert grassland dominated by a monoculture of LL, located on the University of Arizona’s Santa Rita Experimental Range, 45 km southeast of Tucson, USA (318410 N, 1008370 W). A barbed-wire enclosure delineated 32 LL grazing plots (25 m  25 m each) bisected by an alley (Fig. 1). A holding pen and a sorting pen were constructed in the northwest end of the enclosure. Six areas adjacent to the holding and sorting pens were designated as non-trial buffer areas.

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Fig. 1. Enclosure layout and visual cue (D) treatment assignment used for naı¨ve trials. Heifers were housed in the holding pen at the northwest corner of the enclosure. Each square represents 25 m  25 m grazing plot containing high quality (HQ, hatched) and low quality (LQ, no hatch) Lehmann lovegrass feeding sites. Entrances to grazing plots were equally located on the either the HQ or LQ side of a plot. Naı¨ve and experienced with Lehmann lovegrass trials were conducted over 3-day periods (D1 = no shading, D2 = light shading, D3 = dark shading) during which nine heifers (1–9) were exposed to one of the following treatments each day: (1) visual cue in HQ patch, (2) visual cue in LQ patch, or (3) no visual cue in either patch. For the experienced trials, heifers were not exposed to the same plots to which they were exposed in naı¨ve trials.

Previous research has shown that cows preferentially return to heavily grazed patches of LL which results in a pattern with heavily grazed patches surrounded by lightly grazed or ungrazed areas (Ruyle et al., 1988). Dry matter digestibility of the heavily grazed LL patches is greater than in ungrazed patches (Renken et al., 1995). Randomly mowing and fertilizing either the north or south half of each grazing plot in late June, prior to summer rainfall, created HQ forage patches opposing the untreated LQ forage patch. Lehmann lovegrass was mowed to a 2.5 cm stubble height, then urea and phosphorus were applied at rates of 25 kg N/ha and 12 kg P/ha (Stroehlein et al., 1969). The untreated half of each plot served as a LQ forage patch.

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Incidental grazing experience was minimized by mowing all LL to ground level within the holding pen, sorting pen, and alley 1 day prior to the arrival of the experimental animals. At this time, LL tiller (vegetative shoots) production had ceased and negligible re-growth occurred during the experimental periods. 2.3. Field experiments with naı¨ve and experience animals During October 1998, we conducted two, identical 3-day field experiments using nine of the 10 heifers (six Hereford, three Angus). The tenth heifer (Angus) was trained and transported to the field site to be used as a possible substitute in the event that one of the other heifers became sick, injured, or intractable at the field site; however it did not become necessary to use the substitute heifer in the experiment. The first experiment was carried out when the heifers were naı¨ve to LL. The second experiment was conducted after heifers gained 14-day grazing experience within a nearby, lightly grazed pasture dominated by LL. Trials were scheduled to coincide with peak LL standing crop. Heifers were transported to a single holding pen 2 days before each experiment to introduce or reacquaint the animals to the field study site. Each heifer was individually walked to the end of the 250 m alley and fed 0.25 kg protein supplement placed in a cue-marked feed tub. This procedure was conducted for each individual heifer, in no particular order, twice in the morning and then repeated in the afternoon. The primary purpose of the 2-day period before experimentation was to reacquaint animals with the use of visual cues within the field study site. Heifers were not allowed to enter the grazing plots and no data were collected during the 2-day adaptation period. Each experiment consisted of 27, 10-min grazing trials (three trials/heifer) over a 3-day period with cue placement being the treatment. For each grazing trial, the cue was placed in the centre of either the HQ patch, the LQ patch, or no cue was present within the 625 m2 grazing plot. Each heifer was individually herded into a grazing plot, evaluated for 10 min, and returned to the holding pen before the next heifer’s trial was conducted. Order of heifer trials was consistent for each of the 3 experimental days. Entrances to grazing plots were made equally into the HQ and LQ side of a plot, allowing heifers the same amount of initial exposure to HQ and LQ patches throughout the experiment. The three treatments were randomly assigned so that each heifer was exposed to one treatment/day over three consecutive days. Two observers were present during the experiments. One observer recorded the first patch type selected and activity (grazing, moving, or any activity other than grazing or moving, e.g., standing, scratching, defecating) plus location (HQ or LQ patch) by scan sampling every 15 s (Howery et al., 2000). First patch selected was defined as the patch type (HQ or LQ) from which a heifer took two consecutive bites without moving her front feet. Only grazing activity tallies were analyzed due to the small number of non-grazing tallies during activity scan sampling (<8% of all tallies). The second observer recorded the number of bites a heifer took within each patch. A bite was recorded when the heifer’s jaw moved upward and the observer heard the bite tearing the plant. The first observer remained outside the grazing plot and the second observer moved into the grazing plot only as necessary to hear bites, but did not move within the heifer’s flight zone (5 m). A grazing plot was used only once during each experiment to avoid possible visual or olfactory cues (grazed plants or excretory odours) influencing animal behaviour. Each heifer was introduced to a nonadjacent grazing plot from the previous day to prevent animals from using landmarks (e.g., shrubs, fence posts) to make grazing site selections. After accounting for moving animals to and from grazing plots, daily trials typically took about 4 h (about 06:00–10:00 h) after which animals were fed alfalfa hay (about 9 kg/ head) in the holding pen. Water and shade were available at all times within the holding pen. 2.4. Patch forage quality analyses Morphological and chemical techniques were used to analyze forage quality of HQ and LQ patches. Prior to both experiments, 10 grazing plots were randomly selected for tiller height measurement and biomass collections. Five quadrats (0.16 m2/quadrat) were placed in both patch types, the heights of five tillers from within each quadrat were measured and quadrat biomass was clipped to ground level.

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LL biomass was manually separated into live (green) leaves, senescent (yellow or brown leaves), live (green) stems, senescent (yellow or brown) stems and inflorescences. Leaf:stem biomass ratio, live:senescent biomass ratio, and total standing biomass (kg/ha) were calculated from oven-dry weights. Total nitrogen and phosphorus analyses (Association of Official Analytical Chemists, 1990) were used to determine percentage crude protein (%CP) and phosphorus (%P) of the separated biomass components. 2.5. Experimental design 2.5.1. Animal behaviour Each experiment was blocked into three Latin Squares comprising a Latin Rectangle (Kuehl, 1994) with nine columns and three rows consisting of heifers and trial days, respectively. Nine heifers were assigned to the three Latin Squares which were blocked by breed. Treatment effects were cue in HQ patch, cue in LQ patch, or no cue present. Each Latin Square was randomized by heifer and treatment effect. First patch chosen, total number of bites, and grazing time (measured as the number of activity tallies that animals were observed actively grazing) were recorded for each patch. Animals were allowed free choice within either grazing patch, thus an inverse relationship existed between number of bites and grazing tallies in opposing patch types making direct analysis of the dependent variables measured in both patches inappropriate. Thus, we analyzed differences between dependent variables (e.g., HQ bites minus LQ bites) to discern differences in grazing behaviour among treatments. The outcome variables were bite difference and grazing tally difference. Experience effect was analyzed comparing naı¨ve versus experienced data. Data were analyzed with a mixed-effects model appropriate for repeated measures using the ‘‘mixed’’ procedure of SAS (1996). The mixed model analysis appropriately accounts for the random nature of animals chosen for this study and for fixed effects (Littell et al., 1998). Random effects were heifer and trial day; the fixed effect was cue placement. Unstructured covariance was chosen using Akaike Information Criterion (AIC). AIC (Akaike, 1973) are essentially log likelihood values that have been penalised for the number of parameters estimated (Littell et al., 1996). The first patch chosen was analyzed separately for the naı¨ve and experienced trials with a Chi-square test for independence. The Tukey–Kramer adjustment was used to determine mean differences (P = 0.05) when F-tests were significant (P < 0.05). On the first day of the naı¨ve experiment, one Hereford heifer escaped the grazing plot. Each datum for this trial was replaced with a calculated value (Y) using the equation: Y = [r(R + C + T)  2G]/ [(r  1)(r  2)], where R, C, and T are the totals of the observed values for the row, column, and treatment containing the missing value and G is the grand total of the observed valued; r is the number of experimental units per treatment (Steel and Torrie, 1980). 2.5.2. Patch forage quality We used Student’s t-test to analyze differences between the following HQ and LQ patch characteristics: total patch forage biomass (kg/ha); tiller height (cm); leaf:stem biomass ratio; live:senescent biomass ratio; live forage %CP and %P; and senescent forage %CP and %P. Forage biomass collections from naı¨ve and experienced experiments were analyzed separately.

3. Results 3.1. Patch forage quality Morphological and chemical analysis confirmed higher forage quality within the HQ patches compared to the LQ patches for both experiments (Table 1). Tiller lengths in HQ patches were shorter (P < 0.001) than in LQ patches. The HQ patches had higher (P < 0.05) leaf:stem biomass ratio, live:senescent biomass ratio, %CP, and %P compared to LQ patches. Overall

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Experiment

Morphological characteristic

Patch type

Biomass (kg/ha)

Tiller height (cm)

Chemical characteristic Leaf:stem

Naı¨ve Low quality High quality

2220  140 a* 2000  110 a

59  1 a 53  1 b

0.6  0.05 a 0.7  0.05 b

Experienced Low quality High quality

1820  110 a* 1320  60 b

60  1 a 55  1 b

0.7  0.04 a 0.8  0.03 b

*

Values followed by different characters are significant at a = 0.05.

Live:senescent

%Crude protein

%Phosphorus

Live

Senescent

Live

Senescent

1.7  0.10 a 3.8  0.31 b

5.6  0.49 a 10.5  0.98 b

3.7  0.24 a 6.4  0.32 b

0.11  0.008 a 0.14  0.044 b

0.06  0.006 a 0.09  0.013 b

1.1  0.13 a 2.0  0.12 b

6.5  0.62 a 11.2  0.97 b

4.3  0.18 a 7.4  0.50 b

0.11  0.012 a 0.14  0.013 b

0.06  0.005 a 0.09  0.009 b

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Table 1 Morphological and chemical analyses of high quality and low quality Lehmann lovegrass patches for heifers that were naı¨ve and experienced with grazing Lehmann lovegrass trial periods, Santa Rita Experimental Range, Arizona, USA, October 1998

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Table 2 Least square means for number of bites (standard error) from mixed model analysis taken by nine heifers in high quality (HQ) patches, low quality (LQ) patches and the difference between number of patch bites recorded when a visual cue was placed in a HQ patch (C/HQ), a LQ patch (C/LQ), or when no cue was present in either patch (NC). Santa Rita Experimental Range, Arizona, October 1998 Cue placement

C/HQ C/LQ NC *

LS mean number of bites HQ patch

LQ patch

Difference*

234  17 138  17 197  17

22  10 101  10 53  10

212 a  37 45 b  36 135 c  36

Values followed by different characters are significant at P < 0.05.

standing biomass did not differ (P > 0.10) between patches during the naı¨ve experiment but differed during the experienced experiment (P < 0.05) with LQ patches having more total biomass than HQ patches. 3.2. Grazing behaviour 3.2.1. Number of bites in patches There was no interaction between cue and experience (P > 0.10) for number of bites or grazing tallies indicating that 2 weeks of LL grazing experience did not influence those dependent variables. Thus, we report the remaining results as one experiment, pooling experience. Although heifers preferred HQ patches in all treatments, visual cue placement apparently influenced animals to increase their number of bites in cued HQ and LQ patches. Heifers took 212 more HQ patch bites than LQ patch bites when the cue was placed in the HQ patch (P < 0.04), but took only 45 more HQ patch bites than LQ patch bites when the cue was in the LQ patch (P < 0.02) (Table 2). Heifers took 135 more bites from HQ patches than from LQ patches when no cue was present. Statistical analyses detected no difference (P > 0.46) in total bites across the three visual cue treatments (range = 225–255 bites/10 min trial). 3.2.2. Grazing activity Grazing activity within a patch confirmed the heifers’ apparent preference for HQ patches in the absence of visual cues, as well as the influence of visual cue placement in both HQ and LQ patches. When the cue was placed in the HQ patch, the HQ patch grazing tally had 31 more Table 3 Least square means for number of grazing tallies (standard error) from mixed model analysis for nine heifers in high quality (HQ) patches, low quality (LQ) patches and the difference between patch grazing tally recorded when a visual cue was placed in a HQ patch (C/HQ), a LQ patch (C/LQ), or when no cue was present in either patch (NC). Santa Rita Experimental Range, Arizona, October 1998 Cue placement

C/HQ C/LQ NC *

Grazing tallies HQ patch

LQ patch

Difference*

35  2 21  2 25  2

44 17  4 94

31 a  5 4 b5 21 a  5

Values followed by different characters are significant at P < 0.05.

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Table 4 First patch type selected by naive and experienced heifers when a visual cue was placed in a high quality (HQ) patch (C/ HQ), a low quality (LQ) patch (C/LQ), or no cue was present in either patch (NC). Chi-square analysis showed significant differences in cued patch selection by naı¨ve (P = 0.011) and experienced (P = 0.003) heifers. Santa Rita Experimental Range, Arizona, October 1998 Cue placement

Number of trials First patch selected by naı¨ve heifers

First patch selected by experienced heifers

Totals

HQ

LQ

HQ

LQ

HQ

LQ

C/HQ C/LQ NC

9 3 5

0 6 4

8 1 6

1 8 3

17 4 11

1 14 7

Totals

17

10

15

12

32

22

observations than LQ patches (P < 0.07). When the cue was placed in the LQ patch, the HQ patch grazing tally had only 4 more observations than LQ patches (P < 0.002). When no cue was present, the HQ patch grazing tally had 21 more observations than LQ patches (P < 0.10; Table 3). Thus, grazing tallies closely mirrored bite data in that visual cue placement caused animals to increase grazing in cued HQ and LQ patches. 3.2.3. First forage-type Initial patch selection depended upon cue location for both naı¨ve (P = 0.012) and experienced heifers (P = 0.003) (Table 4). Naı¨ve heifers initiated grazing in the HQ patch during all nine trials when the cue was placed in the HQ patch, and initially chose the LQ patch in six of nine trials when the cue was placed in the LQ patch. When no cue was present, naı¨ve heifers chose the HQ patch in five of nine trials. Experienced heifers initiated grazing in the HQ patch eight of nine trials when the cue was placed in the HQ patch, and also initially selected the LQ patch in eight of nine trials when the cue was placed in the LQ patch. When no cue was present, experienced heifers chose the HQ patch in six of nine trials. Collectively, naı¨ve and experienced heifers initially chose the HQ patch 17 of 18 trials when the cue was placed in the HQ patch, they selected the LQ patch first in 14 of 18 trials when the cue was placed in the LQ patch, and chose the HQ patch 11 of 18 trials when no cue was placed in either patch. 4. Discussion Our study demonstrated that cattle learned to generalise positive feeding consequences associated with visual cue training from the pen to the field. Visual cues greatly influenced patch selection, number of bites, and grazing tallies in both HQ and LQ patches in a LL monoculture. Heifers were initially drawn away from HQ patches when the cue was placed in a LQ patch, however, various sensory (i.e. tactile and gustatory responses to forage characteristics) and possible post-ingestive feedback may have overridden the influence of visual cue placement soon after the heifers sampled LQ patches (Launchbaugh et al., 2001). High quality patches were favoured in all treatments regardless of cue placement indicating that heifers were able to quickly sense the disparity between LQ and HQ patches.

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4.1. Grazing experience Biting rate and patch choices of heifers did not change after 2 weeks of LL grazing experience. Prior grazing experience at a young age with particular plant forms (e.g., bunchgrasses) helps animals adapt to varied grazing conditions (Provenza et al., 2003). Heifers in our study had previous experience grazing native bunchgrass pastures in Arizona which likely enhanced their ability to quickly adapt to the non-native bunchgrass, LL dominated, rangelands even though they had not had prior experience with LL. In an Oregon study (Ganskopp and Cruz, 1999), naı¨ve animals had previously grazed two forage species (i.e., tall fescue Festuca arundinacea Schreb. in the summer, and meadow foxtail Alopecurus pratensis L. in winter) but were unfamiliar with eight experimental bunchgrass species prior to the study. Ganskopp and Cruz (1999) reported that naı¨ve steers adjusted their grazing behaviour within minutes to nearly match preferences shown by experienced steers. 4.2. Generalisation Heifers in our study were given a choice between two distinct patches of LL that varied in forage quality (HQ versus LQ). Heifers were previously trained in pens to associate a HQ food reward with a visual cue. Heifers generalised their visual cue training in pens to make initial patch selections in the field (Table 4). Generalisation of visual cues may help rangeland livestock reduce the complexity of locating adequate food and habitats over large, variable landscapes. Livestock can remember the spatial location of HQ forage locations for up to 8 h in mazes (Bailey et al., 1989) but nutrients and toxins constantly change across space and time, limiting the efficacy of using only spatial memory to procure adequate diets on rangelands. Generalising visual cues from one foraging environment to the next would reduce the need for building a vast spatial memory of different grazing environments and also help free-grazing animals adjust more quickly to unfamiliar grazing situations (Howery et al., 2000). Although heifers used the visual cue to make their initial patch selection (Table 2), they ultimately took the majority of their bites from HQ patches regardless of cue placement (Tables 2 and 3). Heifers apparently relied on their senses of smell and taste (discussed in Section 4.4, below), and possibly their sense of touch, to decide whether or not to stay in the patch they first selected (Tables 2 and 3). Although naı¨ve heifers had never seen LL, previous experience grazing native rangeland likely improved their ability to use all of their senses to discern differences between patch quality during this study. 4.3. Visual cue influence The HQ patch was preferred in every treatment but cue location strongly influenced initial patch selection, bite rate, and grazing tallies in both HQ and LQ patches. Our study demonstrated that heifers used the visual cue to locate their first patch. For the two cued treatments, heifers typically traveled directly to the visual cue and immediately started grazing nearby regardless of whether the cue was placed in the HQ or LQ patch (Table 4). When the cue was in the HQ patch, heifers typically remained in the HQ patch for the majority of the 10 min trial (Tables 2 and 3). When the cue was in the LQ patch, heifers took several bites around the cue, but then left the LQ patch in favour of the HQ patch (Tables 2 and 3). When neither patch was cued, heifers slightly favoured the HQ patch (Tables 2–4).

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The overall trend of animals spending more time and taking more bites from HQ patches indicates that heifers may have been selecting for nutrient density. Choice selection trials have demonstrated that sheep can visually discriminate brightness cues (Bazely and Ensor, 1989), and that cows select colour cues paired with grey-scale cues (Dabrowska et al., 1981). Bazely (1990) reported that sheep selected darker green perennial ryegrass that contained higher protein content over lighter green perennial ryegrass that contained lower protein content. Thus in our study, the shorter, greener sward of the HQ patch may itself have been a visual cue given that the heifers had previous experience grazing native bunchgrasses. 4.4. Post-ingestive feedback (PIF) Previous research has demonstrated that ruminants associate the flavour of a food (i.e., taste and smell) with its post-ingestive feedback (PIF). Ruminants quickly learn to associate positive PIF with nutritious foods, and negative PIF with foods that contain toxins, excessive nutrients, or inadequate nutrients (Provenza et al., 2003). While specific patch selection and feeding effort were influenced by the visual cue, heifers in our study took more bites and grazed more in HQ patches regardless of cue presence or absence. The HQ patches were higher in digestibility (i.e. higher leaf:stem) and nutrient density than LQ patches (Table 1). Although visual cues in our study increased the probability of animals initially visiting and consuming more food in both HQ and LQ patches, positive PIF in HQ patches (high nutrient density) and negative PIF in LQ patches (low nutrient density) may also have influenced patch and diet selection. In previous research on these pastures, free-grazing cattle preferred previously grazed patches and avoided rank, mature patches of LL (Ruyle and Rice, 1996). Heavily grazed patches were maintained in a vegetative, immature state and consisted of forage with lower cell wall constituents and higher digestibility (i.e., HQ) compared to ungrazed, mature patches (i.e., LQ) (Renken et al., 1995). In our study, the overall bite rate was lowest when heifers took more of their bites from the cued LQ patch (Table 2), reflecting a possible increase in handling time for the mature LQ forage (Ruyle et al., 1987). 4.5. Management implications Cattle grazing LL dominated rangeland spend 80% of total grazing time within previously grazed patches (Ruyle et al., 1987). Land managers may consider patch grazing (isolated, heavily grazed patches) to be an inefficient use of forage since the patches that are grazed make up only a small percentage of the available forage. However, patch grazing allows free-grazing cattle to preferentially select and maintain patches that contain higher nutrient density within vast stands of LQ ungrazed LL monocultures. Bite rate and handling times were shorter within grazed versus ungrazed LL patches (Ruyle and Rice, 1996; Ruyle et al., 1988), which likely increased nutrient harvest and positive PIF. Rangeland researchers and managers have used supplementation and herding to address animal distribution problems. Cattle were trained to move to LQ (4–5% CP) foraging locations on rugged Montana rangeland by moving 30% CP supplements (Bailey and Welling, 1999; Bailey et al., 2001). Forage use remained higher than pre-study conditions during the 2-mo study period on areas within 600 m of supplementation sites after supplements were moved (Bailey et al., 2001). Budd (1999) trained animals to positively associate herding via horseback with receiving HQ forage within the 14,000 ha Red Canyon Ranch in Wyoming. Neither of these studies was designed to examine the influence of visual cues, but we may reasonably speculate

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that cattle learned to link incidental visual cues associated with the management activities (supplement containers, horseback riders) with a HQ food (supplement, new pasture) even though rangeland topography was steep and rough in both studies (Budd, 1999; Bailey et al., 2001). 5. Conclusions Our study demonstrated that cattle learned to generalise positive feeding consequences associated with visual cue training from the pen to the field. Grazing experience did not appear to enhance foraging efficiency suggesting that previous experience with native bunchgrasses pastures may have also been generalised to LL dominated rangelands. If cattle could be enticed to graze new patches in monotonous stands of ungrazed LL pastures in a way that rests older patches, total carrying capacity could theoretically be increased. In this study, patch selection was initially modified using a visual cue. Managers may be able to train and lure animals to new foraging locations but whether animals choose to remain at a new location will then largely depend on other behavioural influences (e.g., distance from water, PIF from forage ingested at the new location). The feasibility of using a combination of visual cues, supplementation, herding, or range improvement practices such as prescribed burning to ‘‘rotate’’ grazing pressure on rangelands needs to be tested under a variety of stocking densities and grazing rotations. Acknowledgments This research was supported by a grant from the Cooperative States Research, Education, and Extension Service, and with the support of the Arizona Agriculture Experiment Station. We thank Kim Jones-Thome for her valuable technical assistance throughout the study. We credit Todd Edwards and George Burrell for providing animals, facilities and logistical support. References Akaike, H., 1973. A new look at the statistical model identification. IEEE Trans. Autom. Control. 18, 716–723. Association of Official Analytical Chemists, 1990. Official Methods of Analysis of the Association of Official Analytical Chemists, 15th ed. Association of Official Analytical Chemists, Washington, pp. 72–74. Bailey, D.W., 2005. Identification and creation of optimum habitat conditions for livestock. Range. Ecol. Manage. 58, 109–118. Bailey, D.W., Welling, G.R., 1999. Modification of cattle grazing distribution with dehydrated molasses supplement. J. Range Manage. 52, 575–582. Bailey, D.W., Gross, J.E., Laca, E.A., Rittenhouse, L.R., Coughenour, M.B., Swift, D.M., Sims, P.L., 1996. Mechanisms that result in large herbivore grazing distribution patterns. J. Range Manage. 49, 386–400. Bailey, D.W., Rittenhouse, L.R., Hart, R.H., Richards, R.W., 1989. Characteristics of spatial memory in cattle. Appl. Anim. Behav. Sci. 23, 331–340. Bailey, D.W., Welling, G.R., Miller, E.T., 2001. Cattle use of foothills rangeland near dehydrated molasses supplement. J. Range Manage. 54, 338–347. Barker, L.M., 1997. Learning and Behaviour; Biological, Psychological and Sociocultural Perspectives, 2nd ed. Prentice Hall, Upper Saddle River, New Jersey, pp. 357–361. Bazely, D.R., 1990. Rules and cues used by sheep foraging in monocultures. In: Hughes, R.N. (Ed.), Behavioural Mechanisms of Food Selection. NATO Series G Ecol. Sci., vol. 20. Springer-Verlag, NY, pp. 343–367. Bazely, D.R., Ensor, C.V., 1989. Discrimination learning in sheep with cues varying in brightness and hue. Appl. Anim. Behav. Sci. 23, 293–299.

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