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The foraging ecology of mammalian herbivores is determined by plant secondary compounds (PSC) that defend plants against herbivory, by nutrients that are required for maintenance, growth, and reproduction, and by the interaction between these variables. In this study, we explored the influence of an herbivore’s nutritional state and experience on intake of aspen (Populus tremuloides) leaves with contrasting concentrations of a PSC, phenolic glycosides (PG). Thirty-two lambs were randomly assigned to two groups (N = 16). Each group received aspen leaves with either higher (21.2%) or lower (16.3%) concentrations of PG throughout the study. In Experiment 1, half of the lambs within each group received rations with a high (22.2% crude protein [CP]; 3.13 Mcals/kg) or low (11.9% CP; 3.13 Mcals/kg) concentration of CP. During Experiment 2, half of the lambs within each group received rations with a high (3.45 Mcals/kg; 16.1% CP) or low (2.52 Mcals/kg; 18.5% CP) concentration of energy. During Experiment 3, all lambs received a simultaneous offer of aspen leaves containing higher (20.6%) and lower (14.8%) concentrations of PG. Aspen intake was greater when lambs received the high-protein or the low-energy rations (P

Nutrients and plant secondary compounds in aspen (Populus tremuloides) may interact with nutrients in the surrounding vegetation to influence aspen use by herbivores. Thus, this study aimed to determine aspen intake and preference by sheep in response to supplementary nutrients or plant secondary compounds (PSC) present in aspen trees. Thirty-two lambs were randomly assigned to one of four molasses-based supplementary feeds to a basal diet of tall fescue hay (N = 8) during three experiments. The supplements were as follows: (1) high-protein (60% canola meal), (2) a PSC (6% quebracho tannins), (3) 25% aspen bark, and (4) control (100% molasses). Supplements were fed from 0700 to 0900, then lambs were fed fresh aspen leaves collected from stands containing high (Experiment 1, 2) or low (Experiment 3) concentrations of phenolic glycosides (PG). In Experiment 2, lambs were simultaneously offered aspen, a forb (Lathyrus pauciflorus), and a grass (Bromus inermis) collected from the aspen understory. Animals supplemented with high protein or tannins showed greater intake of aspen leaves than animals supplemented with bark or the control diet (P

Targeted livestock grazing is a proven tool for manipulating rangeland vegetation, and current knowledge about targeted livestock grazing is extensive and expanding rapidly. Targeted grazing prescriptions optimize the timing, frequency, intensity, and selectivity of grazing (or browsing) in combinations that purposely exert grazing/browsing pressure on specific plant species or portions of the landscape. Targeted grazing differs from traditional grazing management in that the goal of targeted grazing is to apply defoliation or trampling to achieve specific vegetation management objectives, whereas the goal of traditional livestock grazing management is generally the production of livestock commodities. A shared aim of targeted livestock grazing and traditional grazing management is to sustain healthy soils, flora, fauna, and water resources that, in turn, can sustain natural ecological processes (e.g., nutrient cycle, water cycle, energy flow). Targeted grazing prescriptions integrate knowledge of plant ecology, livestock nutrition, and livestock foraging behavior. Livestock can be focused on target areas through fencing, herding, or supplement placement. Although practices can be developed to minimize the impact of toxins contained in target plants, the welfare of the animals used in targeted grazing must be a priority. Monitoring is needed to determine if targeted grazing is successful and to refine techniques to improve efficacy and efficiency. Examples of previous research studies and approaches are presented to highlight the ecological benefits that can be achieved when targeted grazing is applied properly. These cases include ways to suppress invasive plants and ways to enhance wildlife habitat and biodiversity. Future research should address the potential to select more adapted and effective livestock for targeted grazing and the associated animal welfare concerns with this practice. Targeted livestock grazing provides land managers a viable alternative to mechanical, chemical, and prescribed fire treatments to manipulate rangeland vegetation.

Grazing represents a sustainable alternative for the control of medusahead infestations but intake of medusahead by ruminants is typically low. We determined in sheep whether (1) high-energy supplements enhance medusahead intake and preference relative to a treatment without supplementation and (2) individual differences in medusahead intake transfer to individual differences in the ingestion of a silica-containing ration. Groups of lambs (n= 10) were individually penned and randomly assigned to three supplementation treatments: (1) Control (no supplement); (2) Calcium (Ca) Propionate (beet pulp : barley : Ca propionate, 67 : 30 : 3); or (3) Yeast (beet pulp : barley : yeast culture, 65 : 30 : 5). After supplementation, all animals had ad libitum access to medusahead in late vegetative to mid-reproductive (Trial 1), and late-reproductive phenological stages (Trial 2). Medusahead preferences were assessed by offering sheep a choice between medusahead and tall fescue hay. Plant part preferences were assessed by offering a choice between medusahead tops (mostly seedheads and awns) and mid-plant parts (mostly stems + leaves). Intake of medusahead was low and cyclic, declining towards the end of each trial (P < 0.0001) and there were no treatment differences (P > 0.10). Lambs preferred tall fescue hay to medusahead and medusahead tops to mid-plant parts (P < 0.0001). Supplemented lambs gained more weight than control lambs (P < 0.10). Thus, supplemented lambs performed better than nonsupplemented controls without reducing their intake of medusahead. In Trial 3, two new groups of lambs were formed based on their intake of medusahead during Trials 1 and 2 (n= 10). One group consistently ate more medusahead and more of a ration containing silica (alfalfa : silica, 97 : 3) than the other (P < 0.10). A significant and consistent degree of individual variation was measured among lambs—irrespective of treatment—regarding their ability to ingest medusahead and silica. This variation represents a promising option for maximizing use of medusahead by livestock in rangelands.

We explored in sheep (1) the impact of supplements on medusahead intake and preference, (2) whether medusahead is aversive, and (3) if silica inhibits food intake. Groups of lambs ( n = 8) were individually penned and randomly assigned to 4 supplementation treatments: beet pulp:barley (70:30) (High Energy; HE), alfalfa:soybean meal (60:40; High Protein; HP), a choice of HE and HP (CHOICE), or no supplement (Control). After supplementation all animals had ad libitum access to medusahead in early reproductive – Trial 1, late reproductive – Trial 2, and thatch – Trial 3 phenological stages. On the last day of each trial, lambs had choices between medusahead and tall fescue hay. Lambs in HE tended to ingest ( P P P P n = 10) were fed beet pulp and then received intraruminal infusions of: (1) tall fescue hay (4 g/kg BW), (2) lithium chloride (LiCl; 150 mg/kg BW), and (3) medusahead (4 g/kg BW). Medusahead infusions did not reduce intake of beet pulp relative to infusions of tall fescue hay ( P > 0.10), whereas infusions of LiCl conditioned a food aversion ( P n = 10) were fed: (1) alfalfa, (2) alfalfa-2.5% Silica, and alfalfa-4.5% Silica. Lambs in Group 2 had the lowest intake of alfalfa ( P

Many in the range profession are perplexed by the apparent discrepancy between experimental studies suggesting that rotational grazing carries no advantage over continuous grazing1 and the observations of ranchers and range mana gers who have personally seen benefi ts for livestock pro duction and plant communities by shifting to a rotational system.2,3 We believe one reason for this seeming contradiction is that research on plant and animal production is typically designed to control for the effects of behavior of grazing animals and their owners. As researchers who have spent many years studying the behavior of range livestock and people, we argue that understanding human and animal behavior as it relates to grazing management can help to bridge the gap between science and practice. In this paper we discuss how livestock behavior factors (such as prior experience and stress) and managers’ learning processes can infl uence the outcomes of grazing management practices, why a standard experimental approach may not detect those infl uences, and how an improved knowledge of behavior can help both ranchers and researchers achieve their goals with respect to rotational grazing systems.

Ruminants prefer hay cut in the afternoon to hay cut in the morning, presumably because hay cut in the afternoon contains higher concentrations of non-structural carbohydrates than hay cut in the morning. We determined if adding sugars (glucose and sucrose) to ground hay would account for differences in preference and affect intake of hay. Alfalfa hay cut either in the afternoon (PM) or the following morning (AM) was used in the trials. Glucose and sucrose were added to AM hay (AMS) to make its sugar content similar to PM hay. During the first trial, lambs received a choice of either: (1) AM and PM hay; (2) AMS and PM hay; or (3) AMS and AM hay. Lambs preferred PM to AMS or AM hay. We also studied how increasing the concentration of added sugars affected preference for hay. Lambs received a choice of AM hay and AM hay with either 1, 2, 3, or 4% added sugar. On the first day of the trial, lambs ate similar amounts of each hay type, regardless of the amount of sugar added. By the end of the trial, lambs preferred hay with 2, 3, or 4% added sugar compared with AM hay without added sugar. During the intake trial, lambs ate similar amounts of AM, AM hay with added starch and sugar (AMSS), and PM hay. After the intake trial, a final preference trial determined that prolonged exposure to AMSS hay increased preference for AMSS hay compared with AM hay. Our results indicate that preference for PM hay is likely related to increased levels of sugars, such as glucose and sucrose, and that lambs learn about the post-ingestive benefits of exogenous sugars added to hay.

We added a novel flavor, citric acid (CA), to a familiar test diet and conditioned an aversion in lambs to the flavored diet using lithium chloride. In 1 h feeding trials, we examined the roles of a novel flavor cue, choice and nutritional quality of alternatives on the persistence of an aversion. Availability of alternative foods increased the persistence of the aversion to the CA-flavored test diet. Furthermore, persistence was related to the energy content of the alternative. The higher energy alternative better complimented the high protein content of the basal ration (alfalfa pellets) and increased persistence versus the lower energy alternative. Continued avoidance of the CA-flavored test diet was observed even after a 68-day intermission among lambs with access to alternatives. We submit that application of flavor avoidance learning (FAL) may be useful for minimizing herbivory when a novel flavor is employed and alternative forage is present.

Aspen (Populus tremuloides Michx.) has evolved a chemical defense system comprised of phenolic glycosides (PG), which effectively deter insect herbivory. However, much less is known about the role of PG and the nutritional quality of the associated plant community on aspen browse susceptibility to mammalian herbivores. In three successive periods during the growing season, we conducted experiments with sheep by offering leaves from two aspen stands with different concentrations of PG (LOW, HIGH) or aspen leaves vs. leaves from a forb (Utah pea, Lathyrus pauciflorus) or a grass (smooth brome, Bromus inermis Leyss.) growing in an aspen understory. Intake of aspen (19 to 35 % PG) was low in all periods (1 to 6 g/Kg(0.75) in 2 hr) supporting the notion that aspen's defense system may contribute to its ecological success. However, lambs ate larger amounts of LOW than of HIGH suggesting that sheep could discriminate between aspen stands with different concentrations of PG, even when both stands were relatively well defended. Concentration of nutrients and chemical defenses in aspen leaves remained fairly stable across the growing season, and preference for aspen increased over the growing season. In contrast, preference for the forb and the grass decreased across the growing season in concert with a decline in the nutritional quality of these plants. The data suggest that nutritional context of aspen and associated forage species drove preference more than contrasts in defense chemistry of aspen. There may be periods of "susceptibility" of aspen use by mammalian herbivores, despite high concentrations of chemical defenses, which can potentially be targeted by management to reduce aspen herbivory.

Herbivores foraging on toxic plants may consume a variety of foods that contain different toxins to increase food intake and to avoid toxicosis. We studied whether lambs offered two foods, each containing a different toxin, could ingest more food than lambs offered one food with a single toxin. Thirty-two lambs were allotted to four groups that received: (1) a ration with toxin A, (2) a ration with toxin B, (3) two rations, one with toxin A and the other with toxin B, and (4) a ration with no toxins. Toxin pairs used in the study were (1) amygdalin and lithium chloride (LiCl), (2) LiCl and LiCl, (3) sparteine and saponin, (4) oxalate and nitrate, and (5) tannin and saponin. For an hour each morning, lambs were offered their ration(s) and intakes were measured. Lambs were maintained on an alfalfa pellet or grass hay diet. Each trial lasted either five or six days. Whether or not lambs ate more when offered foods with different toxins depended on the kind and amount of toxin in the food. Lambs offered rations with amygdalin and LiCl or oxalate and nitrate consumed more food than lambs offered a ration with only one of these toxins. Lambs offered rations with sparteine and saponin or tannin and saponin did not eat more food than lambs offered a ration with either saponin or sparteine or tannin alone. Nor did lambs eat more when offered two rations both containing LiCl. In all trials, lambs offered toxins showed no signs of toxicosis, and they ate less food than lambs offered rations without toxins. Our results indicate that in some cases ruminants can increase intake of toxic foods by consuming foods containing different toxins. However, currently the only way to determine how specific toxins may interact in the body to influence intake would be to conduct feeding trials using plants or ground diets that contain toxins.

We studied how moving lambs to an unfamiliar environment affected their intake of novel and familiar foods. In the first experiment, half the lambs (n = 14) were conditioned to avoid a novel food (wheat) by pairing its ingestion with lithium chloride (LiCl); the other half (n = 14) received wheat but no LiCl. Half of the lambs that received LiCl and half that did not were moved to a location unfamiliar to the lambs. Lambs at both locations were offered wheat (familiar but aversive to half the lambs), oats (novel food), and alfalfa pellets (familiar food). In the second experiment, one group of lambs (n = 16) remained at the familiar location; the other group (n = 16) was moved to a novel location. Both groups were offered alfalfa pellets (familiar food) with or without onion powder (novel flavor), wheat bran (novel food), and rye with 1% LiCl (novel and toxic food). We found that: (1) lambs consumed a familiar but aversive food (wheat) more readily at the unfamiliar location than at the familiar location (P = 0.052); (2) lambs ate less of the novel foods (oats and wheat bran) at the unfamiliar location (P = 0.09 and P < 0.001, respectively); (3) intake of the familiar food (alfalfa pellets) did not differ between locations on day 1 of either experiment. These results suggest that: (1) food neophobia is greater in unfamiliar than familiar environments, which may cause animals to eat more familiar foods in unfamiliar environments, even if the familiar foods contain toxins. They further suggest that animals should be: (2) exposed to novel foods in familiar environments to expedite intake of novel foods; (3) provided with familiar foods in novel environments to prevent declines in intake; (4) conditioned to avoid foods (e.g. fruit trees, poisonous plants) in the environments where they will forage to increase the persistence of the aversion.

We studied the acquisition of food aversions in sheep. In the first experiment, we investigated how prior illness affected the formation of a conditioned food aversion. Lambs were offered small amounts (

To better understand some of the mechanisms that control selection of novel foods differing in postingestive consequences, we offered goats current season's (CSG) and older (OG) growth twigs from the shrub blackbrush (Coleogyne ramosissima). CSG is higher than OG in nitrogen (1.04% v. 0.74%) and it is more digestible in vitro in goat rumen fluid (48% v. 38%). Nevertheless, goats acquire a preference for OG because CSG contains much higher levels of a condensed tannin that causes a learned food aversion. When CSG and OG were offered to goat naive to blackbrush, the goats did not choose either OG or CSG exclusively, but when they finally (1) ate more CSG than OG within a meal (averages of 44 g and 16 g, respectively) and (2) ate enough CSG within the meal to acquire an aversion (average of 44 g), they ingested less CSG than OG from then onward. Accordingly, the change in food selection resulting from postingestive feedback was influenced by the amount of each food ingested within a meal. This was further shown when we varied the amounts of CSG and OG that goats ingested within a meal, and then gave them by gavage the toxin lithium chloride (LiCl). They subsequently ate less of the food eaten in the greatest amount, regardless of whether it was CSG or OG. The salience of the flavor (i.e., taste and odor) of CSG and OG also played a role in the acquired aversion to CSG. Salience evidently was due to a flavor common to both OG and CSG that was more concentrated in CSG. We conclude that the relative amounts of different foods ingested within a meal, and the salience of the flavors of those foods, are both important variables that cause goats to distinguish between novel foods that differ in postingestive consequences.

We studied: (1) whether lambs could learn to avoid a novel food given delays of up to 8 h between food ingestion and gastrointestinal illness (long-delay study); (2) how gastrointestinal illness affected the selection of several foods differing in familiarity to lambs (mixed-meal study). Gastrointestinal illness was induced by administering encapsulated lithium chloride (LiCl; 160 mg kg −1 body weight) to lambs using a balling gun. In the long-delay study, lambs were offered a novel food for 5 min. If they consumed 10 g or more of the food, LiCl was administered 0,2,4,6, or 8 h later. Intake of the novel food was measured in 5 min trials for the next 3 days. When the delay between food ingestion and the administration of LiCl was 2 or 4 h, the lambs reduced their intake of the novel food after a single dose of LiCl. The lambs also reduced their intake of the novel food when the delay between food ingestion and the administration of LiCl was 6 or 8 h. However, LiCl was administered twice before the lambs reduced their intake of the novel food; they were also given a stronger dose (320 mg kg −1 body weight) of LiCl on Day 2 than on Day 1. Thus, repeated exposures, greater gastrointestinal distress, or both may be required before lambs reduce their intake of a novel food given delays of 6 h or more. For the mixed-meal study, we used five foods; lambs had eaten two of the foods since weaning, two of the foods for 25 days prior to the onset of the trials, and one food was novel. When lambs were offered the novel food for 5 min followed by the four familiar foods for 20 min, and then given LiCl, they refused to eat the novel food for the next 3 days. Some of the lambs also reduced their intake of the foods they had eaten for 25 days. The lambs did not decrease their intake of the foods they had eaten since weaning.

We determined whether a socially induced diet preference could ameliorate a conditioned food aversion in lambs. To do so, one group of lambs was conditioned to avoid the shrub Cercocarpus montanus by giving them lithium chloride, a toxin that produces strong food aversions, following shrub ingestion. On Day 1 of conditioning, lambs ingested an average of 29 bites of C. montanus, but by Day 2 the number of bites had decreased to two and lambs took even fewer bites on Days 3–5. Following conditioning, averted lambs spent a substantial amount of time foraging on C. montanus when foraging with non-averted conspecifics in pasture trials (10% vs. 19% of time spent ingesting C. montanus) and in pen trials (25 vs. 35 bites). We also examined the effects of group composition during conditioning (heterogeneous vs. homogeneous) on the use of C. montanus during pasture and pen trials. In the heterogeneous groups, lambs being averted to C. montanus were exposed to the shrub in the presence of lambs not being averted to C. montanus. In the homogeneous groups all lambs were averted to C. montanus. Lambs in the heterogeneous groups took numerically more bites of C. montanus than lambs in the homogeneous groups during conditioning (25 vs. 17 bites day−1), but the trend was not significant (P>0.05). When foraging on pastures, however, lambs in the heterogeneous groups spent more (P 0.05). The capacity of social interactions to ameliorate food aversions suggests that social influences are a major determinant of diet selection in sheep.

It has been hypothesized that herbivores instinctively avoid tannin-containing plant parts in response to the adverse effects of tannins on forage digestion. However, we found that goats learned to avoid condensed tannins (CTs) from blackbrush current season's growth by associating the flavor of foods containing CTs with aversive postingestive consequences. The aversive consequences experienced by goats apparently are not related to digestion inhibition and may depend on the structure of CTs and on how CTs are bound with other cell constituents. These observations suggest several areas of inquiry related to the interaction between CTs and herbivores. A better understanding of the physiological effects of CTs and how herbivores perceive these effects is essential to our knowledge of chemically mediated interactions between plants and mammalian herbivores. With few exceptions, the effects of food flavor have not been separated from those associated with postingestive consequences, even though our data show ...

Condensed tannins were isolated from bitterbnish (Purshia tridentata) and blackbrush (Coleogyne ramosissima). Structural analyses showed that both tannins were procyanidins of similar polymer length. The overall stereochemistries at C-3 and C-4, however, differed between the two tannins. These changes in stereochemistry resulted in blackbrush tannins being less preferred than bitterbrush tannins when offered to snowshoe hares (Lepus americanus). It is unlikely that differences in protein-precipitating abilities are the cause for the preference of the bitterbrush over the blackbrush tannins. Instead, we hypothesize that condensed tannins may be depolymerized and absorbed following ingestion. Differences in tannin structure can lead to different depolymerized products and rates of depolymerization, both of which may affect herbivore preferences.

We studied the persistence of conditioned taste aversions in sheep and whether or not sheep averted to one shrub species would avoid another shrub species. Three-month-old lambs were averted to the shrub Cercocarpus montanus by pairing its ingestion with lithium chloride (LiCl), a nonlethal gastrointestinal poison. When lambs were yearlings, they were offered C. montanus plants growing in 8-liter pots. During the persistence trial, averted sheep took fewer (P < .05) bites of C. montanus than controls did (19 vs 64 bites/sheep, respectively). Following the persistence trial, sheep that had been previously averted to C. montanus and consumed C. montanus received LiCl. Complete aversion to C. montanus was re-established in previously averted sheep with a single dose of LiCl. When sheep previously averted to C. montanus were offered potted Amelanchier alnifolia shrubs, averted sheep consumed 21 bites of A. alnifolia but controls consumed 58 bites (P < .05). This result suggests that previously averted sheep were either more food neophobic than controls or generalized their aversion from C. montanus to A. alnifolia. As with C. montanus, a single dose of LiCl completely averted sheep to A. alnifolia. When sheep grazed a pasture containing C. montanus and A. alnifolia averted sheep took fewer (P < .05) bites of the two shrubs than controls did (.2% vs 18%). Sheep showed no signs of extinguishing the aversion to either shrub during the grazing season (May-Sept.). Aversive conditioning may be useful to manipulate diet selection of free-ranging livestock.

Ruminants learn to avoid many foods that contain toxins by associating the flavor of the foods with aversive postingestive feedback. We hypothesized the emetic system is a cause of aversive feedback, and three experiments were conducted to determine whether antiemetic drugs (diphenhydramine, metoclopramide, dexamethasone) would attenuate food aversions caused by the toxicant lithium chloride (LiCl). Lambs were assigned to one of four treatments: antiemetics plus LiCl (A + L), antiemetics alone (A), LiCl alone (L), or neither antiemetics nor LiCl (C). The LiCl was administered immediately after sheep ate oats, wheat, and milo in Exp. 1, 2, and 3, respectively. The antiemetics were given 1 h before and at the time LiCl was administered to sheep. Lambs that received antiemetics (A and A + L) consistently ate more grain than lambs that did not receive the drugs (C and L) (Exp. 1, P < .08; Exp. 2, P < .05; Exp. 3, P < .08), and there was no interaction between antiemetics and LiCl. Thus, the results of all three experiments were consistent with the hypothesis that antiemetic drugs attenuate food aversions caused by the toxicant LiCl because sheep receiving antiemetic drugs (Group A + L) ate more grain than sheep not receiving the drugs (Group L). In addition, we suggest aversive postingestive feedback limited intake of grain because sheep receiving antiemetic drugs (Group A) ate somewhat more grain than sheep not receiving the drugs (Group C).

The concentration of toxins in plants can vary with plant phenology and environmental factors. Changes in toxicity may or may not be associated with changes in plant flavor. These factors may make it difficult for herbivores to avoid toxic plants. We conducted three experiments concerning animals' ability to detect toxins. In experiment 1, we examined whether animals familiar with a tastable toxin on food would adjust intake when toxin concentrations changed. Lambs were initially offered oats with either a low, medium, or high concentration of lithium chloride (LiCl; a salty-tasting toxin). Later, when all lambs were offered oats with the medium concentration of LiCl, lambs that were conditioned with the low LiCl concentration decreased intake while lambs conditioned with the high LiCl concentration increased intake. In experiment 2, we examined flavor aversions formed when animals sampled food with two flavor levels prior to illness. Lambs initially ate the same amount of barley with a low and with a high concentration of either sodium saccharin (a sweet flavor) or aluminum sulfate (a bitter flavor). Lambs then received a mild dose of LiCl. Later, when lambs were offered a choice between barley with either a low or high flavor concentration, lambs preferred the barley with the low flavor concentration. Experiment 3 examined how variable toxicity affected intake when the flavor remained constant. Lambs were initially offered oregano-flavored barley and then received a dose of LiCl. Lambs received either a medium dose, a high dose, or a dose that varied randomly among low, medium, or high amounts of LiCl. Lambs in the medium dose group ate more oregano-flavored barley at the end of the trial than did lambs in either of the other groups.

We studied lambs' preferences for nonnutritive flavors that were paired with a glucose solution. On the 1st d of the experiment, lambs were offered a saccharin solution flavored with either orange or grape. The following day lambs received a glucose solution containing either orange or grape flavor. Lambs that had received grape and saccharin on d 1 received orange and glucose on d 2, and the reverse was true for the remaining lambs. Conditioning lasted 10 d; odd days were like the first and even days like the second. After conditioning, when lambs were offered a choice between orange- or grape-flavored water without sweeteners, lambs chose the flavor that had been paired with glucose. We also tested the initial hedonic response of naive lambs to the flavor of glucose and saccharin solutions. Lambs exhibited no initial preference. Our results indicate that lambs preferred the flavor that was paired with glucose (calories). Furthermore, results of this study suggest that ruminants may not innately recognize specific chemical constituents in foods or select diets based on initial hedonic value. Rather, learning plays a key role in the formation of dietary preference.

We studied how exposure to ammoniated wheat straw (AWS) early in life affected the performance of 32 mature crossbred beef cows (Bos taurus) (mean BW = 615 kg) wintered on AWS. Half (16) of these cows had been exposed as suckling calves to AWS for 66 d (Exposed), while the other 16 cows had no previous exposure to AWS (Naive). Five years after the initial exposure, cows were stratified by BW and bred into 8 groups of 4 cows each. Exposed and Naive cows occurred in each group, and groups of 4 cows were randomly assigned to one of eight pens. Cows were fed in these pens for a 150-d wintering period from December to May for 3 consecutive years. All cows were allowed ad libitum access to AWS and supplemented with alfalfa hay, vitamins, and minerals. Cows and their calves grazed irrigated meadow pastures for the remainder of the year. Cow BW and body condition score (BCS) were monitored monthly during the 3-yr study. Milk production was measured monthly from June to November of each year using the weigh-suckle-weigh technique. For all 3 yr, yearly average BW (P = 0.06, 0.03, 0.07) and BCS (P = 0.07, 0.001, 0.01) were higher for Exposed than Naive cows. Postpartum interval (PPI) to rebreeding, monitored using consecutive calving dates, was shorter for Exposed than Naive cows during yr 1 and 2 (P = 0.004 and 0.02, respectively), but similar in yr 3 (P = 0.19). Exposed cows also produced more milk than Naive cows during yr 1 and 2 (P = 0.04 and 0.07, respectively), but milk production was similar in yr 3 (P = 0.74). Collectively, calves exposed to AWS briefly early in life performed better as cows when reexposed to AWS from 5 to 8 yr later in life. Thus, researchers and managers should consider previous exposure to low-quality forages (LQF) when assigning cattle to studies involving the use of LQF or when considering using LQF to reduce food costs.

We evaluated the influence of supplemental barley and activated charcoal on the intake of sagebrush by lambs in individual pens. In 3 experiments, lambs were fed sagebrush (harvested and chopped to 2-3 cm) during the morning; they were fed a basal diet of alfalfa pellets in the afternoon. In the first experiment, lambs supplemented with activated charcoal + barley ate more A. tridentata ssp. vaseyana than lambs supplemented with barley (304 vs. 248 g; P = .071). A second set of experiments, which consisted of 3 trials, determined the effects of activated charcoal, barley, and subspecies of sagebrush on intake of sagebrush. Lambs supplemented with activated charcoal + barley ate more A. tridentata ssp. vaseyana (Trial 1; 292 vs. 225 g; P = .086), and more A. tridentata ssp. tridentata (Trial 2; 371 vs. 255 g; P = .031) than lambs supplemented with barley. In Trial 3, lambs supplemented with barley ate more sagebrush than lambs that were not supplemented (480 vs. 318 g; P = .0002). A third set of experiments compared activated charcoal + barley, barley, and no supplement in 2 trials. In Trial 1, lambs supplemented with activated charcoal + barley or barley generally ate more A. tridentata ssp. vaseyana than lambs not supplemented (P = .017). In Trial 2, lambs supplemented with activated charcoal + barley ate slightly more A. tridentata ssp. vaseyana than lambs supplemented with barley, and they ate substantially more than lambs not supplemented (P = .032). Collectively, the results suggest that energy from supplemental barley increased intake of sagebrush by lambs fed a basal ration of alfalfa pellets which are high in protein, and that activated charcoal played a minor role in further increasing intake of sagebrush. DOI:10.2458/azu_jrm_v53i4_banner

Tannins occur in many plant species, and they often suppress intake by reducing nutrient availability or by causing malaise. Polyethylene glycol (PEG) binds to tannins and may thereby increase the availability of macronutrients and decrease malaise. Supplemental PEG increases intake of tannin-containing plants by sheep, goats, and cattle. Given the strong response to supplemental PEG, we speculated that animals might self-regulate their intake of PEG when offered foods high in tannins. The objective of the first experiment was to determine if the amount of supplemental PEG (0, 25, 50, 75, or 100 g; molecular weight, 3,350) affected intake by lambs of a food (milo-tannin mix) containing 20% quebracho tannin. There was a linear relationship (Y = 272 + 1.2X; R2 = .86; P = .023) between the amount of supplemental PEG ingested and the subsequent intake of milo-tannin food by lambs. The objective of the second experiment was to determine whether lambs self-regulated intake of PEG when fed a ration that contained 0, 5, 10, 15, or 20% quebracho tannin and whether they adjusted their intake of PEG when tannin was removed from the diet. There was a positive relationship between the amount of PEG ingested and intake of food and tannin (P = .0001). Lambs fed high-tannin diets ate more PEG than controls (P = .03). Lambs fed the 20% tannin diet ate the most PEG, and controls ate the least PEG. Tannin limited intake of the diets, but PEG attenuated the response to a great degree (P = .065). Immediately after tannin was removed from the ration, lambs that formerly had been fed the 20% tannin ration ate more PEG than lambs fed the other rations (P = .0075). Ten of the lambs (5 from the 20% tannin group, 1 from the 15% tannin, and 2 each from the 10 and 5% groups) continued to eat PEG for 7 d after tannin was removed from their ration. When they were tested again 6 wk after the trial and offered tannin-free diets, their intake of PEG had decreased.

We investigated how experience early in life and macronutrient content of the diet influenced intake of mountain big sagebrush (Artemisia tridentata Nutt. ssp. v a s e y a n a (Rydb.) Beetle) by sheep. In the first part of our study, 2-month-old lambs were exposed as a group for 2 mo to a 70% barley-30% soybean meal ration (300 g/hd/day) that contained increasing amounts sagebrush (1 to 20%). Control lambs received grain without sagebrush. All lambs had access to alfalfa hay and pellets ad libitum. When lambs were tested at 6 months of age, prior exposure had no effect on sagebrush consumption after the first 4 days of the trial. When sagebrush comprised 20% of an alfalfa/barley ration, lambs ate the sagebrush ration readily even when a nutritious alternative was offered indicating the flavor of sagebrush did not prevent lambs from feeding. Increasing the amount of sagebrush in the ration from 50% to 75% resulted in lambs eating less of the barley/sagebrush ration, but daily intake of sagebrush remained constant throughout the 4 day trial, presumably because toxins (terpenes) limited intake of sagebrush. In the second part of our study, lambs experienced with sagebrush were fed 250 g/hd/day of barley, and nutritional status was varied by offering alfalfa pellets at 33% or 80% of ad libitum (1.2 and 2.7 times maintenance, respectively) to determine if dietary energy levels affected intake of sagebrush. Each day lambs received a 50/50 sagebrush/barley supplement ad libitum for 1 hour. Lambs fed at 33% of ad libitum consumed more of the sagebrush/barley supplement than lambs fed at 80% of ad libitum. Thus, additional energy did not enable lambs to consume more sagebrush. In the last trial, lambs in both treatments were fed a basal ration of alfalfa pellets at 50% of ad libitum. Each morning for 1 hour, lambs were offered macronutrient supplements containing either 50% barley/50% sagebrush (high energy) or 25% barley/25% soybean meal/50% sagebrush (high energy and protein). Lambs consumed the same amount of sagebrush regardless of supplement. Thus, supplemental protein did not improve sagebrush consumption. We conclude lambs readily ingested a high-energy ration containing sagebrush, regardless of exposure early in life, suggesting toxins, not flavor, control intake of sagebrush. Further, supplementing lambs with energy or protein failed to improve intake of sagebrush, which suggests these macronutrients did not enhance detoxification of sagebrush.

The alcohol insoluble residue (AIR) isolated from 12 foods was acid hydrolyzed and analyzed for neutral and acidic sugars. Aliquots taken at 1 hr were reduced, acetylated and analyzed for neutral sugar content with GLC. Glucose from cellulose, starch and non-cellulosic polysaccharides was analyzed with colorimetric methods. The predominant sugars present in the dietary fiber were arabinose, xylose, galactose, glucose and uronic acids. Pectin and hemicellulose together comprised the majority of cell wall polysaccharides. Samples high in starch generally contained the greatest amounts of dietary fiber and the least amount of water on a fresh plant basis.

Maturing reed canarygrass, Russian wildrye, and smooth bromegrass cell walls were analyzed for lignin, phenolic acids, and neutral sugars. Linear correlation between in vitro dry matter digestibility and the p-coumaric acid content was −.86. The correlation between in vitro dry matter digestibility and ratio of p-coumaric to ferulic acid was −.84. Samples with high percentages of lignin also contained high ratios of p-coumaric to ferulic acid. Thus, p-coumaric acid may be more important than ferulic acid in crosslinking lignin to structural carbohydrates. Percent xylose and in vitro dry matter digestibility also were correlated significantly in all three species. A Russian wildrye regrowth sample contained a relatively high percentage of lignin despite its immature appearance. The lower digestibility of that regrowth sample may have resulted both from its high lignin content as well as branched xylans in the hemicellulosic fraction.

The feasibility of using esophegesl extras to monitor dktuy tsnnin levek vves studkd using 4 &rub specks (Purshia tri&utata, Qucrcusgarnbe& Cwcoca~~usmou&us end Acu gmudideutoha). Browse sumpks were hsnd-harvested in hte summer. Half of the sumple for each specks ~8s fed to esophegeslly fktuluted attk, wbik the other belf served M sn unnustiated control. Extruaa and control umpks were rnrlysed for tote1 phenolks (Folin-Denk), tannin using 3 methods (venillin-HCI, prosnthocymidins, end astringency), crude protein, end in vitro orgsnk matter digestibility (IVOMD). Tannin levels were reduced 10% to 60% in extras, depending on pknt specks end metbod of tannin snelysk. Changes in the nutrition81 constituents of extras were limited but oak extrusn was higher in IVOMD than oek control sumpks. Tannins may hsve bound to pknt or snlivsry proteins or to mucousmembrenes in the mouth during msstiation end inalivetion. Our results indiate that esophagal extras is not suitable for monitoring dietary tsnnin Ievek.

We studied the ability of lambs to select safe foods in the presence of harmful foods. In a series of feeding experiments, 3- to 6-mo-old lambs were offered a choice between 1) a familiar, safe and a novel, harmful food, 2) a novel, safe and a novel, harmful food and 3) a familiar, harmful and a novel, safe food. All harmful foods were palatable feeds that had been treated with lithium chloride (LiCl), a non-lethal gastrointestinal poison. When lambs ingested a meal composed of a novel food containing LiCl and a familiar, safe food, lambs subsequently avoided the novel food. Lambs avoided the novel food even when the familiar food contained LiCl. The response of lambs varied when lambs were given a choice between a novel, safe food and a novel food containing LiCl. Lambs either avoided the novel food containing LiCl and ingested the safe food or they limited their intake of both novel foods. Their response was dependent on the novelty of the food containing LiCl. When a novel, palatable food contained 2% LiCl, lambs always ate some of the food, even after experiencing illness from ingesting it. Lambs experienced with foods containing LiCl displayed greater food neophobia than lambs naive to LiCl-treated foods. Thus, novelty was the major criterion that lambs used to associate foods with gastrointestinal illness.