Lambs form preferences for nonnutritive flavors paired with glucose.

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.

Food aversion learning: ability of lambs to distinguish safe from harmful foods.

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.

Food aversion learning in sheep: persistence of conditioned taste aversions to palatable shrubs (Cercocarpus montanus and Amelanchier alnifolia).

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 less than .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 less than .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 less than .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.

Self-regulation of intake of polyethylene glycol by sheep fed diets varying in tannin concentrations.

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.

Exposure to ammoniated wheat straw as suckling calves improves performance of mature beef cows wintered on ammoniated wheat straw.

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 (Naïve). Five years after the initial exposure, cows were stratified by BW and bred into 8 groups of 4 cows each. Exposed and Naïve 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 Naïve cows. Postpartum interval (PPI) to rebreeding, monitored using consecutive calving dates, was shorter for Exposed than Naïve 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 Naïve 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.

Antiemetic drugs attenuate food aversions in sheep.

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).

How herbivores track variable environments: Response to variability of phytotoxins.

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.

How goats learn to distinguish between novel foods that differ in postingestive consequences.

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.

Ecological implications of condensed tannin structure: A case study.

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.