Influence of supplementing a methionine derivative, N-acetyl-l-methionine, in dairy diets on production and ruminal fermentation by lactating cows during early to mid lactation.

The present study investigated production responses and ruminal fermentation characteristics of lactating dairy cows when supplemented with N-acetyl-l-Met (NALM) as a source of rumen-protected Met in metabolizable protein (MP)-deficient (MPD) or MP-adequate diet (MPA). Eight lactating dairy cows (53 ± 10.4 d in milk, average ± standard deviation) were blocked by parity and days in milk, and the experiment was performed in a replicated 4 × 4 Latin square design. Within each square, cows were randomly assigned to a sequence of 4 diets during each of the four 21-d periods (14 d of treatment adaptation and 7 d of data collection and sampling). A 2 × 2 factorial arrangement was used; MPD or MPA was combined without or with NALM: MPD without NALM, MPD with NALM (MPD+NALM), MPA without NALM, and MPA with NALM (MPA+NALM). A NALM product was supplemented in the MPD+NALM and the MPA+NALM at 30 g/cow per d. Supplementation of NALM did not affect dry matter intake (DMI) and milk yield regardless of MP concentration. In addition, supplementing NALM resulted in a similar milk true protein concentration and yield. In contrast, NALM supplementation increased milk fat concentration and yield and 3.5% fat-corrected milk yield and tended to increase energy-corrected milk yield regardless of MP difference. Additionally, trends were observed for increased 3.5% fat-corrected milk yield/DMI and energy-corrected milk yield/DMI, and the positive effects were greater under the MPA than the MPD diet, resulting in trends toward interactions between MP and NALM. Dietary treatments had similar effects on ruminal fermentation characteristics and microbial protein yield. Plasma concentration of Met increased under the MPD but not the MPA diet, leading to an MP × NALM interaction. Overall results in the current study suggest that NALM exerted a minor influence on ruminal metabolism, but increased milk fat concentration, resulting in increases in milk fat yield and feed efficiency. Yet, potential effects of NALM on intermediary metabolism between the gastrointestinal tract, the liver, and the mammary gland need to be explored to understand utilization efficiency for production of dairy cows.

Elk (Cervus Canadensis) preference for feeds varying in selenium concentration.

Selenium-accumulator plants are reputed to be unpalatable to large ungulates. Elk (Cervus canadensis) populations in southeastern Idaho overlap with populations of Se-rich plants, but there is no information on the influence of plant Se concentration on elk dietary preferences. The objective of this study was to determine, under controlled conditions, the preference of elk for feeds varying in Se concentrations. Seven yearling female elk (128 ± 5 kg) were purchased from a commercial elk farm in southeastern Idaho and adapted to low-Se alfalfa pellets. Three feeding trials using pellets with predetermined Se concentrations were conducted. Alfalfa pellets were commercially made with the addition of Symphyotrichum ascendens (western aster) so that the pellets contained 0.4, 5, 20, 50, or 100 mg/kg (DM basis) Se. In trial 1, 5 Se-containing alfalfa pellets (0.4, 5, 20, 50, and 100 mg/kg Se) were offered for 10 d; trial 2 used 4 Se-containing alfalfa pellet choices (0.4, 20, 50, and 100 mg/kg), and trial 3 used 3 pellet choices (0.4, 50, and 100 mg/kg) for 6 d. In trial 1, consumption of the control pellets by elk was greater than each of the other pellet choices (P < 0.001). Similarly, consumption of the 5-mg/kg Se pellet differed from control pellet and all other Se-containing pellets (P < 0.0001). There were no differences (P > 0.50) in consumption of the 20-, 50-, or 100-mg/kg Se pellets. In trial 2, elk consumed more (P < 0.0001) of the control pellet than the 20-, 50-, and 100-mg/kg Se pellets. Similarly, elk consumed more (P < 0.0001) of the 20-mg/kg Se pellet than the 50- and 100-mg/kg Se pellets. There were no differences (P > 0.99) in elk consumption of the 50- and 100-mg/kg Se pellets. In trial 3, elk consumption of the control and 50- and 100-mg/kg Se pellets differed (P ≤ 0.03) from one another each day except that on d 1 and 2, where elk consumption of the 50- and 100-mg/kg Se pellets did not differ (P ≥ 0.32). Elk clearly discriminated against pellets with the highest Se concentrations when they were given pellets with differing Se concentrations. These results suggest that elk are not likely to select forages with high Se concentrations, particularly when high-Se plants are present in a rangeland situation with numerous other forage choices.

Effects of feeding birdsfoot trefoil hay on neutral detergent fiber digestion, nitrogen utilization efficiency, and lactational performance by dairy cows.

This experiment was conducted to determine effects of feeding birdsfoot trefoil hay-based diets in comparison with an alfalfa hay-based diet on N utilization efficiency, ruminal fermentation, and lactational performance by mid-lactation dairy cows. Nine multiparous lactating Holstein cows (131 ± 22.6 d in milk), 3 of which were rumen fistulated, were fed 3 experimental diets in a replicated 3 × 3 Latin square design with 3 periods of 14 d of adaptation and 7 d of data and sample collection. Within squares, cows were randomly assigned to diets as follows: alfalfa hay-based diet (AHT), alfalfa and birdsfoot trefoil hay-based diet (ABT), and birdsfoot trefoil hay-based diet (BT). Intakes of dry matter and crude protein were similar across treatments, whereas ABT and BT diets resulted in decreased fiber intake compared with AHT. Feeding BT tended to increase neutral detergent fiber digestibility compared with AHT and ABT. Milk yield tended to increase for cows consuming ABT or BT diets. Milk true protein concentration and yield were greater for cows consuming ABT relative to those fed AHT. Concentration of total volatile fatty acids tended to increase by cows fed BT compared with those fed AHT and ABT. Feeding birdsfoot trefoil hay in a total mixed ration resulted in a tendency to decrease acetate proportion, but it tended to increase propionate proportion, leading to a tendency to decrease acetate-to-propionate ratio. Whereas concentration of ammonia-N was similar across treatments, cows offered BT exhibited greater microbial protein yield relative to those fed AHT and ABT. Cows offered birdsfoot trefoil hay diets secreted more milk N than AHT, resulting in improved N utilization efficiency for milk N. The positive effects due to feeding birdsfoot trefoil hay were attributed to enhanced neutral detergent fiber digestion, and thus it could replace alfalfa hay in high-forage dairy diets while improving N utilization efficiencies and maintaining lactational performance compared with alfalfa hay.

Effects of altering alfalfa hay quality when feeding steam-flaked versus high-moisture corn grain on ruminal fermentation and lactational performance of dairy cows.

This experiment was performed to test a hypothesis that nutritive benefits of feeding high-moisture corn (HMC) would be different when fed with different qualities of alfalfa hay (AH) due to associative effects on ruminal fermentation and nutrient utilization efficiency. Eight multiparous lactating Holstein cows were used; 4 were surgically fitted with ruminal cannulas. Days in milk averaged 184 ± 10.7 at the start of the experiment. The experiment was performed in a duplicate 4 × 4 Latin square design. Within each square, cows were randomly assigned to a sequence of 4 diets during each of the four 21-d periods (14 d of treatment adaptation and 7 d of data collection and sampling). A 2 × 2 factorial arrangement was used; fair-quality AH [FAH; 39.6% neutral detergent fiber (NDF) and 17.9% crude protein (CP)] or high-quality AH (HAH; 33.6% NDF and 21.9% CP) was combined with steam-flaked corn (SFC) or HMC to form 4 treatments: FAH with SFC, FAH with HMC, HAH with SFC, and HAH with HMC. The AH was fed at 32% dry matter (DM) content, whereas SFC or HMC was included at 17% DM content. Quality of AH did not affect DM intake, whereas feeding HMC decreased DM intake, regardless of quality of AH. Digestibility of DM was greater for cows fed HAH compared with those fed FAH (70.1 vs. 67.6%). Digestibility of NDF increased by feeding HMC (67.6 vs. 58.4%), but not by quality of AH. Under FAH, starch digestibility decreased by feeding HMC compared with SFC (85.7 vs. 95.0%), but it was similar under HAH, resulting in an interaction between quality of AH and type of corn grain (CG). Feeding different qualities of AH did not affect milk yield; however, feeding HMC decreased milk yield in FAH diet, causing an AH × CG interaction. Efficiency of milk yield/DM intake was improved due to feeding HMC, regardless of the quality of the AH. In addition, dietary N utilization for milk N tended to increase by feeding HMC, but it was not influenced by quality of AH. Yield of microbial protein increased by feeding HAH diets compared with FAH diets, whereas feeding the HMC diet increased microbial protein yield under the HAH diet, leading to an interaction between and AH and CG. Overall results in this experiment indicate that feeding HMC in AH-based diets improved feed efficiency as well as N utilization efficiency, regardless of quality of AH.

Feeding protein supplements in alfalfa hay-based lactation diets improves nutrient utilization, lactational performance, and feed efficiency of dairy cows.

Due to the increasing cost of soybean meal and concerns of excess N being excreted into the environment, new protein supplements have been developed. Two products that have shown potential in increasing N utilization efficiency are slow-release urea (SRU; Optigen; Alltech Inc., Nicholasville, KY) and ruminal-escape protein derived from yeast (YMP; DEMP; Alltech Inc.). The objective of this study was to assess the effects of feeding these 2 supplements in alfalfa hay-based [45.7% of forage dietary dry matter (DM)] dairy diets on nutrient utilization, feed efficiency, and lactational performance of dairy cows. Twelve multiparous dairy cows were used in a triple 4 × 4 Latin square design with one square consisting of ruminally cannulated cows. Treatments included (1) control, (2) SRU-supplemented total mixed ration (SRUT), (3) YMP-supplemented total mixed ration (YMPT), and (4) SRU- and YMP-supplemented total mixed ration (SYT). The control consisted only of a mixture of soybean meal and canola meal in a 50:50 ratio. The SRU and the YMP were supplemented at 0.49 and 1.15% DM, respectively. The experiment consisted of 4 periods lasting 28 d each (21 d of adaptation and 7 d of sampling). Cows fed YMPT and SYT had decreased intake of DM, and all supplemented treatments had lower crude protein intake compared with those fed the control. Milk yield tended to have the greatest increase in YMPT compared with the control (41.1 vs. 39.7 kg/d) as well as a tendency for increased milk fat and protein yields. Feed efficiencies based on yields of milk, 3.5% fat-corrected milk, and energy-corrected milk increased at 10 to 16% due to protein supplementation. Cows fed protein supplements partitioned less energy toward body weight gain, but tended to partition more energy toward milk production. Efficiency of use of feed N to milk N increased by feeding SRUT and YMPT, and milk N-to-manure N ratio increased with YMPT. Overall results from this experiment indicate that replacing the mixture of soybean meal and canola meal with SRU and YMP in alfalfa hay-based dairy diets can be a good approach to improve nutrient utilization efficiencies in lactating dairy cows.

Evaluation of the respiratory elimination kinetics of selenate and Se-methylselenocysteine after oral administration in lambs.

Sheep can be acutely poisoned by selenium (Se) accumulating forages which often contain selenate or Se-methylselenocysteine as their predominant forms. Excess Se can be eliminated via respiration. Sheep were given a single oral dose of 0, 1, 2, 3, 4, or 6 mg Se/kg BW as sodium selenate and Se-methylselenocysteine or 6 mg Se/kg BW as sodium selenite or selenomethionine. Expired air samples were collected and analyzed for Se. The Se concentration of the expired air reflected a dose-dependent increase at individual time points for both Se-methylselenocysteine and sodium selenate, however, Se content was greater and eliminated more rapidly from sheep receiving Se-methylselenocysteine. The mean Se concentration in respired air from sheep administered 6 mg Se/kg BW of different selenocompounds was greatest in sheep dosed Se-methylselenocysteine > selenomethionine > sodium selenate > sodium selenite. The Se concentration in respired air of acutely poisoned sheep is significantly different for different chemical forms of Se.

Effect of selenium concentration on feed preferences by cattle and sheep.

Selenium-accumulator plants are reputed to be unpalatable to livestock. The objective of this study was to determine if sheep and cattle could discriminate between forages and feeds with different concentrations of Se. In the first study, cattle and sheep preferences for intermediate wheatgrass (Thinopyrum intermedium), alfalfa (Medicago sativa), and western aster (Symphyotrichum ascendens) of varying Se concentrations were assessed. The Se concentrations ranged from 0.8 to 50 mg/kg (DM) in grass, 1.4 to 275 mg/kg in alfalfa, and 4 to 4,455 mg/kg in aster. Selenium concentration had no influence (P > 0.05) on the initial or subsequent preferences of sheep or cattle for grass or alfalfa. Cattle developed an aversion to aster after consuming 95% of the plant material during the first brief exposure and subsequently refused to eat any aster. Sheep consumption of aster was variable, but their preference was not driven by Se concentration. In the next study, cattle and sheep were offered pellets at 1.5% of BW (as fed) that contained increasing concentrations of Se from aster (control and 5, 25, 45, and 110 mg/kg Se). In trial 1, all pellets were offered. In Trials 2 and 3, all pellets were offered with the exception of the 5 mg/kg Se pellet and the 5 and 25 mg/kg Se pellets, respectively. In trial 1, consumption of the control pellet by cattle was greater on all days compared with other Se pellets (P < 0.001). Cattle ate more (P < 0.001) of the 5 mg/kg Se pellet than the higher Se pellets on d 3, 4, and 5. Sheep ate greater amounts of the control and 5 and 110 mg/kg Se pellets compared with the 25 and 45 mg/kg Se pellets (P < 0.0001) on d 1, and sheep consumed primarily the control and 5 mg/kg Se pellets thereafter. In trial 2, cattle and sheep consumed more (P < 0.0001) of the control Se pellet than the 25, 45, and 110 mg/kg Se pellets. In trial 3, cattle consumption of the control and 45 and 110 mg/kg Se pellets differed on d 2 and 3 (P < 0.001), except there was no difference (P > 0.95) in cattle consumption of the control and 45 mg/kg Se pellets on d 1. Sheep consumed primarily the control and 45 mg/kg Se pellets. We conclude that high Se concentrations in fresh forages had no effect on initial consumption by cattle or sheep. When given Se pellets, initial responses were variable, but the results indicate that cattle and sheep adjusted their intake over time to avoid excessive intake of Se.

Corn silage hybrid type and quality of alfalfa hay affect dietary nitrogen utilization by early lactating dairy cows.

This experiment was conducted to determine the effects of corn silage (CS) hybrids and quality of alfalfa hay (AH) in high-forage dairy diets on N utilization, ruminal fermentation, and lactational performance by early-lactating dairy cows. Eight multiparous Holstein cows were used in a duplicated 4 × 4 Latin square experiment with a 2 × 2 factorial arrangement of dietary treatments. The 8 cows (average days in milk = 23 ± 11.2) were surgically fitted with ruminal cannula, and the 2 squares were conducted simultaneously. Within square, cows were randomly assigned to a sequence of 4 diets: conventional CS (CCS) or brown midrib CS (BMR) was combined with fair-quality AH [FAH: 46.7% neutral detergent fiber (NDF) and 18.4% crude protein (CP)] or high-quality AH (HAH: 39.2% NDF and 20.7% CP) to form 4 treatments: CCS with FAH, CCS with HAH, BMR with FAH, and BMR with HAH. Diets were isonitrogenous across treatments, averaging 15.9% CP. Each period lasted a total of 21 d, with 14 d for treatment adaptation and 7d for data collection and sampling. Intake of DM and milk yield did not differ in response to CS hybrids or AH quality. Although feeding BMR-based diets decreased urinary N output by 24%, it did not affect fecal N output. Feeding HAH decreased urinary N output by 15% but increased fecal N output by 20%. Nitrogen efficiency [milk N (g/d)/intake N (g/d)] tended to increase for BMR treatments. Ruminal ammonia-N concentration was lower for cows fed BMR-based diets than for those fed CCS-based diets but was not affected by quality of AH. Feeding BMR-based diets or HAH decreased milk urea N concentration by 23 or 15%, respectively, compared with CCS-based diets or FAH. Total volatile fatty acid concentration increased with HAH but was not influenced by CS hybrids. Feeding BMR-based diets decreased urinary N-to-fecal N ratio (UN:FN), and it was further reduced by feeding HAH. Although cows fed the BMR-based diets tended to increase milk N-to-manure N ratio, the quality of AH did not affect the ratio. The lower ratio of UN:FN with a higher ratio of milk N-to-manure N ratio for the BMR-based diets indicates that feeding BMR may reduce manure ammonia-N by reducing excretion of urinary N and increasing secretion of milk N per unit of manure N excreted.

Comparative oral dose toxicokinetics of selenium compounds commonly found in selenium accumulator plants.

Consumption of Se accumulator plants by livestock can result in Se intoxication. Recent research indicates that the Se forms most common in Se accumulator plants are selenate and Se-methylselenocysteine (MeSeCys). In this study the absorption, distribution, and elimination kinetics of Se in serum and whole blood of lambs dosed with a single oral dose of (1, 2, 3, or 4 mg Se/kg BW) of sodium selenate or MeSeCys were determined. The Se concentrations in serum and whole blood for both chemical forms of Se followed simple dose-dependent relationships. Se-methylselenocysteine was absorbed more quickly and to a greater extent in whole blood than sodium selenate, as observed by a greater peak Se concentration (Cmax; P < 0.0001), and faster time to peak concentration (Tmax; P < 0.0001) and rate of absorption (P < 0.0001). The rate of absorption and Tmax were also faster (P < 0.0001) in serum of lambs dosed with MeSeCys compared with those dosed sodium selenate at equimolar doses; however, Cmax in serum was greater (P < 0.0001) in lambs dosed with sodium selenate compared with those dosed MeSeCys at equimolar doses. The MeSeCys was absorbed 4 to 5 times faster into serum and 9 to 14 times faster into whole blood at equimolar Se doses. There were dose-dependent increases in the area under the curve (AUC) for Se in serum and whole blood of lambs dosed with both sodium selenate and MeSeCys. In whole blood the MeSeCys was approximately twice as bioavailable as sodium selenate at equimolar doses as observed by the AUC, whereas in serum there were no differences (P > 0.05) in AUC at the same doses. At 168 h postdosing the Se concentration in whole blood remained much greater (P < 0.0001) in lambs dosed with MeSeCys as compared with lambs dosed with sodium selenate; however, the serum Se concentrations were not different between treatments at the same time point. The results presented in this study demonstrate that there are differences between the kinetics of different selenocompounds when orally dosed to sheep. Therefore, in cases of acute selenosis, it is important to understand the chemical form to which an intoxicated animal was exposed when determining the importance and meaning of Se concentration in serum or whole blood obtained at various times postexposure.

Experimental rayless goldenrod (Isocoma pluriflora) toxicosis in horses.

Rayless goldenrod (Isocoma pluriflora) sporadically poisons horses and other livestock in the southwestern United States. Similar to livestock poisoning by white snakeroot (Ageratina altissima) in the midwestern United States, previous research suggests that benzofuran ketones (BFK: tremetone, dehydrotremetone, 6-hydroxytremetone, and 3-oxyangeloyl-tremetone) are responsible for the toxicity of rayless goldenrod. However, experimental reproduction of rayless goldenrod-induced disease and detailed descriptions of poisoning in horses with known concentrations of tremetone and other BFK has not been documented. In this study four horses were fed increasing amounts of rayless goldenrod to obtain doses of approximately 0, 10, 30, and 60 mg BFK/kg BW for 14 days. After seven days of dosing the horse dosed with 60 mg BFK/kg BW horse developed depression, reluctance to eat, dehydration, trembling, and muscle fatigue. Biochemical alterations including increases in the serum enzyme activities of CK, AST, ALT, and LDH, and increased cardiac troponin I concentration, were also identified. Physiologically the clinically poisoned horse had decreased endurance seen as reluctance to perform on the treadmill with increased resting heart rate and a prolonged recovery of heart rate following treadmill exercise. The condition of the horse continued to decline and it was euthanized and necropsied on day 10. At necropsy the myocardium was pale and soft and many of the appendicular and large apical muscles were pale and moist. Histologically, the myocardium had extensive myocardial degeneration and necrosis with extensive fibrosis and multifocal mineralization. Several of the large appendicular muscles in this horse also had small foci of skeletal muscle degeneration and necrosis. Less severe myocardial changes were also identified in the horse dosed with 30 mg BFK/kg BW after 14 days of dosing. No clinical, biochemical or histologic changes were identified in the control horse and the horse dosed with 10 mg BFK/kg BW. These results suggest that doses of 60 mg BFK/kg BW for seven days produce extensive myocardial lesions in horses. The horse dosed with 30 mg BFK/kg BW developed less severe, but similar myocardial lesions over a longer duration, this suggests that poisoning may be cumulative and lower doses of longer duration are also toxic. Horses seem to be uniquely sensitive to rayless goldenrod-induced myocardial disease, therefore cardiac troponin I may be a useful marker of rayless goldenrod poisoning in horses. More work is needed to determine which BFK produce myocardial toxicity and better determine the effects of dose and duration on poisoning in horses.

Plant secondary compounds as complementary resources: are they always complementary?

Generalist herbivores typically grow better on mixed- than on single-component diets. This response has been attributed to food complementarities that either enhance the utilization of nutrients or dilute the negative impacts of plant secondary compounds (PSC). For instance, when animals choose between foods that contain diverse PSC, they eat more than animals offered a food that contains just one PSC. In addition to their negative impacts on herbivore fitness, recent evidence suggests that at appropriate doses PSC may provide beneficial effects to herbivores (i.e., by reducing parasitic infections). Thus, complementarities among diverse PSC may not only influence an herbivore's ability to consume food but also reduce the incidence of disease. We assessed the complementary effects of two PSC by offering sheep (Ovis aries) a choice of foods containing condensed tannins and saponins while challenged with a parasitic (Haemonchus contortus) infection. Animals offered a choice ate more than animals just offered tannins or saponins in single rations. However, sheep offered choices displayed greater fecal egg counts (an indirect measurement of parasitic burdens) than sheep offered single rations. Thus, saponin- and tannin-containing foods were complementary resources regarding nutrient intake but antagonistic regarding effects on parasitic loads. The nature of the relationship among PSC may depend on the dimension (i.e., nutrient intake, disease) where the interaction occurs. A unifying currency such as growth or reproductive output may help understand the trade-offs between costs (disease) and benefits (nutrient and medicine intake) for herbivores grazing multiple PSC.

A comparison of the metabolism of the abortifacient compounds from Ponderosa pine needles in conditioned versus naive cattle.

Isocupressic acid (ICA) is the abortifacient compound in ponderosa pine (Pinus ponderosa L.) needles, which can cause late-term abortions in cattle (Bos taurus). However, cattle rapidly metabolize ICA to agathic acid (AGA) and subsequent metabolites. When pine needles are dosed orally to cattle, no ICA is detected in their serum, whereas AGA is readily detected. Recent research has demonstrated that AGA is also an abortifacient compound in cattle. The observation has been made that when cattle are dosed with labdane acids for an extended time, the concentration of AGA in serum increases for 1 to 2 d but then decreases to baseline after 5 to 6 d even though they are still being dosed twice daily. Therefore, in this study we investigated whether cattle conditioned to pine needles metabolize ICA, and its metabolites, faster than naïve cattle. Agathic acid was readily detected in the serum of naïve cattle fed ponderosa pine needles, whereas very little AGA was detected in the serum of cattle conditioned to pine needles. We also compared the metabolism of ICA in vitro using rumen cultures from pine-needle-conditioned and naïve cattle. In the rumen cultures from conditioned cattle, AGA concentrations were dramatically less than rumen cultures from naïve cattle. Thus, an adaptation occurs to cattle conditioned to pine needles such that the metabolism AGA by the rumen microflora is altered.

Preference for condensed tannins by sheep in response to challenge infection with Haemonchus contortus.

Herbivores prefer feeds that supply required nutrients and avoid those with excess nutrients and plant secondary compounds (PSC). Nevertheless, PSC such as condensed tannins can provide beneficial medicinal effects to herbivores as they act against infective diseases such as parasitism. The objectives of this study were to determine: (1) if parasitized lambs increased preference for a tannin-rich feed after they experienced the beneficial antiparasitic effects of condensed tannins relative to parasitized lambs that did not experience such benefits, and (2) if preference for the tannin-rich feed in the former group decreased when parasite burdens subsided. Twenty two lambs were familiarized with beet pulp and beet pulp+8% quebracho tannins (beet pulp+tannins) and choices were given between the two feeds (initial preference tests). Subsequently, all animals were dosed with 10,000 L(3) stage larvae of Haemonchus contortus. Twenty-two days later, animals were exposed to beet pulp (Control group; n=11) or beet pulp+tannins (Treatment group; n=11) during 24 d. After exposure (during a parasitic infection) animals in both groups were given choices between the two feeds. Lastly, animals in both groups received an antiparasitic drench and were again given a choice between both feeds (after a parasitic infection). Lambs preferred beet pulp to beet pulp+tannins throughout the study (P<0.001) and no difference in preference for the tannin-rich feed was detected between groups during initial preference tests (P>0.05). However, during a parasitic infection, intake of and preference for the tannin-rich feed was higher for lambs that experienced the beneficial effects of condensed tannins while parasitized (Treatment) than for lambs that did not (Control) (P<0.05). When parasitic infections were terminated by chemotherapy, differences between groups disappeared (P>0.05). Preference by the Treatment group for the tannin-rich feed was lower after than during a parasite infection (P<0.05). In contrast, preference by the Control group did not change during these periods (P>0.05). Lambs in the Treatment group displayed lower FEC than lambs in the Control group (Group × Sampling Date; P<0.05). These results show lambs learned about the antiparasitic effects of condensed tannins and increased their preference for the tannin-rich feed, which subsided after chemotherapy, indicating preference was due to parasite infection. These findings suggest management that allows animals to select tannin-rich feeds can enable parasitized animals to self-medicate.

Selection of tannins by sheep in response to gastrointestinal nematode infection.

Herbivores learn to select compounds that attenuate the aversive effects of plant secondary metabolites (PSM), but can they increase intake of PSM they typically avoid when these PSM provide medicinal effects? We hypothesized that herbivores learn to increase intake of PSM-containing feeds when experiencing a gastrointestinal parasitic infection. Ten lambs with natural gastrointestinal parasitic burdens (PB) and 10 nonparasitized lambs (NP) were offered a choice of alfalfa (Medicago sativa) and alfalfa mixed with 10% quebracho tannin (Schinopsis quebracho-colorado; alfalfa:tannins) before and after they were conditioned with the postingestive effects of tannins. Preference for alfalfa:tannins did not differ between groups before experiencing the postingestive effects of tannins (P = 0.85) or when parasite loads were terminated due to the administration of ivermectin (P = 0.18). In contrast, when tested with a parasite burden, lambs in PB consumed more alfalfa:tannins (P = 0.08), showed greater preference for alfalfa:tannins (P = 0.07), and consumed less alfalfa than lambs in NP (P = 0.06). Ingestion of tannins by lambs in PB was followed by reduced fecal egg counts (FEC; P = 0.006), and there was a direct proportional relationship between preference for alfalfa:tannins and FEC (P = 0.07). In summary, parasitized lambs increased their intake of alfalfa:tannins when they experienced a parasite burden, which suggests they self-medicated with tannins against parasites. Self-selection of PSM has implications for the quest for alternatives to chemoprophylaxis in the treatment and well-being of parasitized wild and domestic animals grazing in pasturelands and in confinement.

Trace element concentrations in wintering waterfowl from the Great Salt Lake, Utah.

The Great Salt Lake (GSL) is an important region for millions of migratory waterbirds. However, high concentrations of some trace elements, including Hg and Se, have been detected within the GSL, and baseline ecotoxicological data are lacking for avian species in this system. We collected common goldeneye (Bucephala clangula), northern shoveler (Anas clypeata), and green-winged teal (A. crecca) from the GSL during the winters of 2004-2005 and 2005-2006 to evaluate sources of variation in liver trace element concentrations. Hg concentrations were among or exceeded the highest values reported in the published literature for common goldeneye, northern shoveler, and green-winged teal. Average Hg (total) concentrations of common goldeneye peaked in midwinter, whereas average Se concentrations peaked during late winter. During late winter, 100% and 88% of female goldeneye contained elevated concentrations of Hg [>or=1.0 microg/g wet weight (ww)] and Se (>or=3.0 microg/g ww), respectively, and 5% and 14% contained potentially harmful amounts of Hg (>or=30.0 microg/g ww) and Se (>10.0 microg/g ww), respectively. Similarly, 30% and 16% of male goldeneye contained potentially harmful concentrations of Hg and Se, respectively. Concentrations of Hg and Se were elevated in 100% and 79%, respectively, of northern shoveler samples (sexes combined) collected during February. We suggest that waterfowl contain biologically concerning amounts of Hg and Se during winter while on the GSL and further research is needed to evaluate the effect of these elements on GSL waterbirds.

Butylated hydroxytoluene chemoprevention of aflatoxicosis - effects on aflatoxin B(1) bioavailability, hepatic DNA adduct formation, and biliary excretion.

The extreme sensitivity of turkeys to aflatoxin B(1) (AFB(1)) is associated with efficient hepatic cytochrome P-450 (P450)-mediated bioactivation, and deficient glutathione S-transferase (GST) mediated detoxification. Butylated hydroxytoluene (BHT) protects against AFB(1) toxicity in turkeys through mechanisms that include competitive inhibition of P450-mediated AFB(1) bioactivation. To test whether dietary BHT alters hepatic AFB(1)-DNA adduct formation, excretion, and bioavailability of AFB(1)in vivo, turkeys were given diets with BHT (4000ppm) for 10 days, given a single oral dose of [(3)H]-AFB(1) (0.05microg/g; 0.02microCi/g), then sampled at intervals up to 24h. Radiolabel in serum, red blood cells, liver, and breast meat was frequently lower in BHT-treated compared to control. Hepatic AFB(1)-DNA adducts in BHT-treated turkeys were significantly lower at 12 and 24h. BHT-fed birds had significant higher bile efflux, though biliary radiolabel excretion was not different from control. The amount of aflatoxin M(1) (AFM(1)) excreted in the bile was lower than in control, but BHT had no effect on the biliary excretion of AFB(1), aflatoxin Q(1) or glucuronide and sulfate conjugates. Thus, the chemopreventive properties of BHT may also occur through a reduction in AFB(1) bioavailability in addition to inhibition of bioactivation.

Learned appetites for calcium, phosphorus, and sodium in sheep.

If supplemental minerals are needed to promote optimal animal performance, what is the best way of providing them: free choice or in the diet? We hypothesized that herbivores discriminate among feeds containing Na, P, and Ca and modify their choices as a function of need. One group of lambs was fed a basal diet low in P and high in Ca (low P-high Ca), whereas another group was fed a basal diet high in P and low in Ca (high P-low Ca). After 73 d of exposure to the unbalanced diets, the lambs were conditioned by offering flavored grape pomace containing NaCl, CaCO(3), or NaH(2)PO(4). Preference for pomace + minerals was determined when all lambs were fed a basal diet of alfalfa pellets and barley grain (initial preference) and during 4 phases. Phases 1 and 2 occurred after 40 and 67 d of feeding the unbalanced basal diets, phase 3 occurred after conditioning with NaCl, CaCO(3), or NaH(2)PO(4), and phase 4 occurred 22 d after the groups were moved to 2 new (separate) locations so the animals in the different groups could not eat dirt, urine, or feces from the other pen. Preference for pomace did not differ between the groups during the initial preference tests (P = 0.62); both groups preferred NaCl > CaCO(3) = NaH(2)PO(4) (P < 0.001). As the study progressed, and lambs fed low P-high Ca had lower P and greater Ca concentrations in serum than lambs fed high P-low Ca (P < 0.001), the preference between groups diverged. In phase 2, lambs in high P-low Ca continued to prefer NaCl (P < 0.001), but lambs in low P-high Ca preferred NaH(2)PO(4) (P < 0.05). After conditioning, both groups preferred NaCl = NaH(2)PO(4) > CaCO(3) (P < 0.01 to 0.11). After the groups were moved to different locations, lambs fed low P-high Ca showed the lowest concentration (3.7 mg/dL) of inorganic P in serum for all phases (P < 0.001), and they preferred NaH(2)PO(4) > NaCl = CaCO(3) (P < 0.001). In contrast, lambs in high P-low Ca avoided NaH(2)PO(4) (P < 0.05). Lambs offered high P-low Ca showed a greater preference for CaCO(3) (P = 0.12) and NaCl (P < 0.05) and a lower preference for NaH(2)PO(4) compared with lambs fed low P-high Ca (P < 0.001). In summary, lambs discriminated among different flavored feeds containing NaCl, CaCO(3), and NaH(2)PO(4) and displayed preferences as a function of the mineral imbalance in their basal diets. Thus, it may be possible to feed Ca and P supplements free choice, such that individual animals within a group can manifest preferences based on their specific needs.

Phosphorus appetite in sheep: dissociating taste from postingestive effects.

We hypothesized that lambs discriminate the postingestive effects of P and associate those effects with feed flavor to modify feed choices. Three predictions were tested based on this hypothesis: 1) lambs will modify preference for arbitrary flavors eaten during intraruminal infusions of NaH2PO4, 2) changes in preferences are more specific than changes in osmotic load induced by salts of Na; and 3) preference for P is inversely related to the concentration of inorganic P in blood. Thirty lambs were depleted of P by the offer of a P-deficient diet, allocated to 3 groups (10 lambs/group), and conditioned during 3 periods as follows: During conditioning period 1, lambs in each of 3 groups ate a poorly nutritious feed (grape pomace), flavored differently for each group, while water was infused into the rumen. During conditioning periods 2 and 3, lambs again ate grape pomace, with 2 new flavors now paired with infusion of an aqueous solution (126 mmol) of NaCl (conditioning period 2) or NaH2PO4 (conditioning period 3), rather than with water. After conditioning, all lambs were offered a choice of the 3 flavors during preference tests immediately after conditioning (period 1) and every 3 wk thereafter (periods 2, 3, and 4). During period 1, when serum inorganic P levels were greatest, lambs preferred flavors paired with water > NaCl > NaH2PO4 (P < 0.05). During periods 2 and 3, as inorganic P concentrations decreased in serum, lambs preferred flavors paired with NaH2PO4 > NaCl (period 2, P = 0.10; period 3, P = 0.05). Lambs preferred flavors paired with water > NaH2PO4 in period 2 (P < 0.001), but those differences disappeared in periods 3 and 4 (P > 0.05). During period 4, lambs preferred flavors paired with NaCl > NaH2PO4 (P < 0.10). The estimate of the slope for the linear relationship between intake of flavors paired with NaH2PO4 and serum inorganic P was negative (P < 0.0001), whereas estimates of the slopes for the relationships between intake of flavors paired with NaCl or water and serum inorganic P were not different from 0. Thus, preference for P was inversely related to the concentration of serum inorganic P. Our results suggest lambs discriminated among the postingestive effects of NaH2PO4, NaCl, and water and associated those effects with specific flavors. Lambs avoided flavors paired with NaH2PO4 during periods of P replenishment, and they increased preference for those flavors during periods of P need.

Excitation of localized rotating waves in plasma density cavities by scattering of fast magnetosonic waves.

An analytic description of electromagnetic waves in an inhomogeneous plasma is applied to investigate excitation of localized rotating waves below the lower hybrid frequency through scattering of fast magnetosonic waves on a density cavity. The magnetosonic wave is focused to left-handed rotating oscillations. We find the amplitude of the localized oscillations, resonance frequencies, and the width of the resonances. The theory is relevant for the lower hybrid solitary structures observed in space plasmas and is shown to be consistent with observations by the Freja satellite.

The toxicity and kinetics of larkspur alkaloid, methyllycaconitine, in mice.

Larkspur poisoning sporadically kills from 5 to 15% of the cattle on North American mountain rangelands. Of the 40 different diterpenoid larkspur alkaloids, the one that is thought to be responsible for much of the toxicity has been identified as methyllycaconitine (MLA). Little is known of MLA toxicokinetics or excretion. The purpose of this study was to further characterize the clinical effects of MLA toxicity in mice and determine the toxicokinetics of MLA excretion. Eight groups of mice were dosed intravenously with 2.0 mg/kg of BW of MLA, killed, and necropsied at 0, 1, 2, 5,10,15, 30, and 60 min after injection. Treated animals were reluctant to move, trembled, and developed dyspnea, muscular twitches, and convulsions. Within several minutes, the clinical signs abated and behavior slowly returned to normal over approximately 20 min. At necropsy serum, brain, liver, kidney, and skeletal muscle were collected and frozen. Blood and tissues were extracted and analyzed for MLA with HPLC and electron spray mass spectrometry. Blood MLA elimination followed a normal biphasic redistribution and excretion pattern (r = 0.99) with a K of elimination of 0.0376 and half-life of 18.4 min. Other tissues had similar clearance rates. These data indicate the MLA is rapidly distributed and excreted. In mice, the clinical effects of poisoning seem to affect the central nervous system, causing dyspnea and "explosive" muscular twitches and convulsions. Because livestock commonly eat larkspur at subclinical doses, they are likely to have larkspur alkaloids in many tissues. These results suggest that animals exposed to larkspur should rapidly excrete MLA (within several hours) and that the residues in animal tissues are not likely to be a problem if animals are given several days to allow toxin clearance.