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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.

We determined whether cows in low (LBC) or high body condition (HBC) would consume different amounts of green pine needles (Pinus ponderosa). Cows (mature; open Hereford and Hereford x Angus) were fed a maintenance basal diet (alfalfa pellets) for Exp. 1 and 2; during Exp. 3 and 4, cows were fed high-protein and high-energy diets, respectively. Experiment 5 was a grazing study on rangeland during winter in South Dakota; diets were determined by using bite counts. Mean BCS (1 = emaciated, 9 = obese) was 7.5 for HBC cows and <4.0 for LBC cows during the experiments. During Exp. 1, LBC cows consumed more (P = 0.001) pine needles than did HBC cows (5.5 +/- 0.25 vs. 1.0 +/- 0.14 g/kg of BW daily, respectively). During Exp. 2, there was a day x treatment interaction (P = 0.001) as LBC cows consumed variable, but greater, amounts of pine needles than did HBC cows (3.7 +/- 0.19 vs. 1.3 +/- 0.12 g/kg of BW daily, respectively). When fed a high-protein/low-energy diet, LBC cows ate more (P = 0.04) pine needles than did HBC cows. When fed a low-protein/high-energy diet, there was a day x treatment interaction (P = 0.001) because LBC cows consumed more pine needles than did HBC cows for the first 3 d of the study, and then consumption by LBC animals decreased during the last 4 d. These experiments suggest that the protein:energy ratio may be an important factor in the ability of cows to tolerate terpenes, and that cows were not able to sustain an increased quantity of needle consumption on a low-protein diet. During the 25-d grazing study, there was a day x treatment interaction (P = 0.001) as LBC animals selected more pine needles (up to 25% of daily bites) on some days compared with HBC cows. Weather influenced pine needle consumption because pine needle bites by LBC cows were related (r(2) = 0.60; P = 0.001) to days of greater snow depth and lower minimum daily temperatures. Both LBC and HBC cows increased selection of pine needles from trees during cold, snowy weather, but the magnitude of the increase was greater for LBC cows. The LBC cows consumed more pine needles than did HBC cows in all experiments, except when cows were fed a low-protein diet. This study indicates that both body condition and protein intake are important factors in pine needle consumption.

Consumption of ponderosa pine needles, as well as needles and bark from a number of other trees, can cause abortions in cattle. The abortifacient compounds in these trees are labdane resin acids, including isocupressic acid and agathic acid. Previous research has demonstrated that cattle conditioned to pine needles metabolize the labdane resin acids more quickly than naïve cattle. The results from that study indicated that changes had occurred in the rumen of conditioned cattle. Therefore, in this study, the changes that occurred in the rumen bacterial microflora of cattle during exposure to ponderosa pine needles were evaluated. Cattle were dosed with ground pine needles twice daily for 7 d. Rumen samples were collected on d 0, 3, 7, and 14 (7 d after treatment stopped) and ruminal bacterial microbiome analyses were performed. There were 372 different genera of bacteria identified in the rumen samples. Principal coordinate analysis indicated that there was a significant difference in the rumen bacterial composition between the time points. There were 18 genera that increased in abundance from d 0 to d 7. Twenty three genera decreased in abundance from d 0 to d 7. The results from this study demonstrated that exposure of cattle to pine needles caused a clear shift in the rumen microbiome composition. In general, this shift lasted less than 1 wk post exposure, which indicates that any prophylactic treatment to manipulate the ruminal metabolism of the abortifacient compounds in pine needles would need to be continuously administered to maintain the necessary microbial composition in the rumen. [ABSTRACT FROM AUTHOR]

Larkspurs (Delphinium spp.) are one of the most serious toxic plant problems on foothill and mountain rangelands in the western United States. A considerable amount of research has been conducted over the years in both field and pen settings. The results of these research efforts have significantly increased our understanding of the poisoning of cattle by larkspurs. However, most of the pen studies conducted thus far have used a dosing regimen of a single bolus dose, which does not accurately mimic the manner by which cattle are poisoned by larkspur while grazing. Consequently, the objective of this study was to evaluate the acute toxicity of tall larkspur (Delphinium barbeyi collected near Manti, UT) when administered in multiple doses, with the intent to identify a no observable adverse effect level (NOAEL). The adverse effect selected for this study was muscle weakness to the point the cattle could no longer remain ambulatory as would be required in a grazing environment, thus becoming sternally recumbent when exercised. Hereford steers were administered various doses of tall larkspur at 12-h intervals for 4 d or until they showed marked signs of muscle weakness. The results suggest that a dose of 2 mg kg-1·d-1 N-(methylsuccinimido) anthranoyllycoctonine (MSAL)-type alkaloids is the NOAEL for a tall larkspur population with a norditerpenoid alkaloid profile containing 4 mg MSAL-type alkaloids/g plant material and 12 mg non-MSAL-type alkaloids/g plant material. Additionally, a computer model was generated to simulate multiple-dosing regimens at the various doses as well as different dosing regimens. The results from this study suggest that a 500-kg steer can consume a daily dose of 1.25 kg of fresh tall larkspur (with a similar alkaloid profile) without becoming severely poisoned (suffering from muscle weakness to the point of recumbency). Additionally, these results indicate that a serum concentration of approximately 355 ng methyllycaconitine/ mL may represent a toxic threshold. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Delphinium spp. contain numerous norditerpenoid alkaloids which are structurally delineated as 7, 8-methylenedioxylycoctonine (MDL) and W-(methylsuccinimido) anthranoyllycoctonine (MSAL)-type alkaloids. The toxicity of many tall larkspur species has been primarily attributed to their increased concentration of MSAL-type alkaloids, such as methyllycaconitine (MLA), which are typically 20 times more toxic than MDL-type alkaloids. However, the less toxic MDL-type alkaloids are often more abundant than MSAL-type alkaloids in most Delphinium barbeyi and Delphinium occidentale populations. Previous research demonstrated that MDL-type alkaloids increase the acute toxicity of MSAL-type alkaloids. In this study, we examined the role of MDL-type alkaloids on the overall toxicity oftall larkspur plants to cattle while controlling for the exact dose of MSAL-type alkaloids. Cattle were dosed with plant material from 2 different populations of tall larkspur containing either almost exclusively MDL- or MSAL-type alkaloids. These 2 plant populations were combined to create mixtures with ratios of 0.3:1,1:1, 5:1, and 10:1 MDL-to MSAL-type alkaloids. The dose that elicited similar clinical signs of poisoning in mice and cattle was determined for each mixture on the basis of the MSAL-type alkaloid content. As the ratio of MDL- to MSAL-type alkaloids increased, the amount of MSAL-type alkaloids required to elicit clinical signs decreased. These results indicate that the less toxic MDL-type alkaloids in tall larkspur exacerbate the toxicity of the MSAL-type alkaloids. Consequently, both the amount of MSAL-type alkaloids and the amount of total alkaloids should be fully characterized to determine more accurately the relative toxicity oftall larkspur plant material. [ABSTRACT FROM AUTHOR]

Several species of lupine (Lupinus spp.) are toxic to livestock, causing death losses in sheep and cattle but more commonly crooked calf disease in pregnant range cows. The major toxic alkaloids in lupine are of the quinolizidine alkaloid group and include the teratogen anagyrine, which. is primarily responsible for crooked calf disease. Lupines also contain teratogenic piperidine alkaloids including ammodendrine. Previous work in sheep has shown that lupine alkaloid clearance may be influenced by the animal's physiological status. Therefore, the purpose of this study was to determine if differences in body condition of cattle would alter the absorption and elimination of anagyrine or ammodendrine given in a single oral dose as Lupinus leucophyllus or Lupinus sulphureus, respectively. Mature non-lactating cows in low body condition (LBC, n = 4) and high body condition (HBC, n = 4) received a single dose of dry ground lupine plant (2.0 g/kg of BW) via oral gavage. Lupinus leucophyilus (anagyrine) was dosed first; then after 21 d the same animals were dosed with L. sulphureus (ammodendrine). Blood samples were taken via jugular venipuncture 0 to 60 h after dosing. Serum anagyrine and ammodendrine concentrations were evaluated. The concentration of anagyrine was greater (P = 0.001) in the HBC group and peaked 2 h after dosing versus 12 h in LBC cows. Similarly for ammodendrine, the alkaloid concentration peaked at 3 h after dosing for the HBC group compared with 6 h for the LBC group (P = 0.001). Area under the curve tended to differ (P ≤ 0.11) for both alkaloids in the HBC group compared with the LBC group. There were also differences in the maximum serum anagyrine (P = 0.02) and ammodendrine (P = 0.06) concentrations. Elimination half-life (E1/2) tended to differ (P = 0.12) between the HBC and LBC groups for ammodendrine. The kinetic profiles suggest that body condition influenced the disposition of these alkaloids. This study also suggests that body condition may impact the risk of toxicity, teratogenicity, or both of these alkaloids. [ABSTRACT FROM AUTHOR]