Larkspur consumption is a major source of cattle losses on mountain and high plains rangelands of western North America. Our objective was to find a suitable laboratory animal model for measuring larkspur toxicity for subsequent use as an estimator of toxicity to cattle. The LD50 for subcutaneous injection and for oral gavage of extract from Delphinium barbeyi, a highly toxic and troublesome rangeland tall larkspur, was compared for mice, hamsters, rats and sheep. Similarity of primary clinical signs of poisoning and lack of significant difference in slope of the dose-response curves implied that the overall effect of the larkspur alkaloids was the same for all rodent species tested. Sheep were the most susceptible to poisoning by subcutaneous injection of larkspur extract with decreasing susceptibility in hamsters, mice and rats, but sheep had least susceptibility when comparing response to oral (by gavage) doses. Also, death occurred rapidly after gavage as compared with subcutaneous doses in mice, hamsters and rats, but was nearly the same for sheep. We conclude that, of the animals tested, mice would be the best choice for a bioassay of the toxicity of larkspur because of their high susceptibility, rapid response time, and small dose requirement.

Larkspur poisoning is a major cause of acute death of cattle on mountain and high plains rangelands of western United States. A nonlethal method to quantify dose response in cattle is needed to better estimate the toxicity of larkspur plants and the response of cattle to larkspur poisoning and to provide a basis for reference during studies. A numerical system of rating the clinical signs of larkspur poisoning was developed and used to describe the response of 10 Hereford cows given a repeated single daily dose of larkspur (Delphinium occidentale x barbeyi) by gavage. Larkspur poisoning resulted from a short-term cumulative effect, and a statistically significant increase in score was essentially maximal by 4 days. At the dose given, this effect did not persist for more than 4 days after cessation of dosing. Poisoning was most severe between 5 and 9 hours after dosing. Early signs of poisoning can be subtle and sometimes brief. The effect of larkspur poisoning can be exacerbated temporarily by exertion. Therefore, cattle could probably repeatedly consume an otherwise toxic daily dose, without manifesting marked signs of poisoning, if consumption decreased to a sufficient degree intermittently at 2- to 4-day intervals.

Fetal movement, observed by ultrasound imaging, was significantly reduced (P less than or equal to 0.001) in pregnant goats gavaged with Conium seed and Nicotiana glauca and temporarily reduced with fresh Conium plant. Conium seed and Nicotiana glauca induced cleft palate and multiple congenital contractures in 100% of the kids born to pregnant goats gavaged with these plants. Multiple congenital contractures included torticollis, scoliosis, lordosis, arthrogryposis, rib cage anomalies, over extension, and flexure and rigidity of the joints. However, in goats gavaged with fresh Conium plant, fetal movement was inhibited for only about 5 hours after each individual dosage and gradually returned to control levels 12 hours after dosing. Fetal malformations in this group were limited from modest to moderate contractures of the front limbs, which resolved by 8-10 weeks post partum. No cleft palates were induced. Fetal movement was not inhibited in goats fed Lupinus caudatus and no cleft palates or multiple congenital contractures were induced in their offspring. The duration of the reduction in fetal movement appears to be an important factor in the severity and permanence of the deformities, particularly with cleft palate, spinal column defects, and severe joint deviation and fixation.

Fetal movement in pregnant ewes gavaged with Conium maculatum (poison-hemlock) was reduced significantly, but temporarily. Fetal movement was observed by radio ultrasound at 45, 54 and 60 days of gestation in control ewes and on days 45, 54, and 60 of gestation immediately before and 1 hour following poison-hemlock feeding in treated ewes. Fetal movement was significantly reduced (P less than 0.01) 1 hour after poison-hemlock administration, but returned to normal within 18 hours post treatment. At parturition seven of eleven lambs born to seven treated ewes had varying degrees of front limb abnormalities. Modest to moderate flexure of the carpal joints, some lateral deviation in the front limbs at the pastern joint and kinked tails were observed. These malformations were transient and resolved spontaneously by 8 weeks after lambing.

Few field studies have attempted to relate effects of actual livestock grazing on soil and plant water status. The present study was initiated to determine the effects of periodic defoliations by cattle during spring on soil moisture and plant water status in a crested wheatgrass (Agropyron cristatum (L.) Gaertn. and A. desertorum (Fisch. ex Link) Schult.) pasture in central Utah. Soil moisture in the top 130 cm of the soil profile was depleted more rapidly in ungrazed plots than in grazed plots during spring and early summer. Soil moisture depletion was more rapid in grazed plots in one paddock after 1 July due to differential regrowth, but there was no difference in soil water depletion between plots in another paddock during the same period. This difference in soil water depletion between paddocks was related to a difference in date of grazing. Although more water had been extracted from the 60 cm to 130 cm depths in ungrazed plots by late September, cumulative soil moisture depletion over the entire 193 cm profile was similar in grazed and ungrazed plots. Prior to 1 July, grazing had no effect on predawn leaf water potentials as estimated by a pressure chamber technique; however, after 1 July, predawn leaf water potentials were lower for ungrazed plants. Midday leaf water potentials were lower for grazed plants before 1 July, but did not differ between grazed and ungrazed plants after 1 July. A 4- to 8-day difference in date of defoliation did not affect either predawn or midday leaf water potentials. The observed differences in water use patterns during spring and early-summer may be important in influencing growth and competitive interactions in crested wheatgrass communities that are subject to grazing by domestic livestock.

Ultrasonographic imaging was used to monitor the effects of locoweed (Astragalus lentiginosus) on fetal, placental, and cotyledonary developments in pregnant ewes and proved to be a useful noninvasive method of monitoring the effects of locoweed poisoning on fetal and placental development. Ultrasonographic imaging may be a good research technique to observe the effects of toxicants on fetal movement, fetal heart action, and growth and development of the fetus and placenta. Known effects of locoweed poisoning in pregnant ewes, such as fluid accumulation in the placenta (hydrops allantois, hydrops amnii), altered cotyledonary development, and fetal death were observed with ultrasonographic imaging. A previously unknown effect of locoweed on fetal heart action also was observed. Locoweed decreased fetal heart rates, caused cardiac irregularity, and decreased the strength of heart contractions. All ewes, except No. 3525, fed locoweed aborted. At necropsy, aborted fetuses had hypertrophy of the heart, right ventricular dilatation, rounded at the apex of the heart, and generalized edema.

Convulsions are characteristic of magnesium deficiency and hypocalcemia. In this study, weanling rats were fed magnesium deficient diets with varying concentrations of calcium and phosphorus. Diets were either normal (Mg =) or low (Mg −) in magnesium and were either low (Ca− or P−), normal (Ca= or P=) or high (Ca+ or P+) in calcium or phosphorus. After consuming the diets for 17 days, the rats were tested for audiogenic seizures and blood was then drawn for serum mineral analyses. Rats fed Mg−Ca=P=, Mg−Ca=P−, Mg−Ca+P= or Mg−Ca+P+ diets had high incidences of seizures. Those fed Mg−Ca−P=, Mg−Ca−P−, Mg−Ca=P+, Mg−Ca−P+ or Mg−Ca+P− diets had low incidences of seizures. In general, animals with low serum magnesium and calcium levels and high serum potassium levels were susceptible to audiogenic seizures. In this model, serum magnesium level is the most important determinant of seizure susceptibility, followed by calcium and potassium.

This study established the preferences of shrubsteppe granivores among seeds of 6 common sagebrushsteppe plants and related the preferences observed to physical and nutritional attributes of the seeds. Seeds of big sagebrush (Artemisia tridentata), cheatgrass (Bromus tectorum), Indian ricegrass (Oryzopsis hymenoides), western wheatgrass (Pascopyrum smithii), bitterbrush (Purshia tridentata) and green needlegrass (Stipa viridula) were placed in groups of petri dishes designed such that seed removal could be ascribed to either diurnal vertebrates, nocturnal vertebrates or ants. Though absolute quantities of seeds removed varied among the 3 granivore classes, calculations of preference based on weights of each seed species removed by each granivore class indicated that all 3 ranked the seeds similarly. Preference hierarchies of the 3 granivore classes were highly positively correlated with both calories per seed and % soluble carbohydrate of the seeds. The first correlation supports a basic prediction of optimal foraging theory —that foragers should maximize energy intake per unit time spent foraging. Both correlations emphasize the role of seed nutritional qualities in granivore seed selectivity in that soluble carbohydrate is a water-efficient energy source and its percentage is a good indicator of the digestible energy available in a food item. A corollary experiment comparing granivore use of an exotic seed (millet [Panicum miliaceum]) and a preferred native seed (Oryzopsis) demonstrated a distinct preference for the exotic. Since millet seeds are particularly high in % soluble carbohydrate, this result reinforced the apparent value of this nutritional attribute as a predictor of granivore seed preference. Among many seed resource characteristics upon which granivore seed selectivity might operate, our results indicate that individual species' nutritional composition may be particularly important. Thus, inferences about seed selectivity and resource partitioning among arid-land granivores should be interpreted with caution, especially those based on experiments using seed introductions, since the influence of seed nutritional attributes has not been widely acknowledged heretofore.

Because fasting and ketogenic diets decrease seizure susceptibility in epileptics, their anticonvulsant effects were studied using sound-induced seizures in the magnesium-deficient rat. Fasting markedly depressed seizure incidence and severity but did not affect latency (sec to seizure onset). High-fat diet increased incidence of audiogenic seizures and seizure severity, and decreased latency. Gavage of medium chain triglyceride, beta-hydroxybutyrate or glucose did not affect seizure incidence, seizure severity or latency. Nonspecific excitability level was not associated with treatment nor with seizure incidence, severity or latency time.

AbstractThe line‐source irrigation system has been used in many studies to determine the influence of several treatment variables and irrigation on yield and other traits. It has the advantage of using a minimum of space and shows visually the irrigation effects for some traits. Valid statistical tests for treatment effects and the treatment by irrigation interaction are possible if the treatments are replicated and randomized in strips at right angles to the sprinkler line. No statistical test is available for the effect of irrigation level on yield because irrigation amount is always applied systematically with no randomization. Since the irrigation effects are usually large and obvious there is no need to assign a probability level to their significance. However, caution should be exercised in the interpretation of small differences between adjacent irrigation levels and for potential bias in the estimates of the regressions of yield on irrigation level brought about by the systematic arrangement.