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In previous experiments, ruminants preferred evening-harvested (PM-alfalfa) over morning-harvested (AM-alfalfa) harvested alfalfa hay when given a choice. Therefore, could strategic use of PM-alfalfa fed as a pellet or included as a component of receiving diets stimulate naive sheep to increase DMI early in the receiving period? Experiments were conducted to 1) determine preferences of naive sheep for pellets prepared from PM- and AM-alfalfa, 2) measure performance of wether lambs fed pellets prepared from PM- and AM-alfalfa, and 3) measure performance and productivity of ewe lambs fed receiving diets formulated with PM- and AM-alfalfa. Pelleting PM-alfalfa resulted in pellets having similar (P > 0.05) palatability to naive sheep as pellets prepared from AM-alfalfa. Inclusion of PM-alfalfa in receiving diets fed to ewe lambs resulted in greater consumption of alfalfa stem fractions (P 0.76). Based on data from this study, strategic dietary use of pellets or hay prepared from evening-harvested alfalfa did not stimulate naive sheep to increase DMI. Lack of commonality between experiments reported herein and other research may be because 1) sheep cannot discriminate as well as other livestock between AM- and PM-alfalfa, or 2) pelleting or including in mixed diets masks sheep-preferred characteristics of PM-alfalfa. Based on the alfalfa hay used in these experiments, it was not advantageous to use pellets or hay prepared from evening-harvested alfalfa for the specific purpose of encouraging naive sheep to increase DMI.

Selenium in certain soils may be taken up by plants in amounts to render them toxic. Seleniferous forage can be found in most of the western states. Intoxication of livestock by seleniferous plants has been classified as acute and chronic. Acute poisoning results from consumption of plants having high levels of Se; chronic Se poisoning has been described in two forms— alkali disease and blind staggers. Alkali disease is said to result from the consumption of seleniferous grains and grasses, and is manifest by loss of hair, lameness, and loss of weight. Blind staggers is slid to result from the consumption of Se indicator plants and is manifest by wandering, circling, loss of ability to swallow, and blindness. Some research casts doubt on the above classification of Se poisoning. Research using pigs (Sus scrofa domesticus) indicates that the source of Se does not alter the type of lesion or signs of poisoning observed. There are data available that suggest that blind staggers is not related to Se poisoning.

We are investigating the biotransfer of accumulated Se by the plant in several phytoremediation systems. In study I, we evaluated the biotransfer of Se from Indian mustard, a Brassica species, to the insect-cabbage looper (Trichoplusia ni); mortality, deterrence, and biomagnification of Se were examined. We determined that feeding behavior of food chain consumers was affected not only by the plant concentration of Se, but also by the mobility of the insects and choice of feed available. In study II, we examined the survival and development of beet armyworm (Spodoptera exigua) fed Se-enriched plant tissues from different lines of saltbush (Atriplex spp.) After feeding on lines of saltbush that produced high biomass and accumulated high concentrations of Se, insect growth and survival was reduced. In studies III, IV, and V, lambs, dairy cows, and rabbits were fed Se-enriched Brassica and Medicago (alfalfa) plants as part of their feed ration. None of the tested animals exhibited any Se toxicity symptoms, but they had increased levels of Se in most tissues sampled (e.g., organs, blood, urine, feces), excluding milk. In study VI, we evaluated biotransfer of Se from broccoli to rats to determine efficacy of Se for reducing colon cancer. We found that Se-enriched plant material was more effective than inorganic sources of Se for preventing precancerous colon lesions. Results from all studies clearly show that Se absorbed by plants can be transferred biologically in an intentional or unintentional manner to insects and animals.

Canola (Brassica napus) grown as a selected plant species for field phytoremediation of selenium (Se) may be harvested and utilized as Se-enriched forage for marginally Se-deficient lambs and cows. Two field studies were conducted under controlled conditions to evaluate the accumulation of Se into different animal tissues, including blood, excreta, and milk. In Study 1, treatments consisted of feeding lambs freshly cut Se-enriched canola (containing approximately 4 mg Se kg(-1) DM) or control canola (containing

Selenium (Se) occurs in various forms in soils, including inorganic selenite and selenate and organic selenomethionine. Plant uptake of the inorganic, but not the organic forms, has been studied extensively. Organic-Se uptake was therefore examined in two-grooved milkvetch (Astragalus bisulcatus (Hook.) Gray), a Se-accumulating forb, and western wheatgrass (Pascopyrum smithii (Rydb.) Love), a non-Se accumulating grass. Plants were grown for 56 days in nutrient culture enriched with 1 or 2 mg Se liter-1 as sodium selenite or 0.3 or 0.6 mg Se liter-1 as Se-DL-methionine or Se-DL-cystine. Growth was not affected by the Se treatments. Selenium concentrations in shoots were proportional to nutrient-solution concentrations for both species grown in sodium selenite and selenocystine, and for wheatgrass when grown in selenomethionine. Selenium concentrations in milkvetch were not increased by the higher concentration of selenomethionine. Shoots of milkvetch, growing in the low-Se treatment contained 243, 283, and 47 micrograms Se g-1, for the sodium selenite, selenomethionine, and selenocystine treatments, respectively, whereas values for the wheatgrass were 20, 32, and 17. Shoot:root Se concentrations were 1.2, 0.7, and 0.4 in milkvetch and 0.1, 0.5, and 0.1 in wheatgrass for the sodium selenite, selenomethionine, and selenocystine, respectively. Selenium is more readily transported to shoots in the accumulator plant, or conversely; there is a barrier to Se movement to shoots in the nonaccumulator plant. Wheatgrass contained sufficient Se to be of concern in animal toxicosis and because of greater dry matter yield accumulated as much or more Se than did the milkvetch.

Grass tetany, a Mg deficiency of ruminants, accounts for significant economic losses to Western cattlemen during the spring grazing period on Agropyron desertorum. This nutritional deficiency may also occur when ruminants graze other temperate grasses, but the soil-plant-animal factors leading to the problem are not well understood. The objective of this study was to provide definitive data relating seasonal changes in the chemical composition of forage to the occurrence of grass tetany on semiarid grasslands. The field experiment was established on two calcareous soils where grass tetany had previously occurred. Agropyron desertorum forage was harvested from both sites at regular intervals during the spring tetany period in each of 5 years. The forage samples were analyzed for mineral elements, N, total water-soluble carbohydrates (TWSC), higher fatty acids (HFA), ash alkalinity, and aconitic acid. High levels of N and HFA, which are known from other studies to reduce Mg availability to the animal, coincided with the occurrence of tetany. The low Mg concentrations measured in the forage probably provided only marginal levels of available Mg to the grazing animals. A rapid increase in the ratio of N/TWSC coincided with the onset of tetany, and may be the primary factor which indirectly decreases Mg availability and precipitates the occurrence of tetany. Although the relationship of the protein/energy imbalance to grass tetany has been suggested previously, as far as the authors are aware this is the first time that N/TWSC values obtained during the growing season have been documented in conjunction with the occurrence of grass tetany.

Publisher Summary Freezing injury in plants represents a major economic loss to agriculture. Early research on freezing phenomena in plants centered on plant selection and classification according to their ability to become cold hardy and survive freezing temperatures. Recent work has centered on the differentiation between plants with or without the ability to harden. This chapter concentrates on the effects of low-temperature stress on cell membranes and other macromolecules in the cell and relates these to the overall plant response to chilling or frost injury. The freezing temperature of plant material is determined by the chemical potential of the plant water. The freezing point drops approximately 1°C for each 12 bars equivalent negative pressure (in the range of 0 to -10°C). Ice does not form spontaneously as the temperature drops to the freezing point of the plant water. Rather, the solution tends to undercool to variable and somewhat unpredictable temperatures. When nucleation does occur, it will generally be in the extracellular space. When tender plants show immediate frost injury from temperatures not lower than -3 or -4°C, the damage is caused primarily by ruptured cell membranes. Some nonhardy plants, such as peas and lettuce, can survive temperatures of -3 or -4°C for a few hours, even though ice is present in the plant tissue.

Increasing available Mg in crested wheatgrass (Agropyron spp.) could reduce the incidence of grass tetany (hypomagnesemia) in ruminants grazing this forage. Raising the Mg levels might be done through genetic processes if enough variation in ion concentration existed in the Agropyrons. The purpose of this study was to determine the genetic variation in Mg, Ca, and K concentrations in 2 crested wheatgrass populations. Parent plants were vegetatively propagated to provide 6 replicates each of 12 clones of crested wheatgrass (A. desertorum) and 16 F3 clones of colchicine-induced tetraploid A. cristatum X natural tetraploid A. desertorum. Each plant was selected on a basis of seedling and mature plant vigor, forage, and seed yield, leafiness, resistance to pests, and response to environmental stress. The 2 populations were grown in separate, space-planted nurseries at Logan, Utah. Herbage was harvested at the pre-boot and early flowering stage in each of 2 years. Magnesium and Ca were determined by atomic absorption and K by flame emission. A reduced tetany potential (RTP) index for each clone was calculated as the sum of normalized Mg and (Ca+Mg)/K values. Significant (P & 0.01) differences for all traits were detected among clones in each population. All traits, except K and RTP, were closely correlated. Broad-sense heritability values for most traits ranged from 0.61 to 0.84. Enough genotypic variation existed in both populations to warrant breeding lines with higher concentrations of Mg and larger RTP values. Such changes could reduce the incidence of grass tetany in livestock grazing crested wheatgrass.