No abstract

High levels of both N and total higher fatty acids (HFA) in forage have been associated with increasing the grass tetany hazard to grazing cattle. The objective of this study was to determine the relationship between forage N, total HFA, and HFA species distribution in several forages.Forage N, ETA, MIAspecies concentration, and total chlorophyll were determined in immature vegetative growth of Agropy,con desertorum (Fisch.) Schult., Cynodon dactylon L., Loliutn perenne L., Trifoliunt repent L., and Trillcum aestiuson L. established with soil fertility levels up to 500 ppm N in the growth chamber. Forage HFA concentrations were positively and linearly related to forage N levels, but regression coefficients were not the same for all species. The HFA concentrations were as high as 16 mmol COOH/100g DM at 6% total N in first cutting Lolium perenne L. The relative HFA species distribution was the same within a given forage, even though total N concentrations ranged from 2 to 6%. The mean HFA specie concentrations (determined by gas-liquidchromatography relative to mean total HFA concentrations determined by titration) when expressed as percent for the grasses were: C14:0 -2 q , C16:0 -13%, C16:1 -1 q , C18:0 plus C18:1 -1%, C18:2 -11%, and C18:3 -67%. The total HFA concentrations were positively correlated with chlorophyll a + b concentrations which was expected, since the HFA of green plants is largely associated with chloroplast membrane.

Contents of Nand nonstructural carbohydrate fractions were measured over a year in herbage from a grazed ryegrass-white clover pasture, which had been fertilised with limeammonium nitrate at an annual rate of 0 (No), 112 (N112), and 448 (N448) kg N/ha. Total N wntent of the mixed herbage was often greater than 4% dry weight, and was highest in earlY spring and lowest in late summer. Levels in many cuts were increased significantly by the N448 treatment; the N112 treatment had little effect. The non-protein N and nitrate N contents were also highest in the N448 herbage, particularly in early spring; the level of nitrate N was also high in autumn. Most of the nitrate N occurred in the grass component. Total watersoluble carbohydrates, and those soluble in hot water but insoluble in cold water, usually comprised less than 12% and 1% dry w¢ight respectively of the mixed herbage. Total water-soluble carbohydrates were negatively and significantly correlated with both total N ;;nd "protein" N contents. The total N/total water-soluble carbohydrate ratio was, with one exception, greater than 0.3. No clear seasonal trends in the carbohydrate fractions were evident. Effects due to N treatments were generally small although sometimes significant for lhe hot-water-soluble fraction. The highest level of fertiliser N brought about high total N/total water-soluble carbohydrate ratios, and high herbage nitrate N contents, namely 0.66% dry weight in early spring and an average of 0.45% in August-January. The implications of these results for animal health are discussed. 231

A simple paper chromatography method is described for the separation of the organic acids in pasture plants using an eluting solvent of tert-amyl alcohol-iso-amyl alcohol-90 % formic acid-water (48 : 32 : 10 : 40). The quantitative estimation of one plant metabolite, trans-aconitic acid, was obtained by eluting the acid from the paper with a mixture of acetic anhydride, pyridine, and 95% ethanol and measuring the absorbence of the resultant complex at 370 nm in a spectrophotometer.Analyses of some typical New Zealand spring forage grasses showed that they could he differentiated into 'accuniulntors' and 'non-iLccIiiiILiIator~' or /miwconitic acid.

The complexing of Ca2+ and Mg2+, in a salt solution of cationic composition similar to that of the duodenal fluid of a ruminant, by polysaccharides, lignin and organic acids from the grass Yorkshire Fog is investigated using an ion-exchange resin method. Regression expressions relating solution cation concentration to the equilibrium resin cation concentrations are derived and used as calibration equations to determine the amounts of bound and ionic Ca2+ and Mg2+ in solutions in equilibrium with the plant fractions. Pectin, lignin and the organic acids are efective in complexing a large proportion of the Ca2+ in a non-ionic form but only lignin and the acids display significant complexing of Mg2+. The hemicelluloses and cellulose have little ability to complex either Ca2+ or Mg2+. The results are discussed in terms of the digestion of these plant fractions in vivo.Introduction MANY of the investigations into the causes of hypomagnesaemia in ruminants have centred on the physico-chemical nature of calcium and magnesium in their passage through, and absorption from, the digestive tract.1-4 Little attention, however, has been paid to the suspended organic material in the digesta and its possible role in the binding of these cations in a non-ionic form. Evidence has been obtained5 for the binding of calcium and magnesium by the calcium-and magnesium-free sediment of abomasal digesta from sheep and it has been shown that 20-30% of the calcium and magnesium in the faeces of cattle are associated with fibrous organic residues4 Both of these studies involved animals fed on grass rations.Studies into the rate of loss of carbohydrates and cell wall constituents from the reticulo-rumen6~7 have shown that a considerable amount of the hemicellulose and virtually all of the lignin in grass rations pass undigested through the gut but little is known of their complexing ability, either in vivo or in vitro. On the other hand, organic acids, particularly ahydroxy carboxylic acids, are effective in complexing cations as water-soluble chelates.* Dietary citric acid9 and transaconitic acid10 have been implicated in the hypomagnesemic tetany syndrome but little is known of the survival of these water-soluble compounds beyond the rumen.Ultrafiltration and dialysis have been used extensively in studying the physico-chemical activities of cations in intestinal digesta1,3,5 but these techniques can be severely criticised since they are non-equilibrium processes. Specific calcium and magnesium electrodes could be used but are easily poisoned in biological solutions. Cation-exchange resins have been used in the study of ionic and complexed cations in milk11 and ruminant intestinal ultrafiltrates,4 and this method bas been used in this investigation since it does involve an equilibrium, namely, between the resin, a salt solution and the potential complexant. The distribution of cations on the resin at equilibrium can then be interpreted to give information on the activities of the cations in the solution.