1. Three experiments were conducted using Lotus pedunculatus containing high concentrations of condensed tannins (CT), and utilizing the principle that polyethylene glycol (PEG) application (molecular weight 3350) will irreversibly bind a portion of the CT and thus reduce the dietary reactive (i.e. non-PEG bound) CT concentration. Lotus diets containing 95, 45 and 14 g total reactive CT/kg dry matter (DM), induced by spraying with three PEG rates, were given to sheep at hourly intervals (600 g DM/d) for 21 d (Expt 1). In Expts 2 and 3, lambs grazed areas oversown with either lotus (89 g CT/kg DM) or clovers (Trifolium repens and Trifolium pratense; < 1 g CT/kg DM) for 42 and 92 d respectively. In Expt 2 half the animals grazing each forage received oral PEG (75 g/d), whilst in Expt 3 half the lambs were sired by rams selected respectively for low or high levels of subcutaneous fat deposition.2. Hormone concentrations in plasma (Expt 1 only) were determined by radioimmunoassay. Rates of [U-14C]-acetate and ~-[U-~~C]glucose incorporation and oxidation by subcutaneous and abdominal adipose tissue removed at slaughter, together with rate of glycerol release, were determined during in vitro incubation in all three experiments.3. Plasma concentration of growth hormone was positively and linearly related to dietary reactive CT concentration, whilst 3,5,3'-triiodothyronine (T,) concentration tended to be negatively and linearly related to dietary reactive CT concentration. Diet CT concentration had no effect on plasma concentrations of the other hormones measured.4. Feeding of lotus high in CT was associated with a consistent but non-significant increase in the rate of glycerol release from adipose tissue, which was reduced as dietary reactive CT concentration was lowered through PEG application, and a reduction in the lipogenesis: lipolysis value. Selection for leanness decreased acetate incorporation and increased glycerol release from adipose tissue, with the effect not interacting with the diet.When tissues of Lotus sp. or sainfoin (Onobrychis viciifolia Scop) plants are disintegrated, such as during chewing, condensed tannins (CT) present in certain specialized cells are known to precipitate the soluble plant proteins by pH-reversible hydrogen bonding (Jones & Mangan, 1977). This action of CT, present in the leaves and stems of these two species, but not in those of white clover (Trifolium repens), red clover (Trifolium pratense) or lucerne (Medicago sativa), is known to increase non-ammonia-nitrogen (NAN) absorption from the intestines (Barry & Manley, 1984; Barry et al. 1986). The presence of CT has also been accompanied by increases in N retention in sheep, both for diets of sainfoin (Egan & Ulyatt, 1980), Lotus corniculatus (John & Lancashire, 1981) and Lotus pedunculatus (Barry et al. 1986). The presence of CT in Lotus pedunculatus has also been associated with reduced carcass fat content in grazing lambs, relative to lambs grazing white clover (Purchas & Keogh, 1984). The objectives of the present work were ...
A technique for ventriculolumba r perfusion of the cerebrospinal fluid space has been used to study the neuromuscular effects of low concentrations of magnesium and calcium in the cerebrospinal fluid of conscious sheep. Perfusion with synthetic cerebrospinal fluid solutions containing less than O' 6 mg magnesium/lOO ml produced episodes of tetany which were abolished by perfusion with a solution of normal magnesium concentration. This suggests that the low cerebrospinal fluid magnesium concentrations reported in cases of hypomagneseam ic tetany may result in changes within the central nervous system that could produce the nervous signs. Perfusates with a calcium concentration below 2·0 mg/lOO rnl caused hyperpnoea and continuous muscle tremors. Magnesium (0' 6 mg/lOO m!) and calcium (2·0 mg/lOO ml) perfused simultaneously acted synergistically to produce signs characteristic of low levels of each of the ions.
SummaryTwo experiments are reported in which mature, castrated male sheep were used to study the effect of a change of magnesium status, as induced by a continuous intravenous infusion of magnesium, on the faecal output of magnesium. In the first experiment, three artificial diets differing markedly in fibre content but extremely low in magnesium were used and in the second experiment, natural diets of frozen grass and of hay and ground barley.With the artificial diets, unit change in plasma magnesium concentration gave the same increase in faecal magnesium output with all three diets but on average faecal magnesium output was highest for the diet containing the highest content of fibre and least for the diet containing an intermediate amount of fibre, and the differences, though small, were statistically significant. With the natural diets, there was no significant difference between diets in the increase in faecal magnesium output in response to a change of plasma magnesium concentration but the order of response was much greater than for the artificial diets. It is concluded that absorption of magnesium from the gut is depressed at high plasma magnesium concentrations.
1. Diets of fresh kale (Brassica oleracea) and ryegrass (Loliumperenne) -clover (Trifolium repens) herbage were fed to growing sheep in three experiments. In Expts 1 and 3 the sheep were confined indoors and fed at hourly intervals, and all were given supplementary iodine to counteract kale goitrogens. Lambs grazed the two forages for 24 weeks in Expt 2, with and without intramuscular injections of iodized oil. The kale and herbage contained respectively 11 and < 0.1 g S-methyl-L-cysteine sulphoxide (SMCO)/kg dry matter (DM) and values for readily fermentable: structural carbohydrate (CHO) were 3.1 and 0.8, respectively.2. Blood samples were withdrawn from indwelling catheters (Expts 1 and 3) or venipuncture (Expt 2) and the plasma analysed for a range of hormones using radioimmunoassay procedures. Glucose irreversible loss (GIL) was measured in Expt 1 using primed continuous infusions of ~-[U-~~C]glucose. Samples of adipose tissue were removed from the shoulder area in Expt 3, and rates of ~-[U-'~C]glucose and [U-"C]acetate incoporation and oxidation were measured in vitro, together with the rate of glycerol release.3. In the presence of supplementary I,, kale feeding was associated with an elevation in plasma concentration of free thyroxine (TJ. Regardless of I, supplementation, sheep fed on kale had much higher plasma growth hormone concentrations than sheep fed on ryegrass-clover herbage, and this was accompanied by reduced plasma somatostatin concentrations.4. Plasma insulin and glucagon concentrations were similar for sheep fed on the two diets; GIL tended to be slightly but not significantly greater (9.4%) for sheep fed on kale than for those fed on ryegrass-clover herbage.5. Kale feeding was associated with increased uptakes of acetate and glucose into adipose tissue, reduced rates of oxidation of both substrates and no difference in rate of glycerol release. Each 1 nmol increase in glucose uptake was associated with 8.7 nmol acetate uptake ( P < 0.001).6. It is proposed that ruminants counteract protein inactivation, caused by production of dimethyl disulphide from SMCO in the rumen, through increasing circulating concentrations of growth hormone and T,, which then stimulate synthesis of replacement body proteins.The feeding value of herbage has been defined as the animal production response to grazing a defined forage, and is a function of both voluntary dry matter (DM) intake and nutritive value: DM eaten (Ulyatt, 1973). Kale (Brassica oleracea) diets are unique in containing much higher values of readily-fermentable : structural carbohydrate (CHO) than normal ryegrass (Lolium perenne)-clover (Trifolium repens) herbage (3.0 v. 0.8), and also containing the free amino acid S-methyl-L-cysteine sulphoxide (SMCO) which is absent from other forage species (Barry et al. 1 9 8 4~) .SMCO in brassica diets is fermented by rumen bacteria to dimethyl disulphide, which inactivates proteins through blocking sulphydryl groups (Fig. l ) , and is the cause of haemolytic anaemia associated with feeding brassica diets to
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