1. Vegetative secondary growth Lotus pedunculatus was cut daily, and fed fresh at hourly intervals (600 g dry matter (DM)/d) to three groups each of three sheep fitted with permanent cannulas into the rumen and duodenum. Lotus fed to two of the groups was sprayed with low and high rates of polyethylene glycol (PEG; molecular weight 3350), which specifically binds the condensed tannins (CT). Nutrient intake and faecal excretion were measured directly, duodenal flows estimated from continuous intraruminal infusion of inert ruthenium phenanthroline (Ru-P) and CrEDTA markers, and rumen pool sizes measured at slaughter.2. Dietary concentrations of total reactive CT (i.e. that not bound to PEG) were 95,45 and 14 g/kg DM, whilst the corresponding values for free CT were 15, 5 and 2 g/kg DM.3. Increasing dietary reactive CT concentration linearly increased duodenal flows of non-ammonia nitrogen, but linearly decreased the apparent digestibility of energy and organic matter, and rumen digestion of hemicellulose but not of cellulose. Rumen digestion as a proportion of total digestion was increased by the higher PEG rate for organic matter, energy, pectin and lignin.4. High dietary CT concentration was associated with increased N retention. Rumen ammonia concentration and pool size showed only a slight decline on this diet, indicating that there must have been increased recycling of N into the rumen.5. Increasing dietary reactive CT concentration had no effect on the rate at which carbohydrate constituents were degraded in the rumen per unit time (FDR), but increased the rate at which their undegraded residues (FOR) left the rumen per unit time. The latter appeared to be the principal mechanism by which rumen digestion as a proportion of total digestion was reduced at high dietary CT concentrations. From a comparison of FDR and FOR of carbohydrate components in lotus and Brassica oleracea diets, it was concluded that hemicellulose digestion was rate-limiting for rumen cell-wall digestion, probably due to bonding with lignin. However, the considerable post-rumen digestion of hemicellulose was not associated with post-rumen lignin digestion.6. It was concluded that a desired concentration of CT in Lotus sp. should represent a balance between the positive effect of CT in improving the efficiency of N digestion and their negative effect in depressing rumen carbohydrate digestion. A recommended concentration is 3 W O g/kg DM.From measurements of duodenal non-ammonia nitrogen (NAN) flow it has been estimated that the absorption of essential amino acids was limiting the output of high producing ruminants consuming fresh forages ad lib., and this has been verified through post-rumen supplementation studies with protein (Barry 198 1, 1982; Beever & Siddons, 1986). From a review of New Zealand (NZ) literature, Barry & Reid (1986) concluded that the presence of condensed tannins (CT) uniformly distributed throughout leaf and stem tissue in forage plants would increase amino acid supply through CT reacting with plant proteins by reve...

1. Voluntary intake was determined with vegetative Lotus pedunculatus cut and fed fresh to growing sheep of 42-46 kg live weight. Effects attributable to condensed tannins were assessed by growing the plant under high and low levels of soil fertility, inducing low and high concentrations of tannin (Expt l), or by binding the tannins through spraying the herbage with polyethylene glycol (molecular weight 3350, PEG; Expt 2). Primary-growth lotus was used in Expt 1 and secondary-growth lotus in Expt 2. Concentrations of total and free condensed tannin were determined in fresh lotus, free tanning being defined as that not bound by mascerates of the plant.2. In Expt 1 the herbages fed contained respectively 46 and 106 g total condensed tannin/kg dry matter (DM) and 3 and 14 g free condensed tannin/kg DM. Mean metabolizable energy (ME) intakes were 0.89 and 0.77 MJ/kg live 3. The lotus used in Expt 2 contained 63 and 5 g total reactive condensed tannin and free condensed tannin/kg DM respectively. After spraying with PEG at 2.4 g/g total condensed tannin, these values were reduced to 7 and 0.5 g/kg DM respectively. PEG addition increased apparent digestibility (proportion of each nutrient ingested) of cellulose, hemicellulose and nitrogen by 0.05,0.08 and 0.26, and increased ME intake from 0.48 to 0.69 MJ/kg live ~eightO'?~ per d.4. It was concluded that high concentrations of condensed tannins depressed ME intake, due to depressions in both the voluntary intake and digestion of organic matter. The stimulation of hemicellulose and cellulose digestion by PEG addition suggests that the condensed tannin was depressing rumen digestion.5. It is considered that free tannins are most likely to have been responsible for the depressive effects in the present study. This could be due to their reaction with microbial enzymes in the rumen, the tannin content of the plant exceeding the capacity of the plant protein to bind it, or to reaction with enzymes secreted into the small intestine following the absorption of amino acids. In either instance free tannins could also react with proteins of the gut wall.Reponses in protein deposition in body tissue and in wool to abomasal infusion of casein + methionine in growing lambs fed on fresh ryegrass (Lolium perenne)-based herbage ad lib. have shown that absorption of one or more essential amino acids from the small intestine is below animal requirements (Barry, 1981). A subsequent review (Barry, 1982) concluded that lactating ewes and dairy cows consuming similar fresh pasture ad lib. of high metabolizable energy (ME; 11.3 MJ ME/kg dry matter (DM)) and total nitrogen (33 g/kg DM) content were also likely to be deficient in the absorption of essential amino acids, relative to the requirements for optimum production at the level of voluntary ME intake achieved. One of the two main predisposing causes of this deficit was identified as the exceptionally high degradation rate of the proteins in fresh forages in the rumen (0.7).

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I. Kale (Brassica oleracea) and ryegrass (Lolium perenne)-clover (Trijolium repens) pasture, grown under similar soil conditions, were grazed in the vegetative state by growing lambs of 23.6 kg initial live weight for 24 weeks. The kale and pasture contained respectively 20 and 270pg iodine/kg dry matter (DM). The kale also contained 8 pmol total glucosinolates/g DM and 11.5 g S-methyl-L-cysteine sulphoxide (SMCO)/kg DM, both of which were nondetectable in the pasture diet.2. Intramuscular injections of I (475 mg) were given during weeks 1 and 12 to half the forty-eight lambs grazing each forage. Wool growth, live-weight gain and cytochrome oxidase (EC 1 .9.3.1) activity of biopsied hind-limb muscle were measured at 6-week intervals. Jugular blood samples were removed every 6 weeks for the determination of haematological factors and serum thyroid hormone concentrations. All animals were slaughtered at the end of the experiment and thyroid weight, thyroid I content, and the weight and cytochrome oxidase activity of heart muscle determined.3. Serum concentrations of thyroxine (T,) increased from 20 to 48 nmol/I during the 24 weeks that control lambs grazed ryegrass-clover pasture. I supplementation increased the concentration and total amount of I in the thyroid gland and increased serum T, concentration, but did not affect any other values measured in the lambs grazing the pasture herbage. Serum concentrations of triiodothyronine (T,) were stable at 2 nmol/l for both groups.4. Control lambs grazing kale for 24 weeks showed marked thyroid enlargement and depletion of thyroid I. By week 6, serum T, and T, concentrations had declined to 2-5 nmol/l and 1 nmol/l respectively and were stable at these values for the remainder of the experiment. I supplementation eliminated the thyroid depletion of this element, caused serum T, concentration to rise and stabilize at 90 nmol/l by week 18, and T, concentration to stabilize at 2 nmol/l by week 6. From week 6 onwards, wool growth was increased 13% by I supplementation, whereas empty body growth was unaffected.5. Lambs grazing kale developed haemolytic anaemia, due to rumen fermentation of SMCO. I supplementation enabled the lambs to resist the anaemia better by increasing erythrocyte reduced gluthathione (GSH) content. Relative to pasture-fed animals, lambs grazing kale and supplemented with I showed increased heart muscle weight and cytochrome oxidase activity. This represented a compensatory mechanism for the reduced blood oxygen-carrying capacity caused by the anaemia. I-deficient (1.e. control) lambs grazing kale showed reduced cytochrome oxidase activity in both heart and hind-limb muscle.6. The findings are in accord with T3 having a greater biological potency than T4 for regulating rates of body and wool growth. Increases in heart weight, heart cytochrome oxidase content and erythrocyte GSH content of kale-fed lambs were, however, associated with elevation in serum T, and not T, concentration.7. I requirements of growing sheep and cattle consuming the pasture diets ar...