RESUMEN
Fresh Lotus corniculatus containing 27 g extractable condensed tannin (CT)/kg dry matter (DM) and 8 g bound CT/kg DM was fed at hourly intervals to sheep held in metabolism cages to study the effects of CT on nutrient digestion and on metabolism of methionine, cystine and inorganic sulphate in plasma. Polyethylene glycol (PEG) was continuously infused into the rumen of half the sheep to remove the effects of CT. Principal measurements in the two groups were plasma irreversible loss (IRL) rate and interconversions of methionine, cystine and inorganic sulphate using 35S labelling. CT in Lotus corniculatus had no effects on the apparent digestion of cellulose and minerals, slightly depressed DM, organic matter and hemicellulose digestion and markedly reduced the apparent digestion of N (P < 0.01). The concentration of NH3 and molar proportions of iso-butyric acid, iso-valeric acid and n-valeric acid in rumen fluid were markedly increased by the PEG infusion (P < 0.01), whereas total volatile fatty acid concentration and molar proportions of acetic acid, propionic acid and n-butyric acid were not affected. PEG infusion temporarily increased rumen protozoa numbers. CT greatly increased the IRL of plasma cystine (13.1 v. 7.0 mumol/min; P < 0.05) and reduced IRL of plasma inorganic sulphate (36.8 v. 48.1 mumol/min; P < 0.01) but had no effect on methionine IRL. CT increased transulphuration of methionine to cystine (4.37 v. 1.24 mumol/min; P < 0.05), increased cystine entering the plasma from whole-body protein turnover plus absorption from the small intestine (9.34 v. 5.75 mumol/min; P < 0.05) and increased cystine flux to body synthetic reactions (11.89 v. 5.41 mumol/min; P < 0.05). CT had no effect on the proportion of methionine total flux transferred to sulphate (0.05 v. 0.06; P < 0.05), reduced the proportion of methionine flux transferred to body synthetic reactions (0.68 v. 0.86) and markedly reduced the proportion of cystine flux transferred to sulphate (0.09 v. 0.27; P < 0.01). It was concluded that CT in Lotus corniculatus reduced rumen protein degradation and markedly increased utilization of plasma cystine for body synthetic reactions.
Asunto(s)
Cistina/sangre , Fabaceae/metabolismo , Metionina/sangre , Plantas Medicinales , Ovinos/sangre , Sulfatos/sangre , Taninos/metabolismo , Alimentación Animal , Animales , Digestión , Ácidos Grasos Volátiles/metabolismo , Masculino , Polietilenglicoles , Rumen/metabolismoRESUMEN
Two experiments were conducted with sheep fed on fresh Lotus pedunculatus containing 50-55 g condensed tannin (CT)/kg dry matter. Effects of CT were assessed by comparing control sheep (CT operating) with sheep receiving a continuous intraruminal infusion of polyethylene glycol (PEG) to bind and inactivate CT. Digestion of methionine and cystine was determined using a continuous intraruminal infusion of indigestible markers, whilst plasma irreversible loss (IRL) of methionine, cystine and inorganic sulphate was determined using 35S labelling. The proportion of microbial non-NH3-N (NAN) in whole rumen digesta NAN and the IRL of reducible S from the rumen were determined using a continuous intraruminal infusion of (NH4)2(35)SO4. The proportion of microbial NAN in whole rumen digesta NAN (0.44 v. 0.71) and the IRL of reducible S from the rumen (0.84 v. 2.49 g S/d) were lower in control than PEG sheep. PEG sheep lost 30% of ingested methionine and cystine across the rumen, whereas the control sheep lost no methionine and cystine across the rumen. Apparent absorption of methionine from the small intestine was 27% higher in control than PEG sheep, but both groups had a similar apparent absorption of cystine. The apparent digestibility of cystine in the small intestine was lower in control (0.42) than PEG (0.53) sheep, whereas the apparent digestibility of methionine was similar (0.78) for both groups. CT had no effect on plasma methionine IRL, but markedly increased the IRL of cystine (39.8 v. 22.4 mumol/min) and reduced the IRL of plasma inorganic sulphate (35.9 v. 50.2 mumol/min). A three-pool model comparing interconversions between the three plasma metabolites showed that CT increased the flow of cystine to body synthetic reactions (36.5 v. 17.3 mumol/min). This was due to trans-sulphuration of methionine to cystine being greater in control than in PEG sheep, whilst the oxidation of both methionine and cystine were reduced in control sheep. It was concluded that CT reduced the proteolysis of forage protein and the degradation of S amino acids to inorganic sulphide in the rumen, resulting in increased net absorption of methionine and increased utilization of cystine for body synthetic reactions in sheep with a high capacity for wool growth (and, hence, high cystine requirement).
Asunto(s)
Cistina/metabolismo , Metionina/metabolismo , Ovinos/metabolismo , Azufre/metabolismo , Taninos/administración & dosificación , Alimentación Animal , Animales , Digestión , Fabaceae , Absorción Intestinal , Masculino , Nitrógeno/metabolismo , Plantas Medicinales , Rumen/metabolismoRESUMEN
1. Five rumen-fistulated cows were given freshly cut ryegrass (Lolium perenne L.) and lucerne (Medicago sativa L.), on separate occasions, to compare rates of particle breakdown and aspects of rumen fermentation. 2. Cattle were required to consume their daily allowance (offered ad lib.) in two 2 h feeding periods daily. 3. During the first 2 h feeding period, dry matter (DM) intakes of ryegrass (4.75 kg) and lucerne (4.85 kg) were similar. Eating reduced 46% of ryegrass and 61% of lucerne to a size able to pass a 2 mm sieve (P less than 0.001). Rumen DM particles retained on the 2 and 4 mm sieves had a low probability of passage out of the rumen, and accounted for only 6% of faecal DM with both feeds. 4. Ryegrass was cleared from the rumen more slowly than lucerne. During eating, rumen DM particles which could not pass the 2 mm sieve increased from 323 to 511 g/kg for ryegrass and from 201 to 389 g/kg for lucerne. The rate of particle size reduction for lucerne stem was similar to that for ryegrass. 5. When lucerne was eaten the increases in rumen volatile fatty acid (VFA) and ammonia concentrations were much greater than for ryegrass (P less than 0.001). The proportions of plant chlorophyll released during eating were similar for both feeds (0.570 and 0.607), but 2 h after eating 22.3 g had been released from lucerne (79.1%) compared with 15.0 g from ryegrass (63.8%). The flux of water from the rumen to the omasum was similar for ryegrass (10.2 litres/h) and lucerne (12.7 litres/h) during eating, but declined to 6.0 litres/h after eating with the lucerne diet.