Chaffed lucerne hay of 64 % apparent organic matter (OM) digestibility was fed to wether sheep under four feeding regimens: two levels of dry matter (D.M.) intake (700 (L) and 1050 (H) g/day) and within each level two feeding frequencies (once a day (daily) and once an hour (hourly)). Three separate groups of sheep were used concurrently: a slaughter group was used to obtain feeding behaviour data and to measure pool sizes and obtain samples from the reticulo-rumen; a digestion group, in which each sheep was prepared with a rumen and a duodenal cannula, was used to measure duodenal digesta flow, rumen microbial growth and reticulo-rumen motility; a balance group was used to measure digestibility and nutrient balances.High D.M. intake increased reticulo-rumen pool sizes and flow rates but it did not affect apparent digestibilities or the proportions of OM, fibre, cellulose, hemicellulose, lipid and nitrogen digested in the stomach and intestines. Increased feeding frequency had a major effect on reticulo-rumen pool sizes but did not affect apparent digestibilities or partition of digestion of non-nitrogenous constituents. Daily feeding resulted in increased total-N flow to the duodenum; however, N retention was significantly greater with frequent feeding. It is suggested that this was due to a more efficient tissue utilization of N.The kinetics of digesta flow within the reticulo-rumen, expressed as fractional flow rates, were studied with data from sheep fed hourly. The fractional inflow, outflow and disappearance rates for OM, fibre, cellulose and hemicellulose did not change with an increase in intake because of an equivalent increase in reticulo-rumen volume. Increasing D.M. intake by 50 % resulted in a 24 % increase in water intake, a 19 % increase in reticulo-rumen water volume, and a 49 % increase in water outflow rate. The data suggest that the increased outflow of water was achieved by increasing the net flow of water across the mucosa into the reticulo-rumen, rather than by increasing salivation.There was no difference between treatments in the frequency of reticulo-rumen contractions. It was calculated that for each A sequence contraction, OM flow was 0-26 and 0-37 g and water flow was 4-38 and 0-36 g on L and H intakes respectively. A 50 % increase in intake resulted in a 42 % increase in OM passage per A sequence contraction. This increased passage with intake was not accompanied by an increase in reticulorumen contraction frequency.TMTTJODTTPTTOIST Waldo, Smith & Cox, 1972; Baldwin, Koong & w Ulyatt, 1977;Mertens & Ely, 1979; Black et al. A large amount of information is available con-1981), has identified areas of research which are cerning digestion and metabolism within the reti-likely to yield useful information on the control culo-rumen. Far less is known about the processes processes. These include: the effects of chewing that control breakdown of food residues and their during eating and rumination on particle size repassage out of the reticulo-rumen. The use of duction and fermentation, t...

Sheep prepared either with a rumen cannula, or with a rumen cannula plus re-entrant cannulae in the duodenum and ileum were fed fresh 'Ruanui' perennial ryegrass (R), 'Manawa' short rotation ryegrass (M) and white clover (C) at dry-matter intakes ranging from 450 to 1000 g/24 h. Paper impregnated with chromic oxide was given once daily via the rumen fistula as a marker.Amounts of non-ammonia-nitrogen (NAN) entering and leaving the small intestine and nitrogen (N) excreted in the faeces were regressed against the intake of N for each sheep and these equations (all significant P < 0-05) were used to calculate the extent of digestion in the stomach, the small intestine and the large intestine at two levels of OM intake (500 and 800 g daily). Amino acid analyses of feed and digesta samples are also presented together with calculations of the apparent absorptions of individual amino acids from the small intestine.At an intake of 500 g OM amounts of NAN entering the small intestine were significantly greater (P < 0-05) in sheep given M than in sheep given R or C. At an intake of 800 g OM amounts in sheep given M were significantly greater (P < 0-01) than in sheep given R. NAN leaving the small intestine and N excreted in the faeces were similar for all three diets.At an intake of 800 g OM apparent absorptions of NAN from the small intestine of sheep given M (0-47 xN intake+ 2-8 g/24 h) and sheep given C (0-51 xN intake -1-3 g/24 h) were significantly greater (P < 0-01 and P < 0-05 respectively) than of sheep given R (0-41 xN intake -0-5 g/24 h). As intake of herbage was increased the partition of digestion altered.Only small differences between herbages were found in the amino acid composition (g amino acid/100 g protein) of either duodenal or ileal digesta, but because of the large differences in the flows of NAN, the apparent absorptions of individual amino acids from the small intestine were much higher in sheep given M than in sheep given the other two species.The results are discussed in the light of available information on sites of digestion of herbage diets in sheep.

In two experiments the intakes and utilisation of pure swards of perennial ryegrass (P), short-rotation ryegrass (S), and whi:e clover (e) were measured with grazing sheep, under conditions where there were differences in live-weight gain between treatments.There were differences in feed intake, but, because of high variability between animals, few were statistically significant. The intake of S was generally higher than that of P. [n one experiment the intake of e appeared to be higher than that of the ryegrasses, hut this was not repeated in the second experiment.There were consistent differences in the gross efficiencies of utilisation of digested energy for live-weight gain in both experiments, in the order e>s>p.Possible reasons for these differences in intake and utilisation are discussed.

Sheep prepared either with a rumen cannula, or with a rumen cannula plus re-entrant cannulae in the duodenum and ileum were fed fresh 'Ruanui' perennial ryegrass (R), 'Manawa' short-rotation ryegrass (M) and white clover (C) at dry-matter intakes ranging from 450 to 1000 g/24 h. Paper impregnated with chromic oxide was given once daily via the rumen fistula as a marker.Amounts of Mg, Ca, P, K and Na entering and leaving the small intestine and excreted in the faeces were regressed against the intake of each element for each sheep and these equations (all, other than the faecal excretion of Na, significant (P < 0-05)) were used to calculate the extent of apparent absorption or secretion in the stomach, the small intestine and the large intestine at two levels of OM intake (500 and 800 g daily).Quantities of Mg (at high intake), Ca and K (except sheep fed M) leaving the stomach were significantly lower (P < 0-05), while the amounts of P and Na were significantly higher (P < 0-01) than the amounts consumed. Quantities of Mg (at high intakes) and Ca leaving the small intestine were significantly higher (P < 0-05) while amounts of P, K and Na (at high intakes) were significantly lower (P < 0-05) than the corresponding quantities entering the small intestine. At both intakes in the case of Na and at the higher intakes in the case of the other mineral elements, quantities of Mg, Ca (except sheep fed C), P, K and Na excreted in the faeces were significantly less (P < 0-05) than the amounts entering the large intestine.Thus at the higher intakes there were net absorptions of Mg, Ca and K (except sheep fed M) from, and net secretions of P and Na into, the stomach. The small intestine was the major site of net absorption for P and K and a minor site for Na, while a net secretion of Mg and Ca occurred into this region. Net absorption of Mg, Ca, P, K and Na occurred from the large intestine at the higher intakes.The retention of Mg, Ca and P is discussed in relation to the animals' minimal daily requirements of these elements.

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