No abstract

A study of the intake and digestion of lucerne and wheaten hays was made with Merino wethers offered chopped hay near ad libitum, ground hay at the same level as the chopped hay, and ground hay near ad libitum. These treatments were imposed to separate the effects of grinding per se from those associated with the increased intakes of roughages permitted by grinding. The following conclusions were reached: (1) Grinding permitted a substantial increase in food consumption on both diets. (2) Grinding per se of both hays produced little change in the relative importance of stomach and intestines as sites of digestion of any of the feed components studied. Grinding had no effect on the digestibility of lucerne hay but reduced that of wheaten hay, mainly by reducing the digestion of the cell wall constituents. (3) When both ground hays were offered near ad libitum, digestibility was reduced, mainly because of a fall in digestibility of the cell wall constituents. With lucerne hay, grinding increased the organic matter intake by 37% above chopped hay but the organic matter digested was increased by only 27%. By contrast, on wheaten hay an increase of 42% in organic matter intake on ground hay resulted in the digestion of only 18% more organic matter than on chopped hay. On both diets the relative extent of digestion occurring in stomach and intestines was similar to that observed with chopped hay. (4) On all three lucerne diets there was a net loss of 22–25% of dietary nitrogen from the stomach. By contrast, on the wheaten hay diets a substantial gain of nitrogen occurred during the passage of digesta through the stomach; the amount of nitrogen gained was independent of feed processing and feed intake. The crude protein apparently digested in the intestines was approximately 17% of the total organic matter digested on the lucerne diets and 10–12% of that digested on the wheaten hay diets. (5) Within diets the relative proportions of individual rumen VFA were the same on chopped and ground hay offered near ad libitum. (6) Grinding probably did not cause any change in the composition of the end products of digestion. (7) On the lucerne hay diets, 16–20% of the organic matter digested in the rumen was soluble carbohydrate, on wheaten hay approximately 40–50%.

Sheep fed the forage Digitaria pentzii fertilized with sulfur were compared with those fed unfertilized forage for the rumen microbial population involved with fiber degradation. No differences were detected in the bacterial population as determined by anaerobic cultures on a habitat-simulating medium, xylan, or pectin, by 35S labeling techniques for microbial protein, or by transmission electron microscopic studies of bacterium-fiber interactions. Rumen volume and water flow from the rumen were not different for sheep fed each of the forages. Rumen fungi were prevalent in sheep fed sulfur-fertilized D. pentzii as shown by sporangia adhering to forage fiber and by colonies developing from zoospores in roll tubes with cellobiose plus streptomycin and penicillin. Fungi were absent or in extremely small numbers in sheep fed unfertilized forage. Nylon bag digestibility studies showed that the fungi preferentially colonized the lignified cells of blade sclerenchyma by 6 h and caused extensive degradation by 24 h. In the absence of bacteria in in vitro studies, extensive hyphal development occurred; other lignified tissues in blades (i.e., mestome sheath and xylem) were attacked, resulting in a residue with partially degraded and weakened cell walls. Nonlignified tissues were also degraded. Breaking force tests of leaf blades incubated in vitro with penicillin and streptomycin and rumen fluid from sheep fed sulfurfertilized forage or within nylon bags in such sheep showed a residue at least twice as fragile as that from sheep fed unfertilized forage. In vitro tests for dry matter loss showed that rumen fungi, in the absence of actively growing bacteria, could remove about 62% of the forage material. The response of rumen fungi in sheep fed sulfur-fertilized D. pentzii afforded a useful in vivo test to study the role of these microbes in fiber degradation. Our data establish that rumen fungi can be significant degraders of fiber and further establish a unique role for them in attacking and weakening lignocellulosic tissues. The more fragile residues resulting from attack by fungi could explain the greater intake consistently observed by sheep eating sulfur-fertilized compared with unfertilized D. pentzii forage. Rees and co-workers (32, 33) showed that sulfur fertilization (+S) reduced retention time of forage in the rumen and increased voluntary intake and digestibility compared with unfertilized (-S) Digitaria sp. forage. The authors suggested that depressed microbial activity due to a sulfur deficiency could have caused poor animal response to-S forage. Similar studies with +S and-S Digitaria pentzii (31) indicated that S fertilization increased voluntary intake and reduced rumen ammonia levels, indicating enhanced microbial activity in the rumen.

Studies have been made of the digestion and metabolism in Merino wethers of the isoflavones in subterranean clover (Trtfolium subterraneurn cv. Clare) and red clover (T. pratense). The dietary intake of isoflavones with both clovers was about 9 g per day. With the subterranean clover, the isoflavones were predominantly genistein and biochanin A, and slight teat length increases in the wethers ingesting this clover indicated a low level of oestrogenicity. With the red clover formononetin represented 60% of the isoflavone present and the wethers on this diet exhibited maximal teat length increases indicating a high level of oestrogenicity. Less than 1 % of the daily intake of the isoflavones was excreted as such in the faeces and urine; hence most of these compounds were metabolized or retained in the sheep. The dietary isoflavones were found to disappear rapidly from the rumen, and it was estimated by using marker techniques that the removal of these compounds from the stomach (rumen, reticulum, omasum, and abomasum) was virtually complete. Equol (7,4'-dihydroxyisoflavan), a metabolite of formononetin, was the predominant phyto-oestrogen in the digesta and excreta when red clover was given. The excretion of 3.9 g/day of this compound, mainly in urine, was equivalent to 70% of the intake of formononetin. It was calculated that about 86% of the equol produced in the rumen was absorbed from that organ; the mean residence time for equol in the rumen was estimated to be 1.7 hr. The isoflavones were present in blood plasma mainly in conjugated forms. Equol predominated with both clovers. The levels of equol were much lower with the subterranean clover than with the red clover diet; the concentrations of the conjugated form were respectively 13 and 300-440 �g/100 ml. Equol in the free form, although not detectable with the subterranean clover, was present at 4-10 �g/100 ml with red clover. The data were considered to be consistent with the conclusion that equol accounts for most of the phyto-oestrogenic activity in sheep fed on clovers containing high levels of formononetin.

[Manu8C1'ipt received Augu8t 13, 1970] Ab8tractPlasma insulin and growth hormone concentrations have been measured by radio· immunoassay in fasting sheep and in sheep fed either a restricted amount of a concentrate diet or virtually ad libitum a variety of dried forage diets providing a wide range of energy and protein intakes.The plasma insulin concentration of sheep on each diet was positively correlated with the amount of organic matter digested in the alimentary tract (I' = O' 74) and to the amount of crude protein digested in the intestines (I' = 0·74), but was less clearly correlated with the ruminal production of the individual volatile fatty acids (acetate, I' = 0·45; propionate, r = 0·51; butyrate, r = 0·40). Plasma insulin was poorly correlated with the plasma glucose concentration (I' = o· 28), but in a group of sheep fed on ryegrass diets it was closely related to the glucose entry rate.The plasma insulin concentration was also correlated with plasma concentra· tions of valine, tyrosine, isoleucine, and phenylalanine.The results suggest that the amount of protein digested in the intestine is the main factor in dietary regulation of the plasma insulin concentration of sheep fed virtually ad libitum.Plasma growth hormone concentrations were negatively correlated with the amount of organic matter digested in the alimentary tract (I' = -0·62), with the amount of crude protein digested in the intestines (I' = -0·63), and with the plasma insulin concentration (r = -0·71). It is suggested that the negative correlation with plasma insulin concentration reflects the existence of a negative feedback system between the rate of glucose utilization and growth hormone secretion.