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The aim of this study was to determine the effects of two forage sources supplemented either from Day 3 or Day 15 of age on growth performance, rumen fermentation, blood metabolites, intestinal enzymes and incidence of diarrhoea in Holstein bull calves. Forty neonatal male Holstein calves (40.6 ± 5.8 kg BW) were randomly assigned to five treatments, with eight replicates each, including calves fed starter feed without any forage provision (Control; CON), and the same starter plus either chopped alfalfa hay started fed from Day 3 (AE) or Day 15 of age (AL) or chopped oat hay fed from Day 3 (OE) or Day 15 of age (OL). The study finished when all calves were weaned at 56 days of age. During the experimental period average daily gain, starter intake and total dry matter intake were similar among calves fed either of five dietary treatments (P > 0.05). Empty rumen weight (proportional to bodyweight) was greater in CON calves than in OL calves (P < 0.05). The AL calves had a lighter small intestine compared with CON, OL and AE calves, but similar to OE. Frequency of diarrhoea was not affected by dietary treatment (P > 0.05). Rumen concentration of total volatile fatty acids and pH were similar among dietary treatments (P > 0.05). Control calves had a lower molar proportion of acetate compared with OL calves, but similar to the other calves (P < 0.05). Forage-fed calves had similar molar proportion of butyrate to CON calves. Acetate to propionate ratio was higher in OL-fed calves than in those fed CON and AE diets (P < 0.05). Rumen concentration of NH3-N tended to be higher (P = 0.059) in CON calves than in forage-fed calves. During experimental period, serum concentrations of globulin, total protein, glucose and total cholesterol were similar among dietary treatments. Calves fed OE had lower serum concentration of albumin than those fed other diets (P < 0.01). Serum concentration of triglycerides (P < 0.05) was greater in calves fed AE followed by those fed AL and then those fed CON, OL and OE. The AL-fed calves had a higher serum lactate dehydrogenase compared with AE and OE fed calves, but similar to calves fed OL and CON. Duodenum amylase concentration was greater (P < 0.05) in AE-fed calves compared with CON-fed calves, but similar to calves fed AL, OL and OE. Calves fed OL had greater (P < 0.05) ileum lipase concentration than those fed OE, but similar to calves fed AL, AE and CON. In conclusion, provision of chopped alfalfa or oat hay to calves either from Day 3 or Day 15 of age resulted in similar starter intake and total dry matter intake and feed efficiency and physical development of the reticulorumen compared with calves fed the CON diet, which justifies the supply of forage to young calves, even at an early age, as forages are generally cheaper than starter concentrates.

The performance of electronic identification transponders encased in ceramic capsules inserted into the reticula-rumen was assessed in 3 groups of cattle: 1059 two-year-old feedlot steers, 11 penned calves and 46 grazing calves. Insertion of capsules presented little difficulty and at slaughter, examination of the reticulorumen showed no visible signs of damage to the reticula-endothelium due to the capsules. The retention rate of the capsules was 100% in adults when slaughtered 55-107 days after capsules were inserted. All losses of capsules from calves occurred before calves were 21 weeks of age. Transponders were successfully read both in the live animal and in the body on the slaughter chain. All transponders in the reticulorumen of grazing calves were functioning normally up to 46 weeks after being implanted. At slaughter, capsules were recovered easily with no risk of contaminating meat or by-products. Small steel metallic objects near the capsule appeared not to affect the reading distance of the transponder.

A number of experiments were undertaken to establish the productivity of lactating dairy cows when offered green, vegetative Persian clover (Trifolium resupinatum) herbage and to study its utilization by these cows. The research included indoor feeding and grazing experiments and intensive metabolism studies. Levels of daily intake varied from 1.3 to 4.5 kg DM/100 kg liveweight and in early-to-mid lactation, milk yields as high as 30 kg/day were sustained. In early-to-mid lactation, marginal returns to additional feeding were 1.24 kg milk, 0.046 kg fat and 0.034 kg protein for each additional kg DM of Persian clover eaten by cows weighing 500 kg. In late lactation, marginal returns were 1.10, 0.050 and 0.035 kg/kg DM for milk, fat and protein, respectively. In a grazing experiment, utilization of herbage on offer was very high, ranging from 58-88% as grazing intensity increased. Consideration of the products of digestion suggested that fermentation of Persian clover herbage in the rumen resulted in a balance of metabolites that is unlikely to be detrimental to animal production. However, there were two aspects of rumen fermentation that could influence the potential utilization of the herbage. First, for much of the year, levels of ammonia in rumen fluid (up to 500 mg/L) were much higher than microbial requirements. Second, rumen fluid pH often dropped to about 5.5, a level which may inhibit cellulolysis. The implications of manipulating these aspects of rumen fermentation are discussed. It was concluded that, while few problems exist with the use of vegetative Persian clover for lactating dairy cows, this herbage may be used more efficiently if fed in conjunction with supplements that provide a better balance of nutrients for fermentation in the reticulorumen.

Twelve mature Merino wethers were offered a diet which supplied 0.44 MJ of digestible energy per kg0.75 liveweight daily, and sufficient nitrogen and sulfur to maintain positive balances of these elements. The wethers were given supplements within a 22 factorial design of L-cystine (2 g day-1) infused into the abomasum and/or volatile fatty acids (VFA) infused into the rumen to increase the availability of digestible energy by 15%. Although intra-abomasal infusions of cystine increased the retention of sulfur by the wethers (P < 0.05), neither this nor the VFA treatment had any effect on the retention of nitrogen or the proportions of digested nitrogen and sulfur retained by the sheep. The non-ammonia nitrogen and sulfur flowing through the abomasum of the wethers consuming the basal ration represented 105 and 112% of the dietary nitrogen and sulfur respectively. The treatments had no significant effect on the flow of these elements, nor on the digestion of organic matter in the reticulorumen. The intra-abomasal infusions of cystme increased the entry rate of cystine into the plasma from 0.55 to 1.12 mg min-1 (P < 0.05). The entry rate was linearly related to the concentration of free cystine in plasma, both within and between treatments (P < 0.05). Consequently, the sheep receiving the supplementary cystine had greater concentrations of free cystine in their plasma (7.1 v. 16.3 .µM; P < 0.05). After L-[35S]cystine was infused intravenously for 14 h, c. 80% of the infused 35S was contained in the following tissues: skin (31%), carcass muscle (12%), small intestine (14%), plasma (12%), liver (8%) and kidneys (3%). The supplementary cystine increased the proportions of the infused 35S taken up by muscle and liver, had no effect on that taken up by the skin, and reduced the proportion taken up by kidneys, intestine and plasma (P < 0.05). The levels of 35S per unit dry weight of tissue were greatest in the kidney and least in muscle (biceps femoris); the level in the kidney being 34 times as great as in muscle. Tissues varied in both the proportions of 35S in various chemical forms and the levels of 35S in these forms. The supplementary cystine generally influenced both traits, but the provision of additional energy had no significant effects. In addition, the responses of both the proportions and levels to the supplementary cystine frequently varied among the tissues, leading to significant interactions. When cystine entering the plasma was taken into the tissues, it was predominantly contained in the proteins of the tissues. Neutral compounds, including cystine, in the acid-soluble fraction from tissues represented the second major form. Acidic and basic compounds in the acid-soluble fraction were minor products. The acidic, however, were quantitatively more important, and more responsive to the treatments, particularly in the liver and kidney. 35S bound by disulfide linkage to the tissue proteins and 35S as inorganic sulfate represented only small proportions of the total 35S in the tissues. The concentration of cystine in the acid-soluble fractions of the tissues varied among the tissues studied, being greatest in the liver (138 µM). Cystine was not detected in the protein-free filtrate from muscle. The supplementary cystine increased the concentration of cystine in the protein-free filtrate of skin (7.2 v. 22.8 µM; P < 0.05). While the supplementary cystine influenced most of the measurements of the availability and utilization of cystine by the various tissues, additional energy, supplied by the VFA infusion to the rumen, had little effect on these measurements. The important role of the skin and the minor role of the large mass of carcass muscle in the utilization of cystine are indicated by the results.

Movement of digesta through the reticulorumen and through the intestines has been studied for four roughage diets (wheaten straw, ws; wheaten hay, WH; lucerne hay, LH; dried subterranean clover, sc; all in chopped form) given to sheep fitted with re-entrant duodenal cannulas. The extent and tbe sites of digestion of plant organic matter and its constituent soluble sugars, polysaccharides, pectin, and protein are described for the four roughages. Sugars, water-soluble polysaccharides and pectin were completely digested on all diets, almost entirely in the stomachs. Together these fractions contributed 16, 21, 25 and 27% of the apparently digested organic matter respectively for ws, WH, LH and sc diets. The digestibility of hemicellulose ranged from 49.5% (WH) to 80.9% (sc); of the hemicellulose digestcd, from 70% (WH) to 81 % (sc) was apparently fermented in the reticulorumen. The digestibility of cellulose ranged from 58 % (WH) to 88 % (sc), and of the cellulose digested, 83 % (WH) to 89 % (sc) was apparently fermented in the reticulorumen. Together, apparently fermented cellulose and hemicellulose contributed from 25 %: (sc, LH) to 55 % (ws) of apparently digested organic matter. Despite evidence of nitrogen loss across the reticulorumen on thee two high nitrogen diets (LH, - 10 %; sc, - 22 %) and net gains in nitrogen on the two lower nitrogen diets (ws, + 50 %; WH, +20%), the yield of all amino acids at the duodenum per 100 g digestible organic matter intake was about 50 % higher for LH and sc (which were similar) than for ws and WH (which were similar). The relative proportions of essential amino acids did not change significantly. Nutritional implications of these changes in the site of digestion and of the proportions of nutrients released to the animal are discussed.

Changes in the composition of digesta along the gastrointestinal tract of scouring sheep fed on wheat grain ad libitum were studied relative to sheep fed on lucerne hay ad libitum. Wheat engorgement significantly (P < 0.005) depressed the pH of the digesta in the reticulorumen and the digestive tract distal to the jejunum. A mean total volatile fatty acids concentration of 10.3mM in the caecum of scouring sheep was significantly lower than the mean of 51.6mM in sheep fed on lucerne hay. Net absorption of water was negligible in the colon of scouring sheep as digesta were only 13.7–14.7% dry matter, whereas in sheep fed on lucerne, the dry matter of digesta increased from 14.7% in the caecum to 27.9% at the rectum.

The effect of potassium chloride infusion to the rumen or duodenum of sheep upon the absorption of magnesium from the stomach and intestinal regions has been examined. Three Merino ewes, each prepared with a cannula into the rumen and a re-entrant cannula into the duodenum, were offered a basal diet (control) which provided 46.3–51.1 mmoles magnesium and 299–320 mmoles potassium per day. Potassium chloride (500–800 mmoles/day) was infused continuously to either the rumen or duodenum. Digesta fluid flows were estimated from the dilution of a Cr-EDTA solution continuously infused to the rumen. Potassium infusion to either gastrointestinal site led to a comparable increase in the water intake, urine volume and levels of plasma and urinary potassium. Infusion to the rumen caused a marked increase in the potassium levels and a decrease in sodium levels in rumen fluid, as well as an increase in the rumen fluid to blood bioelectrical potential. No effect of treatment on digesta fluid flows was observed. Net magnesium absorption was lowered only when potassium was infused to the rumen, and the reduction was almost entirely due to reduced absorption of magnesium from the stomach. There was no consistent effect on absorption of magnesium from the intestines. Plasma magnesium levels were lowered by both the intraruminal infusion and, to a lesser extent, the duodenal infusion of potassium. The results indicate that although one consequence of potassium ingestion by sheep may be an enhancement of the urinary excretion of magnesium, the major effect on magnesium metabolism is a substantial reduction of absorption of magnesium from the reticulorumen.

Various aspects of digestion were studied at a constant level of roughage feeding in ewes bearing single or twin foetuses during pregnancy, and in ewes suckling a single lamb during early lactation. In pregnancy, ewes with twins responded similarly to those with singles, except that they drank more water. The responses to pregnancy generally increased in magnitude as pregnancy progressed. Late pregnancy was associated with increases in (i) digesta flows through the stomach, (ii) marker clearance rates through the alimentary tract, (iii) absorption rate of volatile fatty acids, (iv) non-ammonia nitrogen flow into the intestines, and (v) faecal water output, and decreases in (i) reticulo-rumen liquor volume, (ii) reticulorumen pools of volatile fatty acids, ammonia, sodium and potassium, and (iii) organic matter digestion. Lactation was associated with increases in (i) digesta flows through the stomach, (ii) marker clearance rate from the reticula-rumen, (iii) non-ammonia nitrogen flow into the intestines, (iv) rumen digesta pH and (v) flow of sodium and potassium from the reticulo-rumen, and decreases in (i) reticula-rumen pools of volatile fatty acids, ammonia, sodium and potassium, (ii) organic matter digestion and (iii) blood urea concentration. It was concluded that (i) the digestion responses were large enough to influence the interpretation of various nutrition studies in pregnancy and lactation, and (ii) the relative contributions of physical and hormonal changes to the altered digestion transactions need elucidation.

Sheep fitted with 10-cm rumen fistulae were used to measure the changes occurring in the particle size of digesta under conditions of once daily feeding. Particle size distributions were determined by separation through sieves of various mesh sizes. In one experiment digesta samples were obtained from serial emptyings of the reticulorumen several times within 24-hr periods. In a second experiment particle size distributions resulting from various levels of food intake were measured 24 hr after feeding.

The apparent digestibility of casein infused per duodenum at two levels (providing 3 or 6 g nitrogen per day) was between 90 and 105%. The efficiency of retention of casein nitrogen was investigated at three levels of roughage intake and the effects of level of nitrogen and level of roughage upon nitrogen retention in wool and in tissues other than wool were studied. Casein administration per duodenum resulted in an increased rate of digestion of cotton threads suspended in the reticulorumen, which indicated effective recycling of nitrogen. Actual rates of digestion were lower at higher roughage intakes. Possible reasons for this are discussed. At each level of roughage intake, casein administration led to increased nitrogen retention, the partial efficiency of retention of the added nitrogen being 56-85% for the first 3 g of casein nitrogen and 22-32% for the second 3 g. At a given level of casein, retention and partial efficiency of retention were increased by increased roughage intake. At low levels of roughage intake, the increase in wool nitrogen retention as a response to casein supplements was as great as at higher levels of roughage intake. Wool nitrogen retention was increased by 30%, from about 1.0 to 1.3 g/day, for the first 3 g of casein nitrogen, with a 10% partial efficiency of incorporation of added nitrogen into wool. The second 3 g of casein nitrogen led to a smaller additional increment in wool nitrogen retention, with less than 5% partial efficiency of incorporation of added nitrogen into wool. Increases in the level of roughage intake did improve the partial efficiency of retention of nitrogen in tissues other than wool, from 50 to 75% for the first 3 g of casein nitrogen, and from 15 to 30% for the second 3 g. This effect was not accompanied by any decrease in the partial efficiency of incorporation of administered nitrogen into wool.

In six experiments, sheep were fed ad libitum on either chopped lucerne hay, chopped wheaten straw, or a ground, pelleted lucerne hay/barley diet. On each diet either the dietary material itself, a more highly digestible material, or sawdust was introduced per fistulam into the reticulorumen in amounts equal to c. 25% of the normal daily intake by weight. For each diet, with intraruminal additions on a single occasion only, the most accurate adjustments of oral intake on a weight or a digestible energy basis were observed when the diet itself was added. On the pellet diet, reduction of oral intake was most rapid and of greater magnitude when materials of high digestibility were introduced, though intake was also reduced when sawdust was introduced. On the chopped lucerne hay diet and on the chopped wheaten straw diet, oral intake was depressed more after the introduction of materials of lower digestibility. When pellets were introduced into animals fed on chopped wheaten straw, oral intake was at first reduced but subsequently increased, which indicated an interaction between the basal diet and the supplement. In longer-term experiments, daily introduction per fistularn of the dietary material at c. 25% of the mean daily intake resulted in a rapid decrease in oral intake of each diet. The decreases in intake, expressed as a percentage of the weight of diet added per fistulam (response index), were 95–115% (pellets), 60–80% (lucerne hay), and 76–104% (wheaten straw), and generally became greater with time. With the pellet diet, trends in intake with time showed an increasingly greater adjustment to materials of high digestibility, and an apparent accommodation or compensation for imposition of a load of indigestible material. Such compensation for indigestible material was not apparent on the two all-roughage diets. Introduction of lucerne/barley pellets into the rumen of sheep fed on chopped wheaten straw resulted in no change, or a slight increase, in straw consumption, and an overall increase in intake of digestible dry matter. In two further experiments a bladder, expanded with water to volumes of 1,2, or 3 litres, caused significant decreases in intake of both the pellet diet and the chopped wheaten straw diet, effects being more rapid and more drastic in the case of the wheaten straw diet. Although there was subsequently a partial recovery of oral intake with the pellet diet, no such apparent compensation occurred with the wheaten straw diet. The results indicate that sensitivity to indigestible material can limit the intake of roughage even though the digesta content of the reticulorumen is not at a maximum, and confirm that important relationships exist between the nutritive value of the diet or nutritional status of the animal and the ability to accommodate indigestible material. ____________________ *Part VI, Aust. J. Agric. Res., 21: 735 (1970).

In each of four experiments, individually penned sheep were fed on a range of diets ad libitum, consuming the feed over 24 hr each day. In preliminary feeding periods each experimental animal became stabilized to a feeding pattern giving low standard deviations between days for the amount of feed consumed at a meal when the animal began and left off feeding at will. The amounts of digesta in the reticulorumen at the end of a specific meal (the first meal after presentation of a new allowance of feed) or before the commencement of the next (second) meal were then measured directly by emptying the reticulorumen or indirectly by estimates based upon a polyethylene glycol (PEG) dilution technique. The amount of digesta present in the reticulorumen at the end of the first meal was significantly greater when animals were fed on chopped lucerne hay (1.8 % nitrogen, 68% digestibility) than on either chopped oaten hay (1.2% nitrogen, 62% digestibility) or chopped wheaten straw (0.8 % nitrogen, 56 % digestibility). The quantity of digesta present in the reticulorumen increased as intake per day, or per meal, increased. For each diet, however, the weight of digesta held at the end of the meal was found to be repeatable between separate observations to within 800 g, which indicated a possible regulatory relationship between 'fill' and the termination of that meal, and the order of precision of the regulation. The intake of chopped wheaten straw was less than that of chopped oaten hay or chopped lucerne hay, both per day and in the second meal, even though the amount of digesta present in the reticulorumen immediately before the second meal was substantially lower for sheep given chopped wheaten straw. Though the amount of digesta in the reticulorumen of sheep given a pelleted, ground lucerne hay-barley mixture was also relatively low before the second meal, intakes were very much greater than when animals were given chopped wheaten straw. When casein was given in the diet or per duodenum, the intakes of oaten chaff (0.9 % nitrogen, 59% digestibility) were increased, and the amount of digesta held in the reticulorumen at the end of the first meal increased. Results support the hypothesis that, while for each diet the intake may be regulated to give a relatively constant level of fill of the reticulorumen at the end of a voluntarily terminated meal, this level of fill is not a constant between diets but is influenced by other, presumably nutritional, factors. One such factor is the protein nutrition of the animal.

The relationship between mean apparent retention time of dry matter in the reticulorumen (RD, hr) and the daily voluntary dry matter intake (ID, g/day) of six dried panicum diets was determined on sheep which were offered fresh feed every hour. RD was measured by emptying the reticulorumen via a large rumen fistula. ID for the six diets by the sheep with fistulae was slightly higher than, and correlated (r = 0.99, P < 0.001) with, that previously found when the same diets were offered to intact sheep. ID varied from 659 to 1355 g/day and RD from 13.3 to 27.1 hr. These two factors were inversely related

The absorption of inorganic [35S]sulphate and inorganic [35S]sulphide from the reticulorumen was studied by measuring the decrease of radioactivity and decrease in sulphide concentration in the rumen and by the increase in radioactivity in the bloodstream. Normal rumen contents were replaced with buffer solution (pH 6.6). The pattern of sulphide disappearance from the rumen followed that of a first order reaction and was extremely rapid. The estimated half-life of rumen sulphide ranged from 10 to 22 min. Direct absorption from the rumen appeared to be the main mechanism involved in the sulphide loss. Under similar conditions little sulphate was lost from the rumen and absorption of sulphate across the rumen wall appeared to be negligible.