B. W. Norton

The validity of the critical size theory for particles leaving the rumen

Three grasses and two legumes, each at two stages of maturity, were fed to three fistulated sheep and samples of the feed, and faeces and contents of the reticulo-rumen, abomasum and ileum were collected for the determination of particle size by wet sieving. Modulus of fineness (MF) was calculated for all particulate matter that failed to pass a 0.15 mm screen. Resistance to flow from the rumen of feed particles of different sizes was also calculated. The mean MF of the reticulo-rumen contents was 2.56 compared with 5.72 for the feed. Material leaving the rumen and found in the abomasum had a MF of 1.67 and subsequent changes were small and not significant; ileum 1.63, faeces 1.80. Particles greater than 1.18 mm passed out of the reticulo-rumen although the quantity was small (1-3%). The resistance to flow of particles of different sizes from the reticulo-rumen was closely related to particle size with no difference between grasses and legumes or between young and mature forages. It was concluded that in modelling the flow of particles from the reticulo-rumen a non-compartmentalized approach should be adopted, but if a simple two-compartment model is required then a critical sieve size of about 1.18 mm may be useful, since less than 5 % of the particulate material is retained on this sieve size.

Digestion of 14C-labelled condensed tannins from Desmodium intortum in sheep and goats

An experiment was conducted to investigate the metabolism of condensed tannin (CT) in sheep and goats offered a mixture of Digitaria decumbens (700 g/kg) and Desmodium intortum (300 g/kg) hay. Radioactive 14CO2 was used to label CT in young growing desmodium plants, [14C]CT was extracted, purified and infused intraruminally, and the metabolism of [14C]CT was followed in the rumen and lower digestive tract of both species. Digestion of DM, organic matter (OM), cell-wall constituents (CWC), N and the efficiency of rumen microbial synthesis were determined using a continuous intraruminal infusion of 51Cr EDTA, YbCl3 and Na235SO4. The measurements taken for sheep and goats respectively were: intake, 21 and 30 g/kg0.9 per d; digestibilities (g/g) of DM, 0.566 and 0.505; OM 0.578 and 0.508; neutral-detergent fibre, 0.584 and 0.532; and acid-detergent fibre, 0.535 and 0.435. None of these measurements was significantly different (P > 0.05) between animal species. There was an apparent net gain in lignin across the rumen and whole intestinal tract for both animal species (19 and 29% for sheep and goats respectively). There were no significant differences between sheep and goats (P > 0.05) detected for any measurements of N excretion and utilization. The overall efficiency of N digestion and utilization was also similar between species. The routes of CT metabolism were compared for both colorimetric estimates (butanol-HCl) of dietary CT (DCT) and the specific radioactivity of [14C]CT in digesta (abomasum) and excreta (urine and faeces) of both sheep and goats. [14C]CT showed total losses of 57 and 56% in sheep and goats respectively whilst losses of DCT of 71 and 70% were detected with butanol-HCl in sheep and goats respectively. The apparent losses of DCT across the rumen of sheep and goats were 12 and 9% whilst higher losses (49 and 42% for sheep and goats respectively) were observed for [14C]CT. Losses of DCT in the lower intestinal tract accounted for 69 and 71% of the total CT leaving the abomasum. By comparison, only 40 and 35% of [14C]CT was lost during intestinal passage in sheep and goats respectively. It was concluded that the infused free [14C]CT interacted with DCT and entered the protein and fibre-bound DCT pools. The loss of DCT during passage through the intestines was considered to be a consequence of either absorption of free CT or the degradation products of CT. It was assumed that free CT arose in the lower gastrointestinal tract from protein-CT and fibre-CT dissociation to be digested and/or absorbed. The higher recoveries of [14C]CT in faeces (32 and 35%) compared with DCT (27 and 26%) for sheep and goats respectively) were associated with the excretion of [14C] degradation products or conjugates which were not reactive to butanol-HCl. It was concluded that both methods (butanol-HCl and labelling CT with 14C) detected a substantial disappearance of CT (free, protein, and fibre-bound) during metabolism in the gastrointestinal tract in sheep and goats.

The effect of heat on amino acids for growing pigs

The effect of heat on the availability of lysine in field peas (Pisum sativum cultivar Dundale) was determined using the slope-ratio assay with growing pigs. The field peas were heated to 110 degrees, 135 degrees, 150 degrees, or 165 degrees for 15 min using a forced-air dehydrator. Lysine availability was significantly depressed (P < 0.05) with the application of heat, even at mild temperatures of 110 degrees. Lysine availability values of 0.96, 0.71, 0.77, 0.56, and 0.47 were determined for the raw peas and peas heated to 110 degrees, 135 degrees, 150 degrees or 165 degrees respectively. The effect of dietary protein level on the ileal digestibility of lysine in raw field peas was determined in a second experiment to estimate true ileal digestibility. Five diets were formulated to contain 85, 105, 125, 145 and 165 g protein/kg. Increasing dietary protein from 85 to 105 g/kg resulted in a significant increase in the estimate of apparent ileal digestibility from 0.84 to 0.93. Comparisons were then able to be drawn between the ileal digestibility, availability and utilization of lysine from raw and heat-treated field peas. The results indicate that unlike ileal digestibility values, estimates of lysine availability are sensitive to heat treatment and are a close reflection of lysine utilization in heated protein concentrates. Thus, lysine availability values would be more suitable for use in diet formulations than ileal digestibility estimates when dealing with heat-processed protein concentrates.

The influence of anaerobic fungi on rumen volatile fatty acid concentrations in vivo

Elimination of the rumen anaerobic fungi from sheep fed chemically-treated barley straw diets resulted in elevated proportions of propionic acid in rumen liquor (from ca. 0.15 to 0.30). Subsequent inoculation of these sheep with a pure culture of fungus decreased propionate concentrations within 3 days to the levels observed in control animals that possessed abundant fungal populations throughout the experiment. Confirmation that propionate itself was not responsible for the elimination of the fungi was provided by the results of a second experiment in which intraruminal infusions of propionic acid failed to reduce fungal growth or prevent recolonization in sheep previously rendered fungi-free. In a third experiment with sheep fed untreated barley straw, monensin supplementation produced the well known elevation of propionate concentrations. However, this treatment also resulted in the elimination of rumen anaerobic fungi from the animals. The magnitude of the increased concentration of rumen propionic acid, resulting from the elimination of the anaerobic fungal flora, indicates an important role for the fungi in the fermentation of high-fibre diets. In addition, these findings indicate that the well known elevation of propionate levels produced by monensin may likewise be effected directly by removal of the rumen anaerobic fungi.

A comparison of fresh and dried Calliandra calothyrsus supplements for sheep given a basal diet of barley straw

Leaves from the tropical tree legume calliandra ( Calliandra calothyrsus ) were harvested and fed either fresh frozen (F) or dried (D) as a supplement (200 g dry matter (DM)) to sheep ( n =4) given barley straw ad libitum in metabolism cages in a controlled-environment animal house. Sheep given these diets were intra-ruminally infused (0·5 litres/day) with either water or a solution containing 100 g/l polyethylene glycol (PEG). These treatments were administered in a randomized complete block design, and the results statistically analysed. Drying significantly increased the cell wall (cellulose, hemicellulose) and lignin contents, but decreased the condensed tannin (butanol-HCl method) content (F=35·7, D=21·7 g/kg DM). Both drying and PEG infusion significantly ( P <0·05) increased straw organic matter (OM) intake, but the effects of drying plus PEG were not additive. Organic matter digestibility of the diets was significantly ( P <0·05) increased by drying (F=433 g/kg, D=486 g/kg), but not by the infusion of PEG. Total nitrogen (N) digestibility was significantly ( P <0·05) increased by drying (F=207 g/kg, D=316 g/kg) in the absence of PEG, and by PEG for both frozen (−PEG=207 g/kg, +PEG=392 g/kg) and dried (−PEG=316 g/kg, +PEG=434 g/kg) calliandra. PEG infusion significantly increased the proportion of feed N degraded in the rumen (−PEG=0·41, +PEG=0·52) and rumen ammonia concentrations (−PEG=63, +PEG=103 mgN/l), but had no significant effect on the rate or efficiency of microbial protein synthesis in the rumen. PEG infusions significantly increased the amount and proportion of N intake absorbed from the lower digestive tract, but had no significant effect on overall N balance. Drying decreased the tannin losses (as % intake) occurring in the rumen (F=37·3%, D=24·2%), and PEG infusion increased these losses for both frozen (−PEG=37·3%, +PEG=72·5%) and dried (−PEG=24·2%, +PEG=68·7%) calliandra supplements. It was concluded from these studies that the presence of tannins in fresh (frozen) calliandra depressed feed utilization, and that drying was an effective means of improving the nutritive value of calliandra when fed as a supplement to low quality straws.

Studies with the Australian Cashmere Goat. I. Growth and digestion in male and female goats given pelleted diets varying in protein content and energy level

Some aspects of growth and digestion were studied in Australian cashmere goats in two experiments. In the first experiment, weaner goats (initial LW 13.4 kg) were given three ground and pelleted diets (11.3, 16.0, and 20.9% crude protein) at two levels of intake. Growth rates were highest in males fed the high protein (HP) diet ad libitum (149 g day-1) and lowest in females consuming the low protein (LP) diet at restricted intakes (30 g day-1). Increasing the protein content of the diet resulted in significantly greater liveweight gains, although the improved growth could be largely attributed to increased intake rather than to enhanced feed efficiency. Males grew faster, retained more nitrogen and used feed with greater efficiency than did females. A second experiment with fistulated goats (mean liveweight 16.4 kg) fed the LP and HP diets from experiment 1 showed that organic matter (OM) digestion was greater in goats fed the LP diet (67.9% v. 65.3%). In contrast, the proportion of OM digestion which occurred in the stomach was greater for goats fed the HP diet (76.7 v. 57.4%). For both diets all of the cellulose and hemicellulose digestion took place in the rumen; however, substantial amounts of starch escaped rumen digestion. Large losses of nitrogen across the rumen (4.9 g day-1) in goats given the Hp diet resulted in reduced flows (11.1 g day-1) of non-ammonia nitrogen (NAN) to the small intestine, compared with the LP diet (12.7 g day-1). Digestion of NAN in the intestines was greater in animals consuming the LP diet, possibly reflecting the greater intestinal contribution made by non-microbial NAN. For both diets the ratio of protein to energy available (11.0 and 10.2 g protein MJ-1 ME for LP and HP diets respectively) was estimated to be in excess of maximum tissue requirements for growth.

Oven drying improves the nutritional value of Calliandra calothyrsus and Gliricidia sepium as supplements for sheep given low‐quality straw

Leaves from the tree legumes Gliricidia (Gliricidia sepium) and Calliandra (Calliandra calothyrsus) were fed as supplements (200 g dry matter) to sheep (n=3) given a basal diet of barley straw ad libitum. Tree leaves were fed either freshly harvested (F=fresh) or after drying at 60°C in a forced draught oven (D=dried). Voluntary intakes, digestibility and aspects of nitrogen (N) and phenolic compound metabolism were measured in all sheep. Drying decreased the condensed tannin (CT) content of Calliandra (F 117, D 82 g CT kg−1 DM). Total phenolics (TP) were significantly decreased when Gliricidia was dried (F 39, D 21 g TP kg−1 DM), and CT content was reduced from 20 g CT kg−1 DM to zero. Sheep given Gliricidia had higher rumen ammonia concentrations (73–85 mg N litre−1) than did sheep given Calliandra (37–40 mg N litre−1). For both species, drying significantly increased the voluntary consumption of straw, increased DM digestibility, decreased faecal N excretion and increased N balance. For calliandra, drying decreased the apparent degradability of N in the rumen (DNR) from 0·40 to 0·28 g N g−1 N ingested, and increased the apparent digestibility of N (ADN) in the post-ruminal tract from 0·20 to 0·52 g N absorbed g−1 N flowing into the small intestines. For Gliricidia, DNR decreased from 0·64 to 0·51 and ADN increased from 0·41 to 0·56. There were no significant effects of drying on rates of microbial N synthesis. The above changes were discussed in relation to changes in tannin content and it was concluded that drying facilitates the formation of protein–tannin complexes which protect proteins from degradation in the rumen. These proteins are subsequently released in the small intestines, thereby promoting an increased efficiency of dietary N utilisation. ©1997 SCI

Melatonin and fleece growth in Australian cashmere goats

Three groups each of eight Australian cashmere goats (four males, four females, 10 months old) were implanted at the base of the ear with melatonin pellets (18 mg) between July and October (July group), January and April (January group), or sham implanted (control). Cashmere and hair length changes were measured during the year following implantation. Rates of growth, maximum length, initiation and cessation dates of cashmere growth were calculated from cumulative cashmere length measurements. All goats were maintained on pasture under natural daylight. Control goats showed the normal circannual pattern of growth: no growth from July until the cycle was initiated, on average, on 9 November 1988 and ceased on 27 May 1989 (199 days). Implantation in July permitted the continuation of cashmere growth until 1 November 1988, and this extended cycle was followed by another cycle of short duration (146 days) with initiation (26 January 1989) and cessation (21 June 1989) dates later than those of controls. Hair growth patterns also changed during this period. Implantation with melatonin in January reduced maximum fleece length (59 mm) compared with controls (72 mm) by induction of an early cessation of cashmere growth (3 May 1989). There were no differences (P < 0.05) between sexes in response to treatments. Melatonin implants in July (short days) partially suppressed a rise in blood prolactin concentrations in October, and implants in January (long days) resulted in prolactin levels similar to those found in short days. Melatonin implants had no effect on serum thyroxine concentrations. Results suggest that melatonin implants at strategic times of the year may be a practical method for increasing cashmere production from young goats.

Utilization of endogenous and dietary urea in the large intestine of the mature horse

The dynamics of N metabolism in mature horses were investigated when they were fed on a low-N diet or the same diet supplemented with sufficient urea or soybean meal to meet their theoretical N requirements. There were no differences in DM, organic matter or neutral-detergent-fibre digestibilities for the three diets. N digestibilities and digestible-N intakes were similar for the urea- and soyabean-supplemented diets and very low for the low-N diet. For all three diets plasma urea was degraded in the digestive tract to NH3 which was utilized by the bacterial population as a N source. NH3 was absorbed from the large intestine into the blood and converted to urea. NH3 was also incorporated into plasma proteins. The horses fed on the low-N diet degraded a greater proportion of endogenous urea in the digestive tract than did horses fed on the urea-or soyabean-supplemented diets. However, the horses fed on the urea diet had the highest degradation rate of urea. The quantity of urea degraded in the digestive tract of horses fed on the urea-supplemented and the low-N diets could not compensate for a lack of dietary crude protein in these diets. The horses were in a negative N balance when fed on the low-N and urea-supplemented diets and a positive N balance when fed on the soyabean-supplemented diet. Dietary urea supplementation did not benefit the horses.

The nutritive value of Tipuana tipu and Calliandra calothyrsus as supplements to low-quality straw for goats.

Twenty-four Australian cashmere goats (32-40 kg live-weight (LW)), held in separate metabolism cages, were used in an experiment with a 2x4 factorial arrangement of treatments to study the effects of supplements of the dried leaves (browse) from two species of fodder tree (Tipuana tipu, and Calliandra calothyrsus) at four different levels (0, 0.83, 1.66% LW and ad libitum) on voluntary intake and utilisation of a basal diet of barley straw (BS). A supplement of urea-molasses (UM) (30 g urea, 70 g molasses) was given to control goats (0% browse), and both these goats and those given browse supplements consumed BS ad libitum. The basal diet of barley straw plus UM was consumed in limited amounts (41 g/kg(0.75) day) and was of low DM digestibility (47-53%). At the lowest level of Tipuana supplementation (0.83% LW, 27% DM intake), voluntary consumption of BS was significantly increased above basal, resulting in a 50% increase in total intake, and 73% in digestible DM intake. When Tipuana supplements were increased to 1.66% LW (56% DM intake), BS intakes decreased to the same extent that the supplement increased, resulting in no further improvement in either total intake or efficiency of diet use. When Tipuana was offered as the sole feed, total voluntary intake and digestible DM intake reached a maximum (66.4 and 42.0 g/kg(0.75) per day, respectively), and from a consideration of all aspects of this evaluation, Tipuana tipu compared very favourably with other high-quality browse species. However, Calliandra calothyrus proved to be of less value. The lowest level of supplementation resulted in a small increase in total (18%) and digestible DM (19%) intakes, but a decreased digestibility and availability of N for absorption and use. Further increases in supplement increased digestible intake, but N availability remained low and limiting. When Calliandra was offered as the sole diet ad libitum, total and digestible DM intakes (45.6 and 21.6 g/kg(0.75) per day) were no better than the control (barley straw plus UM) diet (41.5 and 22.0 g/kg(0.75) per day) and may be characterised as low in nutritive value and, in comparison with other browse species, of limited value as either a supplement or sole feed for ruminants in the tropics