D. P. Poppi

Extent of digestion and rumen condition as factors affecting passage of liquid and digesta particles in sheep

Two experiments were carried out at Mt. Cotton, The University of Queensland, from November 1992 to July 1993, to study the effect of extent of digestion or feed type (grass or legume) on particle kinetics in the rumen. Small (0·5–1·18 mm) Yb-labelled grass or legume particles, either digested or undigested, were injected into the rumen of sheep fed on different diets, and their retention time in the reticulo-ruminal compartment measured. In Expt 1, four intact wethers were fed on either pangola grass hay, chaffed lucerne hay, pelleted lucerne hay or commercial pelleted concentrate. Digested particles from the faeces of animals fed on pangola or lucerne and undigested material from the same diets were wet-sieved and the fraction 0·5–1·18 mm collected, labelled with Yb-acetate and injected into the animals together with a solution of Cr-EDTA. Faecal samples were taken and analysed for marker concentrations. In Expt 2, four similar animals, fitted with duodenal and ruminal cannulae, were fed on different proportions of pangola grass hay and lucerne hay, and Cr-EDTA and the above mentioned labelled particles were injected through the rumen cannula. Samples were taken from the duodenum and analysed for marker concentrations.The results indicated that diet characteristics rather than extent of digestion or particle type had the greatest influence on rates of passage of both liquid and particulate phases. Different proportions of pangola and lucerne did not result in marked differences in either the volumes of rumen contents or the rates of passage of the solid phase marker but altered the rates of passage of Cr-EDTA. Increasing the proportion of legume increased intake and decreased retention time markedly, with no additive effects on digestibility.Particles of the same small size escaped with the same fractional passage rate within each diet, irrespective of type (grass or legume) or status (undigested or digested), indicating identical kinetics within each rumen type.It was concluded that rumen conditions as influenced by diet type have most influence on water and particle kinetics and that extent of digestion of the small particles used in our experiments was not important. Particles of legume or grass of the same size behaved similarly within a diet type.

Effects of enzyme addition to canola meal in prawn diets

Copyright (c) 1997 Elsevier Science B.V. All rights reserved. Enhancement of nutritional value of canola meal by the addition of enzymes was investigated in diets for juvenile Penaeus monodon (XpSD; 0.96p0.09 g), with emphasis on liveweight gain and feed conversion ratio (FCR). Six diets were prepared containing either no canola (squid meal based basal diet), basal+20% canola (low canola diet), low canola+0.25% enzyme mixture (Porzyme, Finnfeeds International), basal+64% canola (high canola diet), high canola+0.25% enzyme mixture or basal+54% canola+10% sucrose. All diets were fed ad libitum. Juvenile prawns (three prawns per tank) were fed diets for 42 days with five tank replications per diet. Liveweight gain and feed intake were measured. High canola diet gave significantly lower growth rates (1.79p0.42 g) (P 0.05). The low canola + enzyme diet also resulted in higher liveweight gain (2.40p0.16 g) than the basal and low canola diets (2.29p0.27 g) but it was not significant. Addition of the enzyme mixture to diets also gave a significant improvement in FCRs. The addition of sucrose to the canola based diet resulted in a significantly higher liveweight gain (high canola+sucrose 2.01p0.22 g), but did not change the FCR.

Nitrogen transactions along the digestive tract of lambs concurrently infected with Trichostrongylus colubriformis and Ostertagia circumcincta.

Twelve lambs, paired on the basis of live weight, were cannulated in the abomasum, in the proximal jejunum approximately 4 m distal to the pylorus and in the terminal ileum. Six were infected with 3000 Trichostrongylus colubriformis and 3000 Ostertagia circumcincta larvae each day for 18 weeks and the remainder were pair-fed to individual infected lambs. All animals were offered ryegrass (Lolium perenne)-white clover (Trifolium repens) pasture, cut daily. Dry matter (DM) intake, live weight, faecal egg concentration, plasma pepsinogen and plasma protein concentrations were measured weekly. During weeks 7 and 17 after commencement of infection, the flow of digesta along the gastrointestinal tract was measured together with enteric plasma loss and true digestion and absorption of 125I-labelled albumin in the small intestine. DM intake was depressed by parasitism, being 1331, (SE 70), 423 (SE 32) and 529 (SE 52) g/d during weeks 3, 7 and 17 respectively. The flow of nitrogen at the proximal jejunum and in faeces was increased by parasitism during week 7 and at the abomasum and ileum during week 17. Plasma protein-N loss (g/d) into the gastrointestinal tract was 0.68 (SE 0.091) and 1.97 (SE 0.139) during week 7, and 0.85 (SE 0.158) and 1.96 (SE 0.396) during week 17, in control and infected sheep respectively. True digestion and absorption of albumin in the proximal small intestine, the site of infection, was very low (mean 0.08) and was not affected by parasitism. Between the abomasum and terminal ileum absorption of albumin was high (mean 0.87) and again was not affected by parasitism. It was calculated that of the total increase in endogenous protein passing from the ileum tract as a result of infection, plasma protein comprised only a small percentage (10-36%). The major proportion of digestion and absorption of protein occurred in the distal small intestine beyond the site of infection and was not affected by infection.

The nutritive value for ruminants of tagasaste (Chamaecytisus palmensis), a leguminous tree

The nutritive value of the leguminous tree tagasaste (Chamaecytisus palmensis), commonly known as tree lucerne, was investigated in a series of experiments. The tree grows in dry environments, the leaves are highly palatable and on the basis of its chemical composition it would appear to have a role as a high quality feed source or supplement. In the first experiment, leaf buds were tagged in spring and the effect of leaf maturity on crude protein content (CP) and in vitro dry matter digestibility (DMD) investigated. The CP content decreased significantly with time from 260 to 170 g kg−1 DM, but DMD did not change significantly (average in vitro DMD, 0.73). Most leaf senescence appeared to occur ∼5 months after leaf emergence. In the second experiment, of 6 weeks duration, the liveweight gain of lambs (23 ± 1.5 kg) browsing tagasaste and grazing lucerne or prairie grass was examined and the order of response was lucerne (265 ± 33 g day−1), prairie grass (151 ± 35 g day−1) and tagasaste (81 ± 36 g day−1). Subsequently, a cut and carry system was used to investigate the feeding value of tagasaste for lambs (27 ± 1.5 kg). Liveweight gain was 95 ± 30 g day−1. In a third experiment, the digestion of tagasaste leaf was examined in more detail by measuring the partitioning of digestion of DM, organic matter (OM), neutral detergent fibre (NDF) and crude protein (CP) in the digestive tract of lambs with duodenal and ileal fistulae. At high levels of feeding, there was a net loss of non-ammonia nitrogen (NAN) across the stomachs (30%) and an average NAN absorption across the small intestine of 68%. The average in vivo digestibility of DM, OM and NDF were, respectively, 0.77, 0.78 and 0.65, and the average proportion of in vivo digestion occurring in the stomachs was 0.55 and 0.80 for DM and NDF, respectively. In collating the results of all trials, it was observed that the DMD of leaf ranged from 0.71 to 0.78 and that of stem was 0.46 on average. The chemical composition of leaf was 210–240 g CP kg−1 DM and 300–370 g NDF kg−1 DM, whilst stem had values of 95 g CP kg−1 DM and 660 g NDF kg−1 DM. No significant levels of tannin were detected. A feature of these trials was the low Na content of the leaves, and marginal levels of P and S. No ill health was observed in any animal consuming tagasaste for periods of up to 9 weeks. It was concluded on the basis of the liveweight gain response that tagasaste had a feeding value similar to other conserved forages (e.g., silage, brassica crops), but less than that of intensively managed temperate pastures. Its leaves were high in CP content and DM digestibility.

Nutritional Ecology of Grazing and Browsing Ruminants

Ruminants are, without exception, obligate herbivores subsisting as they do on a diet composed entirely of plant material. However, plant material is a diverse resource and within the Ruminantia there is a range of feeding niches with different herbivore classes focussing their foraging effort on different vegetation types (Hofmann 1989). The plant material available to herbivores comes in a range of morphological types with the major types being grasses, forbs, and browse. Grasses (including the morphologically similar sedges) are monocotyledonous plants characterised by a basal meristem, a low growth form and a relative lack of lignified support structures (except for some of the tall tropical grasses which could be considered to be morphologically classed as browse). Browse plants, comprising shrubs and trees are largely dicotyledonous plants characterised by an apical meristem, a low or high growth form and a well developed system of lignified support structures. Forbs are generally intermediate in character being dicotyledonous, with apical meristems but generally showing low growth forms and a relative lack of lignified growth structures. This variation in growth form, degree of lignification and location of the meristem has implications for resource allocation within the plant, e.g., relative investment in structural tissue and defensive chemicals. This in turn affects the nutritional value of plants for potential herbivores. The purpose of this chapter is to consider the way in which plants are digested by ruminants and how this varies with feeding habit. The chapter will first provide some simple background on digestion of plants by ruminants and how this is influenced by the presence of plant secondary metabolites in plant material. The discussion will then turn to differences between browsers and grazers and review the evidence for differences in the way in which they process the food they consume. Finally, the extent to which browsers and grazers deal differently with plant secondary metabolites will be explored. Chapter 4 Nutritional Ecology of Grazing and Browsing Ruminants

The intake, digestion and protein degradation of grazed herbage by early-weaned lambs

Sixty-four intact lambs and twenty-four lambs fitted with a duodenal cannula were weaned at 6 weeks of age and grazed pure species swards of either lucerne (Medicago sativa), white clover ((Trifolium repens), ryegrass (Lolium perenne) or prairie grass (Bromus catharticus) for 6 weeks. Intake and duodenal digesta flow were estimated when lambs were 8 and 12 weeks of age. Lambs grazing the two legume species grew at a similar rate, as did lambs grazing the two grass species. Legumes promoted a 38% higher growth rate than grasses. The higher growth rate of lambs grazing legumes was associated with a 36% higher digestible organic matter intake (DOMI; 29.5 and 21.7 g/kg body-weight per d for legume and grass respectively) and a 33% higher duodenal non-ammonia-nitrogen (NAN) flow (1.22 and 0.92 g/kg body-weight per d respectively). There was no species difference in the site of organic matter digestion; on average 0.56 of DOMI was apparently digested in the rumen and 0.77 of DOMI was truly digested in the rumen. There was no difference in duodenal NAN flow, relative to DOMI (average, 43 g/kg) or to organic matter apparently digested in the rumen (80 g/kg). Similarly, there was no difference in microbial N flow relative to duodenal NAN (0.50 g/g) and organic matter apparently (41 g/kg) or truly (29 g/kg) digested in the rumen. It was concluded that the higher growth rates achieved by lambs grazing legumes were due to higher intakes which increased the total quantity of nutrients supplied despite more protein being lost in the rumen of lambs consuming legumes.

The effects of a concurrent infection of Trichostrongylus colubriformis and Ostertagia circumcincta on calcium, phosphorus and magnesium transactions along the digestive tract of lambs

Twelve lambs, paired on the basis of live weight, were cannulated in the abomasum, proximal jejunum and terminal ileum. Six were infected with 3000 T. colubriformis and 3000 O. circumcincta larvae per day for 18 weeks. The other six lambs were pair-fed to the infected lambs. All animals were offered fresh ryegrass and white clover pasture, cut daily. Dry matter intake, live weight and plasma Ca, P and Mg concentrations were measured throughout the experiment. During weeks 7 and 17 post-infection, digesta flow along the gastrointestinal tract of infected and control animals was measured. Parasitism depressed dry matter intake by 60 per cent and was associated with a reduction in retention of Ca, P and Mg in both infected and control animals. During weeks 7 and 17, parasitism increased the flow of Ca past the proximal jejunum and, during week 17, the flow of P past the terminal ileum. Increased endogenous Ca and P losses, together with a net reduction in absorption of Ca and P, were associated with depressed plasma Ca and P concentrations. These findings, together with evidence of reduced addition of P to anterior regions of the tract, indicate induced Ca and P deficiency. There was evidence for compensatory absorption of Ca and P in the large intestine and distal small intestine, respectively. Magnesium metabolism was apparently not affected by parasitism.

Marker concentration patterns of labelled leaf and stem particles in the rumen of cattle grazing bermuda grass ( Cynodon dactylon ) analysed by reference to a raft model

Large (>1600 microm), ingestively masticated particles of bermuda grass (Cynodon dactylon L. Pers.) leaf and stem labelled with 169Yb and 144Ce respectively were inserted into the rumen digesta raft of heifers grazing bermuda grass. The concentration of markers in digesta sampled from the raft and ventral rumen were monitored at regular intervals over approximately 144 h. The data from the two sampling sites were simultaneously fitted to two pool (raft and ventral rumen-reticulum) models with either reversible or sequential flow between the two pools. The sequential flow model fitted the data equally as well as the reversible flow model but the reversible flow model was used because of its greater application. The reversible flow model, hereafter called the raft model, had the following features: a relatively slow age-dependent transfer rate from the raft (means for a gamma 2 distributed rate parameter for leaf 0.0740 v. stem 0.0478 h(-1)), a very slow first order reversible flow from the ventral rumen to the raft (mean for leaf and stem 0.010 h(-1)) and a very rapid first order exit from the ventral rumen (mean of leaf and stem 0.44 h(-1)). The raft was calculated to occupy approximately 0.82 total rumen DM of the raft and ventral rumen pools. Fitting a sequential two pool model or a single exponential model individually to values from each of the two sampling sites yielded similar parameter values for both sites and faster rate parameters for leaf as compared with stem, in agreement with the raft model. These results were interpreted as indicating that the raft forms a large relatively inert pool within the rumen. Particles generated within the raft have difficulty escaping but once into the ventral rumen pool they escape quickly with a low probability of return to the raft. It was concluded that the raft model gave a good interpretation of the data and emphasized escape from and movement within the raft as important components of the residence time of leaf and stem particles within the rumen digesta of cattle.

Elevation of feed intake in parasite-infected lambs by central administration of a cholecystokinin receptor antagonist

The role of cholecystokinin (CCK) in modulating feed intake depression in parasite-infected lambs was investigated using CCK receptor antagonists (L364-718 and loxiglumide). Four experiments were carried out using ewe lambs infected with 4000 Trichostrongylus colubriformis larvae/d or non-infected controls (n8, live weight 25 kg). Animals were fed daily on a nutritionally complete pelleted diet and had free access to water. In the first experiment, infected and non-infected animals were injected subcutaneously with CCK antagonist (100 micrograms L364-718) or carrier alone as a single dose. In the second experiment, CCK antagonist (loxiglumide: 0, 5, 10 or 20 mg/kg live weight) was injected into a jugular vein immediately before feeding. In the third experiment, animals were infused continuously with the CCK antagonist (loxiglumide; 10 mg/kg per h) for 10 min before feeding and for the first 2 h of feeding. In the final experiment, lambs were fitted with an indwelling cerebral ventricular cannula and infused with a CCK antagonist (loxiglumide, 162 micrograms/min), CCK agonist (CCK-8, 2.5 pmol/min), loxiglumide plus CCK-8 or sterile saline solution alone via the cannula for 30 min before feeding and for the first 60 min of feeding. In all the experiments short-term feed intake was recorded at 10 and 15 min intervals for the first and second hours of feeding respectively, then at hourly intervals for the remainder of the 8 h recording period. Peripheral injection with L364-718 or loxiglumide did not elevate feed intake in either the infected or non-infected animals. However, feed intake was increased (P < 0.05) in the short term by central infusion of loxiglumide, this effect being greater in the infected animals and apparently due to an elevation in intake during the second hour of feeding. CCK-8 depressed short term feed intake only in the infected animals (P < 0.05). Total daily feed consumption was not influenced by any of the pharmacological agents. The results indicate an involvement of central CCK receptors in regulation of feed intake depression following gastrointestinal parasitism of sheep and the possibility of a similar role in non-infected sheep. They do not support the singular importance of a peripheral action of CCK in determining satiety.

Predictions of food intake in ruminants from analyses of food composition

Equations used to predict intake by cattle from some chemical or physical characteristic of food were examined. The equations are empirical or mechanistic in nature. Mechanistic equations are not used widely, usually only in a research context. The input to mechanistic models requires too much time to quantify to be used routinely. Empirical relationships form the basis of most feeding standards and are based on a wide variety of prescribed characteristics (digestibility, chemical composition, etc.), but the underlying principle is a relationship between intake and digestibility. Equations are modified to take account of feed types, animal weight and physiological state, rumen modifiers, hormone implants, environmental conditions, and whether grazing or hand fed. Quite significant differences exist between the equations in the intakes they predict in response to variation in weight, breed type, and feed digestibility. Equations can be very precise in their prediction when used with feed types and breed types on which they are based. Near infrared reflectance (NIR) offers the most potential for long-term development of equations. At present, NIR is used largely to determine chemical composition because of speed of operation, but long-term storage of data is simple, allowing further associative relationships to be developed readily. More sophisticated statistical procedures being employed to improve the precision of the relationships between intake and prescribed characteristics of food and NIR will be vitally important as they enable extra parameters to be incorporated at no extra cost or time for analysis.