Rate of passage of digesta in sheep. 2. The effect of level of food intake on digesta retention times and on water and electrolyte absorption in the large intestine

SEASONAL FLUCTUATION OF FECAL CONSISTENCY IN ZOO-HOUSED MOOSE (ALCES ALCES)

Fecal consistency is routinely used as an indicator of gastrointestinal health and diet suitability in zoo animals. The underlying processes in ungulate fecal consistency are not often investigated. The authors assessed multiple factors on fecal consistency scores in six adult zoo moose (Alces alces) retrospectively for a 3-yr period. All animals were regularly tested for gastrointestinal parasites and received antiparasitics when noted. Neither the provision of dietary browse nor number of visitors had a significant effect. Seasonally varying intake of the staple pelleted diet was the main explanatory factor, with an additional effect from environmental temperature or season. Higher intakes and higher temperatures were linked to less well-formed feces. The authors hypothesize that during the summer hyperphagia to replete body reserves, the water re-absorption function of the large intestine apparently becomes overtaxed. Heat stress may have an additional, intake-independent effect. Although monitoring fecal consistency is a part of good health surveillance, physiologic seasonal effects, as reported here, need to be taken into consideration when interpreting the observations.

Effects of Mimosa tenuiflora on larval establishment of Haemonchus contortus in sheep

Anthelmintic resistance has limited the ability to control the gastrointestinal nematodes of small ruminants and has therefore awakened an interest in the study of tanniferous plants as a source of anthelmintics. This study was carried out to evaluate the effect of Mimosa tenuiflora intake, a tanniferous plant that is fed to small ruminants in northeastern Brazil, on the larval establishment of Haemonchus contortus in sheep. In this experiment, 18 nematode-free sheep were divided into three groups (n=6) according to live weight. Group 1 was fed M. tenuiflora leaves; Group 2 was fed M. tenuiflora stems; Group 3 served as the control group and was fed Cynodon dactylon, a plant with low levels of tannins. The animals consumed the plants for 13 days (Day -7 to Day 5). On Day 0, the sheep were experimentally infected with 4500 third-stage H. contortus each. Five days after infection (Day 5), the sheep were slaughtered to count the worm burden and perform a histological analysis of the abomasum. The daily plant intake and the live weight gain of the animals were recorded. The groups that ingested M. tenuiflora leaves and stems consumed less dry matter than did those that ingested C. dactylon (P<0.05). The consumption of M. tenuiflora leaves did not reduce the L3 establishment of H. contortus compared to the control (P>0.05). The intake of M. tenuiflora stems tended toward decreasing larval establishment, but the reduction was not significant (P>0.05). No significant differences were observed in the mucosal cellular response and live weight gain among the groups. These data demonstrated that, with the protocol used, M. tenuiflora has no effect on larval establishment of H. contortus in sheep.

A mechanistic model for predicting intake of forage diets by ruminants

Accurate voluntary feed intake (VFI) prediction is critical to the productivity and profitability of ruminant livestock production systems. Simple empirical models have been used to predict VFI for decades, but they are inflexible, restrictive, and poorly accommodate many feeding conditions, such as those of developing countries. We have developed a mechanistic model to predict VFI over a range of forage diets (low- and high-quality grasses and legumes) by wild and domestic ruminants of varying physiological states (growth, lactation, gestation, nonproductive). Based on chemical reactor theory, the model represents the reticulorumen, large intestine, and blood plasma as continuous stirred-tank reactors and the small intestine as a plug flow reactor. Predicted VFI is that which 1) fulfills an empirical relationship between chemostatic and distention feedback observed in the literature, and 2) leads to steady-state conditions. Agreement between observed and actual VFI was great (generally R(2) >0.9, root mean square prediction error <1.4 kg/d, CV <25%). Root mean square prediction error for our model was only 67% that of the Beef NRC (2000) model, the leading empirical prediction system for cattle. Together, these results demonstrate that our model can predict ruminant VFI more broadly and accurately than prior methods and, by consequence, serve as a crucial tool to ruminant livestock production systems.

Influence of hay particle size at different concentrate and feeding levels on digestive processes and feed intake in ruminants. 2. Passage, digestibility and feed intake

In order to study the main effects of particle size, three ruminally fistulated cows (550 to 580 kg BW) were fed a constant low concentrate level (3.56 kg DM/d, 20% of total DMI) and a fibre-rich hay (approximately 60% NDF in DM) in long (28.7 mm), chopped (9.2 mm) and fine ground (2.9 mm) form in a 3 x 3 Latin square design. In another three factorial experiment with 8 wethers (4 animals were ruminally fistulated, mean BW = 68 kg) the main effects and interactions of the above mentioned hay particle sizes at two concentrate levels (10.4 to 13.3% and 29.5 to 40.1% of DMI, resp.) and two intake levels (restricted and ad libitum) were investigated. In comparison to long hay (28.7 mm), feeding of chopped hay (9.2 mm) at low concentrate levels, increased not only the hay intake (7% in dairy cows and 13% in sheep) but also the intake of digestible organic matter (12% in dairy cows and 32% in sheep), due to an increase in the apparent digestibility of OM by 3.8% in dairy cows and 8.2% in sheep. Ad libitum feeding of fine ground hay in combination with low concentrate amount in the ration increased the passage rate in the hindgut and consequently the hay intake, but not the intake of DOM, due to a significant depression of digestibility, especially of fibre fractions (4 to 7% in dairy cows and 4.5 to 14% in sheep), in comparison to 28.7 and 9.2 mm hay particle sizes. The digestibility decreased significantly with restricted feeding of fine ground hay in sheep only in comparison to 9.2 mm particle size. A threefold increase of concentrate amount leveled out all effects of the particle size reduction. The effect of particle size was more pronounced in sheep than in dairy cows.

The effects of condensed tannins supplementation of foods with different protein content on parasitism, food intake and performance of sheep infected with Trichostrongylus colubriformis

The aims of the present study were to investigate (1), the potential anthelmintic properties and (2), the nutritional consequences of commercially available condensed tannins on parasitised sheep fed, ad libitum, either a high- or a low-protein food. For this purpose, forty-eight previously parasite-naïve sheep (n 12) were infected with 2000 Trichostrongylus colubriformis larvae/d for a 67-d experimental period. Two experimental foods were made: a low (L), formulated to be inadequate in meeting the requirements of growing sheep for metabolisable protein (MP), and based on wheat, citrus pulp, and oatfeed; a high (H), expected to be above the requirements of growing sheep for MP, based on similar ingredients but supplemented with protected soyabean meal. Two additional foods were made by adding 60 g Quebracho (a condensed tannins (CT) extract)/kg fresh matter to foods L and H (foods LQ and HQ respectively). This level of Quebracho supplementation has been previously shown to reduce the level of parasitism in restrictedly fed, parasitised sheep. The experiment was divided into two periods: period 1 (P1, day 1-38) and period 2 (P2, day 39-67), each one associated with different phases of an intestinal parasitic infection. Six sheep from each group were slaughtered at the end of P1, and the remaining sheep were slaughtered at the end of P2 (day 67). Although faecal egg counts (FEC; number of parasite eggs/g faeces) and total egg output were reduced in sheep offered the supplemented foods during P1 (P<0.05), worm burdens on day 38 were unaltered. Neither Quebracho supplementation nor food protein content during P2 affected FEC and worm burdens. Food intake and performance were higher in sheep offered food HQ compared with sheep offered food H (P<0.05); no differences were observed in sheep offered foods LQ and L throughout the experiment. The previously shown anthelmintic properties of CT were not observed following ad libitum intake of either low- or high-protein foods supplemented with Quebracho extract. Higher levels of CT supplementation may be required to reduce parasitism and consequently improve the performance of parasitised sheep, when fed ad libitum. Supplementation with CT conferred advantages on the performance of parasitised sheep on a high- but not on a low-protein food.

[Nitrogen metabolism in the large intestine of ruminants. 6. Metabolism of intracecally administered 14C and 15N urea in sheep with simultaneous intracecal doses of heat-damaged hay]

Two wethers (28 kg and 33 kg) were supplied with ileocaecal re-entrance cannulae and received a straw pellet ration rich in crude fibre (70.5% straw, 12% chopped sugar beet, 10% cereals, 2% urea, 3% NH4HCO3 and 2.5% of a mineral mixture). In a preliminary period 50% of the digesta flow was collected on 6 successive days for 18 h each. An amount of digesta sufficient for 24 h was apportioned for hourly application and stored at a temperature of -20 degrees C for the main trial. In the main trial the two animals received intracaecally the collected digesta with a supplement of ca. 6 g hay damaged by heat/kg LW(0.75) in hourly portions over 24 h (hay made up ca. 15 and 20% resp. of the DM amount). In addition, each digesta sample was supplemented with 14C and 15N labelled urea (19.7.10(6) Bq 14C urea and 364 mg 15N excess from 15N urea). About 9% of the applied 15N amount was microbially utilized; the utilization quota was thus lower than after the application of partly hydrolyzed straw meal (16% in a previous trial). The 14C activity from 14C urea was quickly eliminated in the form of CO2 in the respiratory gases (at the 18th hour after the end of the infusion 70% excreted as CO2). The half-lives for the urea resulting from the semi-logarithmic decrease of the atom-% 15N excess in the blood plasma were 7.9 and 7.7 resp. 23% and 34% resp. of the applied 15N excess were excreted in urine. The excretion of radioactive carbon in urine, however, was at 2.8% and 4.3% resp. of the applied amount very low 120 h after the beginning of the trial (96 h after the end of the infusion). On the whole one can conclude from this trial that hay damaged by heat has only a low stimulating effect on microbial activity in the large intestine.

The relation between food intake and abomasal emptying and small intestinal transit time in sheep

The relation between the level of food intake and gastrointestinal motility and digesta flow in the abomasum and small intestine was studied in sheep fitted with nichrome-wire electrodes in the gut wall, an abomasal and a duodenal catheter and a terminal ileal cannula. Abomasal volume and outflow were calculated from CrEDTA dilution in six sheep and small intestinal transit time by the passage of Phenol Red in ten sheep. The frequency of the migrating myoelectric complex of the small intestine was not altered by the level of food intake but the duration of the periods of irregular spiking activity, the amplitude of abomasal activity and the frequency of duodenal rushes were decreased as the level of food intake was decreased. There was a linear relation between the level of food intake (FI) and abomasal outflow (mean with SEM: 327 (69) ml/h for each kg FI/d; P less than 0.01), and abomasal volume (mean with SEM: 344 (50) ml/kg FI per d; P less than 0.001), without any significant change in the half-time of marker dilution in the abomasum. Small intestinal transit time decreased with an increase in food intake (mean with SEM: -54.9 (5.6) min/kg FI per d; P less than 0.001). It is concluded that abomasal volume and the rate of digesta flow from the abomasum and along the small intestine are linearly related to the level of food intake.

Effects of intake of a mixed dairy steers on digestion events

Ruminally cannulated steers were in a 4 X 4 Latin square to determine the effect of amount of feed ingested on fiber digestion and other digestion events. Alfalfa haylage, corn silage, and a corn-soybean meal mix were incorporated in a ratio 45:20:35 (dry matter) and fed at either 100, 85, 70, or 55% of ad libitum intake. Acid-insoluble ash, lanthanum, and chromium-ethylenediaminetetraacetic acid were digestion, particulate, and liquid markers. Apparent digestibility of dry matter, neutral detergent fiber, and cell solubles decreased linearly as feed intake increased. The fiber fraction digested was a larger percentage of the dry matter digested at low than at high intakes of feed. A more rapid rate of cellulose disappearance and a slow rate of passage of particulate matter through the rumen and total digestive tract with decreasing feed intake were key factors responsible for bringing about changes of digestion coefficients. A consistently lower rumen pH of steers at high intakes of feed was thought to account for the slower rate of ruminal fiber disappearance. The lower tract accounted for 11 to 17% of dry matter disappearance, and tended to play a greater role during periods of high feed intake. Rumen and fecal sampling techniques provided similar ruminal rates of solids passage.

Digestive physiology of East African wild ruminants

The physiology of digestion of wild ruminants in their natural habitat was determined. The study consisted of fifty-one adult male animals representing sixteen species. While diet and body weight were both related to the gastrointestinal composition, body weight appeared to be the more influential factor. Reticulo-rumen and caecal-colon composition, relative to abomasal and small intestinal composition, showed the greater species, diet and body weight effects. The buffalo, oryx and gerenuk were somewhat more unique in gastrointestinal composition than were other species of wild ruminants, and were deserving of special consideration.

Studies of the large intestine of sheep. 2. Kinetics of liquid and solid phase markers in the caecum and proximal colon

1. Experiments were undertaken to examine the errors associated with the use of indigestible markers, the 51Cr-labelled complex of chromium ethylenediaminetetra-acetic acid (51Cr-EDTA) and 103Ru-labelled tris-(1,10-phenanthroline)-ruthenium(II) chloride (103Ru-P), to measure liquid- and solid-phase digesta kinetics in the caecum and proximal colon of sheep.

2. First-order kinetics of markers were observed following either single injection or termination of continuous infusion. There were no differences between the half-times (T½) of marker in the caecum plus proximal colon whether calculated from marker concentration in caecal digesta or in faeces. There were also no differences in the T½ values calculated for the liquid- and solid-phase markers. When pool sizes calculated from the marker kinetics were compared with the volume of digesta present in the caecum and proximal colon at slaughter, it appeared that the 51Cr-EDTA and 103Ru-P caecal pools described the digesta contained in the entire caecum and proximal colon.

3. The flow-rates of dry matter (DM) through the caecum of sheep given 694 g lucerne (Medicago sativa) DM/d were similar whether estimated from total collection of faeces, by single injection of marker, or by the ratio, marker concentration: DM in either caecal digesta or faeces during continuous infusion of marker into either the rumen or the caecum.

4. In sheep given 553 g brome grass (Bromus inermus) DM/d the coefficient of variation of estimates of the plateau of 51Cr-EDTA marker during continuous infusion into the caecum was greater when 130 ml infusate/d were administered than with 1000 ml/d.

5. In the sheep given brome grass the lines of best fit of decline in In 51Cr-EDTA marker concentration v. time following termination of the continuous infusions described previously and following single injection of marker in 20 or 2 ml into the caecum were examined. The variation was least when 1000 ml infusate/d had been administered and was unacceptably large following a single injection of 2 ml.

6. These experiments showed that tracer techniques could provide unbiased estimates of trace kinetics in the caecum and proximal colon.

Studies of the large intestine of sheep. 1. Fermentation and absorption in sections of the large intestine

1. Fermentation and absorption of constituents of digesta in segments of the large intestine of sheep given different diets were studied by analysis of gut contents obtained at slaughter after a period during which the sheep had been administered a non-absorbable gut marker. 2. In sheep given chopped, dried lucerne (Medicago sativa) there was net absorption of water throughout the large intestine with concomitant increases in the proportion of dry matter (DM) and organic matter (OM). There was net disappearance of 62 g OM, 1.66 g non-urea non-ammonia-nitrogen (NU-NAN) and 0.6 g (urea + NH3(-N in the caecum and proximal colon. There was no significant change in OM and NU-NAN flow through the remainder of the large intestine but there was a net disappearance of 0.3 g NH3-N. There was also net appearance of volatile fatty acids (VFA) in the caecum, most of which was apparently absorbed before the rectum. 3. Metabolism in the caecum was also studied in sheep grazing fresh pasture or consuming one of three sugar cane-bagasse-based diets, or barley pellets. In the lucerne- and pasture-fed sheep there was a net disappearance of approximately 0.5 g NH3-N/d from the caecum, while in sheep fed on bagasse plus urea, 1.4 g NH3-N/d was apparently absorbed from this region. The addition of fish meal to this latter diet resulted in apparent disappearance of 5.3 g NH3-N/d from the caecum and proximal colon. 4. There was apparent loss of NU-NAN from the caecum of sheep on all diets except the barley diet. With the latter diet there was a net gain of 1 g NU-NAN/d which was associated with relatively high VFA concentration and production; taken together these results indicate that microbial fermentation in the caecum was more extensive in the sheep fed on the barley diet than in those fed on the other diets. 5. The proportions of individual VFA in digesta from the rumen and caecum of lucerne-fed and pasture-fed sheep and in digesta from the caecum of sheep given the bagasse-based or barley diets are also reported and discussed. 6. In general the results indicate that the caecum and to a lesser extent the proximal colon were the major regions of fermentation and absorption of the components of the digesta in the large intestine.

Rate of passage of digesta in sheep. 6. The effect of level of food intake on mathematical predictions of the kinetics of digesta in the reticulorumen and intestines

1.Five sheep were given 400, 625, 850, 1075 and 1300 g lucerne chaff/d according to a 5 × 5 Latin square design to perturbate a mathematical model describing the rate of passage of digesta in terms of rate constants for the reticulo-rumen (k1) and caecum and proximal

2.colon (k2), and a transit time (TT) for the intestines. These values were obtained from the concentration curves of51Cr EDTA and144Ce-144Pr (144Pr) excretion in faeces for comparison with similar measurements obtained directly.

3.The retention times of markers in the reticulo-rumen, caecum and proximal colon and intestines all decreased by approximately 50% as intakes were increased from 400 to 1300 g/d. For both markers, the direct and indirect measures of half-time in the reticulo-rumen were essentially identical. The predicted (indirect) values for half times in the caecum and proximal colon were smaller than the direct values (P< 0.005) but the correlations between them were significant (P< 0.01) for51Cr EDTA (r0.66) and144Pr (r0.78). The direct measures of transit time were smaller (P< 0.025) by 5–10% than the predicted values but correlations between them were significant (P< 0.01) for51Cr EDTA (r0.91) and for144Pr (r0.93). Thus the model predicted the changes produced in the rate of passage of digesta and its usefulness and limitations are discussed.

3.With144Pr1/2k1for the reticulo-rumen andT1/2k2for the caecum and proximal colon were both positively correlated (P< 0.025) with the organic matter digestibilities.T1/2k2decreased at half the rate ofT1/2k1with increasing intakes. This would have favoured compensatory digestion in the large intestine.

Rate of passage of digesta in sheep. 4. Passage of marker through the alimentary tract and the biological relevance of rate-constants derived from the changes in concentration of marker in faeces

1. The rates of passage of markers of fluid and particulate digesta through the sheep alimentary tract have been described mathematically in single-injection experiments by analysing the concentration curves of marker excretion in faecal dry matter and then predicting these concentrations by means of an equation containing two exponential terms. Three components related to this equation are a transit time for digesta in the intestines, a half-time of marker in the reticulo-rumen and a half-time tentatively associated with the passage of marker through the caecum and proximal colon. With this approach no surgical interference with an animal is required to obtain meaningful information about gut function.

2. Abomasal cannulation did not affect the rate of passage of 51Cr EDTA through the gut.

3. The mean half-times (T1/2) for 51Cr EDTA in the reticulo-rumen and hind-gut, respectively, were 646 and 236 min for a roughage diet and 890 and 607 min for a diet consisting mainly of wheat grain, both diets providing approximately the same amounts of digestible dry matter. These results indicated that the changes in half-times were proportionately much greater in the caecum and proximal colon than in the reticulo-rumen. The mean transit time of marker through the digestive tract also increased from 721 to 1345 min when the concentrate diet was given.

4. The complex of chromium-51 with EDTA was excreted faster in faeces than cerium-144–praseodymium-144 when both were given together as a single injection into the reticulorumen. This was caused mainly by differential rates of elimination of water and particulate matter from the reticulo-rumen.

Rate of passage of digesta in sheep. 5. Theoretical considerations based on a physical model and computer simulation

1. Sheep were given 800 g lucerne chaff/d and the mean half-times of cerium-144 – praseodymium-144 and the complex of chromium-51 with EDTA were 811 and 604 min in the reticulo-rumen, 37 and 17 min in the abomasum and 413 and 406 min in the caecum and proximal colon respectively. The average time available for digestion and absorption in the abomasum was therefore very short relative to that in the other two organs.

2. The half-times of the markers also indicated that particulate matter and water had different rates of turn over in the reticulo-rumen and abomasum but not in the caecum and proximal colon.

3. Evidence is presented which suggests imperfect mixing of the digesta in the caecum and proximal colon.

Rate of passage of digesta in sheep. 3. Differential rates of passage of water and dry matter from the reticulo-rumen, abomasum and caecum and proximal colon

1. Three groups of sheep receiving 400, 800 and 1200 g lucerne chaff/d in equal hourly meals were killed. The large intestines were removed and divided into segments 15 cm long to provide information on the amounts and dry-matter contents of digesta and on the rates of passage of digesta and absorption of water along the large intestine.

2. With increasing intakes of food, increases were observed along the entire large intestine in the amounts of wet digesta present, in the transit rates of digesta and in the rates of absorption of water. The mean retention time of digesta in the large intestine decreased with increasing food intake, being 1737, 1056 and 692 min respectively.

3. Four patterns of sodium and potassium concentrations in digesta water along the large intestine were found.