| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
* Animal Nutrition Group, Wageningen UR, P.O. Box 338, 6700 AH Wageningen, the Netherlands
Animal Sciences Group of Wageningen UR, Division of Animal Production, P.O. Box 65, 8200 AB Lelystad, the Netherlands
2 Corresponding author: Walter.Gerrits{at}wur.nl
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
|---|
Key Words: veal calf • concentrate composition • roughage composition • rumen fermentation
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
|---|
In veal calves, typically fed with milk replacer and supplemented with relatively small quantities of concentrates, information concerning the effects of roughage intake on performance and rumen development is scarce (Blokhuis et al., 2000; Cozzi et al., 2002). Feeding roughage without concentrates to young calves generally does not promote rapid papillae development, probably due to insufficient VFA production rates (Nocek and Kesler, 1980). Roughage consumption, however, stimulates muscle development of the rumen wall (Tamate et al., 1962) and promotes rumination (Hodgson, 1971). Furthermore, the physical characteristics present in the roughages, such as coarseness, bulkiness, and abrasiveness, have been reported as necessary to maintain the integrity and healthiness of the rumen wall (Haskins et al., 1969). Therefore, it was hypothesized that adding roughage to a concentrate diet would reduce the incidence of poorly developed mucosa and plaque formation observed in concentrate-fed veal calves (Suárez et al., 2006a,b) and stimulate the development of the rumen wall, without negative effects on performance.
The objective of the present experiment was to determine the effect of various roughage sources, concentrate to roughage ratios, and intake levels of concentrate and roughage fed in addition to a milk replacer diet on rumen development and growth performance of veal calves.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
|---|
Calves, Diets, Transport, and Slaughter Procedure
Sixty-four Holstein-Friesian x Dutch Friesian male calves of approximately 10 d of age (46 ± 3.0 kg) were allotted to 1 of 8 blocks, and within blocks were randomly assigned to 1 of 8 dietary treatments. Calves were housed in individual 0.9-m2, mesh-bottomed pens without bedding material. Ambient temperature was maintained at least at 15°C.
Dietary treatments (Table 1
) consisted of a 100% concentrate control treatment and 7 treatments in which a variety of roughage sources were supplied in various quantities in addition to a commercial milk replacer (970.9 g/kg of DM; 36.8 g/kg of N; 181 g/kg of crude fat; 73.5 g/kg of ash). Milk replacer and dietary treatments were offered to the calves twice daily (0600 and 1600 h). The roughage sources used were either corn silage, barley straw, or dried grass. Treatments were 1) C100 = concentrate only, 2) C70-S30 = concentrate (70%) with straw (30%), 3) C70-G30 = concentrate (70%) with dried grass (30%), 4) C70-G15-S15 = concentrate (70%) with dried grass (15%) and straw (15%), 5) C70-CS30 = concentrate (70%) with corn silage (30%), 6) C40-CS60 = concentrate (40%) with corn silage (60%), 7) C70-CS30-AL = concentrate (70%) with corn silage (30%) fed ad libitum, 8) C70-G15-S15-AL = concentrate (70%) with dried grass (15%) and straw (15%) fed ad libitum. Ingredient and nutrient composition of the concentrate as well as the nutrient composition of roughages is presented in Table 2. Total nutrient composition of the various treatments can be calculated from the diet composition (proportion of roughage and concentrate in the diet; Table 1) and the nutrient composition of roughages and concentrates (Table 2). The concentrate was provided as pellets and the roughages were chopped. Except for the ad libitum treatments, the supplied DMI from concentrates and roughage was maximized at 750 g/d, and for these restricted-fed diets, the daily supply of milk replacer was gradually increased and amounted to 360, 480, 530, 570, 620, 700, 810, 980, 1,170, and 1,360 g/d in wk 1 to 10, respectively. For the ad libitum treatments, the supply of milk replacer was identical to the restricted-fed treatments up to wk 6, but remained constant at 700 g/d thereafter. Concentrates and roughages portions were weighed and mixed separately (50% of the expected daily intake per meal), and supplied in a different bucket immediately after the calves had finished the milk replacer. Buckets were weighed and emptied before the next milk replacer meal, and pooled samples of concentrates, roughage sources, and orts were obtained for chemical analysis. To avoid selective intake of concentrates or roughages, the daily supply was based on minimization of orts. Therefore, the expected DMI of a calf was calculated weekly based on the realized DMI of that calf in the previous week and a projected weekly increase.
|
|
The rumen was dissected along the dorsal line, emptied, and rinsed with cold water. The examination and assessment of the rumen mucosa and sites of sampling of the rumen wall for further morphometric analysis were carried out as described by Suárez et al. (2006b). Briefly, the mucosal surface was visually examined and qualitatively assessed according to the presence and density of rumen papillae as follows: 1 = poor (small number of papillae or short papillae) and 2 = good (numerous papillae or long papillae). The incidence of plaque (rumen mucosa containing focal or multifocal patches with coalescing and adhering papillae covered by a sticky mass of feed, hair and cell debris) was visually assessed. The morphometric analyses were conducted in 4 slides (embedded in paraffin, stained with hematoxylin-eosin) cut from a 2 x 2 cm section of rumen wall tissue taken either from a dorsal or a ventral location in the rumen. The measurements comprised a) the ratio of mucosa length to serosa length (RMSL) as a measure of absorptive area and determined as the length of the mucosal surface within a slide divided by the length of the corresponding serosa (the latter being about 2 cm); b) mucosa thickness (MCT), measured at 3 randomly chosen sites within each slide; and c) muscle thickness (MST), measured at the same sites as for MCT. The measurement of MCT was chosen to avoid bias of the observer by defining suitable, measurable papillae in a slide, as irregular shapes of papillae frequently occurred. Morphometrical analyses were performed at a magnification of 2.5x (Olympus microscope; Olympus Corporation, Tokyo, Japan) by using the image analysis software Image Pro Plus (Media Cybernetics, Silver Spring, MD).
By using a metal sieve (1.5 mm), the solid and liquid phases of the rumen contents were separated and weighed. The separation of both phases was done by gently squeezing the rumen contents until no more leakage of liquid was observed. A representative sample of rumen contents was reconstituted from the solid and liquid phases.
Rumen pH was measured in the rumen liquid. Rumen liquid was centrifuged (1,000 x g, 10 min), sampled, acidified with ortho-phosphoric acid, and stored at –20°C until analysis.
Analytical Procedures
Dry matter was determined by drying at 103°C and ash by combustion at 550°C according to standards ISO 6496 (ISO, 1983) and ISO 5948 (ISO, 1978), respectively. Kjeldahl N and fat content were determined based on ISO 5983 (ISO, 1998) and 6492 (ISO, 1999), respectively, and total starch was analyzed according to Brunt (1993). Reducing sugars (RS) were extracted from the dried rumen samples using 40% ethanol and determined as described by Suárez et al. (2006a). Neutral detergent fiber, ADF, and acid detergent lignin were analyzed according to a method adapted from Van Soest et al. (1991). Briefly, after the neutral detergent treatment incubation, an enzyme cocktail containing termamyl (Novo Nordisk, Copenhagen, DK), amylase (Sigma 6814, Sigma-Aldrich, St. Louis, MO) and protease (Novo Nordisk) in phosphate buffer (pH 7.0) was added to remove starch and proteins from the residue. For ADF determination, the samples were first treated as in the NDF methodology, and then, the residues were incubated with acid detergent as described by Van Soest and McQueen (1973). The acid detergent lignin analysis was based on the treatment of the sample with acid detergent followed by incubation with 72% sulfuric acid.
The VFA and lactic acid concentrations were analyzed using HPLC with a Merck polyspher OA 51272 column as stationary phase (Merck & Co., Inc., Whitehouse Station, NJ) and 0.0025 M sulfuric acid as mobile phase (elution fluid) and a refractive index detector. Calibration and quantification was done by using an external standard solution. Ammonia concentrations were estimated according to the Berthelot method, modified by Schneider (1976).
For the CoEDTA determination, samples of whole rumen contents were freeze-dried, ground, and subsequently incinerated at 250 and 550°C. The remaining ash was destructed with concentrated nitric acid during 2 h at 100°C. The supernatant was diluted with a solution containing lithium-chloride and yttrium (as internal standard). The content of Co was measured by inductively coupled plasma optical emission spectrometry at 228.616 nm.
Isolation of rumen enzymes and subsequent measurement of their activities were carried out as described by Suárez et al. (2006a). The substrates incubated with the enzyme cocktails were suspensions (2% wt/vol) of sugar beet pulp, soybean hulls, native cornstarch, and straw. Incubates, substrate blanks, and enzyme extract blanks were analyzed for RS end-groups according to Somogyi (1952). After correcting by substrate and enzyme extracts blanks, the enzyme activity was expressed as millimoles of RS released per minute per gram of DM in the rumen. If desired, enzyme activity can be expressed on a whole rumen basis by multiplying the enzyme activity per unit of DM and the total rumen DM pool size.
Statistical Analysis
Data for rumen fermentation parameters, empty rumen weight, and rumen wall parameters were analyzed as a complete randomized block design, with dietary treatments as main factor. Continuous data were subjected to ANOVA according to model 1:
 | [1] |
where y is the dependent variable; µ is the average experimental value; dieti is the effect of dietary treatment i; i is diet 1 to 8; slaughter dayj is the effect of slaughter day j; j is 1, ..., 4; 
ijk is the error term; and k = 1, ..., 64 (i.e., calf).
The same model, but excluding the effect of slaughter day, was used to analyze data of DMI and ADG.
The parameters in which the postfeeding slaughter time was expected to have an effect (rumen pH, ruminal VFA concentrations, and CoEDTA recovery) were analyzed using the following model:
 | [2] |
where y is the dependent variable; µ is the average experimental value; dieti is the effect of dietary treatment i; i is diet 1 to 8; slaughter dayj is the effect of slaughter day j; j = 1, ..., 4; intervalk is the effect of interval from feeding to slaughter ; k is 1.5, 2.5, 3.5, 4.5 h; (diet x interval)ik is the effect of interaction between dietary treatment and interval from feeding to slaughter; and ijkl is the error term; and l = 1, ..., 64 (i.e., calf).
The F-test was used to evaluate the effect of dietary treatment. For the analysis of fractions (percentages), a logistic regression model was used with the same main effects as described earlier. Inferences for fractions were based on likelihood ratio tests. Dispersion parameters were estimated from Pearson’s generalized test (McCullagh and Nelder, 1989). Posthoc pairwise comparisons between diets were carried out using the Fisher LSD method (for fractions on a logistic scale), employing the pooled error variance from the ANOVA. In addition, predetermined contrasts between specific (combinations of) feed rations were examined, including A) roughage supplementation: C100 vs. all roughage containing diets, except the 2 ad libitum diets; B) the effect of source of roughage supplementation: C70-S30 vs. C70-G30 vs. C70-CS30; C) the effect of supplementing a single or a combined source of roughage: C70-G15-S15 vs. (C70-S30 and C70-G30); D) the effect of different levels of roughage supplementation: C70-CS30 vs. C40-CS60; and E) the effect of restricted vs. ad libitum roughage supplementation: (C70-G15-S15 and C70-CS30) vs. (C70-G15-S15-AL and C70-CS30-AL). Each contrast was tested for significance with a t-test, again using the pooled error variance from the ANOVA. Measures of rumen fermentation (pH, total VFA concentrations and their molar proportions, lactate, and ammonia), empty rumen weight, and morphometric variables of the rumen wall were also subjected to analyses of covariance, introducing DMI as a covariable in the appropriate ANOVA model (see above). For measures of rumen fermentation, the average DMI during the last week prior to slaughter was used as a covariable and expressed as the deviation from the overall mean. For the empty rumen weight and morphometric variables of the rumen wall, the average DMI during the entire experimental period was used as a covariable and likewise expressed as the deviation from the overall mean. In this manner, least squares means of dependent variables following analyses of covariance were appropriately corrected for differences in DMI. Binary variables were analyzed parameter-free using the Fisher exact test. Significance was determined at P < 0.05 unless indicated otherwise. All calculations were performed with Genstat (Genstat Committee, 2000).
The rumen enzyme activities were analyzed as a complete randomized block design with dietary treatments and substrates as main factors by using the GLM procedure of SAS (SAS Institute, 2002) according to model 3:
 | [3] |
where y is the dependent variable; µ is the average experimental value; dieti is the effect of dietary treatment i; i is diet 1 to 8; substratej is the effect of substrate j, j is soybean hulls, native cornstarch, sugar beet pulp, or straw; and ijk is the error term.
Main effects and the interaction between diets and substrate were evaluated. Moreover, predetermined contrasts between diets (mentioned above) were performed by substrate.
|
RESULTS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
|---|
. If desired, total nutrient intakes (from milk plus solid feeds) can be calculated from the knowledge of the milk replacer composition, solid feeds composition, and their respective intakes.
|
The weight at slaughter was not affected by the diets. Average daily gain ranged from 688 to 779 g/d. Calves fed the C70-G30 and C70-CS30 diets had increased ADG (779 and 774 g/d, respectively) compared with those on the C70-S30 treatment (668 g/d; contrast B; P < 0.05). Feed conversion was not affected by dietary treatments among restricted-fed calves (P > 0.05), but it was increased in the calves of the ad libitum-fed groups (P < 0.001; contrast E).
Rumen Fermentation Parameters
The effects of dietary treatments on rumen weight and fermentation parameters are shown in Table 4. The pH in rumen liquid varied between 5.1 and 5.3 and was higher for calves fed the C70-G15-S15 diet than for calves on the C70-S30 and C70-G30 treatments (contrast C; P < 0.05).
|
The molar proportion of isobutyrate in the rumen liquid was lower in C70-G30 fed calves than in those fed either the C70-S30 or C70-CS30 diets (contrast B; P < 0.05). In addition, lower molar proportions of isobutyrate and of methyl-butyrate were observed in ad libitum-fed calves (contrast E; P < 0.05 and P < 0.01, respectively). The molar proportion of methyl-butyrate was higher in calves fed a roughage combination of dried grass and straw (C70-G15-S15; contrast C; P < 0.001). A tendency to a higher molar proportion of methyl-butyrate was present in calves fed diets with a higher corn silage to concentrate ratio (contrast D; P < 0.1). Finally, lower molar proportions of valerate were observed in calves fed straw compared with calves fed either dried grass or corn silage as additional source of roughage (contrast B; P < 0.001).
Lactate concentrations varied between 2.0 and 11.8 mmol/L and were lower in calves fed ad libitum (contrast E; P < 0.05). Furthermore, rumen lactate concentrations were slightly lower in calves fed C70-CS30 than in calves fed C70-G30 (4.6 vs. 10.9 mmol/L; contrast B; P < 0.1).
Ruminal concentrations of ammonia ranged from 8.2 to 25.8 mmol/L and were lower in ad libitum-fed calves (contrast E; P < 0.01) and higher in calves fed concentrates only (contrast A; P < 0.001). Finally, calves fed a mixture of grass and straw as source of roughage had higher concentrations of ammonia than calves fed either grass or straw as a roughage source (contrast C; P < 0.05).
The concentration of RS varied between 47.7 and 75.1 g/kg of DM of whole rumen content. Calves fed the C70-CS30 diet had a lower RS concentration (47.7 g/kg of DM) than calves fed the C70-G30 diet (75.1 g/kg of DM; contrast B; P < 0.05). Ad libitum feeding did not have an effect on the rumen RS concentration (contrast E, P > 0.05).
The recovery of Co ranged from 21.8 to 34.9% and was highly variable among calves within treatments. Calves fed the C70-G15-S15 diet tended to have lower Co recoveries than calves fed either C70-G30 or C70-S30 diets (P < 0.1; contrast C).
Results from the analysis of covariance showed that variation in DMI (average during the last week before slaughter) significantly explained variation in total VFA, the molar proportion of butyrate, and the concentration of ammonia (estimates of regression coefficients ± SE for DMI: 77.1 ± 22.4, 0.53 ± 0.22, and –11.5 ± 4.7, respectively; P < 0.05). Because DMI in calves fed ad libitum was much higher than in calves fed restricted diets (Table 3
), but dietary treatments did not significantly affect total VFA concentrations (Table 4), the contrast between restricted and ad libitum diets (contrast E) in total VFA concentrations became significant (P = 0.01) after analysis of covariance. Significant differences in the molar proportion of butyrate among dietary treatments C70-S30, C70-G30, and C70-CS30 (contrast B) consistently coincided with differences in DMI (Tables 3 and 4). Thus, following analysis of covariance, contrast B in the molar proportion of butyrate was no longer significant (P > 0.05). Likewise, the significant contrast between restricted and ad libitum diets in the concentration of ammonia (Table 4, contrast E) became nonsignificant after analysis of covariance because of accompanying differences in DMI (Table 3).
Effects of time between last feeding and slaughter on rumen pH, total VFA and lactate concentrations, and Co recovery are shown in Table 5. Rumen pH was not significantly influenced by the time of slaughter (P > 0.05). However, the total VFA concentrations in rumen fluid increased from 108.3 mmol/L at 1.5 h postfeeding to 143.8 mmol/L at 3.5 h postfeeding and decreased to 134.6 mmol/L by 4.5 h postfeeding (P < 0.05). Lactate concentration and Co recovery declined with time post-feeding (P < 0.001).
|
. The incidence of plaque formation was affected by dietary treatments and varied between 0 and 100%. The rumen mucosa of calves fed the C100, C70-CS30, and C40-CS60 diets showed higher incidence of plaque formation (63 to 100%) than those fed the C70-S30, C70-G30, or ad libitum diets (0 to 13%; P < 0.05). Although in some dietary treatments the incidence of calves with poor developed mucosa was 0%, no significant differences (P > 0.05) were observed.
|
. The empty rumen weights of the calves varied between 953 and 1,448 g. Calves in the ad libitum-fed groups had heavier empty rumen weight (P < 0.001; contrast E). Likewise, among restricted-fed treatments, calves on the all-concentrate diet showed the highest averaged empty rumen weight (P < 0.001; contrast A).
|
The analysis of covariance of rumen weight and the rumen wall morphometric parameters revealed that variation in empty rumen weight was significantly explained by variation in DMI (average during the entire experimental period; estimate of regression coefficient ± SE for DMI: 651 ± 145, P < 0.001). Variation in DMI tended to explain variation in the RMSL and MCT in the ventral rumen (estimates of regression coefficients ± SE for DMI: 2.91 ± 1.52, and 695 ± 370, respectively; P < 0.07).
Enzyme Activity in Whole Rumen Contents
The effects of experimental treatments on PDE activities extracted from the whole rumen contents are presented in Table 8. With soybean hulls as substrate, PDE activities varied between 1.8 and 4.1 mmol/min per g of DM. Calves fed C70-G30 showed higher PDE activities than those fed C70-S30 or C70-CS30 (contrast B; P < 0.001). Furthermore, ad libitum-fed calves had decreased PDE activities when compared with restricted-fed calves (contrast E; P < 0.001). With sugar beet pulp as substrate, the PDE activities varied between 3.1 and 6.5 mmol/min per g of DM. Among restricted-fed treatments, the calves fed concentrate showed higher PDE activities than those fed additional roughage (contrast A; P < 0.001). With native cornstarch as substrate, the PDE activities varied between 2.2 and 9.4 mmol/min per g of DM. Calves fed C70-S30 showed lower PDE activities than those fed C70-CS30 or C70-G30, respectively (contrast B; P < 0.001). Ad libitum-fed calves had lower PDE activities than those fed restrictedly (contrast E; P < 0.001). Finally, PDE activities in calves fed a combination of straw and grass (C70-G15-S15) were lower than in calves fed either straw or dried grass (contrast C; P < 0.001). With straw as substrate, the PDE activities varied between 0.4 and 0.7 mmol/min per g of DM. Ad libitum-fed calves had lower PDE activities than restricted-fed calves (contrast E; P < 0.001). Moreover, calves fed concentrates only tended to have lower PDE activity (contrast A; P < 0.1).
|
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
|---|
) where an increased fiber content negatively affected DMI (Mertens, 1997; compare contrast B, Table 3). Substituting a part of the concentrate with roughage, however, did not affect DMI and ADG (contrast A). The lower intake of milk replacer in the ad libitum-fed calves does not allow a direct comparison of calf performance across treatments. Therefore, growth rates on both intake levels of milk replacer were simulated using the growth model of Gerrits et al. (1997). Additional growth (AG) from roughage and concentrate was calculated by the difference between the observed ADG and the simulated ADG on milk replacer only, and expressed per unit of DMI from concentrate and roughage. Additional growth in the various treatments ranged from 0.49 to 0.55 and from 0.46 to 0.50 kg/kg of feed for restricted- and ad libitum-fed calves, respectively. For restricted-fed calves, AG for calves fed the C-100 diet was higher (0.55 kg/kg) than for calves fed C70-S30 (0.49 kg/kg). This may be related to the increased yield of absorbed nutrients of concentrates when compared with straw. Moreover, among ad libitum-fed groups a lower AG was obtained in calves fed the C70-G15-S15-AL diet than in those fed the C70-CS30-AL diet. Finally, restricted-fed calves showed increased average AG (0.52 kg/kg) when compared with ad libitum-fed calves (0.48 kg/kg).
In the present experiment, the observed AG in the restricted treatments was not within the AG range observed in a previous experiment (Suárez et al., 2006a). Moreover, the AG on the all concentrate diet was slightly lower than the AG obtained in a previous experiment where a similar diet was fed to calves until 8 or 12 wk of age (0.86 and 0.61 kg/kg, respectively; Suárez et al., 2006a).
Ruminal Fermentation Parameters
In the present experiment an unexpectedly small range of low rumen pH was observed (5.1 to 5.3) and roughage did not significantly increase rumen pH. The rumen pH of the calves fed the concentrate-only diet is in line with the value of 5.2 reported previously in calves aged 8 and 12 wk fed a similar diet (Suárez et al., 2006a). In rearing calves, maximum VFA concentrations have been reported 3 to 4 h postfeeding (
100 to 110 mmol/L; Stobo et al., 1966). In line with these findings, maximum VFA concentrations in the present experiment were observed 3.5 h after feeding. In this experiment, the total VFA concentrations were close to those observed in adult ruminants (120 to 160 mmol/L; Bergman, 1990) and to those observed in roughage-supplemented rearing calves (120 mmol/L; Vázquez-Anon et al., 1993; 150 mmol/L; Zitnan et al., 1998). Total VFA concentrations of calves fed C-100 observed in this study were higher than those previously recorded in calves fed a similar diet and slaughtered at a similar age (Suárez et al. 2006a), mostly likely reflecting differences in time of sampling postfeeding (1 to 3 h vs. 1.5 to 4.5 h, respectively). Ruminant diets based on roughage, especially those rich in structural carbohydrates, are known to produce high molar proportions of acetate. Furthermore, as the roughage to concentrate ratio decreases, the acetate to propionate ratio also decreases (Bannink et al., 2006). In line with these observations, the molar proportion of acetate in the current trial increased when straw was present in the diet (see Table 4, contrast B). Also, molar proportions of acetate and propionate were lowest and highest, respectively, in calves fed the all concentrate diet (contrast A), in agreement with observations in rearing calves (Bull et al., 1965; Stobo et al., 1966; Anderson et al., 1982; Zitnan et al., 1998). The effect of diet on the molar proportion of butyrate seemed to be mediated by DMI, because the contrast among C70-S30, C70-G30, and C70-CS30 (contrast B) was no longer significant after analysis of covariance with the average DMI during the last week before slaughter acting as a covariable.
Lactate concentration in rumen fluid was reduced in the ad libitum-fed groups (3.1 vs. 8.3 mmol/L). In addition, lactate concentrations in the restricted-fed groups were close to concentrations reported in adult ruminants facing subclinical acidosis (10 mmol/L; Hristov et al., 2001). The lower concentrations in the ad libitum-fed groups may reflect an improved capability of rumen microorganisms to utilize lactate (Counotte et al., 1981; Williams and Martin, 1990; Van Soest, 1994). The rapid decline in lactate concentrations after 1.5 h after feeding is in line with observations reported in dairy cattle (Chamberlain et al., 1983; Counotte et al., 1983). Finally, the lactate concentration of the control group (C-100) observed in this study (9.4 mmol/L) was higher than that previously recorded in calves fed a similar diet (5 mmol/L; Suárez et al., 2006a).
The ammonia concentrations reported in this experiment are within the range reported by Zitnan et al. (1998) of 6 to 21 mmol/L in rearing calves fed concentrate and supplemented with roughage (alfalfa). Ammonia concentrations were clearly associated with DMI; correcting for differences in DMI removed significance of the contrast in ammonia between restricted and ad libitum diets. The reduced ammonia concentrations in calves fed ad libitum may indicate an improved utilization (higher microbial efficiency) by the rumen microorganisms related to increased fractional passage rates that usually occur upon higher DMI levels (Dijkstra et al., 2002), or increased absorption across a more mature rumen wall. The implication of higher microbial efficiency is supported by a decrease in the proportion of branched-chain VFA observed in the ad libitum-fed groups. Branched-chain VFA are mainly endproducts of protein fermentation and are, along with ammonia, often used as quick indicators of protein fermentation in the rumen (Yang, 2002).
The etiology of ruminal drinking (ruminal drinkers refers to calves that develop chronic indigestion because milk is deposited into the rumen as a result of failure of the reticular groove reflex during drinking) has been well described (Pochòn, 2002). The pathology with the clinical symptoms was experimentally reproduced by Van Weeren-Keverling Buisman et al. (1990a, b), and the metabolic and endocrine profiles were characterized by Herrli-Gygi et al. (2006). Quantitative information on ruminal drinking, however, is scarce and absent in calves fed concentrates or roughage in addition to milk replacer. Small amounts of milk leakage have been observed in normal veal calves (3%), but quite considerable amounts have been reported in veal calves considered clinically sick (up to 50%; Dos Santos et al., 1986). In the present study, although the presence of milk replacer in rumen was considerable (25%), the concentrations of lactate were lower than results reported by Gentile et al. (2004) in clinically sick animals (15 to 30 mmol/L). Moreover, despite the on-average high recovery of Co in the rumen, none of the calves showed signs of illness, such as reduced appetite or bloat, which indicates that in veal calves fed additional solid feeds (either concentrate or concentrate with roughage) a substantial amount of milk can flow into the rumen without inducing symptoms of the syndrome. The marker technique used does not allow discrimination between the functioning of the esophageal groove reflex and potential reflux of milk replacer from the abomasum, and the technique may suffer from some limitations. Potential influences of transport and slaughter procedures on Co recovery cannot be excluded, although extreme caution was taken to avoid any such bias. The fractional passage rate of rumen liquid was estimated at 46%/h (see Materials and Methods), which is extremely high when compared with adult cows (15%/h; Offer and Dixon, 2000). Applying this fractional passage rate to estimate the Co pool size at time zero indicates that all milk replacer entered the rumen, suggesting either methodological problems or that variable fractional passage rates apply. Nonetheless, because there is currently no ideal technique available to quantify ruminal drinking and estimate rumen passage rate in veal calves, the high recovery of Co in the rumen illustrates a potentially large problem, worthy of further investigation.
Macroscopic and Microscopic Evaluation of the Rumen Wall
Previously, Suárez et al. (2006b) observed, in concentrate-only supplemented calves, a high incidence of plaque formation (see Figure 1) and poor rumen development when judged macroscopically. The occurrence of plaque has been related to the absence of coarse material in the rumen (Nocek et al., 1984). Similar observations were described by Di Giancamillo et al. (2003) in veal calves fed either pelleted or extruded diets. In the present trial, the macroscopic evaluation of the rumen clearly showed the beneficial effects of roughage (except corn silage treatments fed restrictedly) to reduce incidence of plaque and of poorly developed mucosa (see Table 6). The increased empty rumen weight found in calves fed concentrate only may have been influenced by plaque formation. The ad libitum treatments resulted in significantly higher empty rumen weights related to the higher intake, but no plaque was observed in these calves.
|
Enzyme Activity and Soluble Sugars in Rumen Contents
Quantification of the activity of various enzyme systems in whole rumen contents is a way to evaluate the capability of the ruminal microflora to degrade the dietary substrates (Silva et al., 1987; Suárez et al., 2006a). Treatment effects on PDE (a consortium of enzyme activities incubated with various natural substrates) observed in this experiment generally indicated an adaptation of the rumen microorganism to the diets, similar to effects observed by Suárez et al. (2006a). In the present experiment, the activities of most PDE (except when using sugar beet pulp as a substrate, Table 8) were reduced in the ad libitum-fed groups, indicating a reduced fractional substrate hydrolysis rate at high intake levels. The increased enzyme activity in restricted fed calves may be the result of different patterns of feed intake and consequently of microbial activity. Ad libitum-fed calves consumed the concentrate and roughage portions throughout the day, whereas restricted-fed calves consumed the feed rapidly after supply. Therefore, at time of slaughter, relatively more freshly entered substrate is available for microorganisms in the restricted-fed calves, which may have stimulated enzymatic activity.
In adult ruminants it is assumed that soluble carbohydrates are rapidly taken up by rumen microorganisms. Consequently, concentrations of RS are usually low (0.04 and 5.55 g/kg of DM; Hristov et al., 2000, 2001; Hristov and Ropp, 2003). The results of the present experiment confirm earlier observations of high concentrations of RS in rumen contents (Suárez et al., 2006a). It was suggested that at low pH, high concentrations of RS in rumen contents might result from reduced uptake of RS by the microorganisms to regulate their intracellular pH, while the PDE were still active. The additional supply of roughage in the present experiment did not improve the RS utilization by the rumen microorganisms (see Table 4): concentrations ranged from 47.7 to 75.1 g of RS/kg of DM in the present experiment, and between 45 and 61 g of RS/kg of DM in the concentrate-fed veal calves in an earlier experiment (Suárez et al., 2006a).
|
CONCLUSIONS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
|---|
|
FOOTNOTES |
|---|
Received for publication August 10, 2006. Accepted for publication December 12, 2006.
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
|---|
This article has been cited by other articles:
|
|
 |
|
  M. A. Khan, H. J. Lee, W. S. Lee, H. S. Kim, S. B. Kim, K. S. Ki, S. J. Park, J. K. Ha, and Y. J. Choi Starch Source Evaluation in Calf Starter: I. Feed Consumption, Body Weight Gain, Structural Growth, and Blood Metabolites in Holstein Calves J Dairy Sci, November 1, 2007; 90(11): 5259 - 5268. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
