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1 URH-DVA, INRA-Theix, 63122 St Genès Champanelle, France
2 Limagrain Verneuil Holding, Département Recherche, BP 115, 63203 RIOM Cedex, France
Corresponding author: C. Martin; e-mail: cecile{at}clermont.inra.fr.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Key Words: intake • whole-plant corn silage • chop length • hybrid
Abbreviation key: H1 = conventional corn hybrid slowly degradable in the rumen, H2 = conventional corn hybrid rapidly degradable in the rumen, LP2 = proportion of large particles (>2 mm), TCL = theoretical chop lengths, WPCS = whole-plant corn silage
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Regulation of feed intake combines short-term control of feeding behavior related to the body homeostatic regulation and long-term control that depends on nutritional requirements and body reserves. Feed factors mainly affect short-term control. Numerous studies have been conducted to examine the feedback effects of different postingestive signals on feedback control, which influence the satiation process. Physical signals (rumen fill) and chemical and metabolic signals due to nutrients are generally distinguished (Faverdin et al., 1995). The effect of rumen distension in the control of intake is well documented (Allen, 1996, 2000; Pitroff and Kothmann, 1999). This physical effect depends on the particle-size reduction and degradation rate of forages. Particle size plays a key role in digestion and passage of feed through the gastrointestinal tract of ruminants and, therefore, in DMI. Size and density of digesta particles in the rumen depend on initial size of feeds that can be altered by chopping or grinding and reduction in particle size by chewing.
Objectives for this trial were to study the effects of hybrid and chop length on WPCS intake, giving particular attention to the interrelationships among chewing activity, particle size reduction, rumen fill, ruminal retention time, and voluntary intake.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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The dietary treatments differed in the corn hybrid and chop length of WPCS. Two conventional corn hybrids, a mid-early (H1) and an early hybrid (H2), different by their ruminal degradability, were grown under the same conditions. They were sown in May 2000 in Limagne (France) on the same experimental field, at a density of 100,000 seeds/ha and harvested with a precision-chop harvester (Claas 690 SL model, no roller mill) at 2 theoretical chop lengths (TCL)—fine (5.0 mm) and coarse (13.0 mm). The 4 whole-plant corns were ensiled in 20-tonne silos. Diets were based on the experimental WPCS (75%), supplemented with 24% concentrate mix and 1% minerals. The concentrate contained (on DM basis) 25.7% soybean meal, 37.1% wheat, 13.4% rapeseed meal, 11.1% sunflower meal, 7.4% wheat bran, 1.5% molasses, 1.5% brewers from yeast production, 1.5% calcium carbonate, 0.4% sodium chloride, 0.4% vitamins and oligoelements, and the mineral contained 6% P, 24% Ca, and 5% Mg, respectively. The diets (Table 1
) were formulated to meet energy, protein, and mineral requirements of the cows according to the French feeding system (INRA, 1989). The cows were fed TMR ad libitum, twice daily in equal portions at 0900 and 1600 h. Each period of the Latin square lasted 29 d, with a 14-d adaptation period followed by a 15-d period for sample collection.
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Lactating cows were milked twice daily, and production was recorded at each milking. Milk samples were taken from a.m. and p.m. milking on 4 consecutive days per week during the experimental period (from d 15 to 18 and from d 22 to 25).
Chewing activity was measured on cannulated cows for 3 consecutive days (from d 24 to 26), using a harness and sensors connected to pressure-gauge transducers. Signals from the transducers were recorded to determine ingestion and ruminating times.
All the digestion measurements were realized on cannulated cows. Apparent total tract digestibility was determined by daily total fecal collection from d 15 to 20. To divide urine from feces, a tube connected with a urine collector was fixed on each cow. Feces were weighed and mixed before sampling (5% fresh weight). Fecal samples were pooled for each cow and period, dried (80°C for 48 h), then ground to pass in a 1-mm hammer mill screen for chemical analysis.
The fractional digesta passage was determined from a single dose of Eu (20 g of Eu oxide/kg DM feed) labeled on corn stover (Ellis and Beever, 1984), given just before the morning meal on d 22. After washing (1 h, 40°C) with an EDTA-free commercial detergent, followed by 4 rinses with water, corn stover was macerated in a Eu acetate solution (15 mL/g of stover DM; 0.02 M) for 24 h. Labeled particles of stover were rinsed under tap water for 2 min, immersed for 1.5 h in a water bath (15 mL/g stover DM) to remove loosely or unbound rare earth, then dried (80°C for 48 h). Fecal samples were collected in the rectum of each animal, from d 21 to 26 every 3 h for 12 h, then every 4 h for 36 h, then every 6 h for 36 h, and finally every 24 h until 168 h after marker distribution. Fecal samples were dried (80°C for 48 h) and ground in a hammer mill to pass through a 1-mm screen. The ruminal mean retention time was calculated by plotting the natural logarithm of marker concentration against time, with the linear descending part of the curve corresponding to particulate outflow rate (Udén, 1984).
The fractional passage rate of the ruminal fluid was determined using chromium-EDTA. A single dose of 2 g dissolved in 500 mL of water was given intraruminally on d 18 at the morning feeding time. Six samples were taken via the ruminal cannula over the 24-h period after administration of the marker and then frozen at –20°C. Fractional passage rate of fluid was calculated from the slope of the natural logarithm of the Cr concentration against time.
Fifteen samples (50 mL) of ruminal fluid were collected on d 22 and 23 at regular intervals (between 1 and 2 h according to sampling hour) during a 24-h period. Samples were immediately strained on a 250-µm nylon filter and maintained on a magnetic stirring for pH determination with a digital pH-meter. Mean pH, minimum pH, time pH <6.2, and area pH <6.2 were calculated. Time pH <6.2 represents the duration (h) in a 24-h feeding cycle, during which ruminal pH remains below a 6.2 threshold value. The area pH <6.2 represents the combined effects of magnitude and duration of pH below a 6.2 threshold value and is calculated as an integration of the area under the pH time curve below 6.2 (Philippeau et al., 1999). A 6.2 threshold value was retained according to Grant and Mertens (1992). Samples (5 mL) collected in duplicate at 0900, 1100, and 1400 h were preserved by adding 0.5 mL of 5% (vol/vol) orthophosphoric acid to determine VFA and NH3 contents.
At the end of each period (on d 29), the rumen was manually emptied 5 h after the morning feeding and weighed. After homogenization, DM content was determined, and a representative sample (5 kg) was frozen at –20°C for sieve analysis. Another sample was strained through a 250-µm nylon filter to separate liquid and solid phases and weighed.
When rumen was empty, the cows were fed WPCS alone. Boluses of WPCS chewed and delivered via the cardia were collected by hand through the rumen cannula. Eight boluses were pooled for each animal per period and stored at –20°C for sieve analysis.
At the end of the trial, the WPCS degradation rate was measured with an in situ technique. Dried samples of WPCS, corresponding to the 2 hybrids, were ground to pass a 3-mm sieve in a hammer mill. Approximately 3 g of ground WCPS was placed in nylon bags (Ankom Co., Fairport, NY; pore size, 53 µm; internal dimensions, 5 x 10 cm) and placed in the rumen at the same time, just before the morning meal. They were removed after 3, 6, 9, 15, 24, 48, and 72 h of incubation. Eight measurements (2 repetitions on 4 cows) were made for each incubation time. After removal, bags were washed in a washing machine with 3 successive 2-min washings, dried (80°C for 48 h), and weighed. The residues corresponding to the same incubation time and the same animal were pooled for NDF analysis. The degradation kinetics obtained for each animal and each WPCS were fitted to an exponential model (Dhanoa, 1988):
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where disappearance (t) = percentage disappearance from the bag at time t; a = the immediately disappeared fraction that pooled the rapidly degradable fraction and the fraction lost through bag pores; b = the slowly degradable fraction; c = the fractional degradation rate; and 
= the lag time. The four parameters, a, b, c, and were estimated by an iterative least squares procedure (SAS, 1988). Effective degradability was calculated using the mean particle outflow measured with Eu-labeled stover, 0.035/h (Ørskov and McDonald, 1979).
Chemical and Physical Analyses
Feed, orts, and fecal samples were analyzed for ash, CP (AOAC, 1990), starch (Faisant et al., 1995), and NDF and ADF (Van Soest and Robertson, 1980). The NDF in nylon bags was determined by the same technique.
Silage fermentation characteristics were measured on WPCS juice obtained with a grape press. The pH was immediately determined with a pH-meter (CG840, Ag/AgCl electrode, Schott Gerate, Hofheim, Germany). Acetic acid and ethanol contents were determined by GLC (Jouany, 1982). Lactic acid content (Noll, 1974) and NH3 content (Conway, 1957) were measured. The DM content of corn silage was corrected to account for losses of volatile products during drying (Dulphy et al., 1975). The fermentation analyses were performed in duplicate.
Particle-size distribution in WPCS, boluses, and rumen contents was determined by wet sieving (Fernandez and Michalet-Doreau, 2002). Samples (2 replicates, 50 g of fresh matter) were sieved with a system (Retsch AS 200, Germany) with a water spray and vibrations, equipped with 6 sieves of 8.00-, 4.00-, 2.00-, 0.40-, 0.10-, and 0.05-mm aperture size and a bottom pan. The particle-size distribution was expressed as the DM percentage of particles collected on the different screens. Mean particle size was determined by plotting the cumulative percentage of particles retained on the screen against the logarithm of sieve size and was calculated as the screen size on which 50% of the sample weight was collected (Waldo et al., 1971). The s75-s25 interfractile gap corresponded to a difference between the screen size on which 25 and 75% of the sample weight was collected, and reflected heterogeneity of particle-size distribution (Fernandez and Michalet-Doreau, 2002). The proportion of particles larger than 2 mm (LP2) corresponded to the sum of particles retained on 8-, 4-, and 2-mm aperture sieves, this being considered as the critical size for leaving the reticulo-rumen in cattle (Poppi et al., 1985; Ulyatt et al., 1986). As performed by Bailey et al. (1990), the differences in particle size from feed to bolus and from bolus to rumen were expressed using differences in mean particle size and LP2 proportion.
Chromium-EDTA in the rumen fluid and europium content of feces, after extraction of the marker from dried samples (Hart and Polan, 1984), were determined by atomic absorption spectrophotometry (model 2380 spectrophotometer, Perkin-Elmer, Bois d’Arcy, France).
Ruminal liquid was analyzed for VFA with a GLC procedure (Jouany, 1982) and for ammonia content with a colorimetric method (Van Eenaeme et al., 1969).
Milk fat and protein concentrations were determined by infrared spectrophotometry (Combi-Foss 5000, Foss Electric, Hillerød, Denmark).
Statistical Analyses
Data obtained with lactating cows were analyzed by using the general linear model procedure (SAS, 1988) for a replicated (n = 2) Latin square design, with square, WPCS, period, and cow nested in square as sources of variation. Data obtained with dry cows (except VFA and NH3 concentrations) were analyzed as a 4 x 4 Latin design, with corn silage, period, and cow as sources of variation. When variables were analyzed at different times of the day (VFA and NH3 concentrations), an additional analysis was performed using the repeated statement of the general linear model procedure. Orthogonal contrasts were made for effects of corn silage hybrid (H1 vs. H2) and chop length (fine vs. coarse). Means were considered significant at P < 0.10.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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(data not statistically analyzed). The DM content of WPCS was similar, averaging 33.9% with limited variation (range 33.0 to 35.3%), which implied the same maturity stage for the 4 WPCS. Both NDF and ADF contents were a little higher for H1 than H2 hybrid (43 vs. 40% for NDF and 24 vs. 22% for ADF); there was no difference between coarse- and fine-chopped WPCS. Starch concentration (34.4%) was similar for the 4 WPCS. The pH and lactate concentrations were indicative of desirable silage fermentation. Lactate concentration was higher for the coarse WPCS than the fine WPCS. Fermentation characteristics of WPCS were used to take into account the losses of volatile products during drying (80°C for 48 h) and to correct the DM content of corn silages.
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(data not statistically analyzed). Particle-size distribution of WPCS varied little with the corn hybrid. Mean particle size and extent of distribution did not differ between corn hybrids, respectively, for H1 and H2 corn hybrids 1.27 vs. 1.14 mm and 10.08 vs. 11.06 mm, and LP2 proportion was similar, respectively, to 63 and 61% on DM basis. With coarse-chopped WPCS, the proportion of particles larger than 8 mm increased from 25.6 to 43.9% on DM basis, and this increase was balanced by a decrease in the proportion of particles between 0.4 and 8 mm in size from 24.0 to 41.8% on DM basis. Mean particle size was greater for the coarse than for the fine WPCS, 1.52 vs. 0.89 mm, respectively. The heterogeneity of particle-size distribution, characterized by the extent of dispersion (s75-s25), was then higher for the coarse than fine WPCS, 14.95 vs. 6.19 mm, respectively.
In situ DM and NDF degradabilities were significantly lower (P < 0.05 and P < 0.10, respectively) for H1 than for H2 hybrid, at 54.0 vs. 60.6% of DM and 30.9 vs. 38.3% of NDF, respectively. These differences were mainly due to a lower immediately disappeared fraction and a higher undegradable fraction for H1 than H2 hybrid (Table 3). The WPCS had to be ground before in situ measurements, so it was not possible to characterize variation in ruminal degradability between the different processed WPCS, namely coarse- and fine-chop lengths.
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) and did not significantly vary with chop length, 22.2 and 22.8 kg/d, respectively, for coarse- and fine-chopped WPCS diets.
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Chewing Activities and Digestion
Chewing activities and digestion measurements were achieved with dry, ruminally cannulated cows. Total DMI by dry, ruminally cannulated cows varied in the same way as DMI by lactating cows. Total DMI was 0.7 kg/d lower for H1 than H2 WPCS diets (Table 5), but the difference between hybrids was lower than that observed with lactating cows and were not significant, perhaps in relation to the lower number of cows used in this comparison, 4 dry cows compared to 8 lactating cows. Another hypothesis is that the sensitivity of the response to treatment diet increased with the requirement level of animals, and so variations due to hybrid were more important with lactating cows than with dry cows. As for the lactating cows, total DMI of dry cows did not vary with the chop length of WPCS, 14.04 vs. 12.02 kg/d, respectively, for coarse and fine WPCS diets. As the trend for variations in DMI was similar for lactating and dry cows, we considered that consequently the digestion data obtained on dry cows could be taken in relation to intake measurements obtained on lactating cows.
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). Eating time per unit of DMI was higher (P < 0.05) for H1 than H2 corn hybrid, 29 vs. 25 min/kg of DMI, respectively. Ruminating time per unit of DMI tended to follow the same trend; it decreased from 54 min/kg DMI with an H1 hybrid diet to 47 min/kg DMI with an H2 hybrid diet, but this difference was not statistically significant. Total chewing time per unit of DMI varied significantly (P < 0.05) between the 2 hybrid diets (84 vs. 73 min/kg of diet DMI). Increasing chop length did not modify eating, rumination, and total chewing times per unit of DMI.
In boluses, mean particle size, extent of dispersion (s75-s25), and LP2 proportion were statistically similar between the treatments, on average 0.24 mm, 2.61 mm, and 40.6% on DM basis (Table 6). Ingestive mastication particularly decreased particles larger than 4 mm and thus mean particle size from 52 to 30% on DM basis and 1.20 to 0.24 mm, respectively. The extent of dispersion (s75-s25) changed from 10.58 to 2.61 mm between WPCS and bolus, meaning a reduction in heterogeneity of particle-size distribution in bolus in comparison to WPCS fed to animals. The changes in LP2 and mean particle size varied with the WPCS. The drop involved with ingestive mastication was more important for the coarse than for the fine WPCS but was similar for the 2 corn hybrids. The reduction in mean particle size was 1.31 vs. 0.63 mm for the coarse and fine WPCS, and 0.98 vs. 0.97 mm with H1 and H2 corn hybrids, respectively. In rumen, the proportion of particles larger than 8 mm was significantly higher with the coarse than with the fine chopped diets (16.4 vs. 11.9%) and was balanced by the lower proportion of particles between 2 and 4 mm in size (9.3 vs. 13.0%) (Table 7). For the coarse and fine chopped length diets, mean particle size and LP2 proportion in rumen content were similar between diets. After ingestive mastication and combined action of ruminating mastication and microbial digestion, mean particle size was similar in rumen content.
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). Chop length increasing of WPCS tended to reduce fiber digestibility, but the results were not statistically significant. Corn hybrid did not modify fiber digestibility.
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shows the mean digesta pool sizes in the rumen. Rumen fill was not affected by corn hybrid. But ruminal DM pool size and DM content were significantly higher with coarse chopped diets in comparison with fine chopped diets, 10.4 vs. 9.3 kg and 14.3 vs. 13.1%, (P < 0.05 and P < 0.10, respectively). This increase was accompanied by a change (P < 0.01) in the ruminal solid-phase proportion that passed from 49.5% with the coarse chopped diet to 41.2% with the fine chopped diet. The ruminal mean retention time did not vary significantly with diet but tended to be higher for H1 than H2 diets, and the differences were significant for coarse chopped diets, 34.0 vs. 27.5 h, respectively. The ruminal liquid dilution rate did not vary between treatments, 8.3%/h on average.
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. Mean ruminal pH, minimum pH, and time pH < 6.2 were statistically different between the two hybrid diets (P < 0.05, P < 0.01, and P < 0.01, respectively). Mean pH and minimum pH were lower with H1 than H2 diets, and time pH < 6.2 higher, 3.6 vs. 6.4 h, respectively. The area pH < 6.2 followed the same trend, 0.70 to 1.00, respectively, but this variation was not significant. So the most degradable hybrid resulted in the lowest ruminal pH. The coarse WPCS diets involved lower means and minimum pH, and time under pH 6.2 was higher with the coarse WPCS diets (6.7 h) than with the fine ones (3.3 h). This effect of chop length on pH values was similar for the 2 hybrids.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Although mean particle size of WPCS was similar with the two corn hybrids, time spent eating and chewing per unit of DMI was higher for H1 than H2 silage diets. To our knowledge, little information is available about the effect of corn hybrid on chewing behavior. Except the trials concerning chop length that we will discuss later, time spent chewing was related negatively to DM content and digestibility (De Boever et al., 1993). In our trial, neither DM content nor digestibility varied between corn hybrid, and these parameters could not explain variations in chewing activities.
The H1 hybrid was less acidic than H2. The mean ruminal pH and the minimum pH were lower with H1 hybrid and the time pH < 6.2 showed large differences between hybrids. Bal et al. (2000a) did not report significant differences in mean ruminal pH between hybrids with different NDF content; they did not give information on ruminal pH kinetic. Dragomir et al. (2003) showed the time pH < 6.2 allowed to take into account the variations in pH kinetics and reflected better the variations in feeding situations that mean pH. As the pH curves were not reported by Bal et al. (2000a), it was difficult to conclude on the effect on the hybrid. In our trial, the less acidic hybrid had also the highest chewing activity. It is often assumed that chewing stimulates saliva secretion, and saliva would contribute bicarbonate entering the rumen and buffering the acids produced during fermentation.
In summary, the less degradable hybrid in the rumen is also the less ingested and the less acidic. The difference in ruminal degradation rate was sufficient to induce differences in voluntary intake without significant variation in digestibility. Rumen fill probably played an important role, limiting intake in this case, because the rumen fill of cows consuming the less or the more highly degradable silages was similar.
Effect of Chop Length
In our trial, decreasing chop length modified neither DMI nor milk yield. With corn silage finely chopped by recutting of forage (Buck et al., 1969) or by a finer TCL from 9 to 3 mm (Kuehn et al., 1997) and from 8 to 3 mm (Clark and Armentano, 1999), no effect of chop length on DMI of WPCS was reported. In contrast, De Brabander et al. (1982) and more recently De Boever et al. (1993) evaluated unprocessed WPCS harvested at different maturity stages and with different hybrids and found a variable effect of chop length on corn-silage intake, and this response did not depend on WPCS maturity stage and hybrid. Schwab et al. (2002) and Wilkinson et al. (1978) reported a 1.1 kg/d increase in DMI for the 2 trials when TCL decreased from 19 to 13 mm and from 33 to 8 mm, respectively. But the particle size distribution of WPCS was not determined in the trial of Wilkinson et al. (1978). In the trial of Schwab et al. (2002), the proportion of WPCS large particles (>9 mm) was high, whatever the corn silage chop length, e.g., from 78 to 72% for 19- and 13-mm TCL. In our trial, the proportion of large particles (>9 mm) was lower, from 44 to 20% for 13- and 5-mm TCL. For a given TCL (13 mm) for WPCS, in both trials the proportion of particles larger than 9 mm was very different—72% in the trial of Schwab et al. (2002) against 44% in our trial. This variation could be connected with the difference in DM content of WPCS, i.e., 41.5% in the trial by Schwab et al. (2002) compared with 33.9% in our trial. The effect of mechanical processing on particle size of WPCS appeared to increase as the plant material matured (Shinners et al., 2000). The response of DMI to decreasing TCL in unprocessed WPCS would depend on true particle size, either a decrease for really coarsely chopped silages, or no variation for really finely chopped ones.
In our trial, chewing behavior did not vary with the chop length, but ingestive mastication strongly reduced mean particle size and LP2 proportion of WPCS by 80 and 34%, respectively. With corn silages, either no effect of chopping length on eating time was reported (Bal et al., 1997; Kuehn et al., 1997; Schwab et al., 2002) or a variable response of eating time was reported (De Boever et al., 1993). Accordingly, Bailey et al. (1990) reported an important decrease in mean particle size (57%) and proportion of large particles (24%) for masticates versus corn silage fed to dairy cows. With hay, mastication during consumption reduced the large particle proportion in similar proportion, on average by 44% in sheep (Bernard et al., 2000) and by 51% in cattle (Lee and Pearce, 1984). The mean particle size and LP2 proportion in the boluses from the coarse and the fine WPCS were similar, on average 0.24 mm and 40.6% on DM basis. The decrease in mean particle size and LP2 proportion was greater for the coarse than for the fine WPCS, respectively, 1.31 vs. 0.64 mm and 25 vs. 17% on DM basis. With hays and straws, Lee and Pearce (1984) also reported differences in the extent to which roughage was reduced by ingestive mastication. More recently, researchers (Bailey et al., 1990; Bernard et al., 2000) studied comminution during ingestive mastication with hays with different initial particle sizes, and found a reduction in particle size was greater with the long than with the short form—22 vs. 15% (Bailey et al., 1990) and 50 vs. 32% (Bernard et al., 2000). In a previous trial, with lactating cows fed WPCS in restricted amounts, we obtained similar results: coarsely chopped WPCS were reduced more than finely chopped ones during ingestive mastication (Fernandez and Michalet-Doreau, 2002). As eating time was similar for all WPCS diets, these results suggest that ingestive mastication expressed per unit of DMI was more efficient for the coarse than for the fine silages. Similar results were found by Schwab et al. (2002). They reported no TCL effect on particle size of WPCS masticates differing in chop length. This lack of effect of TCL on particle size of WPCS masticates or material entering the rumen might explain TCL responses on DMI yet to be discussed.
In our trial, neither apparent DM digestibility nor ruminal mean retention time varied with the chop length of WPCS. Schwab et al. (2002) found similar data, although the response of DMI was different for the 2 trials. The effect of WPCS chop length on rumen fill was opposite between the two trials; it decreased with a decrease in TCL in our trial and did not vary in the trial by Schwab et al. (2002).
When animals were offered ad libitum access to feeds, variations in DMI were regularly associated with changes in DM digestibility of forages, and a physical control of DMI would play an important role in these circumstances. Dry matter intake depends on digestibility, rates of digestion, particle passage, and particle-size reduction in the rumen. These relationships suggest that rumen fill limits DMI. But, if rumen fill was the only factor limiting intake, the cows consuming the finely chopped WPCS should have been able to increase intake because they had lower rumen fill than cows feeding on the coarsely chopped WPCS. Recent data obtained with silages (Rinne et al., 2002) or grazing (Chilibroste et al., 2000) differing in grass maturity reported that the cows stopped intake before a maximal ruminal capacity was reached.
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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ACKNOWLEDGEMENTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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FOOTNOTES |
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Received for publication April 16, 2003. Accepted for publication September 29, 2003.
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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