Chewing behaviour and voluntary grass silage intake by cattle

Livestock Production Science, 33 ( 1993 ) 215-227

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Elsevier Science Publishers B.V., Amsterdam

Chewing behaviour and voluntary grass silage intake by cattle E. Teller, M. Vanbelle and P. Kamatali Catholic University of Louvain, AGRO/BNUT, Louvain-la-Neuve, Belgium (Accepted 15 June 1992)

ABSTRACT Teller, E. Vanbelle, M. and Kamatali, P., 1993. Chewing behaviour and voluntary grass silage intake by cattle. Livest. Prod. Sci 33:215-227. Six Friesian heifers (Experiment 1 ) and four lactating dairy cows (83% Holstein; Experiment 2 ) were fed ad libitum with direct-cut or wilted grass silage. All animals were fitted with ruminal and duodenal cannulae. Extent and rate of ruminal forage digestibility were measured and chewing behaviour of the animals was recorded. Mean faecal particle size was also determined. Neither the concentration of fermentation products in the silages, i.e. their palatability, nor the rate and extent of ruminal digestion or the extent of particle-size reduction in the digestive tract could explain the increased dry-matter intake of wilted versus direct-cut silage ( 17.7% in heifers and 28.4% in lactating cows). The time spent eating per kilogram dry-matter intake was substantially reduced after wilting of the grass prior to ensiling (28% in heifers and 37% in lactating cows ), but the time spent ruminating was not significantly different between the two types of silages. It was inferred that ruminating is firmly involved in augmenting functional density of feed particles in the reticulorumen by expelling pockets of air or fermentation gases. This permits sedimentation of the particles and their passage through the reticulo-omasal orifice. As daily chewing capacity of the animals is limited to around 950 min, the farmer can help more efficient eaters by facilitating dry-matter ingestion (wilting, chopping, etc. ) and in this way, liberating more time and more jaw movements for ruminating. More direct evidence is needed to ascertain the exact mechanism and the importance of favouring ruminating at the expense of eating activity in relation to rumen fill. Keywords: cattle; grass silage; voluntary intake, chewing traits

INTRODUCTION

In terms of production on the farm, the introduction of the milk supply quotas in 1984 by the European Community led to a substantial increase of individual milk production capacity accompanied by reduced animal numbers in some countries (CNIEL, 1989 ) or to the greater use of roughages with Correspondence to: E. Teller, Catholic University of Louvain, A G R O / B N U T , Place Croix du Sud 2, Bte. 8, B 1348 Louvain-la-Neuve, Belgium.

0301-6226/93/$06.00

© 1993 Elsevier Science Publishers B.V. All rights reserved.

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a rather constant number of less-producing animals in other countries. The production limitations imposed on the farmers require that the production cost of milk is minimized. In this respect, optimal evaluation of forages grown on the farm is seen to be a prerequisite. However, their incorporation into diets of high-producing dairy cows is limited by their consumption. The exact mechanism governing intake of ensiled forages is still little understood, and factors such as palatability (Wilkins et al., 1971 ), extent and rate of digestion in the rumen (Mertens and Ely, 1982 ), reduction of particle size by chewing (Poppi et al., 1980), variation of functional density of the feed particles in the rumen (Lechner-Doll et al., 1991 ), etc., have variously been considered to be involved. Ruminal fermentation processes and chewing activity of the animals are undoubtedly predominant factors for conditioning rnmen fill and, consequently, level of forage intake (Teller et al., 1989). With the present state of knowledge, the time spent chewing per kilogram dry-matter on the roughage value index seems to be the most reliable parameter for predicting this phenomenon (Sudweeks et al., 1981; Sauvant et al., 1990). Although related to chemical composition and, especially, to the N D F content of the forages (Welch and Smith, 1970), level of intake and roughage value index are affected also by physical parameters, such as dry-matter ( D M ) content and particle length of silages (Teller et al., 1990 ). The objectives of the present study were to examine several parameters which may explain the improved DM intake by cattle of wilted versus directcut grass silage, to propose a model for physical regulation of silage intake as a function of wilting, chop length, silage additives, and growth stage of the grass at harvesting, and to deduce practical implications. MATERIALSAND METHODS

Experiment 1 Six Friesian nonpregnant dairy heifers, approximately 3 years of age, weighing an average of 479 kg at the beginning and 548 kg at the end of the trial, were fed ad libitum direct-cut or wilted grass silage from the same meadow according to a two-period crossover design. The animals had a ruminal cannula and a T-type cannula in the proximal duodenum. Grasses were harvested in early spring and ensiled without additives. Half of the grass was ensiled directly and the other half was wilted for 24 h before ensiling. Chemical composition of the silages is given in Table 1. The heifers were tethered in individual stalls without bedding and had free access to water. They were individually fed ad libitum twice daily at 08.30 and 16.00 h. Amounts offered were calculated to exceed intake on the previous day by at least 10%. Silage refusals were removed and weighed at 08.15

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TABLEI Mean chemical composition of grass silages fed to dairy heifers and lactating cows (Experiments 1 and 2, respectively ) Component

Dry matter (DM, g/kg ~) pH Composition o f D M (g/kg DM) Organic matter Neutral detergent fibre Crude protein Acetic acid Butyric acid Lactic acid Ammonia N (g/kg N) Mean particle length (cm)

Heifers

Lactating cows

Direct-cut

Wilted

Direct-cut

Wilted

Concentrate

203 4.1

403 4.7

170 4.3

381 4.4

842

875 416 141 50 5 118 95 6.5

903 424 160 20 1 127 91 3.2

845 572 142 77 11 15 136 7.9

874 558 145 17 9 94 161 2.5

909 407 236

~Corrected for losses of volatile components during oven-drying.

h each day. The animals were fed experimental forages for 36 days. Daily voluntary intake was recorded on day 15 to day 36. The heifers were fitted with a harness and sensors to record jaw movements for 2 days preceding the recording (Teller et al., 1989 ). Behaviour recordings were made on day 19 to day 23 and categorized into three main activities: eating, ruminating and idling. Total chewing time was calculated as eating time plus ruminating time. Faecal grab samples of 500 g were collected for particle size determination at 10.00 h on day 20 to day 23. For each heifer, samples of day 20 and day 21 on the one hand, and of day 22 and day 23 on the other hand, were combined before sieving with an electromagnetic sieve shaver (FRITSCH Analysette, Idar-Oberstein, Germany) under running water. Sieve apertures were 1120, 560, 280, 140, 71 and 36 #m. Mean particle size was calculated according to Vaage and Shelford (1984) from cumulative weight percentages. From day 19, capsules with 10 g Cr203 and 45 g polyethyleneglycol (PEG) were administered daily at 08.00 and 16.30 h to each heifer through the ruminal cannula. After an adaptation period of 5 days, twelve samples of duodenal contents (300 g per sample) were withdrawn. Samplings were distributed over 2 days and corresponded to every 2nd h throughout a nycthemeral period. All samples from each heifer were pooled. An aliquot was freeze-dried for analysis. Flow of duodenal digesta was calculated on the basis of concentrations of the two markers in the digesta related to the daily amounts administered. Extent of digestion in the forestomachs for organic matter (OM) was calculated by the formula: apparent digestion= [(intake-duodenal total flow )/intake ] X 100; true digestion = [ (intake-duodenal non-bacterial flow ) /

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E.TELLER ETAL.

intake× 100. The bacterial flow was determined by diaminopimelic acid (DAPA) analysis. Ruminal fluid was sampled at hourly intervals from 07.00 h (before feeding) until 16.00 h on day 25 and analyzed for the rate of disappearance of PEG. The turnover rate of ruminal fluid was calculated by determining the slope of the line obtained by regressing the natural logarithm of concentration versus time (Narasimhalu et al., 1989). Thereafter, Cr203 administration was continued from day 26 to day 31 for determination of nutrient digestibility. Faecal grab samples of 500 g were taken twice daily (08.00 h and 16.30 h) and pooled. Daily faecal output was estimated from Cr203 content related to the amount administered. The in sacco degradability of OM was established at the end of all other measurements according to tDrskov and McDonald (1979). The silages were incubated in polyester bags (Dacron) with a mean pore size of 50/tm. Two bags were removed from the rumen of each animal at 0, 2, 4, 8, 16, 24, 48 and 144 h after the start of incubation. Thereafter, they were washed three times during 5 min with tap water in a "mini-wash" machine and dried at 45 ° C. The disappearance curve of OM from the bags with incubation time (t) was described by an exponential equation:

p = a + b ( 1 - e -ct) where a = fraction which is washed out in water; b = slowly degradable fraction; and c = degradation rate of b. Assuming a fractional outflow rate (k) of 6%/h, the effective degradability was estimated as: bc c+k

P =a-F--

Organic matter was determined from absolute DM at 105 °C and ash percentages in silages, duodenal digesta and faeces. Organic matter content of silages was corrected for acid and ammonia losses by the method of Schoch (1949). Crude protein (N × 6.25) was determined by the standard Kjeldahl method. Neutral detergent fibre ( N D F ) was assayed according to the method of Goering and Van Soest (1970). PEG and Cr203 were measured following Hyden ( 1955 ) and Petry and Rapp ( 1971 ), respectively. Volatile fatty acids were determined by gas chromatography and the DAPA according to E1-Shazly and Hungate ( 1966 ). Statistical analysis was by ANOVA for a two-period crossover design, using the General Linear Models procedure of SAS ( 1982 ).

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Experiment 2 Four primiparous Holstein-Friesian cows, 2.6 years of age, weighing an average of 523 kg at the beginning and 513 kg at the end of the trial, and producing an average of 20 kg milk per day, were fed ad libitum direct-cut or wilted grass silage from the same meadow supplemented with an average of 5.2 kg DM of concentrates. They were allotted according to a two-period crossover design. All animals had ruminal and duodenal cannulae. Grasses were harvested in early spring and ensiled without additives. Silages were prepared as stated above for Experiment 1. Their chemical composition is shown in Table 1. All experimental techniques were the same as for Experiment 1 (Teller et al., 1990). RESULTS A N D D I S C U S S I O N

Palatability of the silages Direct-cut silage is more intensively fermented during preservation which generally results in lower pH-values and higher concentrations of fermentation products, especially of acetic acid. The latter has often been blamed for lowering palatability and, hence, reducing voluntary intake (Wilkins et al., 1971 ). In the present experiments, the direct-cut silages had indeed higher acetic acid contents than the wilted silages (Table 1 ) and voluntary DM intake was increased by 17.7% in heifers and 28.4% in lactating dairy cows when wilted instead of direct-cut grass silage was fed (Table 2). When the acetic acid concentration was expressed on a fresh basis instead of DM basis, the figures were as follows: 212 and 263 mM in direct-cut versus 225 and 174 mM in wilted silages for Experiments 1 and 2, respectively. Thus, the lower DM intake with direct-cut vs. wilted silage by heifers cannot be explained by TABLE2 Voluntary intake of silages and their rate and extent of organic matter (OM) digestion by heifers and lactating cows (Experiments 1 and 2, respectively) Heifers Directcut Silage DM intake (kg day) OM digestibility in rumen (%) Apparent True J OM digestibility in totaltract (%) Mean faecal particle size (am)

Lactating cows Wilted Significance Direct-cut Wilted Significance

9.6

11.3

**

7.4

9.5

n.s.

60.0 71.9

53.8 71.0

** n.s.

50.4 62.9

50.2 64.3

n.s n.s

81.3

72.9

**

67.4

64.3

n.s.

284

628

**

~Corrected for bacterial organic matter leaving the rumen.

379

425

n.s.

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E. TELLER ET AL.

TABLE 3 Liquid turnover rate and characteristics of in sacco degradability of OM in the rumen (Experiments 1 and 2, respectively) Heifers

Liquid t u r n o v e r rate ( % / h ) In sacco degradability o f O M a (%) b (%) a+b (%) c (h - ~ ) P (%)

Lactating cows

Direct-cut

Wilted

Significance

Direct-cut

Wilted

Significance

21.6

25.9

**

17.4

21.3

*

42.1 49.8 91.9 0.085 78.8

40.2 52.3 92.5 0.066 76.1

n.s. n.s. n.s ** *

38.9 47.7 86.6 0.041 73.5

30.5 59.0 89.5 0.32 65.7

** ** n.s. ** *

differences in acetic acid contents. Furthermore, the addition of acetic acid/ acetate to grass silages (46.4-51 g acetic acid/kg DM) has resulted in only insignificant reductions in voluntary DM intake by heifers (Deswysen, 1980). Lastly, it has to be noted that, in terms of fresh feed, the high-moisture silage was more rapidly consumed than the wilted silage (Table 3). Consequently, although taste and pH cannot be completely disregarded, they do not appear as dominant factors limiting voluntary intake of grass silage by cattle.

Extent of ruminal digestion If voluntary DM intake is limited by rumen fill, then the more digestible forages will logically be ingested in greater amounts. Indeed, a positive relationship between these two parameters does generally exist (Baile and Forbes, 1974). This was however not the case for wilted-grass silage which was ingested in greater quantities than direct-cut silage although it had a lower apparent organic matter digestibility in Experiment 1 (Table 2). In this respect, special attention has to be paid to the digestion processes occurring in the rumen. No noticeable difference was noted for true organic matter digestibility in the rumen. This means that differences in digestibility between the two types of silage were mainly due to the increased flow of microbial organic matter into the lower gut after wilting of the grass (Narasimhalu et al., 1989); true digestibility of the forages was almost identical as could also be expected from the small differences in chemical composition.

Rate of ruminal digestion The rate at which forages are digested can also give rise to differences in rumen fill and in this way, to differences in voluntary intake. However, the kinetics of ruminal degradation, measured with an in sacco technique, revealed that wilting of the grass diminished the rate of OM degradation and,

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hence, the effective OM degradation (Table 3). This factor could thus not explain the important increase of DM intake with wilted versus direct-cut silage. This agrees with the observations of Mertens and Ely ( 1982 ) and Teller and Vanbelle (1989) that the rate of digestion in the rumen is not the prevailing factor which controls forage intake. Particle size Due to the harvesting conditions, mean particle length was more than double for the direct-cut silages compared to the wilted ones (6.5 and 7.9 cm versus 3.2 and 2.5 cm in Experiments 1 and 2, respectively). In terms of DM intake, sheep respond well to an increasing fineness of chop in silages; cattle appear much less responsive, especially when the silages are supplemented with concentrates. For instance, when silage was the sole feed of cows, intake was increased by 20°/0 as a result of reducing particle length from 7.2 cm to 1.7 cm; when the same silages were supplemented with concentrates (about 20% of dietary D M ) , the increase averaged only 5% (Castle et al., 1979). Similarly, Marsh (1979) concluded from a literature survey that wilting increased DM intake of silage by lactating cows by 25% when not supplemented, and only by 10% when supplemented with cereals or concentrates. In Experiment 2 of the present study, concentrates supplied on average 38% of total dietary DM intake, whereas no supplement was administered in Experiment 1. Nevertheless, the effect of wilting of the grass prior to ensiling was greater in Experiment 2 than in Experiment 1. Other factors, such as silage composition, animals and their physiological stage may have interfered, and this study does not permit conclusions about the interaction amongst silages and concentrates with regard to voluntary intake. The indigestible particles have to pass to the lower digestive tract, but before leaving the rumen, their size has to be reduced sufficiently to permit their passage through the reticulo-omasal orifice. Kennedy and Poppi (1984) estimated the critical particle size for leaving the rumen at 1,178/zm. However, Poppi et al. (1980) and Welch (1986) reported that the majority of feed particles present in the rumen are small enough to pass through the reticuloomasal orifice. On the other hand, important fractions of faecal particles may be longer than the critical size (Teller et al., 1989) and the rumen will generally process the same forage fed as larger particles into smaller faecal particles (Smith et al., 1965 ). In the present experiments, mean faecal particle size was greater for wilted than for direct-cut silage (Table 2 ), although the particle size of the silages themself was more than double for the direct-cut ones. It has also to be noted that mean faecal particle size was less than half of the critical size mentioned above, and this apparently needless comminution of feed particles may represent a marked loss of energy for the animals. These varied observations lead to the conclusion that, although the reduc-

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tion in size of the indigestible particles is necessary for their passage to the lower digestive tract, it is not limiting for voluntary grass silage intake.

Functional density of feed particles in rumen Martz and Belyea ( 1986 ) stated that, in the reticulo-rumen, the less dense particulate digesta float into the cranial sac and are moved into the dorsal rumen; as the digesta become more dense from digestion and mastication, they are transferred to the ventral rumen and eventually into the cranial sac and reticulum where they flow out through the reticulo-omasal orifice. As direct-cut silage is wetter than wilted silage, its particles are less dense at ingestion, but this has apparently no effect on their reticulo-ruminal outflow (Teller et al., 1989). However, density of feed particles in the reticulo-rumen may be influenced by numerous factors: content of fibre which is less dense than water and resists hydration; air contained in spaces surrounding plant cells which is relatively rare in ensiled grass and, especially, direct-cut silage; fermentation gases attached to or entrapped in feed particles (Lechner-Doll et al., 1991 ). It can be thought that one of the main functions of chewing and, particularly, ruminating is to expel these air and gas pockets from the feed particles. This would require that physical or chemical treatments of silages do not profoundly change the amount of rumination required by forages, provided that chemical composition and thus ruminal digestion rate are not markedly modified. Indeed, wilting of the grass prior to ensiling increased nonsignificantlythe duration the animals spent ruminating each kilogram DM intake (Table 4) This tendency towards a higher rumination requirement of the wilted silage was presumably due to the lower number of jaw movements devoted to ingestion (Teller et al., 1990), suggesting less damaging of the anatomical cell structure during eating. A quite similar picture appeared when mean particle length of silages was reduced from more than 10 cm to less than 2 cm at feeding (Deswysen, 1980). Similarly, Dulphy et al. (1984) reported increases in unitary ruminating time [min/g (kg W °75) -1] of 5 and 7% by heifers fed long-chopped grass silage with formic acid or short-chopped silage without formic acid, respectively, in comparison to short-chopped grass silage with formic acid. These results indicate that large variations in grass silage intake, due to physical or chemical treatments which do not markedly affect DM composition, as for instance wilting or chopping, induce relatively small modifications in the time that silage DM has to be ruminated. This agrees well with the theory that ruminating is firmly involved in augmenting functional density of feed particles in reticulo-rumen by expelling air and gas pockets (Fig. 1 ). In this respect, higher fibre contents do markedly increase ruminating requirement per kilogram DM intake (Teller et Vanbelle, 1989) owing to their slow hydration, low fermentation rate, and high rigidity.

GRASS SILAGE INTAKE BY CATTLE

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TABLE 4 Chewing activity by heifers and lactating cows fed direct-cut or wilted grass silage (Experiments 1 and 2, respectively) Lactating cows

Heifers

Eating M i n / k g D M intake M i n / k g wet silage intake Min/day Ruminating ~ M i n / k g D M intake Min/day Total chewing ] M i n / k g D M intake Min/day

Direct-cut Wilted

Significance Direct-cut Wilted

Significance

55.8 11.3 537

40.4 16. l 452

* * n.s.

64.2 10.9 475

40.5 15.4 384

*** ** **

47.7 457

51.3 570

n.s. **

31.1 385

35.4 524

n.s. *

103.5 994

91.7 1022

* n.s.

72.6 901

63.5 941

* n.s.

~The figures reported for lactating cows (Experiment 2 ) take into account the allowance o f 5.2 kg D M concentrates for which data are not shown.

-I

Forage inta.ke

~4 Diminution

of

Fermentation

qases

forage densityI

~i4r

Rumination

Increase of ~forage density Sedime~ntation Passage through reticuloomasal orifice

J Reduction of rumen fill

[

Fig. 1. M o d e l o f passage o f forage particles in r u m e n .

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E. TELLER ET AL.

Chewing capacity of the animals There seems to be a maximum period each day that the animals can spend in chewing (Table 4). With 16 different silages, i.e. wilted versus direct-cut silages examined in the present study, silages with various chop lengths in the trials reported by Deswysen (1980), and grasses ensiled without additives or with formic acid (Dulphy et al., 1984), an average chewing time of 948 + 45 min/day was observed. As the time the animals spent ruminating silages with a given chemical composition was rather constant, it means that the cows have to spend a minimum time in eating in order to allow a maximum period for ruminating. High-fibre diets have greater requirements for rumination, and the animals will spend less time eating and, consequently, consume less dry matter (Martz and Belyea, 1986). CONCLUSIONS AND GENERAL CONSIDERATIONS

Forage intake capacity of dairy cows is the result of rumen volume and ruminal outflow rate of undigested matter. The first parameter depends on genetic traits and on weaning and growth conditions of the animals, whereas the second one is related to chemical and physical characteristics of forages. The farmer can help the animals to become more efficient eaters by ensiling high-quality grass and by treating it in the right way: wilting and chopping or direct-cut plus additives and chopping. Indeed, assuring more time for rumination by accelerating DM ingestion increases voluntary intake of grass silage, but provides also optimal conditions for fermentation process in the rumen by better spreading saliva production over the nycthemeral period. On average, the total number of jaw movements the animals devote to eating and ruminating is around 60,000 per day (Teller et al., 1990). Future research will reveal if the greater roughage eaters are animals able to make more jaw movements and if it would be beneficial to select animals on the basis of their potential number of daily jaw movements, although differences in size of the omasal orifice and other factors may also play a role. Another consideration is that, as a result of the increased genetic selection of the Holstein type in high-producing dairy cows, the animals are characterized by a relatively small muzzle. This may disadvantage great roughage eaters by reducing the amount of nutrients masticated per jaw movement during eating and rumination. ACKNOWLEDGEMENTS

This work was financially supported by IRSIA, rue de Crayer 6, 1050 Bruxelles. Kamatali had a AGCD fellowship.

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Sudweeks, E.M., Ely, L.O., Mertens, D.R. and Sisk, L.R., 1981. Assessing minimum amounts and form of roughages in ruminant diets: roughage value index system. J. Anim. Sci., 53: 1406-1411. Teller, E. and Vanbelle, M., 1989. Voluntary intake of grass silage in relation to chewing activity and rate of disappearance from rumen in dairy heifers. Asian-Australasian J. Anim. Sci., 2: 307-308. Teller, E., Vanbelle, M., Kamatali, P. and Wavreille, J., 1989. Intake of direct-cut or wilted grass silage as related to chewing behaviour, ruminal characteristics and site and extent of digestion by heifers. J. Anim. Sci., 67: 2802-2809. Teller, E., VanbeUe, M., Kamatali, P., Collignon, G., Page, B. and Matatu, B., 1990. Effects of chewing behavior and ruminal digestion processes on voluntary intake of grass silages by lactating dairy cows. J. Anim. Sci., 68: 3897-3904. Vaage, A. and Shelford, J., 1984. Use of a Weibull-type function to describe particle length in chopped forage. In: P.M. Kennedy (Editor), Techniques in Particle Size Analysis of Feeds and Digesta in Ruminants. Can. Soc. Anim. Sci., Publication n ° 1, p. 177. Welch, J.G., 1986. Physical parameters of fiber affecting passage from the rumen. J. Dairy Sci., 69: 2750-2756. Welch, J.G. and Smith, A.M., 1970. Forage quality and rumination time in cattle. J. Dairy Sci., 53: 797-800. Wilkins, R.J., Hutchinson, K.J., Wilson, R.F. and Harris, C.E., 1971. The voluntary intake of silage by sheep. Interrelationships between silage composition and intake. J. Agric. Sci., Cambridge, 77:531-540. RESUME Teller, E., Vanbelle, M. et Kamatali, P., 1993. Le comportement alimentaire et m6rycique et l'ingestion volontaire d'ensilage d'herbe chez les bovins. Livest. Prod. Sci., 33:215-227 en anglais. Six g6nisses frisonnes (Exp6rience 1 ) et quatre vaches en lactation (83% Holstein, Exp6rience 2) ont 6t6 nourries ~ volont6 avec de l'herbe ensil6e directement ou avec la m~me herbe ensil6e apr~s pr6fanage. Tousles animaux 6taient munis de canules ruminale et duod6nale. L'importance et la vitesse de digestion ruminale des fourrages ont 6t6 d6termin6es et le comportement alimentaire et m6rycique des animaux a 6t6 enregistr6. La dimension moyenne des particules f6cales a 6t6 mesur6e. La teneur des ensilages en produits de fermentation, c'est-/t-dire leur app6tibilit6, l'importance et ia vitesse de leur digestion ruminale et la r6duction de la taille moyenne des particules alimentaires dans le tractus digestif n'ont pas expliqu6 la diff6rence dans la mati~re s6che volontairement ing6r6e ( 17,7% chez les g6nisses et 28,4% chez les vaches laiti~res) entre l'herbe ensil6e directement et celle ensil6e apr~s pr6fanage. La dur6e unitaire d'ingestion (min/kg MS ing6r6e) 6tait nettement plus faible avec l'ensilage pr6fan6 comparativement/t celui de coupe directe (28% chez les g6nisses et 37% chez les vaches laiti~res), mais la dur6e de rumination de chaque kilogramme de mati~re s~che ing6r6e n'a pas 6t6 significativement diff6rente entre les deux types d'ensilages. I1 en a 6t6 d6duit que la rumination intervient directement dans l'augmentation de la densit6 fonctionnelle des particules alimentaires dans le r6ticulorumen en expulsant les poches d'air et les gaz de fermentation, ce qui fait s6dimenter ces particules et permet leur passage/i travers l'orifice r6ticulo-omasal. Etant donn6 que la capacit6 journali~re de mastication des animaux est limit6e/l environ 950 min, les grands mangeurs peuvent ~tre aid6s en facilitant l'ingestion de mati~re s~che (pr6fanage, hachage, etc.) et en lib6rant de cette faqon un maximum de temps et de coups de mhchoire pour la rumination. Des essais mieux cibl6s devraient permettre d'61ucider les m6chanismes exacts el l'int6rSt r6el de favoriser la rumination aux d6pens de la dur6e d'ingestion en relation avec rencombrement du rumen.

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KURZFASSUNG Teller, E., Vanbelle, M. und Kamatali, P., 1993. Wiederkauaktivit~it und Aufnahme von Grassilage bei Kiihen. Livest. Prod. Sci., 33:215-227 Sechs schwarzbunte Rinder (Experiment 1 ) und 4 Milchkiihen (83% Holstein Friesian, Experiment 2) wurden mit frisch einsiliertem Gras oder mit Anwelksilage (gleiche Grasart) ad libitum geftittert. Alle Tiere waren mit einer Kaniile im Pansen und im Duodenum versehen. Die Intensit~it und die Geschwindigkeit der Verdauung des Raufutters im Pansen wurde gemessen, und die Kauaktivit~it der Tiere wurde registriert. Die L/inge der Kotpartikel wurde ebenfalls festgestellt. Weder der Gehalt der Silage an Fermentationsprodukten, d.h. ihre Schmackhaftigkeit, noch die Intensit~it und Geschwindigkeit der Verdauungsprozesse im Pansen sowie die Zerkleinerung der Futterpartikel im Verdauungstrakt konnten die h(Shere Aufname an Trockensubstanz mit der Anwelksilage gegeniiber des frisch einsilierten Grases erkl/iren (17,7% bei den Rindern und 28,4% bei den Milchkiihen ). Die Anwelksilage wurde deutlich schneiler aufgenommen als das direkt einsilierte Gras (28% bei den Rindern und 37% bei den Milchkiihen ), dagegen wurde kein significanter Unterschied fiir die Wiederkauaktivit~it pro Kilogramm Trockensubstanzaufnahme festgestellt. Daraus ist zu schluflfolgern daft das Widerk~iuen eine entscheidende Rolle spielt, indem es durch das Auspressen der Luftblasen und der Fermentationsgase die funktionelle Dichte der Futterpartikel im Pansen erhiSht. Dadurch kiSnnen die Futterpartikel absinken und in das Reticulum passieren. Da die t~igliche Kauaktivit~it aufetwa 950 Minuten begrenzt ist, kann die Grundfutteraufnahme stimuliert werden, indem die Grassilage angewelkt und geh~ickselt wird. Dadurch wird die Dauer der Futteraufnahme reduziert und es werden Zeit und Kaubewegungen f/Jr das Wiederkauen freigesetzt. Weitere gezielte Versuche sind erforderlich, um die genauen Mechanismen zu kl~iren, die dazu f'tihren, daft eine schnellere Trockensubstanzaufnahme Zeit zum Wiederkauen freisetzt, wodurch wiederum die Pansenftillung giinstig beeinfluflt wird.