In Situ Particle Size Reduction of Alfalfa and Timothy Hay as Influenced by Form and Particle Size

In Situ Particle Size Reduction of Alfalfa and Timothy Hay as Influenced by Form and Particle Size J. E. N O C E K and R. A . K O H N l Department of Research and Development Agway I nc.

Syracuse, NY 13221 INTRODUCTION

ABSTRACT

Our objectives were to characterize particle size reduction of alfalfa and timothy hay by in situ incubation. Alfalfa and timothy hay were chopped at .64-cm theoretical length of cut. Subsamples were dry sieved through a 3.2mm screen, yielding particles >3.2 and <3.2 turn, and another subsample ground (5.0 ram). Each forage treatment was placed in polyester bags and ruminally incubated for up to 100 h. Original and residues were wet sieved. Change in geometric mean diameter (initial to lowest) with time for both forages was less as particle size decreased from chopped to ground; however, percent change was similar between chopped and ground and between sieved >3.2 and < 3.2 ram. Regression of geometric mean diameter on time for alfalfa exhibited quadratic relationships for all particle categories. For timothy, ground and sieved > 3.2 mm exhibited linear, whereas chopped and sieved <3.2 mm exhibited quadratic relationships with time. Large particle fractions for both forages were reduced proportionately more than particle fractions that were small initially. Particle size distribution showed particles >1.18 mm accounted for 63.0 to 98.4% of the initial DM, which was reduced to 14.9 to 24.1% by 100 h. Microbial fermentation and detrition associated with ruminal movements appear to contribute substantially to particle breakdown.

Received February 6, 1987. Accepted November 9, 1987. I Department of Animal and Nutritional Sciences, University of New Hampshire, Durham 03824. 1988 J Dairy Sci 71:932-945

Several factors associated with ruminal digestion influence delivery of nutrients to the lower gut. Particle size and outflow from the. rumen are two major factors intricately influencing the digestive process (9, 27). Mosely and Jones (10) indicated that the initial and rate-limiting step in ruminant digestion is physical breakdown of feed particles. Research by Poppi et al. (20) has shown that the most important factor influencing DM retention time in the rumen was small particle retention and that change in the rate of large particle breakdown had a small effect. Researchers (10, 20, 23) have indicated that major modes of particle breakdown occur through chewing during eating and rumination, microbial fermentation, and detrition by the muscular activity of the rumen wails. Studies (10, 11) have suggested that microbial action per se plays only a minor role in particle breakdown, and that chewing during eating, especially in the first few hours after feeding (10), is the main factor. However, other studies (7, 16) estimated microbial activity was responsible for a major role in particle size breakdown. Alteration of feed particle size (i.e., grinding, chopping, leaves vs. stems, etc.) can have a substantial influence on rumen function, digestibility, and DM intake (18, 19, 21). In considering the dynamics of forage particle movement from the rumen, one must consider the fate of whole plant material of different particle size and its ultimate potential for digestion and passage. Sifting of various plant parts (i.e., stems vs. leaves) through the rumen strata must also be examined. Few studies have examined these different particle categories in relation to digestion and particle size reduction. The objectives of this study were to characterize the effect of particle size as established by chopping, grinding, and sieving on ruminal particle reduction of alfalfa and t i m o t h y and to examine the potential contribution of micro-

932

IN SITU PARTICLE SIZE REDUCTION bial action and detrition by muscular activity of the rumen on the distribution of particle breakdown utilizing the in situ bag technique. MATERIALS AND METHODS

Approximately 25 kg of both alfalfa and t i m o t h y hay were chopped through a forage harvester set at .64 cm theoretical length of cut. A subsample of each forage was ground through a Wiley mill with a 5-mm mesh screen. Another sample of each forage chopped by forage harvester was dry sieved through a 3.2 mm mesh screen. Thus, four particle category treatments were established for each forage type as follows: forage harvester (chopped), 5.0 m m grind (ground), particles that were retained on a 3.2 mm sieve (sieved >3.2 mm), and particles passing through a 3.2 mm sieve (sieved < 3.2 mm). The in situ rumen bag procedure used was that of Nocek (12). Cows, diets, and detailed description of the in situ procedures were described by Nocek anct Kohn (15). One bag from a group of four to be incubated in the rumen was soaked (39°C tap water for 15 rain) prior to incubation. Ruminal DM and NDF fractionation and digestion rate information was determined on this bag (n = 2 at each incubation time, 1 bag for each of 2 cows). Nutrient fractions included watersoluble or 59 /.tm (bag pore size) filterable (or both), insoluble digestible, and nondigestible. Neutral detergent fiber was conducted on original and residual samples according to Goering and Van Soest (8). The Macro-KjeidahI procedure (3) was used to determine CP on original samples. The basic linear model for determination of DM and NDF digestion rates is described by Nocek and English (13). Natural log transformed residues were analyzed by the covariate technique for homogenity of linear regression (parallelism) (24, 25) to determine differences in digestion profiles for the following treatment comparisons for each forage: chopped vs. ground, sieved >3.2 vs. <3.2 ram, chopped vs. sieved >3.2 and <3.2 ram, and between alfalfa and timothy for chopped, ground, sieved >3.2 and <3.2 ram. A second bag, which was not soaked prior to ruminal incubation, was used for determination of particle size distribution by wet sieving (n =

933

2 at each incubation time). The two other bags attached to each set were used to determine functional specific gravity (15). Initial and residue samples at each ruminal incubation time for each cow were classified into particle pools using eight sieves with sieve apertures of 4.75, 2.36, 1.18, .6, .3, .15, .075, and .038 mm. A portion of small particles (<.038 ram) were lost by sieving and not considered in the summation of DM captured on the respective sieves. This point must be considered in relating to digestion data. The geometric mean diameter (GMD) for each sieve was calculated according to the following equation (2): di = (di × di+l) ½ where di = geometric mean diameter of particles on the ith sieve, d i = diameter of sieve openings of the i th sieve, and di+ 1 = diameter of the openings in the next larger than i th sieve. The GMD for particles on each sieve were 5.158, 3.348, 1.669, .841, .425, .212, .106, and .053 mm. The proportion of DM remaining on each sieve was multiplied by the corresponding GMD. This procedure was conducted at each incubation time point. The following equations (2) were used to calculate GMD geometric and standard deviation for initial and residue samples: dgw = log - 1 [E(Wi log di)/2;Wi] Sgw = log - 1 [2~Wi (log di-log dgw) 2/Y-Wi] V2 where: dg w = geometric mean diameter and Wi = weight of DM recorded on the ith sieve. Distributions of residue samples were based on the a m o u n t of residual DM remaining, adjusted for DM disappearance from the bag as a result of digestion. Use of log normal distribution for expressing particle size is consistent with the adapted standard by the American Dairy Science Association (1). In addition, Ehle (6) and Smith et al. (23) indicated that the log normal distribution was appropriate to describe sieved forage material. Change in GMD was calculated as the difference between GMD of the initial sample and the specific incubation time residue beyond which no further decrease in GMD was detected. F o r GMD and ruminal fractionation data, analysis of variance were conducted on each forage separately by single-way analysis of

Journal of Dairy Science Vol. 71, No. 4, 1988

NOCEK AND KOHN

934

variance techniques for treatment effects blocked on cows. Mean treatment differences were determined according to the following orthogonal comparisons: chopped vs. ground, sieved >3.2 vs. <3.2 mm, and chopped vs. sieved >3.2 and <3.2 mm. Geometric mean diameter was regressed on rurninal incubation time to characterize the relative shift of GMD with regard to the presence of any first, second, or third order time relationships (26). The distribution and difference between corresponding GMD pool sizes for each initial and m i n i m u m residue samples were examined. Change in each corresponding pool size between initial and minimum GMD for each forage was determined by single-way analysis of variance techniques for time effects blocked on cows.

RESULTS A N D DISCUSSION Rumen Availability Fractionation and Digestibilities

The CP and NDF concentration (DM basis) of alfalfa for various treatments were chopped, 23.9, 40.3%: ground, 23.7, 39.6%; sieved >3.2 mm: 23.2, 42.4%; and sieved <3.2 mm: 24.7, 36.1%. No measurable lag time in digestion was observed for alfalfa DM for any treatment (Table 1). The proportion of water-soluble and 59-/am filterable DM was higher (P<.05) for ground than chopped alfalfa. This same parameter was higher for sieved < 3.2 mm than for > 3.2 mm, and higher for sieved treatments than for chopped. The proportion of insoluble digestible and nondigestible DM was higher for chopped than ground. Insoluble digestible DM was higher for sieved <3.2 than for >3.2 ram, whereas nondigestible DM was higher for sieved > 3.2 mm. Chopped was higher in nondigestible DM than sieved treatments. Lag times for NDF digestion ranged from 0 h for >3.2 mm to 7.0 h for >3.2 mm, which were different (P<.02). The reason for differences in lag time is not readily apparent. No water-soluble or 59-lam filterable NDF was detected for any treatments. There were no differences (P>.05) among any treatments for insoluble digestible or nondigestible NDF. Rates of digestion of insoluble digestible alfalfa DM (Table 2) were not different (P>.05) Journal of Dairy Science Vol. 71, No. 4, 1988

between treatments; however, ground tended to have the fastest (4.31%/h) and sieved <3.2 mm the slowest (3.30%/h) rate. Ehle et al. (7) indicated no consistent pattern in influence of particle size on rates of DM digestion of concentrate type ingredients. Rates of NDF digestion followed a similar pattern as DM; however, sieved >3.2 mm was faster (P<.05) than <3.2 mm. Although the ground treatment contained the lowest percentage of insoluble digestible DM and sieved < 3.2 mm the highest, rates of digestion were inversely related to the percentage of DM comprising this fraction. Physically altering alfalfa did not influence percentage distribution of NDF fractions; however, rate of digestion was influenced. Crude protein and NDF concentrations would indicate a slightly higher concentration of leaves were contained in the sieved <3.2 mm than >3.2 mm category. However, these data suggest that NDF concentration does not necessarily reflect rate of digestion. Nocek and Grant (14) showed a correlation coefficient of - . 5 5 for the relationship of NDF concentration to the rate of NDF digestion in situ. Crude protein and NDF concentration (DM basis) of timothy for the various treatments were chopped, 10.9, 61.2%; ground, 11.1, 63.5%; sieved >3.2 ram: 10.7, 64.3%; and sieved <3.2 ram: 11.1, 63.8%. Grinding increased (P<.01) the amount of water-soluble and 59-/2m filterable DM as compared with chopping (Table 3). There was no difference between sieved >3.2 or <3.2-mm particles on water-soluble or 59-#m filterable DM, but both sieved categories were higher (P<.02) than the chopped. Generally, the water-soluble fraction was 4 to 6 percentage units lower for timothy than alfalfa. Percentage of insoluble digestible DM was higher (P<.05) for chopped than for ground with sieved >3.2 mm and <3.2 mm not being different. Treatment did not influence the percentage of nondigestible DM and except for sieved <3.2 mm, tended to be 3 to 5 percentage units lower than alfalfa. Lag time in NDF digestion ranged from 1 to 6 h for ground and sieved <3.2 mm, respectively. The relative proportions of insoluble digestible and nondigestible NDF were not influenced by treatment. Nondigestible NDF was 22.3 to 26.7 percentage units lower for timothy than alfalfa. This finding is consistent with research of others (14, 22) and is most

TABLE 1. Effect of particle size and form on ruminal dry m a t t e r and neutral detergent fiber fractionation of alfalfa ha y in situ. Orthogonal comparisons Sieved 2 Variable

Choppe d 1

Ground

Digestion lag time, h 4 Water-soluble and 59-t~m filterable, %~ Insoluble digestible, % Nondigestible, %s Digestion endpoint, h 9

0s 16.5 54.7 28.9 100

0 22.4 50.7 27.0 100

>3.2 m m

< 3.2 m m

SE 3

Chopped vs. ground

>3.2 m m <3.2 m m

Chopped vs. sieved

p<..

DM 0 17.1 54.2 28.7 88

0 19.4 57.6 23.1 100

.13 .4 .4

.001 .004 .05

.003 .007 .007

.005 NS ~ .007

~q

NDF Digestion lag time, h Water-soluble and 59-#m filterable, % Insoluble digestible, % Nondigestible, % Digestion endpoint, h

4.0 0 48.9 51.1 88

1.0 0 49.0 51.0 88

C >

0 0 49.2 50.5 88

7.0 0 52.1 47.9 88

3.8

NS

.02

NS

2.7 2.3

NS NS

NS NS

NS NS

t~ s O~ t~

c

1 Forages were chopped through a forage harvester (theoretical length of cut = .64 cm) and a subsample was then groun d through a 5-mm screen in a Wiley mill. 2 Chopped material was dry sieved on a 3.2-ram screen.

~7

3 SE = Standard error of the mean. 4 Observed lag time of digestion: ruminal incuba t i on t i me prior to initial decrease in percentage of insoluble digestible residue. s Each mean consists of d e t e r m i n a t i o n s made on t w o cows per t re a t me nt , n = 2. 6 Material escaping 59-#m porosity bags soaked in 39°C tap water for 15 rain prior to ruminal incubation.

< o

7 NS = Nonsignificant (P>.05). 8 Percentage of material remaining after which no further ruminal disappearance was observed.

Z o

00 00

9 Time in r u m e n associated with no further disappearance.

xo L~

936

NOCEK AND KOHN

TABLE 2. Effect of particle size and form on in situ dry matter and neutral detergent fiber digestion rate of alfalfa hay. Orthogonal comparisons Sieved ~ Variable

Chopped 1

Ground

Kd a SEB s r~

3.59 .33 .81

4.31 .30 .88

Kd SEB r2

3.52 .50 .71

3.61 .31 .85

Chopped

Chopped vs. ground

>3.2 vs. <3.2 mm

VS.

sieved

>3.2 mm

<3.2 mm

4.13 .45 .77

3.39 .19 .92

NS 4

NS

NS

2.76 .37 .79

NS

.05

NS

DM

P<

NDF 4.04 .38 .81

Forages were chopped through a forage harvester (theoretical length of cut = .64 cm) and a subsample was then ground through a 5.0-ram screen in a Wiley mill. 2 Chopped material was dry sieved on a 3.2-ram screen. 3Percentage of disappearance per hour of insoluble digestible DM or NDF from polyester bags (rate constant). Each time point residue was corrected for nondigestihle material prior to regression analyses. For each regression, n = 2, with 14 time points. 4 NS = Nonsignificant (P>.05). s SEB = Standard error of the regression coefficient or slope.

likely associated w i t h t h e lower degree of lignification of grasses. R a t e s of d i g e s t i o n for insoluble digestible DM f o r t i m o t h y ( T a b l e 4) were n o t i n f l u e n c e d ( P > . 0 5 ) b y t r e a t m e n t , a l t h o u g h sieved < 3 . 2 m m t e n d e d t o have t h e fastest rate (3.70%). Likewise, N D F digestion rates w e r e n o t different (P>.05) among treatments. Between forages, t i m o t h y was higher ( P < . 0 1 ) in DM d i g e s t i o n rate t h a n alfalfa, w h e r e a s t h e r e were n o d i f f e r e n c e s in N D F d i g e s t i o n rate b e t w e e n forages for a n y t r e a t m e n t s .

Geometric Mean Diameter Reduction

R e d u c t i o n in G M D for t r e a t m e n t particle size categories is s h o w n in T a b l e 5. Initial GMD for alfalfa was h i g h e r ( P < . 0 0 6 ) f o r c h o p p e d t h a n g r o u n d a n d higher ( P < . 0 5 ) for sieved > 3.2 m m t h a n < 3 . 2 m m . M i n i m u m G M D was r e a c h e d for g r o u n d a n d sieved < 3 . 2 m m categories at 6 4 a n d 76 h, respectively, whereas c h o p p e d a n d sieved > 3 . 2 m m did n o t reach a m i n i m a l GMD u n t i l 100 h of r u m i n a l incubat i o n . C h a n g e ( r a m ) in G M D w i t h t i m e was Journal of Dairy Science Vol. 71, No. 4, 1988

g r e a t e r for c h o p p e d t h a n g r o u n d w i t h no d i f f e r e n c e ( P > . 0 5 ) b e t w e e n sieved t r e a t m e n t s or b e t w e e n c h o p p e d a n d sieved t r e a t m e n t s . P e r c e n t a g e change o v e r t i m e in t h e r u m e n was not different between treatment comparisons. T h e initial G M D o f t h e t i m o t h y t r e a t m e n t s f o l l o w e d t h e same d i f f e r e n c e p a t t e r n as alfalfa. T i m e of r u m i n a l i n c u b a t i o n at w h i c h t h e s m a l l e s t GMD was o b s e r v e d ranged f r o m 76 to 100 h. D i f f e r e n c e s a m o n g t r e a t m e n t s for s m a l l e s t size were also t h e same as t h o s e demo n s t r a t e d for alfalfa. C h a n g e ( m m ) in GMD was g r e a t e r ( P < . 0 0 7 ) for c h o p p e d t h a n g r o u n d a n d g r e a t e r ( P < . 0 5 ) for sieved > 3 . 2 m m t h a n for sieved < 3 . 2 m m . Like alfalfa, p e r c e n t a g e c h a n g e w i t h t i m e in t h e r u m e n was n o t different between treatment comparisons. P e r c e n t a g e c h a n g e in G M D r a n g e d f r o m 41.7 to 52.7% for alfalfa a n d f r o m 54.6 t o 62.5% for t i m o t h y ; t i m o t h y g e n e r a l l y e x h i b i t e d a 10 p e r c e n t a g e u n i t g r e a t e r change t h a n alfalfa. B a r n o et al. (4) e x a m i n e d in situ particle size r e d u c t i o n of alfalfa, b i r d s f o o t trefoil, s m o o t h b r o m e g r a s s , and c o r n silage at f o u r d i f f e r e n t p a r t i c l e sizes. T h e y r e p o r t e d t h a t forage source

TABLE 3. Effect of particle size and form on rumhaal dry matter and neutral detergent fiber fractionation of timothy hay in situ. Orthogonal comparisons Sieved 2 Variable

Chopped I

Ground

Digestion lag time, h 4 Water-soluble and 59-pm filterable, %7 Insoluble digestible, % Nondigestible, %a Digestion endpoint, h 9

0s 10.5 67.0 22.6 100

2.0 17.9 58.5 23.7 100

>3.2 m m

<3.2 m m

SE 3

Chopped vs. ground

>3.2 vs. <3.2 m m

0 13.1 64.5 23.4 100

3.0 13.1 63.2 23.3 100

.5 2.0 3.0 3.2

.05 .001 .008 NS

.01 NS NS NS

DM

Chopped vs. sieved

P< NS 6 .02 NS NS

~q

NDF Digestion lag time, h Water-soluble and 59-#m filterable, % Insoluble digestible, % Nondigestible, % Digestion endpoint, h

2.0 0 75.6 24.4 100

1.0 0 73.0 27.0 100

4.0 0 73.5 26.5 100

C

6.0 0 74.4 25.6 100

3.3

NS

NS

NS

3.6 4.3

NS NS

NS NS

NS NS

t~ t~ ~0 t~

1 Forages were chopped through a forage harvester (theoretical length of cut = .64 cm) and a subsample was then ground through a 5-mm screen in a Wiley mill. Chopped material was dry sieved on a 3.2-mm screen. ~7

3 SE = Standard error of the mean. 4 Observed lag time of digestion: ruminal incubation time prior to initial decrease in percentage of insoluble digestible residue. s Each mean consists of determinations made on two cows per treatment, n = 2. # NS = Nonsignificant (P>.05).

<

7Material escaping 59-pm porosity bags soaked in 39°C tap water of 15 rain prior to ruminal incubation. 8 Percentage of material remaining after which no further ruminal disappearance was observed.

Z o

f

9 Time in rumen associated with no further disappearance.

Z

938

NOCEK AND KOHN

T A B L E 4. Effect o f particle size and form on in situ dry m a t t e r and neutral detergent fiber digestion rate of t i m o t h y hay. Orthogonal comparisons Sieved 2 Variable

Chopped ~

Ground

Kd 3 SEB s r2

3.29 .17 .93

3.23 .20 .91

Kd SEB r2

3.93 .18 .95

3.12 .15 .94

Chopped

Chopped vs. ground

>3.2 vs. <3.2 m m

VS.

>3.2 m m

<3.2 mm

3.33 .20 .91

3.70 .29 .88

NS 4

NS

NS

3.90 .29 .89

3.52 .35 .85

.01

NS

NS

DM

sieved

P<

NDF

Forages were chopped through a forage harvester (theoretical length of cut = .64 cm) and a subsample was then ground t h r o u g h a 5.O-mm screen in a Wiley mill. 2 Chopped material was dry sieved on a 3.2-ram screen. 3Percentage of disappearance per hour of insoluble digestible DM or NDF f r o m polyester bags (rate constant). Each time point residue was corrected for nondigestible material prior to regression analyses. For each regression, n = 2, with 14 time points. 4 NS = Nonsignificant (P>.05). s SEB = Standard error of the regression coefficient or slope.

d i d n o t i n f l u e n c e p a r t i c l e size r e d u c t i o n w i t h t i m e in t h e r u m e n . P o o l e d f o r a g e d a t a a f t e r 7 2 h of rumen exposure exhibited the greatest p e r c e n t a g e c h a n g e in size w i t h p a r t i c l e s g r o u n d t h r o u g h < 1 2 . 6 a n d < 6 . 4 m m sieves ( 4 2 . 2 a n d 41.8%). Murphy and Nicoletti (11) showed a

SZJ

*t~LFA

1 9 % r e d u c t i o n in m e a n p a r t i c l e size o f c o u r s e l y ground alfalfa after 96 h of rumen incubation. These workers indicated that particle reduction due to microbial activity and detrition made o n l y a m i n o r c o n t r i b u t i o n t o t h e t o t a l red u c t i o n o f size n e e d e d f o r r u m i n a l p a s s a g e .

A

~

r~xY

B

I

!

'.;-I

oL

|o

..........

~ . . . . . . . . . . . "~". . . . "~. . . . . . . . . . . mN~

ImATm

Tl~.h

mU~INMLi ~ n e ~

TIME,h

Figure 1. Relationship between geometric m e a n diameter (GMD) of A) alfalfa and B) t i m o t h y and time of ruminal incubation. FH (e - - - e): h a y chopped through a forage harvester (theoretical length of cut = .64 cm); 5.0 m m (s- - 4 ) : subsample of FH ground t h r o u g h a 5.0-ram sieve aperture in a Wiley mill, sieved >3.2 ( o - - o ) ; and <3.2 (~ D) m m : FH subsample was dry sieved on a sieve aperture of 3.2 m m . Time of ruminal incubation at which the smallest GMD was observed signified by o. Pool log - 1 standard deviation: alfalfa; FH = .26, 5.0 m m = .19, >3.2 m m = .27, <3.2 m m = .23. T i m o t h y ; FH = .25, 5.0 m m = .21, >3.2 m m = .29, <3.2 m m = .26. Means at each time consists of determinations of one bag f r o m each of two cows, n = 2. Journal o f Dairy Science Vol. 71, No. 4, 1988

TABLE 5. Effect of particle size and form on geometric m e a n di a me t e r (GMD) reduction of alfalfa and t i m o t h y hay. Orthogonal comparisons Sieved2 Variable

Chopped I

Ground

> 3.2 m m

<3.2 m m

log -1 (SD)

Chopped vs. ground

>3.2 vs'. <3.2 m m

Alfalfa Initial. 3 m m Smallest, s m m Time in tureen, 6 h Change over time, ~ m m Change over time, %

3.24 1.53 100 1.71 52.9

1.26 .74 64 .52 41.7

3.99 1.50 88 2.49 62.5

1.74 .78 76 .96 54.9

3.28 1.75 100 1.53 44.5

Ch o p p ed vs. sieved

p< 2.40 1.25 76 1.15 47.2

.26 ,21

.006 .04

.05 NS

NS 4 NS

.01 NS

NS NS

NS NS

.29 .22

.001 .03

.005 NS

.03 NS

.17 2.6

.007 NS

.05 NS

NS NS

.19 1.2

Timothy

e-

Initial, m m Smallest, m m Time in rumen, h Change over time, m m Change over time, %

4.64 1.95 100 2.69 57.9

t~ 3.94 1.79 88 2.15 54.6

o

1 Forages were chopped through a forage harvester (theoretical length of cut = .64 cm) and a subsample was t he n groun d through a 5-mm screen in a Wiley mill.

ga ,,<

3 G e o m e t r i c mean diameter of the initial material prior to ruminal i n c u b a t i o n (n = 2 ; one bag for each of two cows).

N t~ t'3

5

2 Chopped material was dry sieved on a 3.2-ram screen.

4 NS = Nonsignificant (P>.05). s Geometric mean diameter of the time point residue t h a t represented the smallest GMD. <

o

6 Time of ruminal incubation whieh represented the smallest GMD.

~4

7 Difference between initial and smallest GMD.

Z O

4~ 00

00

xO ta~ xO

4~ O

e~

TABLE 6. Effect of particle size category on characterization of geometric mean diameter regressed on ruminal i nc uba t i on tim e for alfalfa and t i m o t h y hay. < o Equ a t i on c o m p o n e n t s X

O

Treatment

Intercept

Time

Timesquared

3.21 1.12

-.0324 --.0145

3.77 2.15

pt Timecubed

rz

Linear

Quadratic

2.09 × 10 - 4 1.37 X 10 - 4

.54 .41

.002 .0002

.05 .0008

NS 3 NS

-.0539 -.0327

3.70 × 10 - 4 2.74 X 10 - 4

.72 .57

.0001 .0001

.002 •0004

NS NS

3•92 1•56

-.0464 -.0070

2.72 × 10 - 4 ...

.75 .57

.0001 .0001

.01 NS

NS NS

4.10 3.68

-.0211 -.0392

2.71 × 10 - 4

.78 .56

.0001 .0001

NS .02

NS NS

Cubic

4~

0¢

Alfalfa Chopped 2 Ground Sieved a >3.2 m m <3.2 m m Timothy Chopped Ground Sieved >3 .2 m m <3.2 m m

1 Level of significance of the linear, quadratic, cubic components.

3 NS = Nonsignificant (P>.05).

> Z o Z

2 Forages were chopped through a forage harvester (theoretical length of cut = .64 cm) and a subsample was t he n ground through a 5.0-mm screen in a Wiley mill.

4 Chopped material was dry sieved on a 3.2-mm screen.

O

IN SITU PARTICLE SIZE REDUCTION Figure 1 illustrates t h e r e l a t i o n s h i p b e t w e e n GMD a n d r u m i n a l i n c u b a t i o n time. F o r b o t h forages (Figures 1A and B) t h e g r e a t e s t c h a n g e in GMD o c c u r r e d w i t h i n t h e first 16 h o f r u m e n e x p o s u r e . F o r alfalfa, G M D t e n d e d t o increase slightly, t h e n decrease, f o l l o w e d b y g r a d u a l p l a t e a u i n g w i t h time. T h i s early q u a d r a t i c e f f e c t m a y b e associated w i t h a rapid e f f l u x o f small particles f r o m t h e bag, rapid d i g e s t i o n o f DM p r o d u c i n g small u n q u a n t i f i a b l e particles, or swelling u p o n h y d r a t i o n . Table 6 shows the characterization of GMD regressed o n r u m i n a l i n c u b a t i o n time. F o r alfalfa, all p a r t i c l e size categories e x h i b i t e d

941

quadratic relationships with time. Quadratic r e l a t i o n s h i p s were also d e m o n s t r a t e d f o r t i m o t h y c h o p p e d a n d sieved < 3.2 m m , w h e r e a s g r o u n d a n d sieved > 3 . 2 m m were linear w i t h time. O t h e r researchers (4) r e p o r t e d linear, q u a d r a t i c , a n d cubic r e l a t i o n s h i p s f o r regression of m e a n particle size o n t i m e o f rurninal incubation.

Distribution of Particle Size Pools with Time of Incubation

Because p a r t i c l e r e d u c t i o n in t h e r u m e n is a d y n a m i c process, a n d b e c a u s e G M D is a f u n c -

ALFALFA

ALFALFA GROUND:

FORAGE HARVESTER: TLC = . 6 4 c m 0 h, 100~

10Oh, 34.3~

• 0hjl0OX

B 5mm

6 4 h , 41.5 ~

50-

~o-

S.IEI 1,eTl.4:S 1.1061

3.35 .841 .212 .063

3.35.841

.212 .053

3.35 .841 .212 .053

S.t8 I:~n 1.42EI.~Oel

3.35 .841 .212 .063

GEOMETRIC MEAN DIAMETER,ram

GEOMETRIC MEAN DIAMETER,ram

60-

ALFALr~ EIEVED= :* 3 . 2 r a m 0 h, 100~

x

C ALFALFA

m

100 h, 3 4 . 9 x

60~

S I E V E D : q: 3 . 2 m m

z

!

0h,100~;

76h, 36.3x

j?

,

,--

S.IE I !,67 [ .4251.1061 3 . 3 5 . 8 4 1 ,212 ,053

5-t6 I ¢671 ~ 1.1061 3.35 .841 .212 .053

GEOMETRIC MEAN DIAMETER, m m

5.16 I 1.67 IA25 1,106 I 3.35 .841 .212 .053

5.161 1.671,4251.106 I 3.35 .841 ,212 .053

GEOMETRIC MEAN DIAMETER, m m

Figure 2. Change in particle subfraction distribution of initial and residual DM for alfalfa with time of ruminal incubation. A) FH; chopped through a forage harvester [theoretical length of cut (TLC) = .64 cm], B) 5.0 ram: subsample of FH ground through a Wiley mill, C) sieved >3.2 mrn: FH particles retained on a sieve aperture of 3.2 mm after dry sieving and D) sieved <3.2 ram: FH particles passing through a sieve aperture of 3.2 mm after dry sieving. Distribution of DM data on the left side of each figure represents that of the initial sample (i.e., 0 h, 100% DM). Data on the right side of each figure represents distribution of DM of the residue which minimum GMD was observed. The hour of rumen incubation and residual DM as a percent of initial DM are designed for each distribution. Symbol (X) indicates pool sizes of the same GMD are significantly different (P<.05) between initial and residue samples. Each mean + SE consists of n = 2 (one bag for each of two cows). Journal of Dairy Science Vol. 71, No. 4, 1988

942

NOCEKAND KOHN

t i o n o f b r e a k d o w n o f smaller p o o l s u b f r a c t i o n s , d a t a were f u r t h e r e x a m i n e d t o d e t e r m i n e t h e r e l a t i o n s h i p a m o n g r u m i n a l i n c u b a t i o n time, initial p a r t i c l e size a n d d i s t r i b u t i o n o f particle size pools. Figures 2 a n d 3 illustrate residual DM d e l i n e a t e d i n t o s u b f r a c t i o n s b y screen size for e a c h t h e initial s a m p l e a n d r u m i n a l i n c u b a t i o n t i m e a t w h i c h t h e smallest G M D w e r e o b s e r v e d . It_

TIMOTHY

A similar p a t t e r n in t h e s h i f t o f DM dist r i b u t i o n was e v i d e n t f o r m o s t all t r e a t m e n t s regardless of forage. T h e larger particle categories ( c h o p p e d a n d sieved > 3.2 m m ) had m o s t of t h e i r D M d i s t r i b u t e d in t h e t w o largest sieves (4.75 a n d 2.36 m m ) . Over t i m e , t h e s e larger p o o l s e x h i b i t e d t h e g r e a t e s t a m o u n t of red u c t i o n in p r o p o r t i o n o f DM. T h e s e results agree w i t h Ehle et al. (7), w h o i n d i c a t e d par-

A

1

J

3.38 ,1141 .21Z .063 ~ .841 .212 GEOMETRIC MEAN DIAMETER,m m

•

i

i

.

.

°

--,C.----.,m.__.

Oh ,100~SIEVED: 1,3.2mm

tl

.

lOOh, ~.9~

-

5.116tI 1,671.4251.t06 1.671.4251.t06 | 5.1Q I 1.871.428 UWI.428 1.106 I 3*36,841 .212 JD53 3.38 .841 .212 .053 QEOMETRIC MEAN mAMETER mm

C

TIMOTHY • 3.2ram

SlaVED:

Oh,lOOs

88h, 28.5~

'tl "

s,Sell.e?l 4s~sI.lOS I 8.16 1 1"1wI.428 I 3061 3,38 .841 .212 .063 3.38 .841 .212 .063 CmOM|TIqI¢ MRAN DIAMETER m m

Figure 3. Change in particle subfraction distribution of initial and residual DM for timothy at the time of ruminal incubation. A) FH: chopped through a forage harvester [theoretical length of cut (TLC) = .64 cm], B) 5.0 mm: subsample of FH ground through a Wiley mill, C) sieved >3.2 ram: FH particles retained on a sieve aperture of 3.2 mm after dry sieving and D) sieved <3.2 ram: FH particles passing through a sieve aperture of 3.2 mm after dry sieving. Distribution of DM data on the left hand side of each figure represents that of thc initial sample (i.e., 0 h, 100% DM). Data on the right side of each figure represents distribution of DM of the residue which minimum GMD was observed. The hour of rumen incubation and residual DM as a percent of initial DM are designated for each distribution. Symbol (X) indicates pool sizes of the same GMD are significantly different (P<.05) between initial and residue samples. Each mean + SE consists of n = 2 (one bag for each of two cows). Journal of Dairy Science Vol. 71, No. 4, 1988

IN SITU PARTICLE SIZE REDUCTION

ticle size reduction was greatest for large particles and decreased as particle size decreased. The next one or two smaller screen sizes were generally similar in the proportion of DM they contained, between initial and the residual sample. Thereafter, a greater proportion of DM was generally retained on the smaller screens for the residual than for the initial samples. Although the ground and sieved >3.2-ram alfalfa treatments were slightly different from other treatments in distribution profile, the same phenomenon as previously described resulted subsequent to the pool containing the largest proportion of DM. In characterizing DM pool size distribution using the in situ technique, one has to be aware that shifts in DM from pool to pool is a d y n a m i c process. Breakdown of particles from larger pools does not necessarily mean progression to the next smallest size pool. Particle size reduction is a function of DM digestion, and delineation is difficult. In this study, DM digestion is quantified as any particle <59/~m. Particle size reduction not only appears to be a function of initial particle size and rate of DM digestion but also a function of quantity of DM that represents a given particle pool size. Data obtained in the present study agree with in vivo particle size distribution results of Moseley and Jones (10) for white clover and perennial ryegrass. These researchers demonstrated a reduction in the 4 mm pool fraction and an increase in the .15-mm pool fraction,

943

but very little change in the percentage of seven other fractions measured. Percentage loss of 4-ram particles from clover was greater than ryegrass, with the greatest rate of change in particle size distribution occurring within the first 3 h after feeding. Dixon and Milligan (5) reported a progressive decline in fractional outflow from the rumen with increasing particle size and negligible outflow of particles greater than 4.0 ram. They further indicated that if ruminal contents were to be considered as two pools, a 3.2-mm mesh screen appeared to be an appropriate division. Poppi et al. (17) indicated that if a two-compartment model to predict flow of particles from the reticulorumen was required, 1.18 mm would be an useful division point. However, differences between sheep and cattle must be considered in interspecies application of ruminal principles. Although some particles greater than 1.18 m m do leave the rumen, the percentage is small (<5%) and may be of little practical significance (17). In addition, Smith et al. (23) have provided evidence that particle reduction does not occur beyond the duodenum. Our intent was to use a specific particle size of 1.18 mm as a benchmark to evaluate in situ particle size reduction as it may relate to ruminal passage. Figures 4A and B illustrate the change in total percent DM of particles > 1.18 mm remaining in the polyester bags with time in the rumen. The additive inverse (100 - X%) represents both

IOOAL~LFA

X

gO-

TIMOraY

e

9O.

|, ~'--'O,

eO-

jo

°i

IC-

R~MI~t~L I h ~ o R ~ r ~ rIME . ~

Figure 4. Change in the percentage of DM greater than 1.18 m m in the residual DM for A) alfalfa and B) t i m o t h y in polyester bags with time of ruminal incubation. FH (e . . . . o): chopped through a forage harvester [theoretical length of cut (TLC) = .64 cm], 5.0 m m (m. . . . t): subsample of FH ground through a 5.0 m m sieve aperture in a Wiley mill, sieved >3.2 m m (o o): FH particles retained on a sieve aperture of 3.2 m m after dry sieving and, sieved <3.2 m m (n []): FH particles passing through a sieve aperture of 3.2 m m after dry sieving. Each mean consists of n = 2 (one bag for each of two cows). Journal of Dairy Science Vol. 71, No. 4, 1988

944

NOCEK AND KOHN

TABLE 7. Relationship between change in geometric mean functional specific gravity and geometric mean diameter for alfalfa and timothy hay with time of ruminal incubation. Ground I

Sieved2

Forage

FH

5.0 mm

>3.2 mm

<3.2 mm

Alfalfa Timothy

--.213 (NS) -.65 (.001)

-.13 (NS) -.42 (.02)

-.47 (.007) -.50 (.004)

-.58 (.001) -.62 (.002)

l Forages were ground through a forage harvester (FH, theoretical length of cut = .64 cm) and a subsample was then ground through a 5.O-ram screen in a Wiley mill. 2The FH material was dry sieved on a 3.2-ram screen. 3Values are coefficients of determination (r 2) for the regression of geometric mean functional specific gravity (14) and geometric mean diameter with time in the rumen. Value in parenthesis is the level of significance of the regression. NS = Nonsignificant (P>.05).

particles that were <1.18 mm and those that escaped from the bag as a result of the digestive process (which also constitutes particle reduction). For alfalfa, a range of 48.8 to 68.7 percentage unit reduction for ground and sieved < 3.2 mm, respectively, of the total DM weight was reduced to particles >1.18 mm. For timothy, percentage reduction of DM of particles >1.18 ranged from 55.6 to 78.6 percentage units for ground and sieved >3.2 mm, respectively. Moseley and Jones (10) presented evidence that physical breakdown of particulate material during early stages of digestion (3 to 6 h postprandial) is due primarily to chewing during eating with rumination or microbial fermentation playing a nonsignificant role. In the present study, a significant proportion of particle reduction occurred during the first 12 h after insertion of material into the rumen, especially for alfalfa. Because chewing and rumination of material contained within the bags was not possible, microbial fermentation and detrition via ruminal activity were the methods by which particle reduction occurred. Coefficients of determination for the relationship between GMD and geometric mean function specific gravity (FSG) change with time in the rumen are shown in Table 7. A negative relationship existed between GMD and FSG, i.e., as particle size decreased, FSG increased with time. However, the strength of this relationship varied by both forage type and treatment. The relationship for alfalfa chopped and ground was not significant (P>.05), although highly significant relationships were Journal of Dairy Science Vol. 71, No. 4, 1988

demonstrated for other treatments.

SUMMARY

Under the conditions of this study, GMD decreased with time in the rumen regardless of forage type or initial particle size. For alfalfa, although differences between treatments in change (mm) in GMD were present, percent change with time was not different between particle categories. T i m o t h y had greater reduction in GMD with time in the rumen than alfalfa. For alfalfa, change in GMD with time was quadratic in nature. This was also true for timothy chopped and sieved <3.2 mm; however, for ground and sieved > 3.2 mm the relationship was linear. Generally, distribution of DM shifted from larger to smaller size subfractions with time in the rumen whether samples were reduced in particle size or were sieved. Microbial fermentation and ruminal movement, as they affect samples in dacron bags, appear to reduce GMD significantly to a point where samples could potentially pass from the rumen with time. A negative relationship between GMD reduction and mean FSG change with time in the rumen was demonstrated. ACKNOWLEDGMENTS

The authors gratefully acknowledge the technical assistance of C. J. Sniffen, Cornell University, and also acknowledge J. E. English, Agway Inc., for his assistance in statistical analysis.

IN SITU PARTICLE SIZE REDUCTION REFERENCES

1 American Dairy Science Association. 1970. A report: committee on classification of particle size in feedstuffs. J. Dairy Sci. 53:689. 2 American Society of Agricultural Engineers. 1981. Method of determining and expressing fineness of feed material by sieving. Page 344 in Agricultural engineers yearbook. Am. Soc. Agric. Eng., St. Joseph, MI. 3 Association of Official Analytical Chemists. 1975. Official Methods o f analysis. 12th ed. Association of Official Analytical Chemists, Washington, DC. 4 Barno, B. J., F. R. Ehle, and M. D. Stern. 1984. In situ particle size reduction of alfalfa, birdsfoot trefoil, smooth bromegrass and corn silage in rumen of Holstein cow. J. Dairy Sci. 67(Suppl. 1):97. (Abstr.) 5 Dixon, R. M., and L. P. Milligan. 1985. Removal o f digesta components from the rumen of steers determined by sieving techniques and fluid, particulate and microbial markers. Br. J. Nutr. 53: 347. 6 Ehle, F. R. 1984. Measurement of mean particle size of forages by wet and dry sieving techniques. P. M. Kennedy, ed. Techniques in particle size analysis of feed and digesta in ruminants. Proc. Workshop Can. Soc. Anim. Sci., Edmonton, Alta. 7 Ehle, F. R., M. R. Murphy, and J. H. Clark. 1982. In situ particle size reduction and the effect o f particle size on degradation of crude protein and dry matter in the rumen of dairy steers. J. Dairy Sci. 65:963. 8 Goering, H. K., and P. J. Van Soest. 1970. Forage fiber analysis. USDA, ARS, Agric. Handbook No. 379. 9 Mertens, D. R., and L. O. Ely. 1982. Relationship of rate and extent of digestion to forage utilization - a dynamic model evaluation. J. Anim. Sci. 54:895. 10 Moseley, G., and J. R. Jones. 1984. The physical digestion of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens) in the foregut of sheep. Br. J. Nutr. 52:381. 11 Murphy, M. R., and J. M. Nicoletti. 1984. Potential reduction of forage and rumen digesta particle size by microbial action. J. Dairy Sci. 67:1221. 12 Nocek, J. E. 1985. Evaluation of specific variables affecting in situ estimates of rurninal dry matter and protein digestion. J. Anim. Sci. 60:1347. 13 Nocek, J. E., and J. E. English. 1986. In situ digestion kinetics: evaluation of rate determination procedures. J. Dairy Sci. 69:77.

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14 Nocek, J. E., and A. L. Grant. 1987. Characterization of in situ nitrogen and fiber digestion and bacterial nitrogen contamination of hay crop forages preserved at different dry matter percentages. J. Anim. Sci. 64:552. 15 Nocek, J. E., and R. A. Kohn. 1987. Initial particle form and size on change in functional specific gravity of alfalfa and timothy hay. J. Dairy Sci. 70:1850. 16 Pearce, G. R., and R. J. Moir. 1964. Rumination in sheep. I. ")'he influence of rumination and grinding upon the passage and digestion of food. Aust. J. Agric. Res. 15:635. 17 Poppi, D. P., B. W. Norton, D. J. Minson, and R. E. Hendricksen. 1980. The validity of the critical size theory for particles leaving the rumen. J. Agric. Sci. 94:275. 18 Poppi, D. P., D. J. Minson, and J. H. Ternouth. 1980. Studies of cattle and sheep eating leaf and stem fractions of grasses. I. The voluntary intake digestibility and retention time in the reticulorumen. Aust. J. Agric. Res. 32:99. 19 Poppi, D. P., D. J. Minson, and J. H. Ternouth. 1981. Studies of cattle and sheep eating leaf and stem fractions of grasses. II. Factors controlling the retention of feed in the reticulorumen. Aust. J. Agric. Res. 32:109. 20 Poppi, D. P., D. J. Minson, and J. H. Ternouth. 1981. Studies of cattle and sheep eating leaf and stem fractions of grass. III. The retention time in the rumen of large feed particles. Aust. J. Agric. Res. 32:123. 21 Santini, F. J., A. R. Hardi, N. A. Jorgensen, and M. F. Finner. 1983. Proposed use of adjusted intake based on forage particle length for calculation of roughage indexes. J. Dairy Sci. 66:811. 22 Seoane, J. R. 1982. Relationships between the physicochemical characteristics of hays and their nutritive value. J. Anim. Sci. 55:422. 23 Smith, L. W., B. T. Weinland, D. R. Waldo, and E. C. Leffel. 1983. Rate of plant cell wall particle size reduction in the rumen. J. Dairy Sci. 66:2124. 24 Snedecor, G. W., and W. G. Cochran. 1980. Analysis of covariance, comparison of regression lines. Pages 385--388 in Statistical methods. 7th ed. Iowa State Univ. Press, Ames. 25 Sokal, R. F., and R. J. Rohlf. 1969. Comparisons of regression lines. Pages 143--145, 4 4 8 - 4 5 8 in Biometry. S. H. Freeman Co., San Francisco, CA. 26 Statistical Analysis System. 1985. SAS User's guide: basics. Version 5 ed. SAS Institute, Inc., Cary, NC. 27 Welch, J. G. 1982. Rumination, particle size and passage from the rumen. J. Anita. Sci. 54:885.

Journal o f Dairy Science Vol. 71, No. 4, 1988