- Email: [email protected]
In Situ Particle Size Reduction and the Effect of Particle Size on Degradation of Crude Protein and Dry Matter in the Rumen of Dairy Steers1
In Situ Particle Size Reduction and the Effect of Particle Size on Degradation of Crude Protein and Dry Matter in the Rumen of Dairy Steers t F. R. EHLE, z M. R. MURPHY, and J. H. CLARK Department of Dairy Science University of Illinois Urbana 61801
ABSTRACT
The contribution of rumen microbes to particle size reduction was examined and the influence of particle size on in situ degradation rates of crude protein and dry matter in the rumen of dairy steers fed ad libitum was determined. In addition to rumination and mastication, microbial action is of major importance in particle size reduction of some feedstuffs in ruminants. Rates of crude protein degradation differed among feedstuffs but were not significantly affected by particle size within feed samples. Primary and secondary rates of dry matter degradation were observed for wheat bran, linseed meal, and cottonseed meal. Soybean meal and formaldehyde-treated soybean meal data displayed only primary degradation rates for dry matter. Differences in primary rates of dry matter degradation among various particle sizes were significant only for linseed meal. Absence of a consistent pattern to the influence of particle size on rates of dry matter and crude protein degradation within a feed indicates the importance of other factors. INTRODUCTION
Particle size of feedstuffs consumed by ruminants plays an important role in the digestive process. As particle size of feed decreases,
Received March 26, 1981. t Supported in part by the Illinois Agricultural Experiment Station and HEW PHS FD 00849. 2Deparmaent of Animal Science, University of MinnesOta, St. Paul, MN 55108. 1982 J Dairy Sci 65:963-971
retention time in the rumen will decrease (3, 9, 14, 15, 16). Therefore, the potential for escape of feed particles from the rumen should be inversely related to particle size of the feed consumed. The rate of feed degradation in the rumen also must be considered because this can affect the amount of feed that passes from the rumen (11). Major factors governing particle size reduction are mastication, rumination, microbial fermentation, and rumen contractions (6, 15, 17). Although rumination generally has been considered most important in particle size breakdown (2, 15, 23), it is difficult to determine the contribution of each factor to the overall process of reduction. There is a lack of quantitative information describing the effects of particle size on feed consumed by ruminants and the rate and extent of breakdown in the rumen of feeds differing in particle size on animal performance (10, 18). Changing the size of particles consumed or altering the rate and extent of breakdown of feed particles in the rumen may influence production by ruminant animals via altering rate of passage of solids from the rumen as well as dry matter intake. Data of Weakley et al. (22) indicate that protein and dry matter in soybean meal that is coarse (2000 /a) is degraded less than finer size (520/a) material. They suggested that the coarse soybean meal had a greater potential to escape fermentation and pass to the small intestine than did the finer material. Subsequent studies with coarse (2400 /a) or fine (250/a) soybean meal produced no significant differences in nonammonia nitrogen flow to the abomasum or in milk production (12). Feeding the fine (250/a) soybean meal, however, did result in a trend toward greater nonammonia nitrogen flow to the abornasum compared to feeding the coarse (2400 /a) soybean meal.
963
964
EHLE ET AL.
We have used the in situ polyester bag technique to estimate the rumen microbial contribution to reduction of particle size and to evaluate the influence of particle size of various feeds on their in situ rates of protein and dry matter degradation in the rumen of Holstein steers. MATERIALS AND METHODS
Trial 1
Animals and Diet. Three mature Holstein steers averaging 660 kg in weight were fed ad libitum throughout the trial a diet that contained 50.0% concentrate, 37.5% corn silage, and 12.5% alfalfa-grass hay on a dry matter basis. Composition of the concentrate mixture is in Table 1. Steers were fed twice daily at 0800 and 1600 h. They were adapted to the diet and feeding schedule for at least 2 wk prior to initiation of the experiment. Feeds and Particle Size. Wheat bran, linseed meal, cottonseed meal, soybean meal, and soybean meal treated with .3% formaldehyde were used in the in situ incubations. Dry matter was determined for all feeds and particle size fractions. Particle size distribution of the feeds was estimated by a dry sieving technique (21). For each feed, fractions were collected that remained on screens of 1180, 600, 300, and 150 /a pore sizes. In Situ Incubations. Treatments for which particle size reduction was measured consisted of either the complete (unseparated) feeds or the four particle size fractions from an individual feed. A 20-g sample of each complete feed or particle size fraction was placed in polyester bags 30 cm by 17 cm with a 70 # median pore size and incubated in the rumen. The complete feed and the four fractions of the same feed that differed in particle size were incubated in the rumen of all three steers on a given experimental day. Bags containing the feed were placed in the rumen at 0800 h and incubated for 12 h. Upon removal from the rumen, bags were placed in ice water and rinsed in cold water until the water leaving the bags was clear. Feed particles then were removed from the bags, dried at 55°C, and weighed. All postincubation samples were resieved for estimation of particle size. Statistical Analyses. Statistical analyses were by the Statistical Analysis System Journal of Dairy Science Vol. 65, No. 6, 1982
TABLE 1. Composition of concentrate mixture fed to dairy steers as a constant proportion of the total diet. 1 Ingredient
(%)2
Ground corn grain Soybean meal (53% CP)3 Formaldehyde-treated (.3%) soybean meal (49% CP) Cottonseed meal (42% CP) Linseed meal (38% CP) Wheat bran (16% CP) Dicaleium phosphate Trace mineral mix
69.3 4.8 4.9 7.4 7.3 4.3 1.0 1.0
1The total diet consisted of 37.5% corn silage, 50.0% concentrate mixture, and 12.5% alfalfa-grass hay on a dry matter basis. 2Dry matter. 3CP, crude protein.
(SAS Institute, Inc., Raleigh, NC). Simple univariate descriptive statistics and general linear models were used. When main effects were significant (P<.05), means were tested by Duncan's multiple range test. Trial 2
Animals and Diet. Two mature Holstein steers were fed the diet described in Table 1. They were fed twice daily at 0430 and 1630 h all of the feed they would consume. The animals were adapted to the diet and feeding regimen for at least 2 wk prior to initiation of the experiment. Feeds and Particle Size. The five feeds were wheat bran, linseed meal, soybean meal, cottonseed meal, and soybean meal treated with .3% formaldehyde. The particle size distribution of the feeds was estimated by the dry sieving technique described by Smith and Waldo (19), and results were expressed as the mean particle size and log standard deviation as described by Waldo et al. (21). For each feed, fractions were collected that were retained on screens with 1180, 600, 300, and 150 g pore sizes. Dry matter (55°C) and nitrogen (Kjeldahl) were determined on all feeds for each particle size. In Vitro Incubations. A l-g sample of each feed, for each particle size, was placed in an individual polyester bag that was 12.5 by 7.5 cm with a 70 /a median pore size. Samples
PARTICLE SIZE AND RUMINAL DEGRADATION were incubated in duplicate at room temperature in distilled water for 30 min. After incubation, bags were rinsed in cold water until the water leaving the bags was clear. Samples were • o . dried at 55 C, weighed, and analyzed for mtrogen (Kjeldahl). In Situ Incubations. Polyester bags approximately 12.5 by 7.5 cm with a 70/a median pore size containing 1 g of feed were used for in situ ruminal incubations. All ruminal incubations were initiated just prior to the 0430 h feeding and lasted for 1, 2, 4, 8, 12, and 24 h. On each of the 12 experimental days, samples of each feed from all particle size fractions, each unseparated feed, and reference samples were placed in the rumen of the steers. The six incubation times were assigned randomly to each of the steers for each experimental day. Thus, the same type of feed samples were incubated daily with only incubation time being changed. Each incubation time was replicated for each steer. Reference samples were a composite of the five experimental feeds. Reference samples were treated similarly to the other samples except they were incubated for 2 and 12 h on each of the 12 experimental days. Upon removal from the rumen bags were placed in ice water and then rinsed, dried, weighed, and analyzed for dry matter and nitrogen as described. Statistical Analyses. Statistical analyses were by the Statistical Analysis System (SAS Institute, Inc., Raleigh, NC), an integrated computer statistical analysis package. Autoregression, general linear models which used the least squares principle to fit a fixed-effects model, and simple univariate descriptive statistics were used. When main effects were significant (P<.05), means were tested by Duncan's multiple range test. Lack of fit tests were run on all regressions (5). Homogeneity of regression slopes also was tested (20).
ruminal incubation because of conglomeration of individual feed particles during drying. Particle size distributions of wheat bran and formaldehyde-treated soybean meal are in Figure 1. A plot of cumulative weight oversize as a percentage of the total sample dry matter against the log of particle size allows the particle size distribution to be described by fitting a linear regression to the data. From this equation the mean particle size (particle diameter at 50% probability) and log10 standard deviation (shape of the distribution) were estimated (1). Mean particle sizes (/1) were 721 and 701, and logt0 standard deviations were .243 and .315 for wheat bran and formaldehyde-treated soybean meal. After 12-h of incubation in the rumen, mean particle size of wheat bran was 605 /a. This is a 16% reduction in mean particle size and indicates the potential for reduction of particle size in the rumen. This is a minimal estimate, because small particles may have escaped from the polyester bags. Escape of small particles from the bag would increase mean particle size and underestimate particle
99.9
\\
99 95 w
• 4
R ESU L T S A N D D I S C U S S l O N
The ration fed contained 17.2% crude protein on a dry matter basis. The mean daily intake of dry matter for the three steers was 14.1 kg. Data for linseed meal, soybean meal, and cottonseed meal have been omitted because they could not be separated reliably by sieving after
\~ 7
3
Trial 1
965
.i WHEATBRAN ~ Y=-4.115X¢"/6.762
~.0
~
-
,3% FORMALDEHYDE TREATEDSOYBEANMEAL Y=- 3.176X'~14.038
\~
.
-"\\
x-----x
"
x~~`
.95
2
,.5 ~
I
1.0
I
-
I
3.0
2£) LOG PARTICLE SIZE (Io9 ~)
3.1
I
4D
~.o=
Figure 1. Particle size distribution of wheat bran and soybean meal with a probit conversion of the cumulative weight percent oversize versus log particle size (~).. Journal of Dairy Science Vol. 65, No. 6, 1982
966
EHLE ET AL.
size reduction. Particle size reduction of formaldehyde-treated soybean meal containing a mixture of all particle' sizes could n o t be estimated because of the extreme variation upon resieving after 12 h of ruminal incubation. Prior to resieving individual postincubation samples, various particle sizes from original feeds were resieved to correct for particle size reduction that occurred during the resieving process. This occurred while the feed particles were shaken on the various screens. Data for particle size reduction after a 12-h rumen incubation are in Table 2. Although the data base is limited (2 feeds with four sizes each) results indicate substantial ruminal reduction of particle size. Particle size reduction was greatest for large particles and decreased as particle size decreased. Particle size reduction for soybean meal samples of various particle sizes was minimal because the meal had been treated with .3% formaldehyde by weight which inhibited its degradation. The steer in which the samples were incubated or the day on which the incubation took place had no significant effect on reduction of particle size. The decrease in particle size in this trial cannot be attributed to rumination. With the polyester bag in situ system, reduction of particle size only can be attributed to action of tureen
microbes, solubilization, and perhaps physical effects of rumen contractions. Gill et al. (7) noted little change in rate of swallowing, rate of jaw movements, average size of swallowed particles, and size of boluses when either T i m o t h y or Italian ryegrass hay was fed to cows or when hay intake b y the cows was increased 50%. As hay intake was increased, Ho Bae et al. (8) observed significant increases in rumination time, number of chews, and number of boluses regurgitated by sheep. These researchers also showed that as hay intake increased there was a linear decline in the number of chews per unit of cell wall intake. Similar studies by Pearce (13) indicated that this latter response may reflect the increasing importance of microbial fermentation in particle size breakdown. If cow and sheep data are comparable, then estimates for microbial particle size reduction in our experiment might be considered as maximum because the steers were fed ad libiturn, and as feed intake increases, chews per unit of cell wall content decline, which would tend to maximize the percentage of particle size reduction attributed to microbes. In addition to rumination and mastication, microbial action is of major importance in reducing particle size of some feedstuffs in ruminants. Studies with a broader range of feed-
TABLE 2. Particle size reduction of wheat bran and formaldehyde-treated soybean meal during a 12-h incubation in the rumen of Holstein steers) Particle size2 (p) 1180
600
72.3 10.4
Wheat bran Control3 Corrected 4
61.9a x 2.2
Soybean meals Control3 Corrected 4
29.6 3.5 26.1 a -+ 1.5
300
150
21.5
8.1
7.2
12.5
10.0
7.5
-1.9 c -+ .9
--.3c -* 1.1
9.0 b -+.8 17.3
4.0 13.3b +- 1.0
10.2
2.5 7.7c ± 1.5
a,b,CMeans with different superscripts in the same row differ (P<.05). l Percent of sample that falls below original screen size. Refers to the pore size of the screen on which the feed samples were retained. ~Particle size reduction of feed samples due to resieving (unincubated samples). 4Means ± SE corrected for weight decrease by the resieving process. sTreated with .3% formaldehyde. Journal of Dairy Science Vol. 65, No. 6, 1982
13.0
8.5 4.5 c -+ .8
PARTICLE SIZE AND RUMINAL DEGRADATION stuffs and incubation times are needed to elucidate further the overall mechanism of particle size reduction. Trial 2
This diet contained 17.2% crude protein, on a dry matter basis. Steers averaged 660 kg bodyweight, and they consumed 17.0 kg of dry matter daily. All animals remained in excellent health throughout the experiment. Mean particle size, log10 standard deviation, and correlation coefficient of the regression line for the feeds are in Table 3. Mean particle sizes of the five feeds formed two particle size groups. Linseed and cottonseed meals had smaller mean particle sizes than the other three feeds. The high correlation coefficients of the regression lines indicate these data conform to the log normal distribution. Dry matter and nitrogen disappearance from the samples soaked in distilled water are in Table 4. Changing particle size (surface area) did not elicit a uniform response in dry matter disappearance from the various feeds when they were soaked in distilled water. Dry matter disappearance was increased as particle size was decreased for wheat bran and cottonseed meal, but linseed meal showed a trend for increased disappearance as particle size increased. Dafaalla and Kay (4), working with timothyryegrass hay of various particle sizes, also noted increased dry matter losses as particle size decreased. Disappearance of dry matter from nontreated or formaldehyde-treated soybean meal was not affected by particle size. Particle size also appeared to have no systematic effect on nitrogen disappearance from the feeds. Disappearance of nitrogen was related only to the quantity of nitrogen solubilized in distilled water, and there was no significant difference within any of the feeds attributed to particle size except for wheat bran. Thus, altering particle size (surface area) of most feeds used in this study did not consistently change nitrogen solubility. These data also indicate that dry matter and nitrogen disappearance during short incubation times in the rumen is probably not from direct microbial degradation, because substantial quantities of both dry matter and nitrogen disappeared from the bag because of solubilization, even under adverse (cold water) experimental conditions.
967
Statistical analysis of ruminal incubation of the various feeds indicated that variation attributable to steer or day of incubation was not significant (P>.05). Therefore, covariance analysis was not necessary, and reference samples were not used. Nitrogen and dry matter disappearance after timed incubation in the rumen was analyzed statistically to ascertain the time at which degradation significantly differed from when feeds were soaked in distilled water. The first times at which nitrogen and dry matter disappearance differed (P<.05) from when feeds were soaked in distilled water are reported in Tables 5 and 6 as "start" times. Subsequent data points were used to calculate rates of protein or dry matter degradation. Therefore, the degradation rates are not influenced greatly by solubilization of feed components during early stages of incubation. Protein and dry matter degradation data were transformed to natural logarithms, and regression lines were fit to the data points. All regressions, regardless of the standard deviation or correlation coefficient, were tested for significant lack of fit (5). When lack of fit was significant (P<.05) for a regression line, a secondary degradation rate was assumed. Therefore data for the last incubation time were omitted sequentially until a nonsignificant (P>.05) lack of fit for the regression was obtained. These times are shown as "stop" time in Tables 5 and 6. This was done to obtain estimates of primary degradation rates. Because of infrequent sampling during later stages of incubation, it was not possible to determine many of the secondary degradation rates. Particle size did not account for a significant (P> .05) proportion of variation in nitrogen disappearance during incubation of feeds in the rumen. Therefore, nitrogen disappearance data used to estimate degradation rates were pooled across particle sizes. The reason for lack of effect of particle size on nitrogen degradation is not clear. Perhaps an unequal attachment of bacteria to feed particles of different sizes resulted in a varied nitrogen contamination of microbial origin. The rate of crude protein degradation in each feed sample, pooled across particle sizes, is in Table 5. Slopes of these regression lines demonstrate dramatically different degradation rates for protein in the various feeds. These Journal of Dairy Science Vol. 65, No. 6, 1982
968
EHLE ET AL.
T A B L E 3. Mean particle sizes, log, o standard deviations, and correlation coefficients o f regression lines for the various feeds. Mean particle size
Sample
Logto standard deviation
r
.33 .31 .24 .37 .24
.92 .x)5 .98 .95 .97
(~) Soybean meal Formaldehyde treated soybean meal Wheat bran Cottonseed meal Linseed meal
750 701 721 429 403
T A B L E 4. Effect of a 30-rain incubation in distilled water on dry m a t t e r and nitrogen removal f r o m feed sampies of various particle sizes.
Sample
Particle size ~
Dry m a t t e r disappearance
Nitrogen disappearance
(%) (#)
~
SE
R
SE
Wheat bran
Unseparated 1180 600 300 150
23 b 14 c 18 bc 22 b 30 a
1 0 2 0 3
14 ab 19 bc 17 b 25 c 9a
3 2 1 0 1
Soybean meal
Unseparated 1180 600 300 150
27 30 27 29 26
0 3 1 0 2
17 13 4 8 13
2 6 2 1 4
Soybean meal treated with .3% formaldehyde
Unseparated 1180 600 3OO 150
23 45 23 22 21
1 19 0 0 0
2 1 3 10 5
1 0 0 8 2
Linseed meal
Unseparated 1180 600 300 150
20 25 21 14 12
5 0 2 6 6
20 21 18 10 15
2 0 4 0 9
C o t t o n s e e d meal
Unseparated 1180 60O 300 150
14 c 10 e 13 d 17 b 20 a
0 0 0 0 0
3 8 9 5 8
0 3 6 1 2
a ' b ' c ' d ' e M e a n s in the same c o l u m n for a given feed with different superscripts differ (P<.05). 1 Unseparated refers to the feed samples as received; 1180 ~, the portion of the sieved sample retained on the 1180 ~ pore size sieve; 6 0 0 #, the portion of the sieved sample that passed t h r o u g h the 1180 # sieve and rem a i n e d on the 6 0 0 # pore size sieve; 300 #, the portion o f the sieved sample that passed through the 600 # sieve and remained on the 300 t~ pore size sieve; 150 ~, t h e portion of t h e sieved sample t h a t passed through the 300 # sieve and remained on t h e 150/~ pore size sieve.
Journal o f Dairy Science Vol. 65, No. 6, 1982
PARTICLE SIZE AND RUMINAL DEGRADATION
96 9
TABLE 5. Slopes and intercepts from regression lines of natural logarithms of percent nitrogen in feeds remaining in polyester bags incubated in the tumen for various times.
Sample
Start time *
Wheat bran Soybean meal Formaldehyde-treated soybean meal Linseed meal Cottonseed meal
2 4 12 1 1
Stop time 1
b Slope2
a Intercept2
12 24 24 24 24
--. 1359 --. 1043 -.0120 --.0657 --.0270
4.471
(h) 4.960 4.689 4.255 4.470
1Start time is the first ruminal incubation time (h) used to calculate the regression line; stop time is the last ruminal incubation time (h) used to calculate the regression line. 2All regressions were highly significant (P<.O01) with nonsignificant (P>.05)lack of fit except formaldehyde-treated soybean meal, which could not be tested for lack of fit (see discussion). Regression equations are in the form YI = a + bx, where x/l -- natural logarithm of percent nitrogen remaining in bag; a = intercept, b = slope; and x -- time of incubation (h). Percent nitrogen disappearance (Y2) can be calculated using the following equation, Y2 = 100 - e¥1.
regressions were all highly significant and had no significant lack of fit, except for formaldehyde-treated soybean meal where not enough degrees of freedom remained to test for lack of fit. Test for homogeneity of regression slopes between soybean meal and formaldehydetreated soybean meal indicated a highly significant difference (P<.001), as would be expected, because treating the soybean meal with formaldehyde decreases the degradation rate of protein. Degradation rates for protein were loglinear from the start until 24 h of incubation for all feeds except wheat bran. Its degradation rate for protein was slower from 12 to 24 h of incubation than during the primary log-linear degradation rate calculated from 2 to 12 h of incubation. Altering particle size did not affect significandy degradation rate of crude protein in these feeds. Netemeyer et al. (12) reported that fineness of grind of soybean meal did not affect significantly the amount of nonammonia nitrogen that reached the abomasum; however, there was a trend for more n o n a m m o n i a nitrogen to reach the abomasum when the fine particle size soybean meal was fed to cattle. Only if reducing particle size increases the rate of passage of dietary protein without increasing the degradation rate or increasing microbial protein synthesis will the quantity of nonammonia nitrogen reaching the abomasum be
increased. Data for dry matter degradation rates are in Table 6. All regressions were highly significant (P<.001) and had no significant lack of fit, except for the unseparated cottonseed meal sample. For the latter sample, significant tack of fit precluded estimation of a primary degradation rate. Lack of fit was significant (P<.05) for all wheat bran and most linseed and cottonseed meal samples when all incubation times were used in calculating regressions. This indicated secondary rates of degradation. However, except for the unseparated cottonseed meal sample, it was not possible to calculate secondary degradation rates due to infrequent sampling intervals for the later incubation times. For the unseparated cottonseed meal sample, the last three incubation times were used to calculate a secondary rate even though significant (P<.05) lack of fit remained. Tests for homogeneity of regression slopes for particle size within each feed sample were conducted. There were no significant (P>.05) differences in primary degradation rates (slopes) attributable to particle size for soybean meal, formaldehyde-treated soybean meal, cottonseed meal, or wheat bran (Table 6). However, except for untreated soybean meal, trends indicated that feeds of 150 /~ particle size were degraded faster than feeds of 300 Journal of Dairy Science Vol. 65, No. 6, 1982
97O
EHLE ET AL.
TABLE 6. Slopes and intercepts from regression lines of natural logarithms of percent dry matter in feeds disappearing from polyester bags incubated in the rumen for various times.
Sample
Particle size
Stag time 1
(U)
..
Stop time I
b Slope 2
a Intercept z
(h)
Wheatbran
Unseparated 1180 600 300 150
2 2 2 2 2
8 12 8 12 12
.7062 .0702 .0848 .0545 .1080
3.4195 3.3389 3.3496 3.5106 3.2615
Soybean meal
Unseparated 1180 600 300 150
2 2 2 2 2
24 24 24 24 24
.0425 .0408 .0454 .0475 .0436
3.4506 3.4227 3.4293 3.4558 3.5296
Formaldehyde~ea~d soybean meal
Unseparated 1180 600 300 150
1 1 1 1 1
24 24 24 24 24
.0346 .0377 .0401 .0366 .0377
3.0710 3.1310 2.9631 2.9455 2.9809
Linseed meal
Unseparated 1180 600 300 150
1 1 1 1 1
12 12 24 12 8
.0625 .0710 .0391 .0656 .0988
3.4343 3.2637 3.4492 3.3795 3.4062
Cottonseed meal
Unseparated 3 1180 600 300 150
8 2 2 2 2
24 12 8 12 8
.0253 .0847 .1038 .0615 .0844
3.1347 2.2827 2.5167 3.2076 3.1760
a Start time is the first ruminal incubation time (h) used to calculate the regression line; stop time is the last ruminal incubation time (h) used to calculate the regression line. Start time to stop time was used to calculate the primary degradation rate. Stop time to 24 h of incubation was used to calculate secondary degradation rate. 2All regressions were highly significant (P<.001) with nonsignificant (.°>.05) lack of fit. Regression equations are in the form Y = a + bx, where Y -- natural logarithm of percent dry matter disappearing from bag; a -intercept; b = slope; and x --- time of incubation (h). 3Secondary regression calculated from 8 to 24 h of incubation. Significant lack of fit (P<.05) remains.
particle size. D i f f e r e n c e s in d e g r a d a t i o n r a t e s were s i g n i f i c a n t ( P < . 0 0 1 ) a m o n g various p a r t i cle size samples o f linseed meal. A c o m p a r i s o n o f u n s e p a r a t e d feed sampies s h o w e d t h a t rates o f d e g r a d a t i o n f o r d r y m a t t e r a n d c r u d e p r o t e i n d i f f e r e d a m o n g feeds. F o r m a l d e h y d e t r e a t m e n t o f s o y b e a n m e a l decreased d e g r a d a t i o n r a t e o f d r y m a t t e r a n d c r u d e p r o t e i n c o m p a r e d t o t h e u n t r e a t e d soyb e a n m e a l s a m p l e (Tables 5 a n d 6). H o w e v e r , d e p r e s s i o n in d r y m a t t e r d e g r a d a t i o n was small
Journal of Dairy Science Vol. 65, No. 6, 1982
c o m p a r e d t o d e p r e s s i o n in c r u d e p r o t e i n degrad a t i o n . T h e r e was n o c o n s i s t e n t p a t t e r n in inf l u e n c e o f particle size o n rates o f d r y m a t t e r a n d c r u d e p r o t e i n d e g r a d a t i o n w i t h i n a feed i n d i c a t i n g t h e i m p o r t a n c e o f o t h e r f a c t o r s such as c h e m i c a l c o m p o s i t i o n . I n v e s t i g a t i o n s are needed to delineate factors that affect rate and e x t e n t of f e e d d e g r a d a t i o n in t h e r u m e n . ACKNOWLEDGMENT The authors
t h a n k H u b b a r d Milling C o m -
PARTICLE SIZE AND RUMINAL DEGRADATION
p a n y for s u p p l y i n g t h e f o r m a l d e h y d e - t r e a t e d s o y b e a n meal. REFERENCES
1 ASAE Standard: ASAE $319. 1975. Method of determining and expressing fineness of feed materials by sieving. Page 436 in Agric. Eng. Yearbook. 2 Balch, C. C., and R. C. Campling. 1962. Regulation of voluntary food intake in ruminants. Nutr. Abstr. Rev. 32:669. 3 Blaxter, K. L., N. McC. Graham, and F. W. Wainman. 1956. Some observations on the digestibility of food by sheep, and on related problems. Br. J. Nutr. 10:69. 4 Dafaalla, B.F.M., and R.N.B. Kay. 1980. Effect of hay particle size on retention time, dry matter digestibility and rumen pH in sheep. Proc. Nutr. Soc. 39:71A. 5 Draper, N. R., and H. Smith. 1966. Applied regression analysis. John Wiley and Sons, Inc., New York, NY. 6 Evans, E. W., G. R. Pearce, J. Burnett, and S. L. Pillinger. 1973. Changes in some physical characteristics of the digesta in the reticulorumen of cows fed once daily. Br. J. Nutr. 29:357. 7 Gill, J., R. C. Campling, and D. R. Westgarth. 1966. A study of chewing during eating in the cow. Br. J. Nutr. 20:13. 8 Ho Bae, D., J. G. Welch, and A. M. Smith. 1979. Forage intake and rumination by sheep. J. Anim. Sci. 49:1292. 9 Hogan, J. P., and R. H. Weston. 1967. The digestion of chopped and ground roughages by sheep. II. The digestion of nitrogen and some carbohydrate fractions in the stomach and intestines. Australian J. Agric. Res. 18:803. 10 King, K. W. 1966. Enzymatic degradation of crystalline hydrocellulose. Biochem. Biophys. Res. Comm. 24:295. 11 Mertens, D. R., and L. O. Ely. 1979. A dynamic model of fiber digestion and passage in the ruminant for evaluating forage quality. J. Anim. Sci.
971
49:1085. 12 Netemeyer, D. T., L. J. Bush, and F. N. Owens. 1980. Effect of particle size of soybean meal on protein utilization in steers and lactating cows. J. Dairy Sci. 63:574. 13 Pearce, G. R. 1965. Rumination in sheep. II. The circadian pattern of rumination. Australian J. Agric. Res. 16:635. 14 Pearce, G. R. 1967. Changes in particle size in the reticulorumen of sheep. Australian J. Agric. Res. 18:119. 15 Pearce, G. R., and J. R. Moir. 1964. Rumination in sheep. I. The influence of rumination and grinding upon the passage and digestion of food. Australian J. Agric. Res. 15:635. 16 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. Camb. 94:275. 17 Reid, C.S.W., M. J. Ulyatt, and J. A. Monro. 1977. The physical breakdown of feed during digestion in the rumen. Proc. New Zealand Soc. Anim. Prod. 37:173. 18 Robles, A. Y., R. L. Belyea, F. A. Martz, and M. F. Weiss. 1980. Effect of particle size upon digestible cell wall and rate of in vitro digestion of alfalfa and orchard-grass forages. J. Anim. Sci. 51: 783. 19 Smith, L. W., and D. R. Waldo. 1969. Method for sizing forage cell wall particles. J. Dairy Sci. 52: 2051. 20 Steel, R.G.D., and J. H. Torrie. 1960. Principles and procedures of statistics. McGraw Hill Book Co., Inc., New York, NY. 21 Waldo, D. R., L. W. Smith, E. L. Cox, B. T. Weinland, and H. L. Lucas, Jr. 1971. Logarithmic normai distribution for description of sieved forage materials. J. Dairy Sci. 54:1465. 22 Wealdey, D. C., F. N. Owens, D. G. Heath, and B. J. Shockey. 1977. Particle size and soybean meal value for ruminants. Page 268 in Program 69th Annu. Mtg. Am. Soc. Anim. Sci. 23 Welch, J. G. 1967. Appetite control in sheep by indigestible fibers. J. Anim. Sci. 26:849.
Journal of Dairy Science Vol. 65, No. 6, 1982
ABSTRACT
The contribution of rumen microbes to particle size reduction was examined and the influence of particle size on in situ degradation rates of crude protein and dry matter in the rumen of dairy steers fed ad libitum was determined. In addition to rumination and mastication, microbial action is of major importance in particle size reduction of some feedstuffs in ruminants. Rates of crude protein degradation differed among feedstuffs but were not significantly affected by particle size within feed samples. Primary and secondary rates of dry matter degradation were observed for wheat bran, linseed meal, and cottonseed meal. Soybean meal and formaldehyde-treated soybean meal data displayed only primary degradation rates for dry matter. Differences in primary rates of dry matter degradation among various particle sizes were significant only for linseed meal. Absence of a consistent pattern to the influence of particle size on rates of dry matter and crude protein degradation within a feed indicates the importance of other factors. INTRODUCTION
Particle size of feedstuffs consumed by ruminants plays an important role in the digestive process. As particle size of feed decreases,
Received March 26, 1981. t Supported in part by the Illinois Agricultural Experiment Station and HEW PHS FD 00849. 2Deparmaent of Animal Science, University of MinnesOta, St. Paul, MN 55108. 1982 J Dairy Sci 65:963-971
retention time in the rumen will decrease (3, 9, 14, 15, 16). Therefore, the potential for escape of feed particles from the rumen should be inversely related to particle size of the feed consumed. The rate of feed degradation in the rumen also must be considered because this can affect the amount of feed that passes from the rumen (11). Major factors governing particle size reduction are mastication, rumination, microbial fermentation, and rumen contractions (6, 15, 17). Although rumination generally has been considered most important in particle size breakdown (2, 15, 23), it is difficult to determine the contribution of each factor to the overall process of reduction. There is a lack of quantitative information describing the effects of particle size on feed consumed by ruminants and the rate and extent of breakdown in the rumen of feeds differing in particle size on animal performance (10, 18). Changing the size of particles consumed or altering the rate and extent of breakdown of feed particles in the rumen may influence production by ruminant animals via altering rate of passage of solids from the rumen as well as dry matter intake. Data of Weakley et al. (22) indicate that protein and dry matter in soybean meal that is coarse (2000 /a) is degraded less than finer size (520/a) material. They suggested that the coarse soybean meal had a greater potential to escape fermentation and pass to the small intestine than did the finer material. Subsequent studies with coarse (2400 /a) or fine (250/a) soybean meal produced no significant differences in nonammonia nitrogen flow to the abomasum or in milk production (12). Feeding the fine (250/a) soybean meal, however, did result in a trend toward greater nonammonia nitrogen flow to the abornasum compared to feeding the coarse (2400 /a) soybean meal.
963
964
EHLE ET AL.
We have used the in situ polyester bag technique to estimate the rumen microbial contribution to reduction of particle size and to evaluate the influence of particle size of various feeds on their in situ rates of protein and dry matter degradation in the rumen of Holstein steers. MATERIALS AND METHODS
Trial 1
Animals and Diet. Three mature Holstein steers averaging 660 kg in weight were fed ad libitum throughout the trial a diet that contained 50.0% concentrate, 37.5% corn silage, and 12.5% alfalfa-grass hay on a dry matter basis. Composition of the concentrate mixture is in Table 1. Steers were fed twice daily at 0800 and 1600 h. They were adapted to the diet and feeding schedule for at least 2 wk prior to initiation of the experiment. Feeds and Particle Size. Wheat bran, linseed meal, cottonseed meal, soybean meal, and soybean meal treated with .3% formaldehyde were used in the in situ incubations. Dry matter was determined for all feeds and particle size fractions. Particle size distribution of the feeds was estimated by a dry sieving technique (21). For each feed, fractions were collected that remained on screens of 1180, 600, 300, and 150 /a pore sizes. In Situ Incubations. Treatments for which particle size reduction was measured consisted of either the complete (unseparated) feeds or the four particle size fractions from an individual feed. A 20-g sample of each complete feed or particle size fraction was placed in polyester bags 30 cm by 17 cm with a 70 # median pore size and incubated in the rumen. The complete feed and the four fractions of the same feed that differed in particle size were incubated in the rumen of all three steers on a given experimental day. Bags containing the feed were placed in the rumen at 0800 h and incubated for 12 h. Upon removal from the rumen, bags were placed in ice water and rinsed in cold water until the water leaving the bags was clear. Feed particles then were removed from the bags, dried at 55°C, and weighed. All postincubation samples were resieved for estimation of particle size. Statistical Analyses. Statistical analyses were by the Statistical Analysis System Journal of Dairy Science Vol. 65, No. 6, 1982
TABLE 1. Composition of concentrate mixture fed to dairy steers as a constant proportion of the total diet. 1 Ingredient
(%)2
Ground corn grain Soybean meal (53% CP)3 Formaldehyde-treated (.3%) soybean meal (49% CP) Cottonseed meal (42% CP) Linseed meal (38% CP) Wheat bran (16% CP) Dicaleium phosphate Trace mineral mix
69.3 4.8 4.9 7.4 7.3 4.3 1.0 1.0
1The total diet consisted of 37.5% corn silage, 50.0% concentrate mixture, and 12.5% alfalfa-grass hay on a dry matter basis. 2Dry matter. 3CP, crude protein.
(SAS Institute, Inc., Raleigh, NC). Simple univariate descriptive statistics and general linear models were used. When main effects were significant (P<.05), means were tested by Duncan's multiple range test. Trial 2
Animals and Diet. Two mature Holstein steers were fed the diet described in Table 1. They were fed twice daily at 0430 and 1630 h all of the feed they would consume. The animals were adapted to the diet and feeding regimen for at least 2 wk prior to initiation of the experiment. Feeds and Particle Size. The five feeds were wheat bran, linseed meal, soybean meal, cottonseed meal, and soybean meal treated with .3% formaldehyde. The particle size distribution of the feeds was estimated by the dry sieving technique described by Smith and Waldo (19), and results were expressed as the mean particle size and log standard deviation as described by Waldo et al. (21). For each feed, fractions were collected that were retained on screens with 1180, 600, 300, and 150 g pore sizes. Dry matter (55°C) and nitrogen (Kjeldahl) were determined on all feeds for each particle size. In Vitro Incubations. A l-g sample of each feed, for each particle size, was placed in an individual polyester bag that was 12.5 by 7.5 cm with a 70 /a median pore size. Samples
PARTICLE SIZE AND RUMINAL DEGRADATION were incubated in duplicate at room temperature in distilled water for 30 min. After incubation, bags were rinsed in cold water until the water leaving the bags was clear. Samples were • o . dried at 55 C, weighed, and analyzed for mtrogen (Kjeldahl). In Situ Incubations. Polyester bags approximately 12.5 by 7.5 cm with a 70/a median pore size containing 1 g of feed were used for in situ ruminal incubations. All ruminal incubations were initiated just prior to the 0430 h feeding and lasted for 1, 2, 4, 8, 12, and 24 h. On each of the 12 experimental days, samples of each feed from all particle size fractions, each unseparated feed, and reference samples were placed in the rumen of the steers. The six incubation times were assigned randomly to each of the steers for each experimental day. Thus, the same type of feed samples were incubated daily with only incubation time being changed. Each incubation time was replicated for each steer. Reference samples were a composite of the five experimental feeds. Reference samples were treated similarly to the other samples except they were incubated for 2 and 12 h on each of the 12 experimental days. Upon removal from the rumen bags were placed in ice water and then rinsed, dried, weighed, and analyzed for dry matter and nitrogen as described. Statistical Analyses. Statistical analyses were by the Statistical Analysis System (SAS Institute, Inc., Raleigh, NC), an integrated computer statistical analysis package. Autoregression, general linear models which used the least squares principle to fit a fixed-effects model, and simple univariate descriptive statistics were used. When main effects were significant (P<.05), means were tested by Duncan's multiple range test. Lack of fit tests were run on all regressions (5). Homogeneity of regression slopes also was tested (20).
ruminal incubation because of conglomeration of individual feed particles during drying. Particle size distributions of wheat bran and formaldehyde-treated soybean meal are in Figure 1. A plot of cumulative weight oversize as a percentage of the total sample dry matter against the log of particle size allows the particle size distribution to be described by fitting a linear regression to the data. From this equation the mean particle size (particle diameter at 50% probability) and log10 standard deviation (shape of the distribution) were estimated (1). Mean particle sizes (/1) were 721 and 701, and logt0 standard deviations were .243 and .315 for wheat bran and formaldehyde-treated soybean meal. After 12-h of incubation in the rumen, mean particle size of wheat bran was 605 /a. This is a 16% reduction in mean particle size and indicates the potential for reduction of particle size in the rumen. This is a minimal estimate, because small particles may have escaped from the polyester bags. Escape of small particles from the bag would increase mean particle size and underestimate particle
99.9
\\
99 95 w
• 4
R ESU L T S A N D D I S C U S S l O N
The ration fed contained 17.2% crude protein on a dry matter basis. The mean daily intake of dry matter for the three steers was 14.1 kg. Data for linseed meal, soybean meal, and cottonseed meal have been omitted because they could not be separated reliably by sieving after
\~ 7
3
Trial 1
965
.i WHEATBRAN ~ Y=-4.115X¢"/6.762
~.0
~
-
,3% FORMALDEHYDE TREATEDSOYBEANMEAL Y=- 3.176X'~14.038
\~
.
-"\\
x-----x
"
x~~`
.95
2
,.5 ~
I
1.0
I
-
I
3.0
2£) LOG PARTICLE SIZE (Io9 ~)
3.1
I
4D
~.o=
Figure 1. Particle size distribution of wheat bran and soybean meal with a probit conversion of the cumulative weight percent oversize versus log particle size (~).. Journal of Dairy Science Vol. 65, No. 6, 1982
966
EHLE ET AL.
size reduction. Particle size reduction of formaldehyde-treated soybean meal containing a mixture of all particle' sizes could n o t be estimated because of the extreme variation upon resieving after 12 h of ruminal incubation. Prior to resieving individual postincubation samples, various particle sizes from original feeds were resieved to correct for particle size reduction that occurred during the resieving process. This occurred while the feed particles were shaken on the various screens. Data for particle size reduction after a 12-h rumen incubation are in Table 2. Although the data base is limited (2 feeds with four sizes each) results indicate substantial ruminal reduction of particle size. Particle size reduction was greatest for large particles and decreased as particle size decreased. Particle size reduction for soybean meal samples of various particle sizes was minimal because the meal had been treated with .3% formaldehyde by weight which inhibited its degradation. The steer in which the samples were incubated or the day on which the incubation took place had no significant effect on reduction of particle size. The decrease in particle size in this trial cannot be attributed to rumination. With the polyester bag in situ system, reduction of particle size only can be attributed to action of tureen
microbes, solubilization, and perhaps physical effects of rumen contractions. Gill et al. (7) noted little change in rate of swallowing, rate of jaw movements, average size of swallowed particles, and size of boluses when either T i m o t h y or Italian ryegrass hay was fed to cows or when hay intake b y the cows was increased 50%. As hay intake was increased, Ho Bae et al. (8) observed significant increases in rumination time, number of chews, and number of boluses regurgitated by sheep. These researchers also showed that as hay intake increased there was a linear decline in the number of chews per unit of cell wall intake. Similar studies by Pearce (13) indicated that this latter response may reflect the increasing importance of microbial fermentation in particle size breakdown. If cow and sheep data are comparable, then estimates for microbial particle size reduction in our experiment might be considered as maximum because the steers were fed ad libiturn, and as feed intake increases, chews per unit of cell wall content decline, which would tend to maximize the percentage of particle size reduction attributed to microbes. In addition to rumination and mastication, microbial action is of major importance in reducing particle size of some feedstuffs in ruminants. Studies with a broader range of feed-
TABLE 2. Particle size reduction of wheat bran and formaldehyde-treated soybean meal during a 12-h incubation in the rumen of Holstein steers) Particle size2 (p) 1180
600
72.3 10.4
Wheat bran Control3 Corrected 4
61.9a x 2.2
Soybean meals Control3 Corrected 4
29.6 3.5 26.1 a -+ 1.5
300
150
21.5
8.1
7.2
12.5
10.0
7.5
-1.9 c -+ .9
--.3c -* 1.1
9.0 b -+.8 17.3
4.0 13.3b +- 1.0
10.2
2.5 7.7c ± 1.5
a,b,CMeans with different superscripts in the same row differ (P<.05). l Percent of sample that falls below original screen size. Refers to the pore size of the screen on which the feed samples were retained. ~Particle size reduction of feed samples due to resieving (unincubated samples). 4Means ± SE corrected for weight decrease by the resieving process. sTreated with .3% formaldehyde. Journal of Dairy Science Vol. 65, No. 6, 1982
13.0
8.5 4.5 c -+ .8
PARTICLE SIZE AND RUMINAL DEGRADATION stuffs and incubation times are needed to elucidate further the overall mechanism of particle size reduction. Trial 2
This diet contained 17.2% crude protein, on a dry matter basis. Steers averaged 660 kg bodyweight, and they consumed 17.0 kg of dry matter daily. All animals remained in excellent health throughout the experiment. Mean particle size, log10 standard deviation, and correlation coefficient of the regression line for the feeds are in Table 3. Mean particle sizes of the five feeds formed two particle size groups. Linseed and cottonseed meals had smaller mean particle sizes than the other three feeds. The high correlation coefficients of the regression lines indicate these data conform to the log normal distribution. Dry matter and nitrogen disappearance from the samples soaked in distilled water are in Table 4. Changing particle size (surface area) did not elicit a uniform response in dry matter disappearance from the various feeds when they were soaked in distilled water. Dry matter disappearance was increased as particle size was decreased for wheat bran and cottonseed meal, but linseed meal showed a trend for increased disappearance as particle size increased. Dafaalla and Kay (4), working with timothyryegrass hay of various particle sizes, also noted increased dry matter losses as particle size decreased. Disappearance of dry matter from nontreated or formaldehyde-treated soybean meal was not affected by particle size. Particle size also appeared to have no systematic effect on nitrogen disappearance from the feeds. Disappearance of nitrogen was related only to the quantity of nitrogen solubilized in distilled water, and there was no significant difference within any of the feeds attributed to particle size except for wheat bran. Thus, altering particle size (surface area) of most feeds used in this study did not consistently change nitrogen solubility. These data also indicate that dry matter and nitrogen disappearance during short incubation times in the rumen is probably not from direct microbial degradation, because substantial quantities of both dry matter and nitrogen disappeared from the bag because of solubilization, even under adverse (cold water) experimental conditions.
967
Statistical analysis of ruminal incubation of the various feeds indicated that variation attributable to steer or day of incubation was not significant (P>.05). Therefore, covariance analysis was not necessary, and reference samples were not used. Nitrogen and dry matter disappearance after timed incubation in the rumen was analyzed statistically to ascertain the time at which degradation significantly differed from when feeds were soaked in distilled water. The first times at which nitrogen and dry matter disappearance differed (P<.05) from when feeds were soaked in distilled water are reported in Tables 5 and 6 as "start" times. Subsequent data points were used to calculate rates of protein or dry matter degradation. Therefore, the degradation rates are not influenced greatly by solubilization of feed components during early stages of incubation. Protein and dry matter degradation data were transformed to natural logarithms, and regression lines were fit to the data points. All regressions, regardless of the standard deviation or correlation coefficient, were tested for significant lack of fit (5). When lack of fit was significant (P<.05) for a regression line, a secondary degradation rate was assumed. Therefore data for the last incubation time were omitted sequentially until a nonsignificant (P>.05) lack of fit for the regression was obtained. These times are shown as "stop" time in Tables 5 and 6. This was done to obtain estimates of primary degradation rates. Because of infrequent sampling during later stages of incubation, it was not possible to determine many of the secondary degradation rates. Particle size did not account for a significant (P> .05) proportion of variation in nitrogen disappearance during incubation of feeds in the rumen. Therefore, nitrogen disappearance data used to estimate degradation rates were pooled across particle sizes. The reason for lack of effect of particle size on nitrogen degradation is not clear. Perhaps an unequal attachment of bacteria to feed particles of different sizes resulted in a varied nitrogen contamination of microbial origin. The rate of crude protein degradation in each feed sample, pooled across particle sizes, is in Table 5. Slopes of these regression lines demonstrate dramatically different degradation rates for protein in the various feeds. These Journal of Dairy Science Vol. 65, No. 6, 1982
968
EHLE ET AL.
T A B L E 3. Mean particle sizes, log, o standard deviations, and correlation coefficients o f regression lines for the various feeds. Mean particle size
Sample
Logto standard deviation
r
.33 .31 .24 .37 .24
.92 .x)5 .98 .95 .97
(~) Soybean meal Formaldehyde treated soybean meal Wheat bran Cottonseed meal Linseed meal
750 701 721 429 403
T A B L E 4. Effect of a 30-rain incubation in distilled water on dry m a t t e r and nitrogen removal f r o m feed sampies of various particle sizes.
Sample
Particle size ~
Dry m a t t e r disappearance
Nitrogen disappearance
(%) (#)
~
SE
R
SE
Wheat bran
Unseparated 1180 600 300 150
23 b 14 c 18 bc 22 b 30 a
1 0 2 0 3
14 ab 19 bc 17 b 25 c 9a
3 2 1 0 1
Soybean meal
Unseparated 1180 600 300 150
27 30 27 29 26
0 3 1 0 2
17 13 4 8 13
2 6 2 1 4
Soybean meal treated with .3% formaldehyde
Unseparated 1180 600 3OO 150
23 45 23 22 21
1 19 0 0 0
2 1 3 10 5
1 0 0 8 2
Linseed meal
Unseparated 1180 600 300 150
20 25 21 14 12
5 0 2 6 6
20 21 18 10 15
2 0 4 0 9
C o t t o n s e e d meal
Unseparated 1180 60O 300 150
14 c 10 e 13 d 17 b 20 a
0 0 0 0 0
3 8 9 5 8
0 3 6 1 2
a ' b ' c ' d ' e M e a n s in the same c o l u m n for a given feed with different superscripts differ (P<.05). 1 Unseparated refers to the feed samples as received; 1180 ~, the portion of the sieved sample retained on the 1180 ~ pore size sieve; 6 0 0 #, the portion of the sieved sample that passed t h r o u g h the 1180 # sieve and rem a i n e d on the 6 0 0 # pore size sieve; 300 #, the portion o f the sieved sample that passed through the 600 # sieve and remained on the 300 t~ pore size sieve; 150 ~, t h e portion of t h e sieved sample t h a t passed through the 300 # sieve and remained on t h e 150/~ pore size sieve.
Journal o f Dairy Science Vol. 65, No. 6, 1982
PARTICLE SIZE AND RUMINAL DEGRADATION
96 9
TABLE 5. Slopes and intercepts from regression lines of natural logarithms of percent nitrogen in feeds remaining in polyester bags incubated in the tumen for various times.
Sample
Start time *
Wheat bran Soybean meal Formaldehyde-treated soybean meal Linseed meal Cottonseed meal
2 4 12 1 1
Stop time 1
b Slope2
a Intercept2
12 24 24 24 24
--. 1359 --. 1043 -.0120 --.0657 --.0270
4.471
(h) 4.960 4.689 4.255 4.470
1Start time is the first ruminal incubation time (h) used to calculate the regression line; stop time is the last ruminal incubation time (h) used to calculate the regression line. 2All regressions were highly significant (P<.O01) with nonsignificant (P>.05)lack of fit except formaldehyde-treated soybean meal, which could not be tested for lack of fit (see discussion). Regression equations are in the form YI = a + bx, where x/l -- natural logarithm of percent nitrogen remaining in bag; a = intercept, b = slope; and x -- time of incubation (h). Percent nitrogen disappearance (Y2) can be calculated using the following equation, Y2 = 100 - e¥1.
regressions were all highly significant and had no significant lack of fit, except for formaldehyde-treated soybean meal where not enough degrees of freedom remained to test for lack of fit. Test for homogeneity of regression slopes between soybean meal and formaldehydetreated soybean meal indicated a highly significant difference (P<.001), as would be expected, because treating the soybean meal with formaldehyde decreases the degradation rate of protein. Degradation rates for protein were loglinear from the start until 24 h of incubation for all feeds except wheat bran. Its degradation rate for protein was slower from 12 to 24 h of incubation than during the primary log-linear degradation rate calculated from 2 to 12 h of incubation. Altering particle size did not affect significandy degradation rate of crude protein in these feeds. Netemeyer et al. (12) reported that fineness of grind of soybean meal did not affect significantly the amount of nonammonia nitrogen that reached the abomasum; however, there was a trend for more n o n a m m o n i a nitrogen to reach the abomasum when the fine particle size soybean meal was fed to cattle. Only if reducing particle size increases the rate of passage of dietary protein without increasing the degradation rate or increasing microbial protein synthesis will the quantity of nonammonia nitrogen reaching the abomasum be
increased. Data for dry matter degradation rates are in Table 6. All regressions were highly significant (P<.001) and had no significant lack of fit, except for the unseparated cottonseed meal sample. For the latter sample, significant tack of fit precluded estimation of a primary degradation rate. Lack of fit was significant (P<.05) for all wheat bran and most linseed and cottonseed meal samples when all incubation times were used in calculating regressions. This indicated secondary rates of degradation. However, except for the unseparated cottonseed meal sample, it was not possible to calculate secondary degradation rates due to infrequent sampling intervals for the later incubation times. For the unseparated cottonseed meal sample, the last three incubation times were used to calculate a secondary rate even though significant (P<.05) lack of fit remained. Tests for homogeneity of regression slopes for particle size within each feed sample were conducted. There were no significant (P>.05) differences in primary degradation rates (slopes) attributable to particle size for soybean meal, formaldehyde-treated soybean meal, cottonseed meal, or wheat bran (Table 6). However, except for untreated soybean meal, trends indicated that feeds of 150 /~ particle size were degraded faster than feeds of 300 Journal of Dairy Science Vol. 65, No. 6, 1982
97O
EHLE ET AL.
TABLE 6. Slopes and intercepts from regression lines of natural logarithms of percent dry matter in feeds disappearing from polyester bags incubated in the rumen for various times.
Sample
Particle size
Stag time 1
(U)
..
Stop time I
b Slope 2
a Intercept z
(h)
Wheatbran
Unseparated 1180 600 300 150
2 2 2 2 2
8 12 8 12 12
.7062 .0702 .0848 .0545 .1080
3.4195 3.3389 3.3496 3.5106 3.2615
Soybean meal
Unseparated 1180 600 300 150
2 2 2 2 2
24 24 24 24 24
.0425 .0408 .0454 .0475 .0436
3.4506 3.4227 3.4293 3.4558 3.5296
Formaldehyde~ea~d soybean meal
Unseparated 1180 600 300 150
1 1 1 1 1
24 24 24 24 24
.0346 .0377 .0401 .0366 .0377
3.0710 3.1310 2.9631 2.9455 2.9809
Linseed meal
Unseparated 1180 600 300 150
1 1 1 1 1
12 12 24 12 8
.0625 .0710 .0391 .0656 .0988
3.4343 3.2637 3.4492 3.3795 3.4062
Cottonseed meal
Unseparated 3 1180 600 300 150
8 2 2 2 2
24 12 8 12 8
.0253 .0847 .1038 .0615 .0844
3.1347 2.2827 2.5167 3.2076 3.1760
a Start time is the first ruminal incubation time (h) used to calculate the regression line; stop time is the last ruminal incubation time (h) used to calculate the regression line. Start time to stop time was used to calculate the primary degradation rate. Stop time to 24 h of incubation was used to calculate secondary degradation rate. 2All regressions were highly significant (P<.001) with nonsignificant (.°>.05) lack of fit. Regression equations are in the form Y = a + bx, where Y -- natural logarithm of percent dry matter disappearing from bag; a -intercept; b = slope; and x --- time of incubation (h). 3Secondary regression calculated from 8 to 24 h of incubation. Significant lack of fit (P<.05) remains.
particle size. D i f f e r e n c e s in d e g r a d a t i o n r a t e s were s i g n i f i c a n t ( P < . 0 0 1 ) a m o n g various p a r t i cle size samples o f linseed meal. A c o m p a r i s o n o f u n s e p a r a t e d feed sampies s h o w e d t h a t rates o f d e g r a d a t i o n f o r d r y m a t t e r a n d c r u d e p r o t e i n d i f f e r e d a m o n g feeds. F o r m a l d e h y d e t r e a t m e n t o f s o y b e a n m e a l decreased d e g r a d a t i o n r a t e o f d r y m a t t e r a n d c r u d e p r o t e i n c o m p a r e d t o t h e u n t r e a t e d soyb e a n m e a l s a m p l e (Tables 5 a n d 6). H o w e v e r , d e p r e s s i o n in d r y m a t t e r d e g r a d a t i o n was small
Journal of Dairy Science Vol. 65, No. 6, 1982
c o m p a r e d t o d e p r e s s i o n in c r u d e p r o t e i n degrad a t i o n . T h e r e was n o c o n s i s t e n t p a t t e r n in inf l u e n c e o f particle size o n rates o f d r y m a t t e r a n d c r u d e p r o t e i n d e g r a d a t i o n w i t h i n a feed i n d i c a t i n g t h e i m p o r t a n c e o f o t h e r f a c t o r s such as c h e m i c a l c o m p o s i t i o n . I n v e s t i g a t i o n s are needed to delineate factors that affect rate and e x t e n t of f e e d d e g r a d a t i o n in t h e r u m e n . ACKNOWLEDGMENT The authors
t h a n k H u b b a r d Milling C o m -
PARTICLE SIZE AND RUMINAL DEGRADATION
p a n y for s u p p l y i n g t h e f o r m a l d e h y d e - t r e a t e d s o y b e a n meal. REFERENCES
1 ASAE Standard: ASAE $319. 1975. Method of determining and expressing fineness of feed materials by sieving. Page 436 in Agric. Eng. Yearbook. 2 Balch, C. C., and R. C. Campling. 1962. Regulation of voluntary food intake in ruminants. Nutr. Abstr. Rev. 32:669. 3 Blaxter, K. L., N. McC. Graham, and F. W. Wainman. 1956. Some observations on the digestibility of food by sheep, and on related problems. Br. J. Nutr. 10:69. 4 Dafaalla, B.F.M., and R.N.B. Kay. 1980. Effect of hay particle size on retention time, dry matter digestibility and rumen pH in sheep. Proc. Nutr. Soc. 39:71A. 5 Draper, N. R., and H. Smith. 1966. Applied regression analysis. John Wiley and Sons, Inc., New York, NY. 6 Evans, E. W., G. R. Pearce, J. Burnett, and S. L. Pillinger. 1973. Changes in some physical characteristics of the digesta in the reticulorumen of cows fed once daily. Br. J. Nutr. 29:357. 7 Gill, J., R. C. Campling, and D. R. Westgarth. 1966. A study of chewing during eating in the cow. Br. J. Nutr. 20:13. 8 Ho Bae, D., J. G. Welch, and A. M. Smith. 1979. Forage intake and rumination by sheep. J. Anim. Sci. 49:1292. 9 Hogan, J. P., and R. H. Weston. 1967. The digestion of chopped and ground roughages by sheep. II. The digestion of nitrogen and some carbohydrate fractions in the stomach and intestines. Australian J. Agric. Res. 18:803. 10 King, K. W. 1966. Enzymatic degradation of crystalline hydrocellulose. Biochem. Biophys. Res. Comm. 24:295. 11 Mertens, D. R., and L. O. Ely. 1979. A dynamic model of fiber digestion and passage in the ruminant for evaluating forage quality. J. Anim. Sci.
971
49:1085. 12 Netemeyer, D. T., L. J. Bush, and F. N. Owens. 1980. Effect of particle size of soybean meal on protein utilization in steers and lactating cows. J. Dairy Sci. 63:574. 13 Pearce, G. R. 1965. Rumination in sheep. II. The circadian pattern of rumination. Australian J. Agric. Res. 16:635. 14 Pearce, G. R. 1967. Changes in particle size in the reticulorumen of sheep. Australian J. Agric. Res. 18:119. 15 Pearce, G. R., and J. R. Moir. 1964. Rumination in sheep. I. The influence of rumination and grinding upon the passage and digestion of food. Australian J. Agric. Res. 15:635. 16 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. Camb. 94:275. 17 Reid, C.S.W., M. J. Ulyatt, and J. A. Monro. 1977. The physical breakdown of feed during digestion in the rumen. Proc. New Zealand Soc. Anim. Prod. 37:173. 18 Robles, A. Y., R. L. Belyea, F. A. Martz, and M. F. Weiss. 1980. Effect of particle size upon digestible cell wall and rate of in vitro digestion of alfalfa and orchard-grass forages. J. Anim. Sci. 51: 783. 19 Smith, L. W., and D. R. Waldo. 1969. Method for sizing forage cell wall particles. J. Dairy Sci. 52: 2051. 20 Steel, R.G.D., and J. H. Torrie. 1960. Principles and procedures of statistics. McGraw Hill Book Co., Inc., New York, NY. 21 Waldo, D. R., L. W. Smith, E. L. Cox, B. T. Weinland, and H. L. Lucas, Jr. 1971. Logarithmic normai distribution for description of sieved forage materials. J. Dairy Sci. 54:1465. 22 Wealdey, D. C., F. N. Owens, D. G. Heath, and B. J. Shockey. 1977. Particle size and soybean meal value for ruminants. Page 268 in Program 69th Annu. Mtg. Am. Soc. Anim. Sci. 23 Welch, J. G. 1967. Appetite control in sheep by indigestible fibers. J. Anim. Sci. 26:849.
Journal of Dairy Science Vol. 65, No. 6, 1982