May 1, 2018 - received polyethylene glycol, 4% of diet. DM, and 21.4 L of bladders in the rumen in a 2 x 2 factorial arrangement. Polyeth- ylene glycol did not ...
Effects of Prepartum Diet, Inert Rumen Bulk, and Dietary Polyethylene Glycol on Dry Matter Intake of Lactating Dairy Cows T. R. JOHNSON and D. K. COMBS' Department of Dairy Science University of Wisconsin Madison 53706
often are proportionally lower than would
ABSTRACT
Effects of prepartum energy intake, replacement of 25% of reticulorumen contents with water-filled bladders, and feeding of polyethylene glycol on DM intake during lactation were assessed in two trials. In trial 1, six rumencannulated cows were assigned to diets of either 1.50 or 1.68 Mcal NE& 70 d prepartum. Animals fed the higher energy diet had greater NEL intake and tended to gain more BW prepartum. Intake from 28 to 70 d postpartum was not affected by prepartum diet but was reduced by 24.2 L of bladders placed in the rumen. Milk production tended to be increased for cows fed high energy prepartum and to be reduced by bladders. Total reticulonunen volume, digesta fractional passage rates, and acetate:propionate ratio were increased by bladders. In trial 2, eight rumencannulated cows, 28 d postpartum, received polyethylene glycol, 4% of diet DM, and 21.4 L of bladders in the rumen in a 2 x 2 factorial arrangement. Polyethylene glycol did not affect DM intake but reduced DM, CP, ADF, and NDF digestibilities. Bladders increased total reticulorumen volume, rumen fluid pH, and acetate:propionate ratio but decreased DM intake. Intake of DM was reduced .099 kg/L added bulk in trial 1 and .130 kgL in trial 2. Compensation for replacement of rumen contents with inert bulk occurred by expansion of organ volume and, in trial 1, by a reduction in rumen retention time. These factors may explain why reductions in voluntary intake after addition of inert bulk to the reticulomen
Received February 26, 1990. Accepted September 14, 1990. '~eprint w e s t s . 1991 J Dairy Sci 74933-944
be predicted from the volume of bulk
added. (Key words: intake, rumen volume, passage, digestibility) Abbreviation key: ADL = acid detergent ligHE = high energy diet, LE = low energy diet, ME = intermediate energy diet, MW = molecular weight, PEG = polyethylene glycol, Yb-CW = ytterbiumcell walls.
nin,
INTRODUCTION
Energy intake in dairy cattle generally is lower than energy output during the first 40 to 70 d postpartum (5,24). During this period, 40 to 70 kg of BW may be mobilized to support lactation energy demands (4). The time required for dairy cows to reach energy equilibrium postpartum has been reduced by increasing diet energy density (14, 24) and prolonged by increased prepartum energy intake and body condition (17, 18, 29). Feed intake is influenced by neural, metabolic, and hormonal signals integrated by the lateral and ventromedial portions of the hypothalamus, producing hunger or satiety (3). Studies of factors affecting feed intake in ruminants fall into two broad categories: metabolic controls of energy homeostasis and limitation of intake by physical distension of the gastrointestinal tract. Literature dealing with the metabolic control of energy intake (3, 16) and physical limitation of DM intake (21) recently have been reviewed. Conrad (12) and Conrad et al. (13) proposed an integration of these concepts and suggested that intake of diets above 66% DM digestibility is limited only by metabolic feedbacks, whereas intake of less digestible diets is controlled by a combination of physical distention of the alimentary tract and metabolic demands. The existence of a critical m e n fill above which DM intake is limited has been suggested in sheep (6) but not con-
933
934
JOHNSON AND COMBS
firmed with cattle (10). French workers have proposed a “fill unit” system in which critical fill is assumed to be a feed-specific characteristic (23). Fill unit values are assigned on the basis of extensive feeding studies with sheep and cattle. The volume of digesta in any compartment of the. gastrointestinal tract is regulated by the proportional rates of influx and removal of digesta by net absorption and passage. Rate of removal of indigestible residue from the reticulorumen may be partially responsible for observed differences in voluntary intake and fill levels of animals on different diets (21) and at different stages of lactation (30). Thus, increased fractional passage rate may allow greater voluntary intake in situations in which physical fill limits intake. Liquid dilution rate in sheep was increased when rumen fluid osmolality was increased from 331 to 347 mOsm/kg by infusion of 1000 molecular weight (MW) polyethylene glycol (PEG) and mineral salt solutions (22). In these studies, infusion of PEG, an inert unabsorbable osmoregulator, also elevated OM flow to the duodenum, presumably by increasing the passage of small particles and OM associated with the fluid phase. Little information is available concerning the effect of inert rumen bulk on DM intake during the first 120 d of lactation in dairy cattle. Thus, the objectives of trial 1 were to evaluate the influence of level of prepartum energy intake on DM intake during the subse quent lactation and on response to addition of water-filled bladders to the rumen during early lactation. Objectives of trial 2 were to study the effects of increasing liquid dilution rate with PEG on DM intake and passage rate and to determine the effect of inert rumen bulk on DM intake, digestibility, and rumen kinetics. MATERIALS AND METHODS General Procedures: Trials 1 and 2
for each period. Milk yield was measured twice daily, and composition was analyzed weekly by infrared spectrophotometry (Wisconsin DHIA Center Lab, Appleton, wr). Body weight was measured weekly at 1300 h on 2 consecutive d, and body condition score (33) was evaluated by three individuals at the end of periods. Fractional passage rates of liquids and solids from the reticulorumen were estimated from the declining slope of the marker concentration in feces after natural logarithmic transformation. Ruminal passage was estimated twice in trial 1 and at the end of each period in trial 2. Cobalt-EDTA, as prepared by Uden et al. (31) served as a liquid marker, and Yb-marked cell walls (Yb-CW) were used to estimate solids passage. Ytterbium was applied by a selective binding procedure (1) to cell walls obtained from the alfalfa and corn silage fed. On the day of marker dosing, the 1100-h feeding was delayed 2 h, and 21 g of Co-EDTA and 350 g of Yb-CW mixed with 250 g concentrate were offered to each cow. Animals had access to the marked feeds for 45 min after which any remaining marked feed was manually placed in the rumen and animals were immediately fed. Fecal grab samples were taken at 6, 10, 14, 18, 22, 26, 30, 36, 42, 50, 58, 70, 82, and 96 h postdose and dried at 6072. Volume and wet weight of reticuloruminal digesta were measured on the last day of each period at 1330 h in precalibrated and tared 114-L barrels. A 1-kg sample of mixed rumen contents was frozen at -Q‘C and used for DM determination by toluene distillation. Rumen fluid was strained through four layers of cheesecloth, acidified, and frozen at 4 - C for later VFA analysis (7). Rumenempty BW, defined as live weight after subtraction of the weight of rumen contents, was calculated at each rumen emptying. Feed and Fecal Analysis
Forage samples were dried at 60°C for 48 h, and concentrates at 1 W C for 24 h to determine vidually and mixed immediately before feeding. DM content. Air-equilibrated feed, orts, and Animals had access to diets 21 h/d. Amounts feces were ground in a Wiley mill (Arthur A. fed were adjusted daily to ensure 5 to 10% feed Thomas, Philadelphia, PA) through a 1-mm refusal. O r t s were removed and weighed daily screen. Absolute DM was determined at l W C , at loo0 h. Samples of om were taken on 2 and the following analyses performed on comconsecutive d/wk and composited within cow posite samples of forages, concentrates, orts, Diets were fed twice daily at 1100 and 2200
h; forage and concentrate were weighed indi-
Journal of Dairy Science Vol. 74, No. 3, 1991
PHYSICAL LIMITATION OF DRY MA=
935
INTAKE
TABLE 1. Formulation and composition of diets fed in trial 1. ~epartumdiets'
LE
HE
Lactation diet
ME
(96 of DM) Diet formulation Alfalfa silage Corn silage Ground corn Soybeau meal, 44% Dicalcium phosphate Monosodium phosphate Calcium carbnate TM salt2 Magnesium oxide vitamin premix3 Diet composition, DM basis NEL: M c W
58.8 40.6
0 0 0 .2
0 2
0
34.7 16.1 .7
0 .4 .7 .2
0
0
.1
.1
1.50
1.68 15.7 19.7 28.8 .49 .19 60.3
1.61 165 24.9 35.7 .69 .2 1 54.8
1.68 21.0 18.5 26.1 .84 .45 65.0
ADF, %
28.9 40.9
p, 9% DM, % as fed
312 15.9
.1
17.0
ca, %
0 0 .3
46.3 33.3 19.1 1.1 0 0 0 .1
.1
CP, %
NDF, %
31.7 24.9 40.6 2.4 0
-86 .30 48.1
lLE = Low energy diet fed at restricted intake, HE = high energy diet ad libitum, ME = medium energy diet ad libitum. h e m i n e r a l salt 95% NaCl, ,3496 Fe, .005% Co, .OM% Cu, 20% Mn, .35% Zn, .007% I, and .002% Se. 3Vitamin A 2665 IU/g, vitamin D 900 W g , and vitamin E .90 IU/g. 4Calculated from NRC 1988 (26).
and feces. Nitrogen was analyzed by AOAC (2) using Se as a catalyst and for OM by AOAC (2). Acid detergent lignin (ADL) and ADF were analyzed according to Goering and Van Soest (20),and NDF as modified by Robertson and Van Soest (27). Fecal samples were prepared for marker analysis by wet ashing (11). Diet energy densities were calculated from diet composition and estimated NEL values (26). Fecal concentrations of Co and Yb were determined by direct current plasma spectroscopy (Spectra Metrics, Inc., subsidiary Beckman Instruments, Inc., Andover, MA 08110). Triul1. Six multiparous Holstein cows with rumen cannulas were assigned to a low energy diet (LE; 1.50 Mcal N E D g ) that was restricted to 11 kg/d or a high energy diet (HE; 1.68 Mcal NEfig) fed for ad libitum intake beginning 70 d prior to expected parturition. All cows received an intermediate energy diet (ME 1.61 Mcal NELjkg) ad libitum for the last 10 d prior to parturition (Figure 1). Estimates of subcutaneous fat cover were made prepartum on a biweekly basis by ultrasonography (Scanoprobe Il model #731C; Scanco Inc., Itha-
ca, NY) between the 12th and 13th rib, 7.6 cm from the midline. All cows were fed the same diet (1.68 McaVkg) ad libitum during lactation. Energy balance was considered to be the difference between calculated NEL intake and estimated NEL output in milk and for maintenance (26). Composition and formulation of diets are listed in Table 1. Treatment during lactation was control (A,
Switchback -70 d
-10 d
28d
42d
__ 56 d
A HE (1.68 Mcal NEUkg)
Calving
A
t (1.61 Mcal NEUkg)
B
B A
t
t
(1.68 Mcal NEUkg)
11 kgld
Figure 1. Experimental design of trial 1. Prepartum diet energy level. Low energy (LE) or high energy (HE) fed from 70 to 10 d prepartum and medium energy (ME) fed the last 10 d before expected parturition. Sequence of postpartum treatments: control (A) and replacement of 25% of rumen contents with water-filled bladders (B). N@L= NEL. Jouxml of Dairy Science Vol. 74, No. 3, 1991
936
JOHNSON AND COMBS
Figure 1) or replacement of rumen contents (voUvo1) with two inner tubes of 30.5-cm 0.d. filled with water. Volume of bladders was 25% of initial pretrial rumen volume determined 10 wk prepartum (B, Figure 1). Bladders were found to be residing in the ventral rumen below the fiber mat but suspended in the fluid phase above the floor of the ventral sac. Treatments were applied in a switchback design with cows randomly assigned to either an ABA or BAB sequence of treatments (Figure 1). Treatments began 28 d postpartum and lasted 14 d. Data collected the last 7 d of each period were used for analysis. Trial 2. Eight multiparous, rumencannulated Holstein cows were used in a replicated 4 x 4 Latin square design balanced for carry-over effects. Treatments were arranged as a 2 x 2 factorial. Factors were feeding 4% PEG lo00 M W (J. T. Baker Inc., F'hillipsburg, NJ and Sigma Chemical Co., St. Louis, MO) and replacing 25% of pretrial rumen volume determined at 21 d postpartum with three waterfilled, 25.4cm 0.d. inner tubes. Treatments began 21 d postpartum and lasted 21 d; data from the last 7 d were used for analysis. Cows in squares 1 and 2 shared periods 2, 3, and 4 but were offset by 21 d to equalize days in milk at the beginning of the trial. Measurements, therefore, extended over a total of five 2 1 d periods. The PEG was added to the grain mix at 8.85% of DM to provide 4.0% PEG in the total diet DM of PEG-treated cows. F0rage:concentrate ratio was adjusted slightly on PEG diets to maintain concentrations of CP, ADF, and NDF similar to the control diet. Diet formulation and composition are in Table 2. At the end of each period, cows were observed every 5 min for 24 h to determine eating, ruminating, and total chewing activity. Rumen fluid was obtained from four locations in the rumen and composited 2 h prior to and 2 h after the 1100 h feeding. Rumen fluid was strained through four layers of cheesecloth and analyzed immediately for pH by glass electrode. A 25-ml subsample of both prefeeding and postfeeding rumen fluid was frozen at -20'C and later analyzed for osmolality by freezing-point depression (Advanced wide-range osmometer Model 3W2; Advanced Instruments Inc., Needham Heights, MA). Blood was collected from the coccygeal vein into heparinized vacutainers and transJournal of Dairy Science Vol. 74, No. 3, 1991
TABLE 2. Formulation and composition of diets with or without polyethylene glycol (PEG) fed in trial 2. Control
PEG
37.0 17.8 26.6 17.2 .6 .2 .1 .4 .1 0
34.6 16.7 26.3 17.0 .6 .2 .1 .4
- (%, DM basis) Diet formulation Alfalfa silage Corn silage Ground corn
Soybean meal, 44% Dicalcium phosphate Calcium carbonate Magnesium oxide TM salt' vitamin premix2 PEG lo00 MW3 Diet composition NEL? McauLg
-
.1
4.0 (Feed D d )
ADF, % NDF, 96
1.62 23.2 19.5 28.5
ADL? %
2.5
a.5%
ca,% p,
DW4 % as fed
.82 .44 52.9
-
1.63 22.9 18.6 27.4 2.4 .82 .44
52.7
lTrace-mineral salt 95% NaCI, .35% Fe, .W%Co, .14% Cu, 55% Mn, .55% Zn. .008% I, .006% Se. 2Vitamin A 2665 W/g, vitamin D 900 W/g, and vitamin E .90 W g . 3 ~ ~ 1 ~ weight l a r 0. 4Values are adjusted to feed DM basis by correcting for PEG addition to DM. 'Calculated from NRC 1988 (26). 6Acid detergent lignin.
ferred within 15 min to NaFcoated centrifuge tubes. Plasma was separated by centrifugation, and an aliquot was frozen for analysis of glucose (Sigma procedure 510; Sigma Chemical Co., St. Louis, MO). The remaining plasma was deproteinized and frozen at -20°C until analyzed for p-hydroxybutyrate (19). Total tract digestibility was estimated by feeding .25 g of La sprayed on 125 g of concentrate twice daily for the last 14 d of each period. Fecal grab samples were collected at 8-h intervals for 3 d. Ort samples were taken 4 consecutive d to estimate La refusal. Marked concentrate, orts, and feces were prepared by wet ashing for La determination using direct current plasma spectroscopy.
937
PHYSICAL LIMITATION OF DRY MA’ITER INTAKE
Statistical Analysls
TABLE 3. Intake and body measufements as affected by prepartum diet energy level, hial 1.
Triul 1. All lactation data were analyzed by the general linear models procedure of SAS (28) as a split plot with cow nested within prepartum diet and a switchback design of subplot treatments. The model was
Prepartum measurements
LE
Days on treatment D W , Wd NEL Intake, McaVd InitialBW kg Final BW? kg Initial RE B W 3 kg P i RE BW?v3 kg P i BCS2*4 Final 12th rib fat thickness,2 cm
61 61 11.1 12.4 16.9 20.6 681 693 742 766
Y i j ~= p
+ di + Ck(i) + tj + S1 + (td)j(i)
+ (ds)l(i) + (tSlj1 + eju(i), where YijM= observation on intake, production, or rumen characteristics; p = overall mean; di = effect of prepartum diet; ck(i) = whole-plot error (cow within prepartum diet); tj = effect of postpartum inert rumen bulk, s1 = effect of stage of lactation; and q ~ ( i=) residual error, used to test tj, si, and interactions. Prepartum DM and NEL intakes were analyzed as a completely randomized design. Final prepartum body measurements were analyzed by covariance on initial body measurements:
HE
SE
619 698
595 668
2
.8 1.0 16 7 37 5
3.41
3.75
.6
.8
P .88 32 .08 .88 .10
.68
.a?
.33 .52 .2
33
‘LE= Low energy (1.50 Mcal NE& DM). HE = high energy (1.68 Mcal NE& DM). 2Measured 10 d before expected parturition. kumen-empty BW defimed as BW after subtraction of weight of rumen contents. %ody condition score 1 = thin, 5 = obese (33).
distributed. Unless otherwise specified, treatment effects stated as different differ significantly (P e .05).
where Yi = observation on final body measurement; p = overall mean; p@’& = covariate adjustment based on pretrial measurement; di = RESULTS AND DISCUSSION effect of prepartum diet; and q = residual error. Rate of passage data were analyzed as a single reversal by a model containing only subplot Trial 1 effects due to the limited number of observaDry matter intake and changes in body tions. measurements for cows fed LE or HE diets Trial 2 . Data were analyzed by the general prepartum are in Table 3. Animals consuming linear models procedure of SAS; the model HE diet tended to have greater net energy incontained linear and quadratic effects of initial take than those consuming LE diet (P = .08). days in milk at the beginning of the trial. The Body weight and nunen-empty BW at parturimodel also contained effect of period, cow, tion tended to be increased by HE compared square, PEG, bladders, and PEG by bladder with LE diet, indicating that greater energy interaction. The 3 df for treatment were divided reserves were present in HE than in LE cows at into separate effects of PEG, bladders, and their parturition. Dry matter intake during wk 5 to 10 interaction. The model for all data in trial 2 was of lactation was not different as a result of prepartum diet (P = .29, Table 4). Water intake (P = .05),milk yield (P = .lo), fat yield (P = .OS),protein yield (P = .08),and 3.5% FCM (P = .06) tended to be increased with HE diet. where Yiy = observations on intake, produc- These data are in agreement with Gamswo~thy tion, or rumen characteristics; p = overall and Topps (18) and Seymour and Polan (29), mean; ci = effect of cow; pj = effect of period; who found that high levels of prepartum energy dk = effect of PEG in the diet; tl = effect of intake increased FCM without an increase in water-filled bladders; ( d t k = interaction of DM intake. PEG and water-filled bladders; and eijkl= residReplacement of rumen contents with inert ual error, assumed independent and normally bulk beginning 28 d postpartum reduced DM Journal of Dairy Science Vol. 74, No. 3, 1991
938
JOHNSON AND COMBS
TABLE 4. Effect of prepartum diet on intake of DM @m),water, and milk production duriug wk 5 to 10 postpartum, trial 1.
prep-
diet'
Item
DML W d Water intake, kg/d Milk, W d 3 5 % FCM, kg/d Fat, % Protein, 96 Fat yield, kg/d Protein yield. W d
L E H E 21.4
104 39.1 34.4 2.78 2.67 1.08 1.04
23.2 127 45.7 39.3 2.63 2.57 1.20 1.17
'LE = Low energy (1S O Mcal NFl& energy (1.68 Mcal NE& DM).
SE
P
A 4 12 1.2 .10 .03
.29
.a5 .10
.06 .46
.M
.os
.05
.03
.08
DM), HE = high
intake and tended to reduce milk yield (P < .lo, Table 5). In this study, DM intake was &ced by .099 kg DM/L of added bulk. This is similar in magnitude to the linear decreases of .054 kg DM/L of added bulk reported by Campling and Balch (9) and .112 kg DM/L observed by Mowat (25) for mature nonlactating cows fed hay. In contrast, Carr and Jacobson (8), using smaller volumes of water-filled bladders, found no decrease in DM intake when nonlactating cows were fed a chopped hay diet. Rumenempty BW change and calculated energy balance were used as indicators of the extent of body energy accretion or mobilization. Change in rumen-empty BW and energy balance were .6 vs. -1.5 kg/d, (P < .01) and 3.87 vs. 1.59 Mcal NEdd for control and bladder treatments, respectively. Both methods predicted low or negative energy retention when bladders were in place. Differences in estimates of tissue energy accretion by these two methods may have been due to the differences in the amount of digesta in the lower tract not removed in the rumenempty BW calculation. Because intake was depressed to a greater extent than was milk production, the priority for available energy intake in early lactation appears to have been directed towards the mammary gland at the expense of tissue deposition. An average of 24.2 L of inert bulk were added to the rumen in trial 1 (Table 6). Cows compensated for this mass by increasing total organ volume by 13 L (P < .01) and by decreasing the volume of digesta by 12 L (P < .Ol). The DM content of digesta was decreased Journal of Dairy Science Vol. 74, No. 3, 1991
TABLE 5. Effect of water-filled bladders on DM intale, milk production and energy balance, trial 1.
Treatment Item
Control Bladders
BW, ks
645 23.5 120 44.0 38.1 2.70 2.67 1.18 1.16
641 21.1* 111* 40.9t 35.5 2.72 2.57* 1.10 1.04*
3.87
1.59*
DM Intake, kg/d Water intake, kg/d Milk, W d 3.5% FCM, W d Fat, % Protein, % Fat yield, kg/d Protein yield, kg/d Energy balance, Mcal NEIjd Rumen empty BW channe, W d
.6
-1.5**
SE 3 .4
4 1.3 1.2
.10 .05
.05 .03 .70 .3
tsignificmtly different from control ( P < .IO). *Si@icantly different from control (P < .OS). **Significantly different from control (P < .01).
by bladder treatment from 17.6 to 15.9% (P< .Ol), as was the weight of digesta DM and NDF (P < .01). Fractional passage rate of Yb-CW was increased from .048 to .065/h by bladder treatment (P < .01). Fractional dilution rate of CoEDTA tended ro be increased from .078 to .091/h by bladder treatment (P = .08). The exponential model of marker disappearance in the feces fit the data well. The mean R2 of the declining slope of the natural log of marker concentration versus time were .988 and .979 for Yb and Co, respectively. Liquid dilution rate was linearly increased in sheep fed a 75% concentrate diet when water-fded plastic bags were added to the m e n at 22,44, and 66% of pretrial rumen volume (32). Rumen digesta volume in these sheep was decreased by added bulk, but DM intake was unaffected These data, and the increase in Yb-CW and Co-EDTA fractional passage rate in the present trial, suggest that a reduction in retention time with little change in total flux of digesta from the rumen may result when inert bulk is added to the rumen. Lactating dairy cows at high levels of feed intake had increased passage rates compared with the same animals in late lactation and in the dry period (30), suggesting that increased passage rate may occur when further expansion of reticdorumen volume is limited.
939
PHYSICAL LJMITATION OF DRY MATTER INTAKE TABLE 6. Effect of inert m e n bulk on rumen characteristics, trial 1.
TABLE 7. EfEect of inert bulk on rumen VPA molar ratios, trial 1. Treatment
Treatment Item
Control Bladders
Rumen volume, L Digesta 102 Digesta and bladders 102 Bladders Rumen digesta Wet digesta, kg 83.4 14.7 DM, kg NDF, kg 7.6 DM, % 17.6 Fractional rate of passage, h-' C~EDTA' .078 Yb-cw2 .048 Flux Liquids, L.h-' 5.2 Solids, gh-I 693
SE
w* 115** 24.2 71.6** 11.3** 5.9** 15.9* .091t
.as**
5.7 772
2 2 .2 1.4 27 25 A
Item
Control
Bladders
SE
57.5 23.6 12.4 6.5 2.4
61.6* 202** 12.0 6.2 3.1*
.8
- (mol/lOo mol) -
Acetate (A) Propionate Cp) Butyrate. Other WA' A:P Ratio
.5
.4 .4 .1
lIsobutyate plus valerate plus isovalerate.
(P < .OS). **Significantly diffenmt from control (P < .01). *Significantly different from control
.003 .002 .2 60
'Used to estimate liquid passage. '-used to estimate solids passage; YMW
= mceu Walls. tsiwicantly different from control (P < .IO). *Significantly different from control (P < .05). **Significantly different from control (P < .01).
Increased passage rates are most likely to occur when high concentrate diets, which require little particle size reduction, are fed. Forbes (15) suggested that internal abdominal fat present in overconditioned ewes and cattle may restrict DM intake by limiting expansion of rumen volume. In this trial, although prepartum treatment differences in rumen-empty BW gain were small, bladder by prepartum diet and bladder by stage of lactation interactions on DM intake and total rumen volume were not significant (P z .30). Therefore, it is unlikely that DM intake was limited by such a mechanism in this trial. Rumen fermentation patterns 2 h postfeeding were altered by bladders (Table 7). The molar proportion of acetate was increased and that of propionate decreased (P < .01) relative to control. Similar changes in acetate:propionate ratios have been reported in sheep when fluid dilution rate was increased by infusion of osmotically active substances (22). Although bladders increased the ratio of acetate:propionate from 2.4:l to 3.1:1,this difference was not reflected in an elevation of the low milk fat
percentage (2.71%) observed for both treatments. Trial 2
Dry matter intake, water intake, and milk yield were not influenced by addition of PEG to the diet, but they were reduced by waterfilled bladders (Table 8). Bladders reduced DM intake (21.7 vs. 24.4 kdd) (P < .01) by a greater proportion than milk yield (35.6 vs. 37.7 kdd) and to a greater extent than in trial 1 (.130 vs. .099 kgK. of added bulk). Greater depression of DM intake by bladders in trial 2 than in trial 1 may be due to the larger proportion of forage (55 vs. 47%) and dietary NDF (28.5 vs. 26.1%) fed in trial 2. Bladders reduced milk protein percentage and yield (P < .01) and tended to reduce fat yield (P < .lo) but had no effect on fat percentage. Rumen-empty BW and BW change were unaffected by PEG but were reduced by inert rumen bulk. Plasma p-hydroxybutyrate concentration was increased by bladders (28.2vs. 18.5 mg/d, P = .OM), whereas plasma glucose averaged 57.8 mg/d and was not affected by treatment (Table 8). As in trial 1, body tissue gain was reduced by bladders with energy intake apparently being directed toward maintenance of high levels of milk production. Polyethylene glycol had no effect on rumen digesta volume or wet weight, but it increased digesta DM percentage and weight (Table 9). Average volume of water-filled bladders in trial 2 was 21.4 L. Bladders tended to decrease volume of digesta by 5 L and increased total Journal of Dairy Science Vol. 74, No. 3, 1991
940
JOHNSON AND COMBS
TABLE 8. Dry matter intake and body measurements, trial 2. ~~
~
Significance Item DW kg/d Feed
PEG^
Total
Control
Bladders
PEG
PEG + bladders
24.1 0 24.1 115 651 0
22.1 0 22.1 99 657 21.3
24.5 1.1 25.6 113 656 0
21.3 1 .o 22.3 103 660 21.4
559 -.5 35.3 35.6 3.59 2.99 1.25 1.05
576 .7 37.2 38.0 3.66 3.1 1.34 1.1
569 -.4 36.0 36.3 3.54 2.85 1.28 1.01
55.1 23.8
59.2 17.1
58.1 32.5
Water intake, U d BW, kg Bladder, L Rumen-empty 573 BW, Lg BW change, kg/d .3 Milk, kg/d 38.1 35% E M , kg/d 39.4 3.69 Pat, % 3.10 Rotein, 96 1.42 Fat, kg/d 1.21 Protein, kg/d Plasma, mg/dl Glucose 58.1 D-6-Hvdroxvbutvrate 19.8
SE
DIM1 L, Q
L, Q .M L, Q .6 L. Q
.5
3 3 1.0
LQ
4 .3 .7 1.6 .14
LQ
NS NS
NS L, Q
L, Q NS
.W L .06 NS .05 L, Q 2.4 6.6
NS NS
Bladders PEG
** *
NS
**
PEG x bladders
NS
*
** ** NS **
NS
t
NS
NS NS NS
** * *
NS NS NS NS NS NS NS
*
NS
* t
** NS
t
NS NS
NS NS NS NS NS NS
NS
NS NS
NS NS
NS NS
'Significant (P < .M)linear or quadratic effects of DIM at the start of the trial. ?PEG = 1000 molecular weight polyethylene glycol. +S@icant bladder or PEG main effects, or bladder by PEG interaction (P < .lo). *Significant bladder or PEG main effects, or bladder by PEG interaction (P < .05). **Si@icant bladder or PEG main effects, or bladder by PEG interaction (P < .01).
rumen volume by 16 L (P < .01). As in trial 1, digesta DM percentage was reduced by waterfilled bladders (P < .01) as a result of a smaller proportional decrease in rumen wet weight than in DM weight. Polyethylene glycol failed to increase rumen fluid osmolality or passage rate of &EDTA and Yb-CW (Table 9). In contrast, Harrison et al. (22) performed short-term infusions of 4 or 8% solutions of PEG loo0 M W in sheep that were fed restricted diets and reported an increase in rumen osmolality and liquid dilution rate. Bladders reduced osmolality both pre- and postfeeding (P < .Ol) but had no effect on CoEDTA or Yb-CW fractional rate of passage. Rumen DM pool size was reduced by bladders (P < .Ol), resulting in a reduction in solids outflow as estimated from Yb-CW passage. Rumen fluid pH increased (P < .01) with addition of inert rumen bulk (Table 10). Acetate:propionate ratio was increased by bladders (P c .01). The combination of PEG and bladders increased acetate:propionate ratio further, Journal of Dairy Science Vol. 74, No. 3, 1991
resulting in a significant PEG by bladder interaction. Increased acetate:propionate ratio caused by bladders in trial 2 may have been a result of the elevation of ruminal pH and a shift in rumen environment favoring fiber digesting microorganisms. Time spent eating and ruminating, expressed as either per day or per weight of NDF intake, was not influenced by PEG flable 11). Time spent ruminating was lower for bladder treatment, but daily eating and total chewing time were not affected by bladders. When data were corrected for differences in intake, eating time per unit of NDF intake was increased by bladders (P< .01). Time spent ruminating and total chewing time per unit of NDF were not affected by treatment and averaged 63.4 and 107.0 min/kg NDF. These values are similar to those reported by Woodford et al. (34) for lactating cows fed similar diets. Total meals and meals greater than 5 min in length were similar between treatments. The number of meals 5 min or less in duration was reduced,
941
PHYSICAL LIMITATION OF DRY MA'ITER INTAKE TABLE 9. Rumen measurements resulting from treatment with water-fiued bladders and feed* (PEG), trial 2.
polyethylene glycol Significance
Item
Control
Volume, L Digesta 97.2 Digesta + bladders 97.2 Weight, kg Digesta Digesta, DM Digesta, NDF DM, 96
78.4 13.5 7.3 17.3
Osmolality, m o d kg 2 h Prefeed 386 2 h Postfeed 3% Fractional passage, h-l
Bladders PEG
PEG+
bladders
94.8 116.3
98.3 98.3
91.1 112.5
72.3 11.1 5.4 15.5
81.2 14.5 7.3 17.9
72.8 12.1 5.4 16.6
322 342
366 380
327 341
L, Q
Bladders PEG
4 4
L, Q
NS
L, Q
**
2.8 .4 .2 .4
L, Q
* ** **
DM1 SE
L, Q
L, Q NS
12 13
NS
NS NS
NS NS
L, Q
**
L, Q
NS
NS NS
NS
.058
.061
.oCn
NS
.089
.090
.092
,003
NS
33 .3
*
NS NS
.060
735 5.6
NS
NS NS NS
NS
.091
836 6.0
*
NS NS
.061
662 5.4
NS
NS NS
** **
Co-EDTA4
8 15 5.9
NS
NS NS
ybcw3
Flux Solids, gh Liquid, uh
**
NS
PEG x bladders
NS
NS
PEG = Polyethylene glycol (1000 molecular weight). 2 s w i m t (P < .05) linear or quadratic effects of DIM at the start of the trial. 'used to estimate solids passage; YMW = %cell W ~ U S . 4Used to estimate liquid passage. *Si@cant bladder of PEG main effects, or bladder by PEG interaction (P < .05). **Signifkant bladder or PEG main effects. or bladder by PEG interaction (P < .01).
TABLE 10. Rumen pH and VFA, trial 2. Significance Item
Control
Bladders PEG
PEG + bladders
PH 2h Prefeediog 2h Postfeeding VFA, moUl00 mol Acetate (A) Propionate (P) Butyrate Others WA3 A P Ratio
5.78 5.57 64.6 18.7 11.5 5.2 3.5
6.03 5.85 66.9 17.5 10.0 5.6 3.9
5.64 5.56 61.4 21.9 11.5 5.2 2.9
5.99
5.88 70.5 15.2 9.0 5.3 4.7
Bladders PEG
PEG x bladders
**
NS
NS
NS
NS
DIM' SE
NS .07 NS .07
1.1
.!
.3 .2 .2
** **
NS
**
NS
NS
** **
NS NS
NS
NS
NS
**
NS
NS
NS NS NS
NS
*
'PEG = Polyethylene glycol (1000 molecular weight). 2significaut (P < .OS)linear or quadratic effects of DIM at the start of the trial. %derate + isovalcrate + isob~tyrate. *Significant bladder or PEG main effects, or bladder by PEG interaction (P < .05). **Significant bladder or PEG main effects, or bladder by PEG interaction (P c .01).
Journal of Dairy Science Vol. 74, No. 3, 1991
942
JOHNSON AND COMBS
TABLE 11. Chewing activities, trial 2. ~~~
~
Significance Item
Chewing activities, min/d Eating Ruminating Total chewing Chewing activities, min/kg NDF Eating Ruminating Total chewing Total meals Meals>Smin Meals < 5 min Average minutes per meal
Control
Bladders
PEG
273 424 697
294
285 426 711
39.9 62.6 103.0
20 12
8 13.6
380
674
PEG + bladders
SE
281 385
13
666
24
18
DIM' L. Q
L, Q NS NS
Bladders PEG
PEG x bladders
NS
NS
*
NS
**
12 6
1 1 1
NS L, Q L, Q NS NS NS
NS NS NS NS
16.0
1.4
NS
NS
46.8
42.0
60.5 107.3
64.0
47.5 66.6 114.1
106.0
19 12 7
20 12 8
18
16.7
14.7
1.8 3.3 4.2
*
NS
NS NS
NS
NS
NS NS NS NS NS
NS
NS
NS
NS
NS
NS
NS NS NS
'PEG = Polyethylene glycol (la00 molecular weight). 2Signifcant (P < .OS) linear or quadratic effects of DIM at the start of the trial. *Si@cant bladder or PEG main effects, or bladder by PEG interaction (P < .05). **Significant bladder or PEG main effects, or bladder by PEG interaction (P < .01).
and average minutes per meal tended to be increased by bladders (P = .13). These data indicate that bladders reduced the rate of feed intake and tended to prolong meal length. Calculations for total tract digestibility of DM and OM were corrected for PEG intake, which was assumed to be totally indigestible (Table 12). The presence of bladders had no effect on apparent digestibility of DM, OM, CP, ADF, or NDF. Polyethylene glycol depressed DM and OM digestibility (P < .Ol); the largest reduction occurred in the fiber fractions. Fecal excretion of non-PEG DM as percentage of BW was 1.44 vs. 1.29% for animals fed and not fed PEG, respectively. Conrad et al. (13) found improved fit in regression equations predicting DM intake by the inclusion of fecal excretion as percentage of BW in addition to BW, digestibility, and milk energy output. Conrad et aL (13) suggest that fecal DM excretion may be a good index of total tract fill and passage of indigestible residue. In contrast, in trial 2 PEG increased rumen DM weight and fecal DM excretion but had no effect on DM intake. However, bladders increased total reticulorumen volume (digesta plus bladders), had little effect on fecal DM excretion, and Journal of Dairy Science Vol. 74, No. 3, 1991
decreased DM intake. This suggests that total volume of retidonunen contents rather than rumen DM or DM excreted per day is responsible for observed decreases in voluntary intake in these studies. Grovum (21) suggested that distention of the reticulum, where tension receptors are most numerous, is responsible for much of the afferent neural feedback to the hypothalamus-limiting intake. Although separating the effects of bladders on ruminal and reticular distention was not possible in our trials, tension receptors in the reticulum and rumen may have been stimulated, resulting in decreased eating rate and reduced intake. Intake was decreased by 10.2 and 10.7% in trials 1 and 2, respectively, after replacement of 25% of rumen contents with inert bulk. Smaller than predicted decreases in voluntary intake after addition of inert bulk to the rumen also were reported in several other studies (8, 9, 25, 32). In our trials, increased organ capacity and, in trial 1, increased fractional passage rate were compensatory mechanisms that allowed the maintenance of high levels of voluntary intake even after challenge with inert bulk Further study of factors affecting reticuloruminal volume and passage during early lactation may
943
PHYSICAL LIMITATION OF DRY MAlTER INTAKE
TABLE 12. Total tract apparent digestibility, trial 2. Significance Item
Digestibility, % DM3
OM^
CP ADF
NDF Fecal excretion, kg DM/d Non-PEd Total
Control
Bladders
PEG
PEG + bladders
SE
DIM1 L. 0
63.6 65.1 66.4 45.7 36.9
63.3 64.6 66.8 48.2 39.3
60.6 62.2 65.3 39.8 30.9
56.7 58.1 62.7 37.2 26.8
1.5 1.5 1.2 1.9 2.3
NS NS NS NS NS
NS NS NS NS NS
** **
8.8 8.8
8.1 8.1
9.7 10.9
9.2 10.2
.4 .4
L. Q L. 0
NS
*
NS
**
I
-
Bladders
PEG
*
** **
PEG x bladders
NS NS NS NS NS NS NS
PEG = Polyethylene glycol (1000 rno1ecular weight). *Si@icant (P < .05) linear or quadratic effects of DIM at the start of the oial. 3 c ~ ~ t for e dPEG excretion. *Significant bladder or PEG main effects, or bladder by PEG interaction (P c .05). **Sigrufcant bladder or PEG main effects, or bladder by PEG interaction (P < .01).
lead to a better understanding of physical constraints to DM intake in highly productive ruminants. REFERENCES
1 Allen, M. S. 1982. Investigation into the use of rare earth elements as gastrointestinal markers. M. S. Thesis, Cornell Univ., Ithaca, NY. 2Association of Official Analytical Chemists. 1975. Official methods of analysis. 12th ed. AOAC, Wash-
'"a". Dc.
3 Bade, C. A., and C. L.McLaughlin. 1987. Mechanisms controlling feed intake in ruminants: a review. J. Anim. Sci. M915. 4Bath, D. L. 1985. Nutritional requirements and economics of lowering feed costs. J. Dairy Sci. 68:1579. 5 Bines, J. A. 1976. Regulation of food intake in dairy cattle in relation to milk production. Livest. Rod. Sci. 3:115. 6Blaxter, K. L., F. W. Wainman, and R. S. Wilson. 1961. The regulation of feed intake in sheep. Anim. Rod. 351. 7Brotz, P. G., and D. M. Schaefer. 1987. Simultatteaus determination of lactic acid and volatile fatty acids in microbial fermentation extracts by gas liquid chromatography. J. Microbiol. Methods 6:139. 8 Carr, S. B.. and D. R. Jacobson. 1967. I naddition of mass or removal of rumen contents on voluntary intake of the bovine. J. Dairy Sci. 50:1814. 9Camphg, R C., and C. C. Balch. 1%1. R e h m m y observations on the effect, on voluntary intake of hay, of chaunes in the amount of reticula-ruminal contents. Br. J. 6utr. 15531. 1OCamuh~~ R.. C., M. Freer, and C. C. Balch. 1961. Fact& &sting the voluntary intake of food by cows. 2. The relationship between the voluntary intake of roughages, the amount of digesta in the reticulo-rumen
and the rate of disappearance of digesta from the alimentary tract. Br. J. Nutr. 15:531. lICombs, D. K. 1985. An evaluation of markers and techniques used to measure nutrient digestion in nlminants. Ph.D. Diss., Univ. Wisconsin,Madison. 12 Conrad, H. R. 1966. Symposium on factors influencing the voluntary intake of herbage by ruminants: physiological and physical factors limiting feed intake. J. Anim. Sci. 25:277. 13Comad, H. R., A. D. Pratt, and J. W. Hibbs. 1964. Regulation of feed intake in dairy cows. 1. Changes in the importance of physical and physiological factors with increasing digestibility. J. Dairy Sci. 47:54. 14Coppock, C. E., C. H. Noller, and S. A. Wolf. 1974. Effect of forage to concentrate ratio in complete feeds fed ad libitum on energy intake in relationship to requirements in dairy cows. J. Dairy Sci. 57:1371. 15Forbes, J. M. 1970. Hormones and metabolites in control of food intake. Page 145 in 3rd Int. Symp. Physiol. Dig. Metab. in the Ruminant. Newcastle Upon Tyne, Engl., Oriel Press Ltd. 16 Forbes, J. M. 1989. Metabolic aspects of regulation of voluntary food intake and appetite. Nutr. Res. Rev. 1: 145. 17 Garnsworthy, P. C., aad G. P. Jones. 1987. The influence of body condition at calving and dietary protein supply on voluntary food intake and performance in dairy cows. Anim. Rod. u 3 4 7 . 18 Gamsworthy, P. C., and J. H.Topps. 1982. The effect of body condition of dairy cows at calving, on their food intake and performance when given complete diets. Anim. Rod. 35:113. 19 Gibbard, S.. and P. J. Watkins. 1968. A micro method for enzymatic determination of D-khydroxybutyrate and acetoacetate. C h . Chim. Acta 19511. 20 Goering, H.K.. and P. J. Van Soest. 1970. Forage fiber analyses (apparatus, reagents, procedures, and some applications). Agric. Handbook No. 379. ARS-USDA,
Journal of Dairy Science Vol. 74, No. 3, 1991
944
JOHNSON AND COMBS
Washington, Dc. 21 Grovum, W.L. 1987. A new look at what’s controlling feed intake. Page 1 in Feed Intake by Beef Cattle Symp. Proc., F. N. Owens, ed. Oklahoma SWe Univ.. MF’ 121 Oklahoma Agric. Exp. Sm,Stillwater. 22 Harrison, D. G., D. E.Beever, D. J. Thompson, and D. E. Osboum. 1975. Manipulation of men fermentation in sheep by increasing the rate of flow of water from the rumen. J. A@. Sci. (Camb.)8593. 23 Janige, R., C. Demaquilly. I. P.Dulphay, A. Hoden, J. Robelin, C. Beranger, Y. Geay. M. Joumet, C. Malteme, D. Micol, and M.Petit. 1986. The INRA “fill unit” system for predicting voluntary intake of forage based diets in ruminants: a review. J. Anim. Sci. 63: 1737. 24 Journet, M., and B. Rbmond. 1976. Physiological factors affecting the voluntary intake of feed by cows: a review. Livest. Rod. Sci. 3:129. 25 Mowat, D. N. 1963. Factors affecting rumen capacity and the physical inhibition of feed intdce. PhD. Diss., Cornel1 Univ., Ithaca, NY. 26National Research Council. 1988. Nutrient requirements of dairy cattle. 6th ed. Natl. Acad. Sci., Washington, Dc. 27Robertson, J. B., and P. J. Van Soest. 1981. The detergent system of analysis and its application to human foods. Page 123 in Tbe analysis of dietary fiber in food. WP.T. James and 0. Theander. ed. Marcell
Journal of Dairy Science Vol. 74, No. 3, 1991
Dekkm, New York, NY. 28 SAS@ User’s Guide: Statistics. 1982. SAS Inst., Inc., C q , NC. 29Seymour. W. M., and C. E. P o h 1986. Dietary energy regulation during gestation on subsequent lactational response to soybean meal or dried brewers grains. J. Dairy Sci. 69:2837. NShaver, R. D., A. J. Nytes, L. D. Satter, and N. A. Jorgewn. 1986. Influence of amount of feed intake and forage physical form on digestion and passage of prebloom alfalfa hay in dairy cows. J. Dairy Sci. 69: 1545. 31 Udea, P., P. E. Coliucci and P. J. Van Soest. 1980. Investigation of chromium, cerium and cobalt as markers in digesta rate of passage studies. J. Sci. Food Agric. 31:625. 32Waybright. T. R.. and G. A. Varga. 1989. Effect of water-filled plastic bags on rumen fluid dynamics and total tract digestibility in sheep. I. Anim. Sci. (Suppl. 1) 67557. (Abstr.) 33 Wildman, E. E.. G. M. Jones, P. E. Wagner, R. L. Boman, H.F. Troun Jr., and T. N. Lesch. 1982. A aairy cow body condition scoring system and its relationship to selected production characteristics. J. Dairy Sci. 65:495. 34 Woodford, J. A., N. A. Jorgensen, and G. P. Barrington. 1986. Impact of dietary fiber and physical form on performance of lactating cows. J. Dairy Sci. 69:1035.
