Juice-Extracted Grass Pellets and Sodium Bicarbonate for Cows Fed Timothy Silage of Two Chop Lengths1. J. R. OROZCO·HERNANDEz2 and G. J. BRISSON3.
Juice-Extracted Grass Pellets and Sodium Bicarbonate for Cows Fed Timothy Silage of Two Chop Lengths 1 J. R. OROZCO·HERNANDEz2 and G. J. BRISSON3 Departement des Sciences Animales Faculte des Sciences de l'Agriculture et de l'Alimentation Universite Laval Sainte-Foy, ac, Canada G1K 7P4 V. GIRARD Service de la Zootechnie Direction de la Recherche et du Developpement Ministere de l'Agriculture, des Pecheries et de l'Alimentation du Quebec Deschambault, ce, Canada GOA 1S0 ABSTRACT
treatments. Reduction of particle size, from 30 to 3 mm, of timothy grass, treated with formic acid at harvest and using compaction at ensiling in bag silos, did not affect silage conservation characteristics but did improve milk, fat, and protein yields when cows were fed high silage diets. (Key words: chop length, timothy silage, sodium bicarbonate, milk)
Eighteen multiparous Holstein cows in midlactation were used in a switchback design trial to evaluate the effect of chop length (3 or 30 mm) of timothy grass silage, containing less than 30% ADF and treated with formic acid, on OMI and cow performance. Within chop length, the addition of NaHC03 (2% of OM!) or the replacement of 30% of silage OM with juice-extracted grass pellets was also evaluated. Cows were fed a TMR composed of 90% silage and 10% concentrate. Silage preservation characteristics were not different between chop lengths. The OM! and apparent digestibility were similar among treatments. Yields of 4% FCM (24.9 vs. 22.7 kg/d), fat (1.03 vs..93 kg/d), and protein (.83 vs..77 kgld) were higher with the short chopped silage. Milk protein, milk NPN content, and serum urea were higher for cows fed long chopped silage. Yields of milk and milk constituents were not affected by the addition of juice-extracted grass pellets or NaHC03. Fat percentage and fatty acid composition of milk remained unchanged by
Abbreviation key: JEGP grass pellets.
INTRODUCTION
Received August 22, 1994. Accepted June 16, 1995. lThis work was supported by a grant from the Conseil des Productions Animales du Quebec, Project Number 3027. 2Recipient of a scholarship granted by the Ministere de I'Education de Quebec. 3To whom correspondence should be addressed. 1995 J Dairy Sci 78:2415-2423
= juice-extracted
Reduction in the particle size of forage results in reduced rumination and lower milk fat percentage (30). Few studies have determined the effect of particle size reduction of grass on its preservation in the silo or the effect of the resulting grass silage on OM! and milk yield of dairy cows (5, 11, 12,23). Savoie et a1. (23), using timothy grass, and Castle et al. (5), using ryegrass, reported that reducing forage particle size (from 38.1 to 6.3 mm and from 72 to 9.4 mm, respectively) prior to ensiling enhanced conservation characteristics of silage, OMI, and milk yield. Particle size reduction to a smaller range (2.6 to 9 mm) had no effect on OMI and milk yield (13, 30). In general, reduced particle size decreases milk fat content. Use of formic acid as a silage additive improves the conservation quality of forage and therefore its nutritive value, which may offset the difference in fermentation characteristics among chop lengths (1, 16) and in-
2415
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OROZCO-HERNANDEZ ET AL.
crease DMI. Few studies (17, 19) have reported on the effect of formic acid addition and compaction for the conservation of timothy grass in plastic bag silos. Partial replacement of the DM of silage treated with formic acid by juice-extracted grass pellets (JEGP) and the utilization of NaHC03 enhanced performance of cows. The DMI, milk yield, and milk fat content increased when cows in midlactation were fed 3-mm timothy grass silage conserved in plastic bag silos (19). The objectives of this trial were to assess the effect of chop length, 3 or 30 mrn, of timothy grass silage treated with formic acid on DMI and cow performance. Within chop length, effects of the addition of NaHC0 3 (2% of DM) or the replacement of 30% of silage DM with JEGP on the DMI, milk output, and milk composition of cows in midlactation were also evaluated. MATERIALS AND METHODS Silages and JEGP
Boot stage timothy grass (Phleum pratense L.) was harvested from May 25 to June 2, 1992
with a precision chopper adjusted to a theoretical chop length of either 3 (short) or 30 mrn (long). At the time of mowing, grass was treated with formic acid (80%) at the rate of 7 Utonne and wilted for 1 h. All material was ensiled (three silos per chop length) using a silage compactor (Roto Press™; Sioux Center, Sioux City, IA) in 8-mm thick polyethylene bag silos (Agripac™; Alberta Ag-Industries Ltd., Westlock, AB, Canada) under mechanical compaction of 5 kg/cm 2. The juice from chopped timothy grass was extracted by pressure at 35 kg/cm 2; the resulting bagasse was further dried to 90% DM and then pelleted without binder to obtain the JEGP (19). Cows and TMR
Eighteen multiparous Holstein cows in midlactation (140 to 180 DIM; mean BW, 620 kg) were assigned to one of three groups according to calving date and milk yield during a 28- .05; Table 1), reflecting similar composition of herbages at ensiling. However, N and ADF contents were higher (P < .05) and the concentrations of propionic (P .07) and N-butyric (P < .01) acids were lower for the long than for the short chopped silage. Preservation was judged to be satisfactory based on pH, concentration of organic acids, ADIN, and NH3 N. Some researchers (1, 5) have reported better conservation with short chopped than with long chopped grass silage; others (11, 12, 23) observed no effect of chop length on silage
=
conservation, as was found in this experiment. The lack of effect of chop length on fermentation parameters may be the result of the addition of formic acid and the use of compaction at ensiling in plastic bag silos. Feed Consumption
Replacement of silage OM by JEGP increased the percentage of OM and NOF without affecting the AOF or N content, and the addition of NaHC03 increased the pH of the experimental TMR (Table 2). The OMI averaged 19.8 kgld (Table 3) and was not affected by the treatments (P > .05). However, NDF intake, as kilograms per day or as a percentage of BW, was increased 10.5 and 14%, respectively, when cows were fed JEGP than when they were fed control TMR. Oiffer-
TABLE I. Chemical composition and fermentation characteristics of short and long chopped timothy silages used in experimental TMR. Silage chop length 1•2 Short OM, %
27.6
29.3
SE
P
.65
.22
.07 .83 .61 .03
.05 .II .03 .41
2.58 1.51 .04 4.33 .01 .03
.27 .23 .07 .54 .007 .37
.39 .33 1.51
.43 .23 .93
(% of total OM) -
-
Total N NDF ADF pH
Long
3.0 43.3 27.2 4.2
3.2 45.8 28.4 4.1
- - (gIkg of OM) - Organic acids Lactic Acetic Propionic Formic N-Butyric Isovaleric
44.4 11.6 .31 22.7 .07
.02
50.5 13.6 .25 24.6 .04 .03
- - (% of total N) - -
ADIN NH3 N Water soluble N Length3 50 mm Arithmetic mean chop length, mm
7.1 5.6 56.1
7.2 6.4 56.4
75.5 12.3 8.0 4.2
5.7 50.2 34.0 10.1
7.5
27.5
lShort = 3-mm; long = 30-mm. 2Means of triplicate values for three silo samples. 3Percentage (wtIwt) in each size category, determined by manual separation. Journal of Oairy Science Vol. 78, No. 11, 1995
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CHOP LENGTH OF TIMOTHY SILAGE IN MIDLACTATION
TABLE 2. Ingredients and chemical composition of TMR (OM basis) including timothy silage at two chop lengths and NaHC03 addition or OM replacement with juice-extraeted grass pellets (JEGP). Shortl Control
NaHC03
Long Control
JEGP
NaHC03
JEGP
60.8 30.0
(% of OM) Ingredient Silage JEGP NaHC03 Rolled barley Mineral and vitamin mix2 Chemical composition OM. % N NOF AOF pH Calculated NEL. 3 Mca1Jkg of OM lShort
=3
mm; long
90.8
88.8
8.9 .3 31.0 2.7 44.7 26.4 4.1 1.66
= 30
60.8 30.0
90.8
88.8
2.0 8.9 .3
8.9 .3
8.9 .3
2.0 8.9 .3
8.9 .3
30.9 2.7 44.5 26.4 5.2
35.8 2.6 47.9 26.6 4.2
33.3 3.1 45.3 26.1 4.1
33.5 3.1 45.2 26.4 4.9
39.7 2.9 49.1 26.5 4.2
1.65
1.62
1.61
1.60
1.62
mm.
2Yitamin and mineral mix provided 2.01 % Ca, 7.52% P, 9.66% Mg, 17.1% Na, 25.4% Cl, 289,223 IU/kg of vitamin A, 86,770 IU/kg of vitamin 03, and 2780 IU/kg of vitamin E. 3CaIcuiated from the metabolizable energy (digestible energy x .82) concentration (l8, 29).
ences in dietary NDF between control and JEGP (Table 2) could account for the difference in NDF intake. The results of the present trial and those of Woodford et al. (30) suggest that NDF intake increases without affecting DM! as the percentage of forage in the ration increases. This observation and our results are contrary to the general opinion that increases
in NDF concentration in diet reduce DMI of lactating cows (3, 6). Intake of N was 10% higher with the long than with the short chopped silage. Similar quantities of NEL were consumed in all treatments (P > .05; Table 3). Our intake results are in agreement with results of Gordon (11, 12), who found no difference when dairy cows were fed ryegrass
TABLE 3. Intake as affected by silage chop length and NaHC03 addition or OM replacement with juice-extracted grass pellets (JEGP). Shortl Control
Effect2
Long
NaHC03 JOOP
Control
NaHC03 JOOP
SE
S
SxA
A p
Intake 3 OM, kgld 19.8 NDF, kgld 8.9 N, kgld .5 32.9 NEL' Mcalld Intake OM, % of BW 3.2 NDF, % of BW 1.4
19.3 8.6 .5 31.8
20.8 10.0 .5 33.7
19.9 9.0 .6 33.4
19.2 8.7 .6 31.2
19.9 9.8 .6 31.9
.85 .36 .02 1.82
.70 .95 .01 .67
.53 .03 .63 .71
.80 .86 .65 .81
3.0 1.3
3.3 1.6
3.1 1.4
3.0 1.4
3.2 1.6
.14
.48 .79
.42
.86 .89
.06
.02
lShort = 3 mm; long = 30 mm. 2S = Silage chop length, A = additive, and S x A = silage chop by additive interaction. 3Mean of nine cows per treatment. Journa\ of Dairy Science Yol. 78, No. 11, 1995
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OROZCO-HERNANDEZ ET AL.
chopped at particle lengths ranging from 12 to 52 mm and ensiled with formic acid. However, Castle et al. (5) reported better fermentation in the silo and higher intake and milk yield when chop length of silage was decreased from 72 to 9.4 mm. In the present trial, the lack of difference in total OM! among silage chop lengths could be the result of similar fermentation characteristics between silages (Table 1) and was probably associated with the low proportion of concentrate in the TMR; Beauchemin et al. (3) observed an interaction between silage chop length and the concentrate percentage. In fact, the low proportion of concentrate used in our trial may have diminished the effect of the chop length on OM!. Neither OM! nor intake of NDF was affected when cows were fed TMR containing sodium bicarbonate (P> .05). Although these results agree with those of Rogers et al. (20) and Stokes et al. (26), intakes are generally higher when silage pH is increased with NaHC03 (8, 19, 24). The lack of effect from the NaHC03 addition could be due to the high silage content of the diets used. Reduced forage particle size and increased TMR pH or OM percentage did not elicit a
positive intake response, suggesting that intake of timothy grass silages containing less than 30% ADF is not influenced by chop length between 3 and 30 mm. No chop length by additive interaction was found for OMI (P > .05). Apparent Total Tract Digestibility
Apparent total tract digestibility coefficients for OM. NDF. ADF. and gross energy averaged (mean ± SO) 77.5 ± 4.1 %, 76 ± 4.1 %, 71.7 ± 4.6%, and 76.1 ± 4.4%, respectively, and were similar among treatments (P > .05). which is in agreement with results of Anderson (1) and Castle et al. (5) in which chop length did not affect digestibility. Nevertheless, in a previous experiment, the addition of NaHC03 to a TMR based on 3-mm chopped timothy silage increased OM! and reduced digestibility of some nutrients (19). Other reports (10, 20, 25) on the use of NaHC03 in diets for dairy cows have shown no effect on OMlor apparent total tract digestibility. No chop length by additive interaction was found for digestibility coefficients (P > .05).
TABLE 4. Milk yield, milk composition, and BW changes as affected by silage chop length and NaHC03 addition or DM replacement with juice-extracted grass pellets (JEGP). Short!
Effect2
Long
Control NaHC03 JEGP
Control NaHC03 JEGP
SE
S
A
SxA
---p--Yield3 Milk, kgld 4% FCM, kgld Fat. kgld Protein. kgld
23.8
2404 .99 .83
23.9 25.6 1.1 .82
Composition Fat, % Protein, % NPN, % of total N Lactose, %
4.2 3.6 b 6.8 4.4
4.5 3Ac 7.3 4.6
Energy balance, Meal of NEL/d BW change, kgld Mi1klDMI, kglkg
.5 2.8 1.2
-1.6 -1.8 1.2
21.1 22.2 .91 .77
21.1 22.7 .92 .76
.91 .84 .04 .03
.01
.84
22.2 23.3 .96 .79
4.5 3.7" 7.1 4.7
404 3.6b 7.9 4.4
4.3 3.7" 8.0 4.7
4.5 3.7" 7.6 5.1
.18 .04 .27 .10
.7 2.3 1.1
2.0 4.1 1.1
.5 4.3 I.I
1.1 2.6 I.I
1.65 3.26 .04
23.4 24.8 1.0
.01 .04
.75 .91 .93 .87
.78 Al .34 .73
.99 .03
.63
.56
.09 .02
.006
.004 .57 .33 .33
.01
a,b.cMeans in the same row with no common superscript differ (P < .05). IShort = 3 mm; long = 30 mm. 2S = Silage chop length, A = additive, and S x A = silage chop by additive interaction. 3Mean of nine cows per treatment. Journal of Dairy Science Vol. 78, No. 11, 1995
.57 .29
.53 .82
.59 .82 .28
.87 .66 .61
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CHOP LENGTH OF TIMOTHY SILAGE IN MIDLACTATION
TABLE 5. Plasma fatty acids and serum metabolites as affected by silage chop length and NaHC03 addition or DM replacement with juice-extracted grass pellets (JEGP).l Short2 Control
Effect 3
Long
NaHC03 1EGP
Control
NaHC03 JEGP
SE
S
SxA
A
p Urea, mglml Serum metabolites, gIL Total protein Albumin Globulin Plasma fatty acids, mglml Lactic Acetic Propionic
3.9
3.4
3.8
4.9
4.4
5.5
.45
JYJ7
.37 .71
76.6 35.1 41.3
73.0 35.7 37.7
74.8 35.6 39.0
76.9 34.1 41.9
79.8 34.5 45.6
78.0 36.8 41.2
1.55 .75 1.87
.02
.98 .15 .25 .34 .76 .17
.11
.09
.06
.10
.II
.06
.05
.04
.06
.003
.002
.001
.003
.06 .004
1Mean
of nine cows per treatment.
2Short
= 3 mm;
3S
= Silage
long
= 30
chop length, A
.13 .03 .001
.52 .04
.01
.09
.006
.88
.002
.86
.62 .07 .45 .57 .66
.02
mm.
= additive,
and S x A
Milk Yield end Composition
Cows fed short cut silage yielded 10.4% more milk (fable 4) and 4% FCM than did those fed long chopped silage. Other researchers also observed higher milk yield, often associated with increased OMI, when grass particle length was reduced from 38.1 to 6.3 mm (23) or from 72 to 9.4 mm (5). However, the response to the present conditions differed from the results of Gordon (11), who found that neither milk yield nor OMI was affected by silage chop length. In the present study, neither OM! nor digestibility were affected by treatments; therefore, the higher milk yield of cows fed the short chopped silage may be associated with the tendency, although not statistically significant, for cows fed this type of silage to gain less BW. Silage chop length had no significant effect on milk fat percentage, but fat yield was higher for cows fed short chopped silage (1.03 vs..93 kg/d; Table 4). These results differ from those of Beauchemin et al. (3), who used alfalfa silage chopped to 5 and 10 mm supplemented with 35 or 65% concentrate, and from those of Grant et al. (13) who used particle sizes ranging from 2 to 3.1 mm and a ration containing 50% concentrate. Our results also differed from those study results of Savoie et al. (23) in which the particle size of timothy grass silage was reduced from 38.1 to 6.3 mm, and the
= silage
chop length by additive interaction.
rations were supplemented with 33.6% of concentrate. Such differences were probably associated with the low concentrate to forage ratio in the TMR used here, because increasing forage in the diet elevated the acetate to propionate ratio in the rumen and increased milk fat percentage. Therefore, the high milk fat percentage observed in the present trial was perhaps the result of the high forage to concentrate ratio in the TMR. The proportions of the fatty acids C6:0 to C14:0, C16:o. CI8:0, CI8:1, and C18:2 in the milk averaged (mean ± SD) 27.7 ± 1.6%, 26.3 ± 3.1%, 9.6 ± 1.1%, 22.1 ± 1.7%, and 1.97 ± .2%, respectively, and were not affected by treatments (P > .05). This result agrees with those of Chouinard et al. (6), who reported similar values for cows in midlactation fed diets based on timothy silage but without concentrate. Feed efficiency (kilograms of milk per kilogram of OMl) was significantly lower for cows fed the long chopped silage, but percentages of milk protein and milk NPN were higher for cows fed the long chopped silage (Table 4). Cows fed the short chopped silage tended (P > .05) to gain less BW (1.1 vs. 3.7 kg/d) than those fed the long chopped silage. Nevertheless, experimental periods were short (21 d) in order to obtain accurate BW change measures. The higher milk protein and NPN content may be associated with the higher N intake and serum urea (fable 5) of cows fed long chopped Journal of Dairy Science Vol.
78. No. 11, 1995
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OROZCO-HERNANDEZ ET AL.
silage. Nevertheless, Gordon (11) reported no effect of chop length on milk composition. The interaction between silage length and additive was likely significant because of the NaHC03 addition to the short chopped silage. In the present trial, addition of NaHC03 of JEGP elicited no effect on milk yield or composition (P > .05; Table 4) in contrast to the results of our previous trial in which DMI and milk yield were higher when NaHC03 or JEGP treatments were compared with controls (19). In general, experimental conditions were similar during both trials, except that the percentage of concentrate in the diet was much higher in the previous study. None of the treatments influenced milk lactose content or BW changes. The absence of an effect on milk composition when NaHC03 was added to the TMR is in agreement with other reports (8, 9, 10, 20). Blood Components
Urea N, total protein, and globulin were higher for the long than for the short chopped silage (Table 5), but albumin was not affected. Savoie et al. (23) reported that cows fed short chopped timothy silage had lower blood urea N concentrations. Our values were similar to those reported for cows by Blum et al. (4). Concentrations of lactic and propionic acids in plasma were not significantly affected by the treatments (P> .05; Table 5). However, plasma acetic acid decreased as a result of the JEGP. No silage by additive interaction was observed for blood components. CONCLUSIONS
The present study showed no effect of silage chop length on timothy grass silage preservation when formic acid was applied at harvest and compaction was used at ensiling in bag silos. For cows in midlactation, diets high in finely chopped timothy silage (Le., 3-mm theoretical chop length) had no effect on DMI, but increased milk, milk fat, and milk protein yield and maintained milk fat content and milk fatty acid proportions. However, the addition of NaHC03 or the replacement of silage DM with JEGP had no effect on DMI or milk yield and composition. Cows fed the 30-mm silage had higher blood urea and milk yield with Journal of Dairy Science Vol. 78. No. 11. 1995
more NPN content than those fed the 3-mm silage. ACKNOWLEDGMENTS
The authors thank Alain Brisson and Serge Gignac of the Ministere de l' Agriculture, des Pecheries et de l' Alimentation du Quebec experimental farm at Deschambault for care and feeding of cows and Martin Tremblay for his technical assistance. We also thank Nancy Bolduc and the laboratory staff of the Departement des sciences animales for their assistance during analysis. REFERENCES 1 Anderson, R. 1982. Effect of stage of maturity and chop length on the chemical composition and utilization of formic acid-treated ryegrass and formic acid silage by sheep. Grass Forage Sci. 37:139. 2 Association of Official Analytical Chemists International. 1990. Official Methods of Analysis. 15th ed. AOAC, Arlington, VA. 3 Beauchemin, K. A., B. 1. Farr, L. M. Rode, and G. B. Schaalje. 1994. Effects of alfalfa silage chop length and supplementary long hay on chewing and milk production of dairy cows. J. Dairy Sci. 77:1326. 4 Blum, J. W., P. Kunz. H. Leuenberger. K. Gautschi, and M. Keller. 1983. Thyroid hormones. blood plasma metabolites, and haernatological parameters in relationship to milk yield in dairy cows. Anim. Prod. 36: 93. 5 Castle, M. E., W. C. Retter, and J. N. Watson. 1979. Silage and milk yield: comparison between grass silage of three different chop lengths. Grass Forage Sci. 34:293. 6 Chouinard. P. Y., M. E. Uriarte. V. Girard. and G. 1. Brisson. 1993. Milk fatty acids in cows fed timothy grass silage: effect of growth stage and concentrate level. J. Dairy Sci. 76(Suppl. 1):212.(Abstr.) 7 Christian, K. R., and M. R. Coup. 1954. Measurement of feed intake by grazing cattle and sheep. VI. The determination of chromic oxide in faeces. NZ. J. Sci. Technol. 36:328. 8 Erdman. R. 1988. Forage pH effects on intake in early lactation dairy cows. J. Dairy Sci. 71:1198. 9 Erdman. R. A., R. L. Botts. R. W. Hemken, and L. S. Bull. 1980. Effect of dietary sodium bicarbonate and magnesium oxide on yield and physiology in early lactation. 1. Dairy Sci. 63:923. 10 Fisher, L. J., and V. G. Mackay. 1983. The investigation of sodium bicarbonate or bentonite as supplement in silage fed to lactating cows. Can. J. Anim. Sci. 63: 939. 11 Gordon. F. J. 1982. The effect of degree of chopping grass for silage and method of concentrate allocation on the performance of dairy cows. Grass Forage Sci. 37:59. 12 Gordon. F. J. 1986. The effect of system of silage harvesting and feeding on milk yield. Grass Forage Sci. 41 :209.
CHOP LENGTH OF TIMOTHY SILAGE IN MIDLACTATION 13 Grant, R. 1., V. F. Colenbrander, and D. R. Mertens. 1990. Milk fat depression in dairy cows: role of silage particle size. J. Dairy Sci. 73: 1834. 14 Lowry, S. R 1992. Use and misuse of multiple comparisons in animal experiments. 1. Anim. Sci. 70:1971. 15 Lucas, H. L. 1956. Switchback trials for more than two treatments. J. Dairy Sci. 39: 146. 16 Muck, R. E. 1988. Factors influencing silage quality and their implications for management. 1. Dairy Sci. 71:2992. 17 Narasimhalu, P., L. J. Halliday, 1. B. Sanderson, H. T. Kunelius, and K. A. Winter. 1992. The composition, intake, and digestibility of timothy silage preserved untreated or treated with fonnic acid or a cellulasehemicellulase preparation. Can. J. Anim. Sci. 72:431. 18 National Research Council. 1989. Nutrient Requirements of Dairy Cattle. 6th rev. ed. Natl. Acad. Sci., Washington, DC. 19 Orozco, H.l.R, V. Girard, and G. Brisson. 1994. Juice-extracted grass pellets and sodium bicarbonate for cows in midlactation fed timothy grass silage. J. Dairy Sci. 77:3644. 20 Rogers, J. A., L. D. Muller, T. J. Snyder, and T. L. Maddox. 1985. Milk production, nutrient digestion, and rate of digesta passage in dairy cows fed long or chopped alfalfa hay supplemented with sodium bicarbonate. J. Dairy Sci. 68:868. 21 Sanders, W. L., and P. J. Gaynor. 1987. Analysis of switchback data using Statistical Analysis System, Inc.~ software. 1. Dairy Sci. 70:2186.
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22 SASI! User's Guide, Statistics, Version 5 Edition. 1985. SAS Inst., Inc., Cary, NC. 23 Savoie, P., D. Tremblay, G. F. Tremblay, J.-M. Wauthy, F. M. Aipot, and R. Theriault. 1992. Effect of length of cut on quality of stack silage and milk yield. Can. J. Anim. Sci. 72:253. 24 Shaver, RD., R A. Erdman, A. M. O'Connor, and J. H. Vandersall. 1985. Effects of silage pH on voluntary intake of com silage and alfalfa haylage. J. Dairy Sci. 68:338. 25 Stokes, M. R, and L. S. Bull. 1986. Effects of sodium bicarbonate with three ratios of hay crop silages to concentrate for dairy cows. J. Dairy Sci. 69:2671. 26 Stokes, M. R, L. S. Bull, and W. A. Halteman. 1985. Rumen liquid dilution rate in dairy cows fed once daily: effects of diet and sodium bicarbonate supplementation. 1. Dairy Sci. 68: 1171. 27 Tyrrell, H. F., and J. T. Reid. 1965. Prediction of the energy value of milk. J. Dairy Sci. 48:1215. 28 Van Soest, P. G., and J. B. Robertson. 1985. Analysis of Forages and Fibrous Foods. Cornell Univ. Press, Ithaca, NY. 29 Walter, J. P., and 1. L. Mao. 1989. Modeling net energy efficiencies as quantitative characteristics in lactating cows. J. Dairy Sci. 72:2362. 30 Woodford, J. A., N. A. Jorgensen, and G. P. Barrington. 1986. Impact of dietary fiber level and physical form on performance of lactating dairy cows. J. Dairy Sci. 69:1035.
Journal of Dairy Science Vol. 78, No. 11, 1995
