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or Soybean Meal1
Nutritional Value of Urea Versus Preformed Protein for Ruminants. I1. Nitrogen Utilization by Dairy Cows Fed Corn Based Diets Containing Supplemental Nitrogen from Urea and/or Soybean Meal z J. E. W O H L T , J. H. C L A R K , and F. S. B L A I S D E L L Department of Dairy Science University of Illinois Urbana 61801
ABSTRACT
INTRODUCTION
Fifteen Holstein cows at various stages of lactation, fed corn-based diets that contained 9 to 14.5% crude protein were used in total collection digestibility and nitrogen balance trials to investigate the efficiency of nitrogen utilization from urea and soybean meal. Digestibility coefficients for dry matter, organic matter, crude protein, and nitrogen-free-extract, as well as total digestible nutrient content of diets that contained 13 to 14.5% crude protein, were 3 to 8 percentage units greater than for diets that contained 9 to 12% crude protein. The concentration of ammonia-N in rumen fluid of cows fed diets that contained 9 to 12% crude protein was less than 5 mg/100 ml and may have decreased digestibility and synthesis of microbial protein in the rumen. When the diet contained 11 to 12% crude protein, nitrogen supplied as urea or soybean meal was used with equal efficiency. The concentration of ammonia-N in r u m e n fluid of cows fed diets that contained 13 to 14.5% crude protein was greater than 5 mg/100 ml and was greatest when urea was the source of supplemental nitrogen. However, more milk and milk protein were produced when soybean meal was fed to the cows. The increased production from feeding soybean meal resulted in nitrogen from soybean meal being utilized more efficiently for milk production than nitrogen supplied as urea when the diet contained 13 to 14.5% crude protein.
The protein requirement for dairy cows has been reported as crude protein or digestible protein (20). When expressed as digestible protein, the protein requirement may be defined incorrectly because digestible protein may not describe the quantity of amino acids absorbed when NPN supplementation provides more ammonia-N than can be converted into microbial protein (3, 4, 32). It has been suggested that NPN supplementation of diets that contain 12 to 13% protein will not increase rumen microbial protein synthesis (3, 4, 32) and, thus, will not increase amino acid absorption or milk production. However, other researchers (14) suggest that high producing dairy cows can benefit from addition of NPN to diets containing crude protein in excess of 11 to 12%. Diets fed to dairy cows in early lactation usually contain more than 12 to 13% crude protein from sources of plant protein. If additions of NPN to diets to increase the crude protein content above 12 to 13% do not increase microbial protein synthesis, or digestibility of substrate in the rumen, then NPN would be of no value to the animal. In this study, lactating dairy cows were fed corn-based diets that contained 9 to 14.5% crude protein to investigate the efficiency of nitrogen utilization from urea and soybean meal for milk production. EXPERIMENTAL PROCEDURE
Received December 2, 1977. 1Supported in part by the Illinois Agricultural Experiment Station, the National Soybean Processors Association, and HEW PHS FD 00849. 1978 J Dairy Sci 61:916--931
916
Three cows assigned to each of the dietary treatments in a companion lactation trial (37) were used in total collection digestibility and nitrogen balance trials at days 16 to 20, 66 to 70, and 176 to 180 of lactation. Management and feeding of these cows were as for cows in (37). Ingredient and chemical composition of the diets are in (37). Quantities of hay, corn silage, and concentrate fed and refused were weighed, sampled daily, and dried in a forced air oven at 55 C. Total fecal excretion of
NITROGEN UTILIZATION BY LACTATING COWS each cow was collected daily, and 3% of the fecal o u t p u t was composited, preserved with thymol, and stored at 4 C until the end of the 5-day collection. An indwelling urinary catheter was placed into the bladder of each cow (9). Urine was collected in polyethylene containers that contained 50 ml of 6 N HC1 and was measured and sampled daily. Daily aliquots of urine were stored at 4 C and composited by volume at the end of each collection period. Milk yield was measured daily, and samples of milk from each of the two daily milkings were composited for each cow, preserved with potassium dichromate, and stored at 4 C. At the end of the 5-day collection all daily milk samples were composited according to milk yield. The day immediately following each collection period, rumen fluid was sampled by stomach tube at 2 and 7 h postfeeding (1100 and 1600 h), and blood samples were drawn from the jugular vein at 2 h postfeeding (1100 h). Ammonia-N in rumen fluid and urea-N in plasma were determined by a modified Conway procedure (12). Dried composite samples of feed, feed refused, and feces from the total collection digestibility trials were analyzed for crude protein, ether extract, ash (2), nitrogen solubility (38), and acid detergent fiber (36). Urine samples were analyzed for nitrogen content by the Kjeldahl m e t h o d (2). Milk samples were analyzed for crude protein (2), fat (Babcock), and solids-not-fat (Golding Bead Test). To determine significant differences among treatments, data collected were analyzed statistically by analysis of variance and Duncan's new multiple range test (34). RESULTS A N D DISCUSSION
Intakes of dry matter and nitrogen as well as milk, 4% FCM, milk protein, and milk fat yields of cows in these digestibility and nitrogen-balance trials (Tables 1, 2) were similar to those for cows in (37). Between days 66 and 70 postcalving, milk yields for cows in the total collection trials and fed the five diets were: 1) 73, 2) 97, 3) 94, 4 ) 9 4 , and 5) 104% of that during days 16 to 20 of lactation (Table 2). Average daily milk production of cows used in the total collection trials and fed diets 2, 3, 4, and 5 did not differ significantly during days 66 to 70 of lactation (Table 2). These results suggest that diets 2 and 3 supplied sufficient
917
nitrogen up to this point in the trial to meet the cows' requirement for amino acids since additional nitrogen fed in diets 4 and 5 did not increase milk production significantly. However, the greater milk production of cows fed diet 5 during days 176 to 180 of lactation (Table 2) indicate that diets 2, 3, and 4 were not meeting the amino acid requirement of these cows over a longer time and that body protein reserves were being depleted (37). Therefore, short studies using a small number of animals to determine the crude protein requirement and efficiency of utilization of protein and urea can lead to erroneous conclusions. Feeding diet 5 which contained soybean meal as the supplemental source of nitrogen resulted in about a 10% greater production of milk, 4% FCM, and milk protein than feeding diet 4 which contained urea (37). A shortage of ammonia-N in rumen fluid must not have been the cause of the depressed milk production of cows fed diet 4 because the concentration of ammonia-N in rumen fluid of cows fed diet 4 was greater than the concentration in rumen fluid of cows fed diet 5 (Table 3). The increase in milk production of cows fed diet 5 compared to cows fed diet 4 (37) probably was due to a great quantity of dietary protein (soybean meal) escaping degradation in the rumen and flowing to the lower gut which resulted in a greater quantity of absorbable amino acids for maintenance, gluconeogenesis, and synthesis of milk protein. Clark (8) has indicated that supplying additional high quality protein postruminally increased milk production, and Orskov and Fraser (22) demonstrated that an increased concentration of plant protein in the diet increased the amount of plant protein that escaped rumen degradation. Insoluble nitrogen intake, although it has limitations, was an indicator of the quantity of protein that escaped rumen degradation and was greatest for cows fed diet 5 (Table 1, Table 3, Fig. 1D; (37)). However, intake of insoluble nitrogen was greater for cows fed diet 3 than for cows fed diet 2, but responses from animals suggest that similar quantities of amino acids were available to cows fed these diets (37). More microbial protein may have been synthesized in the rumen when cows were fed diet 2 compared to diet 3 because of a shortage of ammonia-N in the rumen when cows were fed diet 3 (Table 3). However, more dietary protein probably esJournal of Dairy Science Vol. 61, No. 7, 1978
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TABLE 1. Average dry matter, crude protein, soluble, and insoluble nitrogen intake of cows fed diets containing varying co n cen tr atio n s of crude protein supplem e n t e d with urea and/or soybean meal. Diets < O Ox
Days of lactation
Z 9
1 No supplemental nitrogen (Mean + SE)
2
3
Urea
Soybean meal
(Mean -+ SE)
4 Urea + soybean meal
(Mean + SE)
5 Soybean meal
(Mean + SE)
(Mean + SE)
18.9 20.9 20.4 ab
19.3 21.1 22.4 b
Total dry m a t t e r (kg/day) -q Oo
16 to 20 e
66 to 70 176 to 180
18.1 15.9 15.8 a
.2 1.2
17.3 20.1 20.0 ab
.7 1.6
16.4 20.4 19.4 ab
1.4 1.9
1.6 1.9
3.0 1.3
-v
Crude protein (kg/day) 16 to 20 66 to 70 176 to 180
2.56 1.49 a 1.62 a
.05 .09
2.55 2.33 b 2.38 b
.04 .19
2.65
2.36 2.37 b 2.32 b
.09 .23
2.66
2.87 bc 2.73 bc
.15 .18
.~
2.99 c 3.22 c
.37 .30
Soluble nitrogen (g/day) 16 to 20 66 to 70 176 to 180
144 48 a 62 a
16 to 20 66 to 70 176 to 180
266 190 a 197 a
3 3
143 138 b 129 bc
7 13
264 235 ab 251 ab
11 14
131 88 c 86 d
4 14
150 155 b 152 b
7 11
151 96 c 103 cd
17 9
274 304 b 285 b
31 18
275 383 c 411 c
43 40
Insoluble n i t r o g e n ( g / d a y ) 4 21
246 291 b 286 b
11 27
a'b'C'dMeans within a given row not bearing a c o m m o n superscript are different (P<.05). eDuring days 16 to 20 of lactation all cows were fed diet 4 s u p p l e m e n t e d with urea and soybean meal.
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NITROGEN UTI LI ZATION BY LACTATING COWS caped degradation in the rumen in cows fed diet 3 compared to cows fed diet 2. Therefore, the ratio of fractions of microbial and undegraded dietary protein leaving the rumen of cows fed diets 2 and 3 may have been different, but the combination of microbial and plant protein available from both diets must have supplied similar quantities of amino acids to the lower gut of both groups of cows because production did not differ significantly (37). Effiency of nitrogen utilization was lower when cows were fed diets high in soluble nitrogen in our trials and in the nitrogen-balance trials of Aitchison et al. (1). This probably is due to soluble nitrogen being degraded rapidly and ammonia-N released in the rumen in excess of the requirement for microbial growth not being utilized by the cow. Apparent digestibility and TDN content o f diet 4 did not differ significantly among groups of cows during days 16 to 20 of lactation (Table 4). Digestibility of dry matter was 3 to 8 percentage units greater for diets 4 and 5 than for diets 1, 2, and 3 during days 66 to 70 and 176 to 180 of lactation. When diets 4 and 5 were fed, digestibilities of organic matter, crude protein, and nitrogen-free-extract also were increased compared to the other three diets. Digestibilities of acid detergent fiber and ether extract did not differ significantly among treatments but did increase slightly as crude protein increased in the diet. Thus, as a result of the improvement in digestibility of the various dietary components, the TDN content o f diets 4 and 5 was 4 to 6 percentage units greater than for diets i , 2, and 3. Generally as feed intake is increased, digestibility is depressed (27, 28); however, in this study digestibility increased as feed intake increased, indicating some nutritional factor must have limited digestibility of the low protein diets. Jacobson et al. (17) suggested that the primary reason for feeding a diet that contained a high concentration of crude protein to lactating dairy cows was to encourage greater intake of energy which increased milk production and efficiency of conversion of feed to milk. Feeding diets that contain less than 10% crude protein depressed feed intake (5, 6, 10, 11). Campling et al. (6) have shown that when low protein diets are fed, the low nitrogen content of the rumen digesta was a major factor which limited the rate of fermentation in the rumen and rate
919
of passage of feed through the digestive tract. Also, the addition of urea to corn silage at ensiling (15, 16) increased feed intake and digestibility if adequate nitrogen was not supplied already to the animal. Therefore, the low intake of crude protein in our experiments (Table 1), (37) probably contributed to the lower intakes of corn silage and total dry matter for cows fed diet 1. Digestibility of dietary components (Table 4) did not appear to be depressed until the concentration of ammonia-N in the rumen was below 4 to 5 mg/100 ml (Table 3). Rumen fluid samples obtained 2 and 7 h postfeeding from cows fed diet 1 contained less than 5 mg/ 100 ml ammonia-N (Table 3), suggesting that rumen fermentation was limited by shortage of ammonia (19) and that synthesis of microbial protein may not have been maximal (21, 33). Essentially all of the ammonia-N available in the rumen of cows fed diet 1 must have been incorporated into microbial protein since the concentration of urea-N in plasma (Table 3) and the quantity of nitrogen secreted in the urine (Table 5) were significantly less for these cows than for cows fed the nitrogen supplemented diets. The concentration of ammonia-N at 2 and 7 h postfeeding in rumen fluid of cows fed diet 3 also was below 5 mg/100 ml during days 66 to 70 and 176 to 180 of lactation. Therefore, digestibility and synthesis of microbial protein in the rumen may have been reduced for cows fed this diet. Availability of ammonia-N in the rumen of cows fed diets 1 and 3 may have limited microbial fermentation which decreased dry matter intake, synthesis of microbial protein, and milk production. Cows fed diet 2 had a higher concentration of ammonia-N in the rumen 2 h after feeding than did cows fed diets 1 and 3. At this time the concentration of ammonia-N in the tureen fluid may not have been limiting microbial fermentation and synthesis of microbial protein. However, at 7 h postfeeding during days 66 to 70 and 176 to 180 of lactation the concentration of ammonia-N in the rumen was marginal (2 to 5 mg/100 ml) for maximal microbial fermentation or synthesis of microbial protein. At 7 h postfeeding the concentration of ammonia-N in rumen fluid of cows fed diets 4 and 5 was two-fold higher than the concentration of ammonia-N in rumen fluid of cows fed diets 1, 2, and 3. Therefore, diets 4 Journa| of Dairy Science Vol. 61, No. 7, 1978
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TABLE 2. Average m i l k p r o d u c t i o n and m i l k c o m p o s i t i o n of cows fed diets containing varying concentrations of crude protein s u p p l e m e n t e d with urea an d /o r soybean meal.
< o
Diets
Ox
Z
O -.]
Days of lactation
1 No supplemental nitrogen
2
3
Urea
Soybean meal
(Mean -+ SE)
(Mean + SE)
34.5 25.2 a 17.4 a
35.6 34.6 b 26.7 be
4 Urea + soybean meal
(Mean -+ SE)
5 Soybean meal
(Mean -+ SE)
(Mean -+ SE)
35.8 33.7 b 22.7 ab
38.3 39.9 b 32.0 c
Milk (kg/day) 16 to 20d 66 to 70 176 to 180
.5 .3
2.2 1.8
35.3 33,6 b 23.3 ab
3.0 2.2
.5 1.2
4.3 2.5
>
4% fat-corrected-milk (kg/day) 16 to 20 66 to 70 176 to 180
33.9 22.8 a 15.4 a
16 to 20 66 to 70 176 to 180
3.31 2.83 3.06
.5 .2
28,6 28,8 b 22,4 b
1.3 .8
33.3 30.8 b 20.9 ab
2.7 1.5
32.1 32.5 b 22.2b
1.5 1.1
37.8 33.5 b 27.3 b
4.5 3.3
Milk protein e (%) .05 .08
3.07 2.77 2.90
.03 .07
3.22 2.97 3.21
.18 ,11
3,10 3.09 3,38
.15 .26
3.24 3.08 3.21
.11 .17
Milk protein e (g/day) 16 to 20 66 to 70 176 to 180
1141 715 a 532 a
1087 957 ab 775 ab
17 20
1162 1001 bc 747 a
55 65
1114 1041 bc 779 ab
119 69
1229 1239 e 1025 b
52 59
177 76
Milk fat (%) 16 to 20 66 to 70 176 to 180
4.20 a 3.37 3.23
.03 .06
3.57 b 2.93 2.95
.50 .18
4.20 a 3.47 3.38
.30 .34
© m
3.88ab 3.77 3.87
,29 .35
3.96ab 2.90 3.02
.12 .41
NITROGEN UTILIZATION BY LACTATING COWS 00x 0o ox
xO eq t ~
o~ o6 o6
,0oo~
it~ t ~ ox~
~¢qoo
v
¢q " 0
0
o q v
,~-Ox
q~.
Oxe¢~ eq~eq t ~ Ox 00 ~ox~
~d 06 ~6
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o60d~ ,6 X
z
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Y
921
and 5 may have maintained the minimal ammonia-N concentration required in the rumen longer which increased rumen fermentation and synthesis of microbial protein compared to diets 1, 2, and 3. The increased digestibility and TDN content of diets 4 and 5 (Table 4) support this assumption. The amount of nitrogen consumed and absorbed was not significantly different between cows fed diets 2 and 3 (Table 5). Milk production (Table 2) and nitrogen utilization for synthesis of milk protein (Tables 5, 6, 7) also were similar for cows fed diets 2 and 3, which indicated equally efficient utilization of nitrogen from urea and soybean meal when the diet contained 11 to 12% crude protein. Since nitrogen intake and absorption were greater for cows fed diet 5 than for cows fed diet 4 (Table 5), efficiency of nitrogen utilization expressed as a percentage of nitrogen intake or nitrogen absorbed would be expected to be lower for diet 5 if both soybean meal and urea were utilized equally efficient at equal intakes of nitrogen. However, efficiency of nitrogen utilization for synthesis of milk protein by cows fed diet 5 was 5 to 10 percentage units greater than for cows fed diet 4 (Tables 6, 7). The more efficient utilization of nitrogen supplied as soybean meal may have been due to more efficient utilization of nitrogen in the rumen because the concentration of ammonia-N was low or because a greater quantity of the dietary protein escaped degradation when soybean meal was fed. Until recently, it was assumed that all sources of nitrogen fed to the ruminant would result in equal amounts of amino acids reaching the small intestine, and, therefore, animal production would be equal. However, when NPN supplies the rumen with more ammonia-N than can be incorporated into microbial protein, digestible protein may not describe the quantity of amino acids absorbed from the gastrointestinal tract. Burroughs et al. (3, 4) and Satter and Roffler (32) have advocated metabolizable protein as a means of defining the protein requirement of the ruminant instead of digestible protein or crude protein. Satter and Roffler (32) indicated that the a m o u n t of crude protein needed to supply the amino acids (metabolizable protein) required for maintenance and milk production can be calculated if milk production, feed intake, body weight, and the amount of b o d y weight lost or gained are Journal of Dairy Science Vol. 61, No. 7, 1978
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TABLE 3. Ammonia-N concentration and pH of l u m e n fluid and urea-N c onc e nt ra t i on in plasma of lactating cows fed diets containing varying concentrations of crude protein s u p p l e m e n t e d with urea and/or soybean meal.
x~ tJ tJ
Diets
<
Days of lactation
1 No supplemental nitrogen (Mean _+ SE)
2
3
Urea
Soybean meal
(Mean -+ SE)
Z
(Mean -+ SE)
5 Soybean meal
(Mean +- SE)
(Mean -+ SE)
2 h postfeeding ammonia-N (mg/ 100 ml)
O
.q 00
4 Urea + soybean meal
16 to 20 d 66 to 70 176 to 180
11.13 1.39 a 3.32 a
16 to 20 66 to 70 176 to 180
5.81 1.23 a 1.23 a
16 to 20 66 to 70 176 to 180
7.04 6.70 6.97
16 to 20 66 to 70 176 to 180
6.60 6.72 6.94
16 to 20 66 to 70 176 to 180
11.13 2.73 a 5.46 a
1.15 1.87
9.62 9.50 bc 11.09 b
4.50 2.72
6.90 4.18 ab 6.32 ab
1.16 .39
9.08 12.98 c 11.20 b
3.77 .37
7.55 6.22 abc 1.39 8.09 ab 2.23
7 h postfeeding ammonia-N ( m g / l O 0 ml) .06 .51
6.04 4.13 ab 2.14 ab
.09 .09
7.01 6.65 6.97
.11 .20
6.82 6.59 6.88
2.12 .60
8.92 1.87 a 2.41 ab
1.32 .58
5.88 11.14 c 4.28 ab
0
.78 .81
7.69 6.27 b 5.03 b
7.03 6.57 7.17
.04 .27
6.85 6.60 6.76
.23 .02
6.68 6.57 6.93
.14 .16
7.08 6.89 6.82
.15 .07
1.37 1.03
2 h postfeeding rumen fluid pH .12 .12
6.53 6.63 6.87
.04 .11
7 h postfeeding rumen fluid pH .21 .07
6.37 6.63 6.90
.12 .12
2 h postfeeding plasma urea-N (mg/ 100 ml) .33 .32
11.83 6.48 abc 1.16 10.55 ab 2.68
10.66 5.73 ab 6.64 a
1.66 .38
a'b'CMeans within a given row not bearing a c o m m o n superscript are different (P<.05). dDuring days 16 to 20 of lactation all cows were fed diet 4 s u p p l e m e n t e d with urea and soybean meal.
9.10 11.63 c 13.07 b
.56 3.08
13.55 10.93 bc 13.45 b
2.14 1.58
NITROGEN UTILIZATION BY LACTATING COWS known and certain assumptions accepted. These assumptions are that daily production of milk protein contains 95% true protein (7, 23), that the maintenance requirement for metabolizable protein is 2.4 g per kg body weight -75 (32), and that the effciency with which metabolizable protein is utilized for milk production and gain of body weight is 60%. Digestibility studies during days 16 to 20 of lactation indicated that cows were consuming 1725 g of digestible protein per day. By the assumptions of Satter and Roffler (32), the diet consumed during the same period provided 1721 g of metabolizable protein per day. Therefore, during this period metabolizable protein was equal to digestible protein even though urea was a component of the diet. This suggests that according to guidelines of Satter and Roffler (32), urea was not greatly in excess and was being converted into microbial protein. Burroughs et al. (4) suggest that 1497 g of metabolizable protein were available per day to cows during days 16 to 20 of lactation. According to calculations of Satter and Roffler (32), cows fed diets 1 to 5, respectively, were receiving 1118, 1747, 1777, 1941, and 2113 g of metabolizable protein per day during days 66 to 70 o f lactation. By the metabolizable-protein scheme of Burroughs et al. (4), cows fed diets 1 to 5, respectively, received 1175, 1593, 1655, 1746, and 1851 g of metabolizable protein per day. The metabolizable protein concept of Satter and Roffler (32) estimated that more protein was available to the cows than did the metabolizable protein concept of Burroughs et al. (4) or the measured digestible protein intake. This may be due to the fact that digestible protein and the metabolizable protein concept of Burroughs et al. (4) do not consider the possibility that ureaN may be recycled to the rumen and incorporated into microbial protein. The concepts of metabolizable protein, digestible protein, and insoluble or soluble nitrogen are valuable theoretical tools but at best can give only estimates of amino acid availability to the animal until additional data are accumulated. Experiments using lactating cows with re-entrant cannula are needed to indicate the quantity of amino acids absorbed when various diets are fed. Burroughs et al. (3, 4) and Satter and Roftier (32) also developed concepts which estimate the quantity of urea that can be fed per unit of dry matter in the ration for achieving
923
maximum incorporation of urea-N into microbial protein. Calculated urea fermentation potential (UFP) values (4) predicted that urea would not be beneficial in diet 4 during the first 30 wk of lactation and that only 67% of the urea added to diet 2 would be incorporated into microbial protein. Prior to addition of urea, diet 4 consumed during days 16 to 20 of lactation contained 11.9% crude protein. The calculated TDN content of diet 4 was 76% (20), but the measured TDN content was about 69% (Table 4). In predicting the upper limit of NPN utilization, Satter and Roffler (32) calculated the TDN content of the diets using TDN values for feedstuffs from NRC (20). Therefore, to use values from tables of Satter and Roffler (32) to predict the upper limit of NPN utilization required that the TDN content of the diet be calculated from TDN values obtained from NRC (20) (Satter, personal communication). Since the calculated TDN content of diet 4 was 76%, Satter and Roffler (32) suggest this diet could be supplemented with urea to increase the crude protein from 11.9 to 12.8%. An average concentration of ammonia-N in rumen fluid of 3.5 mg/100 ml was predicted for cows fed diet 4 prior to addition of urea (30). Since 3.5 mg/ 100 ml ammonia-N is below the minimum concentration of ammonia-N adequate for maximum synthesis of microbial protein (21, 32, 33), this also suggests that urea supplementation may contribute ammonia-N that can be used for synthesis of microbial protein. Calculations as suggested by Satter and Roffler (32) indicate that urea would be beneficial in both diet 2 and diet 4 with an estimated 100% and 50%, respectively, of the urea-N being incorporated into microbial protein during days 66 to 70 of lactation. Milk production in the companion lactation trial (37) and results of the total collection trials indicate that urea supplementation was beneficial in both diets 2 and 4 but was not as beneficial in diet 4 as soybean meal was in diet 5. Our data, therefore, support the concept of Roffler and Satter (29, 30) that urea would be beneficial in both diets 2 and 4 but not as beneficial as supplying soybean meal when the diet contained 13.5 to 14.5% crude protein. Urea supplementation of low protein diets definitely increased milk production, but the response in milk production decreased as the concentration o f protein in the diet prior to addition of urea was increased (37). ObservaJournal of Dairy Science Vol. 61, No. 7, 1978
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T A B L E 4. A p p a r e n t d i g e s t i b i l i t y a n d t o t a l d i g e s t i b l e n u t r i e n t c o n t e n t o f d i e t s c o n t a i n i n g v a r y i n g c o n c e n t r a t i o n s o f c r u d e p r o t e i n s u p p l e m e n t e d w i t h u r e a a n d / o r soybean meal.
O O~
Diets
Z O
Days of lactation
1 No supplemental nitrogen
2
3
Urea
Soybean meal
4 Urea + soybean meal
5
( M e a n + SE)
( M e a n + SE)
( M e a n -+ SE)
( M e a n +- SE)
Soybean meal ( M e a n + SE) O .r
D r y m a t t e r (%) 16 t o 2 0 d 66 to 70 176 to 180
68.9 61,0 a 64.1 a
.7 .9
67.0 6 4 . 0 ab 62.9 a
2.7 .8
68.6 62.0 a 65.9 ab
1.3 .7
67.5 66.7 b 69.3 b
.9 .7
67.4 67.8 b 68.8 b
1.7 1.5
"q
68.8 68.4 b 70.8 b
.9 .9
68.6 69.2 b 70.6 b
1.7 1.3
67.0 66.6 c 66.9 bc
.8 .7
67.0 65.3 c 68.7 c
1.9 .5
O r g a n i c m a t t e r (%) 16 t o 2 0 66 to 70 176 to 180
70.3 62.6 a 65.9 a
16 t o 2 0 66 to 70 176 to 180
67.0 55.2 a 57.0 a
.5 1.2
68.6 64.4 ab 64.8 a
.6 1.1
67.7 62.3 be 60.5 a
3.0 .6
69.7 63.4 a 67.3 ab
1.3 .7
C r u d e p r o t e i n (%) 3.0 1.2
68.8 59.5 ab 61.7 ab
3.4 1.9
> .r"
E t h e r e x t r a c t (%) 16 t o 2 0 66 t o 7 0 176 t o 1 8 0
77.7 76.7 75.6
3.9 3.7
76.1 76.4 72.5
6.7 2.1
36.5 b 37.6 41,5
1.3 1.6
76.0 70.7 ab 71.6 a
.8 .9
68.4 6 5 . 1 ab 63.7 a
4.0 3.5
78.5 72.8 77.5
1,2 1.5
2.3 2.7
79.7 74.2 74.9
1.2 2.5
37.1 b 41.0 47.2
76.3 74.2 bc 79.2 c
68.9 68.3 b 70.0 b
79.7 78.9 79.8
1.4 3.0
Z
A c i d d e t e r g e n t f i b e r (%) 16 to 2 0 6 6 to 7 0 176 to 180
46.7 a 41.9 46.5
16 t o 2 0 6 6 to 7 0 176 to 180
76.9 68.0 a 7 3 . 5 ab
16 t o 2 0 66 to 70 176 to 180
70.2 62.8 a 65.6 ab
5.3 4.5
40.3 ab 33.1 44.2
2.4 3.0
39.3 ab 44.2 50.1
.4 3.0
N
1.0 .7
76.6 77.4 c 78.7 bc
2.5 1.4
© Z ,< t"
1.3 1.5
68.7 67.9 b 69.3 b
1.7 1.5
N i t r o g e n - f r e e e x t r a c t (%) 3.2 .3
77.0 70.1 ab 76.1 abc
,8 2,0
Z ,q
T o t a l d i g e s t i b l e n u t r i e n t s (%)
o
3.1 1.0
69.7 62.5 a 66.7 ab
1.0 .6
"]
O
a ' b ' C M e a n s w i t h i n a given r o w n o t b e a r i n g a c o m m o n s u p e r s c r i p t are d i f f e r e n t ( P < . 0 5 ) . d D u r i n g d a y s 16 t o 2 0 o f l a c t a t i o n all c o w s w e r e f e d d i e t 4 s u p p l e m e n t e d w i t h u r e a a n d s o y b e a n m e a l . <
.o O~
Z o
~o *q 00
xO bo ~rt
bo C~,
<
TABLE 5. Nitrogen intake and utilization by lactating cows fed diets containing varying concentrations of crude prot e i n s u p p l e m e n t e d w ith urea and/or soybean meal.
O Ox
Diets
Z O
~q 0o
Days of lactation
1 No supplemental nitrogen
2
3
Urea
(Mean
(Mean _+ SE)
_+
SE)
Soybean meal
4 Urea + soybean meal
5 Soybean meal
(Mean +- SE)
(Mean + SE)
(Mean + SE)
424 457 bc 437 bc
24 29
426 479 c 514 c
59 48
139 154 b 145 ab
12 12
143 167 b 162 b
29 17
104 125 c 111 c
6 3
96 115 c 137 d
13 8
N-intake (g/day) 16 to 20 e 66 to 70 176 to 180
410 238 a 259 a
1 6 t o 20 6 6 t o 70 176 to 180
135 107 a 109 a
16 to 20 66 to 70 176 to 180
98 35 a 38 a
8 15
407 373 b 380 b
2 6
131 140 ab 150 ab
0 4
110 78 b 85 b
7 30
377 379 b 372 b
14 37
~t-
Fecal-N (g/day) 10 13
116 154 b 141 ab
16 7
Urine-N (g/day) 5 10
99 57 ab 63 ab
3 7
"] ~"
Milk-N ( g / d a y ) 16 to 2 0 66 to 70 176 to 180
180 112 a 83 a
I 6 to 2 0 66 to 70 176 to 180
-3 -16 29
3 3
171 150 ab 122 b
8 2
-5 5 23
9 10
182 157 bc 118 ab
18 11
175 163bc 12lab
193 194 c 161 c
28 12
Retained-N (g/day) 10 2
-20 11 50
16 23
6 17 60
2 8
-6 3 54
21 14
285 305 c 292 c
12 17
283 312 c 352 c
32 31
181 180bc 181bc
7 17
Absorbed-N (g/day) 16 to 2 0 66 to 70 176 to 180
275 131 a 150 a
6 7
276 233 b 230 b
14 18
261 225 b 231 b
12 30
Productive-Nf(g/day) e~
16 to 2 0 66 to 70 176to 180
177 96 a 112 a
6 5
166 1 5 5 ab 145 ab
11 12
162 168 bc 168 b
10 31
F
a ' b ' c ' d M e a n s w i t h i n a given r o w n o t b e a r i n g a c o m m o n s u p e r s c r i p t are d i f f e r e n t ( P < . 0 5 ) .
t~
e D u r i n g d a y s 16 t o 2 0 o f l a c t a t i o n all c o w s w e r e f e d d i e t 4 s u p p l e m e n t e d w i t h u r e a a n d s o y b e a n m e a l .
187 197 c
215 c
20 25
fProduetive-N = retained-N + milk-N. < O Ox
Z O
xt~
T A B L E 6. N i t r o g e n u t i l i z a t i o n b y l a c t a t i n g c o w s e x p r e s s e d as a p e r c e n t o f n i t r o g e n i n t a k e .
,~ to 00 Diets
eL
Days of lactation
1 No supplemental nitrogen
2
3
Urea
Soybean meal
( M e a n +- SE)
( M e a n + SE)
( M e a n -+ SE)
< o Ox
Z 9 Y
g 0o
4 Urea + soybean meal
5 Soybean meal
( M e a n +- SE)
( M e a n + SE)
Fecal-N 16 t o 2 0 d 66 t o 7 0 176 to 180
33.0 44.9 a 42.1 a
16 t o 2 0 66 to 70 176 to 180
23.9 14.7 a 14.7 a
16 t o 2 0 66 to 70 176 to 180
44.1 47.1 a 32.0
I6 to 20 66 to 70 176 to 180
-1.0 -6.7 11.2
16 t o 2 0 6 6 to 7 0 176 to 180
67.0 55.0 a 57.9 a
16 t o 2 0 66 to 70 176 to 180
43.2 40.3 43.2
.6 1.0
32.3 37.5 be 39.5 a
.6 1.5
27.0 21.0 b 22.4 b
2.4 1.4
42.0 40.2 b 32.1
3.5 1.8
-i.2 1.3 6.0
3.0 1.1
30.8 40.6 ab 37.9 a
1.5 2.1
26.2 15.0 a 17.0 a
2.2 .4
48.3 41.4 b 31.7
2.6 .6
-5.3 3.0 13.4
3.0 1.2
69.2 5 9 . 4 ab 62.1 ab
3.3 1.0
43.0 44.3 45.2
3.3 1.9
32.8 33.6 c 33.2 b
.9 .6
33.6 34.9 c 31.5 b
1.9 .6
24.5 27.2 c 25.4 b
.5 1.8
22.5 24.0 bc 26.7 b
.3 1.8
41.3 35.5 b 27.7
.4 .8
45.3 40.5 b 31.3
3.0 .7
.6 1.0
-1.4 .6 10.5
4.8 1.9
.9 .6
66.4 65.1 c 68.5 c
1.9 .6
43.9 40.9 41.8
2.0 1.2
Urine-N 1.1 2.0
Milk-N 3.4 1.6
Retained-N 4.3 4.7
1.4 3.7 13.7
Absorbed-N .6 1.0
67.8 62.5 bc 60.5 a
1.2 .9
40.8 41.5 38.1
3.3 1.9
67.2 66.4 c 66.8 bc
Productive-N e 2.5 4.1
a ' b ' C M e a n s w i t h i n a given r o w n o t b e a r i n g a c o m m o n s u p e r s c r i p t are d i f f e r e n t ( P < . 0 5 ) . d D u r i n g d a y s 16 to 2 0 o f l a c t a t i o n all c o w s w e r e f e d d i e t 4 s u p p l e m e n t e d w i t h u r e a a n d s o y b e a n m e a l . eproductive-N = retained-N + milk-N.
42.7 39.2 41.4
2.9 1.2
t'n >
T A B L E 7. N i t r o g e n u t i l i z a t i o n b y l a c t a t i n g c o w s e x p r e s s e d as a p e r c e n t o f n i t r o g e n a b s o r b e d . Diets 1
Days of lactation
2
No supplemental nitrogen ( M e a n -+ SE)
3
4
5
Urea
Soybean meal
Urea + soybean meal
Soybean meal
( M e a n + SE)
( M e a n -+ SE)
( M e a n -+ SE)
_z
( M e a n -+ SE)
©
Urine-N 16 t o 2 0 e 66 to 70 176 to 180
35.6 26.7 ab 25.3 a
16 t o 2 0 66 to 70 176 to 180
65.4 85.5 a 55.3 a
1.4 2.3
39.9 33.5 bc 36.9 b
5.1 1.4
61.9 64.4 bc 53.1 ab
2.3 2.8
37.9 25.3 a 27.3 a
1.9 1.7
69.7 69.8 b 51.1 a b
1.1 3.7
36.5 41.0 d 38.0 b
.8 2.4
33.9 36.8 cd 38.9 b
1.2 2.2
Z
61.4 53.4 c 41.1 b
.5 1.5
68.2 62.2 c 45.7 ab
5.9 .7
.8 1.6
-2.1 1.0 15.4
.8 2.4
66.1 62.8 c 61.1 b
Milk-N 8.3 3.2
Retained-N
o
16 t o 2 0 66 to 7 0 176 to 180
-1.0 -12.2 19.4
6,5 3.3
-1.8 2,1 10.0
4,1 1.2
-7.6 4.9 21.6
7.4 6,9
2.1 5.6 20.6
,q ;~ 7.1 2.8
Productive-N f 16 to 20 66 to 70 176 to 180
64.4 73.3 ab 74.7 a
1.4 2.3
60.1 66.5 bc 63.0 b
4.3 2.8
62.1 74.7 a 72.7 a
1.1. 4.5
< o
a ' b ' c ' d M e a n s w i t h i n a g i v e n r o w n o t b e a r i n g a c o m m o n s u p e r s c r i p t are d i f f e r e n t ( P < . 0 5 ) .
ox
e D u r i n g d a y s 16 t o 2 0 o f l a c t a t i o n all c o w s w e r e f e d d i e t 4 s u p p l e m e n t e d w i t h u r e a a n d s o y b e a n m e a l .
Z
fProductive-N = retained-N + milk-N.
o
.q 0o
t~ ~< t-
u~ 63.5 59.0 c 62.0 b
1.2 2.2
tJ ",O
930
WOHLT ET AL.
t i o n s b y o t h e r investigators (13, 24, 26, 31) have b e e n similar. The e f f i c i e n c y o f urea utilizat i o n f o r milk p r o d u c t i o n d e c r e a s e d as t h e c r u d e p r o t e i n c o n t e n t o f t h e diet was increased b y adding urea w h i c h m a y b e d u e t o t h e inability o f t h e r u m e n m i c r o b e s t o i n c o r p o r a t e all o f t h e a m m o n i a - N released f r o m urea i n t o microbial p r o t e i n or t o the ability o f t h e p l a n t p r o t e i n in t h e diet t o m e e t the p r o t e i n r e q u i r e m e n t o f t h e cow. K e r t z a n d E v e r e t t (18) r e p o r t e d t h a t microbial p r o t e i n s y n t h e s i z e d in t h e r u m e n r a n g e d f r o m 9.6 t o 33.2 g p e r 100 g o f organic m a t t e r digested and suggested t h a t t h e U F P values o f Burroughs et al. (3, 4) m a y u n d e r e s t i m a t e s y n t h e s i s o f m i c r o b i a l p r o t e i n and, t h u s , may underestimate the utilization of ammoniaN in the r u m e n . Van H o r n e t al. (35) and Randel e t al. (25) o b s e r v e d t h a t urea was n o t utilized in diets t h a t were f o r m u l a t e d to c o n t a i n a positive UFP. Since w e (37) o b s e r v e d a similar milk yield f r o m cows fed a d i e t t h a t c o n t a i n e d 9 t o 10% c r u d e p r o t e i n , t h e urea a d d e d to t h e diets in the studies o f Van H o r n e t al. (35) a n d R a n d e l et al. (25) m a y n o t have b e e n n e e d e d t o m e e t the c o w ' s r e q u i r e m e n t for c r u d e p r o t e i n . These data suggest t h a t U F P values o f Burroughs e t al. (4) n e e d t o be re-evaluated to c o n sider n o t o n l y the p o t e n t i a l t o i n c o r p o r a t e ureaN i n t o microbial p r o t e i n b u t also the a n i m a l ' s r e q u i r e m e n t f o r crude p r o t e i n .
REFERENCES
1 Aitchison, T. E., D. R. Mertens, A. D. McGilliard, and N. L. Jacobson. 1976. Effect of nitrogen solubility on nitrogen utilization in lactating dairy cattle. J. Dairy Sci. 59:2056. 2 Association of Official Agricultural Chemists. 1965. Official methods of analysis. 10th ed. Washington, DC. 3 Burroughs, W., D. K. Nelson, and D. R. Mertens. 1975. Evaluation of protein nutrition by metabolizable protein and urea fermentation potential. J. Dairy Sci. 58:611. 4 Burroughs, W., D. K. Nelson, and D. R. Mertens. 1975. Protein physiology and its application in the lactating cow: The metabolizable protein feeding standard. J. Anita. Sci. 41:933. 5 Campliug, R. C., M. Freer, and C. C. Balch. 1961. Factors affecting voluntary intake of food by cows. 2. The relationship between the voluntary intake of roughages, the amount of digesta in the reticulorumen, and the rate of disappearance of digesta from the alimentary tract. Br. J. Nutr. 15: 531. 6 Campling, R. C., M. Freer, and C. C. Balch. 1962. Factors affecting voluntary intake of food by Journal of Dairy Science Vol. 61, No. 7, 1978
cows. 3. The effect of urea on the voluntary intake of oat straw. Br. J. Nutr. 16:115. 7 Cerbulis, J., and H. M. Farrell, Jr. 1975. Composition of milks of dairy cattle. I. Protein, lactose, and fat contents and distribution of protein fraction. J. Dairy Sci. 58:817. 8 Clark, J. H. 1975. Lactational responses to postruminal administration of proteins and amino acids. J. Dairy Sci. 58:1178. 9 Crutchfield, W. O. 1968. A technic for placement of an indwelling catheter in the cow. Vet. Med. and Small Anim. Clin. 63:1141. 10 Elliott, R. C. 1967. Voluntary intake of low protein diets by ruminants. 1. Intake of food by cattle. J. Agr. Sci. 69:375. 11 Elliott, R. C., and J. H. Topps. 1963. Voluntary intake of low protein diets by sheep. Anita. Prod. 5:269. 12 Hawk, P. B. 1965. In Physiological chemistry. B. L. Oser, ed. McGraw-Hill Book Co., New York. 13 Helmer, L. G., and E. E. Bartley. 1971. Progress in the utilization of urea as a protein replacer for ruminants. A review. J. Dairy Sci. 54:25. 14 Huber, J. T. 1965. Protein and nonprotein nitrogen utilization in practical dairy rations. J. Anita. Sci. 41:954. 15 Huber, J. T., and O. P. Santana. 1972. Ammoniatreated corn silage for dairy cattle. J. Dairy Sci. 55:489. 16 Huber, J. T., and J. W. Thomas. 1971. Urea-treated corn silage in low protein rations for lactating cows. J. Dairy Sci. 54:224. 17 Jacobson, D. R., H. If. Van Horn, and C. J. Sniffen. 1970. Lactating ruminants. Fed. Proc. 29:35. 18 Kertz, A. F., and J. P. Everett, Jr. 1975. Utilization of urea by lactating cows-An industry viewpoint. J. Anita. Sci. 41:945. 19 Mehrez, A. Z., and E. R. Orskov. 1976. Rates of rumen fermentation in relation to ammonia concentration. Proc. Nutr. Soc. 35:40A. 20 National Research Council. 1971. Nutrient requiremeats of domestic animals. No. 3. Nutrient requirements of dairy cattle. 4th rev. ed. National Academy of Sciences. Washington, DC. 21 Okorie, A. U., P. J. Buttery and D. Lewis. 1977. Ammonia concentration and protein synthesis in the rumen. Proc. Nutr. Soc. 36:38A. 22 Orskov, E. R., and C. Fraser. 1973. The effect of feeding and protein concentration on the disappearance of protein in different segments of the gut in sheep. Proc. Nutr. Soc. 32:68A. 23 Perkins, A. E. 1957. The effect of rations excessively high and extremely low in protein content for dairy cows. Ohio Agr. Exp. Sta. Bull. 799. 24 Polan, C. E., C. N. Miller, and M. L. McGilliard. 1976. Variable dietary protein and urea for intake and production in Holstein cows. J. Dairy Sci. 59: 1910. 25 Randel, P. F., H. H. Van Horn, C. J. Wilcox, H. Roman-Ponce, S. P. Marshall, and K. C. Bachman. 1975. Complete rations for dairy cattle. IV. Comparison of supplemental nitrogen sources by metabolizable protein concept. J. Dairy Sci. 58: 1109.
N I T R O G E N U T I L I Z A T I O N BY L A C T A T I N G COWS 26 Reid, J. T. 1953. Urea as a protein replacement for ruminants. A review. J. Dairy Sci. 36:955. 27 Reid, J. T., P. W. Moe, and H. F. Tyrrell. 1966. Energy and protein requirements of milk production. J. Dairy Sci. 49:215. 28 Robertson, J. B., C. E. Coppock, C. H. Noller, W. E. Wheeler, and P. J. Van Soest. 1974. Regression o f digestibility on intake in lactating dairy cows. J. Dairy Sci. 57:622. 29 Roffler, R. E., and L. D. Satter. 1975. Relationship between ruminal a m m o n i a and nonprotein nitrogen utilization by ruminants. I. Development of a model for predicting n o n p r o t e i n nitrogen utilization by cattle. J. Dairy Sci. 58:1880. 30 Roffler, R. E., and L. D. Satter. 1975. Relationship between ruminal a m m o n i a and nonprotein nitrogen utilization by ruminants. II. Application of published evidence to the development of a theoretical model for predicting nonprotein nitrogen utilization. J. Dairy Sci. 58:1889. 31 Rys', R. 1967. Urea in rations for dairy cows. Page 239 in Urea as a protein supplement. M. H. Briggs, ed. Pergamon Press, Ltd., New York. 32 Satter, L. D., and R. E. Roffler. 1975. Nitrogen requirement and utilization in dairy cattle. J. Dairy
931
Sci. 58:1219. 33 Satter, L. D., and L. L. Slyter. 1974. Effect of amm o n i a concentration on r u m e n microbial protein production in vitro. Br. J. Nutr. 32:199. 34 Steel, R. G. D., and J. H. Torrie. 1960. Principles and procedures of statistics. McGraw-Hill Book Co., New York. 35 Van Horn, H. H., S. P. Marshall, C. J. Wilcox, P. F. Randel, and J. M. Wing. 1975. Complete rations for dairy cattle. II1. Evaluation of protein percent and quality and citrus pulp-corn substitutions. J. Dairy Sci. 58:1101. 36 Van Soest, P. J. 1963. Use of detergents in the analysis of fibrous feeds. 1I. A rapid m e t h o d for the determination of fiber and lignin. J. Ass. Offic. Agr. Chem. 46:829. 37 Wohlt, J. E., and J. H. Clark. 1978. Nutritional value of urea versus preformed protein for ruminants. 1. Lactation performance of dairy cows fed corn based diets containing varying a m o u n t s of supplemental nitrogen from urea a n d / o r soybean meal. J. Dairy Sci. 61:902. 38 Wohlt, J. E., C. J. Sniffen, and W. H. Hoover. 1973. M e a s u r e m e n t o f protein solubility in comm o n feedstuffs. J. Dairy Sci. 56:1052.
Journal o f Dairy Science Vol. 61, No. 7, 1978
ABSTRACT
INTRODUCTION
Fifteen Holstein cows at various stages of lactation, fed corn-based diets that contained 9 to 14.5% crude protein were used in total collection digestibility and nitrogen balance trials to investigate the efficiency of nitrogen utilization from urea and soybean meal. Digestibility coefficients for dry matter, organic matter, crude protein, and nitrogen-free-extract, as well as total digestible nutrient content of diets that contained 13 to 14.5% crude protein, were 3 to 8 percentage units greater than for diets that contained 9 to 12% crude protein. The concentration of ammonia-N in rumen fluid of cows fed diets that contained 9 to 12% crude protein was less than 5 mg/100 ml and may have decreased digestibility and synthesis of microbial protein in the rumen. When the diet contained 11 to 12% crude protein, nitrogen supplied as urea or soybean meal was used with equal efficiency. The concentration of ammonia-N in r u m e n fluid of cows fed diets that contained 13 to 14.5% crude protein was greater than 5 mg/100 ml and was greatest when urea was the source of supplemental nitrogen. However, more milk and milk protein were produced when soybean meal was fed to the cows. The increased production from feeding soybean meal resulted in nitrogen from soybean meal being utilized more efficiently for milk production than nitrogen supplied as urea when the diet contained 13 to 14.5% crude protein.
The protein requirement for dairy cows has been reported as crude protein or digestible protein (20). When expressed as digestible protein, the protein requirement may be defined incorrectly because digestible protein may not describe the quantity of amino acids absorbed when NPN supplementation provides more ammonia-N than can be converted into microbial protein (3, 4, 32). It has been suggested that NPN supplementation of diets that contain 12 to 13% protein will not increase rumen microbial protein synthesis (3, 4, 32) and, thus, will not increase amino acid absorption or milk production. However, other researchers (14) suggest that high producing dairy cows can benefit from addition of NPN to diets containing crude protein in excess of 11 to 12%. Diets fed to dairy cows in early lactation usually contain more than 12 to 13% crude protein from sources of plant protein. If additions of NPN to diets to increase the crude protein content above 12 to 13% do not increase microbial protein synthesis, or digestibility of substrate in the rumen, then NPN would be of no value to the animal. In this study, lactating dairy cows were fed corn-based diets that contained 9 to 14.5% crude protein to investigate the efficiency of nitrogen utilization from urea and soybean meal for milk production. EXPERIMENTAL PROCEDURE
Received December 2, 1977. 1Supported in part by the Illinois Agricultural Experiment Station, the National Soybean Processors Association, and HEW PHS FD 00849. 1978 J Dairy Sci 61:916--931
916
Three cows assigned to each of the dietary treatments in a companion lactation trial (37) were used in total collection digestibility and nitrogen balance trials at days 16 to 20, 66 to 70, and 176 to 180 of lactation. Management and feeding of these cows were as for cows in (37). Ingredient and chemical composition of the diets are in (37). Quantities of hay, corn silage, and concentrate fed and refused were weighed, sampled daily, and dried in a forced air oven at 55 C. Total fecal excretion of
NITROGEN UTILIZATION BY LACTATING COWS each cow was collected daily, and 3% of the fecal o u t p u t was composited, preserved with thymol, and stored at 4 C until the end of the 5-day collection. An indwelling urinary catheter was placed into the bladder of each cow (9). Urine was collected in polyethylene containers that contained 50 ml of 6 N HC1 and was measured and sampled daily. Daily aliquots of urine were stored at 4 C and composited by volume at the end of each collection period. Milk yield was measured daily, and samples of milk from each of the two daily milkings were composited for each cow, preserved with potassium dichromate, and stored at 4 C. At the end of the 5-day collection all daily milk samples were composited according to milk yield. The day immediately following each collection period, rumen fluid was sampled by stomach tube at 2 and 7 h postfeeding (1100 and 1600 h), and blood samples were drawn from the jugular vein at 2 h postfeeding (1100 h). Ammonia-N in rumen fluid and urea-N in plasma were determined by a modified Conway procedure (12). Dried composite samples of feed, feed refused, and feces from the total collection digestibility trials were analyzed for crude protein, ether extract, ash (2), nitrogen solubility (38), and acid detergent fiber (36). Urine samples were analyzed for nitrogen content by the Kjeldahl m e t h o d (2). Milk samples were analyzed for crude protein (2), fat (Babcock), and solids-not-fat (Golding Bead Test). To determine significant differences among treatments, data collected were analyzed statistically by analysis of variance and Duncan's new multiple range test (34). RESULTS A N D DISCUSSION
Intakes of dry matter and nitrogen as well as milk, 4% FCM, milk protein, and milk fat yields of cows in these digestibility and nitrogen-balance trials (Tables 1, 2) were similar to those for cows in (37). Between days 66 and 70 postcalving, milk yields for cows in the total collection trials and fed the five diets were: 1) 73, 2) 97, 3) 94, 4 ) 9 4 , and 5) 104% of that during days 16 to 20 of lactation (Table 2). Average daily milk production of cows used in the total collection trials and fed diets 2, 3, 4, and 5 did not differ significantly during days 66 to 70 of lactation (Table 2). These results suggest that diets 2 and 3 supplied sufficient
917
nitrogen up to this point in the trial to meet the cows' requirement for amino acids since additional nitrogen fed in diets 4 and 5 did not increase milk production significantly. However, the greater milk production of cows fed diet 5 during days 176 to 180 of lactation (Table 2) indicate that diets 2, 3, and 4 were not meeting the amino acid requirement of these cows over a longer time and that body protein reserves were being depleted (37). Therefore, short studies using a small number of animals to determine the crude protein requirement and efficiency of utilization of protein and urea can lead to erroneous conclusions. Feeding diet 5 which contained soybean meal as the supplemental source of nitrogen resulted in about a 10% greater production of milk, 4% FCM, and milk protein than feeding diet 4 which contained urea (37). A shortage of ammonia-N in rumen fluid must not have been the cause of the depressed milk production of cows fed diet 4 because the concentration of ammonia-N in rumen fluid of cows fed diet 4 was greater than the concentration in rumen fluid of cows fed diet 5 (Table 3). The increase in milk production of cows fed diet 5 compared to cows fed diet 4 (37) probably was due to a great quantity of dietary protein (soybean meal) escaping degradation in the rumen and flowing to the lower gut which resulted in a greater quantity of absorbable amino acids for maintenance, gluconeogenesis, and synthesis of milk protein. Clark (8) has indicated that supplying additional high quality protein postruminally increased milk production, and Orskov and Fraser (22) demonstrated that an increased concentration of plant protein in the diet increased the amount of plant protein that escaped rumen degradation. Insoluble nitrogen intake, although it has limitations, was an indicator of the quantity of protein that escaped rumen degradation and was greatest for cows fed diet 5 (Table 1, Table 3, Fig. 1D; (37)). However, intake of insoluble nitrogen was greater for cows fed diet 3 than for cows fed diet 2, but responses from animals suggest that similar quantities of amino acids were available to cows fed these diets (37). More microbial protein may have been synthesized in the rumen when cows were fed diet 2 compared to diet 3 because of a shortage of ammonia-N in the rumen when cows were fed diet 3 (Table 3). However, more dietary protein probably esJournal of Dairy Science Vol. 61, No. 7, 1978
x~ e~
TABLE 1. Average dry matter, crude protein, soluble, and insoluble nitrogen intake of cows fed diets containing varying co n cen tr atio n s of crude protein supplem e n t e d with urea and/or soybean meal. Diets < O Ox
Days of lactation
Z 9
1 No supplemental nitrogen (Mean + SE)
2
3
Urea
Soybean meal
(Mean -+ SE)
4 Urea + soybean meal
(Mean + SE)
5 Soybean meal
(Mean + SE)
(Mean + SE)
18.9 20.9 20.4 ab
19.3 21.1 22.4 b
Total dry m a t t e r (kg/day) -q Oo
16 to 20 e
66 to 70 176 to 180
18.1 15.9 15.8 a
.2 1.2
17.3 20.1 20.0 ab
.7 1.6
16.4 20.4 19.4 ab
1.4 1.9
1.6 1.9
3.0 1.3
-v
Crude protein (kg/day) 16 to 20 66 to 70 176 to 180
2.56 1.49 a 1.62 a
.05 .09
2.55 2.33 b 2.38 b
.04 .19
2.65
2.36 2.37 b 2.32 b
.09 .23
2.66
2.87 bc 2.73 bc
.15 .18
.~
2.99 c 3.22 c
.37 .30
Soluble nitrogen (g/day) 16 to 20 66 to 70 176 to 180
144 48 a 62 a
16 to 20 66 to 70 176 to 180
266 190 a 197 a
3 3
143 138 b 129 bc
7 13
264 235 ab 251 ab
11 14
131 88 c 86 d
4 14
150 155 b 152 b
7 11
151 96 c 103 cd
17 9
274 304 b 285 b
31 18
275 383 c 411 c
43 40
Insoluble n i t r o g e n ( g / d a y ) 4 21
246 291 b 286 b
11 27
a'b'C'dMeans within a given row not bearing a c o m m o n superscript are different (P<.05). eDuring days 16 to 20 of lactation all cows were fed diet 4 s u p p l e m e n t e d with urea and soybean meal.
i> .t-
NITROGEN UTI LI ZATION BY LACTATING COWS caped degradation in the rumen in cows fed diet 3 compared to cows fed diet 2. Therefore, the ratio of fractions of microbial and undegraded dietary protein leaving the rumen of cows fed diets 2 and 3 may have been different, but the combination of microbial and plant protein available from both diets must have supplied similar quantities of amino acids to the lower gut of both groups of cows because production did not differ significantly (37). Effiency of nitrogen utilization was lower when cows were fed diets high in soluble nitrogen in our trials and in the nitrogen-balance trials of Aitchison et al. (1). This probably is due to soluble nitrogen being degraded rapidly and ammonia-N released in the rumen in excess of the requirement for microbial growth not being utilized by the cow. Apparent digestibility and TDN content o f diet 4 did not differ significantly among groups of cows during days 16 to 20 of lactation (Table 4). Digestibility of dry matter was 3 to 8 percentage units greater for diets 4 and 5 than for diets 1, 2, and 3 during days 66 to 70 and 176 to 180 of lactation. When diets 4 and 5 were fed, digestibilities of organic matter, crude protein, and nitrogen-free-extract also were increased compared to the other three diets. Digestibilities of acid detergent fiber and ether extract did not differ significantly among treatments but did increase slightly as crude protein increased in the diet. Thus, as a result of the improvement in digestibility of the various dietary components, the TDN content o f diets 4 and 5 was 4 to 6 percentage units greater than for diets i , 2, and 3. Generally as feed intake is increased, digestibility is depressed (27, 28); however, in this study digestibility increased as feed intake increased, indicating some nutritional factor must have limited digestibility of the low protein diets. Jacobson et al. (17) suggested that the primary reason for feeding a diet that contained a high concentration of crude protein to lactating dairy cows was to encourage greater intake of energy which increased milk production and efficiency of conversion of feed to milk. Feeding diets that contain less than 10% crude protein depressed feed intake (5, 6, 10, 11). Campling et al. (6) have shown that when low protein diets are fed, the low nitrogen content of the rumen digesta was a major factor which limited the rate of fermentation in the rumen and rate
919
of passage of feed through the digestive tract. Also, the addition of urea to corn silage at ensiling (15, 16) increased feed intake and digestibility if adequate nitrogen was not supplied already to the animal. Therefore, the low intake of crude protein in our experiments (Table 1), (37) probably contributed to the lower intakes of corn silage and total dry matter for cows fed diet 1. Digestibility of dietary components (Table 4) did not appear to be depressed until the concentration of ammonia-N in the rumen was below 4 to 5 mg/100 ml (Table 3). Rumen fluid samples obtained 2 and 7 h postfeeding from cows fed diet 1 contained less than 5 mg/ 100 ml ammonia-N (Table 3), suggesting that rumen fermentation was limited by shortage of ammonia (19) and that synthesis of microbial protein may not have been maximal (21, 33). Essentially all of the ammonia-N available in the rumen of cows fed diet 1 must have been incorporated into microbial protein since the concentration of urea-N in plasma (Table 3) and the quantity of nitrogen secreted in the urine (Table 5) were significantly less for these cows than for cows fed the nitrogen supplemented diets. The concentration of ammonia-N at 2 and 7 h postfeeding in rumen fluid of cows fed diet 3 also was below 5 mg/100 ml during days 66 to 70 and 176 to 180 of lactation. Therefore, digestibility and synthesis of microbial protein in the rumen may have been reduced for cows fed this diet. Availability of ammonia-N in the rumen of cows fed diets 1 and 3 may have limited microbial fermentation which decreased dry matter intake, synthesis of microbial protein, and milk production. Cows fed diet 2 had a higher concentration of ammonia-N in the rumen 2 h after feeding than did cows fed diets 1 and 3. At this time the concentration of ammonia-N in the tureen fluid may not have been limiting microbial fermentation and synthesis of microbial protein. However, at 7 h postfeeding during days 66 to 70 and 176 to 180 of lactation the concentration of ammonia-N in the rumen was marginal (2 to 5 mg/100 ml) for maximal microbial fermentation or synthesis of microbial protein. At 7 h postfeeding the concentration of ammonia-N in rumen fluid of cows fed diets 4 and 5 was two-fold higher than the concentration of ammonia-N in rumen fluid of cows fed diets 1, 2, and 3. Therefore, diets 4 Journa| of Dairy Science Vol. 61, No. 7, 1978
xO bO
e-
~7
q
TABLE 2. Average m i l k p r o d u c t i o n and m i l k c o m p o s i t i o n of cows fed diets containing varying concentrations of crude protein s u p p l e m e n t e d with urea an d /o r soybean meal.
< o
Diets
Ox
Z
O -.]
Days of lactation
1 No supplemental nitrogen
2
3
Urea
Soybean meal
(Mean -+ SE)
(Mean + SE)
34.5 25.2 a 17.4 a
35.6 34.6 b 26.7 be
4 Urea + soybean meal
(Mean -+ SE)
5 Soybean meal
(Mean -+ SE)
(Mean -+ SE)
35.8 33.7 b 22.7 ab
38.3 39.9 b 32.0 c
Milk (kg/day) 16 to 20d 66 to 70 176 to 180
.5 .3
2.2 1.8
35.3 33,6 b 23.3 ab
3.0 2.2
.5 1.2
4.3 2.5
>
4% fat-corrected-milk (kg/day) 16 to 20 66 to 70 176 to 180
33.9 22.8 a 15.4 a
16 to 20 66 to 70 176 to 180
3.31 2.83 3.06
.5 .2
28,6 28,8 b 22,4 b
1.3 .8
33.3 30.8 b 20.9 ab
2.7 1.5
32.1 32.5 b 22.2b
1.5 1.1
37.8 33.5 b 27.3 b
4.5 3.3
Milk protein e (%) .05 .08
3.07 2.77 2.90
.03 .07
3.22 2.97 3.21
.18 ,11
3,10 3.09 3,38
.15 .26
3.24 3.08 3.21
.11 .17
Milk protein e (g/day) 16 to 20 66 to 70 176 to 180
1141 715 a 532 a
1087 957 ab 775 ab
17 20
1162 1001 bc 747 a
55 65
1114 1041 bc 779 ab
119 69
1229 1239 e 1025 b
52 59
177 76
Milk fat (%) 16 to 20 66 to 70 176 to 180
4.20 a 3.37 3.23
.03 .06
3.57 b 2.93 2.95
.50 .18
4.20 a 3.47 3.38
.30 .34
© m
3.88ab 3.77 3.87
,29 .35
3.96ab 2.90 3.02
.12 .41
NITROGEN UTILIZATION BY LACTATING COWS 00x 0o ox
xO eq t ~
o~ o6 o6
,0oo~
it~ t ~ ox~
~¢qoo
v
¢q " 0
0
o q v
,~-Ox
q~.
Oxe¢~ eq~eq t ~ Ox 00 ~ox~
~d 06 ~6
8 Ox~
o60d~ ,6 X
z
O
Y
921
and 5 may have maintained the minimal ammonia-N concentration required in the rumen longer which increased rumen fermentation and synthesis of microbial protein compared to diets 1, 2, and 3. The increased digestibility and TDN content of diets 4 and 5 (Table 4) support this assumption. The amount of nitrogen consumed and absorbed was not significantly different between cows fed diets 2 and 3 (Table 5). Milk production (Table 2) and nitrogen utilization for synthesis of milk protein (Tables 5, 6, 7) also were similar for cows fed diets 2 and 3, which indicated equally efficient utilization of nitrogen from urea and soybean meal when the diet contained 11 to 12% crude protein. Since nitrogen intake and absorption were greater for cows fed diet 5 than for cows fed diet 4 (Table 5), efficiency of nitrogen utilization expressed as a percentage of nitrogen intake or nitrogen absorbed would be expected to be lower for diet 5 if both soybean meal and urea were utilized equally efficient at equal intakes of nitrogen. However, efficiency of nitrogen utilization for synthesis of milk protein by cows fed diet 5 was 5 to 10 percentage units greater than for cows fed diet 4 (Tables 6, 7). The more efficient utilization of nitrogen supplied as soybean meal may have been due to more efficient utilization of nitrogen in the rumen because the concentration of ammonia-N was low or because a greater quantity of the dietary protein escaped degradation when soybean meal was fed. Until recently, it was assumed that all sources of nitrogen fed to the ruminant would result in equal amounts of amino acids reaching the small intestine, and, therefore, animal production would be equal. However, when NPN supplies the rumen with more ammonia-N than can be incorporated into microbial protein, digestible protein may not describe the quantity of amino acids absorbed from the gastrointestinal tract. Burroughs et al. (3, 4) and Satter and Roffler (32) have advocated metabolizable protein as a means of defining the protein requirement of the ruminant instead of digestible protein or crude protein. Satter and Roffler (32) indicated that the a m o u n t of crude protein needed to supply the amino acids (metabolizable protein) required for maintenance and milk production can be calculated if milk production, feed intake, body weight, and the amount of b o d y weight lost or gained are Journal of Dairy Science Vol. 61, No. 7, 1978
e"
TABLE 3. Ammonia-N concentration and pH of l u m e n fluid and urea-N c onc e nt ra t i on in plasma of lactating cows fed diets containing varying concentrations of crude protein s u p p l e m e n t e d with urea and/or soybean meal.
x~ tJ tJ
Diets
<
Days of lactation
1 No supplemental nitrogen (Mean _+ SE)
2
3
Urea
Soybean meal
(Mean -+ SE)
Z
(Mean -+ SE)
5 Soybean meal
(Mean +- SE)
(Mean -+ SE)
2 h postfeeding ammonia-N (mg/ 100 ml)
O
.q 00
4 Urea + soybean meal
16 to 20 d 66 to 70 176 to 180
11.13 1.39 a 3.32 a
16 to 20 66 to 70 176 to 180
5.81 1.23 a 1.23 a
16 to 20 66 to 70 176 to 180
7.04 6.70 6.97
16 to 20 66 to 70 176 to 180
6.60 6.72 6.94
16 to 20 66 to 70 176 to 180
11.13 2.73 a 5.46 a
1.15 1.87
9.62 9.50 bc 11.09 b
4.50 2.72
6.90 4.18 ab 6.32 ab
1.16 .39
9.08 12.98 c 11.20 b
3.77 .37
7.55 6.22 abc 1.39 8.09 ab 2.23
7 h postfeeding ammonia-N ( m g / l O 0 ml) .06 .51
6.04 4.13 ab 2.14 ab
.09 .09
7.01 6.65 6.97
.11 .20
6.82 6.59 6.88
2.12 .60
8.92 1.87 a 2.41 ab
1.32 .58
5.88 11.14 c 4.28 ab
0
.78 .81
7.69 6.27 b 5.03 b
7.03 6.57 7.17
.04 .27
6.85 6.60 6.76
.23 .02
6.68 6.57 6.93
.14 .16
7.08 6.89 6.82
.15 .07
1.37 1.03
2 h postfeeding rumen fluid pH .12 .12
6.53 6.63 6.87
.04 .11
7 h postfeeding rumen fluid pH .21 .07
6.37 6.63 6.90
.12 .12
2 h postfeeding plasma urea-N (mg/ 100 ml) .33 .32
11.83 6.48 abc 1.16 10.55 ab 2.68
10.66 5.73 ab 6.64 a
1.66 .38
a'b'CMeans within a given row not bearing a c o m m o n superscript are different (P<.05). dDuring days 16 to 20 of lactation all cows were fed diet 4 s u p p l e m e n t e d with urea and soybean meal.
9.10 11.63 c 13.07 b
.56 3.08
13.55 10.93 bc 13.45 b
2.14 1.58
NITROGEN UTILIZATION BY LACTATING COWS known and certain assumptions accepted. These assumptions are that daily production of milk protein contains 95% true protein (7, 23), that the maintenance requirement for metabolizable protein is 2.4 g per kg body weight -75 (32), and that the effciency with which metabolizable protein is utilized for milk production and gain of body weight is 60%. Digestibility studies during days 16 to 20 of lactation indicated that cows were consuming 1725 g of digestible protein per day. By the assumptions of Satter and Roffler (32), the diet consumed during the same period provided 1721 g of metabolizable protein per day. Therefore, during this period metabolizable protein was equal to digestible protein even though urea was a component of the diet. This suggests that according to guidelines of Satter and Roffler (32), urea was not greatly in excess and was being converted into microbial protein. Burroughs et al. (4) suggest that 1497 g of metabolizable protein were available per day to cows during days 16 to 20 of lactation. According to calculations of Satter and Roffler (32), cows fed diets 1 to 5, respectively, were receiving 1118, 1747, 1777, 1941, and 2113 g of metabolizable protein per day during days 66 to 70 o f lactation. By the metabolizable-protein scheme of Burroughs et al. (4), cows fed diets 1 to 5, respectively, received 1175, 1593, 1655, 1746, and 1851 g of metabolizable protein per day. The metabolizable protein concept of Satter and Roffler (32) estimated that more protein was available to the cows than did the metabolizable protein concept of Burroughs et al. (4) or the measured digestible protein intake. This may be due to the fact that digestible protein and the metabolizable protein concept of Burroughs et al. (4) do not consider the possibility that ureaN may be recycled to the rumen and incorporated into microbial protein. The concepts of metabolizable protein, digestible protein, and insoluble or soluble nitrogen are valuable theoretical tools but at best can give only estimates of amino acid availability to the animal until additional data are accumulated. Experiments using lactating cows with re-entrant cannula are needed to indicate the quantity of amino acids absorbed when various diets are fed. Burroughs et al. (3, 4) and Satter and Roftier (32) also developed concepts which estimate the quantity of urea that can be fed per unit of dry matter in the ration for achieving
923
maximum incorporation of urea-N into microbial protein. Calculated urea fermentation potential (UFP) values (4) predicted that urea would not be beneficial in diet 4 during the first 30 wk of lactation and that only 67% of the urea added to diet 2 would be incorporated into microbial protein. Prior to addition of urea, diet 4 consumed during days 16 to 20 of lactation contained 11.9% crude protein. The calculated TDN content of diet 4 was 76% (20), but the measured TDN content was about 69% (Table 4). In predicting the upper limit of NPN utilization, Satter and Roffler (32) calculated the TDN content of the diets using TDN values for feedstuffs from NRC (20). Therefore, to use values from tables of Satter and Roffler (32) to predict the upper limit of NPN utilization required that the TDN content of the diet be calculated from TDN values obtained from NRC (20) (Satter, personal communication). Since the calculated TDN content of diet 4 was 76%, Satter and Roffler (32) suggest this diet could be supplemented with urea to increase the crude protein from 11.9 to 12.8%. An average concentration of ammonia-N in rumen fluid of 3.5 mg/100 ml was predicted for cows fed diet 4 prior to addition of urea (30). Since 3.5 mg/ 100 ml ammonia-N is below the minimum concentration of ammonia-N adequate for maximum synthesis of microbial protein (21, 32, 33), this also suggests that urea supplementation may contribute ammonia-N that can be used for synthesis of microbial protein. Calculations as suggested by Satter and Roffler (32) indicate that urea would be beneficial in both diet 2 and diet 4 with an estimated 100% and 50%, respectively, of the urea-N being incorporated into microbial protein during days 66 to 70 of lactation. Milk production in the companion lactation trial (37) and results of the total collection trials indicate that urea supplementation was beneficial in both diets 2 and 4 but was not as beneficial in diet 4 as soybean meal was in diet 5. Our data, therefore, support the concept of Roffler and Satter (29, 30) that urea would be beneficial in both diets 2 and 4 but not as beneficial as supplying soybean meal when the diet contained 13.5 to 14.5% crude protein. Urea supplementation of low protein diets definitely increased milk production, but the response in milk production decreased as the concentration o f protein in the diet prior to addition of urea was increased (37). ObservaJournal of Dairy Science Vol. 61, No. 7, 1978
xO e"
4~
o
<
T A B L E 4. A p p a r e n t d i g e s t i b i l i t y a n d t o t a l d i g e s t i b l e n u t r i e n t c o n t e n t o f d i e t s c o n t a i n i n g v a r y i n g c o n c e n t r a t i o n s o f c r u d e p r o t e i n s u p p l e m e n t e d w i t h u r e a a n d / o r soybean meal.
O O~
Diets
Z O
Days of lactation
1 No supplemental nitrogen
2
3
Urea
Soybean meal
4 Urea + soybean meal
5
( M e a n + SE)
( M e a n + SE)
( M e a n -+ SE)
( M e a n +- SE)
Soybean meal ( M e a n + SE) O .r
D r y m a t t e r (%) 16 t o 2 0 d 66 to 70 176 to 180
68.9 61,0 a 64.1 a
.7 .9
67.0 6 4 . 0 ab 62.9 a
2.7 .8
68.6 62.0 a 65.9 ab
1.3 .7
67.5 66.7 b 69.3 b
.9 .7
67.4 67.8 b 68.8 b
1.7 1.5
"q
68.8 68.4 b 70.8 b
.9 .9
68.6 69.2 b 70.6 b
1.7 1.3
67.0 66.6 c 66.9 bc
.8 .7
67.0 65.3 c 68.7 c
1.9 .5
O r g a n i c m a t t e r (%) 16 t o 2 0 66 to 70 176 to 180
70.3 62.6 a 65.9 a
16 t o 2 0 66 to 70 176 to 180
67.0 55.2 a 57.0 a
.5 1.2
68.6 64.4 ab 64.8 a
.6 1.1
67.7 62.3 be 60.5 a
3.0 .6
69.7 63.4 a 67.3 ab
1.3 .7
C r u d e p r o t e i n (%) 3.0 1.2
68.8 59.5 ab 61.7 ab
3.4 1.9
> .r"
E t h e r e x t r a c t (%) 16 t o 2 0 66 t o 7 0 176 t o 1 8 0
77.7 76.7 75.6
3.9 3.7
76.1 76.4 72.5
6.7 2.1
36.5 b 37.6 41,5
1.3 1.6
76.0 70.7 ab 71.6 a
.8 .9
68.4 6 5 . 1 ab 63.7 a
4.0 3.5
78.5 72.8 77.5
1,2 1.5
2.3 2.7
79.7 74.2 74.9
1.2 2.5
37.1 b 41.0 47.2
76.3 74.2 bc 79.2 c
68.9 68.3 b 70.0 b
79.7 78.9 79.8
1.4 3.0
Z
A c i d d e t e r g e n t f i b e r (%) 16 to 2 0 6 6 to 7 0 176 to 180
46.7 a 41.9 46.5
16 t o 2 0 6 6 to 7 0 176 to 180
76.9 68.0 a 7 3 . 5 ab
16 t o 2 0 66 to 70 176 to 180
70.2 62.8 a 65.6 ab
5.3 4.5
40.3 ab 33.1 44.2
2.4 3.0
39.3 ab 44.2 50.1
.4 3.0
N
1.0 .7
76.6 77.4 c 78.7 bc
2.5 1.4
© Z ,< t"
1.3 1.5
68.7 67.9 b 69.3 b
1.7 1.5
N i t r o g e n - f r e e e x t r a c t (%) 3.2 .3
77.0 70.1 ab 76.1 abc
,8 2,0
Z ,q
T o t a l d i g e s t i b l e n u t r i e n t s (%)
o
3.1 1.0
69.7 62.5 a 66.7 ab
1.0 .6
"]
O
a ' b ' C M e a n s w i t h i n a given r o w n o t b e a r i n g a c o m m o n s u p e r s c r i p t are d i f f e r e n t ( P < . 0 5 ) . d D u r i n g d a y s 16 t o 2 0 o f l a c t a t i o n all c o w s w e r e f e d d i e t 4 s u p p l e m e n t e d w i t h u r e a a n d s o y b e a n m e a l . <
.o O~
Z o
~o *q 00
xO bo ~rt
bo C~,
<
TABLE 5. Nitrogen intake and utilization by lactating cows fed diets containing varying concentrations of crude prot e i n s u p p l e m e n t e d w ith urea and/or soybean meal.
O Ox
Diets
Z O
~q 0o
Days of lactation
1 No supplemental nitrogen
2
3
Urea
(Mean
(Mean _+ SE)
_+
SE)
Soybean meal
4 Urea + soybean meal
5 Soybean meal
(Mean +- SE)
(Mean + SE)
(Mean + SE)
424 457 bc 437 bc
24 29
426 479 c 514 c
59 48
139 154 b 145 ab
12 12
143 167 b 162 b
29 17
104 125 c 111 c
6 3
96 115 c 137 d
13 8
N-intake (g/day) 16 to 20 e 66 to 70 176 to 180
410 238 a 259 a
1 6 t o 20 6 6 t o 70 176 to 180
135 107 a 109 a
16 to 20 66 to 70 176 to 180
98 35 a 38 a
8 15
407 373 b 380 b
2 6
131 140 ab 150 ab
0 4
110 78 b 85 b
7 30
377 379 b 372 b
14 37
~t-
Fecal-N (g/day) 10 13
116 154 b 141 ab
16 7
Urine-N (g/day) 5 10
99 57 ab 63 ab
3 7
"] ~"
Milk-N ( g / d a y ) 16 to 2 0 66 to 70 176 to 180
180 112 a 83 a
I 6 to 2 0 66 to 70 176 to 180
-3 -16 29
3 3
171 150 ab 122 b
8 2
-5 5 23
9 10
182 157 bc 118 ab
18 11
175 163bc 12lab
193 194 c 161 c
28 12
Retained-N (g/day) 10 2
-20 11 50
16 23
6 17 60
2 8
-6 3 54
21 14
285 305 c 292 c
12 17
283 312 c 352 c
32 31
181 180bc 181bc
7 17
Absorbed-N (g/day) 16 to 2 0 66 to 70 176 to 180
275 131 a 150 a
6 7
276 233 b 230 b
14 18
261 225 b 231 b
12 30
Productive-Nf(g/day) e~
16 to 2 0 66 to 70 176to 180
177 96 a 112 a
6 5
166 1 5 5 ab 145 ab
11 12
162 168 bc 168 b
10 31
F
a ' b ' c ' d M e a n s w i t h i n a given r o w n o t b e a r i n g a c o m m o n s u p e r s c r i p t are d i f f e r e n t ( P < . 0 5 ) .
t~
e D u r i n g d a y s 16 t o 2 0 o f l a c t a t i o n all c o w s w e r e f e d d i e t 4 s u p p l e m e n t e d w i t h u r e a a n d s o y b e a n m e a l .
187 197 c
215 c
20 25
fProduetive-N = retained-N + milk-N. < O Ox
Z O
xt~
T A B L E 6. N i t r o g e n u t i l i z a t i o n b y l a c t a t i n g c o w s e x p r e s s e d as a p e r c e n t o f n i t r o g e n i n t a k e .
,~ to 00 Diets
eL
Days of lactation
1 No supplemental nitrogen
2
3
Urea
Soybean meal
( M e a n +- SE)
( M e a n + SE)
( M e a n -+ SE)
< o Ox
Z 9 Y
g 0o
4 Urea + soybean meal
5 Soybean meal
( M e a n +- SE)
( M e a n + SE)
Fecal-N 16 t o 2 0 d 66 t o 7 0 176 to 180
33.0 44.9 a 42.1 a
16 t o 2 0 66 to 70 176 to 180
23.9 14.7 a 14.7 a
16 t o 2 0 66 to 70 176 to 180
44.1 47.1 a 32.0
I6 to 20 66 to 70 176 to 180
-1.0 -6.7 11.2
16 t o 2 0 6 6 to 7 0 176 to 180
67.0 55.0 a 57.9 a
16 t o 2 0 66 to 70 176 to 180
43.2 40.3 43.2
.6 1.0
32.3 37.5 be 39.5 a
.6 1.5
27.0 21.0 b 22.4 b
2.4 1.4
42.0 40.2 b 32.1
3.5 1.8
-i.2 1.3 6.0
3.0 1.1
30.8 40.6 ab 37.9 a
1.5 2.1
26.2 15.0 a 17.0 a
2.2 .4
48.3 41.4 b 31.7
2.6 .6
-5.3 3.0 13.4
3.0 1.2
69.2 5 9 . 4 ab 62.1 ab
3.3 1.0
43.0 44.3 45.2
3.3 1.9
32.8 33.6 c 33.2 b
.9 .6
33.6 34.9 c 31.5 b
1.9 .6
24.5 27.2 c 25.4 b
.5 1.8
22.5 24.0 bc 26.7 b
.3 1.8
41.3 35.5 b 27.7
.4 .8
45.3 40.5 b 31.3
3.0 .7
.6 1.0
-1.4 .6 10.5
4.8 1.9
.9 .6
66.4 65.1 c 68.5 c
1.9 .6
43.9 40.9 41.8
2.0 1.2
Urine-N 1.1 2.0
Milk-N 3.4 1.6
Retained-N 4.3 4.7
1.4 3.7 13.7
Absorbed-N .6 1.0
67.8 62.5 bc 60.5 a
1.2 .9
40.8 41.5 38.1
3.3 1.9
67.2 66.4 c 66.8 bc
Productive-N e 2.5 4.1
a ' b ' C M e a n s w i t h i n a given r o w n o t b e a r i n g a c o m m o n s u p e r s c r i p t are d i f f e r e n t ( P < . 0 5 ) . d D u r i n g d a y s 16 to 2 0 o f l a c t a t i o n all c o w s w e r e f e d d i e t 4 s u p p l e m e n t e d w i t h u r e a a n d s o y b e a n m e a l . eproductive-N = retained-N + milk-N.
42.7 39.2 41.4
2.9 1.2
t'n >
T A B L E 7. N i t r o g e n u t i l i z a t i o n b y l a c t a t i n g c o w s e x p r e s s e d as a p e r c e n t o f n i t r o g e n a b s o r b e d . Diets 1
Days of lactation
2
No supplemental nitrogen ( M e a n -+ SE)
3
4
5
Urea
Soybean meal
Urea + soybean meal
Soybean meal
( M e a n + SE)
( M e a n -+ SE)
( M e a n -+ SE)
_z
( M e a n -+ SE)
©
Urine-N 16 t o 2 0 e 66 to 70 176 to 180
35.6 26.7 ab 25.3 a
16 t o 2 0 66 to 70 176 to 180
65.4 85.5 a 55.3 a
1.4 2.3
39.9 33.5 bc 36.9 b
5.1 1.4
61.9 64.4 bc 53.1 ab
2.3 2.8
37.9 25.3 a 27.3 a
1.9 1.7
69.7 69.8 b 51.1 a b
1.1 3.7
36.5 41.0 d 38.0 b
.8 2.4
33.9 36.8 cd 38.9 b
1.2 2.2
Z
61.4 53.4 c 41.1 b
.5 1.5
68.2 62.2 c 45.7 ab
5.9 .7
.8 1.6
-2.1 1.0 15.4
.8 2.4
66.1 62.8 c 61.1 b
Milk-N 8.3 3.2
Retained-N
o
16 t o 2 0 66 to 7 0 176 to 180
-1.0 -12.2 19.4
6,5 3.3
-1.8 2,1 10.0
4,1 1.2
-7.6 4.9 21.6
7.4 6,9
2.1 5.6 20.6
,q ;~ 7.1 2.8
Productive-N f 16 to 20 66 to 70 176 to 180
64.4 73.3 ab 74.7 a
1.4 2.3
60.1 66.5 bc 63.0 b
4.3 2.8
62.1 74.7 a 72.7 a
1.1. 4.5
< o
a ' b ' c ' d M e a n s w i t h i n a g i v e n r o w n o t b e a r i n g a c o m m o n s u p e r s c r i p t are d i f f e r e n t ( P < . 0 5 ) .
ox
e D u r i n g d a y s 16 t o 2 0 o f l a c t a t i o n all c o w s w e r e f e d d i e t 4 s u p p l e m e n t e d w i t h u r e a a n d s o y b e a n m e a l .
Z
fProductive-N = retained-N + milk-N.
o
.q 0o
t~ ~< t-
u~ 63.5 59.0 c 62.0 b
1.2 2.2
tJ ",O
930
WOHLT ET AL.
t i o n s b y o t h e r investigators (13, 24, 26, 31) have b e e n similar. The e f f i c i e n c y o f urea utilizat i o n f o r milk p r o d u c t i o n d e c r e a s e d as t h e c r u d e p r o t e i n c o n t e n t o f t h e diet was increased b y adding urea w h i c h m a y b e d u e t o t h e inability o f t h e r u m e n m i c r o b e s t o i n c o r p o r a t e all o f t h e a m m o n i a - N released f r o m urea i n t o microbial p r o t e i n or t o the ability o f t h e p l a n t p r o t e i n in t h e diet t o m e e t the p r o t e i n r e q u i r e m e n t o f t h e cow. K e r t z a n d E v e r e t t (18) r e p o r t e d t h a t microbial p r o t e i n s y n t h e s i z e d in t h e r u m e n r a n g e d f r o m 9.6 t o 33.2 g p e r 100 g o f organic m a t t e r digested and suggested t h a t t h e U F P values o f Burroughs et al. (3, 4) m a y u n d e r e s t i m a t e s y n t h e s i s o f m i c r o b i a l p r o t e i n and, t h u s , may underestimate the utilization of ammoniaN in the r u m e n . Van H o r n e t al. (35) and Randel e t al. (25) o b s e r v e d t h a t urea was n o t utilized in diets t h a t were f o r m u l a t e d to c o n t a i n a positive UFP. Since w e (37) o b s e r v e d a similar milk yield f r o m cows fed a d i e t t h a t c o n t a i n e d 9 t o 10% c r u d e p r o t e i n , t h e urea a d d e d to t h e diets in the studies o f Van H o r n e t al. (35) a n d R a n d e l et al. (25) m a y n o t have b e e n n e e d e d t o m e e t the c o w ' s r e q u i r e m e n t for c r u d e p r o t e i n . These data suggest t h a t U F P values o f Burroughs e t al. (4) n e e d t o be re-evaluated to c o n sider n o t o n l y the p o t e n t i a l t o i n c o r p o r a t e ureaN i n t o microbial p r o t e i n b u t also the a n i m a l ' s r e q u i r e m e n t f o r crude p r o t e i n .
REFERENCES
1 Aitchison, T. E., D. R. Mertens, A. D. McGilliard, and N. L. Jacobson. 1976. Effect of nitrogen solubility on nitrogen utilization in lactating dairy cattle. J. Dairy Sci. 59:2056. 2 Association of Official Agricultural Chemists. 1965. Official methods of analysis. 10th ed. Washington, DC. 3 Burroughs, W., D. K. Nelson, and D. R. Mertens. 1975. Evaluation of protein nutrition by metabolizable protein and urea fermentation potential. J. Dairy Sci. 58:611. 4 Burroughs, W., D. K. Nelson, and D. R. Mertens. 1975. Protein physiology and its application in the lactating cow: The metabolizable protein feeding standard. J. Anita. Sci. 41:933. 5 Campliug, R. C., M. Freer, and C. C. Balch. 1961. Factors affecting voluntary intake of food by cows. 2. The relationship between the voluntary intake of roughages, the amount of digesta in the reticulorumen, and the rate of disappearance of digesta from the alimentary tract. Br. J. Nutr. 15: 531. 6 Campling, R. C., M. Freer, and C. C. Balch. 1962. Factors affecting voluntary intake of food by Journal of Dairy Science Vol. 61, No. 7, 1978
cows. 3. The effect of urea on the voluntary intake of oat straw. Br. J. Nutr. 16:115. 7 Cerbulis, J., and H. M. Farrell, Jr. 1975. Composition of milks of dairy cattle. I. Protein, lactose, and fat contents and distribution of protein fraction. J. Dairy Sci. 58:817. 8 Clark, J. H. 1975. Lactational responses to postruminal administration of proteins and amino acids. J. Dairy Sci. 58:1178. 9 Crutchfield, W. O. 1968. A technic for placement of an indwelling catheter in the cow. Vet. Med. and Small Anim. Clin. 63:1141. 10 Elliott, R. C. 1967. Voluntary intake of low protein diets by ruminants. 1. Intake of food by cattle. J. Agr. Sci. 69:375. 11 Elliott, R. C., and J. H. Topps. 1963. Voluntary intake of low protein diets by sheep. Anita. Prod. 5:269. 12 Hawk, P. B. 1965. In Physiological chemistry. B. L. Oser, ed. McGraw-Hill Book Co., New York. 13 Helmer, L. G., and E. E. Bartley. 1971. Progress in the utilization of urea as a protein replacer for ruminants. A review. J. Dairy Sci. 54:25. 14 Huber, J. T. 1965. Protein and nonprotein nitrogen utilization in practical dairy rations. J. Anita. Sci. 41:954. 15 Huber, J. T., and O. P. Santana. 1972. Ammoniatreated corn silage for dairy cattle. J. Dairy Sci. 55:489. 16 Huber, J. T., and J. W. Thomas. 1971. Urea-treated corn silage in low protein rations for lactating cows. J. Dairy Sci. 54:224. 17 Jacobson, D. R., H. If. Van Horn, and C. J. Sniffen. 1970. Lactating ruminants. Fed. Proc. 29:35. 18 Kertz, A. F., and J. P. Everett, Jr. 1975. Utilization of urea by lactating cows-An industry viewpoint. J. Anita. Sci. 41:945. 19 Mehrez, A. Z., and E. R. Orskov. 1976. Rates of rumen fermentation in relation to ammonia concentration. Proc. Nutr. Soc. 35:40A. 20 National Research Council. 1971. Nutrient requiremeats of domestic animals. No. 3. Nutrient requirements of dairy cattle. 4th rev. ed. National Academy of Sciences. Washington, DC. 21 Okorie, A. U., P. J. Buttery and D. Lewis. 1977. Ammonia concentration and protein synthesis in the rumen. Proc. Nutr. Soc. 36:38A. 22 Orskov, E. R., and C. Fraser. 1973. The effect of feeding and protein concentration on the disappearance of protein in different segments of the gut in sheep. Proc. Nutr. Soc. 32:68A. 23 Perkins, A. E. 1957. The effect of rations excessively high and extremely low in protein content for dairy cows. Ohio Agr. Exp. Sta. Bull. 799. 24 Polan, C. E., C. N. Miller, and M. L. McGilliard. 1976. Variable dietary protein and urea for intake and production in Holstein cows. J. Dairy Sci. 59: 1910. 25 Randel, P. F., H. H. Van Horn, C. J. Wilcox, H. Roman-Ponce, S. P. Marshall, and K. C. Bachman. 1975. Complete rations for dairy cattle. IV. Comparison of supplemental nitrogen sources by metabolizable protein concept. J. Dairy Sci. 58: 1109.
N I T R O G E N U T I L I Z A T I O N BY L A C T A T I N G COWS 26 Reid, J. T. 1953. Urea as a protein replacement for ruminants. A review. J. Dairy Sci. 36:955. 27 Reid, J. T., P. W. Moe, and H. F. Tyrrell. 1966. Energy and protein requirements of milk production. J. Dairy Sci. 49:215. 28 Robertson, J. B., C. E. Coppock, C. H. Noller, W. E. Wheeler, and P. J. Van Soest. 1974. Regression o f digestibility on intake in lactating dairy cows. J. Dairy Sci. 57:622. 29 Roffler, R. E., and L. D. Satter. 1975. Relationship between ruminal a m m o n i a and nonprotein nitrogen utilization by ruminants. I. Development of a model for predicting n o n p r o t e i n nitrogen utilization by cattle. J. Dairy Sci. 58:1880. 30 Roffler, R. E., and L. D. Satter. 1975. Relationship between ruminal a m m o n i a and nonprotein nitrogen utilization by ruminants. II. Application of published evidence to the development of a theoretical model for predicting nonprotein nitrogen utilization. J. Dairy Sci. 58:1889. 31 Rys', R. 1967. Urea in rations for dairy cows. Page 239 in Urea as a protein supplement. M. H. Briggs, ed. Pergamon Press, Ltd., New York. 32 Satter, L. D., and R. E. Roffler. 1975. Nitrogen requirement and utilization in dairy cattle. J. Dairy
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Sci. 58:1219. 33 Satter, L. D., and L. L. Slyter. 1974. Effect of amm o n i a concentration on r u m e n microbial protein production in vitro. Br. J. Nutr. 32:199. 34 Steel, R. G. D., and J. H. Torrie. 1960. Principles and procedures of statistics. McGraw-Hill Book Co., New York. 35 Van Horn, H. H., S. P. Marshall, C. J. Wilcox, P. F. Randel, and J. M. Wing. 1975. Complete rations for dairy cattle. II1. Evaluation of protein percent and quality and citrus pulp-corn substitutions. J. Dairy Sci. 58:1101. 36 Van Soest, P. J. 1963. Use of detergents in the analysis of fibrous feeds. 1I. A rapid m e t h o d for the determination of fiber and lignin. J. Ass. Offic. Agr. Chem. 46:829. 37 Wohlt, J. E., and J. H. Clark. 1978. Nutritional value of urea versus preformed protein for ruminants. 1. Lactation performance of dairy cows fed corn based diets containing varying a m o u n t s of supplemental nitrogen from urea a n d / o r soybean meal. J. Dairy Sci. 61:902. 38 Wohlt, J. E., C. J. Sniffen, and W. H. Hoover. 1973. M e a s u r e m e n t o f protein solubility in comm o n feedstuffs. J. Dairy Sci. 56:1052.
Journal o f Dairy Science Vol. 61, No. 7, 1978