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Metabolizable protein supply (PDIE) and restricted level of
ruminally degradable nitrogen (PDIN) in total mixed rations:
effect on milk production and composition and on nitrogen
utilization by dairy cows
*
O. Colin-Schoellen, S. Jurjanz , F. Laurent
ˆ
Laboratoire de Sciences Animales, INRA–ENSAIA, 2 Av. de la Foret de Haye, B.P. 172, 54 505 Vandoeuvre les Nancy Cedex, France Received 7 June 1999; received in revised form 8 November 1999; accepted 14 March 2000
Abstract
21
Three levels of metabolizable protein supply (108, 98–95 and 85 g PDIE kg DM) (PDIE: protein digested in the small intestine when rumen-fermentable energy is limiting) in the diet and three levels of difference between rumen-degradable
21
energy and N (PDIE2PDIN50, 10 and 20 g kg DM) (PDIN: protein digested in the small intestine when rumen-fermentable nitrogen is limiting) were used in two trials with 24 and 32 dairy cows. Trials were conducted using Latin-square designs and all cows were fed a total mixed ration. Dry matter intake, net energy intake, and milk yield were significantly higher (P,0.05) with increasing PDIE level. The PDIE level of the diet did not affect milk true protein content but the results for fat content were different for the two levels of PDIE increase: fat content decreased (P,0.05) between the low and medium PDIE levels and did not vary between the medium and high PDIE level. Milk NPN and urea contents increased with the increased level of PDIE. The milk protein N yield / N intake ratio decreased (P,0.10) as the level of
21
PDIE in the diet increased. A difference of 10 g PDIN kg DM between rumen-degradable N and energy affected neither dry matter, energy or PDIE intake, nor milk yield or composition. However, dry matter, energy and PDIE intake decreased (P,0.10) for a rumen-degradable PDIN deficit of 20 g / kg DM. In this case, milk yield was not significantly affected but milk fat content increased significantly (P,0.10) and milk true protein content decreased (P,0.01). Milk NPN and urea contents decreased as the rumen-degradable PDIN deficit increased (P,0.01). The milk protein N yield / N intake ratio increased with the increase in rumen-degradable PDIN deficit (P,0.01). 2000 Elsevier Science B.V. All rights reserved.
Keywords: Metabolizable protein; Diet; Rumen-degradable N; Dairy cow; Milk NPN
In terms of nitrogen nutrition, the level of microbial
1. Introduction
protein synthesis and the amount of digestible pro-tein in the intestine are important determinants of the Cattle nutrition has been studied for a long time.
response and efficiency with which dietary nitrogen is used for milk production. These two points have
*Corresponding author. Tel.: 133-383-595-889; fax: 1
33-been taken into account in the most advanced protein
383-595-804.
E-mail address: [email protected] (S. Jurjanz). evaluation systems (Madsen, 1985; NRC, 1985;
42 O. Colin-Schoellen et al. / Livestock Production Science 67 (2000) 41 –53
´ ´
Verite and Peyraud, 1988; AFRC, 1993; Tamminga undegraded feed protein (PDIA5ruminally unde-et al., 1994; Kirchgessner, 1997). Progress in de- graded feed protein digested in the small intestine). veloping nitrogen nutrition has mainly focused on The estimation of PDIA requires the calculation of improving output of cattle. More recently, the contri- the degradability of feed protein in the rumen, which bution of ruminants to the deterioration of the is made by the nylon bag technique, and the true environment has also being taken into account. In digestibility in the small intestine. The PDI system fact, the excretion of considerable amounts of non- examines a wide range of values of degradability and digested or non-utilized feed residues (mainly N and digestibility between foodstuffs (Andrieu and De-minerals) contributes to pollution if these effluents marquilly, 1987; Sauvant et al., 1987). The estima-are not properly managed. Nutrition management can tion of PDIM take into account the availability of be used as a tool to help control environmental energy and nitrogen to rumen microbes. The PDI
´ ´
pollution. system (Verite et al., 1987) characterises separately
Nitrogen losses originate from several sources: the PDIME (microbial protein digested in the small important N losses may occur if the rate of protein intestine when rumen fermentable energy is limiting) degradation by microorganisms in the rumen does and the PDIMN (microbial protein digested in the not match the rate of microbial protein synthesis. small intestine when rumen fermentable N is limit-This occurs particularly when the amount of avail- ing). The technique estimates the amount of energy able energy does not correspond to the amount of available to rumen microbes by calculating ferment-available nitrogen. Surplus nitrogen is absorbed from able OM (FOM5DOM2fat2ruminally unde-the rumen and converted into urea. Most of it is graded protein2fermentation products) and
21
excreted via the urine. Other sources of N losses are produces a yield of 145 g MCP kg FOM for the undigested feed and microbial nitrogen, as well as a microbial protein synthesis. The estimation of the proportion of endogenous nitrogen, which are ex- amount of degradable protein is described above. creted in the feces. The undigested N proportion The amino acid content of microbial protein and varies little between diets and depends essentially on their true digestibility in the small intestine are dry matter intake. Lastly, true protein is digested in assumed to be constant, 0.8 and 0.8, respectively. So, the small intestine and used for maintenance, protein the PDI system characterises a diet or a feed using synthesis in milk and tissue, and replacement of two values: the PDIE (protein digested in the small endogenous nitrogen losses. Some N losses result intestine when rumen fermentable energy is limiting) from excess of intestinally available protein with value, which is the sum of PDIA and PDIME, and regard to animal requirements and from the low the PDIN (protein digested in the small intestine efficiency of utilization of protein digested in the when rumen fermentable N is limiting), which is the small intestine for the different metabolic functions. sum of PDIA and PDIMN.
The two simplest ways to reduce nitrogen losses The aim of these trials was to study the effect of by nitrogen nutrition consist of limiting excess the metabolizable protein supply level in the diet, protein digested in the small intestine and balancing through the PDIE level, and the balance between the level of rumen-degradable nitrogen with the rumen-degradable N and rumen available energy, available energy supply for protein synthesis by through the difference between PDIN and PDIE. microorganisms. The PDI (protein digestible in the These effects were studied in a total mixed ration fed
´ ´
2. Material and methods formulated to ensure similar energy contents (0.90
21
UFL kg DM) (1 UFL51700 kcal of net energy 2.1. Experimental design and cow management for lactation) (Vermorel, 1988).
Two trials were performed with the same
ex-2.1.2. Trial 2 perimental design and two standard treatments. In
Two metabolizable protein supply levels
both trials, the cows were housed in free stalls at the 21
(medium595, or low585 g PDIE kg DM) and ENSAIA experimental station in Nancy (France).
three levels of difference between rumen-degradable
The animals were fed a total mixed ration once a day 21
energy and N (PDIE2PDIN50, 10 or 20 g kg in the morning ad libitum to which they had access
DM) were tested in a replicated Latin-square design continuously using electronic feed gates. Each cow
(434) with four diets: medium PDIE content and was fitted with an electronic transponder with access
balanced rumen fermentable energy and N (diet 1), to one of the gates. All cows were milked twice daily
rumen-degradable PDIN deficit of 10 g (diet 2) or 20 and individual milk yields were automatically re- 21
g kg DM (diet 3), and low PDIE content and
corded at each milking time (Isalait 2045 system, 21
rumen-degradable PDIN deficit of 10 g kg DM Boumatic).
(diet 4). Thirty-two Prim’Holstein cows, of which eight were primiparous, were blocked in eight Latin-2.1.1. Trial 1
squares. All cows began experimentation on the Two metabolizable protein supply levels (high5 same day. The lactation stage at the beginning of the
21
108, or medium598 g PDIE kg DM) and two
trial was 55 (623) days and body weight was 622 levels of difference between rumen-degradable
(671) kg. Mean milk yield over the 2
pre-ex-21
energy and N (PDIE2PDIN50 or 10 g PDIN kg 21
perimental weeks was 31.2 (65.9) kg day . The DM) were tested in a replicated Latin-square design
animals were fed a total mixed ration composed of (333) with three diets: high PDIE content and
corn silage, wheat straw, soybean meal,
formalde-21 rumen-degradable PDIN deficit of 10 g kg DM,
hyde-treated mixed meal, minerals and sugar beet medium PDIE content and balanced rumen
ferment-pulp only for the diet with the rumen-degradable N
able energy and N, and medium PDIE content and 21
deficit of 20 g PDIN kg DM. The proportions of
21 rumen-degradable PDIN deficit of 10 g kg DM.
the different components of the diet were varied with Twenty four Holstein cows, of which nine were
the aim of reaching optimum PDIE content and primiparous, were blocked in eight Latin-squares by
rumen-degradable PDIN deficit (Table 2). The diets parity, calving date, milk true protein yield, and milk
were formulated to ensure similar energy contents
NPN content (average over two pre-experimental 21
(0.90–0.92 UFL kg DM). weeks). All cows began experimentation on the same
For both trials, the succession of treatments for day. The lactation stage at the beginning of the trial
each cow in the first Latin square was determined was 83 (637) days and body weight was 588 (650)
randomly. For the seven other Latin squares, the kg. Mean milk yield, fat, true protein, and NPN
succession of treatments was the same as for the first contents for the two pre-experimental weeks were
Latin square. Each experimental period lasted 5
21 21
30.9 (65.0) kg day , 41.6 (66.7) g kg , 31.1
weeks and all measurements were taken during the
21 21
(62.8) g kg and 281 (621) mg l , respectively.
last 2 weeks of each period. The animals were fed a total mixed ration composed
of corn silage, soybean meal, formaldehyde-treated
mixed meal (rape and soybean, 20:80), urea for the 2.2. Sampling and analysis diet with balanced contents of rumen-degradable
44 O. Colin-Schoellen et al. / Livestock Production Science 67 (2000) 41 –53 Table 1
a
Composition and estimated nutritive value of diets in trial 1
High PDIE content Medium PDIE content 21
PDIN deficit510 g kg DM No PDIN deficit PDIN deficit 21
510 g kg DM Composition (% of the DM)
Corn silage 81.7 84.5 85.1
Soybean meal 4.0 4.7 4.7
Formaldehyde treated mixed meal 12.7 8.6 8.7
Urea – 0.7 –
Minerals 1.6 1.5 1.5
21 Chemical composition (g kg DM)
CP 138 144 125
CF 157 159 160
ADF 200 207 209
NDF 374 387 389
Ash 61 59 59
b
DT 0.55 0.64 0.58
a
Nutritive value (/ kg DM) c
UFL 0.90 0.90 0.90
d
PDIN 98 97 87
d
PDIE 108 98 98
e
PDIA 59 48 48
a
Calculated from the analyses of forage and concentrates. b
DT: theoretical degradability in the rumen of the proteins of the total mixed ration. c
UFL: feed unit for lactation (net energy). d
PDIN, PDIE: Protein digestible in the small intestine when rumen fermentable nitrogen or energy, respectively, are limiting. e
PDIA: By-pass protein digestible in the small intestine.
The cows were weighed on two consecutive days, Each foodstuff was sampled monthly and analyzed
approximately 6 h after access to the diet, at the end chemically (DM, CP, CF, ADF, NDF and ash).
of the pre-experimental period, and during the last Energy and PDI values were calculated (Jarrige,
week of each experimental period. 1988).
The percentages of cow energy and PDI require-Milk composition was determined at two
consecu-ments covered were calculated from the energy and tive milkings during the first 3 weeks of each
PDI supplies of the diets and from maintenance and experimental period and at four consecutive milkings
milk production requirements (Jarrige, 1988). The during the last 2 weeks of each experimental period.
efficiency of the utilization of crude protein supplies The milk fat and true protein contents were analyzed
for milk protein synthesis was estimated from the by the infrared method (IRMA analyzer, Hillerød,
milk protein N yield / N intake ratio and milk NPN Denmark) and the somatic cells were counted by
yield / N intake ratio. nuclear coloration (Fossomatic analyzer, Hillerød,
Denmark). During the last 2 weeks of each
ex-perimental period, using the same samples as those 2.3. Statistical analysis used for milk composition, total N, NPN and
Table 2
a
Composition and estimated nutritive value of diets in trial 2
Medium PDIE content Low PDIE content
PDIN deficit5
No PDIN PDIN deficit5 PDIN deficit5 21 10 g kg DM
21 21
deficit 10 g kg DM 20 g kg DM
Composition (% of the DM)
Corn silage 77.3 83.3 72.8 87.4
Wheat straw 3.2 – – –
Soybean meal 17.9 11.5 5.0 11.0
Formaldehyde treated mixed meal – 3.5 6.4 –
Sugarbeet pulp – – 14.2 –
Calculated from the analyses of forage and concentrates. b
DT: theoretical degradability in the rumen of the proteins of the total mixed ration. c
UFL: feed unit for lactation (net energy). d
PDIN, PDIE: Protein digestible in the small intestine when rumen fermentable nitrogen or energy, respectively, are limiting. e
PDIA: By-pass protein digestible in the small intestine.
21 for the last 2 weeks of each experimental period rumen-degradable PDIN deficit of 10 or 20 g kg
DM, all three with a medium PDIE level. were tested for each measured variable. The effects
of the metabolizable protein supply level and of the magnitude of rumen-degradable PDIN deficit were
3. Results
tested by the contrast method (Dagnelie, 1994). In trial 1, the PDIE supply level was studied by
3.1. Effect of PDIE level comparing the diets with a high or medium PDIE
content, both with a rumen-degradable PDIN deficit.
3.1.1. Trial 1 The rumen-degradable PDIN deficit was studied by
DMI was significantly higher for the diet with the comparing the diets with balanced rumen
ferment-21
high PDIE level (10.8 kg DM day , P,0.05) able energy and N or a rumen-degradable PDIN
21
(Table 3). Consequently net energy intake (10.6 deficit of 10 g kg DM, both with a medium PDIE
21 21
UFL cow day , P,0.05) and PDI intake in-level. In trial 2, the PDIE supply level was studied
creased by as much (1286 g PDIE and 1299 g by comparing the diets with a medium or low PDIE
21 21
PDIN cow day , P,0.01). The average daily content, both with a deficit rumen-degradable PDIN
21
gain of the cows was positive for all treatments and deficit of 10 g kg DM. The level of
rumen-degrad-not significantly affected by the PDIE supply level able PDIN was studied by comparing the diets with
46 O. Colin-Schoellen et al. / Livestock Production Science 67 (2000) 41 –53 Table 3
Effect of PDIE level of the diet on intake, energy or nitrogen requirements covered and N utilization (all the diets were calculated to have a 21
PDIN deficit of 10 g kg DM)
Trial 1 Trial 2
High Medium Significance S.E. Medium Low Significance S.E.
PDIE PDIE of PDIE PDIE PDIE of PDIE
level level level level level level
21
DMI (kg day ) 21.3 20.5 ,0.05 1.0 20.2 19.2 ,0.05 1.1
a 21
Net energy intake (UFL day ) 19.2 18.6 ,0.05 0.9 18.7 17.8 0.01 1.3 21
N intake (g day ) 470 411 ,0.01 22 412 341 ,0.01 27
b 21
PDIE intake (g day ) 2300 2014 ,0.01 107 1939 1643 ,0.01 131
b 21
PDIN intake (g day ) 2087 1788 ,0.01 97 1757 1417 ,0.01 114
21
Average daily gain (g day ) 287 471 NS 483 357 107 ,0.10 436
Energy supplies / requirements (%) 101 101 NS 5 111 108 0.10 6
PDIE supplies / requirements (%) 124 112 ,0.01 4 118 104 ,0.01 6
PDIN supplies / requirements (%) 112 100 ,0.01 4 107 90 ,0.01 6
Milk protein N yield / N intake (%) 29.9 32.5 ,0.01 1.2 31.9 36.4 ,0.01 2.9 Milk NPN yield / N intake (%) 1.84 1.86 NS 0.14 1.50 1.61 ,0.05 0.19
a
UFL: feed unit for lactation (net energy). b
PDIE, PDIN: Protein digestible in the small intestine when rumen fermentable energy or nitrogen, respectively, are limiting.
Milk yield increased significantly for the cows fed Total N, protein N and casein N contents in the the diet with the high PDIE level (11.3 milk were not significantly affected by the type of
21 21
kg cow day , P,0.01), but the PDIE level diet. Soluble N and NPN contents increased sig-affected neither milk fat content, nor milk true nificantly for the diet with the high PDIE level
21
protein content. Consequently, fat and protein yields (138 and 122 mg l , respectively, P,0.01), as increased significantly for the diet with the high did the proportion of NPN in total N (5.6%
com-21
PDIE level (140 g day , P,0.10 and 142 pared to 5.2%, P,0.01) (Table 4).
21
g day , P,0.01, respectively) (Table 4). The percentage of cow energy requirements
cov-Table 4
21 Effect of PDIE level of the diet on milk yield and composition (all the diets were calculated to have a PDIN deficit of 10 g kg DM)
Trial 1 Trial 2
High Medium Significance S.E. Medium Low Significance S.E.
PDIE PDIE of PDIE PDIE PDIE of PDIE
level level level level level level
21
Milk yield (kg day ) 29.3 28.0 ,0.01 1.3 24.9 23.5 0.05 2.2
21
Fat corrected milk (kg day ) 30.3 29.2 ,0.05 1.6 25.8 24.7 NS 2.5
21
Fat content (g kg ) 42.3 42.6 NS 1.7 41.4 43.3 ,0.05 2.1
21
Fat yield (g day ) 1232 1192 ,0.10 72 1056 1023 NS 109
21
True protein content (g kg ) 32.1 32.1 NS 0.7 32.2 32.2 NS 1.0
21
Protein yield (g day ) 942 900 ,0.01 41 796 751 0.05 74
21
Total N content (g l ) 5.11 5.06 NS 1.16 5.35 5.31 NS 206
21
Protein N content (g l ) 4.82 4.80 NS 1.17 5.11 5.02 NS 302
21
Casein N content (g l ) 4.09 4.08 NS 1.13 – – – –
21
Soluble N content (g l ) 1.02 0.98 ,0.01 0.33 – – – –
21
NPN content (mg l ) 286 264 ,0.01 12 246 233 NS 27
NPN / N total (%) 5.6 5.2 ,0.01 0.3 4.6 4.4 NS 0.5
21
ered was similar for the two diets and close to 100% PDIE level (107%) but some supplies were clearly (Table 3). The percentages of PDI requirements shown to be below the requirements for the low covered increased significantly (P,0.01) for the PDIE level (90%).
diet with the high PDIE level. Some supplies of The ratio of milk protein N yield to N intake PDIE were clearly shown to be higher than the increased significantly for the diet with the low PDIE requirements for the two diets (124 and 112% for the level (36.4 compared to 31.9%, P,0.01). The ratio high and medium PDIE levels, respectively). PDIN of milk NPN yield to N intake also increased supplies were particularly in excess for the diet with significantly for the diet with the low PDIE level the high PDIE level (112 and 100%, respectively). (1.61 compared to 1.50%, P,0.05) (Table 3).
The ratio of N output in milk proteins to N intake increased significantly for the diet with the medium
3.2. Effect of difference between rumen-degradable PDIE level (32.5 compared to 29.9%, P,0.01), but
energy and N the ratio of milk NPN yield to N intake was similar
for the two diets (Table 3).
3.2.1. Trial 1
3.1.2. Trial 2 Dry matter, net energy and PDIE intake were not
DMI increased significantly for the diet with the significantly affected by the difference between
21
medium PDIE level (11.0 kg DM day , P, rumen-degradable energy and N of the diets (Table 0.05). Consequently net energy intake increased 5). N and PDIN intake were significantly higher for
21 21
(10.9 UFL cow day , P,0.01) and PDI intake the diet with balanced supplies of rumen-degradable
21 21 increased by as much for the diet with the medium energy and N (173 and 1249 g cow day , PDIE level (1296 g PDIE and 1340 g respectively, P,0.01).
21 21
PDIN cow day , P,0.01) (Table 3). Average Neither milk yield, milk composition (fat and true daily gain for the cows was positive. It tended to be protein contents), fat or protein yields, nor average greater for those fed the diet with the medium PDIE daily gain of the cows were significantly affected by
21
level (1250 g day , P,0.10). the rumen-degradable PDIN deficit of the diets Milk yield increased for the cows fed the diet with (Table 6). Milk protein N and milk casein N contents
21 21
the medium PDIE level (11.4 kg cow day , P, were not significantly different for the two diets. But
21
0.05) and milk fat content decreased (21.9 g kg , total N, soluble N and NPN contents in the milk, as P,0.05). Consequently fat yield and fat-corrected well as the proportion of NPN in total N, increased milk were not significantly different for the two diets significantly for the diet with balanced supplies of (Table 4). The PDIE level of the diet did not rumen-degradable energy and N (1109, 168 and
21 21
significantly affect milk protein content, but protein 153 mg cow day and 10.9%, respectively, yield was significantly greater for the diet with the P,0.01).
21
medium PDIE level (145 g day , P,0.05). The percentage of cow energy requirements cov-The PDIE level of the diet did not significantly ered was close to 100% for the two diets and the affect total N, protein N, NPN or urea contents in the percentage of PDIE requirements covered was close milk, even if NPN and milk urea contents increased to 110% (Table 5). The percentage of PDIN require-slightly for the diet with the medium PDIE level ments covered showed some supplies which were in
21
(113 and 122 mg l , respectively) (Table 4). excess for the balanced diet while it decreased Energy supplies were considerably over 100% of significantly for the diet with a rumen-degradable requirements for the two diets (Table 3). The PDIN deficit (P,0.01).
48
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Table 5
Effect of the difference between rumen-degradable energy and N of the diet on intake, energy or nitrogen requirements covered and N utilization (all the diets were calculated to 21
have a medium PDIE content (95–98 g kg DM))
Trial 1 Trial 2
21 21 21
Difference Difference Significance S.E. Difference Difference Difference 0 vs. 10 g kg 0 vs. 20 g kg 10 vs. 20 g kg S.E. 50 510 g of rumen 50 510 g 520 g DM of PDIN DM of PDIN DM of PDIN
21 21 21
PDIN kg DM degradable PDIN kg PDIN kg deficit deficit deficit PDIN deficit DM DM
21
DMI (kg day ) 21.0 20.6 NS 1.0 20.3 20.2 19.1 NS 0.01 0.01 1.1 a 21
Net energy intake (UFL day ) 18.8 18.6 NS 0.9 18.5 18.7 17.8 NS ,0.10 ,0.05 1.3 21
N intake (g day ) 484 411 ,0.01 22 454 412 346 ,0.01 ,0.01 ,0.01 27 b 21
PDIE intake (g day ) 2058 2014 NS 107 1964 1939 1876 NS ,0.05 NS 131 b 21
PDIN intake (g day ) 2037 1788 ,0.01 97 1924 1757 1492 ,0.01 ,0.01 ,0.01 114
21
Average daily gain (g day ) 435 471 NS 483 315 357 101 NS ,0.10 NS 436
Energy supplies / requirements (%) 101 101 NS 5 110 111 106 NS ,0.10 ,0.05 6 PDIE supplies / requirements (%) 112 112 NS 4 118 118 118 NS NS NS 6 PDIN supplies / requirements (%) 111 100 ,0.01 4 116 107 94 ,0.01 ,0.01 ,0.01 6
Milk protein N yield / N intake (%) 28.6 32.5 ,0.01 1.2 29.6 31.9 36.2 0.01 ,0.01 ,0.01 2.9 Milk NPN yield / N intake (%) 1.94 1.86 ,0.10 0.14 1.57 1.50 1.53 NS NS NS 0.19
a
UFL: feed unit for lactation (net energy). b
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Table 6
Effect of the difference between rumen-degradable energy and N of the diet on milk yield and composition (all the diets were calculated to have a medium PDIE content (95–98 21
g kg DM))
Trial 1 Trial 2
21 21 21
Difference Difference Significance S.E. Difference Difference Difference 0 vs. 10 g kg 0 vs. 20 g kg 10 vs. 20 g kg S.E.
21 21 21
50 510 g kg of rumen 50 510 g kg 520 g kg DM of PDIN DM of PDIN DM of PDIN DM degradable DM DM deficit deficit deficit
PDIN deficit
21
Milk yield (kg day ) 28.6 28.0 NS 1.3 25.0 24.9 24.4 NS NS NS 2.2 21
Fat corrected milk (kg day ) 29.3 29.2 NS 1.6 25.7 25.8 25.2 NS NS NS 2.5 21
Fat content (g kg ) 41.8 42.6 NS 1.7 41.1 41.4 44.0 NS ,0.10 NS 2.1 21
Fat yield (g day ) 1187 1192 NS 72 1048 1056 1031 NS NS NS 109 21
True protein content (g kg ) 32.3 32.1 NS 0.7 33.7 32.2 31.5 NS ,0.01 ,0.05 1.0 21
Protein yield (g day ) 919 900 NS 41 811 796 764 NS ,0.05 NS 74
21
Total N content (g l ) 5.17 5.06 ,0.01 1.16 5.52 5.35 5.20 ,0.01 ,0.01 ,0.05 206 21
Protein N content (g l ) 4.86 4.80 NS 1.17 5.24 5.11 4.98 NS ,0.01 NS 302 21
Casein N content (g l ) 4.12 4.08 NS 1.13 – – – – – – – 21
Soluble N content (g l ) 1.05 0.98 ,0.01 0.33 – – – – – – – 21
NPN content (mg l ) 317 264 ,0.01 12 286 246 218 ,0.01 ,0.01 ,0.01 27 NPN / N total (%) 6.2 5.2 ,0.01 0.3 5.2 4.6 4.2 ,0.01 ,0.01 ,0.01 0.5
21
50 O. Colin-Schoellen et al. / Livestock Production Science 67 (2000) 41 –53
3.2.2. Trial 2 decreased significantly (P,0.01) as the difference
21
A rumen-degradable PDIN deficit of 10 g kg between rumen-degradable N and energy increased DM did not significantly affect dry matter intake. (Table 6). Milk protein N also decreased as the But DMI decreased significantly for the diet with a deficit of rumen-degradable PDIN increased but the
21
rumen-degradable PDIN deficit of 20 g kg DM difference was only significant between the diet with
21 21 21
(21.2 kg DM cow day ) compared to the bal- a rumen-degradable PDIN deficit of 20 g kg DM
21
anced diet. Consequently, the net energy intake and the balanced diet (2256 mg l , P,0.01). decreased for the diet with a rumen-degradable PDIN The percentages of cow energy and PDIE
require-21 21 21
deficit of 20 g kg DM (20.7 UFL cow day , ments covered were positive and similar between the P,0.10, Table 5). The PDIE intake was not differ- three diets (Table 5). The percentage of PDIN ent between the diets with a difference between requirements covered showed some supplies in ex-rumen-degradable N and energy of 0 or 10 g PDIN / cess for the balanced diet and the diet with a
rumen-21
kg DM, but decreased significantly for the diet with degradable PDIN deficit of 10 g kg DM, but the
21
a rumen-degradable PDIN deficit of 20 g kg DM supplies of PDIN did not cover the requirements of when compared to the balanced diet (288 g the cows for the diet with a rumen-degradable PDIN
21 21 21
PDIE cow day , P,0.05). As expected, PDIN deficit of 20 g kg DM (Table 5).
intake increased significantly for the diet with a The ratio of milk protein N yield to N intake
21
rumen-degradable PDIN deficit of 10 g kg DM increased significantly with the increased deficit of compared to the diet with a rumen-degradable PDIN rumen-degradable PDIN (29.6, 31.9 and 36.2%,
21
deficit of 20 g kg DM (1265 g respectively, for a difference between
rumen-degrad-21 21 21
PDIN cow day , P,0.01), and for the balanced able N and energy of 0, 10 and 20 g PDIN kg DM, diet compared to the two unbalanced diets (167 and P,0.01). The ratio of milk NPN yield to N intake 432 g PDIN more, respectively, than diets with a was not affected by the rumen-degradable PDIN
21
rumen-degradable PDIN deficit of 10 and 20 g kg deficit (Table 5). DM, P,0.01). The average daily gain of the cows
was positive. It was lower for the cows fed the diet
21
with a rumen-degradable PDIN deficit of 20 g kg 4. Discussion
21 21
DM (2214 g day , NS and 2256 g day , P,
0.10 compared to the balanced diet and the diet with 4.1. Effect of the PDIE level
21 a rumen-degradable PDIN deficit of 10 g kg DM).
Milk yield was not significantly affected by the The effect of the PDIE level was studied by difference between rumen-degradable N and energy. comparing each of the diets with a difference Milk fat content tended to increase for the diet with a between rumen-degradable N and energy of 10 g
21 21
rumen-degradable PDIN deficit of 20 g kg DM PDIN kg DM. Using a diet with a similar
com-21
compared to the balanced diet (12.9 g kg , P, position for the two trials (95 g PDIE and 85 g
21
0.10) (Table 6), but fat yield and fat-corrected milk PDIN kg DM) made it possible to discuss the were not significantly different between the three effects of the three PDIE levels of the diets tested diets. Milk true protein content decreased signifi- during the two trials: 84, 95–98 and 108 g
21
cantly for the diet with a rumen-degradable PDIN PDIE kg DM. DMI increased with the PDIE level
21
deficit of 20 g kg DM and the difference was of the diet. The increase was slightly greater between
21 21
particularly great for the balanced diet (22.2 g kg , 84 and 95 g PDIE kg DM (11.0 kg
21 21
P,0.01). Consequently, milk protein yield de- DM cow day ) than between 98 and 108 g
21
creased significantly for the diet with a rumen-de- PDIE kg DM (10.8 kg DM). These results were
21
gradable PDIN deficit of 20 g kg DM (47 consistent with those of Oldham and Emmans (1988)
21 21
g cow day lower than for balanced diet, P, and Sutton (1989). They have been confirmed more
0.05) (Table 6). recently by Sutton et al. (1996), Weigel et al. (1997)
´ ´
21 (1987) considered that the effect of CP content in the significant decrease in fat content (21.9 g kg ) diet on intake may depend on the composition of the which, however, did not vary between the medium diet: in diets with a high proportion of concentrate and high PDIE levels. Consequently, fat yield was (85%), the increase in CP content may led to a not significantly affected in the first case but in-decrease in intake. Hof et al. (1994), using conven- creased significantly in the second. At the same time, tional diets, did not show any variation in intake average daily gain increased significantly in the first when the supplies of intestinal digestible protein case and varied slightly in the second. These results varied between 80 and 120% of animal requirements. may be due to the different orientation of the lipid
Milk yield increased significantly with the PDIE metabolism.
level of the diet. This increase was similar, on the As was the case for true protein content, total N, one hand, between the low and medium levels and, protein N and casein N contents in the milk were not on the other, between the medium and high levels affected by the PDIE content of the diet. NPN and
21 21
(11.4 and 1.3 kg day cow , respectively). Most milk urea contents increased with the increase in the authors, using conventional diets, (De Peters and PDIE content of the diet, but this increase was only Cant, 1992; Hof et al., 1994; Delaby et al., 1995, significant between the medium and high PDIE 1996; Moorby et al., 1996; Sutton et al., 1996) have supply levels. This increase in milk NPN content observed the same results, even if the milk yield with the increase in the CP content of the diet was
´ ´
difference was not always significant. Verite and also observed by Baker et al. (1995) and Sutton et al. Delaby (1998) showed that milk yield increases with (1996). These authors noted that a higher NPN the PDIE level of the diet and follows the rule of content could mainly be explained by an increase in decreasing yields. This increase reached 1.2 kg of milk urea content. Delaby et al. (1995) also observed milk for 10 g of PDIE for supplies of approximately an increase in milk urea content when, at pasture, a
21
95 g PDIE kg DM. Only Christensen et al. (1993) cereal concentrate was replaced by a formaldehyde-and Weigel et al. (1997), using total mixed rations, treated meal. Variations in milk urea content may be did not observe any variation in milk yield with an the result of a lack of balance between the supply of increase in CP content of the diet, but their trials fermentable nitrogen and energy available in the were conducted with only four and five cows, rumen on the one hand, and / or of the lack of balance respectively. This higher milk yield may be ex- between CP or metabolizable protein supplies and
´
plained by higher energy supplies due to the increase animal requirements on the other (Verite et al., 1995; of the dry matter intake (10.9 and 10.6 Broderick and Clayton, 1997; Hof et al., 1997;
21 21
´ ´
UFL cow day , respectively). The utilization of Faverdin and Verite, 1998). In our trial, the increase the additional energy for milk production was close in the PDIE content of the diet led to an increase in
21
to the acceptable value (2.3 kg milk UFL ): it was the percentage of PDIN requirements covered from
21
1.6 kg of milk UFL for the first increase level and 90 to 107% between the low and medium levels and
21
2.2 kg UFL for the second. from 100 to 112% between the medium and high
The milk true protein content was not affected by levels. The increase in milk NPN or urea contents the PDIE content of the diet. However, due to the could doubtlessly be a result of higher N excretion, a milk yield increase, protein yield was significantly consequence of an excess supply of N in the diet. higher for the two PDIE content increase levels in For the first PDIE increase level, the smaller increase the diet. These results were consistent with those of in milk NPN content indicated a better utilization of Hof et al. (1994), Delaby et al. (1995,1996), Moorby N supplies. In fact, the higher N output in milk
´ ´
52 O. Colin-Schoellen et al. / Livestock Production Science 67 (2000) 41 –53
21 supplies for low PDIE levels and therefore less N balanced diet, between 136 and 127 g N day for
waste in urea. the diet with a rumen-degradable PDIN deficit of 10
21 21
g kg DM, and between 108 and 97 g N day for 4.2. Effect of difference between rumen-degradable the diet with a rumen-degradable PDIN deficit of 20
21
energy and N g kg DM. So, the increased difference between
rumen-degradable N and energy led to a significant In the two trials, the difference between rumen- decrease in N excretion in dairy cows.
21
degradable N and energy of 10 g PDIN kg DM For the three diets with a difference between
21
(i.e. 11 g PDIN UFL ) did not significantly affect rumen-degradable N and energy of 0, 10 and 20 g
21
either DMI, milk yield, milk composition, nor aver- PDIN kg DM, the ratio of urea N to NPN was 44, age daily gain. On the other hand, the increase in this 35 and 25%, respectively. So, the proportion of urea
21
difference to 20 g PDIN kg DM led to a decrease in milk NPN decreased as the deficit of rumen-in DMI, milk proterumen-in content, and average daily garumen-in degradable PDIN increased. These results clearly of the cows, and to an increase in milk fat content. show the importance of N recycling in the rumen
´ ´
So, the ability of dairy cows to balance a rumen (Verite et al., 1987) to maintain performance for degradable PDIN deficit with regard to PDIE seemed diets with a rumen-degradable PDIN deficit. These to be limited. The acceptable deficit would be results supported N utilization in the diet, which was
21
doubtlessly between 10 and 20 g PDIN kg DM. better for the diets with a rumen-degradable PDIN
21
For values of up to 10 g PDIN kg DM of deficit deficit. The ratio of N output in milk proteins to N (i.e. 9–14% of PDIE supplies), the correction of this intake increased significantly for the diet with a
21 deficit did not cause an improvement in the rearing rumen-degradable PDIN deficit of 20 g kg DM
´ ´
performances of the cows. Verite and Peyraud (1988) with regard to the other two diets and for the diet
21 considered that, for lactating cows, this deficit should with a rumen-degradable PDIN deficit of 10 g kg
21 ´ ´
not exceed 8 g PDIN UFL . Verite and Delaby DM with regard to the balanced diet. The greater the (1998) confirmed that a rumen-degradable PDIN difference between rumen-degradable N and energy, deficit of 8% was perfectly acceptable and that the the greater the increase in N fixation in milk proteins performances of the cows were not changed by proportional to nitrogen intake.
correcting this deficit. But the increase in the differ-ence between rumen-degradable N and energy to 20
21
g PDIN kg DM was too great and could not be 5. Conclusion
compensated by the ability of ruminants to recycle
urea. Moreover, the diet with the rumen-degradable As previously noted by several authors, these trials
21
PDIN deficit of 20 g kg DM was the only diet showed that an increase of the level of metabolizable which covered under 100% of PDIN requirements. protein led to a higher DMI and milk yield. At the In further research we will examine the effect of a same time, the milk NPN and urea contents in-rumen-degradable PDIN deficit depending on the creased, leading probably to important N loss for the metabolizable protein level in the diet. diets with higher PDIE levels. The efficiency of N The increased difference between rumen-degrad- utilization for milk protein synthesis was improved able N and energy led to a significant decrease in with the decreased of the PDIE level of the diet. milk NPN and urea contents, which was greater for Moreover, these trials had the advantage of compar-the first deficit level: This decrease was between 40 ing three PDIE levels under conditions of total mixed
21
and 53 mg NPN l of milk when the deficit was of diets for which currently few recommendations
21 21
10 g PDIN kg DM and a further 28 mg NPN l exists in France. The PDIE level which may be
21
of milk when the deficit was of 20 g PDIN kg considered as the optimum metabolizable protein DM. Urinary N excretion could be quantified from level will depend not only on the economics
consid-´
the milk urea content and milk yield (Verite et al., erations of milk production but also on environmen-´ ´
1995; Faverdin and Verite, 1998). Using the equa- tal considerations.
tions proposed by these authors, urinary N excretion These trials confirm that a deficit of rumen
21
¨ ¨ Kirchgessner, M. (Ed.), 1997. Tierernahrung: Leitfaden fur
energy (PDIE) did not decrease the rearing
perform-¨ Studium, Beratung und Praxis. BLV-Verl.-Ges, Munchen, p.
ances of dairy cows. The acceptable PDIN deficit
582. 21
can be determined at 10 g kg DM. The formula- Madsen, J., 1985. The basis for the proposed Nordic evaluation tion of total mixed diets should take this fact into system for ruminants. The AAT-PBV system. Acta Agric. account. Moreover, a deficit of rumen degradable Scand. Suppl. 25, 9–20.
Moorby, J.M., Dewhurst, R.J., Thomas, C., Mardsen, S., 1996.
PDIN caused a considerable decrease in milk NPN
The influence of dietary energy source and dietary protein level
and urea content, and doubtlessly N loss in urine as
on milk protein concentration from dairy cows. Anim. Sci. 63,
well.
1–10.
NRC, 1985. Ruminant Nitrogen Usage. National Academy of Science, Washington, DC.
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