- Email: [email protected]
Milk urea concentration as affected by the roughage type offered to dairy cattle
Livestock Science 103 (2006) 30 – 39 www.elsevier.com/locate/livsci
Milk urea concentration as affected by the roughage type offered to dairy cattle S. De Campeneere *, D.L. De Brabander, J.M. Vanacker Ministry of the Flemish Community-Agricultural Research Centre, Department Animal Nutrition and Husbandry, Scheldeweg 68, 9090 Melle, Belgium Received 1 July 2005; received in revised form 8 December 2005; accepted 29 December 2005
Abstract Milk urea content (MUC) is used to manage protein nutrition and predict nitrogen excretion of dairy cows. However, MUC might depend on the roughage type offered and hence, for comparable MUC values, different N-excretions might be found. To evaluate this, three diets were compared in a feeding trial with 18 lactating Holstein cows in a Latin square design with as roughages 100% maize silage (treatment 100 MS), 50%/50% maize silage/prewilted grass silage (treatment 50 MS) and 100% prewilted grass silage (treatment 100 PGS). For all treatments, cows were fed to supply 105% of their net energy and digestible protein requirements and to have a daily rumen degraded protein balance (RDPB) intake of 100g. This was only possible by feeding soybean meal as a protein corrector to 100 MS and 50 MS and by feeding citruspulp as an energy corrector in 100 PGS. The same balanced concentrate was fed to all groups. In a separate trial, N-balance was determined for both 100% rations. In the feeding trial, the MUC of 100MS (230 mg/l) and 50 MS treatment (214 mg/l) were significantly ( P b 0.001) different from that of 100PGS (171 mg/l). Cows on treatments 50 MS and 100 PGS ingested the same amount of RDPB (71 and 73 g/ day), but when fed 100MS cows ingested 16 g/day. After correction for differences in energy and protein supply, MUC of the 100MS was 71 mg/l higher than that of 100PGS. N-balances indicated that total N-excretion (faecal, urinary and milk) was almost identical for both treatments: 392 for 100MS versus 389 g/day for 100PGS, as was environmental N-excretion (faecal and urinary): 259 for 100 MS versus 272g/day for 100 PGS. However, the MUC content for 100MS was significantly higher: 248mg/l versus 180mg/l for 100PGS. From a correction for differences in energy and protein supply, this difference increased up to 84 mg/l between 100MS and 100PGS. These results suggest that MUC is roughage dependent and that a system to predict N-excretion should account for these differences. Therefore the exact mechanism behind the determined roughage influence should be investigated further. D 2006 Elsevier B.V. All rights reserved. Keywords: Milk urea content; N-excretion; N-balance
Abbreviations: DPI, true protein digested in the small intestine; FPCM, fat protein corrected milk; MUC, milk urea concentration; RDPB, rumen degraded protein balance; NEL, feed unit net energy lactation. * Corresponding author. Tel.: +32 9 2722612; fax: +32 92722601. E-mail address: [email protected] (S. De Campeneere). 1871-1413/$ - see front matter D 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.livsci.2005.12.007
S. De Campeneere et al. / Livestock Science 103 (2006) 30–39
1. Introduction Determination of the milk urea content (MUC) is simple and cheap. As such, MUC has been evaluated to predict various factors. It is used to manage protein nutrition and monitor protein efficiency (Hof et al., 1997; Godden et al., 2001b; Nousiainen et al., 2004). It appeared to have only limited utility as a monitoring tool for reproductive performance or as a predictive parameter of conception (Godden et al., 2001a; Guo et al., 2004). Furthermore, several models have been developed to predict nitrogen (N) excretion of dairy cows from MUC. Such a model could be used to give farmers an incentive to produce milk with a lower N-excretion to the environment. For example from an observed yearly average MUC above or below a fixed value, farmers could be punished or rewarded financially. It remains unclear which parameters should be used for an adequate prediction of the total N-excretion. Jonker et al. (1998) published a model to predict N-excretion from MUC, milk N and dietary crude protein (CP) percentage. Kohn et al. (2002) adapted this model slightly, partly by using body weight (BW) as an additional parameter to estimate urinary excretion. Nousiainen (2004) also derived a model to predict urinary N-excretion from MUC. The accuracy of the above models is affected by nutritional factors, such as feed protein intake and the ratio of protein to energy in the diet, which have been reported frequently (Oltner and Wiktorsson, 1983; Oltner et al., 1985; Carroll et al., 1988; Roseler et al., 1993; Baker et al., 1995; Hof et al., 1997; Schepers and Meijer, 1998; Westwood et al., 1998; Trevaskis and Fulkerson, 1999; Steinwidder and Gruber, 2000; Van Duinkerken et al., 2005). Apart from the latter, none of the above researchers investigated a specific effect of the roughage type on the MUC at comparable energy and protein intakes. Van Duinkerken et al. (2005) compared the same forage combinations as we did (grass silage grass/maize silages and maize silage), but in a factorial design with 3RDPB levels (0, 500 and 1000 g/day). They found forage type to be an explanatory factor (together with RDPB-level) of the NH3 emission. However, they assumed that the forage type itself was not the causing agent, but rather the chemical or nutrient composition of it (Van Duinkerken et al., 2005).
31
At our institute, a model (De Brabander et al., 1999; more details see discussion) was derived to predict the MUC content of a maize silage/prewilted grass silage-based diet. This model was based on trials involving different roughage diets. From the statistical analysis of the total data set, an important influence of the roughage type on the MUC was found. However, the absence of a comparison of different roughages within the same trial includes that the roughage effect, deduced from the pooled data set, may have been confounded with other effects (e.g. trial or year effects). In literature, very little information exists on the influence of diet composition, at comparable protein and energy contents, on MUC. As such, this study was designed to examine that specific roughage type influence.
2. Materials and methods 2.1. Feeding trial 2.1.1. Experimental design and diet composition The experiment was a 3 3 Latin square arrangement. Eight primiparous and 10 multiparous Holstein– Friesian cows, yielding between 22.5 and 38.7 kg milk/ day at the beginning of the experiment, were blocked into three groups of six, based upon parity, body weight (on average 611 kg at start), milk production, fat and protein content of the milk, calving date (on average 145 DIM at start) and gestation stage. The three rations were formulated to provide similar energy (NEL), and protein (CP, DPI and RDPB) levels. The roughages were offered ad libitum, consisted of 100% maize silage, 50% maize silage/ 50% prewilted grass silage and 100% prewilted grass silage in treatment 100 MS, 50 MS and 100 PGS, respectively, and were completed with balanced concentrate (same concentrate for all groups) and soybean meal (diets 100 MS and 50 MS) or citruspulp (diet 100 PGS) until 105% of the net energy for lactation (NEL; Van Es, 1978) and DPI (true protein digested in the small intestine; Tamminga et al., 1994) requirements. If necessary, urea was added to achieve a RDPB (rumen degraded protein balance; Tamminga et al., 1994) intake of 100g daily. Roughages and concentrates were each given in two equal meals: concentrates were fed before milking in two daily
32
S. De Campeneere et al. / Livestock Science 103 (2006) 30–39
portions at 5h30 and 17h30; roughages were fed at 9h00 and 15h00. For the 50 MS diet, maize silage and grass silage was mixed (with Calan) before feeding. The 100 MS diet was completed with 0.3kg of mixed minerals, oligo-elements and vitamins. The trial consisted of three periods of 3 weeks each with the first week for adaptation to the diet, the second and third week for observation. Cows were weighed on two consecutive days at the beginning and end of each experimental period. Cows were housed in a tie stall on rubber beddings with separate mangers. They were milked twice daily between 5h30 and 7h00 and between 16h30 and 18h00. 2.1.2. Roughages Whole crop maize was harvested at the dough stage of maturity. Grass silage originated from perennial ryegrass harvested in May and was prewilted over a 2day period. The theoretical chopping length was 6 and 24mm for maize and grass silage, respectively. To formulate the diets, NEL, DPI and RDPB values of the roughages were estimated from their chemical composition and in vitro digestibility at ensiling. 2.1.3. Sampling and analysis The amount of feed administered was weighed individually each day. Orts from each cow were removed from the manger and weighed on the last day of each week. Only orts of more than 3kg were analysed for DM and CP to determine the origin (MS or PGS). Cows were weighed on two consecutive days during the last week of each adaptation and observation period. Milk yield was measured at each milking and the last four milkings of each observation week were sampled and analysed separately for fat and protein by a near infrared analyser (Infralyzer500, Bran and Luebbe, Norderstedt, Germany). The urea concentration was determined enzymatically (CL-10, Eurochem, Italy) on 2 composed samples of 2 morning (sample 1) and 2 evening (sample 2) milkings of each experimental week. In the observation weeks (two last weeks of each trial period), maize and grass silages were sampled twice a week (Thursday and Monday). The samples of each trial period were pooled and analysed for nutrient composition: Weende-analysis, starch (in maize silage) and sugars (in grass silage) according to the ECmethods, neutral detergent fibre (NDF) (Van Soest et
al., 1991), and rumen fluid organic matter digestibility (Tilley and Terry, 1963) to estimate energy value (De Boever et al., 1999). Dry matter (DM) content and chemical composition of the silages were corrected for the losses of volatile substances during oven drying (Dulphy et al., 1975). During the same weeks, once a week (Monday), samples were taken from the concentrates, soybean meal and citruspulp and pooled at the end of the trial for the same analysis as for the forages. The enzymatic organic matter (OM) digestibility of the concentrates was obtained according to De Boever et al. (1994) and used to estimate net energy values (De Boever et al., 1999). Protein values were estimated from the determined chemical composition (De Boever et al., 2002, 2004). 2.1.4. N-balance trial The N-balance of the 100 MS and the 100 PGS diet was determined with 8 cows. One primiparous and seven multiparous Holstein–Friesian cows, yielding between 17.5 and 30.8kg milk/day at the beginning of the experiment were blocked into two groups of 4, based upon parity (on average 3.3), body weight (on average 660 kg at start), milk production, fat and protein content of the milk, calving date (on average 212 DIM at start) and gestation stage. After an adaptation period of 11 days, faeces and urine were collected separately by using indwelling urinary catheters for 7 days. Individual faeces and urine productions were weighed, homogenised and quantitatively sampled daily. On the pooled (total collection period) samples of faeces and urine, N was determined. The milk was sampled during the last four milkings of the experimental week and analysed for fat and protein by a near infrared analyser (Infralyzer500, Bran and Luebbe, Norderstedt, Germany). The urea concentration was determined enzymatically (CL-10, Eurochem, Italy) on 2 composed samples of 2 morning (sample 1) and 2 evening (sample 2) milkings of each balance week. The roughages and the concentrates fed in the balance trials were sampled, respectively, every second day and daily, pooled and analysed. Orts from each cow were weighed on the last day of each week and analysed for DM and CP content to correct their intake. 2.1.5. Statistical analysis The data of the production trial were analyzed using the SPSS statistical program (SPSS, 2003). The
S. De Campeneere et al. / Livestock Science 103 (2006) 30–39
statistical analysis of results was carried out with the mean data of the two weeks of each experimental period for each animal. Analysis of variance was used to study the effect of treatment (type of roughage). Means were compared with Scheffe´s significant difference test ( P V 0.05). The data of the balance trial were analysed using one-way ANOVA.
3. Results 3.1. Feeding trial 3.1.1. Feed and diet composition The NEL, DPI and RDPB content of the maize silage and the prewilted grass silage amounted to, respectively, 6.61 and 6.09MJ/kg DM, 54 and 65 g/kg DM and 42 and 11 g/kg DM (Table 1). In order to achieve similar protein and energy contents in all three diets, 100 MS and 50 MS diets were supplemented with soybean meal, while the 100 PGS diet was supplemented with citruspulp. The soybean meal had a DPI (g/kg DM), RDPB (g/kg DM) and NEL (MJ/kg DM) value of 283, 133 and 7.96, while for the citruspulp these values were 82, 74 and 7.79, respectively. The balanced concentrate, used in all treatments contained 118 g DPI/kg DM, 5 g RDPB/kg DM and 7.59MJ NEL/kg DM. Dietary composition is shown in Table 2. CP content of the three diets were comparable. Energy concentra-
33
Table 2 Dietary composition of the three diets (feeding trial)
CP (g/kgDM) EE (g/kgDM) CF (g/kgDM) Ash (g/kgDM) Starch (g/kgDM) WSC/sugars (g/kgDM) NDF (g/kgDM) NEL (MJ/kgDM) DPI (g/kgDM) RDPB (g/kgDM)
100MS
50 MS
100PGS
137 31 183 56 260 7 353 6.7 82.4 0.7
135 33 209 88 149 20 398 6.6 74.5 5.4
134 31 209 108 34 98 380 6.7 74.2 3.9
CP= crude protein, EE = ether extract, CF = crude fibre, WSC = water-soluble carbohydrates, NDF = neutral detergent fraction, NEL= feed unit net energy lactation, DPI = true protein digested in the small intestine, RDPB = rumen degraded protein balance.
tion (NEL) amounted to 6.71, 6.56 and 6.66 MJ/kg DM, while DPI amounted to 82.4, 76.3 and 74.2g/kg DM for diet 100 MS, 50 MS and 100 PGS. RDPB (g/kg DM) amounted to 0.7 for diet 100 MS and to 3.7 and 3.9 for diet 50 MS and 100 PGS. The main difference between the diets was the ash content, which was caused by the significantly higher ash content in the 100 PGS. 3.1.2. Milk performance and intake Data on feed intake and milk performance are summarized in Table 3. The MUC for the 100 MS diet (230 mg/l) and the 50 MS (214 mg/l) differed signif-
Table 1 Chemical composition and energy and protein values of the roughagesa
DM (g/kg) CP (g/kgDM) EE (g/kgDM) CF (g/kgDM) NFE (g/kgDM) Starch (g/kgDM) WSC/sugars (g/kgDM) Ash (g/kgDM) NDF(g/kgDM) NEL (MJ/kgDM) DPI (g/kgDM) RDPB (g/kgDM)
Maize silage
Grass silage
Soybean meal
Citruspulp
Concentrate
325 69 30 205 650 305 n.d. 45 384 6.61 54 42
334 132 33 257 443 n.d. 5 135 468 6.09 65 11
874 461 31 82 354 n.d. n.d. 72 194 7.96 283 133
898 67 24 137 717 n.d. 281 55 216 7.79 82 74
884 179 44 112 577 150 98 87 295 7.59 118 5
DM = dry matter, CP= crude protein, EE = ether extract, CF = crude fibre, NFE = nitrogen free extract, WSC = water-soluble carbohydrates, NDF = neutral detergent fibre, NEL= net energy lactation, DPI = true protein digested in the small intestine, RDPB = rumen degraded protein balance, n.d. = not determined. a Means of the results of 3 periods.
34
S. De Campeneere et al. / Livestock Science 103 (2006) 30–39
Table 3 Effect of roughage type on feed intake and milk performance
Feed intake (kg DM/day) Maize silage Grass silage Citruspulp Soybean meal Concentrates RDPB (g/day) DPI (g/day) NEL (MJ/day) DPI (% of requirements) NEL (% of requirements) Performances MUC (mg/l) Corr. for nutr. intake* Corr. for live weight gain** Milk yield (kg/day) Fat content (%) Protein content (%) FPCM (kg/day) Weight gain (kg/day)
100 MS
50MS
100PGS
P-value
MSD1
19.5b 15.8 n.d. n.d. 2.2 1.5 16a 1608a 130.8a 110.8a 104.1a
19.6b 8.3 7.9 n.d. 0.8 2.6 71b 1505b 129.0a 103.9b 104.1a
18.7a n.d. 11.6 5.1 n.d. 1.9 73b 1392c 124.6b 108.3a 107.7b
b0.001 n.d. n.d. n.d. n.d. n.d. b0.001 b0.001 b0.001 b0.01 b0.001
2.6 n.d. n.d. n.d. n.d. n.d. 68 253 19 8.9 4.6
b0.001
42
230b 217 216 26.7b 4.37a 3.22b 27.6b 0.22b
214b 193 187 26.5b 4.32a 3.21b 27.2b 0.07a,b
171a 146 128 24.3a 4.38a 3.12a 24.9a 0.12a
b0.001 0.708 0.006 b0.001 0.036
5.5 0.49 0.19 5.2 0.36
DM = dry matter, RDPB = rumen degraded protein balance, DPI = true protein digested in the small intestine, NEL= net energy lactation, MUC = milk urea concentration, FPCM = fat protein corrected milk, n.d. = not determined. a,b,c Means in the same row with an identical superscript letter are not significantly different ( P N 0.05). 1 Mean standard deviation. * MUC values were corrected for energy and protein supply above or below 100% NEL and 100% DPI and above or below 0g RDPB intake. ** MUC values were corrected for energy and protein supply above or below 100% NEL and 100% DPI and above or below 0g RDPB intake. Energy supply as a proportion of the requirements being estimated from the daily live weight gain.
icantly from the MUC of the 100 PGS diet (171 mg/l). These analysed MUC values were somewhat influenced by some differences found in the protein and energy intake. The daily RDPB intake of cows fed the 100 MS diet ( 16 g/day) was significantly lower than for cows fed both other diets (50 MS: 71 and 100 PGS: 73g/day). The DPI intake differed for the three groups and varied from 1.61 for the 100 MS treatment to 1.39kg/day for the 100 PGS treatment with the 50 MS treatment being intermediary with 1.51kg/day. When the DPI intake is expressed as % of the requirements, the 50 MS diet (103.9%) showed a significantly lower intake than the 100 MS and the 100 PGS diet (110.8% and 108.3%). No difference was found between diets 100 MS and 50 MS (104.1%) for NEL-intake as a portion of the requirements, but the 100 PGS diet had a significantly higher NEL-intake (107.7%). These differences in energy and protein supply had an influence on the analysed MUC-values. Therefore, these values were corrected for differences in nutrient
intake using the coefficients from the model of De Brabander et al. (1999; more details see discussion) which had been derived for maize silage/prewilted grass silage diets. In Table 3, a corrected MUC value (referring to a NEL and DPI supply of 100% of the requirements and to a RDPB of 0 g daily) of 217, 193 and 146mg/l was calculated for the 100 MS, 50 MS and 100 PGS diet, respectively. As such, a discrepancy in MUC of 71 mg/l between 100 MS and 100 PGS was found as an effect of the roughage type. Cows fed the 100 PGS diet lost some body weight, although they appeared to have the highest intake as expressed to their requirements. Both other groups had a small positive daily gain. Possibly, the NELvalue for that diet might have been overestimated. As such the correction as described above might be incorrect for that treatment. However, when that correction becomes smaller, the differences between the corrected MUC-values for 100 MS and 100 PGS increases. For example if the correction of the MUC value was done with %NEL for 100 PGS being 100%
S. De Campeneere et al. / Livestock Science 103 (2006) 30–39
(no weight gain), the corrected MUC value would be 128 mg/l which is lower than 146 mg/l calculated earlier. As such the roughage type effect would even become larger (88 mg/l, see Table 3: 216 vs. 128 mg/l). The treatments slightly influenced milk yield and protein content, but not milk fat content. Fat protein corrected milk (FPCM), fat yield and protein yield were all similar for 100 MS and 50 MS but significantly lower for 100 PGS. 3.1.3. N-balance trial The results of the balance trials are listed in Table 4. Daily N-intake amounted to 388 and 356 g/day for the 100 MS and 100 GS diet, respectively. Total Nexcretion (faeces, urine and milk) during the balance trial was almost identical for both diets: 392 and Table 4 N-balance for the 100MS and the 100PGS diets 100MS 100PGS P-value MSD MUC (mg/l) Corr. for nutr. intake Urine production (l/day) Milk (kg/day) LW (kg) DM-intake (kg/day) Predicted urinary N excretion from MUC according to Jonker et al., 1998 Kauffman and St-Pierre, 2001 Kohn et al., 2002 Nousiainen et al., 2004 N-flows (g/day) Intake Urine Faeces Excretion to environment Milk Total excretion Apparent retention N-flows (% of intake) Faeces Urine Excretion to environment Milk Retained Energy balance Intake (MJ/day) Milk Maintenance Retained
248 252 14.4 24.7 588 17.1
180 168 35.0 20.4 658 16.7
143 201 174 190
104 146 142 145
388 129 130 259 133 392 5
356 117 155 272 116 389 32
0.095 54 n.d. n.d. b0.001 11.2 0.199 4.2 0.089 55 0.836 2.0
n.d. n.d. n.d. n.d. 0.429 0.150 0.158 0.492 0.247 0.902 0.198
n.d. n.d. n.d. n.d. 47 10 22 23 18 35 27
33.5 33.6 67.2 34.4 1.6
43.7 33.1 76.8 32.7 9.5
0.004 0.863 0.064 0.391 0.178
6.0 3.8 7.1 2.3 7.4
114.9 82.3 35.6 3.0
114.8 72.1 38.6 +4.1
0.995 12.9 0.325 12.5 0.117 2.5 0.319 8.7
LW = live weight; MUC = milk urea concentration; n.d. = not determined.
35
389g/day. As such, cows fed the 100 MS and 100 PGS diet had a negative N-balance of 5 and 32g/day, respectively ( P = 0.198). Environmental N-excretion (faeces and urine) was 259 for 100 MS and 272 mg/ l for 100 PGS. N-balances indicated that for the 100 MS diet, 33.5%, 33.6% and 34.4% and for the 100 PGS diet 43.7%, 33.1% and 32.7% of the N-intake, was excreted with the faeces, urine and milk, respectively. Although neither total N-excretion nor environmental N-excretion was different between the diets, MUC of the 100 MS diet was clearly ( P = 0.095) higher (248 mg/l) than that of the 100 PGS diet (180 mg/l). When the MUC values were corrected for differences in protein and energy intake as described above, even a larger difference was found: 252 and 168 mg/l for 100 MS and 100 PGS or a roughage effect of 84 mg/l. Milk production amounted to 24.7 and 20.4kg/day for cows fed the 100 MS and the 100 PGS diet, respectively. Urine production differed largely between the treatments: on average 14.4 kg for 100 MS compared to 35.0 kg for 100 PGS. When expressed as % of the N-intake, % Nexcretion in the milk and urine are not different between both treatments, but faecal N-excretion is relatively more important for the 100 PGS group resulting in a more negative N-balance. Consequently, the percentage of absorbed ( P = 0.004) and productive ( P = 0.064) N is higher in the 100 MS diet, while excretion to the environment is lower ( P = 0.064).
4. Discussion 4.1. Feeding trial In literature, no research was found that was designed to determine a specific influence of the roughage type on the MUC at comparable energy and protein intake levels. Van Duinkerken et al. (2003) published the milk urea contents of the diets described above by Van Duinkerken et al. (2005). At three RDPB levels (0, 500 and 1000g/day) they compared three roughage types (0%, 50% and 100% maize silage besides grass silage; Table 5). For 0 and 500 g RDPB they found a MUC of 139, 159 and 219 mg/l and 265, 302 and 379 mg/l for 0%, 50% and 100% maize silage,
36
S. De Campeneere et al. / Livestock Science 103 (2006) 30–39
Table 5 Corrected values for analysed MUC values (Van Duinkerken et al., 2003) according to the model of De Brabander et al. (1999) for differences in NEL, DPI and RDPB for diets with different % maize silage Treatment
MUC (mg/l) analysed in Van Duinkerken et al. (2003)
%MS
RDPB (g/day)
100 50 0 100 50 0
0 0 0 500 500 500
219 159 139 379 302 265
respectively. (The 1000-g RDPB level has little importance for practice and was therefore ignored here.) To correct for differences in energy and protein intake found in that trial, the model of De Brabander et al. (1999) was used. That model was derived to predict the MUC content of a maize silage/prewilted grass silage diet based on 585 cow observations from 36 treatments of different trials: MUC ðmg=lÞ ¼ 145 1:854% NEL þ 2:324% DPI þ 0:284g RDPB R2 ¼ 0:94; syx ¼ 14 mg=l with % NEL, % DPI and g RDPB being the relative provision of NEL and DPI expressed in % of the requirements and the amount of daily RDPB intake. This equation was derived from trials with diets based on grass silage/maize silage as roughages and completed with soybean meal en balanced concentrates (normal composition, with feed ingredients as used in practice, sometimes with somewhat more dried beet pulp to obtain a low RDPB). Based on the equation, when cows are fed according to the requirements (NEL and DPI: both 100% of requirements, RDPB: 0 g/day), a MUC of 192 mg/l is expected. The MUC values were corrected, referring to NEL and DPI supply of 100% of the requirements and to a RDPB of 0 g or 500g daily as mentioned in Table 5 (Van Duinkerken et al., 2003). The corrected values amounted to: 135, 148 and 236 mg/l for the 0g RDPB level and 244, 297 and 384mg/l for the 500g RDPB level for diets with 0%, 50% and 100% maize silage besides grass silage. This indicates an important influence of the roughage type on MUC of 101 mg/
Proportional energy and protein supply (%)
Supply (g/day)
NEL
DPI
RDPB
103 98 93 107 99 91
100 104 104 103 101 104
42 8 66 505 503 484
MUC (mg/l) corrected
236 148 135 384 297 244
l for the 0 g RDPB level between 100% maize and 100% grass silage and 140 mg/l for the 500 g RDPB level between the same roughage types. These influences are of comparable magnitude as what we have found in our production (71 mg/l) and balance trials (84 mg/l). Steinwidder et al. (1988) compared a maize silage based ration with a grass silage based ration and found a MUC of 116 mg/l versus 296mg/l, respectively. However, they did not provide the same energy and protein levels to both groups: RDPB ( 85 vs. 53 g) and CP intake (1.8 vs. 2.6kg) differed importantly. Hence, the influence of the roughage type and that of the protein and energy supply were confounded. 4.1.1. Balance trial In our balance trials, the cows fed the 100 MS diets had a daily urine production of about 14 kg compared to 35 kg for the 100 PGS diet. The comparable urinary N-excretions (129 and 117 g/day) seem in contradiction with the different MUC values (248 and 180 mg/ l for 100 MS and 100 PGS), although absolute difference in daily milk urea excretion only amounted to 2.4 g (6.1 and 3.7g/day for 100 MS and 100 PGS). Van Duinkerken et al. (2005) also found different urine productions between 100% maize silage and 100% grass silage: 21.9 and 35.1 kg/day, respectively. At least for our study, the difference in urine production was not caused by differences in DM content of the diet, since that was similar for both diets. It was quite surprising to find a negative N-balance for the 100 PGS group. The reason for this is not clear. The energy balance (Table 4) indicates that enough energy was provided by the diet for the 100 PGS
S. De Campeneere et al. / Livestock Science 103 (2006) 30–39
group while the 100 MS group had a slight shortage. The digestibility coefficients show that N digestibility was 17% lower for the 100 PGS group, while the digestibility coefficient of CF was 17% lower for the 100 MS group. DM, organic matter, nitrogen free extracts and ether extract digestibility coefficients were not different between both groups. Faverdin and Ve´rite´ (1998) compared a database of different feeding trials with dairy cows fed maize silage based diets with a database of some feeding trials with grass based diets and concluded that a distinct difference exists between both diet types. They found a higher clearance rate of urea in grass diets. Faverdin and Ve´rite´ (1998) assigned the higher clearance rate to a higher level of urinary Nexcretion or to a higher amount of minerals to be excreted. The results of the present study (comparable urinary N-excretion in combination with the large difference in urine production) do not support the first hypothesis of a higher urinary N-excretion and most probably the higher urine flow on grass based diets is the main cause of the higher clearance rate. According to Fisher et al. (1984), a higher urine production might be due to a higher potassium level in the grass silage. Seldin (2004) concluded in a review on the renal clearance concept, that urine flow influences urea clearance. According to the latter, changes in urine flow affect blood urea levels. More specific, at low filtration rates, blood urea nitrogen is very sensitive to protein loads, while with increasing filtration rate that sensitivity is strongly reduced (Seldin, 2004). Probably, the higher urine production of cows fed 100 PGS (see results in Table 3), will have induced a higher urine flow rate and a higher urea clearance rate. As such, more urea per unit of time was directed away from the blood pool and hence from the milk, inducing a lower MUC for cows fed the 100 PGS diet. In that case, a higher daily urinary urea excretion is expected in the 100 PGS treatment. Unfortunately, urinary urea concentration was not determined in the present study. To indicate that urinary urea N level may vary, we found publications of Archibeque et al. (2001, 2002) presenting values for % urinary N present as urea of 31 and 55 (at comparable N intake levels: 63 g/day) and of 66 and 72 (at comparable N intake levels: 90 and 112 g/day, respectively) in steers.
37
According to the above-mentioned model of Jonker et al. (1998), urinary N-excretion is 12.54 MUN (mg/dl) (milk urea nitrogen). For both diets of our balance trial that model estimates the urinary N (from MUC) excretion to be 143 and 104 g/ day. Other model equations predict the faecal Nexcretion (from MUC, N intake and milk N) to be 111 and 136 g/day for the 100 MS and 100 PGS diet, respectively. Kohn et al. (2002) corrected the model of Jonker et al. (1998) and added the factor body weight as a second parameter to estimate urinary N-excretion: 0.026 MUN (mg/dl) body weight (kg). For the balance trial diets, a urinary N-excretion of 174 and 142g/day was estimated, being higher than with the model of Jonker et al. (1998). Also the model presented by Kauffman and St-Pierre (2001) (17.6 MUN) shows comparable results (Table 4). Although all the predicted excretions are somewhat above the observed values in this study, it is clear that the models of Jonker et al. (1998) and Kohn et al. (2002) predict large differences in N-excretion (on average 43 mg/l), which were not found in this study (only 12mg/l). In this study, the absolute ( P = 0.492) and relative ( P = 0.064) total N-excretion to the environment (faecal + urinary) was higher (not significant) for the 100 PGS diet, while the MUC of the 100 PGS was significantly lower than that of the 100 MS diet. According to a model of De Brabander et al. (1998), based on MUC and milk production, total Nexcretion of our treatments would be 281 and 230 g/ day for 100 MS and 100 PGS. These results again, suggest that the models estimating N-excretion are roughage dependent, which was confirmed by the authors in their publication (De Brabander et al., 1998). The above comparisons indicate that the models can only be applied for rations with comparable roughage composition as the trials of the original data set and that the influence of the roughage type on the MUC can have important implications when such models are used inappropriately.
5. Conclusions This study demonstrated that the roughage type can have an important influence on MUC. The fact that these difference exists between maize silage and grass silage, implies that also other feedstuffs may influence
38
S. De Campeneere et al. / Livestock Science 103 (2006) 30–39
MUC. This and the mechanism behind the differences in MUC should be studied in detail before N-excretion estimation from MUC can be applied in practice. Acknowledgements The authors would like to thank Andre´ Opstal and the laboratory personnel for their excellent technical assistance. Appreciation is also expressed to the animal keepers. References Archibeque, S.L., Burns, J.C., Huntington, G.B., 2001. Urea flux in beef steers: effects of forage species and nitrogen fertilization. J. Anim. Sci. 79, 1937 – 1943. Archibeque, S.L., Burns, J.C., Huntington, G.B., 2002. Nitrogen metabolism of beef steers fed endophyte-free tall fescue hay: effects of ruminally protected methionine supplementation. J. Anim. Sci. 80, 1344 – 1351. Baker, L.D., Ferguson, J.D., Chalupa, W., 1995. Responses in urea and true protein of milk to different feeding schemes for dairy cows. J. Dairy Sci. 78, 2424 – 2434. Carroll, D.J., Barton, B.A., Anderson, G.W., Smith, R.D., 1988. Influence of protein intake and feeding strategy on reproductive performance of dairy cows. J. Dairy Sci. 71, 3470 – 3481. De Boever, J.L., Cottyn, B.G., Vanacker, J.M., Boucque´, Ch.V., 1994. An improved enzymatic method by adding gammanase to determine digestibility and predict energy value of compound feeds and raw materials for cattle. Anim. Feed Sci. Technol. 47, 1 – 18. De Boever, J.L., Cottyn, B.G., De Brabander, D.L., Vanacker, J.M., Boucque´, Ch.V., 1999. Equations to predict digestibility and energy value of grass silages, maize silages, grass hays, compound feeds and raw materials for cattle. Nutr. Abstr. Rev. 69, 835 – 850. De Boever, J.L., Vanacker, J.M., De Brabander, D.L., 2002. Rumen degradation characteristics in maize silages and evaluation of laboratory measurements and NIRS as predictors. Anim. Feed Sci. Technol. 101, 73 – 86. De Boever, J.L., Vanacker, J.M., Fiems, L.O., De Brabander, D.L., 2004. Rumen degradation characteristics and protein value of grassland products and their prediction by laboratory measurements and NIRS. Anim. Feed Sci. Technol. 116, 53 – 66. De Brabander, D.L., Botterman, S.M., Vanacker, J.M., Boucque´, Ch.V., 1998. Milk urea content in relation to energy and protein feeding of dairy cattle as well as to N-excretion (in French). 5e`mes Rencontres autour des Recherches sur les Ruminants, Paris, 2–3 de´cembre 1998, 5, p. 228. De Brabander, D.L., Botterman, S.M., Vanacker, J., Boucque´, Ch.V., 1999. The milk urea concentration as indicator for nutrition and N-excretion. Final conclusions and interpretations (in Dutch). Announcement no. 1109. Department Animal
Nutrition and Husbandry, Centre Agricultural Research, Ghent, Belgium. 8 pp. Dulphy, J.P., Demarquilly, C., Henry, M., 1975. Perte de compose´s volatiles lors de la de´termination a` l’e´tuve de la teneur en matie`re se`che des ensilages. Ann. Zootech. 24, 743 – 756. Faverdin, P., Ve´rite´, R., 1998. Use of milk urea concentration as an indicator of protein nutrition and nitrogen losses in dairy cows. Renc. Rech. Rum. 5, 209 – 212. Fisher, L.J., Dinn, N., Trait, R.M., Shelford, J.A., 1984. Effect of level of dietary potassium on the absorption and excretion of calcium and magnesium by lactating cows. Can. J. Anim. Sci. 74, 503 – 509. Godden, S.M., Kelton, D.F., Lissemore, K.D., Walton, J.S., Leslie, K.E., Lumsden, J.H., 2001. Milk urea testing as a tool to monitor reproductive performance in Ontario dairy herds. J. Dairy Sci. 84, 1397 – 1406. Godden, S.M., Lissemore, K.D., Kelton, D.F., Leslie, K.E., Walton, J.S., Lumsden, J.H., 2001. Factors associated with milk urea concentrations in Ontario dairy cows. J. Dairy Sci. 84, 107 – 114. Guo, K., Russek-Cohen, E., Varner, M.A., Kohn, R.A., 2004. Effects of milk urea nitrogen and other factors on probability of conception of dairy cows. J. Dairy Sci. 87, 1878 – 1885. Hof, G., Vervoorn, M.D., Lenaers, P.J., Tamminga, S., 1997. Milk urea nitrogen as a tool to monitor the protein nutrition of dairy cows. J. Dairy Sci. 80, 3333 – 3340. Jonker, J.S., Kohn, R.A., Erdman, R.A., 1998. Using milk urea nitrogen to predict nitrogen excretion and utilization efficiency in lactating dairy cows. J. Dairy Sci. 81, 2681 – 2692. Kauffman, A.J., St-Pierre, N.R., 2001. The relationship of milk urea nitrogen to urine nitrogen excretion in Holstein and Jersey cows. J. Dairy Sci. 84, 2284 – 2294. Kohn, R.A., Kalscheur, K.F., Russek-Cohen, E., 2002. Evaluation models to estimate urinary nitrogen and expected milk urea nitrogen. J. Dairy Sci. 85, 227 – 233. Nousiainen, J., 2004. Development of tools for the nutritional management of dairy cows on silage based diets. PhD dissertation, Helsinki University, p. 69. Nousiainen, J., Shingdfield, K.J., Huhtanen, P., 2004. Evaluation of milk urea nitrogen as a diagnostic of protein feeding. J. Dairy Sci. 87, 386 – 398. Oltner, R., Wiktorsson, H., 1983. Urea concentrations in milk and blood as influenced by feeding varying amounts of protein and energy to dairy cows. Livest. Prod. Sci. 10, 457 – 467. Oltner, R., Emanuelson, M., Wiktorsson, H., 1985. Urea concentrations in milk in relation to milk yield, live weight, lactation number and amount and composition of feed given to dairy cows. Livest. Prod. Sci. 12, 47 – 57. Roseler, D.K., Ferguson, J.D., Sniffen, C.J., Herrema, J., 1993. Dietary protein degradability effects on plasma and milk urea nitrogen and milk non-protein nitrogen in Holstein cows. J. Dairy Sci. 76, 525 – 534. Schepers, A.J., Meijer, R.G., 1998. Evaluation of the utilization of dietary nitrogen by dairy cows based on urea concentration in milk. J. Dairy Sci. 81, 579 – 584. Seldin, D.W., 2004. The development of the clearance concept. J. Nephrol. 17, 166 – 171. SPSS, 2003. Release 12.0. SPSS Inc., Chicago, IL, 60611.
S. De Campeneere et al. / Livestock Science 103 (2006) 30–39 Steinwidder, A., Gruber, L., 2000. Fu¨tterungs- und tierbedingte Einflußfaktoren auf den Harnstoffgehalt der Milch von Ku¨hen. Die Bodenkultur. Aust. J. Agric. Res. 51, 49 – 57. Steinwidder, A., Schweiger, P., Gruber, L., Lettner, F., Schmid, W., 1988. Einfluß des Fu¨tterungszeitpunktes sowie der Protein- und Energieversorgung auf den Milchharnstoffgehalt. Agribiol. Res. 51, 341 – 355. Tamminga, S., van Straalen, W.M., Subnel, A.P.J., Meijer, R.G.M., Steg, A., Wever, C.J.G., Blok, M.C., 1994. The Dutch protein evaluation system: the DPI/RDPB-system. Livest. Prod. Sci. 40, 139 – 155. Tilley, J.M.A., Terry, R.A., 1963. A two-stage technique for the in vitro digestion of forage crops. J. Br. Grassl. Soc. 18, 104 – 111. Trevaskis, L.M., Fulkerson, W.J., 1999. The relationship between various animal and management factors and milk urea, and its association with reproductive performance of dairy cows grazing pasture. Livest. Prod. Sci. 57, 255 – 265. Van Duinkerken, G., Andre´, G., Smits, M.C.J., Monteny, G.J., Blanken, K., Wagemans, M.J.M., Sebek, L.B.J., 2003. Relation
39
between diet and ammonia emission from the dariy barn (in Dutch). Applied Research Report no. 25, Animal Sciences Group, Applied Research, Lelystad, the Netherlands (66 pp.) Van Duinkerken, G., Andre´, G., Smits, M.C.J., Monteny, G.J., Sebek, L.B.J., 2005. Effect of rumen–degradable protein balance and forage concentration and emission of ammonia from dairy cow houses. J. Dairy Sci. 88, 1099 – 1112. Van Es, A.J.H., 1978. Feed evaluation for ruminants: I. The system in use from May 1977 onwards in the Netherlands. Livest. Prod. Sci. 5, 331 – 345. Van Soest, P.J., Robertson, J.B., Lewis, B.A., 1991. Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. J. Dairy Sci. 74, 3583 – 3597. Westwood, C.T., Lean, I.J., Kellaway, R.C., 1998. Indications and implications for testing of milk urea in dairy cattle: a quantitative review: Part 1. Dietary protein sources and metabolism. N. Z. Vet. J. 46, 87 – 96.
Milk urea concentration as affected by the roughage type offered to dairy cattle S. De Campeneere *, D.L. De Brabander, J.M. Vanacker Ministry of the Flemish Community-Agricultural Research Centre, Department Animal Nutrition and Husbandry, Scheldeweg 68, 9090 Melle, Belgium Received 1 July 2005; received in revised form 8 December 2005; accepted 29 December 2005
Abstract Milk urea content (MUC) is used to manage protein nutrition and predict nitrogen excretion of dairy cows. However, MUC might depend on the roughage type offered and hence, for comparable MUC values, different N-excretions might be found. To evaluate this, three diets were compared in a feeding trial with 18 lactating Holstein cows in a Latin square design with as roughages 100% maize silage (treatment 100 MS), 50%/50% maize silage/prewilted grass silage (treatment 50 MS) and 100% prewilted grass silage (treatment 100 PGS). For all treatments, cows were fed to supply 105% of their net energy and digestible protein requirements and to have a daily rumen degraded protein balance (RDPB) intake of 100g. This was only possible by feeding soybean meal as a protein corrector to 100 MS and 50 MS and by feeding citruspulp as an energy corrector in 100 PGS. The same balanced concentrate was fed to all groups. In a separate trial, N-balance was determined for both 100% rations. In the feeding trial, the MUC of 100MS (230 mg/l) and 50 MS treatment (214 mg/l) were significantly ( P b 0.001) different from that of 100PGS (171 mg/l). Cows on treatments 50 MS and 100 PGS ingested the same amount of RDPB (71 and 73 g/ day), but when fed 100MS cows ingested 16 g/day. After correction for differences in energy and protein supply, MUC of the 100MS was 71 mg/l higher than that of 100PGS. N-balances indicated that total N-excretion (faecal, urinary and milk) was almost identical for both treatments: 392 for 100MS versus 389 g/day for 100PGS, as was environmental N-excretion (faecal and urinary): 259 for 100 MS versus 272g/day for 100 PGS. However, the MUC content for 100MS was significantly higher: 248mg/l versus 180mg/l for 100PGS. From a correction for differences in energy and protein supply, this difference increased up to 84 mg/l between 100MS and 100PGS. These results suggest that MUC is roughage dependent and that a system to predict N-excretion should account for these differences. Therefore the exact mechanism behind the determined roughage influence should be investigated further. D 2006 Elsevier B.V. All rights reserved. Keywords: Milk urea content; N-excretion; N-balance
Abbreviations: DPI, true protein digested in the small intestine; FPCM, fat protein corrected milk; MUC, milk urea concentration; RDPB, rumen degraded protein balance; NEL, feed unit net energy lactation. * Corresponding author. Tel.: +32 9 2722612; fax: +32 92722601. E-mail address: [email protected] (S. De Campeneere). 1871-1413/$ - see front matter D 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.livsci.2005.12.007
S. De Campeneere et al. / Livestock Science 103 (2006) 30–39
1. Introduction Determination of the milk urea content (MUC) is simple and cheap. As such, MUC has been evaluated to predict various factors. It is used to manage protein nutrition and monitor protein efficiency (Hof et al., 1997; Godden et al., 2001b; Nousiainen et al., 2004). It appeared to have only limited utility as a monitoring tool for reproductive performance or as a predictive parameter of conception (Godden et al., 2001a; Guo et al., 2004). Furthermore, several models have been developed to predict nitrogen (N) excretion of dairy cows from MUC. Such a model could be used to give farmers an incentive to produce milk with a lower N-excretion to the environment. For example from an observed yearly average MUC above or below a fixed value, farmers could be punished or rewarded financially. It remains unclear which parameters should be used for an adequate prediction of the total N-excretion. Jonker et al. (1998) published a model to predict N-excretion from MUC, milk N and dietary crude protein (CP) percentage. Kohn et al. (2002) adapted this model slightly, partly by using body weight (BW) as an additional parameter to estimate urinary excretion. Nousiainen (2004) also derived a model to predict urinary N-excretion from MUC. The accuracy of the above models is affected by nutritional factors, such as feed protein intake and the ratio of protein to energy in the diet, which have been reported frequently (Oltner and Wiktorsson, 1983; Oltner et al., 1985; Carroll et al., 1988; Roseler et al., 1993; Baker et al., 1995; Hof et al., 1997; Schepers and Meijer, 1998; Westwood et al., 1998; Trevaskis and Fulkerson, 1999; Steinwidder and Gruber, 2000; Van Duinkerken et al., 2005). Apart from the latter, none of the above researchers investigated a specific effect of the roughage type on the MUC at comparable energy and protein intakes. Van Duinkerken et al. (2005) compared the same forage combinations as we did (grass silage grass/maize silages and maize silage), but in a factorial design with 3RDPB levels (0, 500 and 1000 g/day). They found forage type to be an explanatory factor (together with RDPB-level) of the NH3 emission. However, they assumed that the forage type itself was not the causing agent, but rather the chemical or nutrient composition of it (Van Duinkerken et al., 2005).
31
At our institute, a model (De Brabander et al., 1999; more details see discussion) was derived to predict the MUC content of a maize silage/prewilted grass silage-based diet. This model was based on trials involving different roughage diets. From the statistical analysis of the total data set, an important influence of the roughage type on the MUC was found. However, the absence of a comparison of different roughages within the same trial includes that the roughage effect, deduced from the pooled data set, may have been confounded with other effects (e.g. trial or year effects). In literature, very little information exists on the influence of diet composition, at comparable protein and energy contents, on MUC. As such, this study was designed to examine that specific roughage type influence.
2. Materials and methods 2.1. Feeding trial 2.1.1. Experimental design and diet composition The experiment was a 3 3 Latin square arrangement. Eight primiparous and 10 multiparous Holstein– Friesian cows, yielding between 22.5 and 38.7 kg milk/ day at the beginning of the experiment, were blocked into three groups of six, based upon parity, body weight (on average 611 kg at start), milk production, fat and protein content of the milk, calving date (on average 145 DIM at start) and gestation stage. The three rations were formulated to provide similar energy (NEL), and protein (CP, DPI and RDPB) levels. The roughages were offered ad libitum, consisted of 100% maize silage, 50% maize silage/ 50% prewilted grass silage and 100% prewilted grass silage in treatment 100 MS, 50 MS and 100 PGS, respectively, and were completed with balanced concentrate (same concentrate for all groups) and soybean meal (diets 100 MS and 50 MS) or citruspulp (diet 100 PGS) until 105% of the net energy for lactation (NEL; Van Es, 1978) and DPI (true protein digested in the small intestine; Tamminga et al., 1994) requirements. If necessary, urea was added to achieve a RDPB (rumen degraded protein balance; Tamminga et al., 1994) intake of 100g daily. Roughages and concentrates were each given in two equal meals: concentrates were fed before milking in two daily
32
S. De Campeneere et al. / Livestock Science 103 (2006) 30–39
portions at 5h30 and 17h30; roughages were fed at 9h00 and 15h00. For the 50 MS diet, maize silage and grass silage was mixed (with Calan) before feeding. The 100 MS diet was completed with 0.3kg of mixed minerals, oligo-elements and vitamins. The trial consisted of three periods of 3 weeks each with the first week for adaptation to the diet, the second and third week for observation. Cows were weighed on two consecutive days at the beginning and end of each experimental period. Cows were housed in a tie stall on rubber beddings with separate mangers. They were milked twice daily between 5h30 and 7h00 and between 16h30 and 18h00. 2.1.2. Roughages Whole crop maize was harvested at the dough stage of maturity. Grass silage originated from perennial ryegrass harvested in May and was prewilted over a 2day period. The theoretical chopping length was 6 and 24mm for maize and grass silage, respectively. To formulate the diets, NEL, DPI and RDPB values of the roughages were estimated from their chemical composition and in vitro digestibility at ensiling. 2.1.3. Sampling and analysis The amount of feed administered was weighed individually each day. Orts from each cow were removed from the manger and weighed on the last day of each week. Only orts of more than 3kg were analysed for DM and CP to determine the origin (MS or PGS). Cows were weighed on two consecutive days during the last week of each adaptation and observation period. Milk yield was measured at each milking and the last four milkings of each observation week were sampled and analysed separately for fat and protein by a near infrared analyser (Infralyzer500, Bran and Luebbe, Norderstedt, Germany). The urea concentration was determined enzymatically (CL-10, Eurochem, Italy) on 2 composed samples of 2 morning (sample 1) and 2 evening (sample 2) milkings of each experimental week. In the observation weeks (two last weeks of each trial period), maize and grass silages were sampled twice a week (Thursday and Monday). The samples of each trial period were pooled and analysed for nutrient composition: Weende-analysis, starch (in maize silage) and sugars (in grass silage) according to the ECmethods, neutral detergent fibre (NDF) (Van Soest et
al., 1991), and rumen fluid organic matter digestibility (Tilley and Terry, 1963) to estimate energy value (De Boever et al., 1999). Dry matter (DM) content and chemical composition of the silages were corrected for the losses of volatile substances during oven drying (Dulphy et al., 1975). During the same weeks, once a week (Monday), samples were taken from the concentrates, soybean meal and citruspulp and pooled at the end of the trial for the same analysis as for the forages. The enzymatic organic matter (OM) digestibility of the concentrates was obtained according to De Boever et al. (1994) and used to estimate net energy values (De Boever et al., 1999). Protein values were estimated from the determined chemical composition (De Boever et al., 2002, 2004). 2.1.4. N-balance trial The N-balance of the 100 MS and the 100 PGS diet was determined with 8 cows. One primiparous and seven multiparous Holstein–Friesian cows, yielding between 17.5 and 30.8kg milk/day at the beginning of the experiment were blocked into two groups of 4, based upon parity (on average 3.3), body weight (on average 660 kg at start), milk production, fat and protein content of the milk, calving date (on average 212 DIM at start) and gestation stage. After an adaptation period of 11 days, faeces and urine were collected separately by using indwelling urinary catheters for 7 days. Individual faeces and urine productions were weighed, homogenised and quantitatively sampled daily. On the pooled (total collection period) samples of faeces and urine, N was determined. The milk was sampled during the last four milkings of the experimental week and analysed for fat and protein by a near infrared analyser (Infralyzer500, Bran and Luebbe, Norderstedt, Germany). The urea concentration was determined enzymatically (CL-10, Eurochem, Italy) on 2 composed samples of 2 morning (sample 1) and 2 evening (sample 2) milkings of each balance week. The roughages and the concentrates fed in the balance trials were sampled, respectively, every second day and daily, pooled and analysed. Orts from each cow were weighed on the last day of each week and analysed for DM and CP content to correct their intake. 2.1.5. Statistical analysis The data of the production trial were analyzed using the SPSS statistical program (SPSS, 2003). The
S. De Campeneere et al. / Livestock Science 103 (2006) 30–39
statistical analysis of results was carried out with the mean data of the two weeks of each experimental period for each animal. Analysis of variance was used to study the effect of treatment (type of roughage). Means were compared with Scheffe´s significant difference test ( P V 0.05). The data of the balance trial were analysed using one-way ANOVA.
3. Results 3.1. Feeding trial 3.1.1. Feed and diet composition The NEL, DPI and RDPB content of the maize silage and the prewilted grass silage amounted to, respectively, 6.61 and 6.09MJ/kg DM, 54 and 65 g/kg DM and 42 and 11 g/kg DM (Table 1). In order to achieve similar protein and energy contents in all three diets, 100 MS and 50 MS diets were supplemented with soybean meal, while the 100 PGS diet was supplemented with citruspulp. The soybean meal had a DPI (g/kg DM), RDPB (g/kg DM) and NEL (MJ/kg DM) value of 283, 133 and 7.96, while for the citruspulp these values were 82, 74 and 7.79, respectively. The balanced concentrate, used in all treatments contained 118 g DPI/kg DM, 5 g RDPB/kg DM and 7.59MJ NEL/kg DM. Dietary composition is shown in Table 2. CP content of the three diets were comparable. Energy concentra-
33
Table 2 Dietary composition of the three diets (feeding trial)
CP (g/kgDM) EE (g/kgDM) CF (g/kgDM) Ash (g/kgDM) Starch (g/kgDM) WSC/sugars (g/kgDM) NDF (g/kgDM) NEL (MJ/kgDM) DPI (g/kgDM) RDPB (g/kgDM)
100MS
50 MS
100PGS
137 31 183 56 260 7 353 6.7 82.4 0.7
135 33 209 88 149 20 398 6.6 74.5 5.4
134 31 209 108 34 98 380 6.7 74.2 3.9
CP= crude protein, EE = ether extract, CF = crude fibre, WSC = water-soluble carbohydrates, NDF = neutral detergent fraction, NEL= feed unit net energy lactation, DPI = true protein digested in the small intestine, RDPB = rumen degraded protein balance.
tion (NEL) amounted to 6.71, 6.56 and 6.66 MJ/kg DM, while DPI amounted to 82.4, 76.3 and 74.2g/kg DM for diet 100 MS, 50 MS and 100 PGS. RDPB (g/kg DM) amounted to 0.7 for diet 100 MS and to 3.7 and 3.9 for diet 50 MS and 100 PGS. The main difference between the diets was the ash content, which was caused by the significantly higher ash content in the 100 PGS. 3.1.2. Milk performance and intake Data on feed intake and milk performance are summarized in Table 3. The MUC for the 100 MS diet (230 mg/l) and the 50 MS (214 mg/l) differed signif-
Table 1 Chemical composition and energy and protein values of the roughagesa
DM (g/kg) CP (g/kgDM) EE (g/kgDM) CF (g/kgDM) NFE (g/kgDM) Starch (g/kgDM) WSC/sugars (g/kgDM) Ash (g/kgDM) NDF(g/kgDM) NEL (MJ/kgDM) DPI (g/kgDM) RDPB (g/kgDM)
Maize silage
Grass silage
Soybean meal
Citruspulp
Concentrate
325 69 30 205 650 305 n.d. 45 384 6.61 54 42
334 132 33 257 443 n.d. 5 135 468 6.09 65 11
874 461 31 82 354 n.d. n.d. 72 194 7.96 283 133
898 67 24 137 717 n.d. 281 55 216 7.79 82 74
884 179 44 112 577 150 98 87 295 7.59 118 5
DM = dry matter, CP= crude protein, EE = ether extract, CF = crude fibre, NFE = nitrogen free extract, WSC = water-soluble carbohydrates, NDF = neutral detergent fibre, NEL= net energy lactation, DPI = true protein digested in the small intestine, RDPB = rumen degraded protein balance, n.d. = not determined. a Means of the results of 3 periods.
34
S. De Campeneere et al. / Livestock Science 103 (2006) 30–39
Table 3 Effect of roughage type on feed intake and milk performance
Feed intake (kg DM/day) Maize silage Grass silage Citruspulp Soybean meal Concentrates RDPB (g/day) DPI (g/day) NEL (MJ/day) DPI (% of requirements) NEL (% of requirements) Performances MUC (mg/l) Corr. for nutr. intake* Corr. for live weight gain** Milk yield (kg/day) Fat content (%) Protein content (%) FPCM (kg/day) Weight gain (kg/day)
100 MS
50MS
100PGS
P-value
MSD1
19.5b 15.8 n.d. n.d. 2.2 1.5 16a 1608a 130.8a 110.8a 104.1a
19.6b 8.3 7.9 n.d. 0.8 2.6 71b 1505b 129.0a 103.9b 104.1a
18.7a n.d. 11.6 5.1 n.d. 1.9 73b 1392c 124.6b 108.3a 107.7b
b0.001 n.d. n.d. n.d. n.d. n.d. b0.001 b0.001 b0.001 b0.01 b0.001
2.6 n.d. n.d. n.d. n.d. n.d. 68 253 19 8.9 4.6
b0.001
42
230b 217 216 26.7b 4.37a 3.22b 27.6b 0.22b
214b 193 187 26.5b 4.32a 3.21b 27.2b 0.07a,b
171a 146 128 24.3a 4.38a 3.12a 24.9a 0.12a
b0.001 0.708 0.006 b0.001 0.036
5.5 0.49 0.19 5.2 0.36
DM = dry matter, RDPB = rumen degraded protein balance, DPI = true protein digested in the small intestine, NEL= net energy lactation, MUC = milk urea concentration, FPCM = fat protein corrected milk, n.d. = not determined. a,b,c Means in the same row with an identical superscript letter are not significantly different ( P N 0.05). 1 Mean standard deviation. * MUC values were corrected for energy and protein supply above or below 100% NEL and 100% DPI and above or below 0g RDPB intake. ** MUC values were corrected for energy and protein supply above or below 100% NEL and 100% DPI and above or below 0g RDPB intake. Energy supply as a proportion of the requirements being estimated from the daily live weight gain.
icantly from the MUC of the 100 PGS diet (171 mg/l). These analysed MUC values were somewhat influenced by some differences found in the protein and energy intake. The daily RDPB intake of cows fed the 100 MS diet ( 16 g/day) was significantly lower than for cows fed both other diets (50 MS: 71 and 100 PGS: 73g/day). The DPI intake differed for the three groups and varied from 1.61 for the 100 MS treatment to 1.39kg/day for the 100 PGS treatment with the 50 MS treatment being intermediary with 1.51kg/day. When the DPI intake is expressed as % of the requirements, the 50 MS diet (103.9%) showed a significantly lower intake than the 100 MS and the 100 PGS diet (110.8% and 108.3%). No difference was found between diets 100 MS and 50 MS (104.1%) for NEL-intake as a portion of the requirements, but the 100 PGS diet had a significantly higher NEL-intake (107.7%). These differences in energy and protein supply had an influence on the analysed MUC-values. Therefore, these values were corrected for differences in nutrient
intake using the coefficients from the model of De Brabander et al. (1999; more details see discussion) which had been derived for maize silage/prewilted grass silage diets. In Table 3, a corrected MUC value (referring to a NEL and DPI supply of 100% of the requirements and to a RDPB of 0 g daily) of 217, 193 and 146mg/l was calculated for the 100 MS, 50 MS and 100 PGS diet, respectively. As such, a discrepancy in MUC of 71 mg/l between 100 MS and 100 PGS was found as an effect of the roughage type. Cows fed the 100 PGS diet lost some body weight, although they appeared to have the highest intake as expressed to their requirements. Both other groups had a small positive daily gain. Possibly, the NELvalue for that diet might have been overestimated. As such the correction as described above might be incorrect for that treatment. However, when that correction becomes smaller, the differences between the corrected MUC-values for 100 MS and 100 PGS increases. For example if the correction of the MUC value was done with %NEL for 100 PGS being 100%
S. De Campeneere et al. / Livestock Science 103 (2006) 30–39
(no weight gain), the corrected MUC value would be 128 mg/l which is lower than 146 mg/l calculated earlier. As such the roughage type effect would even become larger (88 mg/l, see Table 3: 216 vs. 128 mg/l). The treatments slightly influenced milk yield and protein content, but not milk fat content. Fat protein corrected milk (FPCM), fat yield and protein yield were all similar for 100 MS and 50 MS but significantly lower for 100 PGS. 3.1.3. N-balance trial The results of the balance trials are listed in Table 4. Daily N-intake amounted to 388 and 356 g/day for the 100 MS and 100 GS diet, respectively. Total Nexcretion (faeces, urine and milk) during the balance trial was almost identical for both diets: 392 and Table 4 N-balance for the 100MS and the 100PGS diets 100MS 100PGS P-value MSD MUC (mg/l) Corr. for nutr. intake Urine production (l/day) Milk (kg/day) LW (kg) DM-intake (kg/day) Predicted urinary N excretion from MUC according to Jonker et al., 1998 Kauffman and St-Pierre, 2001 Kohn et al., 2002 Nousiainen et al., 2004 N-flows (g/day) Intake Urine Faeces Excretion to environment Milk Total excretion Apparent retention N-flows (% of intake) Faeces Urine Excretion to environment Milk Retained Energy balance Intake (MJ/day) Milk Maintenance Retained
248 252 14.4 24.7 588 17.1
180 168 35.0 20.4 658 16.7
143 201 174 190
104 146 142 145
388 129 130 259 133 392 5
356 117 155 272 116 389 32
0.095 54 n.d. n.d. b0.001 11.2 0.199 4.2 0.089 55 0.836 2.0
n.d. n.d. n.d. n.d. 0.429 0.150 0.158 0.492 0.247 0.902 0.198
n.d. n.d. n.d. n.d. 47 10 22 23 18 35 27
33.5 33.6 67.2 34.4 1.6
43.7 33.1 76.8 32.7 9.5
0.004 0.863 0.064 0.391 0.178
6.0 3.8 7.1 2.3 7.4
114.9 82.3 35.6 3.0
114.8 72.1 38.6 +4.1
0.995 12.9 0.325 12.5 0.117 2.5 0.319 8.7
LW = live weight; MUC = milk urea concentration; n.d. = not determined.
35
389g/day. As such, cows fed the 100 MS and 100 PGS diet had a negative N-balance of 5 and 32g/day, respectively ( P = 0.198). Environmental N-excretion (faeces and urine) was 259 for 100 MS and 272 mg/ l for 100 PGS. N-balances indicated that for the 100 MS diet, 33.5%, 33.6% and 34.4% and for the 100 PGS diet 43.7%, 33.1% and 32.7% of the N-intake, was excreted with the faeces, urine and milk, respectively. Although neither total N-excretion nor environmental N-excretion was different between the diets, MUC of the 100 MS diet was clearly ( P = 0.095) higher (248 mg/l) than that of the 100 PGS diet (180 mg/l). When the MUC values were corrected for differences in protein and energy intake as described above, even a larger difference was found: 252 and 168 mg/l for 100 MS and 100 PGS or a roughage effect of 84 mg/l. Milk production amounted to 24.7 and 20.4kg/day for cows fed the 100 MS and the 100 PGS diet, respectively. Urine production differed largely between the treatments: on average 14.4 kg for 100 MS compared to 35.0 kg for 100 PGS. When expressed as % of the N-intake, % Nexcretion in the milk and urine are not different between both treatments, but faecal N-excretion is relatively more important for the 100 PGS group resulting in a more negative N-balance. Consequently, the percentage of absorbed ( P = 0.004) and productive ( P = 0.064) N is higher in the 100 MS diet, while excretion to the environment is lower ( P = 0.064).
4. Discussion 4.1. Feeding trial In literature, no research was found that was designed to determine a specific influence of the roughage type on the MUC at comparable energy and protein intake levels. Van Duinkerken et al. (2003) published the milk urea contents of the diets described above by Van Duinkerken et al. (2005). At three RDPB levels (0, 500 and 1000g/day) they compared three roughage types (0%, 50% and 100% maize silage besides grass silage; Table 5). For 0 and 500 g RDPB they found a MUC of 139, 159 and 219 mg/l and 265, 302 and 379 mg/l for 0%, 50% and 100% maize silage,
36
S. De Campeneere et al. / Livestock Science 103 (2006) 30–39
Table 5 Corrected values for analysed MUC values (Van Duinkerken et al., 2003) according to the model of De Brabander et al. (1999) for differences in NEL, DPI and RDPB for diets with different % maize silage Treatment
MUC (mg/l) analysed in Van Duinkerken et al. (2003)
%MS
RDPB (g/day)
100 50 0 100 50 0
0 0 0 500 500 500
219 159 139 379 302 265
respectively. (The 1000-g RDPB level has little importance for practice and was therefore ignored here.) To correct for differences in energy and protein intake found in that trial, the model of De Brabander et al. (1999) was used. That model was derived to predict the MUC content of a maize silage/prewilted grass silage diet based on 585 cow observations from 36 treatments of different trials: MUC ðmg=lÞ ¼ 145 1:854% NEL þ 2:324% DPI þ 0:284g RDPB R2 ¼ 0:94; syx ¼ 14 mg=l with % NEL, % DPI and g RDPB being the relative provision of NEL and DPI expressed in % of the requirements and the amount of daily RDPB intake. This equation was derived from trials with diets based on grass silage/maize silage as roughages and completed with soybean meal en balanced concentrates (normal composition, with feed ingredients as used in practice, sometimes with somewhat more dried beet pulp to obtain a low RDPB). Based on the equation, when cows are fed according to the requirements (NEL and DPI: both 100% of requirements, RDPB: 0 g/day), a MUC of 192 mg/l is expected. The MUC values were corrected, referring to NEL and DPI supply of 100% of the requirements and to a RDPB of 0 g or 500g daily as mentioned in Table 5 (Van Duinkerken et al., 2003). The corrected values amounted to: 135, 148 and 236 mg/l for the 0g RDPB level and 244, 297 and 384mg/l for the 500g RDPB level for diets with 0%, 50% and 100% maize silage besides grass silage. This indicates an important influence of the roughage type on MUC of 101 mg/
Proportional energy and protein supply (%)
Supply (g/day)
NEL
DPI
RDPB
103 98 93 107 99 91
100 104 104 103 101 104
42 8 66 505 503 484
MUC (mg/l) corrected
236 148 135 384 297 244
l for the 0 g RDPB level between 100% maize and 100% grass silage and 140 mg/l for the 500 g RDPB level between the same roughage types. These influences are of comparable magnitude as what we have found in our production (71 mg/l) and balance trials (84 mg/l). Steinwidder et al. (1988) compared a maize silage based ration with a grass silage based ration and found a MUC of 116 mg/l versus 296mg/l, respectively. However, they did not provide the same energy and protein levels to both groups: RDPB ( 85 vs. 53 g) and CP intake (1.8 vs. 2.6kg) differed importantly. Hence, the influence of the roughage type and that of the protein and energy supply were confounded. 4.1.1. Balance trial In our balance trials, the cows fed the 100 MS diets had a daily urine production of about 14 kg compared to 35 kg for the 100 PGS diet. The comparable urinary N-excretions (129 and 117 g/day) seem in contradiction with the different MUC values (248 and 180 mg/ l for 100 MS and 100 PGS), although absolute difference in daily milk urea excretion only amounted to 2.4 g (6.1 and 3.7g/day for 100 MS and 100 PGS). Van Duinkerken et al. (2005) also found different urine productions between 100% maize silage and 100% grass silage: 21.9 and 35.1 kg/day, respectively. At least for our study, the difference in urine production was not caused by differences in DM content of the diet, since that was similar for both diets. It was quite surprising to find a negative N-balance for the 100 PGS group. The reason for this is not clear. The energy balance (Table 4) indicates that enough energy was provided by the diet for the 100 PGS
S. De Campeneere et al. / Livestock Science 103 (2006) 30–39
group while the 100 MS group had a slight shortage. The digestibility coefficients show that N digestibility was 17% lower for the 100 PGS group, while the digestibility coefficient of CF was 17% lower for the 100 MS group. DM, organic matter, nitrogen free extracts and ether extract digestibility coefficients were not different between both groups. Faverdin and Ve´rite´ (1998) compared a database of different feeding trials with dairy cows fed maize silage based diets with a database of some feeding trials with grass based diets and concluded that a distinct difference exists between both diet types. They found a higher clearance rate of urea in grass diets. Faverdin and Ve´rite´ (1998) assigned the higher clearance rate to a higher level of urinary Nexcretion or to a higher amount of minerals to be excreted. The results of the present study (comparable urinary N-excretion in combination with the large difference in urine production) do not support the first hypothesis of a higher urinary N-excretion and most probably the higher urine flow on grass based diets is the main cause of the higher clearance rate. According to Fisher et al. (1984), a higher urine production might be due to a higher potassium level in the grass silage. Seldin (2004) concluded in a review on the renal clearance concept, that urine flow influences urea clearance. According to the latter, changes in urine flow affect blood urea levels. More specific, at low filtration rates, blood urea nitrogen is very sensitive to protein loads, while with increasing filtration rate that sensitivity is strongly reduced (Seldin, 2004). Probably, the higher urine production of cows fed 100 PGS (see results in Table 3), will have induced a higher urine flow rate and a higher urea clearance rate. As such, more urea per unit of time was directed away from the blood pool and hence from the milk, inducing a lower MUC for cows fed the 100 PGS diet. In that case, a higher daily urinary urea excretion is expected in the 100 PGS treatment. Unfortunately, urinary urea concentration was not determined in the present study. To indicate that urinary urea N level may vary, we found publications of Archibeque et al. (2001, 2002) presenting values for % urinary N present as urea of 31 and 55 (at comparable N intake levels: 63 g/day) and of 66 and 72 (at comparable N intake levels: 90 and 112 g/day, respectively) in steers.
37
According to the above-mentioned model of Jonker et al. (1998), urinary N-excretion is 12.54 MUN (mg/dl) (milk urea nitrogen). For both diets of our balance trial that model estimates the urinary N (from MUC) excretion to be 143 and 104 g/ day. Other model equations predict the faecal Nexcretion (from MUC, N intake and milk N) to be 111 and 136 g/day for the 100 MS and 100 PGS diet, respectively. Kohn et al. (2002) corrected the model of Jonker et al. (1998) and added the factor body weight as a second parameter to estimate urinary N-excretion: 0.026 MUN (mg/dl) body weight (kg). For the balance trial diets, a urinary N-excretion of 174 and 142g/day was estimated, being higher than with the model of Jonker et al. (1998). Also the model presented by Kauffman and St-Pierre (2001) (17.6 MUN) shows comparable results (Table 4). Although all the predicted excretions are somewhat above the observed values in this study, it is clear that the models of Jonker et al. (1998) and Kohn et al. (2002) predict large differences in N-excretion (on average 43 mg/l), which were not found in this study (only 12mg/l). In this study, the absolute ( P = 0.492) and relative ( P = 0.064) total N-excretion to the environment (faecal + urinary) was higher (not significant) for the 100 PGS diet, while the MUC of the 100 PGS was significantly lower than that of the 100 MS diet. According to a model of De Brabander et al. (1998), based on MUC and milk production, total Nexcretion of our treatments would be 281 and 230 g/ day for 100 MS and 100 PGS. These results again, suggest that the models estimating N-excretion are roughage dependent, which was confirmed by the authors in their publication (De Brabander et al., 1998). The above comparisons indicate that the models can only be applied for rations with comparable roughage composition as the trials of the original data set and that the influence of the roughage type on the MUC can have important implications when such models are used inappropriately.
5. Conclusions This study demonstrated that the roughage type can have an important influence on MUC. The fact that these difference exists between maize silage and grass silage, implies that also other feedstuffs may influence
38
S. De Campeneere et al. / Livestock Science 103 (2006) 30–39
MUC. This and the mechanism behind the differences in MUC should be studied in detail before N-excretion estimation from MUC can be applied in practice. Acknowledgements The authors would like to thank Andre´ Opstal and the laboratory personnel for their excellent technical assistance. Appreciation is also expressed to the animal keepers. References Archibeque, S.L., Burns, J.C., Huntington, G.B., 2001. Urea flux in beef steers: effects of forage species and nitrogen fertilization. J. Anim. Sci. 79, 1937 – 1943. Archibeque, S.L., Burns, J.C., Huntington, G.B., 2002. Nitrogen metabolism of beef steers fed endophyte-free tall fescue hay: effects of ruminally protected methionine supplementation. J. Anim. Sci. 80, 1344 – 1351. Baker, L.D., Ferguson, J.D., Chalupa, W., 1995. Responses in urea and true protein of milk to different feeding schemes for dairy cows. J. Dairy Sci. 78, 2424 – 2434. Carroll, D.J., Barton, B.A., Anderson, G.W., Smith, R.D., 1988. Influence of protein intake and feeding strategy on reproductive performance of dairy cows. J. Dairy Sci. 71, 3470 – 3481. De Boever, J.L., Cottyn, B.G., Vanacker, J.M., Boucque´, Ch.V., 1994. An improved enzymatic method by adding gammanase to determine digestibility and predict energy value of compound feeds and raw materials for cattle. Anim. Feed Sci. Technol. 47, 1 – 18. De Boever, J.L., Cottyn, B.G., De Brabander, D.L., Vanacker, J.M., Boucque´, Ch.V., 1999. Equations to predict digestibility and energy value of grass silages, maize silages, grass hays, compound feeds and raw materials for cattle. Nutr. Abstr. Rev. 69, 835 – 850. De Boever, J.L., Vanacker, J.M., De Brabander, D.L., 2002. Rumen degradation characteristics in maize silages and evaluation of laboratory measurements and NIRS as predictors. Anim. Feed Sci. Technol. 101, 73 – 86. De Boever, J.L., Vanacker, J.M., Fiems, L.O., De Brabander, D.L., 2004. Rumen degradation characteristics and protein value of grassland products and their prediction by laboratory measurements and NIRS. Anim. Feed Sci. Technol. 116, 53 – 66. De Brabander, D.L., Botterman, S.M., Vanacker, J.M., Boucque´, Ch.V., 1998. Milk urea content in relation to energy and protein feeding of dairy cattle as well as to N-excretion (in French). 5e`mes Rencontres autour des Recherches sur les Ruminants, Paris, 2–3 de´cembre 1998, 5, p. 228. De Brabander, D.L., Botterman, S.M., Vanacker, J., Boucque´, Ch.V., 1999. The milk urea concentration as indicator for nutrition and N-excretion. Final conclusions and interpretations (in Dutch). Announcement no. 1109. Department Animal
Nutrition and Husbandry, Centre Agricultural Research, Ghent, Belgium. 8 pp. Dulphy, J.P., Demarquilly, C., Henry, M., 1975. Perte de compose´s volatiles lors de la de´termination a` l’e´tuve de la teneur en matie`re se`che des ensilages. Ann. Zootech. 24, 743 – 756. Faverdin, P., Ve´rite´, R., 1998. Use of milk urea concentration as an indicator of protein nutrition and nitrogen losses in dairy cows. Renc. Rech. Rum. 5, 209 – 212. Fisher, L.J., Dinn, N., Trait, R.M., Shelford, J.A., 1984. Effect of level of dietary potassium on the absorption and excretion of calcium and magnesium by lactating cows. Can. J. Anim. Sci. 74, 503 – 509. Godden, S.M., Kelton, D.F., Lissemore, K.D., Walton, J.S., Leslie, K.E., Lumsden, J.H., 2001. Milk urea testing as a tool to monitor reproductive performance in Ontario dairy herds. J. Dairy Sci. 84, 1397 – 1406. Godden, S.M., Lissemore, K.D., Kelton, D.F., Leslie, K.E., Walton, J.S., Lumsden, J.H., 2001. Factors associated with milk urea concentrations in Ontario dairy cows. J. Dairy Sci. 84, 107 – 114. Guo, K., Russek-Cohen, E., Varner, M.A., Kohn, R.A., 2004. Effects of milk urea nitrogen and other factors on probability of conception of dairy cows. J. Dairy Sci. 87, 1878 – 1885. Hof, G., Vervoorn, M.D., Lenaers, P.J., Tamminga, S., 1997. Milk urea nitrogen as a tool to monitor the protein nutrition of dairy cows. J. Dairy Sci. 80, 3333 – 3340. Jonker, J.S., Kohn, R.A., Erdman, R.A., 1998. Using milk urea nitrogen to predict nitrogen excretion and utilization efficiency in lactating dairy cows. J. Dairy Sci. 81, 2681 – 2692. Kauffman, A.J., St-Pierre, N.R., 2001. The relationship of milk urea nitrogen to urine nitrogen excretion in Holstein and Jersey cows. J. Dairy Sci. 84, 2284 – 2294. Kohn, R.A., Kalscheur, K.F., Russek-Cohen, E., 2002. Evaluation models to estimate urinary nitrogen and expected milk urea nitrogen. J. Dairy Sci. 85, 227 – 233. Nousiainen, J., 2004. Development of tools for the nutritional management of dairy cows on silage based diets. PhD dissertation, Helsinki University, p. 69. Nousiainen, J., Shingdfield, K.J., Huhtanen, P., 2004. Evaluation of milk urea nitrogen as a diagnostic of protein feeding. J. Dairy Sci. 87, 386 – 398. Oltner, R., Wiktorsson, H., 1983. Urea concentrations in milk and blood as influenced by feeding varying amounts of protein and energy to dairy cows. Livest. Prod. Sci. 10, 457 – 467. Oltner, R., Emanuelson, M., Wiktorsson, H., 1985. Urea concentrations in milk in relation to milk yield, live weight, lactation number and amount and composition of feed given to dairy cows. Livest. Prod. Sci. 12, 47 – 57. Roseler, D.K., Ferguson, J.D., Sniffen, C.J., Herrema, J., 1993. Dietary protein degradability effects on plasma and milk urea nitrogen and milk non-protein nitrogen in Holstein cows. J. Dairy Sci. 76, 525 – 534. Schepers, A.J., Meijer, R.G., 1998. Evaluation of the utilization of dietary nitrogen by dairy cows based on urea concentration in milk. J. Dairy Sci. 81, 579 – 584. Seldin, D.W., 2004. The development of the clearance concept. J. Nephrol. 17, 166 – 171. SPSS, 2003. Release 12.0. SPSS Inc., Chicago, IL, 60611.
S. De Campeneere et al. / Livestock Science 103 (2006) 30–39 Steinwidder, A., Gruber, L., 2000. Fu¨tterungs- und tierbedingte Einflußfaktoren auf den Harnstoffgehalt der Milch von Ku¨hen. Die Bodenkultur. Aust. J. Agric. Res. 51, 49 – 57. Steinwidder, A., Schweiger, P., Gruber, L., Lettner, F., Schmid, W., 1988. Einfluß des Fu¨tterungszeitpunktes sowie der Protein- und Energieversorgung auf den Milchharnstoffgehalt. Agribiol. Res. 51, 341 – 355. Tamminga, S., van Straalen, W.M., Subnel, A.P.J., Meijer, R.G.M., Steg, A., Wever, C.J.G., Blok, M.C., 1994. The Dutch protein evaluation system: the DPI/RDPB-system. Livest. Prod. Sci. 40, 139 – 155. Tilley, J.M.A., Terry, R.A., 1963. A two-stage technique for the in vitro digestion of forage crops. J. Br. Grassl. Soc. 18, 104 – 111. Trevaskis, L.M., Fulkerson, W.J., 1999. The relationship between various animal and management factors and milk urea, and its association with reproductive performance of dairy cows grazing pasture. Livest. Prod. Sci. 57, 255 – 265. Van Duinkerken, G., Andre´, G., Smits, M.C.J., Monteny, G.J., Blanken, K., Wagemans, M.J.M., Sebek, L.B.J., 2003. Relation
39
between diet and ammonia emission from the dariy barn (in Dutch). Applied Research Report no. 25, Animal Sciences Group, Applied Research, Lelystad, the Netherlands (66 pp.) Van Duinkerken, G., Andre´, G., Smits, M.C.J., Monteny, G.J., Sebek, L.B.J., 2005. Effect of rumen–degradable protein balance and forage concentration and emission of ammonia from dairy cow houses. J. Dairy Sci. 88, 1099 – 1112. Van Es, A.J.H., 1978. Feed evaluation for ruminants: I. The system in use from May 1977 onwards in the Netherlands. Livest. Prod. Sci. 5, 331 – 345. Van Soest, P.J., Robertson, J.B., Lewis, B.A., 1991. Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. J. Dairy Sci. 74, 3583 – 3597. Westwood, C.T., Lean, I.J., Kellaway, R.C., 1998. Indications and implications for testing of milk urea in dairy cattle: a quantitative review: Part 1. Dietary protein sources and metabolism. N. Z. Vet. J. 46, 87 – 96.