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Agricultural Research Service, USDA US Dairy Forage Research Center 1925 Linden Drive West, Madison 53706
E-mail:
glenb{at}dfrc.wisc.edu.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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0.08) between dietary CP and NDF for any trait; thus, effects of CP were not confounded by NDF or vice versa. Intake of DM and fat yield were lower on 15.1% CP than at higher CP. There were linear increases in milk urea and urinary N excretion and linear decreases in N efficiency with increasing CP. Increasing CP from 15.1 to 18.4% reduced milk N from 31 to 25% of dietary N, increased urinary N from 23 to 35% of dietary N, and reduced fecal N from 45 to 41% of dietary N. Decreasing NDF gave linear increases in BW gain, yield of milk, protein, true protein, lactose, and SNF, and milk/DM intake and milk N/N intake, and linear decreases in milk urea. However, fat yield was lower on 28% than 32% NDF. Reducing NDF from 36 to 28% increased purine derivative excretion by 19%, suggesting increased microbial protein. Increasing CP by adding soybean meal to diets fed cows averaging 34 kg/d of milk increased intake and fat yield but depressed N efficiency. Increasing dietary energy by reducing forage improved milk yield and efficiency and decreased excretion of environmentally labile urinary N.
Key Words: protein density • energy density • neutral detergent fiber • nonfiber carbohydrate
Abbreviation key: HMC = rolled high-moisture shelled corn, MUN = milk urea N, NFC = nonfiber carbohydrate, SBM = solvent-extracted soybean meal
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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The main objective of this experiment was to quantify the dietary concentrations of protein and energy under standard feeding conditions that would minimize N excretion without depressing the yield of milk and milk components. A feeding study was conducted using nine diets—three protein levels at each of three NDF (energy) levels—to produce an array of dietary protein and energy concentrations. Energy levels were altered by varying the dietary concentrations of alfalfa and corn silage; CP was varied by changing dietary content of soybean meal.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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). Dietary CP was varied by step-wise replacement of 4.4 percentage units of DM from HMC with an equal amount of SBM. Forage was approximately 60% from alfalfa silage and 40% from corn silage on all diets; NDF was varied by feeding total forage at 75, 63, and 50% of DM. The alfalfa silage fed in this trial was from two different silos. That fed during the first 8 wk was harvested at first cutting from May 25 to 28, 1999; that fed during the second 8 wk was harvested from second cutting from July 1 to 2, 1999. Alfalfa from both harvests was cut using a conventional mower conditioner, field wilted to about 40% DM, chopped to a theoretical length of 2.9 cm, and ensiled in large bunker silos without additives. Corn silage was harvested at about one-half milk line, chopped to a theoretical length of 1 cm, and ensiled in a large upright silo without additives. Rolling was used when both corn silage (Bal et al., 2000) and HMC were removed from the silo; HMC had a geometric mean particle size of about 2 mm (Broderick et al., 2001) when fed. Roasted soybeans, with an estimated RUP value of 57% (Faldet and Satter, 1991), were added at 2.5% of DM in all TMR. Diets were fed for four, 4-wk periods (total of 16 wk) in this incomplete Latin square. The first 2 wk of each period was allowed for adaptation to diet; individual means from each cow for production traits from the last 2 wk of each period were analyzed statistically. Cows were milked twice daily and individual milk yields were recorded at each milking. Milk samples were collected at two consecutive (p.m. and a.m.) milkings midway through wk 3 and 4 of each period and analyzed for fat, protein, lactose, SNF, and milk urea N (MUN) by infrared methods (AgSource, Verona, WI). Milk samples were deproteinized (Shahani and Sommer, 1951) and analyzed for MUN by an automated colorimetric assay (Broderick and Clayton, 1997), adapted to a flow-injection analyzer and by a urease assay (no. 64-100P; Sigma Chemical Co., St. Louis, MO), as well as for NPN using a combustion method (Mitsubishi TN-05 Nitrogen Analyzer; Mitsubishi Chemical Corp., Tokyo). Milk true protein was computed by subtracting NPN from total protein N (from infrared analysis) using the equation: [(total protein/6.38) - NPN] x 6.38. Concentrations and yields of fat, protein, true protein, lactose, and SNF, and MUN concentrations, were computed as the weighted means from p.m. and a.m. milk yields on each test day. Yields of 3.5% FCM were computed (Sklan et al., 1992). Deproteinized milk from four squares (36 cows) was diluted 50%, vol/vol, with acetonitrile then assayed for allantoin concentration using the HPLC procedure of Shingfield and Offer (1998a). Allantoin also was determined in samples from two squares (18 cows) by the method of Vogels and van der Grift (1970) adapted to a 96-well plate reader. Efficiency of conversion of feed DM was computed for each cow over the last 2 wk of each period by dividing mean milk yield by mean DMI; efficiency of utilization of feed N similarly was computed for each cow by dividing mean milk N output (total milk protein/6.38) by mean N intake. Body weights were measured on three consecutive days at the start and end of each period to compute BW change.
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-amylase (Van Soest et al., 1991) and Na2SO3 (Hintz et al., 1995). The TMR composites also were analyzed for NDF-N using the combustion N assay (Leco Instruments, Inc.) on residual NDF and for fat (Dairyland Laboratories, Arcadia, WI) to compute of nonfiber carbohydrate (NFC). Data on composition in Table 1
were from analysis of TMR composites. At the end of the trial, weekly composites of alfalfa silage were thawed, water extracts were prepared, deproteinized, and then analyzed for NPN (Muck, 1987) using the combustion N assay (Mitsubishi Nitrogen Analyzer). On d 28 of each period, two spot fecal and urine samples were collected from four of the squares (36 cows) at about 6 and 18 h after feeding. Fecal samples were dried in a forced draft oven (60°C; 72 h), then ground through a 1-mm screen (Wiley mill). Equal DM from each fecal subsample was mixed to obtain a single composite for each sampled cow during each period. Period fecal and TMR composites were analyzed as described earlier for DM, ash, OM, NDF, ADF, and total N, and for indigestible ADF (the ADF remaining after 12-d of in situ ruminal incubations; Huhtanen et al., 1994). Indigestible ADF was used as an internal marker to estimate apparent nutrient digestibility and fecal output (Cochran et al., 1986). Fresh urine samples were acidified by diluting one volume of urine with four volumes of 0.072 N H2SO4 and storing at -20°C until analyzed. At the end of the trial, urine samples were thawed at room temperature and filtered through Whatman no. 1 filter paper. Filtrates were analyzed for creatinine using a picric acid assay (Oser, 1965) adapted to a flow-injection analyzer, for total N (Mitsubishi Nitrogen Analyzer), for allantoin using the method of Vogels and van der Grift (1970) adapted to a 96-well plate reader, for uric acid with a commercial kit (no. 683-100P, Sigma) and for urea with the colorimetric method also used for MUN. Daily urine volume and excretion of urea N, total N, and purine derivatives (allantoin plus uric acid) were estimated from urinary creatinine concentration assuming a creatinine excretion rate of 29 mg/kg BW (Valadares et al., 1999).
Statistical Analysis
The lactation trial was conducted as an incomplete 9 x 9 Latin square, replicated 7 times. It was intended from the outset to run the trial for four periods only, rather than for a full nine periods, to avoid confounding effects due to decline in production that would have occurred later in the lactation curve. Seven incomplete 9 x 9 Latin squares were constructed by fixing the first column of treatments, ordered A through I, as the diets fed in period 1, then randomly assigning three of eight possible columns of treatments (ordered B, C, . . ., A; C, D, . . ., B; . . .; I, A, . . ., H) as the subsequent series of diets in periods 2, 3, and 4. In this arrangement, columns represented periods, and rows represented cows within squares. The seven groups of cows, blocked as described above, were randomly assigned to one of the seven incomplete 9 x 9 Latin squares; cows were randomly assigned to one of the nine diet sequences within each square. Production results were analyzed with the mixed procedure of SAS (Littell et al., 1996) using a model, including square, period, cow-within-square, dietary CP level (n = 3), dietary level NDF (n = 3), the interactions CP x NDF, CP x period, and NDF x period, plus residual error. All terms were considered fixed, except for cow-within-square and residual error, which were considered random. No significant interactions were found for CP x period (P = 0.09 to 0.99) and NDF x period (P = 0.07 to 0.98) for any trait; therefore, interpretation of results from this Latin square trial were not confounded. Because the CP x NDF interaction was not significant for any trait (P = 0.08 to 0.85), differences between least squares means at each level of CP across all NDF levels and at each level of NDF across all CP levels were reported if the F-test for CP or NDF was significant at = 0.05. Significance of linear and quadratic contrasts of dietary CP and NDF levels were determined for each trait in the model. Concentrations of MUN determined by both colorimetric or infrared methods were regressed on MUN assayed by urease enzyme using Proc GLM (SAS, 1989). Estimated urinary excretion of urea N, total N, and allantoin and dietary concentration and intake of CP, NFC, and NDF, were regressed on MUN (assayed by all three methods) and milk allantoin (assayed by HPLC) using the data from the four squares (36 cows) with Proc GLM (SAS, 1989), using a model that included square, cow-within-square, period, and linear and quadratic effects. In one case, the MUN at the maximum response was determined by taking the first derivative of the quadratic equation for which the squared term was significant (P 
0.05). The same model was used to regress yield of milk, protein, and true protein on intake of CP and NFC with data from all 63 cows and to regress estimated urinary allantoin excretion and dietary concentration and intake of CP, NFC, and NDF, and milk allantoin (HPLC assay of Shingfield and Offer, 1998a) on milk allantoin assayed according to Vogels and van der Grift (1970) with data from two squares (18 cows).
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Milk Production and Nutrient Efficiency
Surprisingly, the CP x NDF interaction was not significant for any trait (P = 0.08 to 0.85). Rinne et al. (1999) observed no interactions among yield of energy-corrected milk, protein and concentrate supplementation, and forage OM digestibility, when feeding lactating cows diets based on grass silages that ranged from 49 to 65% NDF (DM basis). Absence of a CP x NDF interaction made it possible to summarize results from the lactation study as least squares means for each trait at each of the three concentrations of dietary CP (averaged over all NDF) and NDF (averaged over all CP). The principal production effects observed with increasing dietary CP were linear increases in DMI, yield of milk, FCM, fat, and protein, and milk protein content (Table 2). Except for DMI, which was greatest at 18.4% CP, there was no further improvement in yield of milk or milk components beyond 16.7% CP. Most of the incremental increases in going from 15.1 to 16.7% dietary CP were modest: 1.1 kg/d of milk, 1.5 kg/d of FCM, and 0.03 kg/d of protein. Only the increase in fat yield was more substantial—0.08 kg/d at 16.7% CP and 0.05 kg/d at 18.4% CP vs. that at 15.1% CP. Greater fat yield at 16.7% CP gave rise to a significant quadratic effect of dietary CP; maximal fat yield was predicted at 17.1% dietary CP. It is interesting that true protein yield (estimated by correcting total protein assayed by infrared analysis for milk NPN content) was not significantly altered by dietary CP content. Several factors related to nutrient efficiency became less favorable when dietary CP was increased (Table 2). Similar feed efficiency at 15.1 and 16.7% CP suggested that the small response in milk yield at 16.7% CP was due at least partly to the small increase in DMI. The further increase in DMI at 18.4% CP was not accompanied by more milk and milk yield/DMI declined. When dietary CP increased, there was a highly significant linear decrease in N efficiency.
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). Moreover, milk concentrations of protein, true protein, lactose, and SNF also were increased linearly with greater dietary energy. Over this same range of NFC, there were linear and quadratic declines in milk fat content. Fat yield was lower at 28% NDF than at the intermediate energy density (32% NDF); thus, there also was a quadratic effect of dietary NDF on fat yield. Significant linear increases in both DM and N efficiency were observed with increasing dietary energy content. Feed intake was not altered by increasing dietary energy density.
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) and by estimating microbial protein at 130 g/kg of discounted TDN (NRC, 2001). These computations suggested that most of the increased metabolizable protein with increased dietary CP and NFC would have derived from RUP. Computed metabolizable protein supplies were 1890, 2170, and 2380 g/d on 15.1, 16.7, and 18.4% CP diets with 82% of the increase on the two higher CP diets estimated to be from SBM RUP and 18% from greater microbial protein synthesis due to greater DMI. Computed metabolizable protein supplies were 1990, 2180, and 2270 g/d on 36, 32, and 28% NDF. Extra metabolizable protein from greater RUP on the lower NDF diets was, respectively, 119 and 214 g/d and that deriving from greater microbial protein was, respectively, 67 and 63 g/d.
Digestibility and Excretion
There was no change in apparent digestibility of DM and OM with increasing dietary CP; however, NDF and ADF digestibility both increased linearly with dietary CP (Table 4). Digestion of NDF in poor-quality forages fed to beef cows was elevated with SBM supplementation (Mathis et al., 1999). Greater intake of RDP may stimulate fiber digestion by increasing the supply of branched-chain VFA. Supplementing low-protein diets with branched-chain VFA increased OM and fiber digestion in the rumen of cattle (Misra and Thakur, 2001). No ruminal sampling was conducted in the present study; however, we have observed elevated ruminal concentrations of branched-chain VFA with feeding increased dietary CP from alfalfa silage (Hristov and Broderick, 1996) and SBM (Broderick, 1986). The linear increase in apparent N digestibility with elevated dietary CP was the usual result of dilution of metabolic fecal N as well as the effect of greater intake of SBM, a highly digestible protein source.
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). These likely were related to the linear increase in DMI described earlier (Table 2) as well as to excretion of undigested dietary CP. Urinary purine derivative excretion, which derives mainly from catabolism of absorbed purines of ruminal microbial origin (Stangassinger et al., 1995), also was elevated at 16.7% CP vs. 15.1% CP, with purine derivative excretion at 18.4% being intermediate. Greater DMI at the two higher CP diets would have provided more fermentable substrate to the rumen, stimulating greater microbial growth. That an increase of 27 mmol/d (7%) in purine derivative excretion was detected as significant suggested that spot sampling procedures, along with urine output estimated from creatinine concentration, would prove a sensitive method for use in routine lactation studies. Shingfield and Offer (1998b) found spot urine sampling significantly less reliable than total urine collection for estimating excretion of total purine derivatives in lactating cows. The linear increase in urine volume and urinary excretion of urea N and total N with increased dietary CP were expected to parallel the increased absorption of ruminal degradation products and metabolizable protein that would accompany increased SBM intake. The greater quantities of N metabolites requiring excretion likely increased the volume of urinary water required to dilute these compounds (Valadares et al., 1999). Elevation of urinary N output was substantial: urea N and total N went up 82 and 69% when dietary CP increased from 15.1 to 18.4%. Urea N accounted for essentially all of this increase in total N excretion. Over the range of CP intakes in this trial, fecal N declined from about 46 to 41% of consumed N, while the proportion of consumed N appearing in the urine increased from about 27 to nearly 36%. Thus, the net effect of increasing CP intake by increasing dietary SBM was to cause a small (3%) increase milk N secretion but mainly to divert N excretion from the feces to urinary urea. This form of excretory N is the most labile. Following contact with microbial ureases in the environment (e.g., in feces; Muck, 1982), urea will be rapidly hydrolyzed to ammonia and lost by volatilization (James et al., 1999).
As expected, there were linear increases in apparent DM and OM digestibility, and linear declines in apparent NDF and ADF digestibility and fecal DM output, with decreasing dietary NDF content (Table 5). The estimated increase in DM digestibility (2.4 percentage units) over this range of dietary NDF was less than half of the increase (5.3 percentage units; Table 1) in discounted TDN (TDNp) computed for these diets based on NRC (2001) assumptions. Increased dietary NFC is often observed to depress fiber digestion, partly by depressing ruminal pH (Weimer, 1992; Oliveira et al., 1993). However, ruminal pH was not measured in this trial. Apparent N digestibility was not altered by source of dietary carbohydrate, suggesting that total tract digestibility of CP was similar for alfalfa silage, which was reduced, and SBM, which was increased, when diets were formulated to contain reduced NDF. Fecal N output and urinary volume also were not affected by source of dietary carbohydrate. However, there were linear decreases in urinary excretion of urea N and total N with reduced NDF: the proportion of dietary N excreted in the urine fell by 4.0 percentage units over the range of NDF and NFC fed in this study. The decline was consistent with the improvement in N efficiency observed in this trial with increasing dietary energy (Table 3) and reported in earlier studies (Ekinci and Broderick, 1997; Vagnoni and Broderick, 1997; Valadares et al., 2000).
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). Using the regression equation of Vagnoni et al. (1997) to estimate abomasal purine flow from urinary purine derivative excretion and a mean ratio of 3.99 g of microbial CP/per millimole of total purines (Vagnoni and Broderick, 1997), microbial protein was estimated to be 1183, 1383, and 1503 g of CP/per day. Assuming 64% metabolizability (NRC, 2001), 128 and 205 g/d more metabolizable protein from microbial synthesis was computed when dietary fiber was reduced from 36% NDF to 32 and 28% NDF. These estimates were at disparity from the much lower average of 65 g/d more metabolizable protein from ruminal microbes computed earlier based on NRC (2001) assumptions, which suggested that microbial protein may have been more important than increased RUP supply in improving protein status in the present trial.
Milk Nitrogen Fractions
When dietary CP increased, there were stepwise increases in MUN and milk NPN concentrations and in the proportion of MUN in milk NPN; these were highly significant linear trends (Table 2). A significant quadratic effect of dietary CP on milk allantoin also was detected; a minimum was predicted at 17.0% CP. Significant linear increases in milk allantoin and linear reductions in MUN and proportion of MUN in milk NPN were observed with increasing dietary energy content (Table 3). In earlier work, allantoin accounted for about 90% of the total purine derivatives excreted in cow urine (Vagnoni et al., 1997; Valadares et al., 1999) that originate largely from microbial purines from the rumen. There is evidence that milk allantoin may reflect plasma allantoin and thus may be related to urinary allantoin excretion (Giesecke et al., 1994; Stangassinger et al., 1995). Analyzing data from 10 feeding studies with lactating cows, Timmermans et al. (2000) reported that milk allantoin concentrations were correlated (r2 = 0.28) to duodenal flows of microbial N. Although there were quadratic effects of dietary CP (Table 2) and linear effects of dietary NDF (Table 3) on milk allantoin, the changes observed over the ranges fed in the present trial here were small: reducing dietary NDF from 36 to 28% increased estimated urinary excretion of purine derivatives 19%, but milk allantoin increased by only 3%. Moreover, despite trends for linear relationships with dietary NDF (P = 0.07) and NFC (P = 0.07), milk allantoin concentration was unrelated to estimated urinary excretion of allantoin (P = 0.67) and total purine derivatives (P = 0.55). Milk allantoin was measured by an HPLC assay (Shingfield and Offer, 1998a) in this trial and ranged from 0.082 to 0.336 mM. Half of the milk samples also were analyzed for allantoin using a more common and convenient assay based on alkaline then acidic hydrolysis of allantoin to glyoxylate, followed by glyoxylate detection by reaction with phenylhydrazine and an oxidizing agent (Vogels and van der Grift, 1970). Average allantoin concentration using the phenylhydrazine method was 1.14 mM, vs. 0.142 mM (13%) by HPLC, and the results of the two assays were not correlated (P = 0.55). Earlier, we found mean milk allantoin of about 1.0 mM (Vagnoni and Broderick, 1997) and 0.6 mM (Valadares et al., 1999) using phenylhydrazine-based assays. Although the contribution from glyoxylate already present in milk can be removed (Vogels and van der Grift, 1970), other compounds may interfere with this assay, including uric acid that will be partially hydrolyzed to glyoxylate (Vogels and van der Grift, 1970). Uric acid can be synthesized within the mammary gland, and milk uric acid was found to be poorly related to urinary excretion of uric acid or total purine derivatives (Stangassinger et al., 1995). Earlier German work showing positive correlations of urinary purine derivatives to milk allantoin reported mean allantoin concentration of 0.20 mM determined by HPLC (Giesecke et al., 1994). However, Shingfield and Offer (1998c) detected no effect of dietary energy content on milk allantoin assayed using an HPLC technique.
It is well known that MUN levels are sensitive to dietary CP content (e.g., Broderick and Clayton, 1997). Jonker et al. (1998) developed a simple model using MUN to predict CP intake and N excretion. This group recently modified the model’s coefficients to reflect updated infrared calibrations that have lowered apparent MUN concentrations in commercial practice (Kohn et al., 2002). In the present trial, a disparity was apparent between MUN levels determined by infrared scanning and the colorimetric assay used in all of our trials. Therefore, MUN was reanalyzed using a third assay based on urease hydrolysis. Results obtained using urease did not agree precisely with those from the other two methods, but colorimetric data were more similar. Simple regression of infrared MUN data on urease MUN yielded an r2 of only 0.20 (Figure 1a), whereas the r2 from the comparable regression with colorimetric MUN data was 0.72 (Figure 1b). Infrared MUN results resolved into different relationships for each of the eight sets of milk samples analyzed over the course of the trial (Figure 1a). The MUN values within each set were more closely related to urease MUN: simple r2 ranged from 0.45 to 0.89 for the eight sets but there were large differences among slopes (range = 0.88 to 1.55) and intercepts (range = -3.25 to + 3.38) of these eight regressions. Weekly recalibration of the infrared MUN assay may have contributed to this source of variation. A smaller run effect also was noted with the colorimetric MUN determinations. Although these samples were held to the end of the trial, they were assayed in three separate groups, the results of which yielded regressions on urease MUN with r2 ranging from 0.66 to 0.83. There was also less variation among the slopes (range = 0.97 to 1.19) and intercepts (range = -0.29 to 1.75) of these regressions.
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). Most sources of feed CP have high true digestibilities (NRC, 2001); therefore, increased dietary CP intake that does not result in deposited or secreted N will be catabolized largely to urea. Blood urea readily equilibrates with milk (Gustafsson and Palmquist, 1993); hence, it was expected that MUN would be a reliable predictor of urinary N excretion. Although curvilinearity was not anticipated, the quadratic term for the relationship of MUN with dietary CP content was significant (P = 0.002); however, the improvement in fit was small (linear r2 = 0.787 vs. quadratic r2 = 0.798). Dietary energy density, as indicated negatively by NDF and positively by NFC, was less accurately predicted by MUN than dietary CP. Intakes of NDF and NFC were similarly explained by MUN concentration (r2 = 0.70). Milk urea may prove useful for rapidly identifying sudden alterations in dietary CP content or intake—for example, as may occur with a change in source of legume silage. This could aid in closer control of dietary CP content and help reduce overfeeding of CP and excessive excretion of the environmentally labile urinary N accompanying CP overfeeding (James et al., 1999; Rotz et al., 1999). Regressing dietary content and intake of CP, NFC, and NDF on MUN data determined using infrared and urease assays yielded equations with different slopes and intercepts, but correlation coefficients of very nearly the same magnitude as those for colorimetric MUN in Table 6 (r2 = 0.27 to 0.84 for infrared MUN and r2 = 0.27 to 0.86 for urease MUN). Of course, differing numeric relationships among nutrient intake data and MUN values generated by the different assays showed the importance of establishing a standardized MUN assay that could to be used to adjust diets to help minimize N losses to the environment from commercial dairies.
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); these relationships were stronger for NFC than CP. The slopes from regressions relating NFC intake to yield accounted for somewhat more of the predicted affect than did those relating CP intake to yield: at the overall mean NFC intake (9.1 kg/d), 74 to 82% of the response was accounted for by slope vs. only 17 to 25% of the response due to slope at the overall mean CP intake (3.7 kg/d). British workers also recently found that milk and protein yields in cows fed grass silage-based diets were increased much more by starch supplementation (Kebreab et al., 2000), particularly corn starch (Castillo et al., 2001b), than by protein supplementation (Castillo et al., 2001a). As discussed earlier, increasing dietary energy content improves milk production by increasing protein supply through stimulating microbial protein formation and by increasing energy supply to the animal. Decreasing dietary forage gave rise to linear increases in both milk and protein yields over the range from 25 to 43% NFC (Valadares et al., 2000). Grinding of high-moisture corn to enhance ruminal fermentation and microbial growth has been shown to improve both milk and protein yield (Ekinci and Broderick, 1997; Wilkerson et al., 1997). So long as RDP supply is adequate, milk and protein yield will continue to respond to increased energy intake until production is suppressed by the adverse ruminal effects of excessive concentrate intake (Oliveira et al., 1993). |
SUMMARY AND CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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ACKNOWLEDGEMENTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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FOOTNOTES |
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Received for publication August 15, 2002. Accepted for publication October 1, 2002.
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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S. A. Burgos, J. G. Fadel, and E. J. DePeters Prediction of Ammonia Emission from Dairy Cattle Manure Based on Milk Urea Nitrogen: Relation of Milk Urea Nitrogen to Urine Urea Nitrogen Excretion J Dairy Sci, December 1, 2007; 90(12): 5499 - 5508. [Abstract] [Full Text] [PDF]
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M. S. Awawdeh, E. C. Titgemeyer, J. S. Drouillard, R. S. Beyer, and J. E. Shirley Ruminal Degradability and Lysine Bioavailability of Soybean Meals and Effects on Performance of Dairy Cows J Dairy Sci, October 1, 2007; 90(10): 4740 - 4753. [Abstract] [Full Text] [PDF]
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S. J. Krizsan, G. A. Broderick, R. E. Muck, C. Promkot, S. Colombini, and A. T. Randby Effect of Alfalfa Silage Storage Structure and Roasting Corn on Production and Ruminal Metabolism of Lactating Dairy Cows J Dairy Sci, October 1, 2007; 90(10): 4793 - 4804. [Abstract] [Full Text] [PDF]
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 S. C. Kim, A. T. Adesogan, and J. D. Arthington Optimizing nitrogen utilization in growing steers fed forage diets supplemented with dried citrus pulp J Anim Sci, October 1, 2007; 85(10): 2548 - 2555. [Abstract] [Full Text] [PDF]
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 Z. Wu and J. M. Powell Dairy Manure Type, Application Rate, and Frequency Impact Plants and Soils Soil Sci. Soc. Am. J., June 29, 2007; 71(4): 1306 - 1313. [Abstract] [Full Text] [PDF]
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C. Wang, J. X. Liu, Z. P. Yuan, Y. M. Wu, S. W. Zhai, and H. W. Ye Effect of Level of Metabolizable Protein on Milk Production and Nitrogen Utilization in Lactating Dairy Cows J Dairy Sci, June 1, 2007; 90(6): 2960 - 2965. [Abstract] [Full Text] [PDF]
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T. F. Gressley and L. E. Armentano Effects of Low Rumen-Degradable Protein or Abomasal Fructan Infusion on Diet Digestibility and Urinary Nitrogen Excretion in Lactating Dairy Cows J Dairy Sci, March 1, 2007; 90(3): 1340 - 1353. [Abstract] [Full Text] [PDF]
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G. A. Broderick, A. F. Brito, and J. J. O. Colmenero Effects of Feeding Formate-Treated Alfalfa Silage or Red Clover Silage on the Production of Lactating Dairy Cows J Dairy Sci, March 1, 2007; 90(3): 1378 - 1391. [Abstract] [Full Text] [PDF]
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J. M. Powell, D. B. Jackson-Smith, D. F. McCrory, H. Saam, and M. Mariola Validation of feed and manure data collected on Wisconsin dairy farms. J Dairy Sci, June 1, 2006; 89(6): 2268 - 2278. [Abstract] [Full Text] [PDF]
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J. J. O. Colmenero and G. A. Broderick Effect of Amount and Ruminal Degradability of Soybean Meal Protein on Performance of Lactating Dairy Cows J Dairy Sci, May 1, 2006; 89(5): 1635 - 1643. [Abstract] [Full Text] [PDF]
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J. J. O. Colmenero and G. A. Broderick Effect of Dietary Crude Protein Concentration on Ruminal Nitrogen Metabolism in Lactating Dairy Cows J Dairy Sci, May 1, 2006; 89(5): 1694 - 1703. [Abstract] [Full Text] [PDF]
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J. J. O. Colmenero and G. A. Broderick Effect of Dietary Crude Protein Concentration on Milk Production and Nitrogen Utilization in Lactating Dairy Cows J Dairy Sci, May 1, 2006; 89(5): 1704 - 1712. [Abstract] [Full Text] [PDF]
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J. M. Powell, M. A. Wattiaux, G. A. Broderick, V. R. Moreira, and M. D. Casler Dairy Diet Impacts on Fecal Chemical Properties and Nitrogen Cycling in Soils Soil Sci. Soc. Am. J., March 29, 2006; 70(3): 786 - 794. [Abstract] [Full Text] [PDF]
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T. D. Nennich, J. H. Harrison, L. M. VanWieringen, N. R. St-Pierre, R. L. Kincaid, M. A. Wattiaux, D. L. Davidson, and E. Block Prediction and Evaluation of Urine and Urinary Nitrogen and Mineral Excretion from Dairy Cattle J Dairy Sci, January 1, 2006; 89(1): 353 - 364. [Abstract] [Full Text] [PDF]
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T. H. Misselbrook and J. M. Powell Influence of Bedding Material on Ammonia Emissions from Cattle Excreta J Dairy Sci, December 1, 2005; 88(12): 4304 - 4312. [Abstract] [Full Text] [PDF]
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S. M. Reynal and G. A. Broderick Effect of Dietary Level of Rumen-Degraded Protein on Production and Nitrogen Metabolism in Lactating Dairy Cows J Dairy Sci, November 1, 2005; 88(11): 4045 - 4064. [Abstract] [Full Text] [PDF]
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E. B. Groff and Z. Wu Milk Production and Nitrogen Excretion of Dairy Cows Fed Different Amounts of Protein and Varying Proportions of Alfalfa and Corn Silage J Dairy Sci, October 1, 2005; 88(10): 3619 - 3632. [Abstract] [Full Text] [PDF]
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I. R. Ipharraguerre, J. H. Clark, and D. E. Freeman Varying Protein and Starch in the Diet of Dairy Cows. I. Effects on Ruminal Fermentation and Intestinal Supply of Nutrients J Dairy Sci, July 1, 2005; 88(7): 2537 - 2555. [Abstract] [Full Text] [PDF]
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I. R. Ipharraguerre and J. H. Clark Varying Protein and Starch in the Diet of Dairy Cows. II. Effects on Performance and Nitrogen Utilization for Milk Production J Dairy Sci, July 1, 2005; 88(7): 2556 - 2570. [Abstract] [Full Text] [PDF]
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S. A. Flis and M. A. Wattiaux Effects of Parity and Supply of Rumen-Degraded and Undegraded Protein on Production and Nitrogen Balance in Holsteins J Dairy Sci, June 1, 2005; 88(6): 2096 - 2106. [Abstract] [Full Text] [PDF]
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T. H. Misselbrook, J. M. Powell, G. A. Broderick, and J. H. Grabber Dietary Manipulation in Dairy Cattle: Laboratory Experiments to Assess the Influence on Ammonia Emissions J Dairy Sci, May 1, 2005; 88(5): 1765 - 1777. [Abstract] [Full Text] [PDF]
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I. R. Ipharraguerre and J. H. Clark Impacts of the Source and Amount of Crude Protein on the Intestinal Supply of Nitrogen Fractions and Performance of Dairy Cows J Dairy Sci, May 1, 2005; 88(e_suppl_1): E22 - E37. [Abstract] [Full Text] [PDF]
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A. N. Hristov, R. P. Etter, J. K. Ropp, and K. L. Grandeen Effect of dietary crude protein level and degradability on ruminal fermentation and nitrogen utilization in lactating dairy cows J Anim Sci, November 1, 2004; 82(11): 3219 - 3229. [Abstract] [Full Text] [PDF]
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A. T. Adesogan, M. B. Salawu, S. P. Williams, W. J. Fisher, and R. J. Dewhurst Reducing Concentrate Supplementation in Dairy Cow Diets While Maintaining Milk Production with Pea-Wheat Intercrops J Dairy Sci, October 1, 2004; 87(10): 3398 - 3406. [Abstract] [Full Text] [PDF]
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M. A. Wattiaux and K. L. Karg Protein Level for Alfalfa and Corn Silage-Based Diets: I. Lactational Response and Milk Urea Nitrogen J Dairy Sci, October 1, 2004; 87(10): 3480 - 3491. [Abstract] [Full Text] [PDF]
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M. A. Wattiaux and K. L. Karg Protein Level for Alfalfa and Corn Silage-Based Diets: II. Nitrogen Balance and Manure Characteristics J Dairy Sci, October 1, 2004; 87(10): 3492 - 3502. [Abstract] [Full Text] [PDF]
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 J. M. Powell, Z. Wu, K. Kelling, P. Cusick, and G. Munoz Differential Nitrogen-15 Labeling of Dairy Manure Components for Nitrogen Cycling Studies Agron. J., March 1, 2004; 96(2): 433 - 441. [Abstract] [Full Text] [PDF]
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C. Leonardi, M. Stevenson, and L. E. Armentano Effect of Two Levels of Crude Protein and Methionine Supplementation on Performance of Dairy Cows J Dairy Sci, December 1, 2003; 86(12): 4033 - 4042. [Abstract] [Full Text] [PDF]
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