Use of chromium mordanted neutral detergent residue as a predictor of fecal output to estimate intake in grazing high producing Holstein cows

Animal Feed Science and Technology 89 (2001) 155±164

Use of chromium mordanted neutral detergent residue as a predictor of fecal output to estimate intake in grazing high producing Holstein cows R. Ruiz*, P.J. Van Soest, M.E. Van Amburgh, D.G. Fox, J.B. Robertson Department of Animal Science, Cornell University, 317 Morrison Hall, Ithaca, NY 14853 4801, USA Received 8 May 2000; received in revised form 29 August 2000; accepted 21 November 2000

Abstract Two experiments were conducted to evaluate use of chromium mordanted neutral detergent residue (Cr-NDr) and cobalt EDTA (Co-EDTA) as predictors of dry matter intake (DMI) in high producing grazing dairy cows. The ®rst experiment was conducted with 10 lactating Holstein cows individually fed a total mixed ration (TMR) in con®nement, and dosed with Cr-NDr and Co-EDTA twice daily at milking times for 12-days to validate the markers used for the second experiment. The Cr-NDr accounted for 96% of the variation (r2) in DMI, while Co-EDTA underpredicted DMI by 43% (r 2 ˆ 0:65). The second experiment was conducted on a pasture-based dairy farm, to evaluate the use of Cr-NDr to predict DMI of grazing dairy cows. 15 and 14 high producing dairy cows in trial 1 and 2, respectively, were dosed twice a day at milking times with Cr-NDr for 12days. Mean total DMI estimated from marker recoveries were unrealistically high (5.95 and 5.52% of body weight for trials 1 and 2, respectively). It was concluded that either diurnal variation in fecal excretion of the marker or a failure in the technique of collecting pasture samples that re¯ected the cows' true grazing selection in order to determine pasture composition occurred. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Pasture; Intake; Dairy cows; Markers

Abbreviations: Co-EDTA: cobalt EDTA; Cr-NDr: chromium mordanted neutral detergent residue; FINDF: fecal indigestible NDF; FIVNDFD: fecal in vitro NDF digestibility; IVNDFD: in vitro NDF digestibility * Corresponding author. Tel.: ‡1-607-255-1106; fax: ‡1-607-255-9829. E-mail address: [email protected] (R. Ruiz). 0377-8401/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 7 - 8 4 0 1 ( 0 0 ) 0 0 2 2 9 - 7

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1. Introduction There is a lack of controlled research on intake of high producing grazing dairy cows in the US because of the dif®culty of measuring dry matter intake (DMI). In pasture studies where total fecal collection is inconvenient and direct measure of intake is not possible, markers may be used to estimate pasture DM consumed (Van Soest, 1994). The most commonly used markers to estimate DMI are chromic oxide (Cr2O3) and rare earths as particulate markers, and cobalt EDTA (Co-EDTA) as a liquid marker. Particulate markers include the mordants of chromium and the rare earths (Allen, 1986; UdeÂn et al., 1980). Plant alkanes are also used to estimate herbage intake, to estimate the botanical composition of consumed herbage and to study digesta kinetics (Dove and Mayes, 1991). An ideal marker should be chemically discrete, for ease of identi®cation and analysis, and indigestible in the digestive tract (Dove and Mayes, 1991). Intake can be calculated from fecal output and apparent indigestibility, and markers may be fed in order to calculate fecal output. Fecal output has often been estimated by using Cr2O3or another indigestible marker. A major concern using this approach is the possibility of diurnal variation in the fecal concentration of the marker, resulting in intermittent samples of feces, not representative of the mean fecal marker concentration, and a consequent error in the estimation of intake (Dove and Mayes, 1991). Failure to recover 100% of the marker will result in over- or underestimation of fecal output and intake. However, Smith and Reid (1955) demonstrated that although, Cr2O3 excretion varies during the day, accurate estimates of fecal outputs are possible if fecal samples are taken at times when the concentration of the marker is similar to the mean daily value. It is important that the marker ¯ows with the feed, or the portion of the feed that is being investigated (Van Soest, 1994). Poncet (1976) recognized the migratory behavior of rare earths and, according to Van Soest (1994), caution is necessary in choosing and preparing these markers because of their different physical properties. The use of long chain alkanes to estimate herbage intake has been shown to give accurate intake predictions (Dove and Mayes, 1991). However, large differences in alkane levels among pasture species can lead to errors in estimation of intake (Dove and Mayes, 1991). Moreover, the alkane content of the plant will change with its physiological stage (SpoÈrndly, 1996). Therefore, it is important to know the species and alkane contents of the pastures being studied. Chromium oxide is used in grazing studies as an indigestible fecal marker (Berzaghi et al., 1996; Holden et al., 1994a, b; Holden et al., 1995). Given the lack of data on alkane levels of pasture species in New York state, and the possible migratory behavior of rare earths, it was decided to test the ef®ciency of chromium mordanted neutral detergent residue (Cr-NDr), and Co-EDTA in estimating DMI of high producing grazing dairy cows. 2. Materials and methods The objective of experiment 1 was an evaluation of the alternative marker methods (CrNDr and Co-EDTA) subsequently used in experiment 2. Because it was conducted prior

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to the grazing season, a validation trial with a fresh cut forage diet was precluded. However, because previous Cr-NDr validations (UdeÂn et al., 1980; Chamberlain and Thomas, 1983) were conducted with low DMI animals, we tested the accuracy of Cr-NDr in estimating DMI in high producing dairy cows. 2.1. Experiment 1 The experiment was conducted at the Cornell Animal Science research farm. For 12days, ten lactating Holstein cows (523  77 kg of body weight (BW), 37:3  7:8 kg of milk, and 113  26 days in milk (DIM)) were used in accordance with Cornell University Institutional Animal Care and Use Committee approved procedures. Cows were kept in stalls and individually fed. The total mixed ration (TMR) fed to the cows consisted on a DM basis of 35.6% corn silage, 34.3% alfalfa silage, 17% high moisture shelled corn, 10% protein concentrate mix (33% soybean meal, 25% cotton seed meal, 22.5% dried distillers grain, 8.4% canola meal, 4.9% limestone, 2.9% Dynamate1 (Pitman Moore, Inc.; Mundelein, IL), 1.8% NaCl, 0.5% dicalcium phosphate, 0.5% vegetable fat, 0.19% trace mineral premix, 0.17% Se premix (0.06% Se), 0.13% vitamin mix; (Penn®eld Corporation, Lancaster, PA)), 2.6% cotton seed, and 0.4% sodium bicarbonate. Cows were dosed with Cr-NDr timothy hay (90 g/day (6±7% Cr)) and Co-EDTA (20 g/ day) as particulate and liquid markers, respectively, divided into two doses per day (0600 and 1600 h). Markers were prepared according to procedures of UdeÂn et al. (1980). The Cr-NDr was mixed with 1 kg of a grain mix carrier, and the Co-EDTA was dosed in gelatin capsules using a dosing gun. Fecal collection began 3 days after the initiation of marker administration and continued for 10 days. Samples of feces were taken by rectal stimulation at 0600 and 1600 h every other day. Daily samples of the TMR were collected for DM determination, and a composite sample was collected for chemical analysis. Orts were collected, weighed and recorded after each meal before fresh TMR was fed. 2.2. Experiment 2 This experiment was conducted on a well-managed pasture based dairy farm, and was comprised of two 12-day trials during two consecutive months of the 1997 grazing season. Forages available during the grazing season were from grazing, with a new paddock being made available after each milking by moving the fence. Fifteen lactating Holstein cows in trial 1 (571  84 kg of BW, 41:2  10:8 kg of milk, and 124  64 DIM), and 14 in trial 2 (589  63 kg of BW, 32:2  5:6 kg of milk, and 123  65 DIM) were dosed with Cr-NDr and Co-EDTA as described in experiment 1.The Cr-NDr was administered and mixed with the farm grain supplement and the Co-EDTA was dosed as in experiment 1. Both markers were divided into two doses per day (0600 and 1600 h) during the milking time at the barn. Pasture samples were collected during mornings and afternoons every other day during the 12-days of each trial. Immediately after the cows were turned into the ®eld, plant parts being grazed were observed, and samples were taken as described by Abdalla et al. (1988), mixed, and a composite sample was frozen in liquid nitrogen within 45 min of harvest for chemical analysis. The supplemental grain

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mix (79.2% corn, 5% Soy Plus1, 4.5% dried distillers grains, 4.5% molasses, and 6.3% minerals; 8:4  1:0 kg in trial 1, and 8:3  0:7 kg in trial 2) and hay (mostly mixed grasses; 0.8 kg in both trials) fed in the barn were also sampled during each period and composite samples were collected for chemical analysis. Fecal collection was conducted as described in experiment 1. In both trials, pasture allowance was measured using FILIP's rising plate meter ((Development and Prototype Engineering; Palmerston North, New Zealand), (Unruh, 1998)). 2.3. Laboratory analysis and calculations Pasture samples were freeze dried, and individually analyzed. The grain mix, hay, marker carrier, and TMR were composited prior to analysis. All feed samples were ground through a 1 mm screen in a Wiley mill (Model 4, Arthur H. Thomas Co. Philadelphia, PA), and analyzed for DM, N, NDF and ADF. Composite fecal samples for each cow were dried at 608C, ground to pass a 1 mm screen, and analyzed for DM, NDF, Co and Cr. Kjeldahl N was estimated using boric acid (Pierce and Haenisch, 1947). NDF and ADF were determined according to the procedure of Van Soest et al. (1991) with the use of sodium sul®te (Van Soest and Wine, 1967). Both Cr and Co concentrations in Cr-NDr, Co-EDTA, and feces, were determined by a modi®cation of method 984.27 of AOAC (1990). Dry samples (0.2 g) were weighed into 125 ml Erlenmeyer ¯asks, 4 ml of double-distilled nitric acid was added, a hot plate (Model HPA-2235M, Thermolyne Corp., Dubuque, IA) was set at 1208C, and samples were left to digest for 1 h. 10 ml of perchloric acid was then added to each ¯ask and the temperature was slowly raised to 2208C. Samples were re¯uxed for approximately 0.5 h until oxidized. The oxidation point was determined when the green (Cr III) turned to orange (Cr VI) on a concurrently re¯uxed control hay Cr-NDr sample. Cooled samples were transferred quantitatively to 100 ml volumetric ¯asks and ®lled to volume with double-distilled water. The ®nal acid content of the solution was about 10%. Both Cr and Co were determined by optical emission plasma spectroscopy, using a Jarrell-Ash 975 Plasma Atomcomp equipped with a cross ¯ow nebulizer. In vitro NDF 96 h digestibility (IVNDFD) of feeds and feces were determined by the procedure described by Goering and Van Soest (1970) using the DAISYII, ANKOM200/220 Fiber Analyzer ((ANKOM Technology Corp., Fairport, NY) (Cherney et al., 1997; Traxler et al., 1998)). For each trial, the pasture IVNDFD was determined on a sample composited by weight. Samples were analyzed in duplicate, with each being analyzed using ruminal ¯uid obtained on different days. Rumen ¯uid was collected approximately 3±4 h after the morning feeding from a mature, non-lactating, Holstein cow maintained on average quality mixed hay and 1 kg of corn meal per day in accordance with Cornell University Institutional Animal Care and Use Committee approved procedures. Intake calculations were on an NDF basis to avoid metabolic excretions. In experiment 1, the NDF intake from the TMR was determined by difference between total fecal indigestible NDF (FINDF) estimated and known FINDF from the marker carrier fed. In experiment 2, pasture NDF intake was determined by difference between the total FINDF estimated and the known grain mix and hay FINDF.

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Intake of NDF was estimated as NDF intake ˆ

Fecal INDF output ; and 1 ÿ IVNDFD

DMI was calculated as DMI ˆ

NDF intake NDF content of the feedstuff subject to estimation

; and

…TMR and pasture; for experiments 1 and 2; respectively† Fecal output (FO) was calculated as FO ˆ

grams of marker dosed per day ; and grams of marker per gram of fecal DM

FINDF was calculated as FINDF ˆ FO  …1 ÿ FIVNDFD†: 2.4. Statistical analysis In experiment 1, regression analysis was performed with Minitab version 12 (1997). The observed DMI was regressed on the corresponding estimated DMI to determine the coef®cient of variation (r2). The marker DMI estimation bias (over- or under-estimation) was calculated as the slope of regression through the origin ÿ1. Regression through the origin was performed given that the intercept of the regression did not differ from zero (P < 0:05). The r2 and the root mean square error (RMSE) were obtained from the initial regression. All statistical comparisons were performed with GLM procedures of Minitab (1997). 3. Results and discussion 3.1. Experiment 1 The chemical composition and in vitro NDF digestibility of the feeds are in Table 1, while actual and estimated DMI are plotted in Fig. 1. The plotted data indicates that 96% of the variation in actual DMI could be explained by Cr-NDr. In contrast, Co-EDTA explained only 65% of the variation, with a 43% underprediction bias. On this basis, CoEDTA was rejected as a marker and pasture intake in experiment 2 was estimated based on Cr-NDr alone. Diurnal variation in rate of marker recovery will decrease the precision of DMI estimation. For accurate intake estimation, sampling of feces should be done at times of the day when the fecal concentration of the marker is similar to the mean daily value. Chamberlain and Thomas (1983) suggested that the low and variable recoveries of Cr2O3 and Cr2O3-paper were due to retention of the marker in the cows' forestomachs.

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Table 1 Chemical composition and in vitro NDF digestibility of the feedstuffsa

Item (% of DM) CP NDF ADF (% of NDF) IVNDFDc

Experiment 1

Experiment 2

TMR

Pastureb

Marker carrier

Grain mix

Hay

Trial 1

Trial 2

Trial 1

Trial 2

Trial 1

Trial 2

18.7 32.2 20.6

14.2 19.7 8.3

20.4 38.0 21.7

20.7 35.1 23.2

10.9 9.8 3.6

11.1 9.9 3.6

9.0 64.9 42.0

8.8 63.8 40.8

72.8

62.1

88.9

80.4

90.9

87.6

55.5

53.1

a

TMR ˆ total mixed ration; IVNDFD ˆ in vitro NDF digestibility. For CP, NDF, and ADF values are means of 10 replicates for trial 1, and 16 for trial 2. c 96 h. b

Subsequently, Chamberlain and Thomas (1983) reported an experiment that prepared the Cr-NDr marker in a less dense form, but according to the method of UdeÂn et al. (1980), and reported a reduction of the SD of Cr2O3 recovery, dosed as Cr-NDr, compared to the marker dosed as Cr2O3 or Cr2O3-paper. On this basis, Chamberlain and Thomas (1983) concluded that Cr-NDr ¯owed more regularly through the digestive tract, without the chromium being released within the rumen. Data from experiment 1 are consistent with Chamberlain and Thomas (1983), given that accurate DMI estimations were possible with fecal samples collected twice daily. In order to ensure stable conditions of marker passing through the digestive tract, Le Du and Penning (1982) suggested a minimum preliminary dosing period of 7-days, prior to sampling feces, when using Cr2O3. However, the 3-day period used in this study for Cr-NDr appeared to be adequate, and the 10-day fecal sample collection period was over the minimum 5-day period recommended by Le Du

Fig. 1. Actual and estimated TMR DMI (Experiment 1). (*) Cr-NDr (Y ˆ 1:59 ‡ 0:920 X; RMSE ˆ 0:65; r2 ˆ 0:96; no bias). (*) Co-EDTA (Y ˆ 4:24 ‡ 1:13 X, RMSE ˆ 1:89; r 2 ˆ 0:65; underprediction bias of 43%). The line Y ˆ X represents agreement between predicted and observed DMI.

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and Penning (1982). Finally, the 10 h interval between dosing was in agreement with the 8±16 h dose interval recommended by Le Du and Penning (1982). 3.2. Experiment 2 The botanical composition of the pasture species were calculated on a dry weight basis (Tothill, 1978). Pasture consisted of 40.8% orchardgrass (Dactylus glomerata L.); 24% white clover (Trifolium repens L.); 19.6% ®ne grasses such as Canada bluegrass (Poa compressa L.), and Kentucky bluegrass (Poa Pratensis L.); 2% forbs (herbaceous broadleaved plants); and 13.6% dead organic matter (Unruh, 1998). Pasture composition of DM, NDF, ADF and CP did not vary between mornings and evening within trial 1. However, in trial 2, DM differed (morning 17.1%, versus evening 20.4%; P ˆ 0:004), as did CP (morning 21.6%, versus evening 19.9%; P ˆ 0:032). Weather conditions differed between trials. The ®rst trial was characterized by cloudy days while sunny days characterized trial 2. Morning and evening pasture sample composites, within trials 1 and 2, were analyzed for ethanol insoluble residue (EIR) (Hall et al., 1999). Larger morning and evening EIR differences were found in the composited samples for trial 2 compared to trial 1 (morning 70.5%, versus evening 69.7% for trial 1; morning 72.8%, versus evening 69% for trial 2). The lower EIR values for pasture evening samples in trial 2 suggest a higher sugar content, which agrees with Fisher et al. (1999). As a result, the lower pasture evening CP values in trial 2 were likely caused by a sugar dilution effect. The large difference in pasture IVNDFD between trial 1 and 2 was likely due to a combination of a lower NDF (Table 1), and a higher lignin content in trial 2 samples (lignin trial 1, 2.3% versus trial 2, 2.7%; P ˆ 0:01). The estimated pasture and total DMI for both ®eld trials are in Table 2. Marker predicted DMI as a percent of body weight averaged 5:95  0:99%, and 5:52  0:61% for trial 1 and 2, respectively. NDF intake as a percent of body weight averaged 1:88  0:37%, and 1:62  0:19% for trial 1 and 2, respectively. Once the DMI of all diet components were estimated, the diet DM and OM apparent total tract digestibility, and the diet NDF digestibility were calculated (Table 2). Rate of excretion of a marker is related to the rate of passage through the digestive tract (Le Du and Penning, 1982). Herbage availability, which can impact passage, was not Table 2 Estimated DM intake, and diet DM, NDF and OM digestibilities based on Cr-NDr (Experiment 2) Trial 1

DM intake (kg) Pasture intake Total intakea Digestibility (%) DMb Omb NDF a b

Trial 2

Mean

S.D.

Mean

S.D.

24.76 33.95

6.33 6.75

23.24 32.35

3.12 3.42

82.26 83.39 75.20

0.03 0.03 0.05

79.05 80.85 67.63

0.01 0.01 0.02

Pasture plus grain mix and hay fed in the barn. Apparent total tract digestibility.

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judged to be limiting intake during the ®eld trials. Pasture allowances were 42.4 kg and 41.5 kg DM per cow per day for trial 1 and 2, respectively, (Unruh, 1998), which is adequate to allow maximum voluntary intake (Rayburn, 1991). Also, the similar chemical composition of the pasture samples within each trial precludes assuming differences in digestibility, which will impact passage. The pasture DM difference in trial 2 might have in¯uenced DMI throughout the day thereby introducing a bias in the intake estimation. Pasture samples were carefully collected to re¯ect what the cows were consuming. Grazing animals can be selective and manual sample collection depends on the operator's judgment. However, the intensive rotation left little opportunity for selection. Thus, it was assumed that the pasture samples collected by the operators were representative of what the cows were eating. In order to maximize milk production, Mertens (1992) suggested a maximum NDF intake of 1.3% of BW dayÿ1 at week 20 of lactation; however, this may not apply to cows eating high quality fresh forages. Kolver and Muller (1998) reported NDF intakes, as a percent of BW, of 1.47% for cows fed pasture alone. Mackle et al. (1996) also reported NDF intakes as a percent of BW of 1.6% for Friesian cows housed in individual stalls eating freshly cut pasture, and SpoÈrndly (1996) reported NDF intakes as a percent of BW as high as 1.5% for cows eating fresh forage plus a concentrate mix. Kolver et al. (1998) reported NDF intakes as a percent of BW of 1.16 and 1.23% for pasture diets supplemented with a concentrate mix in a synchronous and asynchronous manner, respectively. The NDF values for the pasture samples of trial 2 suggest that the NDF intake predictions are biologically realistic. However, when intake predictions were evaluated on a DM basis, previous studies (Holden et al., 1994b; Holden et al., 1995; Kolver et al., 1998) were within a range of 3.39±3.66% of DMI as a percent of BW, which is considerably below the 5.95 and 5.52% estimated for trial 1 and 2, respectively. For high and low N fertilization with ad libitum and restricted pasture allowances, Mackle et al. (1996) reported DMD similar to the estimated digestibilities reported in this study. However, milk production in that study (19.8 kg of fat corrected milk) was well below the production levels of this study. The authors (Mackle et al., 1996) reported greater OM digestibilities of the diets for cows on restricted versus ad libitum allowance. Van Vuuren et al. (1992) also reported similar OM and NDF digestibilities for cows fed grass fertilized at different N levels, although milk yield was not reported in their study. In another study, Van Vuuren et al. (1993) fed three different diets, and reported a reduction in NDF digestibility, from 79 to 74%, from a grass low-starch to a grass highstarch diet. However, when the grass high-starch diet was compared to the control diet (grass alone) a numerically lower NDF digestibility was reported. Milk yield was not reported. The more digestible the cell wall, the greater the potential for digestibility depression through the effect of intake level, physical form, passage or concentrate addition (Van Soest, 1994). Although, the digestibilities calculated in this study are within the range of reported data, the high NDF intakes as a percent of BW reported in trial 1, and the high DMI as a percent of BW calculated for both trials suggests a failure of the technique in determining the amount of pasture consumed. Collection of pasture samples that are truly representative of what the cows are eating is well recognized as a major technical problem. Even though the intensive rotation left

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little opportunity for selection, the cow replicated pasture samples taken within 45 min after the cows were turned into the ®eld might not have represented the cows' grazing pattern, which would bias the intake calculation. The mean fecal DM values for experiment 1, and trials 1 and 2 within experiment 2 were 13.2, 9.2 and 10.1%, respectively, and the means signi®cantly differed between and within experiment (P < 0:001). The higher IVNDFD of the main diet components (pasture and grain, Table 1) in experiment 2, and the higher fecal water content for experiment 2 compared to experiment 1 suggests a greater passage rate through the digestive tract for the fresh forage diet. With an expected DMI of 20±25 kg/day, the total diet NDF would have been between 26 and 28% for trials 1 and 2 within experiment 2, which is lower than the 31% diet NDF in experiment 1. Diurnal variations in fecal Cr concentrations might have caused low marker recoveries, and therefore, an overestimation of DMI. 3.3. Implications This study compared the use of CrNDr in estimating DMI of stall-fed and pastured dairy cattle. Favorable results were obtained with the stall-fed but not with the pastured animals. Apparently diurnal variations were induced in the experiment on pasture. Sampling of forage under conditions of rotational grazing needs study, as well as more times of sampling feces to determine variations in chromium concentrations in high producing cows. The pattern of rotational grazing and time of daily access to pasture may need to be considered.

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