Effect of feeding non-fibrous carbohydrate before grazing on intake and nitrogen utilization in dairy cows throughout the grazing season

O R I G I N A L A R T I C L E

Effect of feeding non-fibrous carbohydrate beforegrazing on intake and nitrogen utilization in dairy cowsthroughout the grazing seasonasj_922 121..127

Tomohiro MITANI,1,2 Koichiro UEDA,2 Tetsushiro ENDO,2,3 Makoto TAKAHASHI,4 Hiroki NAKATSUJI2 andSeiji KONDO4

1Creative Research Institute and 2Graduate School of Agriculture, Hokkaido University, Kita, Sapporo, 3AnimalResearch Center, Agricultural Research Department, Hokkaido Research Organization, Shintoku, Hokkaido, and4Field Science Center for Northern Biosphere, Hokkaido University, Kita, Sapporo, Japan

ABSTRACT

Ten lactating cows were used to determine the effect of feeding non-fibrous carbohydrate (NFC) supplement before

grazing on feed intake and nitrogen (N) utilization throughout a grazing season. The experiment was conducted from June

to September. Cows grazed twice a day (2.5 h ¥ 2) under a set stocking system and were fed NFC supplement (1 kg/4 kg

of milk yield) 2 h before grazing (PRE) or immediately after grazing (POST). Cows were also fed a grass and corn silage

mixture ad libitum. Herbage dry matter intake (DMI) was greater for PRE than for POST throughout the experiment and

decreased from June to September. Conversely, silage DMI was less for PRE than for POST throughout the experiment and

increased over the grazing season. Consequently, total DMI for PRE did not differ from that for POST. Milk urea-N

concentration and urinary urea-N excretion in June did not differ between the treatments, whereas that after July was

higher for PRE than for POST. Proportion of urinary N excretion to absorbed N intake in June was lower for PRE than for

POST, but that after July was higher for PRE than for POST. Feeding NFC supplement before grazing would improve N

utilization when cows eat large amounts of herbage high in N.

Key words: dairy cow, grazing, nitrogen utilization, timing of supplement.

INTRODUCTIONThe efficiency of nitrogen (N) utilization in grazingcows is reduced by high urinary N excretion whenherbage is fed as the main diet (Kolver 2003). Thisdecline in efficiency occurs because herbage proteincontent is high and it is rapidly degraded in the rumen,resulting in an imbalance between N and energysupply to ruminal microbes. To maximize N utilizationby ruminal microbes, the rate and extent of ruminalcarbohydrate (CHO) degradation needs to be synchro-nized with that of protein (Hoover & Stokes 1991).Therefore, grazing dairy cows need to be fed a supple-ment of non-fibrous carbohydrate (NFC) with a highruminal degradation rate (Muller & Fales 1998; NRC2001).

Timing of feeding such an NFC supplement is alsoimportant for synchronizing the degradation of CHOand herbage protein. Mitani et al. (2005) reported thatfeeding NFC supplement 2 h before grazing improvedN utilization in grazing dairy cows. This study showedthat supplementation 2 h before grazing lowered

urinary N excretion compared with supplementationimmediately after grazing. Similarly, Vaughan et al.(2002) reported a lower level of blood urea-N concen-tration when cows were fed a partial mixed ration 2.5or 1 h before grazing compared with cows fed theration after grazing. Both these results indicate thatfeeding NFC supplement before grazing can reduce Nloss from ammonia-N absorption through the rumenwall.

However, the effect of NFC supplementation on Nutilization can be altered by differences in chemicalcomposition of grazed herbage, mainly N content(Carruthers & Neil 1997), or by differences in herbagedry matter intake (DMI) (Bargo et al. 2002). Chemicalcomposition of herbage, herbage mass and DMIchange during the grazing season and are also

Correspondence: Koichiro Ueda, Graduate School of Agricul-ture, Hokkaido University, Kita, Sapporo 060-8589, Japan.(Email: [email protected])Received 24 December 2010; accepted for publication 24February 2011.

Animal Science Journal (2012) 83, 121–127 doi: 10.1111/j.1740-0929.2011.00922.x

© 2011 The AuthorsAnimal Science Journal © 2011 Japanese Society of Animal Science

influenced by the grazing management system. There-fore, the practical application of NFC supplementationbefore grazing should be tested over a grazing season.The objective of the present study was to determinethe effect of feeding NFC supplement to dairy cowsbefore grazing on feed intake, milk production and Nutilization throughout a grazing season.

MATERIALS AND METHODSAnimals and experimental designTen lactating Holstein cows were used in the experiment. Atthe beginning of the experiment, average (�SD) daily milkyield, body weight (BW), parity and days in milk were30.3 � 8.0 kg, 627 � 51 kg, 2.9 � 1.3 and 110 � 69 days,respectively. The cows were divided into two groups whichdid not differ in average daily milk yield, parity and days inmilk. Two groups of cows were assigned to one of two dietarytreatments: feeding NFC supplement 2 h before grazing(PRE) or immediately after grazing (POST). The experimentwas conducted from 1 June to 30 September. The study wasapproved by the technical committee for experiments onanimals at Hokkaido University, Japan.

Diet and feedingCows were grazed under a set stocking system throughoutthe experiment on 2.0 ha of perennial ryegrass (Loliumperenne L.) and white clover (Trifolium repens L.) pasture.Grazing started from 6 May, but the first month was consid-ered as adaptation period for grazing and supplied externalmarker. Grazing time allowed was limited to 2.5 h twicea day: from 05.30 to 08.00 hours and from 17.00 to19.30 hours. Cows were kept in a barn when not grazing.Pasture was fertilized 45.4, 39.4 and 45.4 kg/ha as N,phosphorus (P) and potassium (K) on 22nd April, and 27.3and 23.7 kg/ha as N and P on 26 June and 30 August,respectively.

In the barn, cows were fed ad libitum a mixture of cornsilage and grass silage (50:50 DM basis) throughout the day.Chemical composition of the silage mixture is shown inTable 1. Daily allowance of silage for each cow was 115% ofaverage daily intake in the previous week. Fresh silage wassupplied at 19.30 and 08.00 hours in equal portions. Amixture of commercial formula feed for dairy cows (crude

protein (CP), 20%; total digestible nutrients, 84.5% on a DMbasis) and flaked corn (50:50 DM basis) was used as the NFCsupplement. The NFC supplement was fed twice a day inequal portions at 15.00 and 03.30 hours for the PRE groupand at 19.30 and 08.00 hours for the POST group by anautomatic feeder (Max feeder, Kitahara denboku, Sapporo,Japan). Daily allowance of the NFC supplement for each cowwas calculated as 25% of average daily milk yield (kg/day) inthe previous week. Cows also had free access to water andmineralized salt blocks.

Measurement and analysisSward mass was measured using 45 quadrats (50 ¥ 50 cm) at2-week intervals. Sward height was measured 225 points perpaddock at 2-week intervals. Herbage was sampled everyweek and combined every 2 weeks for chemical analysis,which was similar to the parts of plant fed to cows by hand-plucking. NFC supplement and silage were sampled every2 weeks. Samples of each feed were dried at 60°C in anair-forced oven for 48 h, then ground to pass through a1 mm screen. Samples were analyzed for DM, CP and crudeash content according to AOAC (1984), and NDF contentwas measured according to Van Soest et al. (1991). For etherextract content of each feed, the values in the StandardTables of Feed Composition in Japan (National AgriculturalResearch Organization 2001) were used. The NFC contentfor each feed was calculated using the following equationof Van Soest et al. (1991): NFC = 100 - (crude ash + CP +neutral detergent fiber + ether extract).

Daily silage intake of each cow was measured by weighingorts every morning. Daily herbage intake of each cow wasestimated by a double-indicator method with Lanthanum(La) as an external marker and alkane (C31 + C33) as aninternal marker. The external marker was prepared bysoaking grass silage in 0.3% lanthanum chloride solution for48 h, then washing in tap water and drying at 60°C in anair-forced oven (Marder et al. 1984). Cows were fed 10 g ofthe external marker twice a day (08.00 and 19.30 hours)throughout the experiment. Fecal rectal grab samples werecollected twice a day (04.30 and 16.30 hours) throughoutthe experiment. Fecal samples were combined at weeklyintervals, dried at 60°C in an air-forced oven for 72 h, thenground to pass through a 1 mm screen. N content of the fecalsamples was measured by the Kjeldahl method (AOAC1984). The marker silage and the dry fecal sample were

Table 1 Sward height and mass and chemical composition of hand-plucked herbage, silage and non-fibrous carbhydrate(NFC) supplement

Herbage Silage† NFCsupplement‡

June July August September

Sward height, cm 16.9 12.5 10.7 10.6Ground level sward mass, gDM/m2 326 287 277 266

Chemical composition, % of DMDM 20.4 20.9 20.3 16.4 28.9 86.2OM 88.5 87.8 88.0 88.1 89.6 96.1CP 20.7 22.3 25.5 29.7 12.3 13.6NDF 48.3 44.4 41.1 38.6 63.0 16.3NFC§ 15.6 17.2 17.4 15.8 10.3 61.9

†Mixture of grass and corn silage at the ratio of 1:1; ‡Mixture of commercially formulated concentrate and flaked-corn at the ratio of 1:1;§NFC = OM - (CP + NDF + EE¶); ¶A value of EE was used in Standard Tables of Feed Composition in Japan (National Agricultural ResearchOrganization 2001). CP, crude protein; DM, dry matter; NDF, non-fibrous carbohydrate; NFC, non-fibrous carbohydrate; OM, organic matter;EE, ether extract.

122 T. MITANI et al.


Animal Science Journal (2012) 83, 121–127

dissolved by wet ashing with nitric acid and perchloric acid,and then the concentration of La in the dilution was mea-sured by an inductively coupled plasma atomic emissionspectrometer (SPS-5600; Seiko Instruments Inc, Chiba,Japan). The alkane content of each sample was analyzed bya minor modification of the method of Dove (1992). Eachsample was saponified by 1 M-etanolic KOH with C34 alkaneas an internal marker at 90°C for 4.5 h. After extraction withn-hexane, the extracted sample was purified through a silica-gel column (Silica-gel 60; Nacalai tesque, Kyoto, Japan).Alkane contents of the purified samples were quantifiedusing a gas chromatographic method with a capirary column(TC-1, 30 m ¥ 0.25 mm; GL Science, Tokyo, Japan) in a GC-2010 (Shimadzu, Kyoto, Japan) fitted with a flame ionizationdetector (FID). Chromatographic conditions were the follow-ing: carrier gas He at 175.4 kPa constant pressure; inlettemperature 350°C; oven programmed from 200°C (heldfor 0.5 min) with 20°C/min to 320°C (held for 13.5 min);FID temperature 350°C. Daily feces excretion for each cowwas calculated as: feces excretion (kg DM/day) = La dosed(mg/day)/La content in feces (mg/kg DM). Daily herbageintake for each cow was calculated as: herbage intake (kgDM/day) = (alkane (C31 + 33) excretion in feces (g/day) –alkane (C31 + 33) intake from silage and NFC supplement(g)(/alkane (C31 + 33) content in herbage (g/kg DM).

Milk yield was recorded at each milking every day (08.30and 16.00 hours). A milk sample from consecutive p.m anda.m. milkings was collected from each cow at 2-week inter-vals. The composite milk sample of each cow was analyzedfor fat and protein content using an infrared spectrophotom-eter (Milko Scan C54A; Foss Electric, Hillerød, Denmark).For the analysis of milk urea nitrogen (MUN) content, a partof the milk sample was centrifuged at 3000 ¥ g for 10 min at4°C to remove milk fat, and analyzed for urea-N concentra-tion by the urease-indophenol reaction method (Wetherburn1967). Body weight of individual cows was measured at2-week intervals.

Urine samples were collected at 05.00, 11.00, 17.00 and23.00 hours from each cow at 2-week intervals. A part of theurine sample was acidified by 10% H2SO4 solution, and thenstored at -20°C prior to analysis. Another urine sample wasdirectly stored at -20°C. The acidified urine samples wereanalyzed for urea-N concentration (Wetherburn 1967), allan-toin and uric acid concentration according to the methodof Chen and Gomes (1992). The non-acidified urine sampleswere analyzed for creatinine concentration using a WakoCreatinine kit 277–10501 (Wako Chemical Industries, Osaka,Japan). Urine volume per day for each cow was estimatedby creatinine concentration of urine samples by the follow-ing equation proposed by Asai et al. (2005): urine volume(L/day) = BW ¥ 22.8/creatinine concentration (mmol/L).Daily excretion of urea-N, allantoin and uric acid wasalso calculated for each cow. Daily ruminal microbialprotein synthesis was calculated by the following series ofequations (Chen & Gomes 1992): total purine derivatives(PD) excretion (mmol/L) = allantoin excreted (mM/L) + uricacid excreted (mmol/L), endogenous PD excretion (mmol/L) = 0.385 mmol/BW0.75 per day, microbial purine absorption(mmol/L) = (total PD excretion - endogenous PD excretion)/0.85, and microbial N flow into the duodenum (g/day) =(microbial purine absorption ¥ 70)/(0.116 ¥ 0.83 ¥ 1000).

Statistical analysisAll data from individual cows were averaged by month andanalyzed by analysis of variance ( ANOVA) for a completely

randomized design as repeated measures using the fit modelplatform in JMP 7.01 (SAS 2007). The model included treat-ment (PRE or POST), month (June, July, August and Sep-tember) and treatment by month interaction as the fixedeffects and cow as the random effect. Results were describedby least square means and standard error of the mean (SEM).Differences were considered to be significant at P < 0.05 andto be a tendency at P < 0.10.

RESULTSPasture characteristics and chemicalcomposition of dietsSward height and mass, and chemical composition ofherbage, silage and NFC supplement are shown inTable 1. Sward height and mass decreased from Juneto July, then decreased more gradually until Septem-ber. Herbage CP content increased over the grazingseason from just over 20% of DM in June. Conversely,herbage neutral detergent fiber content decreased overtime, from just below 50% of DM in June. HerbageNFC content changed little over the grazing season,ranging between 15% and 17% of DM.

DM and N intakeIntake of DM and N for each feed are shown in Table 2.Herbage DMI was greater for PRE than for POSTthroughout the experiment (P < 0.05) and bothdecreased over the grazing season (P < 0.01). Con-versely, silage DMI was less for PRE than for POSTthroughout the experiment (P < 0.01) and bothincreased over the grazing season (P < 0.01). Feedingtreatment had no effect on DMI of NFC supplement,but that for both treatments decreased over thegrazing season (P < 0.01). Consequently, the propor-tion of herbage in the total DMI was greatest in June(PRE: 59.7, POST: 45.8%) and decreased over thegrazing season. There was an interaction betweenmonth and treatment in herbage (P < 0.05) and totalDMI (P < 0.05), caused by the large difference betweenthe treatments in June compared with other months.

Cows in the PRE group ingested more herbage Nand less silage N than those in the POST group. TotalN intake did not differ between PRE and POST. Forboth treatments, the proportion of herbage N in totaldietary N intake decreased over the grazing season.

Milk production and compositionDaily milk yield, milk composition and MUN concen-tration are shown in Table 3. Feeding treatment hadno effect on daily milk yield, although milk yielddecreased over the grazing season (P < 0.01). Milk fatcontent was higher for PRE than for POST, but milkfat yield did not differ between PRE and POST. Theychanged over the grazing season (P < 0.01). Feedingtreatment did not affect daily milk protein content andyield, and they changed little over the grazing season.

NON-FIBROUS CARBOHYDRATE BEFORE GRAZING 123



The concentration of MUN was higher for PRE thanfor POST (P < 0.05), but there was an interaction(P < 0.05) between treatment and month, indicatingthat their change differed over the grazing season.Although the MUN concentration for both treatmentswas similar in June and increased for both over thegrazing season, the concentration was higher for PREthan for POST between July and September (P < 0.05).

N utilization

Nitrogen excretion into feces, urine and milk, andmicrobial N flow into the duodenum, are shown inTable 4. Feeding treatment did not affect fecal N excre-tion, although there was an interaction between treat-ment and month (P < 0.01). Fecal N excretion wasgreater in June than in other months for PRE and was

Table 2 Average of dry matter and nitrogen intake with two different timings of feeding concentrate mixture (PRE: 2 hbefore grazing, POST: immediately after grazing)

June July August September SEM Significance§

PRE POST PRE POST PRE POST PRE POST T M T ¥ M

Dry matter intake, kg/dayHerbage 11.4 7.6 7.9 6.4 5.3 3.6 6.2 3.9 0.7 * ** *Silage† 1.0 2.8 4.7 6.4 7.8 10.1 7.3 9.9 0.5 ** ** NSNFC supplement‡ 6.7 6.2 5.7 5.3 4.7 4.3 5.0 4.2 0.6 NS ** NSTotal 19.1 16.6 18.2 18.1 17.8 18.0 18.4 17.9 1.0 NS NS *

Nitrogen intake, g/dayHerbage 365 239 280 224 204 139 287 179 30 * ** NSSilage† 21 60 94 129 144 187 134 181 10 ** ** NSNFC supplement‡ 146 135 123 115 101 92 112 94 13 NS ** NSTotal 532 434 497 469 449 418 533 454 34 NS * NS

**P < 0.01, *P < 0.05. †Mixture of grass and corn silage at the ratio of 1:1; ‡mixture of commercially formulated concentrate andflaked-corn at the ratio of 1:1; §significance: T = significance between PRE and POST, M = significance among months, T ¥ M = interactionbetween T and M, NS = not significant; NFC, non-fibrous carbohydrate.

Table 3 Milk yield and composition of cows fed a non-fibrous carbohydrate (NFC) supplement 2 h before grazing (PRE) orimmediately after grazing (POST)

June July August September SEM Significance§


Milk yield, kg/day 30.0 27.7 24.7 23.2 22.2 19.6 22.7 19.4 2.7 NS ** NSFat yield, kg/day 1.13 1.21 1.03 1.09 0.88 0.86 0.86 0.81 0.11 NS ** NSProtein yield, kg/day 0.92 0.87 0.76 0.74 0.69 0.62 0.75 0.64 0.07 NS ** NSFat content, % 3.76 4.35 4.19 4.76 3.97 4.44 3.79 4.23 0.20 * * NSProtein content, % 3.08 3.20 3.10 3.20 3.11 3.19 3.32 3.39 0.10 NS ** NSMilk urea N, mg/dL 13.1 11.9 15.0 11.4 18.3 14.7 23.8 17.3 1.1 * ** *

**P < 0.01, *P < 0.05. §Significance: T = significance between PRE and POST, M = significance among months, T ¥ M = interaction betweenT and M, NS = not significant; N, nitrogen.

Table 4 Nitrogen (N) output and microbial N flow of cows fed a non-fibrous carbohydrate (NFC) supplement 2 h beforegrazing (PRE) or immediately after grazing (POST)

June July August September SEM Significance §


Nitrogen outputFeces, g/day 194 164 146 151 159 160 145 149 8 NS ** **% of total N intake 36.5 38.4 30.1 32.4 35.9 38.5 27.4 33.1 1.7 NS ** NS

Urine, g/day 123 119 113 86 131 107 172 131 11 NS ** †% of total N intake 23.3 27.7 23.6 18.8 29.2 25.6 32.0 28.8 2.1 NS ** *% of N absorbed 36.7 45.3 34.4 28.1 45.7 41.7 44.0 43.0 3.5 NS ** †

Milk, g/day 144 137 120 115 108 96 117 101 11 NS ** NS% of total N intake 27.2 31.5 24.6 24.5 24.3 23.0 22.1 22.1 1.8 NS ** NS% of N absorbed 43.1 51.4 35.8 36.4 38.3 37.5 30.5 33.0 3.4 NS ** NS

Microbial nitrogen flow, g/day 350 334 249 242 216 232 252 259 26 NS ** NS

**P < 0.01; *P < 0.05; †P < 0.10. §Significance: T = significance between PRE and POST, M = significance among months,T ¥ M = interaction between T and M, NS = not significant.




maintained at around 150 g/day for POST over thegrazing season. Fecal N excretion was greater for PREthan for POST only in June. Urinary urea-N excretiondid not differ between treatments throughout theexperiment, but tended to be affected by feedingtreatment over the grazing season (P = 0.10). Urinaryurea-N excretion for PRE did not differ from that forPOST in June, but it was greater for PRE than for POSTafter July. The change in urinary urea-N excretionover the grazing season was similar to that in MUNconcentration for both treatments. Nitrogen excretioninto milk did not differ between PRE and POST.

The proportion of fecal N excretion to total N intakewas not affected by feeding treatment, meaning thatdigestibility of N compounds did not differ betweentreatments. The proportion of urinary urea-N excre-tion, when expressed as a function of both total Nintake and N absorbed, did not differ between treat-ments, but there was an interaction (% of total Nintake: P < 0.05; % of N absorbed: P = 0.06). The pro-portions of urinary urea-N excretion for PRE werelower than those for POST in June and increased forboth over the grazing season. Those for PRE werehigher than those for POST after July. The proportionsof milk N as total N intake and N absorbed were notaffected by feeding treatment. Furthermore, there wasno difference between treatments in microbial N flowinto the duodenum.

DISCUSSIONIn the present study, treatment effect of feeding NFCsupplement 2 h before grazing on N utilization was notconstant throughout the grazing season. This wasattributed to a drastic decline of herbage DMI for bothtreatments after summer. The experiment conductedunder a set stocking system would be one of thereasons for the decline in herbage DMI. Endo et al.(2009) reported that seasonal change of sward heightand mass under a set stocking was more rapidly thanthose under rotational grazing. Especially after sum-mer, the sward height and mass under set stocking felldrastically.

Silage DMI in the present study was greater forPOST than PRE throughout the experiment. Cows inthe POST group would have shown a preference forsilage, and hence eaten more than cows in the PREgroup, because cows in the POST group were fed freshsilage and NFC supplement at the same time aftergrazing. Generally, an increase in supplement allow-ance decreased herbage DMI of grazing dairy cows, butMayne and Wright (1988) reported that this decreasewas greater when silage allowance was increased thanwhen concentrate allowance was increased. Thus, anincrease of silage intake for POST would decreaseherbage intake in the present study. Feeding NFCsupplement before grazing would not have affected

herbage DMI in the PRE group. Previous reports haveshown that feeding corn silage-based supplement 2 hbefore grazing (Mitani et al. 2005) and feeding partialtotal mixed rations 1 or 2.5 h before grazing (Vaughanet al. 2002) did not affect herbage DMI.

Milk yield did not differ between treatments, a resultsimilar to that of other studies (Kolver et al. 1998;Vaughan et al. 2002; Mitani et al. 2005). Low milk fatcontent for PRE would be affected by diluting effect ofmilk yields because milk yield for PRE was numericallyhigher than that for POST. Thus, the timing of NFCsupplement had little effect on milk fat and proteincontent and yield.

The increase of N intake in grazing dairy cowsincreased linearly with urinary N excretion and thenreduced the efficiency of N utilization (Mulligan et al.2004). In the present experiment, herbage N intakewas greater and total N intake was numerically greaterfor PRE than for POST throughout the experiment.Nevertheless, urinary urea-N excretion in June wasnot affected by feeding treatment. However, in themonths after July, urinary urea-N excretion wasgreater for PRE than for POST, corresponding to thegreater total and herbage N intake for PRE comparedwith POST. These results indicate that in June, but notafter July, feeding NFC supplement before grazingimproved N utilization efficiency by reducing the pro-portion of urinary urea-N excretion to the total Nintake. For cows in the PRE group, degradation of NFCsupplement CHO would synchronize well with the CPdegradation of herbage in the rumen during grazing inJune only.

A peak time of ruminal ammonia-N concentrationfor grazing cows was 2 and 5 h after feeding herbagebecause herbage CP was degraded rapidly in therumen (Holden et al. 1994; Peyraud et al. 1997). Con-sidering the CP degradation pattern of herbage, thepresent study hypothesized that feeding NFC supple-ment 2 h before grazing would synchronize betweenthe degradation of herbage CP and NFC supplementCHO when flaked corn was used as an NFC supple-ment, because the degradation rate of corn CHO is notas fast as the degradation rate of herbage CP (Tam-minga et al. 1990). Conversely, it was hypothesizedthat feeding NFC supplement after grazing would notachieve this synchrony because a lot of ammonia-Nwould already have been absorbed through the rumenwall at the time when cows were fed NFC supplement.

In the present study, the treatment effect dependedon the amount of herbage N intake. Cows ingested Nmainly from herbage in June, and then PRE treatmentimproved N utilization more compared with POSTtreatment. However, after July, and especially afterAugust, N intake from herbage decreased and thatfrom silage increased for cows in both treatments.Although CP content of silage is lower than that ofherbage, the degradation rate of silage CP is as fast as




that of herbage, because the CP of silage had beendegraded to easily degradable fractions by microbesduring storage in the silo (Holden et al. 1994). Forcows in the PRE group, even if NFC supplementationachieved a synchrony between degradation of herbageCP and NFC supplement CHO during grazing, a syn-chrony between degradation of silage CP and NFCsupplement CHO after grazing could not be achieved.Thus, after July, PRE treatment had little effect on Nutilization.

In contrast, for cows in the POST group, the degra-dation of NFC supplement CHO would synchronizewell with the degradation of silage CP in the rumenafter grazing but not with the degradation of herbageCP. When herbage N intake decreased and that fromsilage increased, such as during the months after July,the effect of the PRE treatment did not differ from thatof the POST treatment.

Ruminal microbial protein synthesis was notaffected by feeding treatment throughout the experi-ment, but NFC supplement before grazing decreasedurinary N excretion in June. Theoretically, synchro-nizing the degradation of NFC supplement CHO withdegradation of herbage CP in the rumen of grazingcows reduces urinary urea-N excretion throughincreasing ruminal microbial protein synthesis (Carru-thers & Neil 1997; Bargo et al. 2002). However, littleresearch has been done to show a positive effect ofaltering the timing of NFC supplementation on micro-bial protein synthesis in the rumen (Trevaskis et al.2001). The present study has shown that synchroniz-ing substrates to promote microbial synthesis would bedifferent for each treatment, which synchronizing deg-radation of NFC supplement CHO before grazing withdegradation of herbage CP such as PRE, and synchro-nizing degradation of NFC supplement CHO immedi-ately after grazing with degradation of silage CP suchas POST. A previous study has reported a similarresult, that feeding NFC supplement 2 h before grazingdecreased the proportion of urinary N excretion tototal N intake but did not increase ruminal microbialprotein synthesis compared with feeding NFC supple-ment after grazing (Mitani et al. 2005).

Generally, pasture characteristics change markedlythroughout a grazing season. For example, cows caneat large amounts of herbage high in CP on springpasture but not on summer or autumn pasture.Throughout a grazing season, changing the timing offeeding NFC supplement before or after grazing didnot consistently influence milk production and theefficiency of N utilization, although herbage and silageintake did change. When cows consumed a substantialamount of herbage N, feeding NFC supplement beforegrazing improved N utilization efficiency due to areduction in urinary urea-N excretion. Because chang-ing the supplement feeding procedure may alter the Nsubstrate for microbial protein synthesis, the difference

in feeding timing of NFC supplement in grazingcows would not affect microbial protein synthesis inthe rumen. In order to achieve a high N utilizationefficiency in grazing cows throughout the year, theNFC supplement feeding strategy should be changedin relation to changes in herbage intake or silagesupplementation, or both, as the season progresses.

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Effect of feeding non-fibrous carbohydrate before grazing on intake and nitrogen utilization in dairy cows throughout the grazing season