Acta agriculturae Slovenica, suplement 2 (september 2008), 135–142. 
 
16th Int. Symp. “Animal Science Days”, Strunjan, Slovenia, Sept. 17–19, 2008. 
  
Agris category codes: L50 COBISS Code 1.08 
EFFECT OF FEED PROCESSING ON IN SITU RUMINAL DEGRADATION OF 
CEREAL GRAINS AND ON THE DEGREE OF SYNCHRONY OF ORGANIC 
MATTER AND NITROGEN RELEASE IN THE RUMEN OF GRAZING LACTATING 
DAIRY COWS  
Róbert TÓTHI a), Johannes PIJNENBURG b) and Seerp TAMMINGA b) 
a) Kaposvár University, Faculty of Animal Science, Department of Animal Nutrition, P.O. Box 16, H-7401 
Kaposvár, Hungary 
b) Wageningen Institute of Animal Science, Animal Nutrition Group, Marijkeweg 40, NL-6709 PG Wageningen, 
The Netherlands 
ABSTRACT 
Three rumen-cannulated, lactating Holstein-Friesian cows grazed in a controlled experimental 
pasture and supplemented daily with concentrates were used to measure effects of different heat 
treatment of cereal grains (pelleted barley, toasted barley, pelleted maize, toasted maize) on in 
situ degradability of protein and starch and to estimate of the possible rumen synchrony after 
feeding processed cereal grains as a supplement to perennial ryegrass (Lolium perenne). Pressure 
toasting treatment increased (P < 0.05) the undegradable fraction of DM and OM and tended to 
reduce (P > 0.05) in situ protein degradability of the cereal grains. Undegraded intake protein 
increased (P > 0.05) after pressure toasting from 36.4 to 52.5% for barley and from 50.3 to 
58.2% for maize, respectively. Undegraded intake starch increased (P > 0.05) from 14.9 to 
16.7% after toasting barley and decreased from 36.1 to 31.3% for toasted maize, respectively. 
Pressure toasting reduced washable fractions of each cereal grains for both constituents. The 
fractional rate of degradation of starch increased in maize, but decreased in barley. From the 
calculated synhrony index which describes the synchrony of nitrogen and organic matter 
degradation in the rumen it appears that supplementing grass with processed cereal grains can 
alter microbial growth and efficiency of utilization of nutrients and results in a more 
synchronous substrate for the microbes.  
Key words: cattle / dairy cows / feed processing / barley / maize /grass / in situ ruminal degradation 
VPLIV OBDELAVE KRME NA IN SITU RAZGRADNJO ŽITNIH ZRN V VAMPU IN 
NA STOPNJO SINHRONOSTI RAZGRADNJE ORGANSKE SNOVI IN SPROŠČANJA 
DUŠIKA V VAMPU MOLZNIC NA PAŠI 
IZVLEČEK 
Pri treh črno-belih kravah v laktaciji in s kanilo v vampu na paši na poskusnem pašniku in 
dodatkom dnevne količine močnih krmil smo preučevali vplive različno toplotno obdelanih 
žitnih zrn (peletiran ječmen, pražen ječmen, peletirana koruza, pražena koruza) na in situ 
razgradnjo beljakovin in škroba in na morebitno sinhronost razgradnje v vampu po krmljenju s 
toplotno obdelanimi žitnimi zrni kot dodatkom k ljulki (Lolium perenne). Postopek praženja pod 
pritiskom je povečal (P < 0,05) nerazgradljivo frakcijo suhe snovi in organske snovi ter 
zmanjševal (P > 0,05) in situ razgradnjo beljakovin iz zrnja. Delež nerazgrajenih zaužitih 
beljakovin se je povečal (P > 0,05) po praženju pod pritiskom od 36,4 na 52,5 % pri ječmenu 
oziroma od 50,3 na 58,2 % pri koruzi. Delež nerazgrajenega zaužitega škroba se je povečal 
(P > 0,05) od 14,9 na 16,7 % po krmljenju s praženim ječmenom, oziroma se je zmanjšal od 36,1 
na 31,3 % pri praženi koruzi. Praženje pod pritiskom je znižalo topne frakcije v vseh vrstah žita 
in obeh sestavinah. Frakcijska stopnja razgradnje škroba se je povečala pri koruzi, vendar znižala 
pri ječmenu. Iz izračunanega sinhronega indeksa, ki opisuje sinhronost razgradnje dušika in 
http://aas.bf.uni-lj.si 
Acta agriculturae Slovenica, suplement 2 (september 2008). 
 
136 
organske snovi v vampu, izhaja, da dopolnjevanje trave s toplotno obdelanimi žiti lahko 
spremeni rast mikrobov in učinkovitost porabe hranil, kar se kaže v bolj sinhronem substratu za 
mikrobe. 
Ključne besede: govedo / krave / molznice / krma / predelava / ječmen / koruza / trava / vamp / razgkroj / in situ 
INTRODUCTION 
Fresh grass from intensively fertilized swards contains high concentrations of crude protein, 
of which 70–90% is present as true protein (Tamminga, 1986). It is not only rapidly degraded in 
the rumen, but its extent of degradation is high and often in asynchrony with that of energy 
yielding substrates. Hence, only part is captured by rumen microbes. It is estimated that 45–50% 
of the crude protein ingested with such grass may be lost (Van Vuuren, 1993). This not only 
means a severe loss of protein, but it may have a detrimental impact on the environment and also 
on animals health and reproduction. A possible way to reduce N consumption is to supplement 
fresh grass with concentrates, low in protein but rich in either rapidly degradable structural or 
non-structural carbohydrates (Van Vuuren et al., 1993; Peyraud, 2001). The availability of 
protein and energy may not only be imbalanced on a daily basis, but also within a day because of 
differences in rate of degradation. Maize and barley are sources of readily available energy, but 
their starch degradabilities are very different (Rooney and Plugfelder, 1986). Heat treatments of 
grains affect rumen protein degradability and also affects degradability of cereal starch (Nocek 
and Tamminga, 1991; McAllister et al., 1993; Sauvant et al., 1994; Owens, 2006). The main 
objective of this experiment was to compare the effects of pressure toasted and subsequently 
pelleted and grains which were only pelleted on rumen in situ degradability of protein and starch. 
This could result in a range of supplements differing in rumen degradation rates for energy and 
protein and therefore tailor-made for grasses may differing in quality. It is known that the 
synchronisation of available N and available OM for rumen microbes seems advantageous for an 
optimum N economy of a grazing cow. Therefore the second objective of this study was to 
estimate of the possible rumen synchrony after feeding processed cereal grains as a supplement 
to grazing dairy cows.  
MATERIAL AND METHODS 
Animals and management 
The in situ trial was carried at the experimental farm ‘De Ossekampen’ of Wageningen 
University, The Netherlands. Three multiparous lactating Holstein-Friesian dairy cows fitted 
with a ruminal cannula (10 cm id., Bar-Diamond Inc., Parma, Idaho, USA) were used. At the 
beginning of the experiment the cows produced 31.0 ± 4.3 kg/day milk. The experimental 
animals grazed an experimental pasture and were supplemented daily with two equal proportions 
of 3 kg of a concentrates mixture (1 kg of mixture contained the following ingredients: 250 g 
pelleted barley, 250 g pelleted corn, 250 g toasted barley and 250 g toasted corn. Chemical 
composition of the mixtue was 972 g DM /kg mixture, 982.3 g OM/kg DM, 103.4 g CP/kg DM, 
640.4 g starch/kg DM, 109.2 g NDF/kg DM and 7.9 g ADL/kg DM) fed in the milking parlour 
during milking time (06.30 h and 17.00 h).  
Experimental feedstuffs and grass 
Two cereal grains, that is barley and maize were used in the experiment. The cereals were 
pelleted for 10 s at 80 oC (pelleted barley PB, pelleted maize PM) or pressure toasted for 15 min 
Tóthi, R. et al. Effect of feed processing … cereal grains … in the rumen of grazing lactating dairy cows. 
 
137
at 135 oC (toasted barley TPB, toasted maize TPM) at the Wageningen Feed Processing Centre 
(WFPC). After toasting, the grains were dried in a forced air oven for 16 h at 35 oC, subsequently 
pelleted through a 5 × 65 mm (bore × hole) die. Sward management and perennial ryegrass 
sampling are reported elsewhere (Tóthi et al., 2003). Chemical composition of perennial ryegrass 
(Lolium perenne) are shown in Table 1. 
 
Table 1. Chemical composition and the effect of maturation on washable (W) and undegradable 
fractions (U) and rate of disappearance of the insoluble potentially degradable fraction 
(kd, %/h) of dry matter (DM), organic matter (OM), crude protein (CP), acid detergent 
lignin (ADL) and neutral detergent fibre (NDF) of perennial ryegrass (Lorium 
perenne) (sampled in June 2 to July 31). 
 
Period 1 Period 2 Period 3 Period 4 Period 5 Date of sampling 2–6 June 16–20 June 30 June–4 July 14–18 July 28–31 July 
DM% 23.82 22.82 17.04 16.39 21.78 
kd, %/h 6.9 6.7 6.4 6.0 5.3 
W, % 54.1 46.5 49.9 44.9 44.4 
D, % 17.8 27.8 29.1 31.4 30.4 
U, % 28.1 25.7 21.0 23.7 25.2 
OM, % of DM 91.22 90.82 89.46 89.98 90.24 
kd, %/h 6.1 6.0 5.8 5.4 4.8 
W, % 53.0 45.6 48.0 42.7 42.8 
D, % 18.2 28.3 30.8 33.2 32.3 
U, % 28.8 26.1 21.2 24.1 24.9 
CP, % of DM 15.65 21.07 24.79 23.68 20.41 
kd, %/h 16.8 7.5 6.5 6.1 6.1 
W, % 54.4 55.8 60.5 52.4 49.8 
D, % 24.1 29.2 28.8 34.0 34.0 
U, % 21.5 15.0 10.7 13.6 16.2 
NDF, % of DM 36.09 38.29 37.10 38.2 37.86 
kd, %/h 2.7 5.1 5.9 5.1 4.3 
D, % 59.9 55.9 62.0 59.0 57.2 
U, % 40.1 44.1 38.0 41.0 42.8 
ADL, % of DM 2.17 2.15 1.88 2.02 2.26 
Residue, % of DM 39.48 31.46 27.54 28.1 31.97 
ADL/NDF% 6.0 5.6 5.0 5.3 6.0 
Nylon bag experiments 
Rumen incubations were carried out according to Dutch standard methods (CVB, 1996) and 
nylon bags with a pore size of 40 µm (PA 40/30, Nybolt, Switzerland) were used. The processed 
grain samples were ground through a 3.0 mm sieve (Retsch ZM1 centrifugal mill). The coded 
nylon bags were filled with 5.0 g of DM of cereal grain samples for incubation times of 0, 2, 4, 
8, 24 and 48 h, respectively. After incubation the nylon bags were immediately placed in cold 
water and rinsed with tap water to stop fermentation. The bags were subsequently washed in a 
domestic washing machine for 50 minutes with 70 l of cold water, without centrifugation. After 
this procedure the bags were freeze dried, air equilibrated and weighed. 
Acta agriculturae Slovenica, suplement 2 (september 2008). 
 
138 
Chemical analysis 
All the grain samples were analyzed for DM, ash, crude protein (6.25 × N) and starch 
contents. Prior to analyses, the samples were ground through a 1 mm sieve. All chemical 
analyses were carried out following procedures as described by Tóthi et al. (2003a).  
Calculation of degradabilit 
Crude protein and starch degradation characteristics of processed grains were classified in 
three fractions as described by Tamminga et al. (1994) and Sauvant et al. (1994). Washable 
fraction (W) is readily available measured as the fraction disappearing after washing only (0 h 
incubation). Undegradable fraction (U) is the fraction which will not be degraded, measured as 
100 minus the asymptote of the degradation curve at infinite incubation time. Potentially 
degradable fraction (D) is calculated as D = 100 – W – U. The fractional rate of degradation of 
the D fraction (kd in%/h) was calculated using a first order degradation model, without a lag 
time, as described by Robinson et al. (1986). The fraction of effectively rumen undegraded 
intake starch (%UIS) and rumen undegraded intake protein (%UIP) were also calculated based 
on the following equations (Tamminga et al., 1994). For starch it was assumed that 10% of W 
escapes rumen fermentation and U is 0 (Tamminga et al., 1994). Thus %UIS is 0.1 × W + D × kp 
/ (kd + kp) and %UIP is U + D × kp / (kd + kp).  
Calculation of synhcrony index 
With the calculated grass intake, grain intake (Tóthi et al., 2003a) and in situ degradation 
results of grass (Table 1), processed grains (Table 2) and rumen content (Tóthi et al., 
unpublished data) we estimated on an hourly basis, the degradation of OM and N for over 24 
hours. The patterns of the first grazing event is based on our own observations and more 
information for the later hours was adapted from other work about grazing behaviour of dairy 
cows (Rook et al., 1994; Gibb et al., 1997, 1998, 2002; Orr et al., 2001). The synchrony index 
(IS) which describes the synchrony of nitrogen and organic matter degradation in the rumen was 
calculated according to an equation similar to the one proposed by Sinclair et al. (1993).  
25
24
N/OM)²hourly  - (25
25
121
∑
−
−
=SI  
where 25 = 25 g N/kg OM truly digested in the rumen which was assumed to be the optimal ratio 
(Czerkawski, 1996). An IS of 1.0 represents perfect synchrony between nitrogen and energy 
supply throughout the day whilst values less than 1.0 indicate the degree of asynchrony (Sinclair 
et al., 1993). The supply of N and OM was calculated from the sum of the hourly degradation 
and the ratio of N to OM calculated. Statistical analysis. Variance analyses were performed with 
GLM procedure in the Statistical Analysis System (SAS, 2001) with treatment and cow included 
in the model. Significance was declared when P < 0.05. 
RESULTS AND DISCUSSION 
Rumen degradability of processed cereal grains.  
DM, OM, CP and starch degradation characteristics are presented in Table 2. No effect of 
pressure toasting treatment was observed on effective dry matter degradability in barley or in 
Tóthi, R. et al. Effect of feed processing … cereal grains … in the rumen of grazing lactating dairy cows. 
 
139
maize. Hovewer the washable DM fraction significantly (P < 0.001) decreased in barley by 7.2% 
and in maize by 6.8% units while the degradable DM fraction significantly increased in barley 
by 5.8% units (P < 0.001). The size of the undegradable DM fraction was significantly elevated 
by toasting in maize. Pressure toasting elevated OMD by 5.4% units in barley (P < 0.05). 
Undegraded intake protein increased (P > 0.05) after toasting from 36.4 to 52.5% for barley and 
from 50.3 to 58.2% for maize, respectively. Undegraded intake starch increased (P > 0.05) from 
14.9 to 16.7% after toasting barley and decreased from 36.1 to 31.3% for toasted maize, 
respectively. The fractional rate of degradation (kd) of protein decreased, while the kd of starch 
increased for maize and decreased for barley. Pressure toasting increased the degradable starch 
fraction in barley and maize as well (P < 0.05). The effect of pressure toasting on the decreased 
W and the increased UIS% may have been related to the change in starch distribution over the 
different particle size classes after pressure toasting. The crystallization of gelatinized starch 
molecules, i.e. retrogradation has received considerable attention because after retrogradation it 
is difficult to solubilize and this may decrease W as well.  
 
15
20
25
30
35
40
45
7:00 10:00 13:00 16:00 19:00 22:00 1:00 4:00 7:00
Time (h)
R
at
io
 N
:O
M
NS PB TPB PM TPM
 
Figure 1. Predicted ratio of nitrogen to organic matter degraded in the rumen of non 
supplemented (NS) and supplemented dairy cows. Supplement (6 kg per day) 
consumed two equal meals per day, times of supplement feeding are indicated by the 
arrows. For abbreviations see Table 2. 
 
NS 
Acta agriculturae Slovenica, suplement 2 (september 2008). 
 
140 
Table 2. Chemical composition of the processed grains 1 and in sacco rumen degradation 
characteristics 2 of dry matter (DM), organic matter (OM), crude protein (CP), and 
starch 
 
 Barley grain  Maize grain P 3 
 PB TPB  PM TPM SEM G H GxH 
DM, % 97.2 97.3  97.1 97.2     
W, % 45.9 a 38.7 b  36.6 c 29.8 d 0.41 <0.001 <0.001 NS 
D, % 40.8 a 46.6 b  52.9 c 56.4 c 0.56 <0.001 <0.001 NS 
U, % 13.3 a 14.7 b  10.5 b 13.8 a 0.56 <0.05 <0.05 <0.05 
kd , %/h 18.0 a 15.3 a  4.9 b 6.0 b 2.14 <0.05 NS <0.05 
EDMD, % 76.5 a 72.3 a  60.5 b 58.0 b 2.75 <0.05 NS NS 
OM, % of DM 97.8 97.9  98.7 98.6     
W, % 51.1 44.3  42.3 38.1 0.35 NS NS NS 
D, % 35.8 a 41.2 b  47.4 c 48.3 c 0.59 <0.001 <0.05 <0.05 
U, % 13.1 a 14.5 a  10.3 b 13.6 a 0.58 <0.05 <0.05 <0.05 
kd , %/h 17.8 a 15.3 a  4.8 b 5.9 b 2.16 <0.05 NS NS 
EOMD, % 77.9 a 74.0 a  63.4 b 62.0 b 2.92 <0.05 NS NS 
CP, % of DM 11.5 11.4  9.2 9.3     
W, % 35.5 27.5  34.9 32.4 4.12 NS NS NS 
D, % 59.0 69.2  63.8 64.1 4.24 NS NS NS 
U, % 5.4 3.3  1.3 3.5 4.2 NS NS NS 
kd , %/h 5.5 2.4  1.8 1.0 1.2 NS NS NS 
% UIP 36.4 52.5  50.3 58.2 3.60 NS NS NS 
ECPD, % 48.6 47.5  49.7 41.8 4.32 NS NS NS 
Starch, % of DM 57.2 59.7  68.3 71.0     
W, % 57.0 a 49.5 b  39.6 c 35.0 d 1.26 <0.05 <0.05 <0.05 
D, % 43.0 a 50.5 b  60.4 c 65.0 d 1.33 <0.05 <0.05 <0.05 
kd , %/h 20.6 a 19.0 a  4.8 b 6.6 b 2.53 0.012 NS 0.04 
% UIS 14.9 a 16.7 a  36.1 b 31.3 b 2.12 <0.05 NS NS 
ESD, % 88.6 a 86.7 a  65.0 b 65.7 b 2.27 <0.05 NS NS 
1 PB = pelleted barley, TPB = toasted and pelleted barley, PM = pelleted maize, TPM = toasted and pelleted maize. 
2 W = washable fraction; U = undegradable fraction; D = not soluble, but potentially degradable fraction; kd the 
fractional rate of degradation of D fraction; UIP = rumen undegraded intake protein, calculated for a passage rate of 
6%/h., UIS = rumen undegraded intake starch, calculated for a passage rate of 6%/h., EDMD, EOMD, ECPD,ESD = 
effective degradability of dry matter, organic matter, crude protein, or starch = W + D × kd / (kd – kp). 
3 = G = effect of type of grain, H = effect of type of heat, GxH = effect of grain type and heat interaction.  
a,b,c,d figures with different superscript in the same row differ significantly, NS = not significant (P > 0.05) 
Effect of feed intake on the synchronisation level 
The predicted hourly ratio of N to OM degraded in the rumen throughout the day in the 
paddock-grazing system where the dairy cows were given their daily pasture allocation after the 
morning milking, is illustrated in Fig. 1. As could be expected the non supplemented animals 
(NS) have a higher N to OM ratio throughout the day than the supplemented animals. The high 
concentrations of ammonia in the rumen (Tóthi et al., 2003) and the calculated synchrony index 
(Is = 0.37, for 24 h) indicate a high degree of asynchrony and a substantial degradation of protein 
in the rumen. Compared with the non supplemented diet, supplementation with 6.0 kg of 
processed cereal grains fed in two equal amounts per day in the milking parlour during milking 
results in a lower ratio of N to OM release in the rumen during the day. In the morning, after 
feeding 3 kg of concentrates, the easily available fraction of cereal starch increases the OM 
Tóthi, R. et al. Effect of feed processing … cereal grains … in the rumen of grazing lactating dairy cows. 
 
141
release in the rumen, therefore the N to OM ratio drops. The first two active grazing hours after 
milking result in a fast rate of release of herbage nitrogen compared with the release of OM. The 
ruminal degradation of processed cereals is quite intensive a few hours after feeding and this 
may result in high amounts of OM available for the microbes and higher propionate and butyrate 
concentrations (Tóthi et al., 2007) and VFA productions than with NS. In the milking parlour at 
the evening milking time the dairy cows receive the second part (3 kg) of their concentrate meal. 
In the rumen starch from the morning feeding is still present, because until this time point around 
80% of the starch from barley had disappeared and 30 to 35% of the starch from maize. 
However, the drop in N to OM ratio is smaller than the observed fall in the morning. The reason 
may be the degradation of protein from the cereal grains, which also elevate the N pool in the 
rumen. In the first hours of the second large grazing event in the afternoon, the available N and 
OM for the microbes seems more synchronised than in the morning grazing event. The 
synchrony index is highest in dairy cows supplemented with pelleted maize (IS = 0.93) than with 
toasted and pelleted maize ((IS = 0.87) and with barley supplements (pelleted barley nad toated 
and pelleted barley IS = 0.84 and 0.86, respectively). The starch disappearance of barley is 
higher than that of maize, which synchronises the rumen shortly after the feeding but the starch 
release from the lower amount of barley during the day does not provide a sufficient balance of 
protein and energy for the microbes. 
CONCLUSIONS 
The rate of crude protein degradation of ryegrass is relatively high, thus for better microbial 
availability of protein and energy the supplement should have a rate of starch fermentation at 
least as fast as that of the CP of the grass. The effect of toasting in this respect is favorably than 
pelleting alone, because this heat treatment decreased the rate of degradation of barley starch but 
increased the rate of degradation of maize starch. Pressure toasting increased the undegradable 
fraction of DM and OM in barley and maize compared to pelleting alone. Therefore further 
research will have to concentrate on the question which chemical compound(s) give a reaction 
when grains are pressure toasted. From the calculated synchrony indexes it appears that 
supplementing grass with processed cereal grains can alter microbial growth and efficiency of 
utilization of nutrients and results in a more synchronous substrate for the microbes.  
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