Effect of fiber content of roughage on energy cost of eating and rumination in Holstein cows

Animal Feed Science and Technology 196 (2014) 42–49

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Effect of fiber content of roughage on energy cost of eating and rumination in Holstein cows Tomoyuki Suzuki a,∗ , Yuko Kamiya a , Masahito Tanaka a , Ikuo Hattori a , Takeo Sakaigaichi b , Takayoshi Terauchi b , Itoko Nonaka a , Fuminori Terada c a Livestock and Grassland Research Division, NARO Kyushu Okinawa Agricultural Research Center, 2421 Suya, Koushi, Kumamoto 861-1192, Japan b Crop and Agribusiness Research Division, NARO Kyushu Okinawa Agricultural Research Center, 1742-1 Anno, Nishinoomote, Kagoshima 891-3102, Japan c NARO Institute of Livestock and Grassland Science, 2 Ikenodai, Tsukuba, Ibaraki 305-0901, Japan

a r t i c l e

i n f o

Article history: Received 12 August 2012 Received in revised form 3 June 2014 Accepted 17 July 2014 Keywords: Cow Eating Energy cost Fiber content Roughage Rumination

a b s t r a c t The effect of the fiber content of roughage on energy cost of chewing was determined by indirect calorimetry. Four Holstein non lactating cows [779 ± 71 kg body weight (BW)] were used in a cross over design with 14-day periods. Two cows were fed sugarcane silage as high fiber roughage (HF) and the other two cows were fed oaten hay as low fiber roughage (LF), along with soybean meal [0.5 g/kg BW on a dry matter (DM) basis]. The aNDFom and peNDF contents were different (718 vs. 542 g/kg DM and 554 vs. 402 g/kg DM, respectively), whereas the physical effectiveness factors (pef) was similar between sugarcane silage and oaten hay (771 vs. 741 g/kg DM). The study was performed in open circuit respiration chambers over a 14-day period, consisting of a 9-day adaptation and a 5-day energy balance measurements. Energy cost of chewing per minute was determined using a multiple linear regression model, with heat production per 10 min as the dependent variable and duration of activities per 10 min as independent variables. DM intake (DMI) of roughage in HF was lower than that in LF (5.46 vs. 9.79 kg/day; P=0.006), whereas duration in total chewing (Eating + rumination) was higher for HF than for LF (120 vs. 77 min/kg DMI; P=0.006). Energy cost of rumination per unit DMI tended to be higher for HF than for LF (0.71 vs. 0.48 MJ/kg DMI, P=0.062), whereas energy cost of each eating and rumination per unit time was similar between treatments (17.7 vs. 18.4 J/min/kg BW for eating, P=0.272; 12.0 vs. 12.7 J/min/kg BW for rumination, P=0.285). Energy cost of total chewing per unit metabolizable energy (ME) was higher for HF than that for LF (14.3 vs. 9.0 MJ/100 MJ ME, P=0.009). These results indicate that fiber content in roughage possibly affects energy cost of chewing per DMI and consequently results in loss of ME available for production. © 2014 Elsevier B.V. All rights reserved.

Abbreviations: ADFom, acid detergent fiber expressed exclusive of residual ash; aNDFom, neutral detergent fiber assayed with ␣-amylase and expressed exclusive of residual ash; BW, body weight; CP, crude protein; DEI, digestible energy intake; DM, dry matter; DMI, DM intake; GE, gross energy; HF, high fiber roughage; HP, heat production; LF, low fiber roughage; Lignin(sa), lignin determined by solubilization of cellulose with sulfuric acid; ME, metabolizable energy; MEI, ME intake; peNDF, physically effective NDF; pef, physical effectiveness factors. ∗ Corresponding author at: Present address: Japan International Research Center for Agricultural Sciences, 1-1 Ohwashi, Tsukuba, Ibaraki, 305-8686, Japan. Tel.: +81 29 838 6313: fax: +81 29 838 6316. E-mail address: [email protected] (T. Suzuki). http://dx.doi.org/10.1016/j.anifeedsci.2014.07.005 0377-8401/© 2014 Elsevier B.V. All rights reserved.

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1. Introduction In ruminants, the physical properties of feed affect intake and chewing activity as well as salivary secretion that have a buffering effect in the rumen. Lack of physical properties, such as short particles or low fibrousness, results in rumen acidosis, inhibition of milk fat synthesis, and disorders in cows. Fiber content (Waldo, 1986; Mertens, 1997), roughage value index (Sudweeks et al., 1981), or physically effective neutral detergent fiber (peNDF; Mertens, 1997) are generally used to evaluate the physical properties of feed. It is known that the energy cost of eating is affected by acid detergent fiber (ADF) or acid detergent lignin (ADL) content (Lachica et al., 1997) and by roughage species (Adam et al., 1984; Lachica et al., 1997; Susenbeth et al., 2004). Thus, the energy cost of chewing might also be available as an index of the physical properties of feed. Susenbeth et al. (1998, 2004) reported that the proportion of energy cost of chewing to metabolizable energy intake (MEI) differed with the roughage species, and it was in the range of 6–9 MJ/100 MJ MEI for eating, and estimated at 2–5 MJ/100 MJ MEI for rumination. Therefore, ME loss caused by chewing has some effect on animal productivity. There is very little information on energy cost of rumination compared to that during eating, especially in cattle (Susenbeth et al., 1998). The most of studies determined the energy cost of chewing as the difference between heat production (HP) during chewing and HP during no chewing using indirect calorimetry. Eating generally occurs at feeding in a standing position, but rumination occurs either in standing or lying throughout the day. Energy cost also depends on the position of the cow, and HP while standing is 1.19 times as high as that while lying (Susenbeth et al., 2004). The lack of data on rumination is primarily due to the difficulty in controlling the rumination and the position of an animal. Suzuki et al. (2012) suggested calculation of HP with respective activities using multiple linear regression model including HP per unit time as dependent variable, and duration of eating, rumination and standing per unit time as independent valuables. There is a possibility to evaluate the effect of feed on energy cost of chewing using this multiple regression model. The objective of this study was to investigate the effect of fiber content, which is one of the factors affecting physical properties, on energy cost of chewing in cows fed roughage with high fiber (HF) content (sugarcane silage) or low fiber (LF) content (oaten hay), by using multiple regression model. 2. Materials and methods 2.1. Feed preparation Sugarcane (KRFo93-1) developed for animal feed (Suzuki et al., 2010) and oaten hay were used in this study. The sugarcane was harvested at 4 months after regrowth and chopped at a theoretically cutting length of 9 mm (MCH2830; IHI STAR Machinery Co. Ltd., Hokkaido, Japan). It was baled using a round bailer (TSB1000; IHI STAR Machinery Co. Ltd.), wrapped (MWM1060 W; IHI STAR Machinery Co. Ltd.), and stored for about 4 months until the animal trial. Oaten hay was chopped at a theoretically cutting length of 50 mm using a chopping machine (KEIYO Machinery Co. Ltd., Chiba, Japan). 2.2. Animals and experimental design Four non lactating Holstein cows averaging 779 ± 71 kg in body weight (BW) and fitted with ruminal canula were randomly divided into two groups in a cross over design. Two cows were fed the sugarcane silage as HF roughage, and the other two cows were fed the oaten hay as LF roughage. Each experimental period consisted of 14 days, with the first 9 days for feed adaptation and the last 5 days for the energy and nutrient balance measurements. Experimental cows were housed individually in open circuit respiration chambers (Suzuki et al., 2012) throughout the experiments, whereas the doors of chambers were kept open during 9 day of adaptation period. The cows were fed roughage at 1.1 times of the previous day’s intake, and were also fed soybean meal at 0.5 g/kg BW on a dry matter (DM) basis. One third of the daily feed was provided at 11:00 h and the remainder at 18:00 h. Water and mineral salt block (E100TZ; Nippon Zenyaku Kogyo Co. Ltd., Fukushima, Japan) were freely accessed. This experiment was approved by the Animal Care Committee of the NARO Kyushu Okinawa Agricultural Research Center (KARC). 2.3. Sample and data collection The amount of orts was recorded at 10:30 h. During the balance measurements, orts, urine, and feces were collected and weighed at 10:30 h, and their constant aliquot were combined into one sample at each period. Portions of the feed samples were kept in a refrigerator at 5 ◦ C, and the remaining portions and orts and fecal samples were dried in a 55 ◦ C forced air oven for 72 h and then ground in a mill (1 mm; P-15; FRITSCH, Idar-Oberstein, Germany) for chemical analysis. A filtered extract of sugarcane silage was prepared from a mixture of sugarcane silage (25 g) and distilled water (100 mL) that was stored at 5 ◦ C overnight. The extract was kept at −20 ◦ C until analysis of fermentation quality. Body weights of experimental cows were measured at 10:30 h on days 9 and 14. Ruminal liquor was collected at 11:00 h of day 14 and was filtered immediately through 8 layers of gauze. The pH of the filtered ruminal liquor was determined immediately using a pH meter (PH82; Yokogawa Electric Co., Tokyo, Japan). The ruminal liquor was centrifuged (1940 × g, 15 min, 4 ◦ C) and then kept at −20 ◦ C for further analysis.

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T. Suzuki et al. / Animal Feed Science and Technology 196 (2014) 42–49

Oxygen (O2 ) consumption and carbon dioxide (CO2 ) and methane (CH4 ) production were measured from 11:00 h until to 10:30 h of the following day throughout the 5-day balance measurement period. The air temperature, humidity, and air exchange rate in the chambers were adjusted 20 ◦ C, 60%, and 470 L/min, respectively. The concentrations of gases from each chamber and in the ambient air were measured each 4.5 min using O2 (4100; Servomex Ltd., Crowborough, UK), CO2 (VIA510; HORIBA Ltd., Kyoto, Japan), and CH4 (VIA510; HORIBA Ltd.) analyzers. Gas concentrations were calculated in 1-min intervals. The air flow rate from each chamber was measured in 1-min intervals using a gas flow meters (EJ110; Yokogawa Electric Co.), and the measurements were corrected to the conditions 0% humidity, 0 ◦ C, and 1 atm barometric pressure. Periodic (1-min intervals) gas metabolisms, including O2 consumption and CO2 and CH4 production, were calculated according to the fast response algorithm of McLean and Watts (1976). Daily gas metabolisms were calculated from multiplication of total volume of each gas during measurement by 24/23.5. Daily HP was calculated according to an equation by Brower (1965). The oxyenergetic equivalent was calculated from the daily HP and daily O2 consumption of each cow in each period. Periodic (1-min intervals) HP was calculated by multiplying the periodic O2 consumption by the oxyenergetic equivalent. To determine the standing time and position changes of the cows, their positions were detected continuously by photoelectronic sensors (E3S-CD12; OMRON Co., Kyoto, Japan). Chewing activity was monitored and recorded at 0.5 s intervals using a network camera (BB-HCM311; Panasonic Co., Osaka, Japan). The chewing activity was classified into eating, rumination, or other chewing activities consisting of grooming, licking, and drinking. Each chewing activity was classified at 10-s intervals, and that less than 1 min was assumed to persist for the entire 1 min. When several activities were observed in 1 min, predominant activity was assumed to persist for the entire 1 min. The time spent total chewing was defined as sum of time spent eating and rumination. 2.4. Chemical and particle size analysis The DM, crude ash, and ether extract of the dried feed, orts, and fecal samples were determined according to methods 930.15, 9442.05, and 920.39 of AOAC (2000), respectively. The neutral detergent fiber exclusive of residual ash without inclusion of sodium sulfite (aNDFom) of the dried samples was determined according to the method of Van Soest et al. (1991). The samples for aNDFom assays were pre-digested with amylase solution at 38 ◦ C for 16 h. The acid detergent fiber exclusive of residual ash (ADFom) and lignin determined by solubilization of cellulose with sulfuric acid [Lignin(sa)] of the dried samples were determined according to the method of Robertson and Van Soest (1981). The crude protein (CP) of the dried feed and fresh urine was determined according to method 976.05 of AOAC (2000). The gross energy of the dried feed, orts, and feces, and freeze dried urine was determined using a bomb calorimeter (CA-4PJ; Shimadzu Co., Kyoto, Japan). The volatile fatty acid (VFA) composition of the ruminal liquor was analyzed using a gas chromatograph (Hewlett–Packard 6890, Wilmington, DE, USA). The pH and organic acid composition of the silage extract were measured using the pH meter and an HPLC (LC-20000; JASCO Co., Tokyo, Japan), respectively. The fermentation quality of the silage was evaluated using Flieg’s score, which is calculated by sum of the points based on the weight percentage of lactic, acetic + propionic, and butyric + valeric + capronic acids (Ohyama and Shirata, 1972), Flieg’s score ranges 0–100 and correlates positively with the intake and digestibility of silages (McCullough, 1978). The particle size distribution of the feeds was determined using a wet sieve shaker (AS200; Retsch GmbH, Haan, Germany) with a stack of sieves (pore sizes 13.20, 6.70, 4.75, 2.36, 1.18, 0.60, 0.30, and 0.15 mm). Quadruplicate samples of approximately 12 g of feed were shaken for 20 min with a constant vibration amplitude (0.8 mm). Particles remaining on each sieve or escaping from the 0.15-mm sieve were filtered onto a pre-weighed screen (pore size 55 ␮m), dried at 105 ◦ C for 3 h following 55 ◦ C air forced drying for 24 h, and weighed. Physical effectiveness factors (pef) were calculated as the sum of the DM (g) retained on the upper 5 sieves (pore size ≥1.18 mm) per feed DM (kg). Physically effective NDF (peNDF) was determined by multiplying the aNDFom content by pef. 2.5. Calculation and statistical analysis The apparent digestibilities for nutrients were calculated by the following formula: (nutrient consumed − nutrient in feces)/nutrient consumed. The digestible energy intake (DEI) was calculated by gross energy intake less energy lost in feces. The MEI was calculated by DEI less energy lost in urine and methane. The energy balance was calculated by ME less HP. To determine the energy cost of activities, 8 datasets (2 treatments×4 cows) including HP, time spent chewing activities, and time spent standing recorded in 1-min intervals were converted to datasets in 10-min intervals. Each dataset was adapted to the multiple linear regression model using procedure REG of SAS (2004), as follows: Y = aX1 + bX2 + cX3 + dX4 + eX5 + f where Y is HP (kJ/10 min); X1 is time spent eating (min/10 min); X2 is time spent rumination (min/10 min); X3 is time spent chewing excluding eating and rumination, i.e., grooming, mineral block licking, or water drinking (min/10 min); X4 is time spent standing (min/10 min); X5 is no. of posture changes (no./10 min); a, b, c, d, and e are regression coefficients that represent the energy cost of eating (kJ/min), rumination (kJ/min), chewing excluding eating and rumination (kJ/min), standing (kJ/min), and position change (kJ/no.), respectively; and f is the intercept that represents HP during lying with no

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Table 1 Physical effectiveness factors (pef), chemical composition, and energy content of experimental feeds. Sugarcane silage

Oaten hay

Soybean meal

pef (g/kg)a

771

741

538

Chemical composition (g/kg DM) Crude ash EE CP aNDFom peNDFb ADFom Lignin(sa)

94 17 36 718 554 445 58

50 16 62 542 402 285 29

67 19 496 131 71 106 4

GE (MJ/kg DM)

17.7

18.3

19.8

DM, dry matter; EE, ether extract; CP, crude protein; aNDFom, neutral detergent fiber assayed with amylase and expressed exclusive of residual ash; peNDF, physically effective NDF; ADFom, acid detergent fiber expressed exclusive of residual ash; Lignin(sa), lignin determined by solubilization of cellulose with sulfuric acid; GE, gross energy. a Sum of the dry matters retained on 13.20-, 6.70-, 4.75-, 2.36-, and 1.18-mm sieves per feed dry matter. b Determined as aNDFom content of feed multiplied by pef.

chewing activity (kJ/10 min), i.e. HP during resting. Position changes were counted when the animal changed position from lying to standing or from standing to lying. All data were analyzed with the procedure GLM of SAS (2004) according to the model: Yijk =  + Fi + Aj + Pk + eijk where Y is the observed value,  is the mean, F is the effect of feed (i = 1–2), A is the effect of the animal (j = 1–4), P is the effect of the experimental period (k = 1–2), and e is the residual error. For comparison between eating and rumination, data on energy cost of chewing per minute was also analyzed for each treatment using the procedure GLM (SAS, 2004) according to the following model: Yij =  + Ci + Aj + eij where Y is the observed value,  is the mean, C is the effect of the chewing type (i = 1–2; 1 and 2 represent eating and rumination, respectively), A is the effect of the animal (j = 1–4), and e is the residual error. Significance was declared at P<0.05, and a trend was accepted at 0.05≤P<0.10, unless otherwise stated. 3. Results 3.1. Feed composition The pH, DM content, and DM based concentrations of lactic, acetic, propionic, and butyric acids of sugarcane silage were 3.49, 216.5 g/kg, 79.8 g/kg, 11.2 g/kg, 0.0 g/kg, and 0.0 g/kg, respectively. The Flieg’s score of sugarcane silage was 100 that means the highest quality (McCullough, 1978). The aNDFom, ADFom, and Lignin(sa) contents of the sugarcane silage were higher than those of oaten hay, whereas the CP and gross energy contents of the sugarcane silage were lower than those of the oaten hay (Table 1). These characteristics of sugarcane were also observed by Suzuki et al. (2010). The pef of the sugarcane silage was similar to that of the oaten hay. The peNDF content of the sugarcane silage was higher than that of the oaten hay because of the higher aNDFom content of sugarcane silage. 3.2. Intake, digestibility, ruminal profile and energy utilization The lower DM intake (DMI) of roughage in HF compared with that in LF reflected in the lower aNDFom, ADFom, peNDF, DEI and MEI, and reflected in tendency of lower total ruminal VFA concentration in HF (Table 2). The daily HP of HF was lower than that of LF. The energy balance of HF was negative and lower than that of LF. The apparent aNDFom and ADFom digestibilities of HF were numerically higher than those of LF, whereas the apparent DM digestibility of HF was similar to that of LF. 3.3. Time spent eating and rumination Daily time spent rumination of HF was similar to that of LF, whereas time spent rumination per DMI was higher for HF than for LF (Table 3). Time spent in total chewing, consisting of time spent eating plus time spent rumination, per DMI for HF was higher than for LF.

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Table 2 Body weight, nutrient and energy intake, heat production (HP), energy balance, apparent digestibility, and ruminal profile of cows fed high fiber roughage (HF) or low fiber roughage (LF).

Body weight (kg)

HF

LF

SEM

P

754.9

774.4

7.4

0.202

Dry matter intake Roughage (kg/day) Soybean meal (kg/day)

5.06 0.38

9.40 0.37

0.24 0.00

0.006 0.078

Nutrient intake DM (kg/day) aNDFom (kg/day) ADFom (kg/day) Lignin(sa) (kg/day) peNDF (kg/day)

5.46 3.70 2.30 0.28 3.08

9.79 5.06 2.67 0.25 4.13

0.24 0.03 0.02 0.01 0.01

0.006 0.001 0.008 0.165 <0.001

DE intake (kJ/day/kg BW) ME intake (kJ/day/kg BW) HP (kJ/day/kg BW) Energy balance (kJ/day/kg BW)

72.7 60.9 83.2 −22.3

Apparent digestibility DM aNDFom ADFom Ruminal pH Ruminal VFA Total (mmol/L) Acetic (mol/mol total VFA) Propionic (mol/mol total VFA) Acetic to propionic ratio

138.0 118.8 105.6 13.2

2.7 2.9 0.6 3.1

0.003 0.005 0.001 0.015

0.569 0.576 0.580 7.18

0.586 0.470 0.454 7.10

0.012 0.027 0.038 0.03

0.438 0.110 0.145 0.209

53.7 0.715 0.203 3.55

74.4 0.707 0.169 4.25

4.4 0.006 0.003 0.17

0.081 0.486 0.018 0.096

SEM, standard error of the mean where n = 4 per treatment; DM, dry matter; aNDFom, neutral detergent fiber assayed with amylase and expressed exclusive of residual ash; peNDF, physically effective NDF; ADFom, acid detergent fiber expressed exclusive of residual ash; Lignin(sa), Lignin determined by solubilization of cellulose with sulfuric acid; DE, digestible energy; ME, metabolizable energy; BW, body weight; VFA, volatile fatty acid.

Table 3 Time spent in eating, rumination, and total chewing (eating + rumination) of cows fed high fiber roughage (HF) or low fiber roughage (LF). Activity

HF

LF

SEM

P

Eating min/day min/kg DMI

207.5 39.4

257.4 26.5

12.2 3.4

0.102 0.117

Rumination min/day min/kg DMI

432.4 80.2

478.3 50.2

30.7 1.3

0.401 0.004

Total chewing min/day min/kg DMI

639.9 119.6

735.7 76.7

19.9 2.4

0.076 0.006

SEM, standard error of the mean where n = 4 per treatment; DMI, dry matter intake.

3.4. Energy cost of activities Mean adjusted R2 of eight multiple regression models (2 treatments×4 cows) was 0.70 ± 0.05 (mean ± SE), and P values of those models were under 0.001. Additionally, P values of all coefficients and intercept in those eight multiple regression models were under 0.001. HP per unit time during resting and energy costs of activities per unit time or per unit activity determined by the multiple regression models were shown in Table 4. HP per unit time during resting was higher for LF than for HF. Other parameters showed no significant differences between treatments. Energy cost of eating per unit time tended to be higher than that of rumination for both HF and LF (P=0.10 and P=0.06, respectively). In the present study, energy costs of eating and standing per unit time, were close to the observed values in cattle (Susenbeth et al., 2004). The energy cost of position change averaged over treatments was 56 J/kg BW. This value was rather similar to the energy cost of rising to a standing position for cattle and for sheep (52 and 47 J/kg BW, respectively; Toutain et al., 1977). Daily energy costs of eating and total chewing were lower for HF than for LF, whereas that of rumination was similar between treatments (Table 5). The proportion of daily energy cost of chewing to daily HP was not affected by the treatments, regardless of the type of chewing. The daily energy cost of total chewing pooled with treatments accounted for 10 MJ/100 MJ

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Table 4 Heat production (HP) during resting per unit time, and energy costs of activities per unit time or per unit activity in cows fed high fiber roughage (HF) or low fiber roughage (LF). Present study

Literature value

HF

LF

SEM

P

Mean ± SE

HP during resting (J/min/kg BW)a

46.5

60.3

0.9

0.009

50.9 ± 1.3b

Energy cost of activity Eating (J/min/kg BW) Rumination (J/min/kg BW) Chewing excluding eating and rumination (J/min/kg BW) Standing (J/min/kg BW) Position change (J/kg BW)

17.7 12.0 16.6 8.4 53.5

18.4 12.7 15.6 7.4 59.1

0.3 0.4 1.8 1.0 5.6

0.272 0.285 0.715 0.534 0.553

20 ± 3b 8.9 (8.0–9.3d )c – 9.7 ± 2.0b –

SEM, standard error of the mean where n = 4 per treatment; BW, body weight. a HP during lying without chewing. b Data from Susenbeth et al. (2004). c Data from Susenbeth et al. (1998). d Minimum and maximum values. Table 5 Daily energy costs of eating, rumination, and total chewing (eating + rumination) in cows fed high fiber roughage (HF) or low fiber roughage (LF). Activity

HF

LF

SEM

P

Eating MJ/day MJ/100 MJ HP MJ/100 MJ MEI MJ/kg DMI

2.59 4.22 5.90 0.50

3.43 4.27 3.85 0.36

0.10 0.15 0.41 0.04

0.025 0.832 0.071 0.119

Rumination MJ/day MJ/100 MJ HP MJ/100 MJ MEI MJ/kg DMI

3.94 6.23 8.38 0.71

4.56 5.70 5.15 0.48

0.32 0.60 0.60 0.04

0.299 0.598 0.064 0.062

Total chewing MJ/day MJ/100 MJ HP MJ/100 MJ MEI MJ/kg DMI

6.53 10.45 14.28 1.21

7.99 9.97 9.00 0.83

0.22 0.47 0.35 0.01

0.043 0.545 0.009 0.003

SEM, standard error of the mean where n = 4 per treatment; HP, heat production; MEI, metabolizable energy intake; DMI, dry matter intake.

of daily HP. Energy cost of rumination per DMI tended to be higher for HF than for LF and that of total chewing per MEI and per DMI was also higher for HF. 4. Discussion 4.1. Intake Nørgaard et al. (2011) summarized literature values of intake, in which DMI per BW ranged 10.7–38.9 g/kg and forage NDF intake per BW ranged 4.7–10.8 g/kg, both for cattle fed hay or silage with or without concentrate. The DM and aNDFom intakes of LF (12.6 g/kg BW and 6.5 g/kg BW, respectively) were in those ranges. The DMI per BW of HF (7.2 g/kg) was lower than the summarized values, whereas forage aNDFom intake per BW of HF (4.8 g/kg) was in the range. It has been reported negative correlation between NDF content and DMI in steers or heifers fed silage (Waldo, 1986) and in lactating cows fed total mixed ration (Tafaj et al., 2007). It is therefore considered that lower DMI of HF rather than literature values was due to the higher aNDFom content of roughage in HF. The MEI of HF (319 kJ/kg of metabolic BW) was lower than ME requirement for maintenance calculated using Japan feeding standard for daily cattle (435 kJ/kg of metabolic BW; NARO, 2007), whereas the MEI of LF (626 kJ/kg of metabolic BW) was higher than the maintenance requirement. The CP intake of HF and LF were 378 g/day and 770 g/day, respectively, whereas the CP requirements of cows in these treatments according to Japan feeding standard for dairy cattle (NARO, 2007) were 648 and 661 g/day, respectively. Meanwhile, NDFom and ADFom digestibilities and total chewing time per DMI were higher for HF than LF. These results indicate that nitrogen supply, including feed nitrogen and recycling nitrogen, for rumen microbes in HF was not insufficient. Therefore, the lower MEI of HF compared with LF was considered to result from the lower DMI (Table 2), but not from the lower nitrogen intake. The efficiency of ME utilization would differ between treatments. Meanwhile, because the oxyenergetic equivalent was calculated in each cattle at each treatment, energy costs of activities are considered to be comparable between treatments without the effects of MEI and ME utilization efficiency.

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4.2. HP during resting HP per unit time during resting is considered to mainly consist of basal metabolism and heat increments of nutrient digestion and metabolism (Table 4). When the basal metabolism is estimated to 335 kJ/day/kg of metabolic BW according to Japan feeding standard for dairy cattle (NARO, 2007), the basal metabolism per unit time in HF and LF are 44.4 and 44.1 J/min/kg BW, respectively, and the heat increments of nutrient digestion and metabolism in HF and LF are consequently estimated 2.1 and 16.2 J/min/kg BW, respectively. Therefore, this higher HP during resting in LF than HF due to a higher MEI (Table 2).

4.3. Eating vs. rumination The energy cost of eating per unit time tended to be higher than that of rumination, for both treatments (Table 4). This difference in energy cost between eating and rumination could be mainly caused by differences in chewing manner that is affected by bolus size in the mouth (Ulyatt et al., 1986), and physical characteristics of the feed and ruminal particles (Evans et al., 1974). The frequency of rumen contraction during eating is higher than that during resting or rumination (Waghorn and Reid, 1983). On the other hand, increased HP with putting feed to the rumen through a fistula is very small compared to that during eating (Osuji et al., 1975). Young (1966) found that HP during normal feeding was similar to that during sham feeding in which ingested feed were removed through an esophageal fistula. These findings suggest that increased HP during eating is little affected by heat increment associated with rumen motility. Additionally, heat increment during eating is not including any excitement, because the HP during eating was not affected by the injection of ␤-adrenergic blockade (Webster and Hays, 1968). Suzuki et al. (2008) suggested that the increased HP during eating also includes energy cost of neck motility and the changes in body posture. These findings suggest that the energy cost of eating in the present study included eating per se, i.e. chewing, salivation and swallowing, and other skeletal muscle activities associated with eating. Suzuki et al. (2008) determined heat increment at head during chewing in sheep using arterial-venous oxygen difference technique. They compared heat increment during rumination between at head and at whole body (literature data) that was determined using respiration chamber, and found that those heat increments were similar. This finding indicates that the increased HP during rumination mainly occurs at head associated with chewing and salivation. Therefore, it is considered that the difference in energy cost of eating and rumination is caused by difference in chewing manner and some skeletal muscle activities. The energy cost of eating per unit time was close to mean of literature data, but that of rumination per unit time was numerically higher than mean of literature data (Table 4). It is difficult to discuss the difference between present and literature data on energy cost of rumination, because limited data on energy cost of rumination is available compared to that of eating in cattle.

4.4. Energy cost of chewing It is known that time spent in total chewing per DMI (min/kg) increases with feed particle size and NDF content, whereas that inversely relates to DMI (Sudweeks et al., 1981). In the present study, longer time spent for total chewing per DMI in HF than LF (Table 3) was caused by higher aNDFom content and might be partially caused by lower DMI. The peNDF content, which is more consistent measure rather than time spent for total chewing per DMI (Mertens, 1997), was also higher for HF than for LF (Table 1). These longer time spent for total chewing per DMI and higher peNDF content of HF indicate higher fibrousness of HF compared to LF. Energy cost of eating or rumination per unit time remained constant throughout roughage (Table 4). This result agrees with the previous studies, for eating in cattle (Adam et al., 1984; Susenbeth et al., 1998) and in sheep (Suzuki et al., 2008), and for rumination in sheep (Suzuki et al., 2008). Variations of energy cost of eating and rumination per MEI or DMI were higher than those of total chewing (Table 5). Balch (1971) found compensatory relationship between eating and ruminating time per DMI, and suggested that total chewing time is likely to reflect physical property of feed rather than eating or ruminating time. Therefore, the smaller variation and lower P values of energy cost of total chewing rather than eating and rumination might resulted from this compensatory relationship. Higher energy cost of total chewing per DMI in HF than LF (Table 5) suggests that the energy cost of total chewing per DMI relates to the NDF content in feed. This finding is partially supported by the previous study indicating that energy cost of eating per DMI increased with increasing of fiber contents of feed, measured as ADF or acid detergent lignin (Lachica et al., 1997). Conversely, Susenbeth et al. (2004) found that no constant relation between energy cost of eating and NDF intake through various feeds. Their result might be affected other factors such as particle size. Energy cost of total chewing per MEI of HF was higher than that of LF (Table 5), indicating the contribution of increasing energy cost of chewing to significant loss of ME available for production. Because physical treatments, such as chopping or grinding, decrease peNDF content and time spent chewing (Teimouri Yansari et al., 2004; Woodford and Murphy, 1988), physical treatments of feed possibly decrease loss of ME available for production that is caused by chewing activity.

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Conflicts of interest None declared. Acknowledgments The authors thank the technical staff of the Experimental Dairy Barn, Research Support Center, KARC, for feed preparation, feeding and animal care, and also the technical staff of the Sugarcane Breeding Laboratory, Research Support Center, KARC, for management of sugarcane cultivation. This study was supported, in part, by a Grant in Aid under the Integrated Research Project for Developing a Japanese style Forage Feeding System to Increase the Forage Self support Ratio from the Ministry of Agriculture, Forestry and Fisheries of Japan. References Adam, I., Young, B.A., Nicol, A.M., Degen, A.A., 1984. Energy cost of eating in cattle given diets of different form. Anim. Prod. 38, 53–56. AOAC, 2000. Official Methods of Analysis of AOAC International, 17th ed. AOAC International, Gaithersburg, MD. Balch, C.C., 1971. 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