Effect of feeding wood kraft pulp on the growth performance, feed digestibility, blood components, and rumen fermentation in Japanese Black fattening steers

Abstract This study aimed to examine the effects of feeding kraft pulp (KP) on the growth performance, feed digestibility, and rumen fermentation of Japanese Black fattening steers. Ten Japanese Black fattening steers (aged 26 months) were randomly divided into control and KP groups. The control group (n = 5) was fed concentrate feed without KP, and the KP group (n = 5) was fed concentrate feed containing 10% KP. Both the groups were provided rice straw as roughage. The experiment was conducted over a period of 12 weeks. There was no significant difference in dry matter intake, daily body weight gain, and nutrient digestibility between both groups. No difference was observed in the ruminal concentrations of volatile fatty acids among the groups. At weeks 8 and 12 after the onset of the experiment, the acetate‐to‐propionate ratio in the ruminal fluid of the KP group was significantly higher than that of the control group. The average daily pH of ruminal fluid and activity of ruminal lipopolysaccharide did not differ between the groups. Our results suggested that the growth performance and feed digestibility in the Japanese Black fattening steers were not influenced by replacing concentrate feed with KP.

production of volatile fatty acids (VFAs) (Owens, Secrist, Hill, & Gill, 1998). Particularly, the oversupply of concentrate feed during fattening may lead to a daily decrease in the pH of ruminal fluid, thus increasing the risk of metabolic disorders. A sustained decrease in the pH of ruminal fluid in daily cattle is diagnosed as subacute ruminal acidosis (SARA). SARA is defined as ruminal fluid pH depression below 5.8 for more than 3 hr per day (Gozho, Plaizier, Krause, Kennedy, & Wittenberg, 2005). SARA causes reduced feed intake (Enemark Jorg, 2008;Plaizier, Krause, Gozho, & McBride, 2008), decreased fiber component digestibility (Guo et al., 2013), and liver dysfunction (Plaizier et al., 2008). Although SARA has not been reported in the Japanese Black fattening steer, a sustained decrease in the pH of ruminal fluid is assumed to induce metabolic disorders and to decrease productivity. Nutritional management of the Japanese Black steer during fattening is therefore necessary to control rumen fermentation without reducing the energy level of the feed, thereby improving the health and productivity of the animals.
Recently, wood kraft pulp (KP), which is high in total digestible nutrients (TDN) and neutral detergent fiber (NDF), has been developed as a feed. Kraft pulp is a feed that is primarily cellulose; it results from the selective removal of lignin, which is difficult to break down in the gastrointestinal tract, using alkaline treatment. Kraft pulp contains the same level of TDN as rolled corn, but it has an in vitro fermentation pattern which falls between that of concentrate feed and roughage (Hada, Yashro, Machida, & Kajikawa, 2016).
When provided to the lactating cows as a substitute for rolled corn, KP contributes to stable rumen fermentation by increasing the pH of ruminal fluid and decreasing the activity of ruminal lipopolysaccharide (LPS) (Nishimura et al., in press). Providing KP to the Japanese Black fattening steer is expected to both stabilize the ruminal environment and improve productivity; however, to the best of our knowledge, no reports are available on the effect of feeding KP to the Japanese black fattening steer.
Therefore, this study aimed to investigate the effects of feeding KP on the growth performance, blood characteristics, rumen properties, and feed digestibility of the Japanese Black fattening steer.

| Animals and diets
Ten Japanese Black fattening steers (aged 26 months) were used in this study, and the experiment was conducted over a period of 12 weeks. The steers were housed in individual barns and had free access to fresh water and mineral blocks. The steers were randomly divided into control and KP groups. The control group (n = 5) was fed concentrate feed without KP, and the KP group (n = 5) was fed concentrate feed containing 10% on a dry matter (DM) basis KP, which was supplied by Nippon Paper Industries Co., Ltd (Tokyo, Japan). The ingredients and nutritional composition of the diets are presented in

| Feed intake, growth performance, blood metabolites, and ruminal profile
The feed intake was calculated by subtracting the amount of ort from the amount of feed provided daily. Every 2 weeks at 13:00 hours just after the morning feed (lasting 4 h), the body weight (BW) of the steers was measured.
After BW measurement, blood samples were collected in heparin-containing sodium test tubes (Venoject II VP-H100K; Terumo Co., Ltd., Tokyo, Japan) via a jugular vein puncture at −4, 0, 4, 8, and 12 weeks after the onset of the experiment. The tubes were immediately placed on ice in a light-shielded box and were then centrifuged at 1,870 × g for 15 min at 4°C. Aliquots of plasma obtained from blood samples were transferred into micro tubes and were preserved it at −30°C until further analysis.
The ruminal fluid samples were aspirated after collecting blood samples using an oral tube (NFM90; Fujihira industry Co., Ltd., Tokyo, Japan) and were then filtered with four layers of sterile gauze. A portion of the filtered sample was processed as previously reported (Hirabayashi et al., 2017) to determine the activity of LPS.
Another portion of the filtered sample was transferred to a vial and centrifuged at 1,840 × g for 10 min at 4°C. After centrifugation, the supernatant was collected in a screwcap vial and stored it at −30°C until analyzing it for VFAs and ammonia nitrogen (NH 3 -N).

| Feed digestibility, nitrogen balance, and daily changes in the pH and temperature of ruminal fluid
From weeks 4 to 8, after the onset of the experiment, the feed digestibility, nitrogen balance, and ruminal fluid pH and temperature of the steers were measured.
Feed digestibility and nitrogen balance were measured by collecting total feces and urine produced. The experimental period comprised a 7-day adaptation period and 3-day collection period.
The urine sample was preserved by acidification, and the samples collected during the collection period were pooled and stored at 4°C. The samples were subsequently blended and analyzed.
The pH and temperature of the ruminal fluid were measured using a wireless radio transmission pH measurement system. The pH sensor had previously been developed principally for the academic research on SARA in dairy cattle Sato et al., 2012). The pH and temperature of the ruminal fluid were continuously measured every 10 min for 10 days between 6 and 8 weeks, after the onset of the experiment. The ruminal fluid pH and temperature data were summarized every 60 min.

| Sample analyses
The experimental feed, ort, and fecal samples were dried for 1 day in

| Statistical analysis
The data were analyzed using the FIT model procedure of JMP ® (13.2.1; SAS Institute Inc., Cary, NC, USA). As one of the steers in the KP group presented decreased feed intake and DG due to illness, the data associated with it were excluded from statistical analyses.
The growth performance, feed digestibility, and nitrogen balance of the steers were analyzed using one-way analysis of variance. The The results were considered significant if the p value was <0.05 in the F-test.

| RE SULTS
The BW, DG, DM intake, and feed efficiency during the experimental period are presented in Table 2. There was no significant difference in the DG during the experimental period and the BW by the end of experiment in both the groups. There was no significant difference in the DM intake per metabolic body size (BW 0.75 ) between the groups. The TDN intake per BW 0.75 in the KP group tended to be lower (p < 0.10) than that in the control group. The feed efficiency was not different between the groups.
The nutrient digestibility of the Japanese Black fattening steers is shown in Table 3. There was no significant difference in the DM intake between the control and the KP groups. The DM, TDN, and CP intake per BW 0.75 and concentrate feed ratio did not differ between the groups. The same applied to the digestibility of the DM, OM, CP, EE, aNDFom, NFC, and starch between the groups. Data pertaining to nitrogen balance are presented in Table 4. There was no significant difference between the control and KP groups in the ratio of feces N, urine N, and N retention.
The ruminal profiles of the steers during the experimental period are presented in Table 5. The acetate-to-propionate (A/P) ratio in the rumen fluid is illustrated in Figure 1. There was no significant difference in the total VFA concentration in the ruminal fluid between the two groups. The ratio of acetic acid, propionic acid, and butyric acid in both the groups was not influenced by the diet. However, at weeks 8 and 12 after the onset of the experiment, the A/P ratio in the KP group was significantly higher than that in the control group The blood components of the steers during the experimental period are presented in Table 6. There were no differences in the blood concentrations of plasma TP, Alb, albumin-to-globulin ratio, T-Cho,

| D ISCUSS I ON
In this study, the DM intake was unaffected by the addition of KP, and the growth performance and feed efficiency were comparable between the groups. Several diverse reports on the effects of additive wood-based feed on feed consumption and growth arrive at inconsistent conclusions regarding the effect on growth, which appears to depend on whether the wood-based feed replaces the concentrate feed or the roughage. No effect on the DM intake or DG was observed when the steam-treated wood-based feed was supplied to Holstein steer as a substitute for alfalfa hay cubes (Kajikawa et al.,1987). In contrast, when the sulfite-treated wood-based feed was supplied to beef cows instead of barley, no effect was observed on the DM intake but the DG decreased (Clarke & Dyer, 1973). In this study, the addition of KP was not found to affect the DM intake; which is in agreement with the findings of the previous report.
However, unlike in the previous report, replacing concentrate feed with KP was not found to affect the DG in this study. It is considered that the digestibility of wood-based feed influenced the variance between the results. The digestibility of wood-based feed changes depending on the processing method of wood (Baker, 1973;Millett, Baker, Satter, McGovern, & Dinius, 1973). Baker (1973) indicated that an increase in the lignin removal rate from 0% to 96.5% increased the in vitro DM digestion rate from 12% to 90%. The lignin content and the DM digestion rate of steam-treated wood-based feed are 13.0% and 60.6%, respectively (Takigawa, 1987). The lignin content of alkali-treated KP was reduced to no more than 5%, whereas the in situ DM digestion rate was at least 90% (Hada et al., 2016). In this study, the addition of KP was not found to affect the digestion rate of each feed component or nitrogen utilization. Kraft pulp is more digestible than conventional woodbased feeds, and its digestion rate is comparable with that of concentrate feed. In consequence, feeding KP instead of concentrate feed to the Japanese Black fattening steer is not considered to affect their growth or feed efficiency. Furthermore, no effect on feed digestibility was observed in lactating cows even when 12% of KP was admixed into the feed instead of rolled corn (Nishimura et al., in press).  The data pertaining to one of steers in the KP group was excluded due to illness.
The levels of blood biochemical components observed in this study were within the clinically normal ranges for the Japanese Black fattening steer (Adachi et al., 1999;Kaneko, 1983;Nakamura et al., 2008). The addition of KP was found to affect the plasma concentrations of Glu and IP. Ruminants depend on gluconeogenesis in the liver for endogenous Glu, and one of the substrates of gluconeogenesis is propionic acid (Young, 1977). In this study, the A/P ratio in the rumen fluid of steers in the KP group was significantly higher than that in the control group at weeks 8 and 12, which was considered to be associated with the simultaneous decrease in the plasma Glu concentration in the KP group. The plasma IP concentration is related to carbohydrate metabolism (Kaneko, 1983). The plasma IP concentration may rise on the fasting (Kaneko, 1983). However, in this study, there was no significant difference in the DM intake and concentrate feed ratio between the groups. Therefore, there was no clear relationship between plasma IP concentration and carbohydrate metabolism in the KP group.
The A/P ratio in the rumen fluid increased with the addition of KP. The same increase in the A/P ratio was obtained when the woodbased feed was provided as a substitute for concentrate feed (Clarke & Dyer, 1973;Nishimura et al., in press (Zebeli et al., 2012). In this study, the substitution of 10% of the concentrate feed with KP had an effect on the amount of starch and aNDFom consumed. However, steers still intake large quantities of starch and small quantities of NDF. This was considered to be the reason for no effect on the ruminal fluid pH or LPS activity. In future, the effect of KP addition during the early period (when the proportion of concentrate feed supplied is low) and middle period of fattening (when the roughage-to-concentrate ratio in the feed supplied fluctuates) both need to be further explored.
The death of microorganisms and production of LPS, which is a component of bacteria, are promoted by a decrease in the pH of ruminal fluid due to the oversupply of concentrate feed (Plaizier et al., 2012). The LPS released into the gastrointestinal tract is transferred to the blood vessels, where it might cause a systemic inflammatory reaction (Plaizier et al., 2008(Plaizier et al., , 2012. In several studies, the LPS activity in the ruminal fluid and the plasma concentration of acute phase proteins (SAA, Hp, and LBP) are mutually related and are considered as inflammatory markers. For instance, a decrease in the ruminal fluid pH increases the activity of LPS in the ruminal fluid, and the concentration of SAA (Gozho, Krause, & Plaizier, 2006;Gozho et al., 2005;Khafipour, Krause, & Plaizier, 2009a), Hp (Gozho et al., 2005(Gozho et al., , 2006Khafipour et al., 2009a), and LBP (Khafipour et al., 2009a) in the blood. However, it has also been reported that an increase in the activity of LPS in the ruminal fluid does not affect the blood concentration of the SAA, Hp, and LBP (Khafipour, Krause, & Plaizier, 2009b;Plaizier et al., 2014). These inconsistent findings regarding the relationship between LPS activity in the ruminal fluid and acute-phase protein concentrations in the plasma may be due to the differing individual responses of rumen fluid LPS activity to the same feed (Hirabayashi et al., 2017).
Furthermore, the reason for the transfer of ruminal fluid LPS to the bloodstream remains unclear. In this study, the addition of KP was not found to affect the activity of LPS in the ruminal fluid or the concentration of SAA and Hp in the plasma. At week 8, the plasma LBP concentration in the KP group increased significantly compared with that of the control group. It was conjectured that this was influenced by feeding KP as well as due to the differing individual responses.
The administration of KP as a substitute for a portion of concentrate feed exhibited no effect on the growth or feed efficiency of the Japanese Black fattening steer. Additionally, the addition of