Effects of physically effective fiber on chewing activity, ruminal fermentation, and digestibility in goats 1

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1 Published December 4, 2014 Effects of physically effective fiber on chewing activity, ruminal fermentation, and digestibility in goats 1 X. H. Zhao, T. Zhang, M. Xu, and J. H. Yao 2 College of Animal Science and Technology, Northwest A&F University, Yangling Shaanxi, China ABSTRACT: The objective of this study was to evaluate the effects of physically effective NDF (pendf) in goat diets containing alfalfa hay as the sole forage source on feed intake, chewing activity, ruminal fermentation, and nutrient digestibility. Four rumen-fistulated goats were fed different proportions of chopped and ground alfalfa hay in a 4 4 Latin square design. Diets were chemically similar but varied in pendf content: low, moderate low, moderate high, and high. Dietary pendf content was determined using the Penn State Particle Separator with 2 sieves (8 and 19 mm) or 3 sieves (1.18, 8, and 19 mm). The dietary pendf content ranged from 1.9 to 11.7% using the 2 sieves and from 15.2 to 20.0% using the 3 sieves. Increasing forage particle length increased intake of pendf, but decreased DMI linearly (P = 0.05). Ruminating and total chewing time (min/d) were increased linearly (P = and 0.007, respectively) with increased dietary pendf, resulting in a linear reduction (P < 0.001) in the duration of time that ruminal ph was less than 5.8 (10.9, 9.0, 1.2, and 0.3 h/d, respectively). Increasing dietary pendf tended to increase the molar proportion of propionate linearly (P = 0.08) and decrease the molar proportion of butyrate (P = 0.09), but did not affect total VFA concentration. Increasing dietary pendf linearly decreased the apparent digestibility of OM, NDF, and ADF in the total tract (P = 0.009, 0.003, and 0.008, respectively). This study demonstrated that increasing the dietary pendf contained in alfalfa hay forage stimulated chewing activity and improved ruminal ph status, but reduced nutrient intake and efficiency of feed use. Key words: chewing, digestibility, goat, physically effective neutral detergent fiber, rumen ph 2011 American Society of Animal Science. All rights reserved. J. Anim. Sci : doi: /jas INTRODUCTION Subacute ruminal acidosis (SARA) is a common health and production problem occurring in ruminants and is often triggered by low ruminal ph from a low-fiber diet. In addition to the quantity of fiber consumed, the physical form of feed also plays an important role in the cause of SARA. Feed with shorter particle sizes usually result in reduced chewing time and ruminal ph (Grant et al., 1990). Mertens (1997) introduced the concept of physically effective NDF (pendf) related to the physical characteristics of fiber (primarily particle size) affecting chewing activity. It was proposed that pendf content in feed could be measured by the NDF content of feed multiplied by the proportion of feed retained 1 This research was supported by Scientific & Technological Innovation Project of Shaanxi, P. R. China (2007ZKDG-15, 2009K01-02, 2009ZDKG-18, 2010ZDGC-02), and R & D Special Fund for Public Welfare Industry (Agriculture, nyhyzx ). 2 Corresponding author: yaojunhu2004@sohu.com Received March 23, Accepted October 1, on a 1.18-mm sieve using a dry-sieving technique. Although recent studies have determined the effects of dietary pendf on chewing activity, rumen function, and feed utilization using dairy cows (Einarson et al., 2004; Yang and Beauchemin, 2009), little information is available in goats. Goats have different feeding behavior, intake, diet selection, and rate of eating from other ruminants (Lu et al., 2005); thus, knowledge obtained from different species may not extrapolate well to goats. In addition, although pendf incorporates information on particle size and chemical NDF content of feed, the physical effectiveness of fiber is also likely related to particle shape, fragility, type of preservation, and feed moisture (Mertens, 1997). Krause and Combs (2003) reported that partially replacing alfalfa silage with corn silage increased rumination time, even though forage particle sizes were similar. Although silage has been used as a sole forage source or partial forage source to determine the effects of dietary pendf in numerous studies (Teimouri Yansari et al., 2004; Yang and Beauchemin, 2005), few data are available on alfalfa hay as the sole forage source. The objective of this study was to evaluate the effects of dietary pendf on feed intake, chewing activity, ruminal fermentation, 501

2 502 Table 1. Particle size distribution 1 of alfalfa hay Chopped Alfalfa hay and nutrient digestibility of goats using alfalfa hay as the sole forage source. MATERIALS AND METHODS Ground % of DM retained on sieves 19 mm mm mm Pan pef pef pendf 8.0, % of DM pendf 1.18, % of DM Particle size distribution of alfalfa hay was measured using the Penn State Particle Separator (Kononoff et al., 2003); pef 8.0 and pef 1.18 = physical effectiveness factor determined as the proportion of particles retained on 2 sieves (Lammers et al., 1996) and on 3 sieves (Kononoff et al., 2003), respectively; pendf 8.0 and pendf 1.18 = physically effective NDF determined as NDF content of alfalfa hay multiplied by pef 8.0 and pef 1.18, respectively. Zhao et al. Four wether goats with an average BW of 40.0 ± 2.2 kg were assigned to a 4 4 Latin square. Each goat was fitted with a rumen cannula (i.d. = 4 cm). Goats were housed indoors under continuous light in individual metabolism crates (0.75 m 1.5 m). Diets were manually mixed, and total mixed rations were supplied to the goats twice daily at 0800 and 2000 h for ad libitum intake (at least 10% orts). Fresh water was available for ad libitum consumption throughout the study. Alfalfa hay was cut into 20-mm lengths using a forage cutter (9Z-4C, Luoyang Sida Agricultural Machinery Co. Ltd., Luoyang, China) equipped with 6 knives and ground through 4-mm sieves using a forage grinder (9FQ-50, Luoyang Sida Agricultural Machinery Co. Ltd.) equipped with 16 hammers (Table 1). Goats were offered 1 of 4 diets that contained 45% concentrate and 55% alfalfa hay but differed in pendf content; low (diet containing low pendf content; 1.9 and 15.2% for pendf 8.0 and pendf 1.18 content, respectively), ML (diet containing moderate low pendf content; 5.4 and 16.7% for pendf 8.0 and pendf 1.18 content, respectively), MH (diet containing moderate high pendf content; 8.6 and 18.2% for pendf 8.0 and pendf 1.18 content, respectively), and high (diet containing high pendf content; 11.7 and 20.0% for pendf 8.0 and pendf 1.18 content, respectively; Tables 2 and 3). The 4 different dietary pendf contents were obtained using forage differing in chopped alfalfa hay and ground alfalfa hay proportions (DM basis): 7:48 (low), 23:32 (ML), 39:16 (MH), and 55:0 (high). Particle size distribution of alfalfa hay and mixed diets was determined using the Penn State Particle Separator containing 3 sieves (19, 8, and 1.18 mm) and 1 pan (Kononoff et al., 2003). Physical effectiveness factors (pef) for alfalfa hay and mixed diet were calculated as the sum of the DM proportion retained on 2 sieves: 19 and 8 mm (pef 8.0 ; Lammers et al., 1996) or 3 sieves: 19, 8, and 1.18 mm (pef 1.18 ; Kononoff et al., 2003). The pendf 8.0 and pendf 1.18 content of the alfalfa hay and mixed diet were calculated by multiplying NDF content of the feed by pef 8.0 and pef 1.18, respectively (Yang and Beauchemin, 2007). All diets were formulated to exceed the requirements of a 40-kg goat based on NRC (1981). Each study period consisted of 14 d of diet adaptation and 7 d of experimental measurements. Chromic oxide was used as the external marker to estimate nutrient apparent digestibility of the total tract. A filter paper containing 1 g of chromic oxide was dosed through the rumen cannula 4 times daily at 6-h intervals (total of 4 g of Cr 2 O 3 /d) from d 9 to 17, with a priming dose of 4 g on d 9. This study was approved by the Animal Care and Use Committee of the College of Animal Science and Technology of the Northwest A&F University. Experimental Design, Goats, and Diets Sampling and Measurements Feed offered and the orts collected were measured and recorded daily during the last 7 d of the study period to calculate feed intake. Alfalfa hay (chopped or ground, approximately 170 g) and mixed diet (approximately 350 g) samples were collected once every 3 d to determine particle distribution. Particles retained on the different sieves were then collected, weighed, dried at 70 C, and stored for DM analysis. The samples were then composited by period and stored to determine chemical composition. Orts were collected daily, pooled by goat, and used to determine the particle distribution on the last day of the study period as described above. Samples of premix concentrate were collected daily (approximately 100 g), pooled by goat for the study period, dried at 70 C, and stored for chemical analysis. Beginning at 0200 h on d 15 of each period, samples of ruminal fluid (20 ml) were collected from multiple sites in the rumen using a suction pump at 6-h intervals for 3 d. The sampling time was adjusted ahead 2 h daily so that a sample was obtained for each 2-h interval of the day (12 samples in total). Ten milliliters of ruminal fluid was preserved by adding 1 ml of 1% HPO 3 to determine VFA. Ten milliliters of ruminal fluid was preserved by adding 1 ml of 1% H 2 SO 4 to determine NH 3 N concentration. The samples were frozen at 20 C until analyzed. Fecal grab samples were collected at the same time as the ruminal fluid. Fecal samples (200 g) were pooled by goat within the study period, dried at 70 C, ground, and stored for OM, Kjeldahl N, NDF, ADF, ether extract, and chromium analysis.

3 Physically effective fiber for goats 503 Table 2. Ingredients and chemical composition of the diets (DM basis) Dietary pendf 1 Low ML MH High Diet ingredient, % of DM Chopped alfalfa hay Ground alfalfa hay Concentrate supplement Chemical composition, 3 % DM OM CP NDF NDF from forages ADF Ether extract NFC Low = diet containing low physically effective fiber (pendf) content (1.9 and 15.2% for pendf 8.0 and pendf 1.18 content, respectively); ML = diet containing moderate low pendf content (5.4 and 16.7% for pendf 8.0 and pendf 1.18 content, respectively); MH = diet containing moderate high pendf content (8.6 and 18.2% for pendf 8.0 and pendf 1.18 content, respectively); high = diet containing high pendf content (11.7 and 20.0% for pendf 8.0 and pendf 1.18 content, respectively). 2 Concentrate supplement: 89.07% corn, 8.44% soybean meal, 0.40% calcium carbonate, 0.49% dicalcium phosphate, 0.60% sodium chloride, and 1% vitamin-mineral mix. Vitamin-mineral mix (per kg): 450 mg of nicotinic acid, 600 mg of Mn, 950 mg of Zn, 430 mg of Fe, 650 mg of Cu, 30 mg of Se, 45 mg of I, 20 mg of Co, 800 mg of vitamin E, 45,000 IU of vitamin D, and 120,000 IU of vitamin A. 3 Values determined from analysis. All values except DM, %, are expressed on a DM basis. 4 NFC = nonfiber carbohydrate calculated by the difference of 100 (% NDF + % CP + % ether extract + % ash). Ruminal ph was continuously monitored for 24 h during d 18 to 19 of the study period with a combination device. The device consisted of an industrial electrode (IP , Jenco, San Diego, CA), a ph transmitter (691, Jenco), and a data logger linked to a computer. The electrodes were calibrated using ph 4.0 and 7.0 standards and suspended in the rumen using a cable anchored to the ruminal cannula plug. A weight (approximately 200 g) was attached to the electrode to prevent it from shifting in the rumen. Ruminal ph was recorded every 5 s and stored in the data logger. Ruminal ph data were summarized for each goat as mean ph, minimum and maximum ph, area between the curve and a horizontal line at ph 5.8 and 5.6, and duration less than ph 5.8 and 5.6 (Yang and Beauchemin, 2007). Chewing activity was continuously monitored for 24 h during d 20 to 21 of the study period per Krause and Combs (2003). Eating and ruminating activities were noted every 5 min, and each activity was assumed to persist for the entire 5-min interval. The data were used to estimate the eating time, ruminating time, and time spent eating and ruminating per gram of DM, NDF, pendf 8.0, and pendf 1.18 (Teimouri Yansari et al., 2004). Total time spent chewing was calculated as the total time spent eating and ruminating. Chemical Analyses Chemical analyses were conducted in triplicate. Feed, feces, and orts were analyzed for DM by drying at 135 C in an airflow-type oven for 2 h (AOAC, 1990; method ), for OM by ashing at 550 C for at least 4 h, for N using the Kjeldahl procedure (AOAC, 1990; method ), and for ether extract (AOAC, 1990; method ). The NDF and ADF content in all samples were analyzed according to Van Soest et al. (1991). Heat-stable α-amylase (Sigma A3306, Sigma- Aldrich, Shanghai, China) and sodium sulfite were used for NDF determination, and NDF was not corrected for ash content. Nonfiber carbohydrate was calculated as 100 (% CP + % NDF + % ash + % ether extract). Reported nonfiber carbohydrate (NFC) values were not corrected for NDF-CP. Ammonia N in ruminal fluid was analyzed according to Chaney and Marbach (1962). Chromium concentration in fecal samples was determined per Fenton and Fenton (1979) using a spectrophotometer (U-3900, Hitachi, Tokyo, Japan). Dry matter excreted in feces was calculated by dividing daily chromium intake by chromium concentration in feces. Nutrient flows were calculated by multiplying DM flow by fecal concentration. Acidified rumen fluid was centrifuged at 13,000 g for 30 min at 4 C and decanted, and the supernatant was centrifuged at 18,000 g for an additional 30 min at 4 C. The supernatant was filtered through a 0.45-μm filter. Ruminal VFA concentrations in the filtered samples were determined by HPLC (L-2000, Hitachi) according to Akalin et al. (2002) with a modification of flow rate (0.8 ml/min). The column used was a reversed-phase Agilent TC-C18 column (4.6 mm 250 mm; 5 μm, Agilent Technologies, Santa Clara, CA).

4 504 Zhao et al. Table 3. Effects of reducing alfalfa hay particle length on particle distribution, physical effectiveness factor (pef), and physically effective fiber (pendf) contents of diets and orts (n = 16 1 ) Low ML MH High SEM Linear Quadratic Diets offered % of DM retained on sieves 4 19 mm < mm < mm < Pan pef < pef pendf 8.0, % of DM < pendf 1.18, % of DM Orts % of DM retained on sieves 1.18 mm Pan pef pendf 1.18, % of DM Diets consumed (adjusted for particle size of orts) % of DM retained on sieves 19 mm <0.001 < mm <0.001 < mm <0.001 <0.001 Pan < pef < pef < pendf 8.0, % of DM < pendf 1.18, % of DM < Low = diet containing low pendf content (1.9 and 15.2% for pendf 8.0 and pendf 1.18 content, respectively); ML = diet containing moderate low pendf content (5.4 and 16.7% for pendf 8.0 and pendf 1.18 content, respectively); MH = diet containing moderate high pendf content (8.6 and 18.2% for pendf 8.0 and pendf 1.18 content, respectively); high = diet containing high pendf content (11.7 and 20.0% for pendf 8.0 and pendf 1.18 content, respectively). 4 Particle size distribution of mixed diets or orts was measured using the Penn State Particle Separator (Kononoff et al., 2003); pef 8.0 and pef 1.18 = physical effectiveness factor determined as the proportion of particles retained on 2 sieves (Lammers et al., 1996) and on 3 sieves (Kononoff et al., 2003), respectively; pendf 8.0 and pendf 1.18 = physically effective NDF determined as NDF content of alfalfa hay multiplied by pef 8.0 and pef 1.18, respectively. Statistical Analyses Data were analyzed by ANOVA according to the GLM procedure (SAS Inst. Inc., Cary, NC) for a 4 4 Latin square design. Terms in the model were goat, period, and treatment. Treatment means were calculated using the LSMEANS option. Data for ruminal VFA and NH 3 N were analyzed using the PROC MIXED procedure for repeated measures. Sampling time was considered as the repeated factor. The model included the fixed effects of treatment, sampling time, and the interaction of treatment sampling time. Random effects consisted of goat and period. For each variable analyzed, data were subjected to 4 covariance structures: variance components, compound symmetric, unstructured, and autoregressive of order 1. The most desirable covariance structure was determined according to Schwarz s Bayesian criterion (Littell et al., 1998). Data for particle distribution, pef, and pendf of forages and diets were averaged by period and analyzed by including particle length as a fixed effect and period as a random effect. Linear and quadratic orthogonal contrasts were tested using the CONTRAST statement of SAS. Significance was declared at P 0.05, and trends were discussed at P RESULTS Particle Length and Physically Effective Fiber For the diets offered, the proportion of particles retained on the 8- and 19-mm sieves, thus pef 8.0, increased linearly (P < 0.001) with increased particle length (Table 3). In contrast, the proportion of particles retained on the 1.18-mm sieve and pan decreased linearly (P < and P = 0.001, respectively). The reduced proportion of short particles (1.18 mm) was compensated for by the increased proportion of long particles (8 and 19 mm), resulting in increased pef 1.18 (P = 0.001). The pendf 8.0 and pendf 1.18 content of the diets increased

5 Physically effective fiber for goats 505 Table 4. Effects of reducing dietary physically effective fiber (pendf) on intake in goats (n = 16 1 ) Low ML MH High SEM Linear Quadratic Intake, g/d DM 1, , , OM 1, NDF ADF NFC N pendf < pendf Low = diet containing low pendf content (1.9 and 15.2% for pendf 8.0 and pendf 1.18 content, respectively); ML = diet containing moderate low pendf content (5.4 and 16.7% for pendf8.0 and pendf 1.18 content, respectively); MH = diet containing moderate high pendf content (8.6 and 18.2% for pendf 8.0 and pendf 1.18 content, respectively); high = diet containing high pendf content (11.7 and 20.0% for pendf 8.0 and pendf 1.18 content, respectively). 4 NFC = nonfiber carbohydrate calculated by the difference of 100 (% NDF + % CP + % ether extract + % ash). 5 pendf 8.0 and pendf 1.18 = physically effective NDF determined as NDF content of mixed diet multiplied by pef 8.0 and pef 1.18, respectively (Table 3). pef 8.0 and pef 1.18 = physical effectiveness factor determined as the proportion of particles retained on 2 sieves (Lammers et al., 1996) and on 3 sieves (Kononoff et al., 2003), respectively. linearly (P < and P = 0.009, respectively) with increased particle length and reflected the same trend for pef. Particle distribution of the orts differed for the diets offered. Particles of orts were mainly retained on the 1.18-mm sieve and pan, which demonstrated that ort particle length was less than 8 mm. The pef 1.18 and pendf 1.18 values were greatest (P = and 0.03, respectively) for the high treatment because of more long particles in the original high diets. The trends of particle distribution for diets consumed were in line with original diets after adjustment for ort particle size. Intake Data on nutrient intake are presented in Table 4. Intake of DM and NFC decreased linearly (P = 0.05 and 0.03, respectively) with increased dietary pendf. The largest difference in DM and NFC intakes occurred between the low and high treatments (155 and 72 g/d). Increased dietary pendf resulted in a linear decreasing trend (P = 0.06 and 0.07, respectively) in OM and N intake due to decreased DMI. Intake of NDF and ADF were not affected by dietary pendf, but numerically smaller values were observed in the high treatment. Because increased pendf 8.0 content compensated for reduced DMI, pendf 8.0 intake showed a significant linear increase (P < 0.001) from 27 to 126 g/d. Chewing Data on goat chewing activity are presented in Table 5. Eating activity (min/d) tended (P = 0.10) to respond quadratically as dietary pendf content increased. Ruminating and total chewing (eating + ruminating) time increased linearly by 175 (P = 0.001) and 155 min/d (P = 0.007), respectively. Ruminating and total chewing time per unit of NDF intake showed a linear increase (P < 0.001) with increasing dietary pendf. Chewing activity (eating, ruminating, or total chewing time) per unit of pendf 8.0 intake and eating time per unit of pendf 1.18 intake decreased linearly (P 0.001) with increasing dietary pendf, but ruminating and total chewing time per unit of pendf 1.18 intake increased linearly (P < and P = 0.001, respectively) with increasing dietary pendf. Rumen ph and Fermentation Data on goat ruminal fermentation are presented in Table 6. Increasing dietary pendf content had a significant effect on ruminal ph. Mean and smallest values of ruminal ph increased linearly by 0.42 (P = 0.001) and 0.32 (P = 0.002), respectively, and time that ph was less than 5.8 and 5.6 was reduced by 10.6 (P < 0.001) and 3.2 h/d (P = 0.002), respectively. Increasing dietary pendf content also linearly decreased the area under ph 5.8 and 5.6 (P < and P = 0.01, respectively). Increased dietary pendf had no effect on total VFA concentration, molar proportion of acetate, acetate:propionate, and NH 3 N concentration, but tended to increase the molar proportion of propionate linearly (P = 0.08) and decrease the molar proportion of butyrate (P = 0.09). Total Tract Apparent Digestibility Data on apparent digestibility are presented in Table 7. With increasing dietary pendf, total tract apparent digestibility of OM, NDF, and ADF showed a linear reduction of 6% (P = 0.009), 15% (P = 0.003), and 20%

6 506 Zhao et al. Table 5. Effects of reducing dietary physically effective fiber (pendf) on chewing activity in goats (n = 16 1 ) Low ML MH High SEM Linear Quadratic Eating Min/d Min/g of DM Min/g of NDF Min/g of pendf < Min/g of pendf Ruminating Min/d Min/g of DM < Min/g of NDF < Min/g of pendf Min/g of pendf < Chewing Min/d Min/g of DM < Min/g of NDF < Min/g of pendf < Min/g of pendf Low = diet containing low pendf content (1.9 and 15.2% for pendf 8.0 and pendf 1.18 content, respectively); ML = diet containing moderate low pendf content (5.4 and 16.7% for pendf 8.0 and pendf 1.18 content, respectively); MH = diet containing moderate high pendf content (8.6 and 18.2% for pendf 8.0 and pendf 1.18 content, respectively); high = diet containing high pendf content (11.7 and 20.0% for pendf 8.0 and pendf 1.18 content, respectively). 4 pendf 8.0 and pendf 1.18 = physically effective NDF determined as NDF content of mixed diet multiplied by pef 8.0 and pef 1.18, respectively. pef 8.0 and pef 1.18 = physical effectiveness factor determined as the proportion of particles retained on 2 sieves (Lammers et al., 1996) and on 3 sieves (Kononoff et al., 2003), respectively. (P = 0.008), respectively. Digestibility of NFC tended to show a linear reduction (P = 0.06), although the difference was minor. Increasing dietary pendf did not affect digestibility of N in the total tract. DISCUSSION Results of this study indicate that dietary particle distribution is affected by forage particle length. In- Table 6. Effects of reducing dietary physically effective fiber (pendf) on ruminal ph and fermentation characteristics in goats (n = 16 1 ) Low ML MH High SEM Linear Quadratic ph Mean Greatest Least Area under ph 5.8, ph h/d < Area under ph 5.6, ph h/d ph <5.8, h/d < ph <5.6, h/d VFA Total, mm Acetate, mol/100 mol Propionate, mol/100 mol Butyrate, mol/100 mol A:P NH 3 N, mm Low = diet containing low pendf content (1.9 and 15.2% for pendf 8.0 and pendf 1.18 content, respectively); ML = diet containing moderate low pendf content (5.4 and 16.7% for pendf 8.0 and pendf 1.18 content, respectively); MH = diet containing moderate high pendf content (8.6 and 18.2% for pendf 8.0 and pendf 1.18 content, respectively); high = diet containing high pendf content (11.7 and 20.0% for pendf 8.0 and pendf 1.18 content, respectively). 4 A:P = acetate:propionate.

7 Physically effective fiber for goats 507 Table 7. Effects of reducing dietary physically effective fiber (pendf) on total tract digestibility in goats (n = 16 1 ) Low ML MH High SEM Linear Quadratic OM NDF ADF NFC N Low = diet containing low pendf content (1.9 and 15.2% for pendf 8.0 and pendf 1.18 content, respectively); ML = diet containing moderate low pendf content (5.4 and 16.7% for pendf 8.0 and pendf 1.18 content, respectively); MH = diet containing moderate high pendf content (8.6 and 18.2% for pendf 8.0 and pendf 1.18 content, respectively); high = diet containing high pendf content (11.7 and 20.0% for pendf 8.0 and pendf 1.18 content, respectively). 4 NFC = nonfiber carbohydrate calculated by the difference of 100 (% NDF + % CP + % ether extract + % ash). creasing forage particle length significantly increased the pef and pendf content of diets, which is similar to results obtained in previous studies (Teimouri Yansari et al., 2004). A larger reduction in dietary pendf 8.0 content (84%) compared with pendf 1.18 content (24%) with decreased dietary particle length suggests that measures using 2 sieves (19 and 8 mm) of the Penn State Particle Separator were more sensitive to changes in forage particle length. The particle length of orts was less than 8 mm, which suggests that long particles were preferred by goats in the present study and may be associated with the diet selections of goats. Cooper et al. (1996) found that sheep voluntarily choose a large proportion of long forage in an attempt to maintain certain ruminal conditions (such as ph and osmolality). Campion and Leek (1997) reported that sheep may ingest long fibers to carry out rumination. The proportion of diet passing through the 1.18-mm sieve was very large (39 to 52%) in our study, which indicates that the dietary particles were very fine. Therefore, the goats may actively select long feed particles to induce rumination and maintain certain ruminal conditions. In addition, the preference for long particles may be related to the physiological reactions of goats. Ouédrago et al. (1996) showed that goats generally preferred coarse particle feed to fine or very fine particle feed because of greater respiratory tract sensitivity to irritation by very small solid particles. In the present study, increasing dietary pendf resulted in decreased DMI and consequently decreased daily intake of OM, N, and NFC. These results are similar to previous studies in which reducing forage particle size resulted in increased intake (Quick and Dehority, 1986; McSweeney and Kennedy, 1992). Voluntary DMI can be constrained by rumen fill and clearance of digesta from the rumen (Teimouri Yansari et al., 2004). Reducing particle size may decrease the fill of forage and increase ruminal passage rate, resulting in increased DMI. The effect of forage particle size and dietary pendf on chewing activity has been investigated in previous studies using different forage sources and animals. It is well recognized that increasing forage particle size increases ruminating activity (Lu, 1987; Teimouri Yansari et al., 2004). In the present study, increasing dietary pendf resulted in improved ruminating time, which is consistent with results by Lu (1987) and McSweeney and Kennedy (1992) using goats and hay. A strong positive correlation (r = 0.88; data not displayed) between time spent chewing and ruminating was observed in our study, which indicates that increased chewing time mainly resulted from increased ruminating time rather than eating time. This result is consistent with Lu (1987), in which only ruminating time, and consequently total chewing time, increased with increased forage particle length. The balance between the production of fermentation acid and acid removal through salivary neutralization and absorption within the rumen is a major determinant of ruminal ph (Allen, 1997). The pendf is a measure that reflects the ability of fiber to stimulate chewing and saliva buffering in the rumen. In the present study, ruminal ph status was improved significantly with increased dietary pendf, which is similar to results reported by Beauchemin et al. (2003). The significant reduction in duration that ph was less than 5.8 and 5.6 for goats consuming the MH diet relative to those consuming the ML diet reflects the corresponding increase in chewing time (from 556 to 642 min/d). These results indicate that chewing activity affected by dietary pendf played a decisive role in the regulation of ruminal ph. Research has shown that to minimize the risk of SARA, rumen ph should not be less than 5.8 for more than 5.24 h/d (Zebeli et al., 2008a). In addition, when formulating healthy diets for dairy cows, the ratio of pendf 1.18 to rumen-degradable starch from grains (RDSG) in the diet should not be less than 1.45 (Zebeli et al., 2008a, 2010). Dietary RDSG content in our

8 508 study was about 20.4 to 20.8% (estimated according to Offner et al., 2003; Zebeli et al., 2008a), and the ratio of pendf 1.18 to RDSG in low, ML, MH, and high diets were about 0.74, 0.82, 0.88, and 0.96, respectively. However, the goats fed the MH and high diets in which the ratios of pendf 1.18 to RDSG were more than 0.88 did not appear at risk of SARA, which indicates that the ratio of pendf 1.18 to RDSG required in the healthy diets of goats may be less than that for dairy cows. These discrepancies may be related to different digestive physiologies and intakes between goats and dairy cows. Research has shown that when ruminating and chewing time were 410 and 642 min/d, respectively, dietary pendf 1.18 content was 26.5% (Yang and Beauchemin, 2006b). Similar results were reported by Yang and Beauchemin (2007) using 28.6% pendf In the present study, however, time spent ruminating and chewing reached 406 and 642 min/d, respectively, when dietary pendf 1.18 content was only 18.2%. This indicates that long fiber can stimulate extensive chewing in goats compared with dairy cows. In addition, the duration that ph was less than 5.8 was significantly reduced from the ML to MH diet, but the difference in the ratio of pendf 1.18 to RDSG between them was minor (0.06). In contrast, the difference in the ratio of pendf 8.0 to RDSG was much larger (0.16). Forage with a similar percentage of material retained above a 1.18-mm sieve can be chopped at different lengths (Leonardi et al., 2005). Therefore, the ratio between pendf 8.0 and RDSG may be an important factor to consider when formulating healthy diets. In the present study, increasing dietary pendf tended to increase the molar proportion of propionate linearly and decrease the molar proportion of butyrate. Although these results are consistent with Zebeli et al. (2008b), they are inconsistent with Beauchemin and Yang (2005). These disparities might be explained by many factors that affect rumen VFA, such as forage source, rumen volume and flow rate, animal-to-animal variation, and interactions between these factors and dietary particle size (Einarson et al., 2004). In addition, sampling time and frequency may also be an important factor affecting ruminal VFA. Total tract apparent digestibility of nutrients (except N) was significantly reduced with increased dietary pendf in the present study. The results may be inconclusive, however, owing to contradiction with other studies using goats (Quick and Dehority, 1986; Hadjigeorgiou et al., 2003) and dairy cows (Le Liboux and Peyraud, 1999; Teimouri Yansari et al., 2004; Yang and Beauchemin, 2005). Zebeli et al. (2008a) suggested that NDF digestibility in the total tract increased linearly with increasing ruminal ph, decreasing rate of rumen outflow, or both. Several previous studies have, however, reported similar observations to findings in the current study (Soita et al., 2002; Kononoff and Heinrichs, 2003; Yang and Beauchemin, 2006a). Soita et al. (2002) found that total digestibility of DM and fiber Zhao et al. components was greater for steers fed short barley silage (theoretical chop length, 4.7 mm) than long barley silage (theoretical chop length, 18.8 mm). Yang and Beauchemin (2006a) reported that the digestibility of ADF and OM in the total tract was reduced with increased pendf content. Increased surface area for microbial attachment with reduced forage particle length was mentioned as a possible reason for improving the digestibility of nutrients in the above studies. Allen and Mertens (1988) reported that microbial penetration of feed particles occurred at the chopping and grinding fracture sites, and the increased surface area caused by grinding increased the rate of fiber digestion. Weimer et al. 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