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Effect of diet composition on digestion and rumen fermentation parameters in sheep and cashmere goats
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Animal Feed Science and Technology 146 (2008) 337–344
Short communication
Effect of diet composition on digestion and rumen fermentation parameters in sheep and cashmere goats Dabiao Li a , Xianzhi Hou a,∗ , Yuanyuan Liu b , Yanling Liu a a
College of Animal Science and Animal Medicine, Inner Mongolia Agricultural University, Hohhot 010-018, PR China b College of Science, Inner Mongolia Agricultural University, Hohhot 010-018, PR China
Received 14 February 2007; received in revised form 26 December 2007; accepted 16 January 2008
Abstract The study was carried out to compare the voluntary intake, digestibility, mean retention times (MRTs) and rumen fermentation parameters in sheep and cashmere goats offered three pellet diets. Four Mongolian and Han crossbred sheep and four Inner Mongolian white cashmere goats, each fitted with a rumen cannula, were used in this study. The results showed that there were differences between sheep and goats in voluntary intake (P<0.05), apparent digestibility of fiber and MRT (P<0.01). Dietary types affected voluntary intake, apparent digestibility and rumen fermentation parameters (except pH). Sheep showed high voluntary dry matter (DM) intake, long rumen MRT and high apparent digestibility of fiber. When opportunity for diet selectivity was avoided, cashmere goats, compared with sheep, showed lower voluntary DM intake, shorter rumen MRT and lower apparent digestibility of fiber. Rumen fermentation parameters did not show differences between sheep and goats. © 2008 Elsevier B.V. All rights reserved. Keywords: Intake; Digestion; Mean retention times; Fermentation; Sheep; Goats
Abbreviations: ADCs, apparent digestibility coefficients; ADFom, acid detergent fiber expressed exclusive of residual ash; CEL, cellulose; CP, crude protein; DM, dry matter; FOR, fractional outflow rate; NDFom, neutral detergent fiber not assayed with a heat stable amylase and expressed exclusive of residual ash; MRTs, mean retention times; OM, organic matter; VFA, volatile fatty acids. ∗ Corresponding author. Tel.: +86 471 431 7654; fax: +86 471 430 1530. E-mail address: [email protected] (X.Z. Hou). 0377-8401/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.anifeedsci.2008.01.003
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1. Introduction Comparative studies have shown differences between ruminant species in the utilization of roughage diets. These differences may represent distinct feeding strategies as the result of the adaptation for survival in their characteristic natural environment (Van Soest, 1994). According to feeding characteristics, ruminant species can be classified into concentrate selectors, grazers or roughage eaters and an intermediate type called mixed feeders (Hofmann, 1985). Main evolutionary adaptations from concentrate selectors to grazers include a reduction in diet selectivity, an increase in food intake, rumen size and mean retention times (MRTs), and a greater capacity for digestion of roughages. Among the domestic ruminants, sheep are considered as typical grazers and goats as typical intermediate feeders (Hofmann, 1985). Sheep and goats are the most common ruminant species in China playing an important role in food, fiber and leather production. In order to raise the two species scientifically, the differences between them in digestion need to be evaluated. However, direct comparisons between the two species have often produced conflicting results and it is therefore difficult to draw clear conclusions, especially with respect to the influence of diet selectivity on intake and digestibility. The present study was conducted to compare apparent digestibility, rumen fermentation parameters and fractional outflow rate (FOR) between Mongolian and Han crossbred sheep and Inner Mongolian white cashmere goats when opportunity for diet selectivity was avoided.
2. Materials and methods 2.1. Animals and diets Four castrated Mongolian and Han crossbred sheep and four castrated Inner Mongolian cashmere goats, aged 1.5–2 years and weighing 30–35 kg were used, each animal was fitted with a permanent rumen cannula (35 mm internal diameter). Three different pellet diets were used in this study to eliminate the possibility of diet selection. The ingredients and chemical composition of the pellets are presented in Table 1. 2.2. Experimental design and measurement This experiment was conducted in three periods, and animals received one of the three diets in each period. The voluntary feed intake, apparent digestibility, rumen fractional outflow rate and fermentation parameters were measured in each period. Samples of feeds and refusal were taken and pooled in composite samples for each animal during the phrase of digestibility measurement. Each animal’s daily feces were collected for 2 weeks, and the samples (10% of daily fecal output) of each day were pooled to provide a representative sample. The samples were stored individually at −20 ◦ C until analysis. 40 g chromium (Cr) mordanted neutral detergent fiber (NDFom), prepared as described by Ud´en et al. (1980), were administered to the rumen through the rumen cannula approximately 40 min after morning meal of each period. Rumen digesta were sampled immediately prior to Cr-NDFom administration and 1, 2, 4, 6, 9, 12, 15, 18, 21, 24, 28, 32, 36, 40, 44, 48,
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Table 1 Ingredients and chemical composition of diets offered (DM basis) Ingredients (g/kg)
Diets Grass hay diet
Cornstalk diet
Wheat straw diet
Grass hay Cornstalk Wheat straw Corn Soybean meal Sunflower seed meal Limestone Salt CaHPO4 Mineral premix
700 – – 183 84 21 3 3 3 3
– 700 – 183 84 21 3 3 3 3
– – 800 122 56 14 2 2 2 2
Chemical composition (g/kg DM) DMa OM CP NDF ADF CEL
930 934 113 475 315 240
920 937 100 583 370 329
908 892 96.4 516 400 307
a
DM: dry matter; OM: organic matter; CP: crude protein; NDF: neutral detergent fiber; ADF, acid detergent fiber; CEL, cellulose.
54, 60, 66, 72, 84, 96, 108, and 120 h after administration of each period. After drying in a ventilated oven at 65 ◦ C, approximately 0.5 g of rumen samples were taken and subjected to acid digestion in 5 ml of perchloric acid plus 15 ml of nitric acid by heating until total dissolution. After cooling, the sample was diluted with distilled water and was quantitatively transferred through a filter paper (Whatman ashless no. 41) to a 50 ml volumetric flask and was brought to volume for Cr analysis. Samples of rumen fluid were also collected through the cannula of each animal at 07:00, 09:00, 11:00, 13:00, 16:00 and 19:00 h on the last day of each period for pH, ammonia-N and volatile fatty acids (VFAs) determination. 2.3. Chemical analysis Dry matter (DM) in feedstuffs, refusal and pooled fecal samples were determined by drying at 105 ◦ C until constant weight. Organic matter (OM) was determined by ashing overnight at 550 ◦ C. Nitrogen was analyzed by the AOAC method 990.03 (Bellomonte et al., 1987). The NDFom and acid detergent fiber (ADFom) were determined as described by Van Soest et al. (1991). Sulphite and amylase were not used as reagents in the determination of NDFom. Both ADFom and NDFom were expressed exclusive of residual ash. Cellulose (CEL) were determined as described by Robertson and Van Soest (1981). Ammonia-N concentration was determined by using spectrophotometry as described by
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Feng and Gao (1993). VFA concentration was determined as described by Qin (1982) by using gas chromatography. The Cr concentration was determined through atomic absorption spectrophotometry and the data were fitted with the following model: C = C0 × e−kt , in which C is the marker concentration at time t, C0 is the initial marker concentration, k is the FOR of the marker in the rumen, and MRT in the rumen were calculated as 1/k. 2.4. Statistical analysis The means of parameters measured in voluntary feed intake, apparent digestibility coefficients (ADCs) and FOR were analyzed by 2 × 3 factorial analysis of variance using the SAS package (1998). Rumen fermentation data were analyzed as a split-plot design. The difference of means for the treatments was tested by using Duncan’s new multiple range test. Differences among means with P<0.05 were accepted as representing statistically significant differences.
3. Results 3.1. Voluntary intake and apparent digestibility coefficients The voluntary DM intake and ADC are presented in Table 2. DM intake differed among diets and highest voluntary intake was achieved when wheat straw diet was offered (P<0.05). There was difference between species in voluntary DM intake (P<0.05) with mean DM intake values of 70.46 and 60.22 g DM/(kg W0.75 day) for sheep and goats, respectively. The ADC of DM, OM, NDFom, ADFom and CEL differed among diets (P<0.01). When compared with goats, sheep showed higher ADC of ADFom (P<0.01). The same effect was also observed for the ADC of NDFom and CEL. There were interactions (P<0.05) between species and diets for ADC of DM, OM, CEL and crude protein (CP). 3.2. MRT and rumen fermentation parameters FOR (%/h) and MRT (h) of the undigested residues of the diets in the rumen of sheep and goats are given in Table 3. Compared with goats, sheep showed slower rumen FOR (5.06%/h and 6.46%/h for sheep and goats, respectively), and longer rumen MRT (20.12 and 15.75 h for sheep and goats, respectively) (P<0.01). No interaction between species and diets on rumen FOR or MRT was observed. Rumen fermentation parameters of sheep and goats are presented in Table 4. There were no differences between species in rumen fermentation parameters except molar percentage of butyrate. Differences were observed among diets in ammonia-N concentration, total VFA concentration, acetate to propionate ratio (Ac/Pr), molar proportion of acetate and molar proportion of propionate (P<0.01). The percentage of acetate and Ac/Pr was highest when the animals were fed grass hay diets.
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Table 2 Voluntary intake and apparent digestibility coefficients of the diets by sheep and goats Treatmenta Grass hay diet
S.E.M. Cornstalk diet
Intake (gDM/(kgW0.75 day)) Sheep 66.3 B 63.9 B Goats 58.6 55.3
Species
Diet
Species × diet
2.36
*
*
NS
Wheat straw diet 81.1 A 66.8
Source of variationb
DMc Sheep Goats
0.512 0.537 A
0.525 0.477 AB
0.486 0.453 B
0.008
NS
**
*
OM Sheep Goats
0.531 0.562 A
0.542 0.496 AB
0.515 0.477 B
0.008
NS
**
*
CP Sheep Goats
0.645 A 0.648 ab
0.619 AB 0.592 b
0.568 B 0.670 a
0.009
NS
*
**
NDF Sheep Goats
0.415 B 0.418
0.554 A 0.497
0.529 B 0.474
0.015
*
**
NS
ADF Sheep Goats
0.375 B 0.378
0.489 A 0.406
0.388 B 0.333
0.013
**
**
NS
CEL Sheep Goats
0.432 B 0.454
0.540 A 0.470
0.493 AB 0.429
0.011
*
**
*
a
Means with different letters within rows are significantly different (A, B, C: P<0.01; a, b, c: P<0.05). *P<0.05, **P<0.01, NS = P>0.05. c DM: dry matter; OM: organic matter; CP: crude protein; NDF: neutral detergent fiber; ADF, acid detergent fiber; CEL, cellulose. b
Table 3 Fractional outflow rates (%/h) and mean retention times (h) in the rumen Treatmenta Grass hay diet
S.E.M. Cornstalk diet
Source of variationb Species
Diet
Species × diet
0.31
**
NS
NS
0.86
**
NS
NS
Wheat straw diet
FORc Sheep Goats MRTd Sheep Goats a b c d
4.77 5.78 b 21.0 17.3 a
4.73 6.06 b 21.2 16.5 a
5.48 7.76 a 18.9 13.0 b
Means with different letters within rows are significantly different (a, b, c: P<0.05). *P<0.05, **P<0.01, NS = P>0.05. FOR: fractional outflow rate. MRTs: mean retention times.
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Table 4 Fermentation parameters in the rumen of sheep and goats Speciesa
Dietsb
S.E.
Sheep
Goats
G
C
W
6.54 10.7 52.7
6.50 9.10 49.4
6.52 11.8 A 48.4 B
6.54 11.0 A 65.4 A
6.52 7.26 B 39.2 C
0.03 0.68 2.52
Molar proportion of VFA (%) Acetate 57.8 Propionate 28.5 Butyrate 13.3 b Ac/Pr 2.10
57.8 27.3 14.9 a 2.21
60.5 A 24.6 B 14.7 a 2.53 A
58.1 AB 27.0 B 14.9 a 2.19 A
55.1 B 31.7 A 12.6 b 1.77 B
0.73 0.77 0.59 0.08
Ruminal pH NH3 –N (mg/100 ml) Total VFAc (mmol/L)
a b c
Means with different letters within rows are significantly different (A, B, C: P<0.01; a, b, c: P<0.05). G: grass hay diet; C: cornstalk diet; W: wheat straw diet. VFA: volatile fatty acids.
4. Discussion 4.1. Intake and digestion between sheep and goats In the present study, the voluntary intake of sheep (means of three diets) 15% higher than that of goats. Previous study (Ramanzin et al., 1997) showed that with little possibility to choose dietary components, goats, compared with sheep, showed lower food intakes. Results of present experiment were consistent with the above study. The superiority in voluntary DM intake of sheep over goats is possibly due to differences between the species in rumen pool size, rumen FOR of digesta and particle size distribution of rumen content. In this study, digestibility coefficients for fibrous fractions were lower for goats than those for sheep, which was in agreement with previous study (Ramanzin et al., 1997). In contrast, other study (Huston et al., 1988) had presented evidences that goats digested fiber fractions more efficiently than sheep especially for diets high in cell wall content. As described by Morand-Fehr et al. (1991), goats were more selective when roughage diets were offered. As a result, the diet consumed by goats was of higher nitrogen and of lower cell wall content. However, in present study, diet selectivity of goats was avoided. It could explain the difference between this experiment and previous studies. Moreover, a negative relationship between digestibility and rumen FOR had been found (Grovum and Williams, 1977). In this experiment, rumen FOR of goats was faster than that of sheep. The faster FOR and shorter rumen MRT in goats resulted in lacking of sufficient time for rumen microbes adhering to plant tissue and action, thus lower digestion of the fibrous fractions. As shown in Table 2, ADC of CP in goats was highest when wheat straw diet was offered, most probably due to high efficiency of goats to recycle urea through the gut for microbial protein resynthesis under low quality diet.
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4.2. Rumen mean retention times In the present study, the rumen MRT in sheep was longer than that in goats, which was in accord with the conclusion of previous study (Ramanzin et al., 1997). According to Hofmann (1985), the ability of the rumen of different species to retain food particles is related to differences in gut morphology, rumen size, and physiology. Moreover, in this experiment voluntary DM intake was still lower in goats though the faster rumen outflow rates, this suggests that the rumen volume of goats should be comparatively smaller. 4.3. Ruminal fermentation Maintaining a stable rumen environment is critical for the diet utilization. In this experiment, ruminal pH was in the optimal pH ranges (6.5–7.0) and was not affected by species. The differences in ammonia-N concentration among diets may be related directly to the difference of dietary CP contents. In the present experiment, diet had significant effect on total VFA concentration, molar proportion of acetate, propionate and butyrate as well as Ac/Pr. As is well known, VFA produced from the breakdown of carbohydrates, the difference among diets in the content of structural carbohydrates and CP can account for the difference of VFA concentration among diets. 5. Conclusions The comparative study in digestive characteristics showed important differences between sheep and cashmere goats. With elimination of diet selectivity, cashmere goats showed, compared with sheep, lower voluntary DM intake, shorter rumen MRT and lower fiber digestibilities. Thus sheep fitted the characteristics of the typical ‘grazers’. Acknowledgements The authors would like to express their most sincere gratitude to Chinese National Natural Science Foundation (project number: 30360074). References Bellomonte, G., Costantini, A., Giammarioli, S., 1987. Comparison of modified automatic Dumas method and the traditional Kjeldahl method for nitrogen determination in infant food. J. Assoc. Official Anal. Chem. 70, 227–229. Feng, Z.C., Gao, M., 1993. Improvement of method for determination ammonia concentration in rumen fluid by colorimetry. Inner Mongolia J. Anim. Sci. 4, 40–41. Grovum, W.L., Williams, V.J., 1977. Rate of passage of digesta in sheep: 6th. The effect of level of food intake on mathematical predictions of the kinetics of digesta in the reticulorumen and intestines. Br. J. Nutr. 38, 425– 436. Hofmann, R.R., 1985. Digestive physiology of the deer, their morpho-physiological specialization and adaption. In: Biology of Deer Production. Bulletin no. 22. The Royal Society of New Zealand, pp. 393– 407.
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Huston, J.E., Engdahl, B.S., Bales, K.W., 1988. Intake and digestibility in sheep and goats fed three forages with different levels of supplemental protein. Small Rumin. Res. 1, 81–92. Morand-Fehr, P., Owen, E., Giger-reverdin, S., 1991. Feeding behavior of goats at the trough. In: Morand-Fehr, P. (Ed.), Goat Nutrition. EAAP Publication no. 46, Pudoc, Wageningen, pp. 3–12. Qin, W.L., 1982. Improvement of method for measurement volatile fatty acids in the rumen by gas chromatography. J. Nan Jing Agric. Univ. 4, 111–115. Ramanzin, M., Bailoni, L., Schiavon, S., 1997. Effect of forage to concentrate ratio on comparative digestion in sheep, goats and fallow deer. Anim. Sci. 64, 163–170. Robertson, J.B., Van Soest, P.J., 1981. The detergent system of analysis. In: James, W.P.T., Theander, O. (Eds.), The Analysis of Dietary Fiber in Food. Marcel Dekker, NY, pp. 123–158 (Chapter 9). Statistical Analysis Systems Institute, 1998. SAS/STAT User’s Guide. Version6.12. SAS Institute Inc., Cary, NC. Ud´en, P., Colucci, P.E., Van Soest, P.J., 1980. Investigation of chromium, cerium and cobalt as markers in digestion rates of passage studies. J. Sci. Food Agric. 31, 625–632. Van Soest, P.J., Robertson, J.B., Lewis, B.A., 1991. Methods for dietary fiber, neutral detergent fiber and non-starch polysaccharides in relation to animal nutrition. J. Dairy Sci. 74, 3583–3597. Van Soest, P.J., 1994. Nutritional Ecology of the Ruminant, second ed. Cornell University Press, Ithaca, New York.
Animal Feed Science and Technology 146 (2008) 337–344
Short communication
Effect of diet composition on digestion and rumen fermentation parameters in sheep and cashmere goats Dabiao Li a , Xianzhi Hou a,∗ , Yuanyuan Liu b , Yanling Liu a a
College of Animal Science and Animal Medicine, Inner Mongolia Agricultural University, Hohhot 010-018, PR China b College of Science, Inner Mongolia Agricultural University, Hohhot 010-018, PR China
Received 14 February 2007; received in revised form 26 December 2007; accepted 16 January 2008
Abstract The study was carried out to compare the voluntary intake, digestibility, mean retention times (MRTs) and rumen fermentation parameters in sheep and cashmere goats offered three pellet diets. Four Mongolian and Han crossbred sheep and four Inner Mongolian white cashmere goats, each fitted with a rumen cannula, were used in this study. The results showed that there were differences between sheep and goats in voluntary intake (P<0.05), apparent digestibility of fiber and MRT (P<0.01). Dietary types affected voluntary intake, apparent digestibility and rumen fermentation parameters (except pH). Sheep showed high voluntary dry matter (DM) intake, long rumen MRT and high apparent digestibility of fiber. When opportunity for diet selectivity was avoided, cashmere goats, compared with sheep, showed lower voluntary DM intake, shorter rumen MRT and lower apparent digestibility of fiber. Rumen fermentation parameters did not show differences between sheep and goats. © 2008 Elsevier B.V. All rights reserved. Keywords: Intake; Digestion; Mean retention times; Fermentation; Sheep; Goats
Abbreviations: ADCs, apparent digestibility coefficients; ADFom, acid detergent fiber expressed exclusive of residual ash; CEL, cellulose; CP, crude protein; DM, dry matter; FOR, fractional outflow rate; NDFom, neutral detergent fiber not assayed with a heat stable amylase and expressed exclusive of residual ash; MRTs, mean retention times; OM, organic matter; VFA, volatile fatty acids. ∗ Corresponding author. Tel.: +86 471 431 7654; fax: +86 471 430 1530. E-mail address: [email protected] (X.Z. Hou). 0377-8401/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.anifeedsci.2008.01.003
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1. Introduction Comparative studies have shown differences between ruminant species in the utilization of roughage diets. These differences may represent distinct feeding strategies as the result of the adaptation for survival in their characteristic natural environment (Van Soest, 1994). According to feeding characteristics, ruminant species can be classified into concentrate selectors, grazers or roughage eaters and an intermediate type called mixed feeders (Hofmann, 1985). Main evolutionary adaptations from concentrate selectors to grazers include a reduction in diet selectivity, an increase in food intake, rumen size and mean retention times (MRTs), and a greater capacity for digestion of roughages. Among the domestic ruminants, sheep are considered as typical grazers and goats as typical intermediate feeders (Hofmann, 1985). Sheep and goats are the most common ruminant species in China playing an important role in food, fiber and leather production. In order to raise the two species scientifically, the differences between them in digestion need to be evaluated. However, direct comparisons between the two species have often produced conflicting results and it is therefore difficult to draw clear conclusions, especially with respect to the influence of diet selectivity on intake and digestibility. The present study was conducted to compare apparent digestibility, rumen fermentation parameters and fractional outflow rate (FOR) between Mongolian and Han crossbred sheep and Inner Mongolian white cashmere goats when opportunity for diet selectivity was avoided.
2. Materials and methods 2.1. Animals and diets Four castrated Mongolian and Han crossbred sheep and four castrated Inner Mongolian cashmere goats, aged 1.5–2 years and weighing 30–35 kg were used, each animal was fitted with a permanent rumen cannula (35 mm internal diameter). Three different pellet diets were used in this study to eliminate the possibility of diet selection. The ingredients and chemical composition of the pellets are presented in Table 1. 2.2. Experimental design and measurement This experiment was conducted in three periods, and animals received one of the three diets in each period. The voluntary feed intake, apparent digestibility, rumen fractional outflow rate and fermentation parameters were measured in each period. Samples of feeds and refusal were taken and pooled in composite samples for each animal during the phrase of digestibility measurement. Each animal’s daily feces were collected for 2 weeks, and the samples (10% of daily fecal output) of each day were pooled to provide a representative sample. The samples were stored individually at −20 ◦ C until analysis. 40 g chromium (Cr) mordanted neutral detergent fiber (NDFom), prepared as described by Ud´en et al. (1980), were administered to the rumen through the rumen cannula approximately 40 min after morning meal of each period. Rumen digesta were sampled immediately prior to Cr-NDFom administration and 1, 2, 4, 6, 9, 12, 15, 18, 21, 24, 28, 32, 36, 40, 44, 48,
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Table 1 Ingredients and chemical composition of diets offered (DM basis) Ingredients (g/kg)
Diets Grass hay diet
Cornstalk diet
Wheat straw diet
Grass hay Cornstalk Wheat straw Corn Soybean meal Sunflower seed meal Limestone Salt CaHPO4 Mineral premix
700 – – 183 84 21 3 3 3 3
– 700 – 183 84 21 3 3 3 3
– – 800 122 56 14 2 2 2 2
Chemical composition (g/kg DM) DMa OM CP NDF ADF CEL
930 934 113 475 315 240
920 937 100 583 370 329
908 892 96.4 516 400 307
a
DM: dry matter; OM: organic matter; CP: crude protein; NDF: neutral detergent fiber; ADF, acid detergent fiber; CEL, cellulose.
54, 60, 66, 72, 84, 96, 108, and 120 h after administration of each period. After drying in a ventilated oven at 65 ◦ C, approximately 0.5 g of rumen samples were taken and subjected to acid digestion in 5 ml of perchloric acid plus 15 ml of nitric acid by heating until total dissolution. After cooling, the sample was diluted with distilled water and was quantitatively transferred through a filter paper (Whatman ashless no. 41) to a 50 ml volumetric flask and was brought to volume for Cr analysis. Samples of rumen fluid were also collected through the cannula of each animal at 07:00, 09:00, 11:00, 13:00, 16:00 and 19:00 h on the last day of each period for pH, ammonia-N and volatile fatty acids (VFAs) determination. 2.3. Chemical analysis Dry matter (DM) in feedstuffs, refusal and pooled fecal samples were determined by drying at 105 ◦ C until constant weight. Organic matter (OM) was determined by ashing overnight at 550 ◦ C. Nitrogen was analyzed by the AOAC method 990.03 (Bellomonte et al., 1987). The NDFom and acid detergent fiber (ADFom) were determined as described by Van Soest et al. (1991). Sulphite and amylase were not used as reagents in the determination of NDFom. Both ADFom and NDFom were expressed exclusive of residual ash. Cellulose (CEL) were determined as described by Robertson and Van Soest (1981). Ammonia-N concentration was determined by using spectrophotometry as described by
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Feng and Gao (1993). VFA concentration was determined as described by Qin (1982) by using gas chromatography. The Cr concentration was determined through atomic absorption spectrophotometry and the data were fitted with the following model: C = C0 × e−kt , in which C is the marker concentration at time t, C0 is the initial marker concentration, k is the FOR of the marker in the rumen, and MRT in the rumen were calculated as 1/k. 2.4. Statistical analysis The means of parameters measured in voluntary feed intake, apparent digestibility coefficients (ADCs) and FOR were analyzed by 2 × 3 factorial analysis of variance using the SAS package (1998). Rumen fermentation data were analyzed as a split-plot design. The difference of means for the treatments was tested by using Duncan’s new multiple range test. Differences among means with P<0.05 were accepted as representing statistically significant differences.
3. Results 3.1. Voluntary intake and apparent digestibility coefficients The voluntary DM intake and ADC are presented in Table 2. DM intake differed among diets and highest voluntary intake was achieved when wheat straw diet was offered (P<0.05). There was difference between species in voluntary DM intake (P<0.05) with mean DM intake values of 70.46 and 60.22 g DM/(kg W0.75 day) for sheep and goats, respectively. The ADC of DM, OM, NDFom, ADFom and CEL differed among diets (P<0.01). When compared with goats, sheep showed higher ADC of ADFom (P<0.01). The same effect was also observed for the ADC of NDFom and CEL. There were interactions (P<0.05) between species and diets for ADC of DM, OM, CEL and crude protein (CP). 3.2. MRT and rumen fermentation parameters FOR (%/h) and MRT (h) of the undigested residues of the diets in the rumen of sheep and goats are given in Table 3. Compared with goats, sheep showed slower rumen FOR (5.06%/h and 6.46%/h for sheep and goats, respectively), and longer rumen MRT (20.12 and 15.75 h for sheep and goats, respectively) (P<0.01). No interaction between species and diets on rumen FOR or MRT was observed. Rumen fermentation parameters of sheep and goats are presented in Table 4. There were no differences between species in rumen fermentation parameters except molar percentage of butyrate. Differences were observed among diets in ammonia-N concentration, total VFA concentration, acetate to propionate ratio (Ac/Pr), molar proportion of acetate and molar proportion of propionate (P<0.01). The percentage of acetate and Ac/Pr was highest when the animals were fed grass hay diets.
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Table 2 Voluntary intake and apparent digestibility coefficients of the diets by sheep and goats Treatmenta Grass hay diet
S.E.M. Cornstalk diet
Intake (gDM/(kgW0.75 day)) Sheep 66.3 B 63.9 B Goats 58.6 55.3
Species
Diet
Species × diet
2.36
*
*
NS
Wheat straw diet 81.1 A 66.8
Source of variationb
DMc Sheep Goats
0.512 0.537 A
0.525 0.477 AB
0.486 0.453 B
0.008
NS
**
*
OM Sheep Goats
0.531 0.562 A
0.542 0.496 AB
0.515 0.477 B
0.008
NS
**
*
CP Sheep Goats
0.645 A 0.648 ab
0.619 AB 0.592 b
0.568 B 0.670 a
0.009
NS
*
**
NDF Sheep Goats
0.415 B 0.418
0.554 A 0.497
0.529 B 0.474
0.015
*
**
NS
ADF Sheep Goats
0.375 B 0.378
0.489 A 0.406
0.388 B 0.333
0.013
**
**
NS
CEL Sheep Goats
0.432 B 0.454
0.540 A 0.470
0.493 AB 0.429
0.011
*
**
*
a
Means with different letters within rows are significantly different (A, B, C: P<0.01; a, b, c: P<0.05). *P<0.05, **P<0.01, NS = P>0.05. c DM: dry matter; OM: organic matter; CP: crude protein; NDF: neutral detergent fiber; ADF, acid detergent fiber; CEL, cellulose. b
Table 3 Fractional outflow rates (%/h) and mean retention times (h) in the rumen Treatmenta Grass hay diet
S.E.M. Cornstalk diet
Source of variationb Species
Diet
Species × diet
0.31
**
NS
NS
0.86
**
NS
NS
Wheat straw diet
FORc Sheep Goats MRTd Sheep Goats a b c d
4.77 5.78 b 21.0 17.3 a
4.73 6.06 b 21.2 16.5 a
5.48 7.76 a 18.9 13.0 b
Means with different letters within rows are significantly different (a, b, c: P<0.05). *P<0.05, **P<0.01, NS = P>0.05. FOR: fractional outflow rate. MRTs: mean retention times.
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Table 4 Fermentation parameters in the rumen of sheep and goats Speciesa
Dietsb
S.E.
Sheep
Goats
G
C
W
6.54 10.7 52.7
6.50 9.10 49.4
6.52 11.8 A 48.4 B
6.54 11.0 A 65.4 A
6.52 7.26 B 39.2 C
0.03 0.68 2.52
Molar proportion of VFA (%) Acetate 57.8 Propionate 28.5 Butyrate 13.3 b Ac/Pr 2.10
57.8 27.3 14.9 a 2.21
60.5 A 24.6 B 14.7 a 2.53 A
58.1 AB 27.0 B 14.9 a 2.19 A
55.1 B 31.7 A 12.6 b 1.77 B
0.73 0.77 0.59 0.08
Ruminal pH NH3 –N (mg/100 ml) Total VFAc (mmol/L)
a b c
Means with different letters within rows are significantly different (A, B, C: P<0.01; a, b, c: P<0.05). G: grass hay diet; C: cornstalk diet; W: wheat straw diet. VFA: volatile fatty acids.
4. Discussion 4.1. Intake and digestion between sheep and goats In the present study, the voluntary intake of sheep (means of three diets) 15% higher than that of goats. Previous study (Ramanzin et al., 1997) showed that with little possibility to choose dietary components, goats, compared with sheep, showed lower food intakes. Results of present experiment were consistent with the above study. The superiority in voluntary DM intake of sheep over goats is possibly due to differences between the species in rumen pool size, rumen FOR of digesta and particle size distribution of rumen content. In this study, digestibility coefficients for fibrous fractions were lower for goats than those for sheep, which was in agreement with previous study (Ramanzin et al., 1997). In contrast, other study (Huston et al., 1988) had presented evidences that goats digested fiber fractions more efficiently than sheep especially for diets high in cell wall content. As described by Morand-Fehr et al. (1991), goats were more selective when roughage diets were offered. As a result, the diet consumed by goats was of higher nitrogen and of lower cell wall content. However, in present study, diet selectivity of goats was avoided. It could explain the difference between this experiment and previous studies. Moreover, a negative relationship between digestibility and rumen FOR had been found (Grovum and Williams, 1977). In this experiment, rumen FOR of goats was faster than that of sheep. The faster FOR and shorter rumen MRT in goats resulted in lacking of sufficient time for rumen microbes adhering to plant tissue and action, thus lower digestion of the fibrous fractions. As shown in Table 2, ADC of CP in goats was highest when wheat straw diet was offered, most probably due to high efficiency of goats to recycle urea through the gut for microbial protein resynthesis under low quality diet.
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4.2. Rumen mean retention times In the present study, the rumen MRT in sheep was longer than that in goats, which was in accord with the conclusion of previous study (Ramanzin et al., 1997). According to Hofmann (1985), the ability of the rumen of different species to retain food particles is related to differences in gut morphology, rumen size, and physiology. Moreover, in this experiment voluntary DM intake was still lower in goats though the faster rumen outflow rates, this suggests that the rumen volume of goats should be comparatively smaller. 4.3. Ruminal fermentation Maintaining a stable rumen environment is critical for the diet utilization. In this experiment, ruminal pH was in the optimal pH ranges (6.5–7.0) and was not affected by species. The differences in ammonia-N concentration among diets may be related directly to the difference of dietary CP contents. In the present experiment, diet had significant effect on total VFA concentration, molar proportion of acetate, propionate and butyrate as well as Ac/Pr. As is well known, VFA produced from the breakdown of carbohydrates, the difference among diets in the content of structural carbohydrates and CP can account for the difference of VFA concentration among diets. 5. Conclusions The comparative study in digestive characteristics showed important differences between sheep and cashmere goats. With elimination of diet selectivity, cashmere goats showed, compared with sheep, lower voluntary DM intake, shorter rumen MRT and lower fiber digestibilities. Thus sheep fitted the characteristics of the typical ‘grazers’. Acknowledgements The authors would like to express their most sincere gratitude to Chinese National Natural Science Foundation (project number: 30360074). References Bellomonte, G., Costantini, A., Giammarioli, S., 1987. Comparison of modified automatic Dumas method and the traditional Kjeldahl method for nitrogen determination in infant food. J. Assoc. Official Anal. Chem. 70, 227–229. Feng, Z.C., Gao, M., 1993. Improvement of method for determination ammonia concentration in rumen fluid by colorimetry. Inner Mongolia J. Anim. Sci. 4, 40–41. Grovum, W.L., Williams, V.J., 1977. Rate of passage of digesta in sheep: 6th. The effect of level of food intake on mathematical predictions of the kinetics of digesta in the reticulorumen and intestines. Br. J. Nutr. 38, 425– 436. Hofmann, R.R., 1985. Digestive physiology of the deer, their morpho-physiological specialization and adaption. In: Biology of Deer Production. Bulletin no. 22. The Royal Society of New Zealand, pp. 393– 407.
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