effects of feeding salt-tolerant forage cultivated in saline-alkaline land on rumen fermentation,...

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Research ArticleReceived: 29 March 2010 Revised: 6 November 2010 Accepted: 19 December 2010 Published online in Wiley Online Library: 15 February 2011

(wileyonlinelibrary.com) DOI 10.1002/jsfa.4308

Effects of feeding salt-tolerant foragecultivated in saline-alkaline land on rumenfermentation, feed digestibility and nitrogenbalance in lambCong Wang,a Kuan Hu Dong,a∗ Qiang Liu,a Wen Zhu Yang,a,b Xiang Zhao,a

Sheng Qiang Liu,a Ting Ting Hea and Zhuang Yu Liua

Abstract

BACKGROUND: Mixing salt-tolerant plants with other plants may affect rumen fermentation, which could result in an increaseof feed conversion rate. The objective of this study was to evaluate the effects of partially or entirely replacing the corn stoverwith a mixture of salt-tolerant forage (Dahurian wildrye grass, weeping alkaligrass and erect milkvetch) in the diet of lambs onruminal fermentation, feed digestibility and nitrogen (N) balance. Ratios of corn stover to the mixture of salt-tolerant foragesin the four experimental diets were 100 : 0, 67 : 33, 33 : 67 and 0 : 100, respectively, for control, low (LF), medium (MF) and high(HF).

RESULTS: Ruminal pH was lower (P = 0.048) with LF and MF than with control and HF diets. Total VFA concentration wasconsistently higher (P = 0.039) for LF and MF than for control and HF with increasing amount of salt-tolerant forage. Ratio ofacetate to propionate was linearly (P = 0.019) decreased due to the decrease in acetate production. Digestibilities of OM, NDFand CP in the whole tract linearly (P < 0.002) decreased with increasing amount of salt-tolerant forage. Similarly, retained Nand ratio of retained N to digestible N also linearly (P < 0.005) decreased.

CONCLUSION: Feeding salt-tolerant forage cultivated in saline-alkaline land improved rumen fermentation with increased totalVFA production, and changed the rumen fermentation pattern to increased butyrate production. However, the decreased feeddigestibility in the whole digestive tract of lamb may reduce nutrient availability to animals and thus adversely affect animalproductivity. Additionally, feeding salt-tolerant forages may require more protein supplement to meet animal requirements,because of the low protein content and low protein digestibility of the salt-tolerant forages.c© 2011 Society of Chemical Industry

Keywords: salt-tolerant forage; rumen fermentation; digestibility; nitrogen balance; lamb

INTRODUCTIONSalinity is one of the most prominent problems in the world.1

Approximately 20% of agricultural land and 50% of crop landin the world is salt affected.2,3 Farmers of salt-affected areascan face scarcity of livestock feed and often purchase fodderor grain at high cost for their livestock from other areas. Salt-tolerant forage can be grown on salt-affected lands. Improvedeconomic efficiency can be achieved if salt-tolerant forage canbe grown and utilized.4 Considerable effort has been invested indeveloping or improving production through the establishmentand grazing of salt-tolerant forages.5 Although there are many salt-tolerant forages available, evaluation of these plants has focusedon persistence and forage production, which has often resultedin poor nutritive value for ruminants.6 In general, salt-tolerantplant species contain high crude protein but low metabolizableenergy and high salt.7,8 Norman et al.7 reported that grazinga combination of salt-tolerant grasses, legumes and saltbushspecies improved feeding value and animal production. Henceimproved animal productivity should be achieved if salt-tolerant

plants are offered with other plants because of differences intheir nutritional profile. Weeping alkaligrass (Puccinellia distans [L.]Parl.), a salt-tolerant plant typically occupying high-pH soils,9,10 iswidespread across arid and salt-affected lands.11 Dahurian wildryegrass (Elymus dahuricus Turcz.) and erect milkvetch (Astragalusadsurgens Pall.) are grown across arid areas in the north of China.Information on feeding values of weeping alkaligrass, Dahurianwildrye grass and erect milkvetch cultivated in saline-alkalineland for ruminants is limited. The objectives of this work were toinvestigate the effects of feeding salt-tolerant forage (a mixture of

∗ Correspondence to: Kuan Hu Dong, College of Animal Sciences and VeterinaryMedicines, Shanxi Agricultural University, Taigu, Shanxi 030801, PR China.E-mail: [email protected]

a College of Animal Sciences and Veterinary Medicines, Shanxi AgriculturalUniversity, Taigu, Shanxi 030801, PR China

b Agriculture and Agri-Food Canada, Research Centre, PO Box 3000, Lethbridge,Alberta, Canada

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www.soci.org C Wang et al.

Table 1. Chemical composition of salt-tolerant forage versus cornstover (g kg−1 dry matter)

Chemical composition Salt-tolerant foragea Corn stover

Organic matter 934 946

Crude protein 67 76

Neutral detergent fibre 695 637

Acid detergent fibre 424 353

Calcium (Ca) 4.60 3.70

Phosphorus (P) 3.33 2.60

Potassium (K) 0.38 0.34

Sodium (Na) 0.28 0.15

Chlorine (Cl) 0.31 0.25

Sulfur (S) 2.38 1.17

Magnesium (Mg) 0.21 0.22

a Dahurian wildrye grass (Elymus dahuricus Turcz.), weeping alkaligrass(Puccinellia distans (L.) Parl.) and erect milkvetch (Astragalus adsurgensPall.) were mixed together in a ratio of 45 : 35:20.

Dahurian wildrye grass, weeping alkaligrass and erect milkvetch)cultivated in saline-alkaline land on rumen fermentation, feeddigestibility and nitrogen balance in lambs.

MATERIALS AND METHODSForage preparationDahurian wildrye grass (Elymus dahuricus Turcz., Tianjin BarenbrugForage Co., Ltd, Tianjin, China), weeping alkaligrass (Puccinelliadistans (L.) Parl., Gansu Xintiandi Ecological Agriculture Co., Ltd,Lanzhou, China) and erect milkvetch (Astragalus adsurgens Pall.,Inner Mongolian Clover Seed & Turf Co., Ltd, Huhhot, China)were cultivated in saline-alkaline soil (pH 8.99, total soluble salt8.33 g kg−1, Ca2+ 0.17 g kg−1, Mg2+ 0.06 g kg−1, K+ 0.12 g kg−1,Na+ 0.66 g kg−1, Cl− 4.99 g kg−1) at the Youyu, Shanxi, China.The region is located between 39◦ 59′ 09′′ and 39◦ 59′ 18′′ N,and 112◦ 19′ 27′′ and 112◦ 19′ 33′′ E, at an altitude range of1329–1338 m over sea level. Corn (Danyu401, Liaoning DandongAgricultural Science and Technology Co., Ltd China) was cultivatedin non-saline soil (pH 6.02, total soluble salt 3.45 g kg−1, Ca2+

0.09 g kg−1, Mg2+ 0.05 g kg−1, K+ 0.11 g kg−1, Na+ 0.36 g kg−1,Cl− 2.39 g kg−1) located between 40◦ 12′ 03′′ and 40◦ 12′18′′ N,and 112◦ 19′ 46′′ and 112◦ 19′ 52′′ E, at an altitude of 1359 m abovesea level. Climate is classified as dry area with annual precipitationof 400 mm. The grasses were harvested at soft dough stagesby forage harvester (9G-1.25, Luoyang Sida Farm Machinery Co.,Ltd, Luoyang, China), air-dried and gathered into square bales(approximately 35 kg) and stored indoors. All forages were groundin a tub grinder through a 6.35 cm screen before feeding. Amixture of Dahurian wildrye grass, weeping alkaligrass and erectmilkvetch were prepared in a ratio of 45 : 35:20, respectively.Chemical composition of the saline-alkaline forage and corn stoverare shown in Table 1.

Animals and experimental designTwenty-eight first-generation (F1) lambs of a cross betweenChinese Inner Mongolian Fine-wool and German Mutton Merino(5.0 ± 0.15 months; 34.6 ± 0.57 kg of body weight (BW)), werearranged into four treatments in a randomized block design.Treatments were: control (51% corn stover and 49% concentrate,

Table 2. Ingredient and chemical composition of diet (g kg−1 drymatter)

Treatmenta

Control LF MF HF

Ingredients

Corn stover 510.0 340.0 170.0 . . .

Salt-tolerant forage . . . 170.0 340.0 510.0

Corn grain, ground 272.0 272.0 272.0 272.0

Wheat bran 47.5 47.5 47.5 47.5

Soybean meal 50.0 50.0 50.0 50.0

Cottonseed cake 75.0 75.0 75.0 75.0

Rapeseed meal 30.0 30.0 30.0 30.0

Calcium carbonate 5.0 5.0 5.0 5.0

Salt 5.0 5.0 5.0 5.0

Dicalcium phosphate 5.0 5.0 5.0 5.0

Mineral and vitamin mixtureb 0.5 0.5 0.5 0.5

Chemical composition

Organic matter 946.8 944.8 942.7 940.7

Crude protein 130.8 129.3 127.9 126.4

Neutral detergent fibre 443.7 453.5 463.3 473.1

Acid detergent fibre 274.6 286.7 298.9 311.0

Calcium 9.6 9.8 9.9 10.1

Phosphorus 4.2 4.3 4.4 4.6

DEc (MJ kg−1) 13.3 13.1 12.8 12.5

a LF, low forage; MF, medium forage; HF, high forage; in which themixture of salt-tolerant forages (Dahurian wildrye grass, weepingalkaligrass and erect milkvetch in a ratio of 45 : 35:20) replaced one-third, two-thirds or all of the corn stover, respectively.b Contained 5000 mg kg−1 Co, 16 000 mg kg−1 Cu, 55 000 mg kg−1 Fe,50 000 mg kg−1 Mn, 70 000 mg kg−1 Zn, 4000 mg kg−1 I, 6000 mg kg−1

Se, 10 000 IU g−1 vitamin A, 600 IU g−1 vitamin D and 80 IU g−1 ofvitamin E.c DE, digestible energy; estimated based on the gross energy of dietsand the digestibility of gross energy.

dry matter (DM) basis), LF (low forage), MF (medium forage) andHF (high forage) in which the mixture of salt-tolerant forages(Dahurian wildrye grass, weeping alkaligrass and erect milkvetchin a ratio of 45 : 35:20) replaced either one-third, two-thirds orall of the corn stover, respectively (Table 2). Lambs were fedtwice daily at 0700 and 1900 h with water provided ad libitum.Experimental periods were 21 days with 11 days of adaptationand 10 days of sampling. Lambs were housed in metabolismcrates with expanded metal flooring.12 Lambs were removed fromthe metabolism crates and exercised for 30 min twice daily in apaddock during the acclimation period. Lambs were weighed atthe beginning and the end of sampling period. The experiment wasconducted at Youyu Elite Lamb Breeding Base of Shanxi AgricultureUniversity. The experimental protocol was approved by the AnimalCare and Use Committee of Shanxi Agriculture University.

Measurements and collection of samplesFeed offered and refusals were individually recorded daily fromday 12 to 19 of the sampling period to calculate feed intake.Samples of concentrate, roughage and feed refusals werecollected once daily for DM determination, and then pooled bylamb. The samples were dried in an oven at 55 ◦C for 48 h, andground to pass a 1 mm screen with a mill (FZ102, Shanghai HongJi instrument Co., Ltd, Shanghai, China) for chemical analysis.

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The daily output of faeces and urine were measured for sixconsecutive days from day 12 to 19 of the sampling period. Aharness system fitted with a faecal collection bag and a urinefunnel was put on the lamb the day prior to starting the collectionperiod. Urine was collected under continuous vacuum into acontainer containing 50 mL of 12 mol L−1 sulfuric acid. Faecaloutput and urine quantity were recorded daily. Faecal samples(1/10 of wet weight) were collected and pooled by lamb. Afterdrying at 55 ◦C for 48 h, the samples were ground to pass a 1 mmsieve for chemical analysis. Urine volume was recorded daily,pooled by lamb, and an aliquot frozen for chemical analysis.

At 0, 3, 6 and 9 h after the 0700 h feeding on days 20 and 21,rumen fluid (about 100 mL) was collected via the oesophagususing a stomach tube (outside diameter 1 cm., inside diameter0.8 cm, length 200 cm) connected to a mild vacuum pump(Speedivac 2, Edwards High Vacuum, Crawley, UK) from severalsites within the rumen.13 When the tube was employed, aback-and-forth action was found to be desirable in obtaininglarge quantities of contents from different sites within therumen.14 The samples were then strained through four layersof cheesecloth. The pH was immediately measured using anelectric pH meter (Sartorius Basic pH Meter PB-20, Sartorius AG,Goettingen, Germany). Five millilitres of filtrate was preservedby adding 1 mL of 250 g L−1 metaphosphoric acid, and a second5 mL of filtrate was preserved by adding 1 mL of 20 g L−1 H2SO4

to determine, respectively, volatile fatty acid (VFA) and NH3. Thesamples were subsequently stored frozen at −20 ◦C until analysis.

Chemical analysesThe DM content of samples was determined by drying at 135 ◦Cfor 3 h (AOAC method 930.15).15 The organic matter (OM) contentwas calculated as the difference between DM and ash contents,with ash determined by combustion at 550 ◦C for 5 h. The amylase-treated neutral detergent fibre (aNDF) and acid detergent fibre(ADF) contents were determined using the methods describedby Van Soest et al.16 with heat-stable alpha-amylase and sodiumsulfite used in the NDF procedure, and expressed inclusive ofresidual ash. Content of N in the samples was determined by theKjeldahl method (AOAC method 976.05).15 VFAs were separatedand quantified by gas chromatography (GC102AF; ShanghaiSpecialties Ltd, China) using a 2 m (4 mm diameter) fusedPEG2000, Chromsob W AW DMCS column (GC102AF; ShanghaiSpecialties Ltd) with 2-ethylbutyric acid as internal standard.Ammonia N was determined using the method of AOAC.15

Content of ether extract in the samples was determined by theCodex-adopted AOAC method (AOAC method 920.39).15 Contentof phosphorus in the samples was determined by the photometricmethod (AOAC method 965.17) in a spectrophotometer.15

Content of soluble chlorine in the samples was determined by thetitrimetric method (AOAC method 943.01).15 Content of sodium,potassium and calcium were determined by atomic absorptionspectrophotometric method (AOAC method 985.35).15 Grossenergy (GE) contents of concentrate, forages, refusal and faecalsamples were measured by oxygen bomb calorimeter (XRY-1CPC, Shanghai Changyi Gealogical Instruments Co., Ltd, Shanghai,China) using benzoic acid as a standard (26 436 J g−1, NationalInstitute of Standards Material Research Center, Beijing, China).

Calculations and statistical analysesDigestible energy of the diets was calculated by multiplying thegross energy content of the diet by its digestibility. The last was

calculated from gross energy intake and output in the faeces.Apparent digestibility of DM in the total tract of lambs wascalculated from DM intake and DM faecal output. Digestible N wascalculated as the difference between N intake and faecal N output.Retained N (RN, g d−1) was calculated as the difference betweendigestible N and urinary N output. Data were analysed using themixed model procedure of SAS (Proc Mixed)17 to account for thetreatment as fixed effect and block as a random effect. Data forruminal pH, VFA and ammonia N were summarized by samplingtime and then analysed using the same mixed model but withtime included as a repeated measure using compound symmetry.Linear and quadratic orthogonal contrasts were tested using theCONTRAST statement of SAS with coefficients estimated based onthe forage application rates. Least squares means were calculatedfor each experiment. Effects of the factors were declared significantat P < 0.05 unless otherwise noted and trends were discussed atP < 0.10.

RESULTSRuminal pH, ammonia N and VFA profiles are shown in Table 3.Mean ruminal pH was lower (P = 0.048) for LF and MF thanfor control and HF diets (quadratic response; P = 0.045). Inconsistency with ruminal pH, total ruminal VFA concentration washigher (P = 0.039) with LF and MF than with control and HF(quadratic response; P = 0.005). The molar proportion of acetatelinearly (P = 0.001) decreased with addition of salt-tolerant forage,bur there was no difference in the molar proportion of propionatewith increasing amount of salt-tolerant forage cultivated in saline-alkaline land. Consequently, the ratio of acetate to propionatedeclined linearly (P = 0.019). Additionally, the molar proportionof butyrate and valerate linearly (P < 0.03) increased, with nodifferences in that of isobutyrate and isovalerate for increasingamount of salt-tolerant forage. Ruminal ammonia N contentquadratically (P = 0.019) responded to the addition of salt-tolerant forage, being lowest for control and HF and highestfor MF (P = 0.018).

Intake and nutrient digestibilities in the total tract are shownin Table 4. Intakes of DM, OM, aNDF and ADF were not affected(P > 0.05) by the treatments. However, the digestibilities of DM,OM, crude protein (CP), aNDF and ADF in the total digestivetract of lambs linearly (P < 0.002) decreased with increasingamount of salt-tolerant forage. Furthermore, the digestibilities ofall nutrients followed the same variation pattern such that thedigestibility declined considerably from control to LF and MF, andthen decreased again from MF to HF.

Nitrogen balance is shown in Table 5. The intake of N linearly(P = 0.001) decreased with the addition of salt-tolerant forage.However, the amount of N excreted from faeces or urine wasnot affected (P > 0.05) by the addition of salt-tolerant forage.Consequently, digestible N, retained N and the ratio of retained Nto digestible N all linearly (P < 0.005) decreased with increasingamount of salt-tolerant forage.

DISCUSSIONThe lack of difference in DM intake with the substitution of cornstover for salt-tolerant forage in the diet of lambs suggested thatthe palatability of salt-tolerant forage was not different from thecorn stover, despite its higher salt content. Despite the lack ofdifference in DM intake, ruminal VFA concentrations were higherfor lambs fed a mixture of salt-tolerant forage and corn stover than

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Table 3. Effects of feeding salt-tolerant forage cultivated in saline-alkaline land on ruminal pH and fermentation in lambs

Treatmenta Contrast (P)

Control LF MF HF SE Treatment Linear Quadratic

PH 7.04a 6.92b 6.96b 7.08a 0.026 0.048 0.600 0.045

Total VFA (mmol L−1) 60.04b 74.22a 75.17a 62.94b 2.205 0.039 0.526 0.005

(mol 100 mol−1)

Acetate (A) 75.25a 69.43b 67.48b 65.50b 0.791 0.002 0.001 0.187

Propionate (P) 15.52 18.27 18.29 18.61 0.585 0.550 0.177 0.370

Butyrate 7.69b 10.52ab 12.44ab 13.73a 0.767 0.014 0.021 0.638

Valerate 0.20b 0.29a 0.30a 0.35a 0.013 0.007 0.001 0.454

Isobutyrate 0.79 0.83 0.76 0.97 0.054 0.509 0.467 0.477

Isovalerate 0.52 0.63 0.70 0.80 0.042 0.222 0.055 0.954

A : P 4.91a 4.10b 3.99b 3.83b 0.125 0.021 0.019 0.227

Ammonia N (mg 100 mL−1) 5.76b 6.40ab 7.58a 5.86b 0.241 0.018 0.539 0.019

Means with different letters in the same row differ significantly (P < 0.05).a LF, low forage; MF, medium forage; HF, high forage; in which the mixture of salt-tolerant forages (Dahurian wildrye grass, weeping alkaligrass anderect milkvetch in a ratio of 45 : 35:20) replaced one-third, two-thirds or all of the corn stover, respectively.

Table 4. Effects of feeding salt-tolerant forage cultivated in saline-alkaline land on nutrient digestibility in the total digestive tract of lamb



Intake (g d−1)

Dry matter 1110 1104 1109 1109 25.1 0.326 0.481 0.521

Organic matter 1051 1043 1045 1044 19.0 0.432 0.568 0.285

Neutral detergent fibre 492 501 514 525 16.5 0.165 0.101 0.632

Acid detergent fibre 305 317 331 345 14.3 0.187 0.124 0.785

Digestibility

Dry matter 0.732a 0.676b 0.688b 0.636c 0.007 0.001 0.001 0.835

Organic matter 0.755a 0.693b 0.705b 0.654c 0.007 0.001 0.001 0.623

Crude protein 0.735a 0.680b 0.687b 0.647c 0.006 0.001 0.001 0.523

Ether extract 0.759a 0.667b 0.673b 0.584c 0.012 0.001 0.001 0.542

Neutral detergent fibre 0.683a 0.576b 0.586b 0.521c 0.011 0.001 0.001 0.192

Acid detergent fibre 0.639a 0.544b 0.570b 0.494c 0.013 0.005 0.002 0.677


Table 5. Effects of feeding salt-tolerant forage cultivated in saline-alkaline land on nitrogen (N) balance in lambs



N intake (g d−1) 23.83a 23.12a 22.47ab 21.04b 0.489 0.001 0.001 0.055

Faecal N (g d−1) 6.73 7.42 7.20 7.38 0.106 0.106 0.232 0.857

Urinary N (g d−1) 9.93 9.72 9.17 9.26 0.164 0.125 0.077 0.237

Total N excreted (g d−1) 16.67 17.14 16.36 16.64 0.241 0.186 0.446 0.408

Urinary N : total excreted N 0.595a 0.566b 0.560b 0.556b 0.004 0.047 0.008 0.168

Digestible N (g d−1) 21.09a 15.70b 15.77b 13.65b 0.524 0.001 0.001 0.067

N retained (g d−1) 7.16a 5.97b 6.11b 4.39c 0.536 0.002 0.001 0.205

Retained N : digestible N 0.419a 0.381b 0.399b 0.322c 0.021 0.009 0.005 0.731



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for those fed either alone, whereas the digestibilities of DM, OM,NDF and CP in the whole tract of lambs decreased. The increasein VFA concentration for lambs fed a mixture of salt-tolerantforage and corn stover indicated that the fermentability of the dietincreased. As a result, fermentability decreased the digestibilitiesof DM, OM, NDF and CP in the whole tract of lambs. Bradford andAllen reported that increased fermentability of the diet resultedin decreased NDF digestibility.18 Similarly, Allen reported thatincreased ruminal fermentability decreased fibre digestibility andincreased feed conversion rate.19

The lower ratio of acetate to propionate was due to the decreaseof the molar proportion of acetate with increasing substitutionof corn stover with salt-tolerant forage. Increased butyrate pro-duction suggests that feeding salt-tolerant forage may potentiallyimprove feed efficiency and growth rate due to a more glucogenicfermentation. DeFrain et al.20 suggested that ruminal-producedbutyrate could be beneficial since butyrate may indirectly providemore glucose by sparing glucose precursors or sparing glucoseuse by extramammary tissues. In addition, altering rumen fer-mentation could be attributed to greater secondary compoundssuch as essential oils21,22 or other specific plants that containhigh secondary compounds.23 Plants produce a variety of sec-ondary compounds to protect against microbial and insect attack,and plants containing secondary compounds such as terpenoids,polysaccharides, polyphenolics and tannins have recently beenused to manipulate gut function in both ruminant and non-ruminant animals.24 Therefore, the altered rumen fermentationmay be attributed to secondary compounds in the salt-tolerantforages, which may have specific effects on particular microorgan-isms. For example, Varel and Jung25 reported that forage phenolicscan inhibit digestibility of cellulose and xylan by influencing at-tachment of the fibrolytic microorganisms to fibre particles.

Inclusion of salt-tolerant forages to partially or entirely replacecorn stover in the diet of lambs reduced the provision of digestibleenergy due to linear reduction of the total digestibility of OMwithout altering DM intake. The decreased digestibilities of OMand NDF could be mainly due to the increased NDF contentand partly from the increased total soluble salt content withincreasing amount of salt-tolerant forage. The latter has beenshown to reduce the apparent energetic value and increase theflow of nutrients through the digestive system.26 Dakheel et al.27

reported a decrease of feed conversion rate for lambs fed salt-tolerant forages (Sporobolus or Distichlis) compared with those fedRhodes grass. Youssef et al.28 also reported that feed conversionrate decreased when lambs were fed hay and haylage of a salt-tolerant forage (mixture of Kochia india and pearl millet) consumedmore DM compared with those fed berseem hay.

Inclusion of salt-tolerant forage to partially or entirely replacecorn stover in the diet of lambs also reduced N availability to thelambs, as shown by the reduction in both digestible and retained Nwith increasing inclusion rates of salt-tolerant forage. In agreementwith the present result, depression of CP digestibility when lambswere fed salt-tolerant forage (mixture of Kochia india and pearlmillet) compared with those fed berseem hay was reported byYoussef et al.28 The synthesis of microbial protein may be compro-mised by the presence salt-tolerant forage as ruminal ammonia Nwas increased with the MF diet. Results indicated that feeding salt-tolerant forage used in our work may be deficient in CP provisiondue to lowered CP content in the feed and reduced digestibilityof CP in the total digestive tract, as well as reduced retention of N.Therefore, CP availability should be particularly considered whenusing salt-tolerant forage to formulate the diet fed to lambs.

Whole tract digestibility between LF and MF diets did not diff,which is consistent with the similar ruminal VFA concentrationbetween LF and MF. The inconsistency between ruminal VFAconcentration and total digestibility for LF and MF (i.e. higherVFA but lower total digestibility) is likely due to secondarycompounds contained in the salt-tolerant forage which mightstimulate some microbial activity in the rumen but inhibit intestinalenzyme activity.29,30 However, further increasing the secondarycompounds when feeding salt-tolerant forage alone (HF) mayadversely inhibit ruminal microbial activity.29,30 Additionally,partially substitution of corn stover with salt-tolerant forage inthe diet would cause increased content of total soluble saltand result in higher ruminal osmolality, and growth of ruminalmicroorganisms might be stimulated. However, entire substitutionof corn stover with salt-tolerant forage, which would result inexcessively high ruminal osmolality, and growth of fibre-degradingmicroorganisms can be suppressed.31

Feeding lambs salt-tolerant forage as a mixture with corn stoveror alone may reduce the growth performance or feed efficiencydue to lower digestibility in the whole digestive tract. However,this adverse effect may be partly offset by a fermentation patternof increased buyrate production with increasing inclusion rate ofsalt-tolerant forage. The inclusion of salt-tolerant forage used inthis study as sole forage in the diet is not recommended becauseof substantial reduction of the total digestibility of OM. However,salt-tolerant forages may still be a useful component in a mixeddiet with other forages because it is cost-effective.

CONCLUSIONIncreasing the amount of salt-tolerant forage in the diet oflambs did not affect feed intake; however, it linearly decreasedthe digestibilities of DM, OM, NDF and CP in the whole tract oflambs. Ruminal VFA concentrations were higher for lambs feda mixture of salt-tolerant forage and corn stover than for thosefed either alone. Feeding salt-tolerant forage also altered theruminal fermentation pattern to increased butyrate production.The decreased ratio of acetate to propionate, and hence a moreglucogenic fermentation, may partially offset the decline in OMdigestibility that occurred with feeding salt-tolerant forages.Results suggest that feeding lambs diets containing salt-tolerantforage as part of the forage source would increase rumen VFAproduction compared to a diet containing corn stover as soleforage source, but the reduction in the whole tract digestibilityand in retained N suggests that feeding salt-tolerant forage mayadversely affect animal performance. Additionally, the lowerprotein provision is also another particular consideration whenusing salt-tolerant forage to formulate a diet fed to lambs.

ACKNOWLEDGEMENTSThis work was supported by a grant from the 11th Five-Year keyproject of the National Scientific Research Foundation of China(2007BAD56B01). The authors thank the staff of Shanxi AgricultureUniversity lamb unit for care of the animals.

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