Research On Roughage Utilization For Grazing System Of Sheep In The Farming-pastoral Zone Of The Songnen Plain

The abundant forage resources in the farming pastoral zone of the Songnen Plain is an advantage for the development of ruminant production. Studies on the nutrition and utilization of forage resources (introduced and natural Leymus chinensis grassland, crop residues and foliage) in grazing system of sheep in this region would provide the basal data for designed feeding of sheep, and strategy for grassland management and grazing ruminant production.Studies were carried at Field Station in Changling county of Jilin province (E123?51′02″, N44?12′11″) and in Duerbote Mongol Nationality Autonomous Country of Heilongjiang province (E123?45′28″,N45?53′40″) from 2004 to 2005. The n-alkanes characteristic, daily intake, diet composition and nutrients digestibility of sheep grazing in introduced and natural grassland as well as maize and soybean crop residues were evaluated at different seasons using alkane technique, total fecal collection and two-stage technique for in vitro digestibility, The nutritive value of poplar foliage and the effect of tannin were also evaluated by metabolism experiment and PEG supplement.The n-alkanes profiles of forage from grassland and crop residues had special character among different species. In the range of C21~C35, the content of odd n-alkanes are more abundant than that of even n-alkanes. Many forages, as whole Leymus chinensis growing at different stage, Echinochloa crusgalli and Artemisia anethifolia collected in May, Sonchus bracyotus growing in May and August, Setaria viridis , foliage of elm(Ulmus pumila), as well as stem, leaf, pod of soybean and maize crop residues,had a maximum alkane concentration for C31. The concentration of C29 n-alkanes was most abundant in Iris pallasii and Chenopodium album. Ear head of Leymus chinensis, Echinachloa crusgalli in July, Artemisia anethifolia in August had a maximum alkane concentration for C27. Amaranthus retroflexus was special because the content of C28 was most abundant among them.In vitro DM digestibility of whole Leymus chinensis gradually decreased with plant maturity. A negative relationship between in vitro DM digestibility and growth days could be expressed by function relationship: y=189.04X-0.342(R2=0.9466). The DM digestibility of other forage growing in natural L. chinensis grassland was higher than that of L. chinensis growing at same period, especially for Sglauca bunge and Sonchus brachyotus. In vitro DM digestibility of stem of maize was affected significantly by harvest time, but not for leaves of maize. In vitro DM digestibility of combination between Alfalfa and L. chinensis hay or maize straw was improved significantly.The seasonal changes in the digestibility of gross energy, dry matter (DM), OM, CP, NDF and ADF of introduced Leymus chinensis pasture were significant. The digestibility of gross energy, dry matter (DM), OM, CP, NDF and ADF of L. chinensis were significantly higher (P <0.05) in spring and summer than in autumn and winter. Metabolizable energy (ME) contents were 12.13, 11.62, 8.66 and 10.40 MJ/kg DM for L. chinensis in spring, summer, autumn and winter respectively, and the corresponding voluntary feed intakes were 91, 119, 59 and 58 g/d per kg metabolic weight (BW0.75). The ME contents and DM intakes in autumn and winter were significantly lower than in summer and in spring (P<0.05). The intake of L. chinensis pasture was sufficient to provide ME requirement for maintenance by the ewes in all the seasons, but inadequate for protein requirement for maintenance in winter.The fecal alkanes and nutrients content for every sheep was similar at same season in natural L. chinensis pasture, which showed dietary composition was similar. Dietary composition of sheep in spring mainly included 51.22% of L. chinensis, 22.56% of Sonchus bracyotus, 26.08% of Echinachloa Crusgalli and 0.2% of Artemisia Anethifolia, it mainly included 65.92%of L. chinensis, 16.30%of Sonchus brachyotus, 14.45% of Chloris virgata and 4.0% of Artemisia anethifolia in summer. The voluntary intake of DM, ME and CP for grazing sheep in Spring were 132.02 g/d kgBW0.75,1.44MJ /d kgBW0.75 and 14.28 g/d kgBW0.75,the corresponding values in summer were 117.18 g/d kgBW0.75,1.26MJ /d kgBW0.75,11.77g/d kgBW0.75. The sheep could attain 185g/d weight gain when grazing on natural L. chinensis pasture from June to August.The average available dry matter was 1722 kg ha-1 and 408 kg ha-1 for soybean and maize crop residues respectively. The botanical composition for the maize residues were 80.88%, 4.90% and 14.46 % of leaf, stem and weed respectively; the soybean residue contained 53.95 %,42.10%, 2.38% and 1.57% leaf, stem, pod and weed. The voluntary intake of DM,ME and CP for grazing sheep in soybean residue were 94.33 g/d kgBW0.75,0.84MJ/d kgBW0.75 and 6.62g/dkgBW0.75 , The corresponding values for maize residues were 81.16 g/d kgBW0.75,0.53MJ /d kgBW0.75 and 3.34 g/d kgBW0.75 . For soybean residue, the daily intake of sheep included 27.92 %, 40.91%, 14.29% and 17.53% leaf, stem, pod and weed. The diet of sheep grazing in maize residues contained 39.39% leaf and 60.61% weed. The ME and CP intake for soybean residues can satisfy the requirement for body weight gain to some extent. But maize residues can only satisfy the ME and CP maintenance requirement of sheepThe CP content of foliage for Populus spp. decreased and ADF increased after falling. When used foliage as single feed source, voluntary feed intakes of sheep was 56.53g /d kgBW0.75,the content DE and ME of foliage was 7.10MJ/kg DM and 5.82MJ/kg DM respectively. Supplement PEG in foliage diet, the digestibility of DM, energy, OM, ADF and NDF was not affected, but the digestibility of CP was improved. While containing 66% or 33% foliage in diet, the digestibility and utilization of CP were not affected by PEG supplement.