@article{oai:repository.naro.go.jp:00001371,
 author = {池田, 哲也 and IKEDA, Tetsuya},
 journal = {北海道農業研究センター研究報告, Research BUlletin of the NARO Hokkaido Agricultural Research Center},
 month = {Mar},
 note = {Perennial ryegrass (Lolium perenne L.) is a superior grass species for intensive grazing. However, it has low tolerance to cold and snow mold (Sclrelotinia Borealis). Therefore, it is difficult to cultivate in regions where the soil freezes in winter, as it does in eastern Hokkaido. On the other hand, timothy (Phleum pratense L.) is cultivated mainly in Hokkaido and in low-temperature area of Tohoku district, and partly in mountainous areas of the central region of Japan ; timothy is an extremely winter-hardy grass among major grass species. Although timothy is used for hay and silage production in general, the characteristics of timothy under conditions of intensive grazing have not been clarified. This study is intended to develop an intensive grazing system for raising cattle using timothy pasture in regions where perennial ryegrass has difficulty surviving through. Two intensive grazing systems were investigated in this study. Moreover, meat productivity was shown for the intensive grazing systems developed in this study. 1. Short time rotational grazing with adjustment grazing area and a silage supplement system Herbage and animal performance were investigated under intensive grazing conditions on timothy (cv. Hokushu) swards, which used 2.4 ha/plot in the first year and second year and 1.2ha/plot in the third year and fourth year. Each experiment sward was divided into 35 paddocks, and grazed rotationally from May to October. During May to mid June, 14 or 15 paddocks were used for grazing one paddock a day. The other paddocks (20 or 21 paddocks) were used to harvest forage for ensiling in early June. During mid June to October, all paddocks were used for rotational grazing by joining several paddocks to adjust productivity. The number of grazing animals per unit land area was six or seven heads per hectare in each experiment year. 1) Vegetation and yield changes in timothy pasture over four years in this intensive grazing system were compared with those of a timothy meadow that was managed by cutting three times annually. The averages grass lengths of timothy were maintained around 30 cm by moving cattle into a new paddock through the grazing season in every experiment years. Although timothy has been considered better suited to cutting than grazing, the percentage of timothy in botanical composition in the intensive grazing system was higher than that in meadow management at spring in the fourth year. Annual herbage production in the intensive grazing system was estimated as 7,485kgDM/ha by pasture and 3,173kg/ha by cutting at early June in the cutting and grazing plot. The total yield in the intensive grazing system was higher than that by cutting meadow management, which was 7,370kg/ha. 2) This study investigated animal performance of steers and heifers (Aberdeen Angus) grazed under this intensive grazing without supplement. The average daily gains of steers (0.78kg/day) and cumulative body weight gains per unit land area over grazing season (668kg/ha) were higher than those of previous reports. The timothy grass length was kept short ; thereby, the in vitro dry matter digestibility of timothy was maintained over 70% in major part of grazing season. However, this value at dry summer was under 65%. The daily gains of animals during summer were very low. 3) Silage processed with forage harvested from the sward at early June was supplied to grazing animals to improve animal performance at summer in this intensive grazing system. Therefore, the decrease in the daily gain of this herd was low through the summer. The daily gain and cumulative gain per unit land area over the grazing season were 0.81kg/day and 721kg/ha, respectively. These values were higher than those without silage supply. 4) An intensive grazing system was developed using rotational grazing with silage from the sward. Because this intensive grazing system necessitates a broad cutting area, this is adaptable to flat locations such as those in Hokkaido. 2. Put-and-take stocking with an adjustment sward system Animal performance of Holstein steers under the intensive grazing system with put-and-take stocking was investigated to develop an intensive grazing system that is suitable for the regions where area is limited. 1) The put-and-take stocking herd, which consisted of seven heads in each plot (1.2 ha × 2 replications), were grazed continuously on timothy swards without supplement from May to October. After early August, two heads of each herd were excluded from the put-and-take stocking plots. The short time rotational grazing herd was grazed rotationally on a timothy sward (1.2 ha × 2 replications) with adjustment grazing area. Furthermore, silage processed with forage harvested from the same sward was supplied to this herd after summer. The average daily gain of the put-and-take stocking herd and the short time rotational grazing herd were 0.87kg/day and 0.97kg/day, respectively. The average cumulative body weight gain of these were 668kg/ha and 718kg/ha, respectively. 2) On the timothy plot (1.2 ha × 4 paddocks), 39 steers were grazed rotationally from May to early July. After early July, 21 - 24 heads of this herd were transferred to the adjustment plot (2.3 ha) to adjust the grazing pressure. The other steers continued to graze rotationally on the timothy plot until the end of the grazing season. The herd on the adjustment plot was grazed continuously with silage that was made from this sward. The average daily gain of all steers in this intensive grazing system was 0.91kg/day. The cumulative body weight gain of the steers over the grazing season was 815kg/ha of grazed pasture, which was higher than those of the short-time rotational grazing described above. 3) An intensive grazing system was developed : it was a put-and-take stocking combined adjustment sward. Results indicate that high animal performance was obtained from this system ; results resembled those of the intensive grazing system by short-time rotational grazing. Because this system requires no wide cutting area, it is thought to be suitable to public pasture for raising cattle in north-eastern and central mountainous region. 3. Meat production system with intensive grazing through the raising period Animal performance and carcass quality of Holstein steers grazed on a farm 5-12 months prior to fattening periods (Grazing herd : G herd), were compared with those fattened using a conventional system (Control herd : C herd). The G herds, replicated three times during 3 years, comprised of 34-39 Holstein steers (Average mean body weight 243kg). Grazing of G herds was conducted intensively through the raising period. The respective feeding periods of G herds including grazing periods and C herds were 545 days and 536 days, respectively. Average daily gain of the G herd through the grazing period (0.93kg/day) was lower than that of the C herd during the same period (1.01kg/day). However, the daily gain of the fattening period of the G herd was higher than that of the C herd. Therefore, the body weights at the end of respective fattening periods of the G and C herds were 805kg/head and 835kg/head. Furthermore the percentages of carcasses over grade 3 of the Japanese beef carcass grading standards were 58% and 59%, respectively, in the G and C herds, and condemned viscus cows in G herd (3/39 heads) were fewer than these in C herd (9/36 head). These results showed that animal performance and meat quality of this system were sufficiently good for practical use. Conclusion Two types of intensive grazing methods using Hokushu timothy swards were developed in this study. One is a short-time rotational grazing system that includes adjustment grazing area and silage supply ; another is the put-and-take stocking system combined with an adjustment sward. The former was suitable for a broad and flat area ; the latter was suitable for mountainous locations. This meat production system using intensive grazing systems is applicable to a Holstein steer raising system., 本研究は, 気象条件が厳しく集約放牧に適した草種であるペレニアルライグラス（以下PR）の栽培が難しい北海道東部や本州中部以北の高冷地を対象とし, このような地域で安定栽培が可能な耐寒性に優れ, 放牧適性が高いチモシー（以下TY）の晩生品種ホクシュウを用いた育成牛のための集約放牧技術を確立することを目的とした。そこで, 季節生産性の変動が大きい TY 草地において放牧牛への牧草供給量を一定に保つ方法として, 牧草の季節生産性に合わせて放牧地面積を調整する方法と放牧牛の頭数を調整する方法について, それぞれ牧草生産性と家畜生産性を明らかにした。また, 実際の飼養体系への集約放牧の導入の可能性について, ホルスタイン種去勢牛の肥育牛生産体系に集約放牧を組み込んだ場合の産肉性を明らかにした。 1. TY 草地を35の小牧区に分割し、5月上旬の放牧開始から6月中旬までは、15牧区を使い短期輪換放牧を行い、残りの20牧区は、6月上旬まで禁牧した後、サイレージとして収穫し、6月中旬から全牧区を用いて短期輪換放牧を行う集約放牧方式を4年間繰り返して行った。この放牧方式により放牧地面積を調整しながら利用した結果, TY の草丈を放牧期間中を通して30cm程度の短草型に維持できた。また, 放牧地からの牧草生産量7,485kgDM/haは, 年3回刈り取り利用した採草利用方式における年間乾物収量の7,370kgDM/haと同程度であったが, これに兼用草地において春季に収穫した牧草を加えることによりさらに高い牧草生産量が得られ, 本集約放牧方式に牧草生産性の高さが明らかとなった。さらに, このような放牧を4年間行っても, TY の乾物重量構成割合は, 採草利用した TY 草地より高く維持でき, 集約放牧を行うことによって TY 草地の植生が悪化することはないことが明らかとなった。 2. 1に示した集約放牧方式を行ったアンガス種去勢牛の日増体量および単位面積当たり増体量は, それぞれ0.73kg/dayと668kg/haで, いずれも既往の報告より高く, 本放牧方法により高い家畜生産が得られることが明らかとなった。しかし, 夏季間の放牧牛の増体速度は春季, 秋季に比べ低下する傾向があり, この原因として TY の栄養価の低下が考えられた。そこで, 夏季間の放牧牛の増体速度の低下を改善するため, 面積調整に用いた兼用草地において春季に刈取り調製したサイレージを夏季以降に併給する方法を検討した結果, 併給した場合の夏季間の日増体量は0.70kg/dayで, 無給与の場合の0.28kg/dayに比べ高く, サイレージ併給による増体量改善効果が認められた。 3. これらの結果, TY の放牧・採草兼用品種のホクシュウを用いて, 兼用草地を利用して放牧地面積を調整しながら短期輪換放牧を行い, 兼用草地で収穫した余剰草を放牧草の栄養価が低下する夏期間に併給することにより, 採草利用よりも高い牧草生産性と従来の放牧方式より高い家畜生産性が得られる短期輪換放牧を主体とする集約放牧方法が開発できた。なお, 本放牧方式は, 兼用利用可能な草地が6割以上確保できる平坦地での利用が適している。 4. 頭数調整放牧と3において開発した短期輪換放牧を主体とする集約放牧の家畜生産性を比較した。頭数調整放牧の日増体量と面積当たり増体量は，それぞれ0.87kg/day，668kg/haで, 短期輪換放牧の0.97kg/day, 718kg/haに比べ若干低い値であったが, 頭数調整放牧によっても短期輪換放牧を主体とした集約放牧と同様な高い家畜生産が得られる可能性があることが示唆された。 5. 頭数調整放牧により, TY 草地から退牧した牛を収容する調整草地を設け, 両草地を組み合わせた放牧方法により2年間実施した。この放牧方法は, （1）5月上旬から7月上旬まで, 放牧牛全を TY 草地で輪換放牧し, 7月上旬以降, このうちの一部を調整草地に移して頭数調整を行う, （2）調整草地は, 春季にロールベールサイレージを収穫し, 夏季以降, TY 草地から移牧してきた牛群にこのサイレージを併給しながら連続放牧を行う方法である。なお, 調整草地は, 春季に乾物消化率70％程度で500kgDM/10a以上の牧草収穫が必要と考えられた。 6. TY 草地と調整草地を組み合わせて利用した結果, 2年間の牛群全体の平均日増体量は0.91kg/dayで, 草地全体の面積当たりの増体量は815kg/haが得られ, 短期輪換放牧を主体とした集約放牧と同程度の家畜生産性が得られた。 7. これらの結果, 頭数調整放牧を主体とする集約放牧方法が開発できた。本放牧方法は, 頻繁な転牧を行わなう必要がなく, 採草可能地面積比率が低くても利用できることから, 管理が難しい山地傾斜地に位置する公共牧場のようなより省力管理が必要とされる条件において, 育成牛の増体を高める技術として利用が期待できる。 8. 6ヶ月齢から6ヶ月間集約放牧により育成した後, 約12ヶ月間肥育したホルスタイン去勢牛群の放牧試験期間中の平均日増体量は, 現行の方式で6ヶ月齢で導入され放牧は行わずに約18ヶ月間肥育した牛群の同時期の値に比べ低かったが, 肥育期間中の日増体量は高く, その結果, 飼養期間通算の日増体量は対照区と同程度となり, 平均飼養日数もそれそれ545日と536日であった。また, 肉質等級3以上の割合に差はなかった。この結果, 集約放牧を行うことにより, 現行の肥育体系と同様の期間で同程度の肉質の牛肉の出荷が可能なことを明らかにした。さらに, 屠場における内臓の一部廃棄牛の頭数は, 放牧育成区が対照区より少なく, 放牧育成の効果が窺えた。以上の結果から, これまで放牧に適さないとされてきた TY を用いて, 短期輪換放牧を主体とした集約放牧と頭数調整放牧を主体とした集約放牧の2つの集約放牧方法が提示できた。また, これらの集約放牧を肥育牛生産体系の育成期に取り入れることにより, 現行の濃厚飼料多給型の肥育牛生産体系と同様の肉生産が可能であることが明らかとなり, 集約放牧の家畜生産性の高さが実証された。},
 pages = {1--108},
 title = {育成牛のためのチモシー草地における集約放牧技術の開発に関する研究},
 volume = {185},
 year = {2006},
 yomi = {イケダ, テツヤ}
}