Antibiotic growth promoters have been practiced in animal industry since it’s discovery in the 1940s. But in recent years, the use of feed additives in animal feeds is facing reduced social acceptance due to the increasing public concerns about the bad residual effects of antibiotics on human health. The European Union (EU) and other developed countries have taken widespread steps to ban antibiotics as feed additives. In particular, the use of antibiotics as growth promoters has been banned in the EU since January 2006 (OJEU, 2003). Consequently, it becomes the challenge for animal scientists to explore alternatives of antibiotics growth promoters for animal industry. For this reason, attention has recently shifted to various herbs and aromatic plants. Garlic (Allium sativum) is one of the medicinal plants which have been paid a lot of interests throughout human history as a medicinal panacea in almost every known culture due to it’s antiviral, antifungal, antiparasitic, antioxidant, anticancer, immune enhancing and liver functioning activities. It has a complex mixture of many secondary plant products including alliin, allicin, diallyl sulfide and diallyl disulfide. During harvesting, only garlic bulb is used for human consumption in various purposes and remaining residues consisted of stem, leaf and flowers have no commercial use and are simply thrown or disposed. The aim of the present study was to know the feeding effects of garlic stem and leaf on ruminal fermentation characteristics, nitrogen (N) balance, microbial N supply (MNS) and the intermediate nutrients metabolism in sheep which ultimately introduce it as a potential ruminant feeds towards coming centuries.

Initially, an experiment was conducted to assess the feeding effects of garlic stem and leaf silage on N balance, ruminal fermentation patterns, rates of plasma leucine turnover (LeuTR), whole body protein synthesis (WBPS) and degradation (WBPD) in sheep using an isotope dilution method of [1-¹³C]Leu (Experiment 1). The experimental diets fed in this trial consisted of mixed hay (Hay-diet, as control) and hay plus garlic stem and leaf silage (GS-diet, at ratio of 9:1) in a crossover design for each 21 day period. Diets were formulated at maintenance ME level and were around isoenergetic and isonitrogenous. The isotope dilution method using [1-¹³C]Leu was performed on the 21^st day of each dietary treatment for measuring plasma LeuTR. Nitrogen digestibility, N absorption and N retention did not differ between the diets. Ruminal total volatile fatty acids (VFA) concentration as well as concentrations of principal VFA did not differ between the diets. Plasma non-esterified fatty acids (NEFA) concentration was significantly lower (P < 0.01) and glucose concentration was greater (P = 0.03) for GS-diet compared with Hay-diet. Feeding garlic silage did not influence plasma LeuTR, WBPS and WBPD in sheep.

It was assumed that during ensiling process some nutrients and bioactive components of garlic stem and leaf might be lost. Furthermore, for better understanding about the feeding effects of garlic stem and leaf on N metabolism in sheep, 2^nd experiment was conducted to assess the feeding effects of fresh garlic stem and leaf on turnover rates of plasma phenylalanine (PheTR), tyrosine (TyrTR) and WBPS in sheep using an isotope dilution method of [²H₅]Phe and [²H₂]Tyr (Experiment 2). Effects of feeding garlic stem and leaf on MNS also studied. The sheep were fed either mixed hay (Hay-diet, as control) or hay plus garlic stem and leaf diet (GL-diet) at ratio of 9:1. The experiment was performed using a crossover design with two 21 day periods. The isotope dilution method using [²H₅]Phe and [²H₂]Tyr was performed on the 21^st day of each dietary treatment to measure the turnover rates of Phe and Tyr in sheep. Nitrogen intake did not differ between the diets and N absorption and N digestibility were higher (P < 0.05) in GL-diet than Hay-diet. Plasma PheTR tended to be higher (P = 0.06) during GL feeding and TyrTR did not differ between the diets. Further, WBPS tended to be greater (P = 0.05) for the GL-diet compared with the Hay-diet. Total purine derivatives excretion and MNS were higher (P < 0.05) in GL-diet than Hay-diet. A positive relationship (R² = 0.58, P < 0.05) was found between MNS and WBPS in the study.

In the succeeding study, isotope dilution methods using [1-¹³C]Na acetate and [U-¹³C]glucose was simultaneously performed to know the feeding effects of garlic stem and leaf on plasma acetate and glucose metabolism in sheep (Experiment 3). The sheep were offered either mixed hay (Hay-diet) or hay plus garlic stem and leaf (GL-diet, in a 9:1 ratio) in a crossover design for 21 day period. The isotope dilution method using [1-¹³C]Na acetate and [U-¹³C]glucose was performed on the 21^st day of each period to measure turnover rates of plasma acetate and glucose in sheep. Concentration of ruminal total VFA as well as concentrations of acetate and butyrate tended to be higher (P < 0.10) in GL-diet than Hay-diet. Further, propionate concentration was significantly higher (P = 0.03) for GL-diet. Turnover rate of plasma acetate tended to be higher (P = 0.06) for GL-diet than Hay-diet and that of glucose did not differ between the diets.

To the best of my knowledge, it was the first work using garlic stem and leaf as a ruminant feed. The present study showed some noble findings using garlic stem and leaf as ruminant feed. Ruminal fermentation characteristics, N balance, MNS and WBPS were influenced by garlic stem and leaf feeding. Further, garlic stem and leaf might have stimulating effects on plasma acetate metabolism in sheep.

This investigation therefore suggested that garlic stem and leaf can be used as a potential alternative feed source for ruminants and this supplementation will facilitate the proper use of the residue as well as reduce feed scarcity and minimizing environmental pollution. In addition, further investigations can be performed using garlic stem and leaf in ruminants on various aspects to establish it as a potential ruminant feed in future.

（和訳）

　畜産業では1940年代から抗生物質が実用化されてきた。しかしながら、最近、人の健康に対する抗生物質残留の懸念から、飼料添加物の使用は社会的許容を失いつつある。ヨーロッパ連合(ＥＵ)や他の先進国では飼料添加物としての抗生物質の使用が制限されており、特に、ＥＵでは2006年1月から全面的に使用が禁止された。その結果、畜産学に携わる研究者たちは抗生物質に替わる新たな成長促進剤の開発に着手した。このような背景から種々のハーブやアロマ植物が注目されている。ニンニク(Allium sativum)は、alliin、allicin、diallyl sulfide、diallyl disulfideなどの二次代謝産物を豊富に含み、抗ウィルス作用、抗菌作用、抗酸化作用、抗癌作用、免疫賦活作用、肝機能強化作用など、様々な機能を有するため、古くから知られている薬草の一つである。ニンニク球根は種々の目的に利用されるが、花、茎、葉部には市場価値がなく、廃棄されている。本研究の目的は、ニンニク茎葉部の有効利用のため、ヒツジにおいてルーメン発酵、窒素(Ｎ)出納、微生物態Ｎ供給量(MNS)および体内の栄養素代謝に及ぼすニンニク茎葉給与の影響を明らかにし、反芻家畜の飼料として確立することである。

　はじめに、ヒツジのＮ出納、ルーメン発酵、血漿ロイシン代謝回転速度(LeuTR)、全身のタンパク質合成速度(WBPS)および分解速度(WBPD)に及ぼすニンニク茎葉サイレージ給与の影響を測定した（実験１）。実験飼料は混播牧草区(Hay区)および牧草＋ニンニク茎葉サイレージ区(9:1、ＧＳ区)とし、１期21日のクロスオーバー法にしたがって実施した。給与量は両飼料区とも維持量の代謝エネルギー(ME)とし、ほぼ同等のME、粗タンパク質(CP)を給与した。血漿LeuTRを測定するため、それぞれの飼料区21日目に[1-¹³C]Leuの同位元素希釈法を実施した。Ｎ消化率、Ｎ吸収およびＮ蓄積は飼料間に差がなかった。ルーメン内総揮発性脂肪酸（VFA）および主要VFA濃度は飼料間に差がなかった。血漿遊離脂肪酸（NEFA）濃度はHay区と比較してＧＳ区が低く(P < 0.01)、血漿グルコース濃度は高かった(P = 0.03)。ニンニク茎葉給与は血漿LeuTR、WBPSおよびWBPDに影響を与えなかった。

　サイレージ調製期間中にニンニク茎葉の栄養素および生理活性成分が失われると推測される。そこで、ヒツジに生のニンニク茎葉を添加した飼料を給与し、[²H₅]Pheおよび[²H₂]Tyrの同位元素希釈法を用いて血漿フェニルアラニンおよびチロシン代謝回転速度(PheTR、TyrTR)およびWBPSを測定した（実験２）。MNSに及ぼすニンニク茎葉給与の影響も測定した。混播牧草(Hay区)あるいは牧草＋生のニンニク茎葉(9:1、ＧＬ区)を給与した。実験は１期21日間のクロスオーバー法にて実施した。血漿PheTR、TyrTRを測定するため、それぞれの飼料区21日目に[²H₅]Pheおよび[²H₂]Tyrの同位元素希釈法を実施した。Ｎ摂取量は飼料間に差がなく、Ｎ吸収量およびＮ消化率はHay区よりＧＬ区が高かった(P < 0.05)。総プリン誘導体排泄量およびMNSはHay区よりＧＬ区が高かった(P < 0.05)。血漿PheTRはＧＬ区が高い傾向を示し(P = 0.06)、TyrTRは飼料間で差がなかった。さらに、WBPSはHay区と比較してＧＬ区が高い傾向を示した(P = 0.05)。

　実験３では、ヒツジの血漿酢酸およびグルコース代謝に及ぼすニンニク茎葉給与の影響を明らかにするために、[1-¹³C]酢酸Naおよび[U-¹³C]グルコースの同位元素希釈法を実施した。混播牧草(Hay区)あるいは牧草＋ニンニク茎葉(9:1、ＧＬ区)を給与し、実験は１期21日のクロスオーバー法にしたがって実施した。血漿酢酸およびグルコース代謝回転速度を測定するため、それぞれの飼料区21日目に[1-¹³C]酢酸Naおよび[U-¹³C]グルコースの同位元素希釈法を実施した。ルーメン総ＶＦＡ、酢酸および酪酸濃度はHay区よりＧＬ区が高い傾向を示し (P < 0.10) 、プロピオン酸濃度は有意に高かった(P = 0.03)。血漿酢酸代謝回転速度はHay区よりもＧＬ区が高い傾向を示し(P = 0.06)、血漿グルコース代謝回転速度は飼料間に差がなかった。

　反芻家畜の飼料としてニンニク茎葉を使用した研究はこれが最初であり、いくつかの貴重な知見を得た。ルーメン発酵特性、Ｎ出納、MNSおよびWBPSはニンニク茎葉給与によって影響された。さらに、ニンニク茎葉はヒツジの血漿酢酸代謝を刺激する効果を有するかもしれない。

　したがって、本研究の結果は、ニンニク茎葉が反芻家畜における有望な代替飼料となり得ること、ニンニク茎葉添加は飼料不足の軽減、環境汚染の最小限化と同時に農産廃棄物の適切使用を促進することを示した。さらに、反芻家畜においてニンニク茎葉を用いたさらなる研究を実施すべきであろう。