牛吃草，
为什么能长肌肉？Why can cows build muscle on grass? 而我们天天吃菜叶，只会越来越瘦…while we'd only get thinner on lettuce

先看片：钻进牛肚子里First, climb inside a cow

中文配音，画面里烧录了英文字幕；点「CC」可以打开中文字幕。点下面的章节可以跳转。Chinese narration with burned-in English subtitles. Tap a chapter to jump.

拼一条蛋白质Build a protein

肌肉的主要材料是蛋白质，蛋白质由一颗颗氨基酸像积木一样连成长链。点下面的积木，拼够 12 颗，看看会发生什么。Muscle is built mostly of protein, and protein is a chain of amino acids snapped together like building blocks. Tap the blocks below — add 12 and see what happens.

所以真正的问题是：牛的积木，从哪来？草里的蛋白质并不多啊。So the real question is: where does a cow get its blocks? Grass isn't exactly packed with protein.

谁能打开这把锁？Who can pick this lock?

草里的能量，大多锁在纤维素里。选一把「钥匙」试试。Most of the energy in grass is locked in cellulose. Try a key.

点开牛的四个胃Open up the four stomachs

红点逐个点开，每个都看过会变蓝。全部看完有彩蛋。Tap each red dot; it turns blue once you've seen it. See them all for a surprise.

👆 从 ① 瘤胃开始吧。👆 Start with ① the rumen.

示意图：为了一眼看全，四个胃画在同一侧；真实的牛里，瓣胃和皱胃主要在身体右侧。Illustrative: all four chambers are shown on one side; in a real cow the omasum and abomasum sit mostly on the right.

陪一根草走完全程Follow one blade of grass

按「下一步」，看草怎样变成肌肉的积木。Press "Next" and watch grass turn into muscle-building blocks.

←下一步 →Next →↺

养微生物，再吃微生物Farm microbes, then eat them

你是瘤胃的厂长。先「喂氮」让微生物长大分裂，再把它们「冲进皱胃」消化成氨基酸。目标：攒够 60 颗氨基酸。You run the rumen. "Feed nitrogen" so the microbes grow and divide, then "flush to abomasum" to digest them into amino acids. Goal: collect 60 amino acids.

人 vs 牛Human vs cow

点人体上的红点；再点表格每一行，猜完再揭晓牛那一栏。Tap the dots on the body, then tap each table row to reveal the cow's column after you guess.

👈 从「胃」开始。👈 Start with the stomach.

算算你的蛋白质Work out your protein

我们没有瘤胃，得直接吃够蛋白质，再配合力量训练。研究发现，做力量训练的成年人，每天每公斤体重约 1.6 克时，增肌效果基本到顶。We have no rumen, so we need protein directly, plus strength training. In adults doing resistance training, muscle gains level off around 1.6 g of protein per kg of body weight a day.

体重Body weight: 60 kg

≈ 96 克/天g/day

1.6 g/kg/day · Morton et al., BJSM 2018

食物换算为约数，品牌与做法不同会有差异。肾病等慢性病患者、孕妇及青少年，请先咨询医生或营养师。Food amounts are rough. If you have kidney disease or another chronic condition, are pregnant, or are a teenager, check with your doctor or dietitian first.

🥗 只吃菜叶Lettuce only 🍳 吃够蛋白Enough protein 🍳+🏋️ 蛋白+训练Protein + training

卡皮的小秘密Kapi's little secret

水豚也吃草，可是没有瘤胃。那它怎么把微生物蛋白吃回来？Capybaras eat grass too, but have no rumen. So how do they get microbial protein back?

答案：早上吃掉自己的Answer: in the morning they eat their own 软便soft droppings 💩

（点卡皮或黑条揭晓。科学上这叫食粪行为，兔子也会。别学我！）(Tap Kapi or the black bar. It's called coprophagy; rabbits do it too. Don't try this at home!)

你能讲给别人听吗？Could you explain it to a friend?

一句话记住：牛吃的不是草，是微生物。One line to remember: a cow doesn't live on grass. It lives on microbes.

• FAO, Roughage utilization in warm climates (500–600 kg cattle; rumen ≈100 L) — fao.org
• MDPI Fermentation 2023, 9(2):114 (ruminants make no cellulolytic enzymes) — mdpi.com
• Purina, Rumen microbes 101 (≈25 billion bacteria / mL) — purinamills.com; Penn State Extension — psu.edu
• CSIRO, Ruminant physiology (VFAs ≈70% of energy) — csiro.au
• Grant, Cornell (rumination 480–540 min/day) — cornell
• U Alaska Extension, Ruminant GI anatomy (urea recycling, microbial protein) — uaf.edu
• U Minnesota, Rumen Physiology (60–80% microbial amino acids) — umn.edu
• Stephen & Cummings 1980, J Med Microbiol (≈55% of faecal solids are bacteria) — PubMed
• Morton et al. 2018, Br J Sports Med (protein plateau ≈1.6 g/kg/day) — PubMed
• Borges et al. 1996, J Comp Physiol B (capybara coprophagy)
• 食物蛋白质为常见约数（USDA FoodData Central）。插画为 AI 生成的示意图。Food protein values are common approximations (USDA FoodData Central). Illustrations are AI-generated and illustrative.