Old MacDonald function
Javascript ES6 - 204


  Aim to type the fewest amount of Unicode characters in your code.


Not the shorter but probably the most obfuscated.

f=(a,b)=&gt;{for(c=[b,a].concat('!,-ADEHIMOWacdefhilmnortvwy \n'.split(o='')),i=62;i;o+=c[e&gt;&gt;10]+c[e/32&amp;31]+c[e&amp;31])e='ⱞᄤ⒇瓤抣瘭㾭癍㚏᫶⦮函࿋Π疽䌐獲樘ྰ㞠戝晐}疽䌐࿈䌐眲Π疽㛏戝癐Π疽伲࿌⒋ფᲉѽ疽䦯䨝抽瘭䦹容㾷碶ᅣᲉᄤྦྷ㜕㞱㗽㾲妴㣗畍⺏'.charCodeAt(--i);alert(o)}


If your browser do not support ES6 :

function f(a,b){for(c=[b,a].concat('!,-ADEHIMOWacdefhilmnortvwy \n'.split(o='')),i=62;i;o+=c[e&gt;&gt;10]+c[e/32&amp;31]+c[e&amp;31])e='ⱞᄤ⒇瓤抣瘭㾭癍㚏᫶⦮函࿋Π疽䌐獲樘ྰ㞠戝晐}疽䌐࿈䌐眲Π疽㛏戝癐Π疽伲࿌⒋ფᲉѽ疽䦯䨝抽瘭䦹容㾷碶ᅣᲉᄤྦྷ㜕㞱㗽㾲妴㣗畍⺏'.charCodeAt(--i);alert(o)}


Copy/Paste that code into your browser console and try f('cow','moo'), f('pig','oink'), f('sheep','baa')

How it works ?

c is an array of 29 letters plus the animal and its sound (let call this our alphabet).
So, all the 31 characters fit in 5 bits (2^5 = 32).
A Unicode character is 16 bits long, so it can encode 3 characters of our alphabet with a padding bit.
The full text with the new lines is 186 characters of our alphabet, it can be encoded with 62 Unicode characters.  

For example, Old is encoded like this :

alphabet value         O      l      d
alphabet index         11     20     15
unicode           0  01011  10100  01111  ===&gt; \u2e8f (⺏)


If you have troubles to read some Unicode chars, install Code2000 font