javascript Split an array into chunks and fill another

Question

(scenario) I have an array with N number of animals, and I have to distribute with a range between 4 and 5 every day for 6 days. So the range for entire week can be 28 => 30.

axample:

var animals = ["Antelope", "Bisont", "Crocodile", "Dingo","Elephant","Fly","Gnu","Hyena","Porcupine","Llama","Macaque","Nasica","Orangutan","Piton","Quetzal","Rinho"];

animals = 16, min animals request = 28

this snippet below solve two problems: chunk as explained here and randomize as explained here:

i need to improve groupsize variable from fixed value to range value.

var animals = ["Antelope", "Bisont", "Crocodile", "Dinosaur","Elephant","Fly","Gnu",
              "Hyena","Porcupine","Llama","Macaque","Nasica","Orangutan","Piton","Quetzal","Rinho"];

var groupSize = 4; // here need range

var groups = _.map(animals, function(item, index){
  return index % groupSize === 0 ? animals.slice(index, index + groupSize) : null; 
  })
  .filter(function(item){ return item; 

});

function shuffle(array) {
  var m = array.length, t, i;
  // While there remain elements to shuffle…
  while (m) {
    // Pick a remaining element…
    i = Math.floor(Math.random() * m--  );   
    // And swap it with the current element.
    t = array[m];
    array[m] = array[i];
    array[i] = t;
  }

  return array;
}

console.log(shuffle(groups));

console

[["Porcupine", "Llama", "Macaque", "Nasica"], ["Antelope", "Bisont", "Crocodile", "Dinosaur"], ["Elephant", "Fly", "Gnu", "Hyena"], ["Orangutan", "Piton", "Quetzal", "Rinho"]]

jsbin here

chunk and shuffle are good, but at least 6 are needed and have 4. For the remining two some animals must do a second turn.

So the question is: how i can fill Array[6] whit chunk of minimum of 4 shuffled animals? Any suggestion for find right path is is widely appreciated.