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When a calf is born, it’s stomach (the abomasum) is 2–4 litres in size. It secretes enzymes that digest milk, providing the calf with energy and protein for growth. However, over time, we need to turn a calf’s stomach into a cow’s stomach: a 150–200 litre rumen where microbial enzymes do the digestion to provide a cow’s nutrient needs.

To put this change into perspective: stack up eight or ten 20-litre buckets to make a “rumen” and put a 3-litre milk bottle “calf stomach” next to your tower for comparison!

The most important ingredient: water!

The sooner a calf starts eating solid food, the sooner it’s rumen starts to develop…and drinking water improves calf dry matter intake. Think of it as a bit like adding milk to your cornflakes, it makes them go down easier! Provide calves with ad lib clean, fresh water from birth.

Next up: concentrates! (aka starter/grain/pellets/muesli)

The microbes in the rumen ferment carbohydrates to produce acids. The calf and cow absorb these acids across the lining of the rumen, which is composed of finger-like projections called papillae. The concentrates in a calf’s diet are what are responsible for developing these papillae. As you can see in the photos below, quite a change takes place!

The concentrates fed to calves (whether they’re pellets, muesli or grain mixes) need to contain:

  • At least 18–20% good quality protein
  • 11.5–12.5 MJ of energy per kg dry matter
  • Rumensin or Bovatec to control coccidiosis

Calves must have access to concentrates from birth, but don’t put out too much at once (it can go mouldy/stale). Instead, change daily to keep fresh and clean. Minimal fines and added molasses will improve palatability (it’s like sprinkling a spoonful of brown sugar over your Cornflakes!).

These photos show the papillae of a calf and cow: look how much they grow!


Step three: roughage (hay/fibre)

Feeding calves roughage helps grow rumen size and the strength of rumen contractions. Roughage also stimulates rumination: this “chewing the cud” helps microbes digest plant matter. The physical effect of roughage also helps keep the rumen papillae healthy and improves nutrient absorption. Ideally offer short chopped (1–2cm) high quality hay at 10–25% of the ration (by weight). Ensure calves aren’t eating hay at expense of grain as hay isn’t as energy dense.

Weaning: minimising the stress

Weaning is when milk feeds stop. And for calves, this can be stressful! Stress can suppress the immune system and calves may fall sick with diseases that they would otherwise have been able to fight off. To reduce any negative impacts from weaning, stagger it and other stressful events (such as disbudding, vaccination, moving or weather extremes).

Milk should not be withdrawn until the nutrients from ruminal digestion can provide the protein and energy needs for maintenance and growth of bones, muscles and the developing immune system. Calves should be weaned based on grain consumption (minimum 18% protein). If calves are being fed large volumes of milk they may not eat much solid feed: milk will need to be reduced so that they start eating more. The aim is for pens of calves to be eating for 3 consecutive days an average of:

  • Friesians: 1.5–2kg grain per calf per day
  • Jerseys: 1–1.5kg grain per calf per day

It is also important to consider roughage and rumination development: aim for 50% of calves ruminating at rest