🍼 Calf

A calf is the young of a cow; the young of yak, zebu and mithun are also called calves. A Holstein calf weighs about 43 kg at birth. It is born without protective antibodies, so what matters most in its first hours is colostrum: 3–4 litres within 1–2 hours of birth.

Why the hurry? In cows the placenta separates the mother's blood from the foetus's, so no antibodies reach the calf before birth. All come with colostrum, and the calf's gut absorbs them less and less well, stopping after about 24 hours. So calves get colostrum in the first 1–2 hours, and no later than 6 hours.

Colostrum is nothing like ordinary milk. A Holstein cow's first milking has 14% protein versus 3.1% in milk, 6.7% fat, and 6% immunoglobulins versus 0.09%. The first feed should be 10–12% of body weight: about 3.8 litres for a 43 kg calf. Farms test colostrum with a refractometer; 22% or more on the Brix scale counts as good.

Next comes milk or milk replacer, and gradually calf starter. The FAO and International Dairy Federation guide advises weaning once the calf eats enough dry feed. US BAMN guidelines say no earlier than 6 weeks, and only after the calf eats at least 1.4 kg of starter a day for three days running; the US average weaning age is 9 weeks.

Why it matters to you. The first hours shape the future cow's health: in one US study, 41% of 2,177 calves had too few antibodies in their blood. Do not rely on the calf suckling in time: a 2008 review found that 46% of calves from cows that had calved before did not suckle within 6 hours. So farms feed colostrum from a bottle or bucket and count the litres.