Bovine colostrum (often called gold colostrum) is a yellow and viscous secretion produced in the udder of cows immediately after calving. Colostrum is an essential first feed for the calf and is rich in nutrients and non-nutritive biologically active substances, such as immunoglobulins (defence molecules), hormones, and growth factors.

Beyond the importance of colostral immunoglobulins for calves to acquire immune molecules from their mothers, colostrum has broad importance for the health, performance and development of calves. After the first milking, the concentrations of nutrients, defence molecules and growth promoters decline rapidly.

The concentration and type of defence molecules in colostrum can vary between cows because of their genetics, parity, stress, vaccination and nutritional status. Therefore, it is recommended to pool colostrum (first milking after calving) from different cows before feeding to calves. A refractometer (available from veterinary supply stores) is an easy way to measure colostrum quality on the farm. A Brix value > 22% is considered high-quality colostrum for giving to calves in the first 24 hours after calving.

The milk produced by the cow during the first 4 days after calving is known as transition milk – a mixture of colostrum and milk (commonly the 2^nd to 8^th milking after calving) has lower concentration of defence molecules than colostrum. However, transition milk contains a substantial amount of nutrients and growth promoters to support the health and growth of calves.  Transition milk should be fed to calves on day 2 to 4  after birth and can be fed longer if available.

Calves are born with an immature digestive system and with no ability to fight against disease-causing organisms. Therefore, calves are completely reliant on colostrum feeding to acquire defence molecules critical for their survival for the first 6 weeks of their life before their immune system starts to develop. The acquisition of defence molecules just after birth is a race against time because of the declining ability of the intestine to absorb antibodies into the bloodstream.

The ability of a calf to absorb antibodies decreases rapidly after birth (30-50% within 6 hours of birth) and stops 24-36 hours after birth. Recent research indicates that leaving the calf to suckle on the cow for 24 hours does not guarantee sufficient colostrum intake. Recent research also shows that one-third of New Zealand calves fail to acquire the desired levels of antibodies (>10 mg/ml of immunoglobulin G or ≤ 52 g/L of serum total protein) in their bloodstream from colostrum. 

This is known as “failure of passive transfer”. This may be the result of not feeding sufficient amounts of colostrum, feeding poor quality colostrum or transition milk, or feeding too long after calving. Ideally, a calf should ingest the equivalent of 15% of its body weight in the first 12-24 hours as colostrum.

Early calf care and colostrum management are logistically challenging in our seasonal dairy operations because the whole herd calves over a few weeks. Colostrum and transition milk storage and feeding practices also vary greatly which likely contributes to the high rate of immunodeficiency in calves. 

AgResearch has demonstrated that for calves removed from cows within 24 hours of birth, feeding high-quality colostrum (Brix=22%) versus a low-quality (Brix=12%) transition milk for the first 2 feedings, reduces the incidence of scours and thus electrolyte use, and improves feed efficiency. The development of the small intestine, which is important for the absorption of nutrients and gut-associated immune function, was also improved. This research, combined with other published international literature, indicates that improvements in gut development associated with high-quality colostrum feeding may deliver lifetime performance benefits such as improved lactation performance. We are currently investigating these potential benefits in partnership with commercial farms in New Zealand.

Investing in calf care and good colostrum management will reduce labour and veterinary costs associated with treating sick calves and improved calf health and welfare with potential lifetime performance benefits. Recommendations from recent research to help improve colostrum management  and improve calf health and immunity include:

• Measure the quality of colostrum (first milking after calving) using a refractometer
• High quality (>22 % Brix) colostrum should be pooled before feeding to calves
• Colostrum should be harvested and stored in clean containers
•  Colostrum could be stored in the fridge for 72 hours and in the freezer for a few weeks
• Provide at least 2 feeds (equivalent of 15% of birth weight of calf ) of high-quality warm colostrum within 24 hours after birth
• Feed warm transition milk (4-6 L/day/calf) split into two equal feeds per day on days 2-4 after birth before gradually switching calves to vat milk or high-quality milk replacers