Assessing Colostrum Quality
Good quality colostrum is essential if calves are to survive and thrive. Colostrum contains immunoglobulins (Ig, antibodies) that protects the calf from disease and kick-starts its immune system during the first few weeks of life. Therefore, ensuring calves receive sufficient, quality colostrum as soon as possible after birth is critical to any dairy operation.
As there are no placental transfer of immunoglobulins (Ig, antibodies) from cow to calf, the calf relies on passive transfer of Ig from colostrum to the calf’s blood until its own immune system starts to produce Ig around one month of age. However, the calf’s ability to absorb Ig from the colostrum decreases by 50% by around six hours of life and is negligible by one day of age. This highlights the importance of ensuring adequate colostrum as soon as possible after birth and calves fed colostrum soon after birth will have higher blood Ig levels (indicating better passive transfer) from the same volume and quality of colostrum compared with calves fed later (Weaver et al. 2000). There is a threshold for serum Ig level (10mg/ml) below which failure of passive transfer (FPT) is said to have occurred rendering those individual animals at much greater risk of morbidity and mortality.
Guidelines for feeding colostrum are based on when and how much to feed. Each calf should receive four litres of good quality colostrum by 4 hours of age, with the majority of that offered within the first two hours of life where possible.
Colostral quality is often measured on farm using a hydrometer/colostrometer, which determines the specific gravity of the sample and uses that to infer the concentration of IgG (the most prevalent Ig in colostrum), which gives an indication of quality. A threshold of 50g/L is given below which, the colostrum is deemed of low quality with regards to Ig level. This method does have drawbacks with regards to its sensitivity and specificity, as well as being affected by temperature. However, it is a relatively rapid and easy way to estimate colostral quality. Another method used to determine colostrum quality is the Brix refractometer. This device values related to Ig level in the sample and a Brix value of 22% usually corresponds with the 50g/L threshold on a hydrometer.
Failure of passive transfer
Although calves have a function immune system from birth, they appear unable to respond sufficiently to disease challenges until around one month old (Osburn et al., 1982) and thus rely on the colostral Ig until that time. Failure of passive transfer is responsible for a great deal of morbidity and mortality in dairy operations and it’s crucial to identify those animals that have FPT. Refractometry can also be used to assess whether passive transfer has taken place. Serum total protein can be used to estimate whether the calf has received sufficient Ig. Blood samples taken from 2-7 of age can be tested and samples with values below 5.5g serum total protein/dL are deemed to have FPT (Weaver et al, 2000). There are other methods, such as ELISA and zinc sulphate turbidity test, that can be used to assess passive transfer.
Aside from measuring and monitoring colostrum and passive transfer, basic management practices can also help to reduce calf loss, including clean, warm environments, refrigeration of colostrum, feeding colostrum at body temperature and ensuring any buckets containing colostrum (or milk/milk replacer) have lids to prevent contamination.
Author: Helen Warren
Osburn et al. (1982), Ontogeny of the immune system, Journal of the American Veterinary Medical Association, 181: 1049-1052
Weaver et al. (2000) Passive transfer of colostral immunoglobulins in calves, Journal of Veterinary Internal Medicine, 14(6): 569-577