ZBx’s bovine IgG test is intended to help veterinarians and owners make timely decisions. Newborn calf digestive tracts have low proteolytic activity and actively absorb macromolecules and proteins such as immunoglobulins (antibodies) from colostrum via specialized cells. A calf should consume good quality colostrum equal to ~10% of body weight to ensure transfer of “passive immunity” – protective levels of maternal IgG antibodies – during this absorptive period. With adequate transfer of maternal antibodies to organisms in same environment as the calf, the calf is protected during the time it takes for its own immune system to mount a response. A well-managed colostrum feeding program is thus an important factor in the health of newborn calves.
Calf serum IgG levels of 10 mg/ml at 1 to 7 days of birth are generally considered protective (BAMN 2001 & Vet Intern Med 10:304-7).
Intestinal “closure” is said to occur when IgGs and other protective molecules can no longer be absorbed. Closure occurs, on average, at 24 hours, with a standard deviation of 4 hours (J Dairy Sci 62:1632-8). Closure is earlier in animals fed colostrum at birth (~21-22 hours). It is delayed when any consumption is delayed (26 to 30+ hours)(Ibid), but time is variable and consumption of anything can initiate GI changes. Rate of absorption is usually fastest earlier in life. One study found hypoxic calves to have closure delayed as long as 40 hours (J Dairy Sci 74:1953-6).
This test evaluates whether protective levels of IgG have been transferred from the dam to the calf. The test works by comparing the level in the calf’s blood to the reference level considered protective, providing a visual result.
One study suggests that a rapid test could be used at 12 hours after ingestion of colostrum. See Bovine Passive Transfer for additional information.
ZAPvet™ Bovine IgG* is a rapid, calf-side test for the qualitative determination of immunoglobins (IgG) concentration in blood, plasma or serum.
A study by the US National Animal Health Monitoring System (NAHMS) found that calves with serum IgG levels <10mg/ml experienced mortality rates twice that of calves with serum levels of ≥10mg (see Figure 1).