Short communication: Neonatal calves coagulate first-milking colostrum and produce a large curd for efficient absorption of immunoglobulins after first ingestion.

Calves are fed milk and milk replacer for their growth until approximately 2 mo after birth. During this period, their abomasa produce curd and whey from milk. It has been thought that curd formation is important for digestion and absorption of milk nutrients and immune substances in calves. However, no study has been done observing abomasal contents in neonatal calves after first ingestion of first milking colostrum. Here we report curd formation in neonatal calves and its physiological function with a focus on immunoglobulin absorption. We first examined curd formation by ultrasonography in 3 neonatal calves after first ingestion of first-milking colostrum. Between 0.5 and 8 h after colostrum ingestion, a curd was visualized as a large echogenic image with a clear outline, which was surrounded by an anechoic image corresponding to whey. We next compared serum IgG and IgA concentrations in 10 calves fed the pooled colostrum and 7 calves fed the whey solution that did not coagulate into curds. Serum from 1 calf in the pooled colostrum sample set was excluded due to incomplete curd formation in that the whole colostrum did not coagulate into a large mass of curd and a portion of the colostrum remained as its residue caseins detectable from the abomasal fluid. Serum IgG and IgA concentrations were significantly higher in the 9 calves fed the colostrum than the 7 calves fed the whey solution. One calf exhibiting incomplete curd formation showed low levels of serum IgG and IgA after ingestion, similar to the calves fed the whey solution. These results indicate that curd formation is associated with IgG and IgA absorption in neonatal calves after first ingestion of colostrum.