Providing newborn calves with adequate IgG supply from colostrum is recognized as an essential management practice in calf rearing. Calves that fail to reach serum IgG levels above 10 g/L within the first two days of life are considered to undergo failure of passive transfer (FPT).
Economic losses associated with FPT have been estimated to average $65 per calf when accounting for calf mortality, morbidity, and decrease in average daily weight gain. Industry standards define colostrum as high quality when IgG concentration is greater than 50 g/L (measured with radial immunodiffusion assay). Parity, pre-partum diet, season, breed, dry-period length, vaccination of the dam, and delayed colostrum collection are factors associated with colostrum quality.
In a recent survey, almost 30% of maternal colostrum failed to reach IgG concentrations above 50 g/L. Thus, to prevent FPT, it is essential to know the IgG concentration of colostrum and to restrict the first feeding to colostrum that meets that standard of quality. On-farm evaluation with a Brix refractometer can be used to successfully estimate IgG concentration.
In a recent Extension meeting, a dairy producer asked if percent Brix reading on second- milking colostrum is an appropriate method to estimate colostrum IgG. It was an interesting question to which we did not have a defined answer, so we conducted a study to investigate it.
After evaluating multiparous Jersey-cow colostrum samples from first and second milkings, we are able to provide an answer: YES. In Figure 1, we see there was a strong association between IgG concentrations of colostrum from first and second milkings and Brix readings.
We also found that nearly half (42.7%) of the second-milking colostrum samples from cows on their third or greater lactation met industry standards for desirable IgG concentrations. This warrants percent Brix readings on second-milking colostrum from mature cows, and retention and storage of that colostrum for first feedings, especially during colostrum shortages.