If the heifer has swelling and/or inflammation (not just fluid), treating her with a lactating or dry cow commercial product would be recommended. If more heifers exhibit this, have your veterinarian culture the fluid to identify the organism. Research generated over the past 10 years or so has found that a considerable number of heifers have mastitis infections around calving. There has been success in treating bred heifers with an intramammary dry cow antibiotic at approximately 6 to 8 weeks before calving or using intramammary lactating therapy at approximately 14 days before calving. Both procedures are extra-label use of antibiotics and require a valid veterinarian/client/patient relationship (VCPR) and therefore should be discussed with the herd veterinarian. Prior to shipping, the milk of these first-lactation cows should be tested with an antibiotic residue test for milk. A third option is to start bred heifers coming through the milking parlor 14 days before expected calving and applying the milking unit for the last week. Colostrum from these cows after calving will be low in antibodies, but colostrum in first-lactation cows is often low in immunity. The calves born to these heifers should be fed colostrum from a cow with high levels of antibodies.

Mike Hutjens, Extension Dairy Specialist, University of Illinois - Illini DairyNET