For milk quality reasons, all cows should have their colostrum milk withheld from the vat for at least eight milkings after calving (10 milkings for heifers and induced cows).
Different arrangements are in place for farmers that supply colostrum to the dairy company. Refer to your dairy company's colostrum supply agreement for more information.
3.1 - Ensure each cow has exceeded her antibiotic Dry Cow Treatment (DCT) Minimum Dry Period before putting her milk in the vat or selling her calf
For cows that have received an antibiotic DCT, a withholding period for milk after calving is specified for each product. Accurate record keeping is critical for withholding period management and preventiing DCT residues from causing an inhibitory substance (IS) grade.
All DCT products are registered with a specified Minimum Dry Period after treatment. If a cow calves within this time, withholding periods for milk and calf meat may be much longer than in the usual situation. Always read the label and follow withholding periods. Consult with your vet if you have any questions.
Your vet can advise you on using the most appropriate antibiotic DCT for your herd, and avoiding residues in milk. Your dairy company representative or farm dairy assessor can help you review your systems to reduce the risk of residues in milk.
Registration of veterinary medicines
The Ministry for Primary Industries (formerly New Zealand Food Safety Authority) is responsible for assessment and registration of pesticides and veterinary medicines. All veterinary medicines and treatments are listed on the Animal Compounds and Veterinary Medicines (ACVM) List. See the www.foodsafety.govt.nz website for up-to-date information on DCT products.
3.2 - Ensure that milk from the colostrum period (first eight milkings) is not included in the supply vat
Colostrum levels in milk cannot be accurately seen by eye. Withhold milk for the recommended number of milkings and ensure udders are completely milked out. At the start of the season, when the number of cows producing milk for the vat is low, cows with undetected clinical mastitis can cause the bulk milk SCC to increase dramatically and may cause a SCC grade.
Check all cows with a Rapid Mastitis Test (RMT) before moving them from the colostrum herd to the milk supply herd. High SCC cows (cows with a positive RMT result) should be kept in the colostrum herd for an extra 2-4 milkings to allow the mastitis to self-cure or turn clinical, and reduce the risk of a SCC grade. Don’t treat RMT-positive cows with antibiotics. Check closely for clinical signs and only treat if signs such as clots or milk discolouration are found.
Feed the withheld colostrum and milk to replacement heifers rather than calves for sale. Feeding this milk to replacement heifers minimises the risk of antibiotic residues from antibiotic DCT in bobby calves. It also provides good nutrient intake for heifers even after the antibody absorption period has passed.
Good milk quality at the start of the season
Observe all withholding periods for colostrum and antibiotic DCT to avoid grading. The minimum volume of milk for collection is 400L and it must be continuously agitated. Strip cows every day that they are in the colostrum herd to detect clinical mastitis. Test with a RMT before they enter the milk supply herd to find cows with very high SCC that could cause a SCC grade.
See Healthy Udder - Find 1 for practical tips on stripping cows to look for clinical signs.
See Healthy Udder - Find 2 for practical tips on testing cows with a RMT to find subclinical mastitis.