RENNET COAGULATION PROPERTIES OF MILK FROM COWS AT 3 STAGES OF LACTATION SUPPLIED WITH GRADED-LEVELS OF AN ANTIMICROBIAL FEED SUPPLEMENT

The effects of Flavophospholipol on Gelograph coagulation properties o f milk were evaluated in an experiment employing a total df 104 Holste in cows. The antibiotic was provided in amounts of 0 mg, 30 mg, 60 mg and 90 mg per day throughout the whole lactation. Milk samples were ob tained in the 5th, 17th and 34th week of lactation. Isoelectric focusi ng was used to determine the individual milk protein genotypes of the cows. Furthermore, data on milk yield and composition, pH and acidity were obtained. Only minor effects of Flavophospholipol on rennet coagu lation properties and on milk composition occurred. In the rate of cur d firming significant group differences were observed which, however, were non-systematic in terms of a dose-response relationship. As the l actation proceeded, milk protein content increased with the consequenc e of considerably shorter coagulation times and higher curd firmness 1 5 min and 30 min after incubation with rennet. The differences between the least square means were partially reduced if milk protein was exc luded by covariance analysis. The differences between cows of kappa-ca sein genotype AA and AB were according to expectations as far as coagu lation traits we reconcerned, however there was no difference in milk protein content. Milk from beta-lactoglobulin genotype AA cows showed higher protein contents, shorter coagulation times and, unexpectedly, an improved curd firming behaviour as AB, BE and BC milk. The comparab ly close relationship between milk protein content and coagulation pro perties as determined by covariance and correlation analysis indicates that Flavophospholipol might be favourable if milk casein content is increased.