15B-16

Cow stage of lactation and number of offspring influence the levels of plasmin (PL) and plasminogen (PG) in milk.  An increased level of plasmin in milk has been shown to accelerate the ripening of Cheddar and Swiss cheeses. Understanding the relationship between heifer characteristics (i.e. stage of lactation and number of offspring) and cheese curd PL and PG levels could be used to select milk for the production of ripened cheeses. The objective of this study was to determine the effect milk taken from cows at various stages of lactation and cows with varying numbers of offspring have on PL and PG levels in milk casein fraction and pasteurized milk cheese curd. Milk from 36 cows was collected and pasteurized.  Compositional analysis of the milk was conducted along with total bacterial and somatic cell counts.  Cheese curds were prepared by following a standard cheese procedure.  Milk casein and whey fractions were prepared by ultracentrifugation of each milk sample.  All casein/curd and whey fractions were tested for PL and PG activities using a synthetic substrate. Stage of lactation had a significant (P < 0.05) effect on the PL and PG levels in milk casein fractions but did not in cheese curd (b > 0.99).  Number of calves did not have a significant (b > 0.99) effect on PL and PG levels in milk casein fractions but did in cheese curd (P < 0.05).  PL and PG levels were highest in curd made from milk taken from cows with 2 or 3 offspring. Understanding the relationship between heifer characteristics (i.e. stage of lactation and number off offspring) and cheese curd PL and PG levels allows cheese producers the opportunity to select milk from cows that will result in reduced ripening time cheeses.