Date of Award:

1982

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Nutrition, Dietetics, and Food Sciences

Department name when degree awarded

Nutrition and Food Sciences

Advisor/Chair:

Gary H. Richardson

Abstract

Milk samples from fifty individual Holstein cows at the Utah State University Dairy Farm were tested monthly for 10 months for total protein, casein, fat, somatic cells and pH. A new instrument (Foss Formagraph) was used to measure the coagulation properties of the samples. Simulated cheese making procedures were utilized to measure recovery of fat and protein. All the data were statistically analyzed in relation to individual animals, stage of lactation, number of lactation and milk yield.

Significant variations in clotting time and curd firmness were observed in relation to period of lactation, season, individual cow difference, and milk pH. A high, negative correlation (-0.86) was observed between clotting time and curd firmness. The mean clotting time generally increased as lactation progressed and milk yield decreased. '!his coincided with the change in seasons from Summer, when the cows were generally in mid lactation, to Winter when they were in late lactation. Curd firmness was generally greater in Summer than in Fall or Winter. Milk samples from 38% of the cows did not coagulate, one month prior to their dry periods. Frequency of the failure of milk to coagulate one month before the dry period was highest in Winter (68.4%) and Fall (31.6%). All samples from cows dried in the Summer coagulated one month before drying. A procedure was developed for measuring the coagulation efficiency of milk from individual cows.

Milk pH was the most significant and independent source of variation affecting clotting time and curd firmness. Stage of lactation correlated significantly and positively with total protein, casein, fat, pH and negatively with milk yield. Total protein, casein, fat, pH and somatic cell counts were highest in Winter, when milk yields were lowest and average days in lactation were longest.

The amounts of casein plus fat that were measured were substituted in the Van Slyke and Price formula to estimate cheese yields during Winter months (January through March). Values ranged from 5.42 to 14.03 lb per 100 lb milk from individual cows with a mean value of 9.18 lb/100 lb milk. Percentages of milk fat plus casein lost in whey ranged from 13.3 to 23.9% with a mean of 17.8% for individual cows.

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