Date of Award
Doctor of Philosophy
Data were collected from the Iowa State University Research Farm at Ankeny, Iowa. The objectives of this study were: (1) to investigate the correlated responses in milk flow, udder and teat measurements to selecting sires for high and average milk production, (2) to find estimates of heritability and repeatability of these measurements, (3) to examine their relationship with udder health and milk production, and (4) to investigate the relationship of teat-end classification with udder health, lactation milk yield, and milk flow. The realized differences in milk production due to selection adjusted for the year of calving were 1275 lb. for foundation cows, and 2525, 2637, and 2843 lb. for progeny of high minus average sires in generations one, two, and three, respectively;Progeny of high sires had a significantly higher average rate of milk flow, and maximum rate than progeny of average sires in generation one; higher initial rate, 2-min milk, average rate, and maximum rate in generation two; and higher 2-min milk, average rate, and maximum rate in generation three. Cows, lactations, and year-seasons had significant effects on measurements of milk flow. Estimates of repeatability for measurements of milk flow ranged from .22-.47 and estimates of heritability ranged from .13-.26. Phenotypic correlations indicated that high yielders had faster rates of milk flow and higher incidences of mastitis;Selection for higher milk yield caused udders to be closer to the ground, closer to the hock, and to have greater distances between teats pre- and postmilking. Cows and lactations had significant effects on udder and teat measurements. Estimates of repeatability for udder and teat measurements ranged from .27-.75 and estimates of heritability ranged from .52-.70. Lactation milk yield had negative phenotypic correlations with udder height and depth of cleft and positive correlations with total distances between teats. Low udders, greater distances between teats, and longer teats were associated with higher incidences of mastitis;Funnel followed by plate teat-end shapes had higher clinical mastitis cases than other shapes. Round teat ends were associated with slower rate of milk flow while plate-shaped teat ends were associated with faster rate of milk flow.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Sawsan Ali Magid
Magid, Sawsan Ali, "The effect of selection for milk yield on milk flow and udder measurements " (1983). Retrospective Theses and Dissertations. 8419.