HETEROSIS FOR GROWTH AND YIELD TRAITS FROM CROSSES OF FRIESIAN STRAINS

Heterosis for growth and yield traits was estimated for Fl and backcross generations that resulted from crosses of Holstein or Friesian bulls from Canada, Denmark, Israel, The Netherlands, New Zealand, Sweden, the United Kingdom, the US, and West Germany with Polish Black and White cows. Growth traits included BW at 6 and 12 mo and mean daily gain from birth to 6 mo and 6 to 12 mo for bulls and BW at 6, 12, and 18 mo and mean daily gain from birth to 6 mo, 6 to 12 mo, and 12 to 18 mo for heifers. Yield traits were first lactation 305-d milk and fat yields and fat percentage. For bulls, heterotic and additive effects were not significant for 6- and 12-mo BW and mean daily gains. However, heterotic and additive effects for heifers were highly significant for 6- and 12-mo BW and mean daily gain from birth to 6 mo. Heterotic and additive effects were highly significant for milk and fat yields, but only additive effects were significant for fat percentage. Heterosis relative to the Polish mean was greatest for the Canadian strain (about 110% for milk and fat yields) and the US strain (106% for milk yield and 110% for fat yield).