Lactation curves of Holstein-Friesian and Jersey cows in Zimbabwe

Mean daily milk yield for 478 Holstein-Friesian cows from two herds, recorded between 1984-1985, and for 218 Jersey cows from two herds, recorded between 1984-1985, were used to estimate lactation curve parameters for Wood's gamma function: Y n = A n b e -cn . Y n is the predicted average daily milk yield in the n th week; A is a scalar representing 'starting yield'; and e is the base of natural logarithm. The values of b and c (lactation curve constants describing the rates of rise to and decline from peak lactation, respectively), lactation persistency (s), goodness of fit (R 2 ) and projected 44 week milk yield were estimated. The analysis of variance indicated significant effects ( P 0,05) in the Holstein-Friesian. The use of monthly or weekly milk yield totals to calculate mean daily yield had highly significant effects ( P O,05) by die Holstein-Fries nie. Die gebruik van maandelikse of weeklikse melkproduksie totale om gemiddelde daaglikse produksie te bereken, het hoogs betekenisvolle effekte ( P <0,01) op die laktasiekurwe parameters van die Jersey gehad. Keywords : Milk production, lactation curves, Holstein-Friesian, Jersey.