Lactation curves of Holstein-Friesian and Jersey cows in Zimbabwe

Abstract

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^be^-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 (R²) and projected 44 week milk yield were estimated. The analysis of variance indicated significant effects (P<0,01) of herd, parity and season on most of the lactation curve parameters in both breeds. The year effects were significant (P<0,05) in the Jersey but non-significant (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 <0,01) on the lactation curve parameters of the Jersey.

Die gemiddelde daaglikse melkproduksie van 478 Holstein-Frieskoeie uit twee kuddes, vir die tydperk 1984-1985, en van 218 Jerseykoeie uit 2 kuddes, vir die tydperk 1984-1986, is gebruik om die laktasiekurwe parameters vir Wood se gammafunksie te bereken: Y_n = A n^be^-cn. Y_n is die beraainde gemiddelde daaglikse melkproduksie in die n^de week, A verteenwoordig aanvangsproduksie en e is die grondtal van die natuurlike logaritme. Die waardes van b en c (laktasiekurwe konstantes wat, respektiewelik, die styging voor en daling na pieklaktasie aandui), laktasie volhouvermoë (s), akkuraatheid van passing (R²) en voorspelde 44-week melkproduksie is bepaal. Die variansieanalise het betekenisvolle effekte (P<0,01) aangedui vir kudde, pariteit en seisoen vir meeste van die laktasiekurwe parameters by beide rasse. Jaareffekte was betekenisvol (P<0,05) by die Jersey, maar nie betekenisvol (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.