Lactation curves of friesian-bunaji crosses in Nigeria

The validity of the gamma function to describe lactation curves of $\text{1}\text{2}$ and $\text{3}\text{4}$ bred Friesian-Bunaji crosses was investigated. The function explained 71% of the variation in yield in lactations which differed in duration, parity and season of calving. The effect of these variables on the components of the lactation curve was analysed by least-squares procedures. The goodness of fit of the function did not differ between classes of varying duration of lactation; short lactations, however, in addition to a lower persistence, also showed a low level of production. Lactation curves of first parity were flatter and also had a greatly reduced level of production compared to higher parities.Multiplying factors for estimating total lactation yield from part records were obtained from the fitted curves. The accuracy of prediction was greater when separate factors were used for each class of lactation length. The usefulness of part records in progeny testing is also discussed.