Test-day model of daily milk yield prediction across stages of lactation in Egyptian buffaloes
Abstract. farms in Ismailia region, which exist east of Cairo. Two data sets were considered for analysis of variance according to lactation length. The first data set is TDY of the short lactation (5–10 months: LPS). The 2nd data set is the TDY of the long lactation (LPL > 305 days). Daily milk yield prediction equations were investigated using multiple lactations, separate lactations, and three groups of age at first calving. Polynomial regression functions were fitted to study the effect of stage of lactation on variation in test-day milk yield observations (TDY). Results of the present study showed that the effect of herd (farm, season and year of calving) on variation of TDY were significant and accounted for 35.22% of the total variance for the data set of LPL. Variations in TDY due to the effect of either order of lactation or age at first calving groups were significant and accounted for 8.25% and 13.50%, respectively of the total variance. The overall least-square means of TDY were 5.5 and 7.8 Kg for LPS and LPL, respectively. The highest frequencies of similar TDY observations appeared in the early months across stage of lactation. The peak of the measured TDY obtained among the 4th and the 6th month of lactation of the pooled parity data set. Prediction equation of TDY across days of lactation (Days in Milk:DIM) using pooled parities was as the following:
Y = 3.4103 +.0466X − .0004X2 + .00001X3 − 1.03E-8X4
Prediction equation of TDY across months of lactation (Months in Milk:MIM) using pooled parity data set was as the following:
Y = 1.9634 + 2.7927X − .8931X2 + .1602X3 − .0138X4.
Prediction equations for TDY per parity and for each age at first calving group were computed.
