Persistency Within and Between Lactations in Morning, Evening and Daily Test Day Milk in Dairy Goats (short communication)
Abstract. Persistence in dairy animals can be used as selection criteria. Peak value in lactation can be used to predict total lactation production if within lactation persistence is high. This will provide information on early lactation and shorten generation interval. Major purpose of this study was to determine persistency within and between lactations of Turkish Saanen goats in morning, evening and daily milk yields. Two different methods were employed. One used ratios of the succeeding test days as dependent variables. The multivariate analyses indicated that effects of parity (P=0.05), year (P < 0.01), lactation length (P=0.05) and parity by year interaction (P < 0.01) were large. The other approach was to use within correlations and measure changes in milk production in different parities by using repeated measures analysis and modeling covariance structure using compound symmetry. The within correlations can be used as indicators of persistency. Effects of parity, test day and days in milk (DIM), DIM2, ln(DIM) and [ln(DIM)]2 on morning and evening values and total daily milk weights were analyzed to characterize the lactation curve. Values of DIM and repeated measure id number of the goats were added to the model within parity. Within lactation correlations were estimated as 0.22 for morning, 0.28 for evening and 0.27 for daily milk yield. Evening milk tests can alone be used to estimate lactation milk yield, instead of the total test day milk yield. Milk yield increased until lactation four, and decreased in lactation five in morning, evening and daily milk yields. There was a sharp increase from first lactation to second (ranged from 22.0 to 26.8%) and second lactation to third (ranged from 20.0 to 22.2%).