Use of Spline function for the characterisation on peak yield, peak day and persistency in lactation curves in Murciano-Granadina goats

The objective of this study was to characterise the peak yield (PY), peak day (PD) and the persistency (P) of the lactation curve of Murciano-Granadina goats by Spline considering the variation factors (region, type of kidding, lactation number and season) and their levels. A total of 1,349,347 test-day records from 180,872 lactations, of 85,404 goats were used. The analysed data with Spline model was considered for adequate fit in lactation curves for others traits in these goats. All factors affected the scale and/or shape of the lactation curve. In the region factor, significant differences (SD, p < .05) were observed in terms of the total milk yield (TY), final persistency (FP) and total persistency (TP) variables in favour of Almeria versus Cordoba and Granada; the PD variables, PY and initial persistency (IP) did not show SD (NSD, p > .05) between regions. The type of kidding presented SD among its levels (evident between double versus single and triple) with the exception of the PY. The lactation number for the variables of PD, PY and TY from second to fifth lactation showed NSD among themselves; but it did in the case of the first. The P of first lactation was longer, with a decrease in subsequent lactations. In the season factor, PD, TY and P presented SD; where the PD was divided into two groups: late group (winter-spring) and early group (fall-winter). The P, PY and PD can be considered as an additional selection criterion and thus modify the lactation curve.