Genetic (co)variance across age of fiber diameter and standard deviation in Huacaya alpacas, estimated by repeatability, multi-trait and random regression models

•Heritability of fiber diameter across age was higher under random regression model.•Variance of fiber diameter tended to increase across age.•Genetic improvement of fiber diameter was achieved in the population study.•Persistency of breeding values for fiber diameter across age can be calculated. A total of 14,378 records of fiber diameter (FD) and its standard deviation (SD) from Huacaya alpaca recorded between 2001 and 2017 at Pacomarca genetic center were used in this study. These records were analyzed by a repeatability (RM), multitrait (MT) and random regression (RRM) models. The heritability (h2) estimates were 0.263 and 0.368 for FD and SD respectively under a RM model; these ranged from 0.653 to 0.742 for FD and 0.627 to 0.764 for SD under MT and from 0.561 to 0.614 for FD and 0.556 to 0.702 for SD under RRM. The MT and RRM show a pattern of increase in variances and heritability as age increases for SD and till 6 years of age for FD, while the genetic correlation (rg) decrease for both traits between 1 and 5 years of ages. The breeding value for the three models show a linear relationship for FD and SD across age at shearing, meaning that any of these models can be used in the selection process. The results of this study shows that during this period of time a highly favorable selection response was obtained for fiber quality in Huacaya alpaca using RM, however the use of the RRM approach can offer more valuable information, particularly in the persistence of the genetic merit of the animals at 5 years respect to 1 years old at shearing. More research is needed on the use and relationship between persistence and others economical traits in alpaca.