Feeding system and birth type shape short- and long-term morphometric development in goats from the Moroccan argan area

Introduction The aim of this study was to assess the longitudinal effects of measurement time, concentrate supplementation, birth type, sex and geographic region on morphometric development in goats. Methods The data consisted of 1,932 observations from 322 goats followed over six measurement occasions. Linear mixed models were used to analyze body weight (BW), chest circumference (CC), body length (BL), withers height (WH), total length (TL), neck length (NL), head length (HL), and head width (HW). Results Measurement month had significant effects on all traits (p < 0.001), indicating pronounced time-related changes in body mass and conformation. No significant overall main effect of concentrate supplementation was found for any trait. However, the interaction between supplementation and month was significant for CC (p < 0.001), suggesting a time-dependent nutritional response in thoracic development. Birth type affected BW, CC, WH and TL and showed significant interactions with month for BW, WH, TL, NL, HL, and HW. Sex had a significant effect on CC, BL, WH, and TL, while sex × month interactions were observed for all eight traits, indicating age-dependent sexual dimorphism. Region had a significant main effect only on CC, whereas region × month interactions were found for BW and HL. Predicted trajectories also showed convergence between singleton-born and twin-born goats for BW and WH at later measurements, while males maintained greater predicted CC than females. Residual diagnostics suggested that prediction errors were largely centered around zero, although some traits showed departures from strict normality and homogeneity of variance. Discussion Overall, time was the major factor affecting goat morphometric development, whereas the effects of concentrate supplementation, birth type, sex and geographic region were trait-specific and dependent on developmental stage. CC was especially informative as a field trait for monitoring growth because of its sensitivity to several biological and management factors.