Statistical modelling of growth curve for longitudinal data on a feeding trial in goat breeds 

Authors

• Ihab Mostafa Shaat Livestock Research Center, Directorate General for Agricultural and Livestock Research, Ministry of Agriculture, Fisheries and Water Resources, Oman ; Mawarid, Ministry of Higher Education, Research & Innovation, Oman
• Alaa Alhamadani Livestock Research Center, Directorate General for Agricultural and Livestock Research, Ministry of Agriculture, Fisheries and Water Resources, Oman 
• Khafan Al-Shargi Livestock Research Center, Directorate General for Agricultural and Livestock Research, Ministry of Agriculture, Fisheries and Water Resources, Oman 
• Rashid Al-Habsi Livestock Research Center, Directorate General for Agricultural and Livestock Research, Ministry of Agriculture, Fisheries and Water Resources, Oman 
• Talal Al-Sedeiri Livestock Research Center, Directorate General for Agricultural and Livestock Research, Ministry of Agriculture, Fisheries and Water Resources, Oman 
• Asila Al Naabi Mawarid, Ministry of Higher Education, Research & Innovation, Oman 
• Asko Maki-Tanila Department of Agricultural Sciences, University of Helsinki, Finland

DOI: https://doi.org/10.23986/afsci.145198

Keywords:

growth rate, concentrate feeding, polynomial regression, mixed model, Omani goats

Abstract

The growth curve parameters were estimated extending a linear regression to higher degree polynomial with
attempts to use also the biologically appealing Gombertz function. The data contained monthly weight records from weaning to the age of 14 months of kids in two Omani goat breeds Sahrawi and Jabbali used in a feeding trial assessing the effect of concentrate supplement (14% crude protein). The growth curve parameters were estimated within the fixed effects breed and feed concentrate level (2 or 3% of live body weight) with an extension to mixed models using animals as random effects. The parameters and model contrasting were performed with ML or REML as appropriate with relative comparison relying on AIC and significance testing of estimated parameters. The mixed model analyses were performed with publicly available R software package programs. The fixed effect cubic regression with linear random effect model fitted into the data. The higher level of concentrates improved the immediate post-weaning growth in the same way in the breeds while the subsequent growth curve differed with more pronounced weight increments in the Jabbali breed.