Non-genetic sources of variation influencing yield and composition of milk production parameters in South African Saanen goats

Abstract

This study tested the importance of non-genetic effects on average lactation performance in yields of milk, fat, protein, and lactose; urea concentration; persistency; somatic cell count; net returns; as well as estimated phenotypic relationships between dam kidding age and these parameters in the South African Saanen goat population kidding between 1955 and 2018. Analysis of variance was carried out to test for effects; Pearson’s correlation coefficients between phenotypic traits were estimated. Dam parity and birth year substantially influenced all parameters studied. Dam birth season was an important factor of variation for all parameters except milk yield, urea concentration, and net returns. There was a substantial variation due to dam kidding season in all parameters except protein yield and urea concentration, with dams kidding in spring attaining the highest average lactation milk and lactose yields. Dams giving birth to triplets attained the highest values for average lactation milk yield, lactose yield, and net returns. Pearson’s correlation estimations indicated negative associations between dam kidding age and all parameters investigated except somatic cell count (r_p= 0.189). Nongenetic factors determine to what extent the genetic potential of animals is expressed. Dam parity, birth year, kidding age, litter size, birth, and kidding season should be adjusted for when comparing average lactation performance of various milk production parameters in this population. For optimal lactation performance, planned breeding should be applied for spring kidding. There is a need to estimate genetic correlation values for the various traits studied to evaluate their response to selection.