Genetic group, age and season effects on lactation curve shape in goats

Abstract

Monthly records from 1525 lactations obtained from a stall fed herd in Mexico, were used to estimate lactation curves with the Wood model ( Y d = ad b e − cd , where Y d is production in day d, e is the base of natural logarithms and a, b and c are the parameters to be estimated), within genetic group × age × season combination, for several characteristics of lactation curves. Genetic group 1 ( 1 2 to 15 16 crosses of Alpine, Saanen and Toggenburg X local Mexican goats) had significantly greater values for a, maximum production, average daily production, persistency 1 (100 ∗ average production/maximum milk production), persistency2 (100 ∗ cumulated milk production for days 201–300/cumulated milk production for days 101–200), and average milk production and was lower for b and c than genetic group 2 ( 1 2 to 15 16 crosses of Granadina and Nubian X local Mexican goats). Two and 3 year old goats had flatter curves of lactation with higher persistency than older goats, but the effect was different by genetic group. Goats kidding in season 1 (November–February) had lower peak production and more persistency than goats kidding in season 2 (March–October). Initial production advantage of season 2 over 1 was greater in genetic group 1 than in group 2. It is concluded that genotype, age and season affect the characteristics of lactation curve in goats. Significant interactions of genetic group × age and genetic group × season on various measures of the lactation curve shape were found. Results suggest differential physiological responses in each genotype to season and age effects.