Estimation of Genetic Parameters for Reproductive Traits in Murciano–Granadina Dairy Goats

The primary objective of this study was to estimate the variance and covariance components, genetic parameters, and genetic trends for key reproductive traits in Murciano-Granadina (MG) dairy goats reared under Iranian breeding conditions. Data were collected over 6 years (2016-2021) from a commercial dairy goat farm located in the Chahshahi region of Kerman Province, southern Iran. The analysed reproductive traits included age at first service (AFS), age at first kidding (AFK), kidding interval (KI), gestation length (GL), service period (SP) and dry period (DP). The dataset comprised 7573 animals with detailed pedigree information involving 337 sires and 3772 dams. The flock was reared under standardised nutritional and management conditions within an intensive breeding system, ensuring optimal conditions for reliable genetic parameter estimation. Variance component and genetic parameters were estimated by Bayesian inference fitting a univariate animal model using the GIBBS1F90 program. Direct heritability estimates ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msubsup><mml:mi>h</mml:mi> <mml:mi>a</mml:mi> <mml:mn>2</mml:mn></mml:msubsup> </mml:mrow> <mml:annotation>$$ {h}_a^2 $$</mml:annotation></mml:semantics> </mml:math> ) ranged from low to moderate, with GL showing the highest <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msubsup><mml:mi>h</mml:mi> <mml:mi>a</mml:mi> <mml:mn>2</mml:mn></mml:msubsup> </mml:mrow> <mml:annotation>$$ {h}_a^2 $$</mml:annotation></mml:semantics> </mml:math> (0.23 ± 0.03), followed by DP (0.12 ± 0.05), AFK and AFS (both 0.12 ± 0.03). KI had a low <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msubsup><mml:mi>h</mml:mi> <mml:mi>a</mml:mi> <mml:mn>2</mml:mn></mml:msubsup> </mml:mrow> <mml:annotation>$$ {h}_a^2 $$</mml:annotation></mml:semantics> </mml:math> of 0.10 ± 0.02, while SP showed the lowest estimate (0.007 ± 0.001), suggesting stronger environmental and management influences on this trait. Repeatability was moderate for GL (0.45 ± 0.06) and DP (0.19 ± 0.04), but low for SP (0.04 ± 0.01), reflecting variable trait consistency across parities. Genetic and phenotypic trend analyses revealed minimal, statistically non-significant (p > 0.05) fluctuations in all reproductive traits. The study demonstrates that reproductive traits in Murciano-Granadina goats under Iranian breeding conditions exhibit low to moderate <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msubsup><mml:mi>h</mml:mi> <mml:mi>a</mml:mi> <mml:mn>2</mml:mn></mml:msubsup> </mml:mrow> <mml:annotation>$$ {h}_a^2 $$</mml:annotation></mml:semantics> </mml:math> , yet maintain sufficient additive genetic variance to allow for potential genetic improvement through selection.