A simulation-based assessment of longitudinal and distributed-lag models for seasonal reproductive responses in three indigenous goat ecotypes

Seasonal reproductive variations in goats

Abstract

This study used a fully synthetic dataset to evaluate an analysis framework for a future longitudinal investigation of seasonal reproductive variation in indigenous Namibian goats. No live animals were screened or enrolled, and no specimens or environmental observations were collected. A single reproducible simulation generated 36 virtual bucks (12 Ovambo, 12 Kavango and 12 Caprivi), 12 monthly records per buck, correlated semen, endocrine and oxidative outcomes, measurement error and pre-specified missingness. The data-generating model used beta distributions for percentage outcomes, log-normal distributions for positively skewed outcomes and Gaussian mixed models for approximately symmetric outcomes, with buck-level random effects, first-order temporal autocorrelation and correlated reproductive, endocrine and oxidative latent factors. Seasonal and heat-lag parameters were calibrated as scenario inputs, not estimated biological truths. In the resulting synthetic dataset, model-adjusted progressive motility was 13.3 percentage points lower in the hot-dry than in the cool-dry scenario (95% confidence interval [CI]: -15.4 to -11.2; p < 0.001). This simulated reduction was 15.2, 14.0 and 10.6 percentage points for virtual Ovambo, Kavango and Caprivi bucks, respectively (interaction p = 0.004). Simulated testosterone levels were lower during the hot-dry period (geometric-mean ratio 0.63; 95% CI: 0.57-0.69), while malondialdehyde was higher and antioxidant indices were lower. Under the pre-specified lag coefficients, the largest modeled association with progressive motility occurred for heat exposure 36-49 days before collection. These outputs show that the proposed data structure and models can recover imposed seasonal, ecotype and lag patterns. They do not provide evidence of actual seasonal effects, ecotype differences, fertility or heat tolerance in Namibian goats. Multiyear, multisite empirical validation is required.