# Evaluating High Ambient Temperature Effects on Milk Production in Local Tunisian Goats: Toward Resilient Breeding Strategies for Arid Environments

## TL;DR

This study shows how rising temperatures reduce milk production in Tunisian goats and suggests breeding strategies to improve heat tolerance in arid regions.

## Contribution

The study quantifies the impact of high ambient temperature on milk yield in local Tunisian goats and identifies optimal temperature indicators for modeling heat effects.

## Key findings

- High ambient temperatures significantly reduce milk yield in Tunisian goats, with losses of 4–5% per degree above thermoneutrality.
- Cubic polynomial models provided better accuracy than quadratic models in predicting milk yield under heat stress.
- Individual goats showed high variability in heat tolerance, with some maintaining stable production while others declined steeply under high temperatures.

## Abstract

In the arid south of Tunisia, local goats are known for their ability to adapt and stay productive under harsh conditions. However, increasing temperatures intensified by climate change can reduce their milk production. In this study, the effect of high ambient temperature (HT) on milk yield was quantified in Tunisian local goats, considering milk production as a primary economic and nutritional trait in smallholder and pastoral systems. The results showed a significant negative effect of high ambient temperature with relevant reductions in milk yield under both moderate and severe heat load conditions. These findings provide valuable insights for designing selective breeding programs aimed at improving heat tolerance in dairy goats, leading to support the sustainability and productivity of goat farming in arid regions.

This study evaluates the impact of high ambient temperature (HT) on milk production in Tunisian local goats using both fixed and random regression models with quadratic and cubic Legendre polynomials. Daily minimum (Tmin), maximum (Tmax), and average (Tavg) temperatures were tested as heat load indicators, measured on the milking day and averaged over the 1–3 preceding days. The deviance information criterion (DIC) consistently showed that models including temperature effects provided a better fit than a baseline model without heat load. Cubic polynomials showed superior accuracy compared with quadratic models, even if the differences were relatively small. The best model was obtained with Tavg on the milking day, followed closely by Tmax averaged across one or two preceding days. The population response showed a thermoneutral plateau at lower temperatures, followed by declines beyond the HT thresholds. For Tmax, moderate and severe thresholds were detected at 20–23 °C and 25–27 °C, respectively, while for Tavg, thresholds occurred at 11–13 °C and 16–19 °C. Milk losses ranged from 22 to 85 g/°C depending on the temperature indicator, representing an average 4–5% decline in daily yield per degree above thermoneutrality. High variability in individual responses was observed. Some goats maintained stable production, while others showed steep declines under HT, with slope differences reaching over 150 g/°C. Correlations of milk yield across contrasting thermal environments were low, indicating that animal ranking changes with temperature. High-producing goats are more affected by heat, showing the need for a balance between production and heat tolerance.