Genetic parameters for novel climatic resilience indicators derived from automatically-recorded vaginal temperature in lactating sows under heat stress conditions

Abstract

Background: Longitudinal records of automatically-recorded vaginal temperature (T_V) could be a key source of data for deriving novel indicators of climatic resilience (CR) for breeding more resilient pigs, especially during lactation when sows are at an increased risk of suffering from heat stress (HS). Therefore, we derived 15 CR indicators based on the variability in T_V in lactating sows and estimated their genetic parameters. We also investigated their genetic relationship with sows' key reproductive traits.

Results: The heritability estimates of the CR traits ranged from 0.000 ± 0.000 for slope for decreased rate of T_V (Slope_De) to 0.291 ± 0.047 for sum of T_V values below the HS threshold (HSU_B). Moderate to high genetic correlations (from 0.508 ± 0.056 to 0.998 ± 0.137) and Spearman rank correlations (from 0.431 to 1.000) between genomic estimated breeding values (GEBV) were observed for five CR indicators, i.e. HS duration (HSD), the normalized median multiplied by normalized variance (Nor_medvar), the highest T_V value of each measurement day for each individual (Max_Tv), and the sum of the T_V values above (HSU_A) and below (HSU_B) the HS threshold. These five CR indicators were lowly to moderately genetically correlated with shoulder skin surface temperature (from 0.139 ± 0.008 to 0.478 ± 0.048) and respiration rate (from 0.079 ± 0.011 to 0.502 ± 0.098). The genetic correlations between these five selected CR indicators and sow reproductive performance traits ranged from - 0.733 to - 0.175 for total number of piglets born alive, from - 0.733 to - 0.175 for total number of piglets born, and from - 0.434 to - 0.169 for number of pigs weaned. The individuals with the highest GEBV (most climate-sensitive) had higher mean skin surface temperature, respiration rate (RR), panting score (PS), and hair density, but had lower mean body condition scores compared to those with the lowest GEBV (most climate-resilient).

Conclusions: Most of the CR indicators evaluated are heritable with substantial additive genetic variance. Five of them, i.e. HSD, Max_Tv, HSU_A, HSU_B, and Nor_medvar share similar underlying genetic mechanisms. In addition, individuals with higher CR indicators are more likely to exhibit better HS-related physiological responses, higher body condition scores, and improved reproductive performance under hot conditions. These findings highlight the potential benefits of genetically selecting more heat-tolerant individuals based on CR indicators.

Fig. 1

Example of the derivation of climate resilience indicators. Deviations in observed versus expected vaginal temperature in two example individuals, pig A (panel a), pig B (panel b). Panel c shows how the measures HSD, Slope_In, Slope_De, and Max_Tv were obtained for pig A. In panel d, the light blue area represents the HSU_A for pig A, which is the sum of the vaginal temperatures above the heat stress threshold, while the dark blue area represents the HSU_B for pig A, which is the sum of the vaginal temperatures below the heat stress threshold. HSD: length of time during which the body temperature of each individual remains above the heat stress threshold value for each collection day; Slope_In: slope of the increase in Tv; Slope_De: slope of the decrease in Tv. Max_Tv: the highest T_V of each collection day for each individual; HSU_A: sum of the Tv values above the HS threshold during the whole data collection period; HSU_B: sum of the Tv values below the HS threshold during the whole data collection period

Fig. 2

Venn diagram of the count and overlapping of (a) the top 100 individuals and (b) the bottom 100 individuals identified based on four of the climatic resilience indicators, i.e. HSD, Max_Tv, HSU_B, Nor_medvar. HSD: length of time during which the body temperature of each individual remains above the heat stress threshold value for each collection day; Max_Tv: the highest T_V of each collection day for each individual; Nor_medvar: normalized median T_V multiplied by the normalized T_V variance; HSU_B: the sum of the Tv values below the HS threshold during the whole data collection period