Energy partition patterns and plasma metabolomics profiles of modern growing pigs under different ambient temperatures: modelling and integrative analysis
Authors: Zhang Shuai , Gao Hang , Yuan Xiongkun , Wang Junjun , Zang Jianjun 
Published: July 2020

Abstract
Background

Most of the studies focusing on energy partition patterns of growing pigs and the related mechanisms under different ambient temperatures were carried out during 1970s to early 2000s. With the rapid developments in pig breeding, research updates on such topics concerning modern growing pigs have been absent in the last decade. This study developed mathematical models to predict the energy partition patterns of modern growing pigs with different BWs at gradient-ambient temperatures, and investigated the underlying changes in plasma under such conditions based on the integrative analysis of indirect calorimetry and non-target metabolomics profiling.
Methods

In trial 1, 36 barrows with initial BW of 26.4 ± 1.9 kg were allotted to a 6 × 6 Latin Square Design with ambient temperatures set as 18 °C, 21 °C, 23 °C, 27 °C, 30 °C, and 32 °C. In trial 2, 24 barrows with initial BW of 64.2 ± 3.1 kg were allotted to a 4 × 6 Youden Square Design with ambient temperatures set as 18 °C, 23 °C, 27 °C, and 32 °C. Each pig was kept in individual metabolic crate and consumed feed ad libitum, then transferred into the respiration chamber for 5-day indirect calorimetry assay and 1-day fasting. The energy and nitrogen balance as well as energy utilization efficiency were determined, and mathematical models were developed to predict the voluntary feed intake (VFI), metabolizable energy intake (MEi) and energy retention as protein (REP) and lipid (REL) using BW and ambient temperature (T) as predictors. Moreover, plasma samples were collected from pigs at 25 kg under different temperatures, and the levels of hormone and metabolites in plasma were determined using biochemical and the metabolomics approaches, respectively.
Results

As the ambient temperature increased from 18 °C to 32 °C, the VFI, MEi, N intake and retention, total heat production (THP) and REP of growing pigs at 25 kg all linearly decreased (P < 0.05). There were interaction effects between BW and T on VFI, MEi, N balance, adjusted THP, REP and REL (P < 0.05). Parallel curves were observed between the VFI model developed in the current study and that built previously, but our MEi model showed discrepancy from the previous model especially at high temperatures. The models simulated for REP and REL are: REP (kJ/kg BW0.6/d) = -233.38–67.28 × BW0.6 + 3.16 × (BW0.6)2 + 39.58 × T – 0.76 × T2 – 0.26 × BW0.6 × T + 0.26 × MEi, and REL (kJ/kg BW0.6/d) = -465.10 + 8.10 × BW0.6 – 1.03 × (BW0.6)2 – 53.73 × T + 1.34 × T2 + 0.67 × BW0.6 × T + 0.69 × MEi, respectively. The cortisol and thyroid hormone levels in plasma linearly decreased as the ambient temperature increased from 18 °C to 32 °C, and 13 compounds were identified through metabolomics analysis, including up-regulated metabolites involved in fatty acid metabolism such as adrenic acid and down-regulated metabolites involved in amino acid metabolism such as spermidine at 32 °C.
Conclusion

These results suggested that pigs at heavier body weight were more sensitive to high temperatures on energy intake and partition, and pigs with modern genotypes could be more sensitive to heat stress than pigs with older genotypes. Most of the identified metabolites altered under high ambient temperatures are associated with suppressed fatty acid oxidation and elevated lipogenesis and protein degradation.