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Effects of in utero heat stress and core body temperature on tissue accretion during the growing phase (30 to 60 kg) in pigs
Environmentally-induced heat stress (HS) negatively influences production variables. However, the extent to which in utero HS affects tissue deposition during the rapid lean tissue accretion phase of postnatal growth is unknown. Study objectives were to compare the future tissue accretion rates in pigs exposed to differing in utero and postnatal thermal environments when lean tissue deposition is likely maximized. Pregnant gilts were exposed to thermal neutral (TN; cyclical 15ºC nighttime and 22ºC daytime; n = 9) or HS (cyclical 27ºC nighttime and 37ºC daytime; n = 12) conditions during their entire gestation. Twenty-four offspring from gestational TN (GTN; n = 6 gilts, 6 barrows; 30.8 ± 0.2 kg BW) and gestational HS (GHS; n = 6 gilts, 6 barrows; 30.3 ± 0.2 kg BW) gilts were euthanized as an initial slaughter group (ISG). Following the ISG, 48 pigs from GTN (n = 12 gilts, 12 barrows; 34.1 ± 0.5 kg BW) and GHS (n = 12 gilts, 12 barrows; 33.3 ± 0.3 kg BW) were exposed to constant HS (34.1 ± 2.4°C) or TN (21.5 ± 2.0°C) conditions until they reached 61.5 ± 0.4 kg BW, when they were sacrificed and body composition determined. Homogenized carcasses were analyzed for N, crude fat, ash, water, and gross energy content. Data were analyzed using PROC MIXED in SAS 9.3. Rectal temperature (Tre) and respiration rates increased during postnatal HS compared to TN (39.4 vs. 39.0°C and 94 vs. 49 bpm, respectively; P < 0.01). Regardless of in utero environment, postnatal HS reduced (P < 0.01) feed intake (2.06 vs. 2.37 kg/d) and ADG (0.86 vs. 0.98 kg/d) compared to TN conditions. Postnatal HS did not alter water, protein, and ash tissue accretion rates, but reduced adipose tissue accretion rates (198 vs. 232 g/d; P < 0.04) compared to TN-reared pigs. Gestational environment had no effect on tissue deposition. Regardless of prenatal or postnatal treatment, a post-hoc analysis indicated that pigs with chronically elevated Tre (39.3 ± 0.1°C) consumed more feed (2.27 vs. 2.15 kg/d; P > 0.11), had similar rates of protein accretion (169 vs. 170 g/d; P > 0.40), but had increased adipose deposition (232 vs. 193 g/d; P < 0.01) compared to those with a sustained lower Tre (39.0 ± 0.1°C). In summary, postnatal HS reduces lipid accretion rates, but prenatal HS does not appear to effect tissue accretion during this specific growth phase.
Keywords:
heat stress, tissue accretion, epigenetics