Pork quality traits and associated muscle metabolic changes in pigs under chronic prenatal and postnatal heat stress

Chronic heat stress (HS) is a major concern affecting pig growth performance and metabolism, with potential consequences on carcass and meat quality traits. The objective of this study was to assess the influence of prenatal (PE) and growing (GE) thermal environments, and their combination, on muscle metabolism, carcass characteristics, and pork quality. From 6 to 109 d of gestation, 12 sows (1 per block) were kept under thermoneutral (TN) conditions (cyclic 18 to 24 °C; PTN) and 12 sows under chronic HS (cyclic 28 to 34 °C; PHS). Two female offspring per sow were selected based on body weight at weaning, for a total of 48 female pigs (12 blocks of 2 sisters from each PE), and one sister was placed in each GE. Gilts were housed from 82 to 140 d of age under cyclic GTN (18 to 24 °C; n = 24) or GHS (28 to 34 °C; n = 24) environments. Data were analyzed using a mixed model including PE, GE, and PE × GE interaction as main effects, and sire, sow within PE, pen within PE × GE, and slaughter day (for plasma, muscle, and meat traits) as random effects. No significant PE × GE interaction was found on any trait under study (P ≥ 0.05). Prenatal HS did not affect growth performance and carcass traits (P ≥ 0.05). Compared with GTN, GHS pigs had lower average daily feed intake, average daily gain, and hot carcass weight (P < 0.01), but similar carcass lean meat content (P ≥ 0.05). Prenatal HS had scarce effects on pork quality, with only higher a* and C* values (P < 0.05) in the Gluteus superficialis. Growing HS led to a higher pH 24 h (P < 0.05) in the Longissimus thoracis et lumborum (LTL) and ham muscles, and higher meat quality index in the ham muscles. In contrast, quality traits of the Semispinalis capitis (SC) were not affected by either PE or GE (P > 0.05). Except a tendency for a higher citrate synthase activity in the SC (P = 0.065), PHS did not affect muscle metabolism. Growing HS induced muscle-specific metabolic responses, with reduced glycolytic potential (P < 0.01) and metabolic enzyme activities (P < 0.05) in the glycolytic LTL, but not in the oxidative SC (P > 0.05). Plasma glucose content at slaughter was lower in the GHS compared with GTN pigs (P = 0.002), indicating an altered energy metabolism in pigs under GHS. Altogether, growing HS altered growth without affecting carcass traits, but improved technological quality of loin and ham. Prenatal HS, alone or combined with GHS, had limited or even no effect on carcass and pork quality.

Direct genetic effects, maternal genetic effects, and maternal genetic sensitivity on prenatal heat stress for calf diseases and corresponding genomic loci in German Holsteins

The aim of this study was to infer the effects of heat stress (HS) of dams during late gestation on direct and maternal genetic parameters for pneumonia (PNEU, 112,563 observations), diarrhea (DIAR, 176,904 observations), and omphalitis (OMPH, 176,872 observations) in Holstein calves kept in large-scale co-operator herds. The genotype dataset included 41,135 SNPs from 19,247 male and female cattle. Temperature-humidity indices (THI) during the last 8 wk of pregnancy were calculated, using the climate data from the nearest public weather station for each herd. Heat load effects were considered for average weekly THI larger than 60. Phenotypically, regression coefficients of calf diseases on prenatal THI during the last 8 wk of gestation were estimated in 8 consecutive runs. The strongest detrimental effects of prenatal HS on PNEU and DIAR were identified for the last week of pregnancy (wk 1). Thus, only wk 1 was considered in ongoing genetic and genomic analyses. In an advanced model considering prenatal HS, random regression coefficients on THI in wk 1 nested within maternal genetic effects (maternal slope effects for heat load) were considered as parameters to infer maternal sensitivity in response to prenatal THI alterations. Direct heritabilities from the advanced model ranged from 0.10 (THI 60) to 0.08 (THI 74) for PNEU and were close to 0.16 for DIAR. Maternal heritabilities for PNEU increased from 0.03 to 0.10 along the THI gradient. For DIAR, the maternal heritability was largest (0.07) at the minimum THI (THI = 60) and decreased to 0.05 at THI 74. Genetic correlations smaller than 0.80 for PNEU and DIAR recorded at THI 60 with corresponding diseases at THI 74 indicated genotype by climate interactions for maternal genetic effects. Genome-wide associations studies were performed using de-regressed proofs of genotyped sires for direct genetic, maternal genetic, and maternal slope effects. Thirty suggestive and 2 significant SNPs were identified from the GWAS. Forty-three genes located close to the suggestive SNPs (±100 kb) were annotated as potential candidate genes. Three biological processes were inferred on the basis of the these genes, addressing the negative regulation of the viral life cycle, innate immune response, and protein ubiquitination. Hence, the genetics of prenatal heat stress mechanisms are associated with immune physiology and disease resistance mechanisms.

Genotype by heat stress interactions for production and functional traits in dairy cows from an across-generation perspective

The aim of this study was to analyze time-lagged heat stress (HS) effects during late gestation on genetic co(variance) components in dairy cattle across generations for production, female fertility, and health traits. The data set for production and female fertility traits considered 162,492 Holstein Friesian cows from calving years 2003 to 2012, kept in medium-sized family farms. The health data set included 69,986 cows from calving years 2008 to 2016, kept in participating large-scale co-operator herds. Production traits were milk yield (MKG), fat percentage (fat%), and somatic cell score (SCS) from the first official test-day in first lactation. Female fertility traits were the nonreturn rate after 56 d (NRR56) in heifers and the interval from calving to first insemination (ICFI) in first-parity cows. Health traits included clinical mastitis (MAST), digital dermatitis (DD), and endometritis (EM) in the early lactation period in first-parity cows. Meteorological data included temperature and humidity from public weather stations in closest herd distance. The HS indicator was the temperature-humidity index (THI) during dams' late gestation, also defined as in utero HS. For the genetic analyses of production, female fertility, and health traits in the offspring generation, a sire-maternal grandsire random regression model with Legendre polynomials of order 3 for the production and of order 2 for the fertility and health traits on prenatal THI, was applied. All statistical models additionally considered a random maternal effect. THI from late gestation (i.e., prenatal climate conditions), influenced genetic parameter estimates in the offspring generation. For MKG, heritabilities and additive genetic variances decreased in a wave-like pattern with increasing THI. Especially for THI >58, the decrease was very obvious with a minimal heritability of 0.08. For fat% and SCS, heritabilities increased slightly subjected to prenatal HS conditions at THI >67. The ICFI heritabilities differed marginally across THI [heritability (h²) = 0.02-0.04]. For NRR56, MAST, and DD, curves for heritabilities and genetic variances were U-shaped, with largest estimates at the extreme ends of the THI scale. For EM, heritability increased from THI 25 (h² = 0.13) to THI 71 (h² = 0.39). The trait-specific alterations of genetic parameters along the THI gradient indicate pronounced genetic differentiation due to intrauterine HS for NRR56, MAST, DD, and EM, but decreasing genetic variation for MKG and ICFI. Genetic correlations smaller than 0.80 for NRR56, MAST, DD, and EM between THI 65 with corresponding traits at remaining THI indicated genotype by environment interactions. The lowest genetic correlations were identified when considering the most distant THI. For MKG, fat%, SCS, and ICFI, genetic correlations throughout were larger than 0.80, disproving concerns for any genotype by environment interactions. Variations in genetic (co)variance components across prenatal THI may be due to epigenetic modifications in the offspring genome, triggered by in utero HS. Epigenetic modifications have a persistent effect on phenotypic responses, even for traits recorded late in life. However, it is imperative to infer the underlying epigenetic mechanisms in ongoing molecular experiments.

Chronic prenatal heat stress alters growth, carcass composition, and physiological response of growing pigs subjected to postnatal heat stress

Postnatal heat stress (HS) effects on pig physiology and performance are widely studied but prenatal HS studies, albeit increasing, are still limited. The objective of this study was to evaluate the chronic prenatal HS effects in growing pigs raised in postnatal thermoneutral (TN) or in HS environment. For prenatal environment (PE), mixed-parity pregnant sows were exposed to either TN (PTN; cyclic 18 to 24 °C; n = 12) or HS (PHS; cyclic 28 to 34 °C; n = 12) conditions from day 9 to 109 of gestation. Two female offspring per sow were selected at 10 wk of age and allotted to one of two postnatal growing environments (GE): GTN (cyclic 18 to 24 °C; n = 24) and GHS (cyclic 28 to 34 °C; n = 24). From 75 to 140 d of age, GTN pigs remained in GTN conditions, while GHS pigs were in GTN conditions from 75 to 81 d of age and in GHS conditions from 82 to 140 d of age. Regardless of PE, postnatal HS increased rectal and skin temperatures (+0.30 and +1.61 °C on average, respectively; P < 0.01) and decreased ADFI (-332 g/d; P < 0.01), resulting in lower ADG and final BW (-127 g/d and -7.9 kg, respectively; P < 0.01). The GHS pigs exhibited thicker backfat (P < 0.01), lower carcass loin percentage (P < 0.01), increased plasma creatinine levels (P < 0.01), and decreased plasma glucose, nonesterified fatty acids, T3, and T4 levels (P < 0.05). Prenatal HS increased feed intake in an age-dependent manner (+10 g·kg BW-0.60·d-1 for PHS pigs in the last 2 wk of the trial; P = 0.02) but did not influence BW gain (P > 0.10). Prenatal HS decreased the plasma levels of superoxide dismutase on day 3 of GHS (trend at P = 0.08) and of T4 on day 49 (P < 0.01) but did not affect T3 on day 3 nor 49 (P > 0.10). Prenatal HS increased rectal and skin temperatures and decreased temperature gradient between rectal and skin temperatures in GTN pigs (+0.10, +0.33 and -0.22 °C, respectively; P < 0.05) but not in GHS pigs (P > 0.10). There were also PE × GE interactions found with lower BW (P = 0.06) and higher backfat (P < 0.01) and perirenal adiposity (P < 0.05) for GHS-PHS pigs than the other groups. Overall, increased body temperature and altered thyroid functions and physiological stress responses suggest decreased heat tolerance and dissipation ability of pigs submitted to a whole-gestation chronic prenatal HS. Postnatal HS decreased growth performance, increased carcass adiposity, and affected metabolic traits and thyroid functions especially in pigs previously submitted to prenatal HS.