Effects of warm exposure on adipose tissue and muscle metabolism in growing pigs

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.

Impact of Heat Stress on Meat Quality and Antioxidant Markers in Iberian Pigs

Heat stress is associated with impaired meat quality and disruption of redox balance. This study investigated the effect of chronic exposure to high temperature on meat quality and antioxidant markers of muscles (longissimus lumborum and gluteus medius) of growing Iberian pigs. Twenty-four pure Iberian pigs were allocated during 28 days to one of three treatments (n = 8/treatment): thermoneutral conditions (20 °C) and ad libitum feeding (TN), heat stress conditions (30 °C) and ad libitum feeding (HS) and thermoneutral and pair-fed with HS (TN-pf). Muscles of the HS group had greater intramuscular fat content than the TN-pf group and higher Zn levels than TN and TN-pf, whereas differences on fatty acid composition were negligible. Heat exposure did not affect pH, color coordinates of redness (a*) and yellowness (b*) and MDA values but had a positive influence on lightness and drip losses. Moreover, chronic heat stress stimulated the activity of antioxidant defenses SOD, CAT and GPx. The statistical factor analysis adequately classified the muscles studied, but was unable to differentiate samples according with treatments. Findings of the present study support an adaptive response of the Iberian pig to high temperatures and show the high Iberian meat quality even under adverse climate situations.

Effect of dietary near ideal amino acid profile on heat production of lactating sows exposed to thermal neutral and heat stress conditions

BACKGROUND

Reduced protein diet manifested potential to mitigate heat production based on the concept of ideal amino acid profile. The hypothesis of this study was that lactating sows fed a low crude protein (LCP) diet with supplemental amino acid produce less heat compared to those fed a high crude protein (HCP) diet under both thermal neutral (TN) and heat stress (HS) conditions.

METHODS

Thirty-two lactating sows were allotted to HCP (193 g CP/kg) and LCP (140 g CP/kg) diets under thermal neutral (TN, 21 ± 1.5 °C) or cycling heat stress (HS, 32 ± 1.5 °C daytime and 24 ± 1.5 °C nighttime) conditions. Diets contained 0.90% SID lysine and 10.8 MJ/kg net energy. Positive pressure indirect calorimeters were used to measure gas exchange in individual sows with litters, and individual piglets on days 4, 8, 14 and 18. Sow and litter weights were recorded on days 1, 10 and 21.

RESULTS

Sow total heat production (THP) was calculated by subtracting litter THP from sow + litter THP based on BW0.75. Sow BW and body protein (BP) loss was greater for LCP diet compared to HCP diet in peak lactation (P < 0.05 and P < 0.01, respectively) and throughout the entire lactation period (P < 0.05 and P = 0.056, respectively) under HS conditions. Heat-stressed sows fed HCP diet had higher (P < 0.05) rectal temperature at 13:00 (P < 0.05) and 19:00 (P < 0.01), and higher respiration rate at 07:00 (P <  0.05), 13:00 (P < 0.05) and 19:00 (P < 0.05) compared to TN sows fed HCP diet. In sows fed LCP diet, those under HS tended to have higher (P = 0.098) rectal temperature at 13:00 and had higher (P <  0.05) respiration rate at 07:00, 13:00 and 19:00 compared to TN sows. The relationship between daily THP and days in lactation of sows fed LCP diet was quadratic (P < 0.05), with an ascending trend until day 14 and a descending trend from days 14 to 18. Sows fed LCP diet had lower daily THP at day 18 (P < 0.001) compared to those fed the HCP diet under HS conditions.

CONCLUSION

Reduction in THP in sows fed LCP diet was largely associated with THP on day 18 of lactation under HS conditions. Feeding LCP diets alleviated the increased body temperature in sows under HS conditions throughout lactation, which was accompanied by a reduction in respiration rate. Total heat production is associated with days in lactation, in particular under HS conditions with THP appearing to peak between days 14 and 18.

Effects of heat stress on animal physiology, metabolism, and meat quality: A review

Heat stress is one of the most stressful events in the life of livestock with harmful consequences for animal health, productivity and product quality. Ruminants, pigs and poultry are susceptible to heat stress due to their rapid metabolic rate and growth, high level of production, and species-specific characteristics such as rumen fermentation, sweating impairment, and skin insulation. Acute heat stress immediately before slaughter stimulates muscle glycogenolysis and can result in pale, soft and exudative (PSE) meat characterized by low water holding capacity (WHC). By contrast, animals subjected to chronic heat stress, have reduced muscle glycogen stores resulting in dark, firm and dry (DFD) meat with high ultimate pH and high WHC. Furthermore, heat stress leads to oxidative stress, lipid and protein oxidation, and reduced shelf life and food safety due to bacterial growth and shedding. This review discusses the scientific evidence regarding the effects of heat stress on livestock physiology and metabolism, and their consequences for meat quality and safety.

Mechanism of continuous high temperature affecting growth performance, meat quality, and muscle biochemical properties of finishing pigs

Background

The mechanism of high ambient temperature affecting meat quality is not clear till now. This study investigated the effect of high ambient temperature on meat quality and nutrition metabolism in finishing pigs.

Methods

All pigs received the same corn-soybean meal diet. A total of 24 Landrace × Large White pigs (60 kg BW, all were female) were assigned to three groups: 22AL (fed ad libitum at 22 °C), 35AL (ad libitum fed at 35 °C), and 22PF (at 22 °C, but fed the amount consumed by pigs raised at 35 °C) and the experiment lasted for 30 days.

Results

Feed intake, weight gain, and intramuscular fat (IMF) content of pigs were reduced, both directly by high temperature and indirectly through reduced feed intake. Transcriptome analysis of longissimus dorsi (LM) showed that downregulated genes caused by feed restriction were mainly involved in muscle development and energy metabolism; and upregulated genes were mainly involved in response to nutrient metabolism or extracellular stimulus. Apart from the direct effects of feed restriction, high temperature negatively affected the muscle structure and development, energy, or catabolic metabolism, and upregulated genes were mainly involved in DNA or protein damage or recombination, cell cycle process or biogenesis, stress response, or immune response.

Conclusion

Both high temperature and reduced feed intake affected growth performance and meat quality. Apart from the effects of reducing feed intake, high temperature per se negatively downregulated cell cycle and upregulated heat stress response. High temperature also decreased the energy or catabolic metabolism level through PPAR signaling pathway.

Electronic supplementary material

The online version of this article (10.1186/s12263-019-0643-9) contains supplementary material, which is available to authorized users.

Effects of heat stress and insulin sensitizers on pig adipose tissue

Heat stress (HS) negatively impacts several swine production variables, including carcass fat quality and quantity. Pigs reared in HS have more adipose tissue than energetically predicted, explainable, in part, by HS-induced hyperinsulinemia. Study objectives were to evaluate insulin's role in altering fat characteristics during HS via feeding insulin-sensitizing compounds. Forty crossbred barrows (113 ± 9 kg BW) were randomly assigned to one of five environment by diet treatments: 1) thermoneutral (TN) fed ad libitum (TNAL), 2) TN and pair-fed (TNPF), 3) HS fed ad libitum (HSAL), 4) HS fed ad libitum with sterculic oil (SO) supplementation (HSSO; 13 g/d), and 5) HS fed ad libitum with dietary chromium (Cr) supplementation (HSCr; 0.5 mg/d; Kemin Industries, Des Moines, IA). The study consisted of three experimental periods (P). During P0 (2 d), all pigs were exposed to TN conditions (23 ± 3 °C, 68 ± 10% RH) and fed ad libitum. During P1 (7 d), all pigs received their respective dietary supplements, were maintained in TN conditions, and fed ad libitum. During P2 (21 d), HSAL, HSSO, and HSCr pigs were fed ad libitum and exposed to cyclical HS conditions (28 to 33 °C, 58 ± 10% RH). The TNAL and TNPF pigs remained in TN conditions and were fed ad libitum or pair-fed to their HSAL counterparts. Rectal temperature (TR), respiration rate (RR), and skin temperature (TS) were obtained daily at 0600 and 1800 h. At 1800 h, HS exposed pigs had increased TR, RR, and TS relative to TNAL controls (1.13 °C, 48 bpm, and 3.51 °C, respectively; P < 0.01). During wk 2 and 3 of P2, HSSO pigs had increased 1800 h TR relative to HSAL and HSCr (~0.40 and ~0.42 °C, respectively; P ≤ 0.05). Heat stress decreased ADFI and ADG compared to TNAL pigs (2.24 vs. 3.28 and 0.63 vs. 1.09 kg/d, respectively; P < 0.01) and neither variable was affected by SO or Cr supplementation. Heat stress increased or tended to increase moisture content of abdominal (7.7 vs. 5.9%; P = 0.07) and inner s.c. (11.4 vs. 9.8%; P < 0.05) adipose depots compared to TNAL controls. Interestingly, TNPF pigs also had increased adipose tissue moisture content and this was most pronounced in the outer s.c. depot (15.0 vs. 12.2%; P < 0.01) compared to TNAL pigs. Heat stress had little or no effect on fatty acid composition of abdominal, inner, and outer s.c. adipose tissue depots. In summary, the negative effects of HS on fat quality do not appear to be fatty acid composition related, but may be explained by increased adipose tissue moisture content.

Physical and chemical characteristics of the longissimus dorsi from swine reared in climate-controlled and uncontrolled environments

The aim of this study was to evaluate the effect of ambient temperature on the physical and chemical characteristics of the longissimus dorsi muscle by comparing the quality of meat from pigs reared in a controlled and in an uncontrolled environment, the latter provided with a shallow pool. Twenty castrated male pigs of the Topigs line were randomly allotted to two treatments: a controlled environment, with constant temperature (22 °C) and relative humidity (70%); and an uncontrolled environment in a conventional shed for rearing pigs equipped with a shallow pool, where pigs were subject to climatic variations. Meat from pigs kept in the controlled environment showed a greater capacity to retain intracellular water, higher tenderness, and lower cholesterol levels than meat from pigs reared in the uncontrolled environment, but displayed higher lipid oxidation and a lower concentration of DHA. Treatments had no effect on color, pH, chemical composition, or fatty acid profile (except DHA concentration). Rearing pigs in sheds equipped with a shallow pool minimizes the effects of environmental heat on meat quality, allowing the production of high-quality meat in warm climate regions without expensive investments. Animals reared in an uncontrolled environment equipped with a shallow pool are able to produce meat with characteristics within the quality standards and with similar quality to that of meat from animals raised in controlled environment.

Effects of high ambient temperature on meat quality, serum hormone concentrations, and gene expression in the longissimus dorsi muscle of finishing pigs

This study examined the effect of high ambient temperature on the growth performance, meat quality, activity of the hypothalamo-pituitary-adrenal axis, and related gene expression in finishing pigs. All pigs received the same corn-soybean meal-based diet. Twenty-four Landrace pigs (initial bodyweight of 77.64 ± 0.67 kg) were assigned into three groups: Group 1 (22°C, ad libitum, 81% humidity); Group 2 (22°C, pair-fed to Group 3, 78% humidity); Group 3 (35°C, ad libitum, 78% humidity). The experiment lasted for 30 days. The average daily feed intake and average daily gain were markedly reduced in Group 3 compared with Group 1 (P < 0.05). The intramuscular fat content of longissimus dorsi muscle was decreased in Groups 2 and 3 (P < 0.05) when compared with Group 1. Muscle pH at 24 h post-mortem was higher in Group 3 (P < 0.05) compared with Groups 1 and 2, and the pH at 48 h post-mortem was higher in Group 3 (P < 0.05) than in Group 1. The MyHC IIb transcript abundance was lower in Group 3 (P < 0.05) than in the other two groups and that of MyHC IIx was higher in Group 3 than in Group 2 (P < 0.05). The relative abundance of calpastatin transcripts was lower in Group 3 (P < 0.05) than in the other two groups. Cortisol concentrations were lower in Group 3 (P < 0.05) than in Groups 1 and 2 on Day 3. Corticotropin releasing hormone concentrations in Group 3 were lower at Day 3 (P < 0.05) when compared with Group 2 and at Day 30 when compared with Groups 1 and 2. Glucagon concentrations were lower in Group 3 (P < 0.05) when compared with Groups 1 and 2 on Day 30. These results indicate that the decreased intramuscular fat content of pigs at high ambient temperature results from the reduction in feed intake. Independently of its effect on feed intake, high ambient temperature affected the meat quality of finishing pigs by increasing pH value probably due to the lower serum concentrations of corticotropin releasing hormone, and inducing a transition of muscle fibre types from IIb to IIx.

Effects of in utero heat stress on postnatal body composition in pigs: I. Growing phase

Environmentally induced heat stress (HS) negatively influences production variables in agriculturally important species. However, the extent to which HS experienced in utero affects nutrient partitioning during the rapid lean tissue accretion phase of postnatal growth is unknown. Study objectives were to compare future whole-body tissue accretion rates in pigs exposed to differing in utero and postnatal thermal environments when lean tissue deposition is likely maximized. Pregnant sows were exposed to thermoneutral (TN; cyclical 15°C nighttime and 22°C daytime; n = 9) or HS (cyclical 27°C nighttime and 37°C daytime; n = 12) conditions during their entire gestation. Twenty-four offspring from in utero TN (IUTN; n = 6 gilts and 6 barrows; 30.8 ± 0.2 kg BW) and in utero HS (IUHS; n = 6 gilts and 6 barrows; 30.3 ± 0.2 kg BW) were euthanized as an initial slaughter group (ISG). Following the ISG, 48 pigs from IUTN (n = 12 gilts and 12 barrows; 34.1 ± 0.5 kg BW) and IUHS (n = 12 gilts and 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 ± 0.8 kg BW, at which point they were sacrificed and their whole-body composition was determined. Homogenized carcasses were analyzed for N, crude fat, ash, water, and GE content. Data were analyzed using PROC MIXED in SAS 9.3. Rectal temperature and respiration rate increased (P < 0.01) during postnatal HS compared to TN (39.4 vs. 39.0°C and 94 vs. 49 breaths per minute, respectively). 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 accretion rates but reduced lipid accretion rates (198 vs. 232 g/d; P < 0.04) compared to TN-reared pigs. In utero environment had no effect on future tissue deposition rates; however, IUHS pigs from the ISG had reduced liver weight (P < 0.04; 17.9%) compared to IUTN controls. In summary, postnatal HS reduced adipose tissue accretion rates, but IUHS did not appear to impact either lean or adipose tissue accretion during this specific growth phase.

Effects of in utero heat stress on postnatal body composition in pigs: II. Finishing phase

The detrimental effects of heat stress (HS) on animal productivity have been well documented. However, whether in utero HS interacts with a future thermal insult to alter tissue deposition during the finishing phase of pig growth is unknown. Study objectives were to compare the subsequent rate and quantity of whole-body tissue accretion in pigs exposed to differing in utero and postnatal thermal environments. Pregnant sows were exposed to thermoneutral (TN; cyclical 15°C nighttime and 22°C daytime; n = 9) or HS (cyclical 27°C nighttime and 37°C daytime; n = 11) conditions during their entire gestation. Twenty-four offspring from in utero TN (IUTN; n = 6 gilts and 6 barrows; 62.4 ± 0.7 kg BW) and in utero HS (IUHS; n = 6 gilts and 6 barrows; 61.9 ± 0.8 kg BW) were euthanized as part of an initial slaughter group (ISG). After the ISG, 48 pigs from IUTN (n = 12 gilts and 12 barrows; 66.1 ± 1.0 kg BW) and IUHS (n = 12 gilts and 12 barrows; 63.4 ± 0.7 kg BW) were exposed to constant HS (34.4 ± 1.8°C) or TN (22.7 ± 2.5°C) conditions until they reached 80.5 ± 1.5 kg BW, at which point they were sacrificed and their whole-body composition was determined. Homogenized carcasses were analyzed for N, crude fat, ash, water, and GE content. Data were analyzed using PROC MIXED in SAS 9.3. Rectal temperature and respiration rate increased during postnatal HS compared to TN (39.6 vs. 39.3°C and 92 vs. 58 breaths per minute, respectively; P < 0.01). Postnatal HS decreased (P < 0.01) feed intake (2.13 vs. 2.65 kg/d) and ADG (0.70 vs. 0.94 kg/d) compared to TN conditions, but neither variable was influenced by in utero environment. Whole-body protein and lipid accretion rates were reduced in HS pigs compared to TN controls (126 vs. 164 g/d and 218 vs. 294 g/d, respectively; P < 0.04). Independent of postnatal environments, IUHS reduced future protein accretion rates (16%; P < 0.01) and tended to increase lipid accretion rates (292 vs. 220 g/d; P < 0.07) compared to IUTN controls. The ratio of lipid to protein accretion rates increased (95%; P < 0.01) in IUHS pigs compared to IUTN controls. In summary, the future hierarchy of tissue accretion is altered by IUHS, and this modified nutrient partitioning favors adipose deposition at the expense of skeletal muscle during this specific phase of growth.

Constant heat stress reduces skeletal muscle protein deposition in broilers

BACKGROUND

This experiment was conducted to evaluate the effects of constant heat stress on growth performance and protein metabolism in skeletal muscle of Arbor Acres broilers.

RESULTS

Two hundred and seventy 21-day-old Arbor Acres broilers with similar body weight (1298 ± 28 g) were selected for a 3-week trial (29-49 days of age). The broilers were randomly assigned to three groups including the control group, constant heat stress group and pair-fed group. Up-regulation of the rectal temperature and the mRNA expression of heat shock protein 70 in liver indicate that the model for constant heat stress was success. The average daily gain, feed conversion ratio, breast and thigh muscle weight, percentage of breast muscle, crude protein content in breast and thigh muscle in constant heat stress group were significantly lower than in control group and pair-fed group. Serum uric acid content and the glutamic-oxaloacetic transaminase activity were significantly higher, while protein content and glutamic-pyruvate transaminase activity were significantly lower in liver of heat stress group than of the control and pair-fed groups. The expression of insulin-like growth factor 1, phosphatidylinositol 3-kinase and p70S6 kinase associated with protein synthesis were lower in breast muscle but higher in thigh muscle in heat stress group compared to the control or fed-pair groups. In thigh muscles, the expression of muscle ring-finger protein-1 and MAFbx associated with protein degradation were higher in the heat stress group than in the control and pair-fed groups.

CONCLUSION

Poor performance of the birds under heat stress may be due to lower synthesis and increased degradation of proteins.

Altered regulation of contraction-induced Akt/mTOR/p70S6k pathway signaling in skeletal muscle of the obese Zucker rat

Increased muscle loading results in the phosphorylation of the 70 kDa ribosomal S6 kinase (p70S6k), and this event is strongly correlated with the degree of muscle adaptation following resistance exercise. Whether insulin resistance or the comorbidities associated with this disorder may affect the ability of skeletal muscle to activate p70S6k signaling following an exercise stimulus remains unclear. Here, we compare the contraction-induced activation of p70S6k signaling in the plantaris muscles of lean and insulin resistant obese Zucker rats following a single bout of increased contractile loading. Compared to lean animals, the basal phosphorylation of p70S6k (Thr389; 37.2% and Thr421/Ser424; 101.4%), Akt (Thr308; 25.1%), and mTOR (Ser2448; 63.0%) was higher in obese animals. Contraction increased the phosphorylation of p70S6k (Thr389), Akt (Ser473), and mTOR (Ser2448) in both models however the magnitude and kinetics of activation differed between models. These results suggest that contraction-induced activation of p70S6k signaling is altered in the muscle of the insulin resistant obese Zucker rat.

Metabolic and endocrine changes induced by chronic heatexposure in broiler chickens: growth performance, body composition and energy retention

The present study was performed in order to investigate the effect of chronic heat exposure (32",constant) on growth, body composition and energy retention of broiler chickens in relation to age. At 2and 4 weeks of age, fifty-four male Shaver broiler chickens were allocated to three treatments accordingto the following design: 22", ad lib. feeding (22AL); 32", ad lib. feeding (32AL); and 22", pair-feeding with the 32" group (22PF). Ambient temperature was kept constant at either 22 or 32" for 2 weeks. Heatexposure decreased feed intake by 14% YO between 2 and 4 weeks and by 24% YO between 4 and 6 weeks of age. Even with the same feed intake, chicks gained less weight at 32" than at 22", 55% less in young chickens and 22% less in older ones. Hot environmental conditions thus resulted in decreased feed efficiency; the feed:gain ratio was 2·85 at 32" compared with 2·06 at 22" in 22AL birds for the period4—6 weeks. Body composition appeared significantly affected by high ambient temperature. Feathering was reduced at 32" in absolute weight but not as a proportion of body weight. Heat-exposed birds showed a decrease in body protein content, protein gain and protein retention. Group 32AL birds were fatter than the pair-fed (22PF) or ad fib.-fed (22AL) groups at 22". The percentage of energy retained as fat was 79 in heat-exposed chickens compared with 64 in the control groups. The energy retained as protein:energy retained as fat for groups maintained at 22" (0·56) was twice that forthose maintained at 32" (0·28). These modifications should be investigated further in relation to metabolic and endocrinological changes.

Deposition of dietary fatty acids and ofde novosynthesised fatty acids in growing pigs: effects of high ambient temperature and feeding restriction

Predicting aspects of pork quality becomes increasingly important from both a nutritional and a technological point of view. Little information is, however, available concerning the quantitative relation between nutrient intake and fatty acid (FA) deposition at the whole-animal level. In this study, eight blocks of five littermate barrows were used in a comparative slaughter trial. At 24 kg body weight (BW), one pig from each litter was slaughtered to determine the initial FA composition. The other littermates were assigned to one of four feeding levels (ranging from 70 % to 100 % of intakead libitum) and were given a diet containing 0·36 g/kg lipid and 0·22 g/kg FA. The temperature for each block was maintained at either 23 or 30°C. At 65 kg, the pigs were slaughtered and the body lipid and FA composition was determined. Seventy per cent of the digestedn-6 FA and 50 % of then-3 FA were deposited. The average composition ofde novosynthesised FA corresponded to 1·7, 30·3, 2·4, 19·7 and 45·9 % for 14: , 16: , 16: 1, 18: and 18: 1 FA, respectively. At 23°C and for feedingad libitum, 33 % of 16: FA was deposited, 1·7 % shortened to 14: , 63 % elongated to 18: and 2·8 % unsaturated to 16: 1. Twenty-eight per cent of 18: FA was deposited and 72 % unsaturated to 18: 1. At 30°C, 18: FA desaturation was reduced by 3·5 %. Feed intake and temperature independently affected the elongation of 16: FA. A reduction in feed intake increased the elongation rate, whereas the increase in temperature reduced the elongation rate.

Free-range rearing of pigs during the winter: Adaptations in muscle fiber characteristics and effects on adipose tissue composition and meat quality traits1

This research aimed to determine whether outdoor free-range rearing during the winter (average ambient temperature of 5 degrees C) vs. indoor housing (22 degrees C) affects meat quality, muscle metabolic traits, and muscle fiber characteristics. Forty Large White gilts and barrows were blocked by weight within each gender (20 per gender) and allotted randomly into two groups of pigs, with one reared indoors (IN) in individual pens (2.6 m2) and the other reared outdoors (OUT) from December to March in a 0.92-ha pasture. Both groups had free access to the same grower-finisher diet from 23 to 105 kg. At slaughter, adipose (backfat [BF] and omental fat [OF]) and muscle tissues (longissimus muscle [LM], rectus femoris [RF], and semitendinosus [ST]) were obtained from the right side of each carcass. Muscle fibers were stained and classified on the basis of stain reaction as slow-oxidative (SO), fast oxidative-glycolytic (FOG), and fast glycolytic (FG); fiber area and distribution were determined. Also assessed were carcass characteristics, initial and ultimate pH, L*a*b* values, drip loss percent, glycolytic potential (GP), and intramuscular lipid content, as well as the fatty acid profile of each muscle and adipose tissue. The OUT pigs had lower (P < 0.05) ADG and leaner (P < 0.05) carcasses than IN pigs. Rearing environment did not (P > 0.63) affect the intramuscular lipid content of the ST, but intramuscular lipid content was lower (P < 0.01) in the LM and tended to be higher (P = 0.06) in the RF of OUT than in those of IN pigs. In the BF outer layer of the OUT pigs, the higher PUFA content was compensated by both a lower (P < 0.01) saturated and monounsaturated fatty acid (MUFA) content, whereas in the OF, LM, and dark portion of the ST, only the percentage of MUFA was decreased (P < 0.01). In all tissues of the OUT pigs, the linolenic acid content was higher (P < 0.01) and the n-6:n-3 ratio was lower (P < 0.01). The GP of all muscles was higher (P < 0.01), and the ultimate pH of the RF and ST was lower (P < 0.01), in OUT compared with IN pigs. Lightness (L*) values were lower (P < 0.01) in the LM. Percentages of drip loss were higher (P < 0.05) in the LM and light portion of the ST of OUT than in those of IN pigs. The LM and RF of OUT pigs had more (P < 0.01) FOG and fewer (P < 0.01) FG fibers than muscles of IN pigs. Results suggest that rearing pigs outdoors increases aerobic capacity of glycolytic muscles but has little concomitant influence on meat quality traits.

Effect of high temperature on feeding behaviour and heat production in group-housed young pigs

To assess the acclimation of pigs to heat stress, the effects of high (33 degrees C) or thermoneutral (23 degrees C) constant temperatures on feeding behaviour and components of energy balance were studied in group-housed young pigs. Three groups of five pigs were used at each temperature. After 1 week of adaptation, voluntary feed intake (VFI) and heat production (HP) were recorded for thirteen consecutive days. Animals were fed ad libitum. Fasting HP was measured on the last day. Average initial body weights (BW) were 21.4 and 20.9 kg at 23 and 33 degrees C respectively. Feeding behaviour was measured individually and rate of feed intake and characteristics of feeding behaviour were calculated. The O(2) consumption, CO(2) production and physical activity of the group were used to calculate total HP (HP(tot)) and its components, i.e. fasting HP (HP(fas)), HP due to physical activity (HP(act)) and thermic effect of feed (TEF). The BW gain and VFI were reduced by 37 and 30 % respectively at 33 degrees C. The decrease in VFI corresponded to reduced consumption time (-34 %) and size of the meals (-32 %). Feeding behaviour was mostly diurnal (66 % of the VFI), and the rate of feed intake (28 g/min) was not affected by temperature. Daily HP(tot), HP(fas) and TEF, expressed per kg metabolic weight (BW(0.60)), were significantly decreased at 33 degrees C by 22, 18 and 35 % respectively, whereas HP(act) was not affected; TEF expressed per g feed was not affected (2 kJ/g). The decrease in HP(tot) at 33 degrees C was caused by a reduction in TEF and HP(fas) (kJ/d per/kg BW(0.60)), which are both related to reduction in VFI.

Influence of a high ambient temperature on stearoyl-CoA-desaturase activity in the growing pig

An experiment was conducted to determine the influence of a high ambient temperature on the stearoyl-CoA-desaturase activity and fatty acid composition of backfat, leaf fat, Longissimus dorsi muscle and liver, in the growing pig. Eighteen Large White X Landrace castrated pigs (20 kg body weight) were divided into three groups: I (31 degrees C, ad libitum), II (20 degrees C, pair-fed on the 31 degrees C group) and III (20 degrees C, ad libitum) until 35 kg body weight. At 20 degrees C, the level of feed intake had no effect on stearoyl-CoA-desaturase activity, whatever the tissue (groups II and III). At similar levels of feeding, (groups I and II), the stearoyl-CoA-desaturase activity was lower at 31 degrees C (P < 0.001) than at 20 degrees C, regardless of the tissue, with the exception of the hepatic stearoyl-CoA-desaturase activity, which was similar in all three groups. This reduction of the stearoyl-CoA-desaturase activity at 31 degrees C could be related to a decrease in the monounsaturated fatty acid percentage in all the tissues, in hot conditions. The present results show that changes in fatty acid composition caused by environmental temperature, in the pig, may be attributed at least in part to an alteration in the stearoyl-CoA-desaturase activity.

Metabolic and endocrine changes induced by chronic heatexposure in broiler chickens : biological and endocrinological variables

Abstract:

The present study was designed to investigate the effect of chronic heat exposure (32° constant) on plasma metabolites and hormone concentrations in broiler chickens. At 2 and 4 weeks of age, fifty-four male Shaver broiler chickens were allocated to one of three treatments: 22° ad lib. feeding (22AL), 32°ad lib. feeding (32AL) and 22°,pair-feeding with the 32AL group (22PF). Ambient temperature was kept constant at either 22 or 32° for 2 weeks. Plasma glucose, triacylglycerols, phospholipids, non-esterified fatty acids (NEFA), individual amino acids, uric acid, insulin, triiodothyronine (T3), thyroxine, corticosterone were determined. Sensitivity to exogenous insulin was also measured at 7 weeks of age. At 4 and 6 weeks of age, i.e. after 2 weeks at high ambient temperature, fasted 32AL chickens displayed similar concentrations of glucose and triacylglycerols to those of 22AL birds. When fed, 32AL chickens exhibited higher plasma levels of glucose and decreased concentrations of NEFAand amino acids. Feed restriction resulted in intermediate values. Concentrations of all plasmafree amino acids were decreased under heat exposure except for aspartic acid, glutamic acid andphenylalanine. At 6 weeks of age, plasma T3 was reduced irrespective of the nutritional state, while plasma corticosterone concentrations were increased in 32AL birds compared with 22AL birds. Heat exposure did not change plasma insulin concentration in either fasted or fed chickens. The 32AL chickens displayed significantly reduced sensitivity to exogenous insulin when fasted,but an enhanced response to insulin when fed, compared with both 22° groups. Such endocrinological changes could stimulate lipid accumulation through increased de novo lipogenesis, reduced lipolysis and enhanced amino acid catabolism under chronic heat exposure.

Effect of low-fat colostrum on fat accretion and lipogenic enzyme activities in adipose tissue in the 1-day-old pig

Fat accretion, body fatty acid (FA) composition and adipose tissue lipogenic enzyme activities were determined in 1-day-old piglets fed during the first day of life sow colostrum that was either normal (control) or low in fat and high in lactose, galactose or glucose as the sole source of carbohydrate. Malic enzyme activity did not change during the first postnatal day while increases (P < 0.01) were found for glucose-6-phosphate dehydrogenase and acetyl-CoA-carboxylase. However, fat accretion was closely dependent on the amount of ingested fat and FA composition of piglets indicates a shift toward that of colostrum, the extent of which was dependent on the amount of ingested fat. Plasma glucose and insulin levels were the highest (P < 0.01) in piglets fed the colostrum high in glucose and plasma free fatty acid (FFA) levels were the lowest (P < 0.01) in piglets fed the low-fat, high-carbohydrate colostra. Liver weight and glycogen concentration were higher (P < 0.01) in piglets fed the colostra low in fat and high in carbohydrate than in those on the control colostrum. It is suggested that synthesis of fatty acids from carbohydrate is negligible in the newborn pig even in the presence of high plasma insulin and low plasma FFA levels. The metabolic fate of carbohydrate is discussed.