Patrick Herpin

Development of thermoregulation and neonatal survival in pigs

Neonatal mortality is still a source of serious loss to the swine industry. We know that optimal development of thermoregulation is a prerequisite of utmost importance for successful adaptation to extra-uterine life. Indeed, a comprehensive knowledge of piglet thermoregulation is now available and may be helpful to increase our understanding of the biology of neonatal losses. The newborn pig is poorly insulated and maintenance of its homeothermic balance depends essentially on its capacity to produce heat. However, unlike most newborn mammals, piglets do not possess brown adipose tissue and rely almost exclusively on shivering thermogenesis for thermoregulatory purposes. Therefore, skeletal muscle plays an essential role in preserving homeothermy. Key factors involved in the limited cold tolerance of the new-born and enhancement of thermoregulatory abilities early after birth have been identified. Most of them, and especially the maturation of skeletal muscle metabolism and function are suggestive of the relative physiological and metabolic immaturity of piglets at the time of birth. Therefore, physiological, biochemical, molecular and ultrastructural adjustments involved in the maturation of skeletal muscle energy metabolism after birth are presented. Finally, effects of key factors such as birth weight, genotype, colostrum intake, hypothermia and hypoxia on thermoregulatory abilities are described.

Nutritional and hormonal regulation of energy metabolism in skeletal muscles of meat-producing animals

In meat-producing animals, skeletal muscle is a tissue of major economic importance. Energy metabolism of skeletal muscle should be assessed in relation to its main physiological functions which are growth as well as posture, physical activity and thermogenesis. These functions have specific energy requirements which may entail competition in the utilization of energy-yielding nutrients, and modify the efficiency of ATP production and use. In this review, the energy requirements of muscles will be presented as well as the main metabolic pathways involved in the utilization of carbohydrate and lipids for energy supply and deposition. Regulation of metabolism will also be tackled in relation to the major physiological functions of skeletal muscle in various domestic species. Special focus will be given to the energy metabolism of growing muscle and its interactions with meat quality. The question will be asked whether the optimization of the efficiency of ATP production and utilization in muscle for nitrogen retention is compatible with an improvement of meat quality (as partly determined by glycogen and lipid deposition)? For this purpose, the interactions between muscle carbohydrate, lipid and protein metabolism will be reviewed.

Nutritional and immunological importance of colostrum for the new-born pig

The nutritional and immunological importance of colostrum for the survival and development of the neonatal pig are reviewed. The pig is born with low body energy stores and devoid of serum immunoglobulins. Colostrum provides the piglet with both energy and maternal antibodies but its fat and protein composition is very variable. Colostrum is very digestible, and both colostral energy and nitrogen (N) are retained with a very high efficiency. Colostrum production by the sow assessed from the weight gain of the litter from birth to 24 h of age is very variable (from 1900 to 5300 g). There is no clear effect of litter size or parity, suggesting that colostrum production is a characteristic of the sow. Within a litter, colostrum consumption by the individual piglets varies considerably. It is independent of birth order, but related positively to birth weight and negatively to litter size. Other factors influencing colostrum consumption, including cold stress, premature birth and birth hypoxia, are discussed. Because of the epitheliochorial nature of the porcine placenta, the new-born piglet must acquire maternal immunoglobulin G (IgG) from ingested colostrum for passive immune protection until the immune system of the piglet becomes fully developed. Colostrum IgG concentrations in milk vary widely between individual sows both in initial concentration and in the rate at which concentrations decline during the first 24 h of life. The piglet can only absorb intact IgG prior to gut closure, which occurs in the first 24 h of life and is induced by intakes of colostrum which are insufficient to maintain piglet live-weight. As a result, the amounts of intact IgG absorbed by the piglet vary widely. The effects of colostrum consumption on neonatal survival are discussed. Consumption of colostrum in amounts sufficient to meet the energy requirement of the piglet is a major determinant for survival. Since most neonatal losses occur in the first 2 days of life, before acquisition of a maternal IgG for immune protection becomes important for survival, piglet serum IgG concentration does not correlate well with early survival but is important in later resistance to disease challenge. It is concluded that colostrum production is a good marker for the maternal quality of the sow. Future research should focus on the ability of the sow to produce more colostrum and on the possible delayed effects of passive immunisation on the health and performance of piglet at weaning and later in life.

Effect of oxygen inhalation at birth on the reduction of early postnatal mortality in pigs

Asphyxia during delivery is considered a main cause of stillbirth in pigs, but piglets suffering from intermittent asphyxia during delivery are also less viable at birth and less prone to adapt to extrauterine life. In an effort to improve pig viability, one attractive solution would be to increase oxygen supply through oxygen inhalation by the newborn pig. The objective of this study was to test effects of oxygen inhalation immediately after birth on various physiological parameters and piglet survival. The experiment was performed on 252 Piétrain x Large White piglets, half of them reoxygenated immediately after birth. They were maintained during 20 min in a chamber where oxygen concentration was monitored at 40% and were then put back with the sow and the control pigs. Oxygen inhalation affected piglet metabolism. Through stimulation of oxidative metabolism (reduction of circulating levels of lactate) and lowering of the level of postnatal hypothermia (particularly for the lightest pigs), oxygen inhalation increased piglet viability and reduced mortality during the 1st d of life by 75% (2 vs 8%). No additional effects were observed during the following days and overall mortality between birth and weaning at 21 d was reduced from 12 to 8%.

Effects of climatic conditions on the performance, metabolism and health status of weaned piglets: a review

Abstract This review discusses current information on the effects of climatic conditions on performance, metabolism and health status of weaned piglets raised in intensive conditions, and on the acclimation mechanisms of the piglets to cold environment. Ambient temperature is the predominant component of the climatic environment, and since weaning is associated with rapid changes in food intake, requirements for ambient temperature are examined in relation to food intake. The critical period immediately postweaning, corresponding to the time required to attain the preweaning level of food intake, is characterized by a loss of body fat and a decrease in thermal insulation. During this period current recommendations are for constant temperature of 26–28°C for piglets penned on perforated floors. During the postcritical period, i.e., once regular food intake is established, the ambient temperature can be reduced by 2–3°C per week until the temperature to be maintained in the finishing house is reached. Ways of reducing the heating cost, including provision of a microenvironment, reduction of the nocturnal temperature and of overall temperature are discussed. Effects of other thermal components including, air movement, relative humidity and type of floor are assessed by their effects on the lower critical temperature, performance and behaviour. Mechanisms of acclimation to cold environment are presented in terms of behavioural, physiological and metabolic adjustments. There is evidence that the increase in heat production in cold is associated with an increase in the turnover of both FFA and glucose and involves changes in thyroid hormones and catecholamines. Finally, diarrhoea is the most common clinical problem encountered in the first weeks after weaning. Data suggest a complex effect of weaning, level of food intake and non optimal climatic conditions on the health status of the weaned piglet.

Shivering thermogenesis in the neonatal pig

Abstract (I) Shivering intensity and metabolic rate were determined in Large White pigs aged 2, 24, 48 h and 5 d, at temperatures ranging from thermoneutrality (36°C) to cold (20°C). (2) Shivering is the main heat producing mechanism, the absence of nonshivering thermogenesis being implied by both the absence of delay between the onset of shivering (Stt) and the increase in metabolic rate (Lct) and by the linearity of the relationship between metabolic rate and shivering intensity in the cold. (3) For a comparable thermal demand, shivering intensity decreased with age whereas cold induced heat production remained constant, which suggests that the thermogenic efficiency of shivering is improved during the first 5 days of life.

Characterisation of oxidative phosphorylation in skeletal muscle mitochondria subpopulations in pig: a study using top-down elasticity analysis

In skeletal muscle, two mitochondrial populations are present which, on the basis of their localisation, are termed intermyofibrillar and subsarcolemmal mitochondria (IMF and SS, respectively). These two populations have different biochemical characteristics and show different responses to physiological stimuli. In this paper, we characterise the oxidative phosphorylation of SS and IMF using ‘top‐down’ elasticity analysis. We excluded the possibility that their different characteristics can be attributed to a different degree of breakage of the two types of mitochondria due to the different isolation procedures used in their preparation. The higher respiration rate and higher respiratory control ratio shown by IMF compared with those shown by SS are principally due to the higher activities of the reactions involved in substrate oxidation as confirmed by the measurement of cytochrome oxidase activity. There is no difference in the leak of protons across the inner mitochondrial membrane between IMF and SS; a faster rate of ATP synthesis and turnover is driven by the lower membrane potential in SS compared with in IMF.

First evidence of uncoupling protein-2 (UCP-2) and -3 (UCP-3) gene expression in piglet skeletal muscle and adipose tissue.

Uncoupling proteins (UCPs) facilitate proton transport inside the mitochondria and decrease the proton gradient, leading to heat production. Until now, the presence of UCP1 or other UCP homologs had not been detected in tissues of pig, a species where evidence for the presence of brown adipose tissue has only been provided in 2-3 month old animals. In the light of the improving knowledge on the UCPs family, we decided to examine both UCP2 and UCP3 mRNA expression in piglet skeletal muscle and adipose tissue. Using RT-PCR we have successfully cloned a partial UCP2 sequence and a complete UCP3 cDNA. UCP3s open reading frame (936bp) shares 90, 89 and 85% similarity with bovine, human and rat UCP3 nucleotide sequences, respectively. In 3-5 day old piglets, these genes are expressed in adipose tissue and in both longissimus thoracis (LT) and rhomboïdeus (RH) muscles, without any effect of muscle metabolic type. This is in good agreement with the measurement of the same membrane potential in mitochondria isolated from both types of muscles. In triiodothyronine-treated piglets, UCP3 mRNA is more expressed in LT than in RH muscle. These genes may be involved in the control of the energy metabolism of the piglet.

Estimation of genetic trends from 1977 to 1998 of body composition and physiological state of Large White pigs at birth

Genetic trends for body composition and blood plasma parameters of newborn piglets were estimated through the comparison of two groups of pigs (G77 and G98, respectively) produced by inseminating Large White (LW) sows with semen from LW boars born either in 1977 or in 1998. Random samples of 18 G77 and 19 G98 newborn piglets were used for whole carcass and tissue sampling. Plasma concentrations of glucose, albumin and IGF-1 were determined on 75 G77 and 90 G98 piglets from 18 litters. The G98 piglets had less carcass dry matter, protein and energy (P < 0.01) than their G77 counterparts. When expressed in g/kg birth weight, livers were lighter (P < 0.001) and contained less glycogen (P < 0.01) in G98 piglets, with no difference in the activity of the hepatic glucose-6-phosphatase between G98 and G77 piglets. Concentrations of protein, DNA, RNA in longissimus dorsi muscle were unaffected by selection. Plasma concentrations of glucose (P < 0.05) and IGF-1 (P < 0.01) were lower in G98 than in G77 piglets. On the whole, the results suggest that the improvement in lean growth rate and in sow prolificacy from 1977 to 1998 has resulted in a lower maturity of piglets at birth.

Assessment of thermoregulatory and postprandial thermogenesis over the first 24 hours after birth in pigs

Heat production was continuously measured from birth to 24 h after birth in pigs tube‐fed 14 g kg‐1 of colostrum or water (sham‐fed animals) at hourly intervals, and maintained at thermoneutrality (34 degrees C) or in moderate cold (24 degrees C). Results indicate that colostrum was necessary to initiate and sustain the postnatal rise in metabolic rate observed at 34 degrees C. It provided about 75% of the energy required for heat production at 24 degrees C. Heat production was increased by 74% in the cold and decreased by 30% during starvation. In both cases, maintenance of the energy balance was achieved with a compensatory drop in body temperature. At 34 degrees C, variations in postmeal heat production represented 12% of the total 24 h energy expenditure and were almost equally due to the thermogenic effect of colostrum and to confounding factors, including physical activity. In the cold, calculated postmeal thermogenesis accounted only for 3% of 24 h energy expenditure and for 9% of the extra heat produced in the cold. Our results highlight the main role of colostral energy in the energy metabolism of the newborn pig in a typical birth environment (24 degrees C) and in thermoneutral conditions (34 degrees C). Thermoneutral postmeal thermogenesis is low and its contribution to the extra heat produced in the cold very limited.