Thermoregulatory responses of the newborn pig during experimentally induced hypothermia and rewarming

Abstract

SUMMARYExposure to a temperature of 14°C was used to induce a progressive hypothermia in fourteen conscious newborn piglets. Heat production, body (rectal) and skin (between the shoulders) temperatures and shivering intensity assessed as the electromyographic activity (EMG) of longissimus thoracis muscle were measured until body temperature reached 30°C and during a recovery period of 2 h at an ambient temperature of 24°C (n = 7) or 34°C (n = 7). During body cooling, heat production increased up to 9.67 + 1 28 W (kg BW)-1, but started to decrease below a body temperature threshold of 34-4 + 0-7 'C. EMG activity increased (P < 0.023) curvilinearly during body cooling; the main increase occurred between body temperatures of 38 and 33 'C (+142 %, P < 0.001), and changes in EMG activity between 33 and 30°C were not significant (+18%, P > 0 1). A marked increase in circulating levels of glucose (+312 %, P < 0.001), glucagon (+76%, P < 0.05), adrenaline (+172 %, P < 0.05) and noradrenaline (+113 %, P < 0.05) occurred during body cooling. Insulin levels were not detectable at 2 h of life and increased during body cooling. During 2 h of rewarming at 24°C, heat production and EMG activity remained elevated, changes in carbohydrate metabolism were not completely reversed and the final body temperature was only 35-6 + 0-9 'C. Rewarming of the piglets was faster at 34 'C. There was a net influx of heat into the animals and heat production and shivering activity decreased when body temperature reached 33-9 + 0-5 'C; the final body temperature was 37.5 + 0-2 'C. Circulating levels of lactate, glucagon and catecholamines returned to control levels. These results show that in conscious piglets exposed to a constant cold temperature there is an inverse relationship between EMG activity and body temperature during moderate hypothermia and that the thermoregulatory response and carbohydrate metabolism of the piglet are seriously impaired below a body temperature of 34°C.

Effect of radiant heat at the birth site in farrowing crates on hypothermia and behaviour in neonatal piglets

“…The lowest RT was measured 30 min after birth in the present study, corresponding to the time frame found in previous studies with air temperature around 20°C (Malmkvist et al, 2006;Pedersen et al, 2013). RT_0.5 h in CG (34.3°C) was close to the lower limit (~34°C) where thermoregulatory responses and carbohydrate metabolism are seriously impaired (Lossec et al, 1998). Adding radiant heat at the birth place reduced the drop in RT_0.5 h, even though the piglets left the heated zone after 11.4 min on average.…”

“…The extent of the initial drop and the rate of the subsequent rise depend on the external environment (Le Dividich and Noblet, 1981;Malmkvist et al, 2006;Pedersen et al, 2013) and are negatively correlated to the chance of survival of the piglets (Tuchscherer et al, 2000;Baxter et al, 2009;Pedersen et al, 2011). The first critical step to avoid hypothermia is to reduce the initial fall in RT as much as possible (Lossec et al, 1998). The lowest RT was measured 30 min after birth in the present study, corresponding to the time frame found in previous studies with air temperature around 20°C (Malmkvist et al, 2006;Pedersen et al, 2013).…”

Microenvironments in swine farrowing rooms: the thermal, lighting, and acoustic environments of sows and piglets

“…Some degree of relationship between indoor and outdoor temperatures was expected for both rooms. However, low temperature levels such as the average 15.6 °C found at the crate level in Room 1 were not expected and are a dangerous risk for the survivability of piglets, as they are poorly insulated at birth, and thus subject to cold stress (Lossec et al, 1998). Crates with temperatures of 15.6 °C or below were found to be located below attic inlets, which suggests that air from the attic inlets was flowing directly towards the animals, instead of properly mixing with the indoor air first before reaching them.…”

“…Keeping sows and piglets within their thermal comfort zones in conventional farrowing crates is challenging, even in thermally controlled environments, as sows can be heat stressed above 22 °C (Quiniou and Noblet, 1999), whereas piglets feel comfortable within the range of 29.0 °C to 34.0 °C (Johnson and Marchant-Forde, 2009;Lossec et al, 1998;Renaudeau et al, 2003). While heat stressing sows has negative behavioral, physiological and productivity consequences (Quiniou and Noblet, 1999;Renaudeau and Noblet, 2001), piglets commonly experience a 2.0 °C to 4.0 °C drop in body temperature at High relative humidity reduces the efficiency of heat loss through evaporation and adds heat to the air, all of which can contribute to pig heat stress when combined with high ambient temperatures.…”

“…Figure 3A, B, C, and D illustrates the temperature distribution among crates for a representative day of summer and winter. Generally, the crates located in the centre towards the fan end birth and, if not provided with enough heat, excessive hypothermia may lead to reduced vigour, reduced colostrum and milk intake, and eventually death (Lossec et al, 1998). Thus, the sows in this study were likely to be heat stressed for most of the summer, as average daily temperatures reached levels above 28.0 °C in both rooms (Figure 2A and B), as they were at or above 22.0 °C for 100 % of the summer in both rooms ( Figure 2C and D).…”