Schouten W G, Wiegant V M
Department of Animal Husbandry, Wageningen Agricultural University, The Netherlands.
Acta Physiol Scand Suppl. 1997;640:88-91.
Pigs can be characterised as resistant (R) or non-resistant (NR) at an early age (1 to 2 weeks) by means of a backtest. In the test the animal is put on its back and the number of bouts of resistance is used to characterise the animal. The test is performed twice with 1 week interval and only pigs that show a consistent response in both tests are classified as either R or NR pigs. On average eighty percent of a population can be classified by this test. R and NR pigs show consistent behavioural, physiological and immunological differences when tested in various challenge test in later life. The R pigs are more sympathetically dominated and showing an active coping style (fight/flight) as described in rats and mice. The NR pigs are more para-sympathetically dominated, resembling the passive coping style (conservation/withdrawal). In intensive husbandry, breeding sows are housed individually and often tethered. After long term tethering these sows show signs of chronic stress; overreaction of the sympathetic nervous system, hypercortisolaemia and disturbed behaviour. The most common disturbed behaviour found in tethered sows is stereotyped behaviour. Most sows develop stereotypies within 1 month after first tethering. Again great differences are found in the amount of stereotypies shown between sows. Some sows spent up to 80% of their active time on this behaviour while others hardly develop stereotypies. Sows showing high levels of stereotypies manage to counteract the sympathetic overreaction caused by the chronic stress of tethering as was shown by a decrease in heart rate during bouts of stereotyped behaviour. In this view stereotypies help the animal to cope with the averse situation of tethering. However, after 8 months of tethering stereotypies are no longer effectively attenuating heart rate. The effect of stereotypies is limited to the initial phase of chronic stress when the animal is striving to regain control. When chronic stress persists stereotypies get dissociated from their effect on the sympatho-adreno-medullary system and the animal loses control.
通过背部测试，猪在幼年（1至2周龄）时可被分为抗性（R）或非抗性（NR）。在测试中，将动物仰卧，通过其抵抗发作的次数来对动物进行分类。测试间隔1周进行两次，只有在两次测试中表现出一致反应的猪才被归类为R或NR猪。平均而言，该测试可对80%的猪群进行分类。R猪和NR猪在后期的各种挑战测试中表现出一致的行为、生理和免疫差异。R猪更受交感神经支配，表现出如大鼠和小鼠中所描述的积极应对方式（战斗/逃跑）。NR猪则更受副交感神经支配，类似于被动应对方式（保守/退缩）。在集约化养殖中，繁殖母猪单独饲养且常被拴系。长期拴系后，这些母猪会出现慢性应激的迹象；交感神经系统过度反应、高皮质醇血症和行为紊乱。在拴系母猪中发现的最常见的行为紊乱是刻板行为。大多数母猪在首次拴系后1个月内就会出现刻板行为。同样，在母猪表现出的刻板行为数量上也存在很大差异。一些母猪在其活跃时间的80%都表现出这种行为，而另一些母猪则几乎不出现刻板行为。表现出高水平刻板行为的母猪能够抵消因拴系的慢性应激引起的交感神经过度反应，这在刻板行为发作期间心率下降中得到体现。从这个角度来看，刻板行为有助于动物应对拴系的不利情况。然而，拴系8个月后，刻板行为不再能有效降低心率。刻板行为的作用仅限于慢性应激的初始阶段，即动物努力重新获得控制时。当慢性应激持续时，刻板行为与其对交感-肾上腺髓质系统的影响脱节，动物失去控制。
