This study revealed that the addition of Xylazine to Lignocaine does not bring significant change in the onset of analgesia even if xylazine delays the onset. A similar study in ruminant (goat) and camel in Oregon state university indicate no significant change in the onset of Lignocaine and Lignocaine –Xylazine [10] in large ruminants; a caudal epidural block is a commonly used block. However, under this block, in many instances, the motor fibers of the hind limb are completely or partially blocked by the drugs used. In the present investigation, the caudal epidural route was used to achieve analgesia of the hind part. Xylazine, on the other hand, is known to produce a delayed onset of action in comparison with lignocaine (Kumar and Thurmon, 2003). The combination produced complete analgesia of the hind leg, tail, and inguinal region after the injection of drugs. It has been observed that the distribution of the anesthetic solution in the cerebrospinal fluid determines the uptake of anesthetics [10]. Furthermore, uptake found to be the greatest where the concentration of the solution was greater (i.e. at the site of injection) and decreased above and below the site of highest concentration.
This study showed that a combination of Xylazine (an alpha-2 adrenergic against) and Lignocaine (a local anesthetic agent) was additive for the duration of analgesia. Followed administration of the drug epidurally to cattle, prolonged duration of epidural anesthesia observed and a similar study was reported in horse and dogs [11], [12], [13]. However, the mechanism of prolonged duration is unknown. Some researchers said that alpha-2 adrenergic agonists may produce vasoconstriction or inhibit local anesthetic agents that induced vasodilatation and subsquientelly decrease vascular uptake of anesthetic agents [14]. Alternatively, the additive effect could be related to the fact that the provision of analgesia, by administering either alpha-2 adrenergic agonists or opioids, will intensify and prolong local and regional blockage provided by the local anesthetic agent [12]. This study also similar to the study of the effect of Lignocaine, Xylazine, and Lignocaine-Xylazine in cows in India [15]. The study in goats confirmed that an additive interaction between xylazine and lignocaine would produce Longer duration and greater depth of analgesia (Kumar and Thurmon, 2003).
The difference in Decrease Rectal temperature between both groups is not significant and this study contradicts with a significant change in rectal temperature in Lignocaine (0.3 ± 0.25), Xylazine (0.9 ± 0.42), and Lignocaine-Xylazine (0.66 ± 0.32) in cows between three groups each group having four cows in India [15]. In this study, the absence of significant difference in rectal temperature may be due local environmental factor that was Lignocaine was injected in the morning in which the sunlight is not as much hoot. Lignocaine-Xylazine was injected at midday after all cow feed grass and drink water so that the metabolism very increased during this time and the temperature decrease only slightly in group-II. A general decrease in temperature in both groups probably was due to reduced basal metabolic rate, reduced muscle activity, and depression of thermoregulatory centers. The alpha2-agonists also found to depress the hypothalamic nor-adrenergic alpha2-receptors to cause hypothermia. The present study shows that a decrease in rectal temperature observed following administration of Lignocaine in cattle was believed to be due to heat loss from the relaxation of thoracic and abdominal skeletal muscles and a combination of Lignocaine with Xylazine don't have an additive effect in decreasing the rectal temperature.
Respiration rate (RR) decreased in groups-II was severs as compared to group-I and this result is similar to study in ruminant (goat) and camel in Oregon state university [10]. Moreover, the South Africa veterinary association research center [16]. A decrease in RR may be due to direct depression of the respiratory centers by Xylazine [17]. These indicate an additive depressant effect of both classes of drugs on the respiratory function and confirmed the earlier findings. A slight respiratory depression by lignocaine alone in the present study probably may be due to the blockade of nerves innervating the muscles of respiration.
In group-two significant decrease was observed in heart rate as compared to group-one. A similar in Oregon state university indicated that a significant difference in heart rate was obserbed between Lignocaine and Lignocaine-xylazine [10]. This decrease can be explained by several mechanisms, which include decreased sympathetic outflow during Xylazine from CNS, inhibition of noradrenaline release from sympathetic nerve terminals, direct depression of cardiac pacemaker and conduction tissue, increased vagal tone and a direct increase in the release of acetylcholine from parasympathetic nerves in the heart. However, the mechanism of decreased heart rate not examined in this study.
Mild ataxia was observed in some of the group-I cows which may be due to local anesthetic agents block both sensory and motor fiber [8]. Moderate to severe ataxia noted in group-II cows may be due to xylazine postulated local anesthetic properties at the spinal cord level. Through venous sinuses, Blockade of motor fibers might be the reason for extreme ataxia initially; however, as the effect of lignocaine was off the animal’s regained normal gait. It may be also due to structural similarity with lignocaine or because of its systemic uptake. No sedation observed on group-I cows at all, but medium to severe sedation observed in group-II cows. The sedation produced in this group may be the manifestation of the central effects of alpha2-agonist xylazine probably after its absorption from the epidural space. There was no salivation and falling noted in group-I cows due to lignocaine does not reach the central-nervous-system only block the fast voltage-gated Na+ channels in the neuronal cell membrane responsible for signal propagation and don’t have the ability to affect cerebellum as well as to induce salivation. Oppositely, Xylazine can defuse directly to the cerebellum it affects the balance system of the animal and thereby cause falling, and stimulate salivation by binding to the receptor site of saliva stimulator on the brain [18].