Age-related anesthetic effect of ketamine in the chickens

Article history: Received May 12, 2020 Accepted July 14, 2020 Available online June 23, 2021 Little works of literature studied the anesthetic effect of ketamine in different ages of broiler chickens, hence this study intended to examine these alterations in chickens at different ages. The doses of ketamine that causes hypnosis in 50% of the chickens (hypnotic ED50) were 7.90, 7.90 and 6.80 mg/kg, intramuscular (IM) at 10, 20 and 40-day-old chickens, respectively, whereas the doses that resulted in analgesia in 50% of the chickens (analgesic ED50) were 12.92, 12.92 and 6.50 mg/kg, IM. The onset, duration and recovery from ketamine hypnosis were in an age-dependent manner and significantly longer at 40day-old, although the depth and sensitivity of chickens to ketamine hypnosis rises as the age advancing forward. Ketamine analgesia is more effective at 40-day-old. There are neurobehavioral deficits, according to the age of chickens when injecting ketamine in a subtle dose of 1 mg/kg, IM. The concentrations related to alanine transaminase (ALT) and aspartate transaminase (AST), tested in the serum, reveal that the 40-day-old chicken group differs significantly from 10 and 20-day-old chicken’s groups which all treated with single ketamine dose (25 mg/kg, IM). In conclusion, the present work discovered that ketamine’s efficacy, including hypnosis, analgesia and neurobehavioral activity will be increased as the age is progressing, suggesting that the veterinarians need to take it into account when preparing the dose regimen of ketamine anesthesia for different ages of animals.


Introduction
Ketamine is used broadly for induction of anesthesia in veterinary surgery, offers hypnosis with weak analgesia via blocking N-methyl D-aspartate (NMDA) receptors that located at the nervous tissue, producing a reduce in the calcium ion inflowing inside nervous cells with eventual anesthesia (1,2). Age acts vital role concerning the pharmacological responses to various drugs (like affinity and efficacy) and considered a physiological factor that affect the responses of the body to various drugs, especially the neuroacting agents due to its relation to up and down regulation of the receptor protein and the effect of oxidative stressinducing degenerative disorders of the neurons related to different ages beside its impact on the blood-brain barrier (3,4). Ketamine may interact with different facilitating effects on the release of hippocampal acetylcholine (Ach) neurotransmitter and this is attributed to the aging process which can inhibit the ability to recover from the anesthetic effect (5). Certain functional enhancements in adult mice, for example, with different growth hormone signals, may be due to NMDA receptor improvement are proposed in previous study (4). Insulin like growth factor-1 (IGF-1) and growth hormone (GH) fulfill biological portion to age-related vascular density and propose that vascular thickness may have significant changes of concerns for age in blood flow of the cerebrum and brain function (6), specifies a possible important role in the age related reverse of rodent's behavior for IGF-1 (7). The detached aim was to investigate the ketamine anesthetic efficacy and its correlation with different ages of broiler chickens to address the effect of age on ketamine narcosis and its neurobehavioral changes.

Chickens and drug preparation
Broiler chickens (both genders) of ages 10, 20 and 40days were included in this study with mean body weight between 0.15-1.7 kg. They held in pens of 30-34ºC temperatures with incessant light, and the ground litter involved of wood shreds. Chickens had allowed admission to water and food. The ketamine (5% Hameln pharmaceuticals, Germany) was equipped at 5 ml/kg to be given IM.

Animal ethics
The scientific committee of the College of Veterinary Medicine at University of Mosul has valid and authenticate this study for the application of experimental chicken and for ethical concerns.

Ketamine's hypnotic ED50 in chickens at different ages
The hypnotic ED50 dose of ketamine was valued according to up and down pattern at different ages 10, 20 and 40-days-old (8). The first dose of ketamine injected was 12 mg/kg, IM hanged on pilot study. Chickens were watched alone along with 2 h following ketamine administration (to check for righting reflex loss which indicates the hypnotic effect) and then, the ketamine's dosages reduced or raised 3 mg which hangs on for appearance or absence of the hypnosis.

Measurement the analgesic ED50 for ketamine in chickens at different ages
The ED50 value of ketamine that causes analgesia in 50% of the chickens was measured according to the above method defined in the first trial at different ages 10, 20 and 40-daysold (8). Ketamine's analgesia recorded via an electro stimulator apparatus (scientific research, UK) for induction of ache sensation in chickens (9)(10)(11)(12)(13)(14)(15)(16)(17). The ketamine's first IM dose injected at 12 mg/kg by elevates or reduces 3 mg/kg of the dosage. In this experiment, the pain in the chickens (categorized by distress call) was recorded as a voltage for each one individually before and after 10 minutes of ketamine injection (9,10,17). Ketamine has seen to result in an anti-nociceptive effect when the recorded voltage after injection was raised in relative to voltage measured prior ketamine injection (The chicken will be assigned as X), and if there is no analgesia, the chicken will be marked as O. Then the table value was extracted from Dixon's table (8) to determine the ED50 dose of ketamine.

Effect of single anesthetic dose of ketamine hypnosis at different ages of chickens
The hypnotic effects of ketamine (losing the righting reflex) were monitored in three age-groups of chickens 10, 20 and 40-day-old chickens, that treated with single IM dose of ketamine at 25 mg/kg. The dose of ketamine was adopted from the its values related to hypnotic and analgesic ED50s. Each individual chicken was observed to register the hypnosis in addition to the duration and the recovery from hypnosis in all ages groups (18,19).

Effect of single anesthetic dose of ketamine analgesia at different ages of chickens
The difference in the analgesic effect of ketamine was determined throughout all studied ages of chickens by applying one IM dose of ketamine at 25 mg/kg in response to the analgesic ED50 dose of ketamine. Voltage of the electro-stimulator device that produce nociception registered prior and post ten min related to ketamine administration for every chicken independently. The delta voltages for each group were also considered for estimation (9).

Assessment of subtle neurobehavioral effects induced by ketamine in different ages of broilers chickens
Different measurements of open-field were used to investigate the neurobehavioral changes of ketamine in different ages 10, 20 and 40 days (20,21). Activity in the open field for chicken watched thirty min post IM ketamine treating at 1 mg/kg and this dose did not produce any apparent effect so that, the subtle effect determined resembling the neurobehavioral deficits (22). Each chicken was individually placed in middle of the arena with 50 grams of grains spread at the surface. The listed below behavioral parameters estimated after thirty min of ketamine injection within 5-minute period as designated earlier (21,22). The open-field parameters included moving latency in seconds; sum of escapes jumps; frequency of defecations; distress calls scores and pecking behavior scores. After this test, every chicken undergoing test of tonic immobility (20,22) through picking the chicken by two hands and setting it 15 seconds on a table. The hands will withdraw and then, the standing-up of chicken itself unassisted were registered.

Measurement of serum ALT and AST concentrations in the chickens treated with ketamine at the ages of 10, 20 and 40-days-old
Following 2 hours of IM injection of ketamine at 25 mg/kg, the blood was gained from the vein of each chicken at different studied ages, then the blood collected in gel tubes and undergoing centrifugation to alleviate of serum that freeze awaiting analysis during 48 hours. Serum ALT (23) and AST (24) concentrations were determined by using Chemistry Analyzer Smart-150 apparatus (GenoTEK, USA).

Statistics
Parametric statistical analysis was directed by variance analysis of one way (ANOVA) tracked by the LSD (25,26). The data of non-parametric origin undergoes analysis by the Fisher exact probability and Mann-Whitney U tests (26,27). The probability (p) of the results was considered significantly differs at less than 5%.

Ketamine's hypnotic ED50 in chickens at ages of 10, 20 and 40-days-old
The doses of ketamine that cause hypnosis in 50% of the chickens were 7.90, 7.90 and 6.80 mg/kg, IM at 10, 20 and 40-day-old respectively, and the fastest onset of hypnosis was at age 40-day-old as shown in table 1. Table 2 shows the doses of ketamine that caused analgesia in 50% of the chickens were 12.92, 12.92 and 6.50 mg/kg, IM at 10, 20 and 40 days-old chickens correspondingly. As reported increase in ketamine efficacy that causes analgesia at age 40-day-old chicken in comparison to younger ages.

Single dose of ketamine and its effect on hypnosis at different ages of chickens
The onset, duration and recovery from ketamine hypnosis were 2.17, 22.50 and 29.83 minutes respectively at 10-dayold of chickens. The same measurements were 3.50, 25.00 and 69.67 minutes respectively at 20-day-old, while the onset, duration and recovery from ketamine hypnosis were 2.83, 46.17 and 96.67 minutes respectively at 40-day-old. Table 3 reflects that the results of ketamine hypnosis were in an age dependent manner and the shorter onset with significantly longer duration and recovery of hypnosis were at 40-day-old, although the depth and sensitivity of chickens to ketamine hypnosis increases as the age is progress.

Ketamine's single dose and its analgesic effect at different ages of chickens
The 10-day-old chickens displays that the volts recorded (prior, and post 10 minutes of ketamine treatment) was significantly different (9.17 and 13.83 volts respectively). The same measurements were 10.67 and 15.17 volts respectively at 20-day-old chickens whereas these volts were 15.00 and 23.00volts respectively at 40-day-old. The results indicate the analgesic effect of ketamine is greater and more effective at 40-day-old chickens as shown in table 4.

Assessment of subtle neurobehavioral effects induced by ketamine in different ages of chickens
The IM administration of ketamine at 1 mg/kg causes many (non-significant) neurobehavioural changes at different ages, especially in relation to frequency of defecation and escape jump except the latency to move and tonic immobility response test (which are significant at 40days-old). All these changes refer to increase in the subtle depressant effect of ketamine as the age progressing forward (table 5).

Serum ALT and AST in the different ages of chickens treated with ketamine
The serum concentrations of ALT and AST were found close to normal ranges of chickens. The serum ALT and AST in 40-day-old group significantly different (at P<5%) from 10 and 20-days-old groups after treatment with 25 mg/kg, IM ketamine as shown in table 6.    The values represented as Average±Std. Error for 6 chickens/group. Pain sensation was measured by electrostimulator pre-and post-10 minutes of treating of ketamine (25 mg/kg, IM) for all the groups. * Differs significantly from 10 days-old (P<5%). a Differs significantly from 20 days-old (P<5%). + Differs significantly from the same group (volts pre-injection) (P<5%). The values represented as Average±Std. Error for 6 chickens/group. The Test was conducted after 30 minutes of ketamine injection at a subtle dose (1 mg/kg , IM). * Differs significantly from 10 days-old (P<5%). a Differs significantly from 20 daysold (P<5%).

Discussion
Ketamine considered a widely usage drug for anesthetic induction of surgical operations of the veterinary medicine field and produces good hypnotic with weak analgesia by its blocking effect of NMDA receptor in the nervous tissue, leading to an inhibition of the calcium current inflowing the neuronal cells causes induction the anesthesia (1,2). Ketamine used with xylazine in chickens and considered appropriate anesthesia for pain killing procedures in pigeons (28). However, it is preferable to combine ketamine with diazepam as this combination is moderately safer (29). The hypnotic and analgesic ED50s of ketamine measured in this trial at different ages of chicken were in close to prior study in the same field (11,30). In current work, the hypnotic besides analgesic ketamine's effects were enhanced in the efficacy as the ages of the chicken progress and this could be attributed to the effect of ketamine on the release of Ach neurotransmitter from the hippocampus as reported previously in older rats compared to the youngers (5). Another reason might be attributed to a regional and specific alteration of NMDA receptor with age and because IGF-1 modulates the NMDA receptor expression suggesting a changes in the heterogeneity of NMDA receptors can lead to modification of functional receptors which are relevant to aging process (3) such as the occurrence of receptor upregulation. Some of the functional enhancements in older chickens, for example, with different growth hormone signals, may be due to NMDA receptor improvement that found in mouse model (4). Growth hormone and IGF-1 work a vital role in age-related vessels density and propose that reductions in vascular thickness may have significant concerns for age-related involvement related to cerebral blood flow and brain function (6), which possibly have an important role in the opposite of age dependent behavioral deficits in chickens for IGF-1 as found in rodents (7). Other factors and age have a significant effect on the ketamine's availability, reflected in modification of the pharmacokinetics criteria, metabolism of liver of the drug and its pharmacodynamics (31). Intraperitoneal ketamine injections for both sex revealed a significant relationship between increased age and the duration of hypnosis and this alteration in hypnosis appeared to be associated with changes in production of ketamine cyclohexanone oxidation metabolites (32) and the age-related effects of NMDA may be related to impaired release of glycine (33). Some behavioral changes explored in this study were associated with ketamine anesthesia that recorded in other study (34). Ketamine administration showed differential neurobehavioral effects on activity levels of chickens depending on the animal's age which is correspondence with another study in rats (35). The serum concentrations of ALT and AST were found close to normal ranges of chickens (36) which indicate the effect of ketamine on the liver function at different ages, and the 40-day-old chickens group differs significantly from 10 and 20-days-old chickens (that all treated with one ketamine's dosage 25 mg/kg, IM) suggesting alteration in metabolism, and a possible pharmacokinetics, of ketamine during that ages of chickens.

Conclusion
The present work discovered that ketamine's efficacy, including hypnosis, analgesia and neurobehavioral activity will be increased as the age is progressing forward, suggesting that the veterinarians need to take it into account when preparing the dose regimen of ketamine anesthesia for different ages of animals.