Piglets' acute responses to local anesthetic injection and surgical castration: Effects of the injection method and interval between injection and castration.

Although applied in some countries, efficacy of local anesthetics based on procaine to mitigate acute responses to piglet castration remains questioned. This paper presents results from a factorial study examining the effects of two methods of injection of a procaine-based drug (intra-funicular, IF, vs. intra-testicular, IT), and four intervals between drug injection and castration (2.5, 5, 10, and 30 min) on acute responses of 3-4 day old piglets. The study involved 597 male piglets, and 13 treatments: surgical castration without anesthesia (CC), local anesthesia followed by castration involving all combinations of injection method and interval, and sham handling separated by the same four intervals (SH). Responses of piglets to drug injection, castration and sham handling were evaluated based on quantification of intra-procedural vocalizations and leg movements, as well as saliva cortisol concentration in samples taken before and after castration. No differences were found between IF and the simpler IT injection method. Intervals of 2.5 or 30 min led to stronger piglet responses than the other intervals. Overall, treatments involving anesthesia led to significantly stronger responses than sham handling, during both injection and castration. All treatments, even sham handling, led to a significant increase in saliva cortisol, with no differences between anesthesia treatments and controls. Based on these results, castration 5-10 min after intra-testicular injection of procaine seems to be preferable as compared to the other treatments tested. However, piglets still showed measurable signs of pain and stress during both injection and castration, while handling alone (including the use of a castration bench) triggered a noticeable stress response. In light of these findings, the overall benefit of the procedure in terms of piglet welfare remains arguable.

Piglets' acute responses to procaine-based local anesthetic injection and surgical castration: Effects of two volumes of anesthetic.

Surgical castration of piglets is painful, but practiced routinely in commercial pig production. Procaine-based local anesthetics are used to mitigate piglet pain during castration in some countries. Yet, effects of the volume of anesthetic injected remain under-studied. The volume of drug administered may modulate the pain mitigating effect via variation in intra-testicular pressure at injection, potentially leading to pain or discomfort, as well as variation in the dose of active ingredient administered. The present study investigated the effects of injection with two volumes of a procaine-based local anesthetic, 0.3 vs. 0.5 mL per testis, on acute responses of 3-4 day old piglets. A total of 290 piglets were divided into 5 treatment groups: castration without anesthesia, castration after intra-testicular injection of 0.5 or 0.3 mL of drug per testis, and sham handling with one or two stays in a castration bench. Acute responses to drug injection, castration and sham handling were evaluated based on quantification of intra-procedural vocalizations and foreleg movements, as well as saliva cortisol concentrations before and after castration. Regardless of the volume, injection of anesthetic as well as castration led to significantly stronger responses than sham handling. Responses to the two drug volumes did not differ significantly, and responses to castration following injection of 0.3 mL did not differ from piglets castrated without anesthesia. All treatments, including sham handling, led to a significant increase in saliva cortisol, and no difference was found between anesthesia treatments and sham handling. Overall, the results suggested that injection of 0.5 mL led to better pain mitigation at castration compared to injection of 0.3 mL, but even when the local anesthetic was used, the combined procedures of injection and castration led to intra-procedural signs of pain and stress.

Exploratory behaviour towards novel objects is associated with enhanced learning in young horses.

The mechanisms underlying individual variation in learning are key to understanding the development of cognitive abilities. In humans and primates, curiosity has been suggested as an important intrinsic factor that enhances learning, whereas in domesticated species research has primarily identified factors with a negative effect on cognitive abilities, such as stress and fearfulness. This study presents the first evidence of a link between object-directed curiosity and learning performance in young horses in two very different learning tasks (visual discrimination and pressure-release). We exposed young horses (n = 44) to standardised novel object tests at 5 months and 1 year of age and found consistency in responses. Standard indicators of fearfulness (e.g. heart rate and alertness) were unrelated to learning performance, whereas exploratory behaviour towards the novel objects correlated to performance in both learning tasks. Exploratory behaviour was unreinforced in the novel object tests and likely reflects the animal's intrinsic motivation (i.e. curiosity), suggesting that this trait is favourable for learning performance. In addition to the insights that these results provide into cognition in a domesticated species, they also raise questions in relation to fostering of curiosity in animals and the impact that such manipulation may have on cognitive abilities.

Maternal temperament modulates curiosity and cortisol responses in farmed mink.

Early life events can shape the development of individual behavior and stress sensitivity. This study explored whether the temperament of the mother modulates curiosity, fear, and Hypothalamic-Pituitary-Adrenal (HPA)-axis hormones in different lines of mink. We designed a study with all combinations of cross-mating between males and females from lines of Confident (C) and Fearful (F) mink. The offspring (N = 600) were cross-fostered by C or F mothers until weaning after 1.8 months. Fearfulness and exploration in three behavioral tests plus plasma ACTH and cortisol were measured in the 6-9 months old offspring. Mink of confident parents (line CC) were consistently more curious, the mixed (CF, FC) showed intermediate reactions, and mink of fearful parents (FF) were the least curious and most fearful in all tests. A higher proportion of the offspring was curious when raised by a C foster mother, regardless of the genetic origin (stick test: 45.1% vs. F foster mother: 34.5%). Cortisol was influenced by line of the biological mother, but not by the sire or by the foster mother; offspring of C dams (CC, CF) had consistently lower cortisol concentration (P < .001) than offspring of F dams (FF, FC) in response to acute stress. In conclusion, besides the selection lines (inheritance from both parents) being a major factor determining curiosity/fearfulness of mink, the confident foster mothers increased offspring curiosity. Additionally, we found maternal effects on the HPA-axis, leading to a higher cortisol response to acute stress in adult mink offspring gestated by fearful mothers. The results add to the existing knowledge on maternal influence on offspring development and are particularly relevant for on-farm welfare where selection for low-fear and explorative dams can decrease offspring fearfulness and stress responses.

Selection for temperament has no negative consequences on important production traits in farmed mink1.

Danish and European legislation recommend mink breeding programs that include selection for "confidence," defined as exploratory activity in a standardized behavioral test. Although this recommendation may improve mink welfare, farmers may consider this criterion risky due to possible negative consequences on other traits. The overall objectives of this study were to estimate the heritability of exploratory/fearful behavior and to identify genetic correlations with other traits of major economic importance in mink fur production. Various aspects of social influence on exploratory/fearful behavior, such as effects of the mother and litter siblings before weaning, the mother's age, and cage mates after weaning, were analyzed. In total, 26,371 1-yr-old Brown mink (Neovison vison) individuals born during the period of 2013 to2016 were included in the study. Exploratory/fearful behavior was the main trait analyzed. The production traits analyzed were live pelt quality and body weight. Both of these traits were assessed during live grading in November. Pelt length and quality were determined using the dried pelts of nonbreeders. Fertility data were obtained from the Fur Farm database. Linear mixed models were run using the restricted maximum-likelihood method. The genetic correlation between female and male behavior was 0.95 (SE = 0.06), indicating similar genetic backgrounds for both sexes (P = 0.40). For both sexes, the estimated heritability of behavior was 0.19 (SE = 0.03). We found no significant genetic correlation between behavior and production/fertility traits (P > 0.05). Common litter variance indicated a preweaning effect of litter mates and/or dam on postweaning temperament. There was a tendency for offspring from older mothers to explore more than offspring from 1-yr-old mothers. This trend was especially pronounced for males of 2-yr-old mothers (P = 0.05) and females of 4-yr-old mothers (P = 0.06). We conclude that confidence may be selected for among farm mink without detrimental effects on economically important production traits, such as pelt quality and fertility.

Development of vocalization and hearing in American mink (Neovison vison).

American mink (Neovison vison) kits are born altricial and fully dependent on maternal care, for which the kits' vocalizations appear essential. We used auditory brainstem responses (ABRs) to determine: (1) hearing sensitivity of adult females from two breeding lines known to differ in maternal behaviour and (2) development of hearing in kits 8-52 days of age. We also studied sound production in 20 kits throughout postnatal days 1 to 44. Adult female mink had a broad hearing range from 1 kHz to above 70 kHz, with peak sensitivity (threshold of 20 dB SPL) at 8-10 kHz, and no difference in sensitivity between the two breeding lines (P>0.22) to explain the difference in maternal care. Mink kits showed no signs of hearing up to postnatal day 24. From day 30, all kits had ABRs indicative of hearing. Hearing sensitivity increased with age, but was still below the adult level at postnatal day 52. When separated from their mothers, kits vocalized loudly. Until the age of 22 days, 90% of all kits vocalized with no significant decline with age (P=0.27). From day 25, concurrent with the start of hearing, the number of vocalizing kits decreased with age (P<0.001), in particular in kits that were re-tested (P=0.004). Large numbers of mink are kept in fur industry farms, and our results are important to the understanding of sound communication, which is part of their natural behaviour. Our results also suggest mink as an interesting model for studying the development of mammalian hearing and its correlation to sound production.

Responses of mink to auditory stimuli: prerequisites for applying the 'cognitive bias' approach.

The aim of the study was to determine and validate prerequisites for applying a cognitive (judgement) bias approach to assessing welfare in farmed mink (Neovison vison). We investigated discrimination ability and associative learning ability using auditory cues. The mink (n=15 females) were divided into two groups (High, n=8; Low, n=7, representing the frequency of the tone they were habituated to, 18 and 2 kHz respectively) and were tested using a habituation-dishabituation procedure in experiment 1. In experiment 2 one auditory stimulus was followed by an inter-trial-interval (safe/neutral situation), whereas another auditory stimulus was followed by an aversive stimulus (air blow) before the inter-trial-interval (danger situation). We observed behaviour including latencies to show a response during both experiments. The High mink showed significant habituation in experiment 1 but the Low mink only showed habituation in experiment 2. Regardless of the frequency used (2 and 18 kHz), cues predicting the danger situation initially elicited slower responses compared to those predicting the safe situation but quickly became faster. Using auditory cues as discrimination stimuli for female farmed mink in a judgement bias approach would thus appear to be feasible. However several specific issues are to be considered in order to successfully adapt a cognitive bias approach to mink, and these are discussed.

Hippocampal neurogenesis increase with stereotypic behavior in mink (Neovison vison).

UNLABELLED: We investigated the hypothesis that performance of abnormal behavior is a stress response concurrent with reduced cell formation in the hippocampal region of the brain, using groups of adult female American mink with high occurrence of stereotypic behavior (STEREO, n=12), high occurrence of fur-chewing behavior (FURCHEW, n=12), or without abnormal behavior (CONTROL, n=12). Following repeated injections of Bromodeoxyuridine (BrdU) as a marker of dividing cells, animals were sacrificed and brain tissue fixated. After brain sectioning and a mink-adapted free-floating BrdU/NeuN doublestaining protocol, we counted the number of cells formed in the subgranular zone (SGZ) and the granular cell layer (GCL) of the dentate gyrus (DG) in the mink hippocampus. RESULTS: (1) proliferation of cells in the SGZ and the GCL of the ventral hippocampal DG was demonstrated for the first time in adult mink, (2) with no significant difference between the experimental groups ( CONTROL: 1509 (191.1); FURCHEW: 1377 (199.8); STEREO: 1968 (288.8); P=0.18), (3) however, with a positive correlation between the amount of stereotypic behavior performed and the number of new hippocampal cells formed (P=0.016). In conclusion, our results do not support that abnormal behavior in mink is concurrent with reduced hippocampal neurogenesis. On the contrary, cell proliferation increased with increasing performance of stereotypic behavior, being of an active/locomotory nature in mink.

Exploration of the hypothalamic-pituitary-adrenal function as a tool to evaluate animal welfare.

Measuring HPA axis activity is the standard approach to the study of stress and welfare in farm animals. Although the reference technique is the use of blood plasma to measure glucocorticoid hormones (cortisol or corticosterone), several alternative methods such as the measurement of corticosteroids in saliva, urine or faeces have been developed to overcome the stress induced by blood sampling itself. In chronic stress situations, as is frequently the case in studies about farm animal welfare, hormonal secretions are usually unchanged but dynamic testing allows the demonstration of functional changes at several levels of the system, including the sensitization of the adrenal cortex to ACTH and the resistance of the axis to feedback inhibition by corticosteroids (dexamethasone suppression test). Beyond these procedural aspects, the main pitfall in the use of HPA axis activity is in the interpretation of experimental data. The large variability of the system has to be taken into consideration, since corticosteroid hormone secretion is usually pulsatile, follows diurnal and seasonal rhythms, is influenced by feed intake and environmental factors such as temperature and humidity, age and physiological state, just to cite the main sources of variation. The corresponding changes reflect the important role of glucocorticoid hormones in a number of basic physiological processes such as energy metabolism and central nervous system functioning. Furthermore, large differences have been found across species, breeds and individuals, which reflect the contribution of genetic factors and environmental influences, especially during development, in HPA axis functioning. Usually, these results will be integrated with data from behavioral observation, production and pathology records in a comprehensive approach of farm animal welfare.

Effect of the serotonin agonist buspirone on behaviour and hypothalamic-pituitary-adrenal axis in confident and fearful mink.

Behavioural and hypothalamic-pituitary-adrenal (HPA) axis responses were investigated in farm mink (Mustela vison) selected for either confident or fearful behaviour for nine generations. Two groups of 2-year-old confident (n=12) and fearful (n=12) female mink were given the serotonin (5-HT) 1A receptor agonist buspirone (1.25 mg/kg/day), whereas two other groups of 2-year-old confident (n=12) and fearful (n=12) female mink were given saline, continuously for 5 weeks via osmotic minipumps. Behavioural reactions towards a novel object and towards humans were tested after 19-25 days, and HPA axis reactivity [adrenocorticotropic hormone (ACTH), cortisol] was measured after 28-31 days of treatment. Confident mink were more exploratory than fearful mink towards humans and a novel object. Confident mink spent more time in contact with the object than did fearful mink during saline-but not during buspirone-treatment. buspirone increased approach-withdrawal conflict behaviour towards a object in fearful mink only. The chronic dose of buspirone did not reduce fear towards humans and did not affect latencies to reaction, number of contacts, number and duration of manipulations, and stereotypic behaviour in a Novel Object test. Different HPA axis responses have emerged between confident and fearful mink, together with a different degree of fear-related behaviour. Fearful mink have a higher cortisol combined with a lower ACTH secretion than confident mink in response to capture and blood sampling. The central serotonergic system may be involved, and even though the precise underlying mechanisms are presently unknown, treatment with a 5-HT(1A) receptor agonist reduces the difference between confident and fearful mink in HPA axis reactivity.