Jan Ladewig

Effects of individual versus group stabling on social behaviour in domestic stallions

Domestic horses (Equus caballus) are typically kept in individual housing systems, in which they are deprived of physical contact. In order to study the effects of social restrictions on behaviour in young horses, nineteen 2-year-old stallions were housed either singly (n=7), or in groups of three (n=12) for 9 months. Subsequently, the stallions were released into two separate 2 ha enclosures according to treatment, and recordings were made on social interactions and nearest neighbours during a 6-week-period, 28 h per week. Previously group stabled stallions frequently had a former group mate as their nearest neighbour (P=0.001), whereas previously singly stabled stallions did not associate more with their former box neighbours, to whom physical contact was limited by bars during the previous treatment. The nearest neighbour was more frequently recorded to be within one horselength of singly stabled than of group stabled stallions (P=0.005). More aggressive behaviour was recorded in the group of previously singly stabled stallions, i.e. bite threats (P=0.032), whereas group stabled stallions tended to make more use of subtle agonistic interactions (displacements, submissive behaviour). Singly stabled stallions also responded to the 9 months of social deprivation by significantly increasing the level of social grooming (P<0.001) and play behaviour (P<0.001), when subsequently interacting freely with other horses. The increased occurrence may relate to a build-up of motivation (a rebound effect), as well as to external factors, such as playful pasture companions and the increased space allowance of the pasture. It is concluded that 2-year-old domestic stallions are sensitive to social deprivation and that stabling has long-term effects, lasting 6 weeks at least, on the social behaviour in stallions.

Effects of acute stressors on nociception, adrenocortical responses and behavior of dairy cows.

Effects of acute stressors on behavioral, adrenocortical and nociceptive responses were examined in 24 dairy cows kept in tie stalls, using 15 min of social isolation in novel surroundings (ISOL), fixation by the head in the home stall (FIX) and the provision of novel neighbors/stall (NEIGH) as acute stressors as well as a control treatment (CON). Each cow was exposed to one treatment daily in a balanced order. All stressors led to signs of hypoalgesia as indicated by slower (P=0.01) and reduced responses (P<0.10) toward nociceptive laser stimulation after exposure to the acute stressors. ISOL, however, had stronger effects than FIX or NEIGH. ISOL or FIX led to increased plasma concentration of cortisol (P<0.001), whereas NEIGH or CON did not. The behavioral responses were affected by treatments as well, as shown by decreased rumination for all stressors (P<0.001) and a gradual increase in active avoidance from CON to NEIGH to FIX (P<0.001). Furthermore, exposure to NEIGH led to increased exploration (P<0.001), aggression (P<0.10) and self-grooming behavior (P<0.10) compared with the CON treatment. The results suggest that nociceptive changes are part of responses toward acute stress in dairy cows. The nociceptive changes, however, were not direct reflections of the adrenocortical or behavioral responses toward the acute stressors. Therefore, quantification of nociceptive changes, in combination with behavioral and physiological registrations, can be one way to broaden the range of biological systems, considered for the study of animals under stress, and thereby extend the understanding of responses toward acute stress in dairy cows.

Altered adrenocortical response to acute stressors or ACTH(1–24) in intensively housed pigs

In two experiments, the effect of intensive housing on behavior and adrenocortical reactivity was studied in 68 castrated male German Landrace pigs. In both experiments, half of the pigs were tethered on a partially slatted floor without straw and half were kept, as controls, in groups on straw. Prior to the study, 32 of the pigs used in the first experiment were selected according to their reaction to halothane anesthesia; for the second experiment, 36 pigs were selected according to their adrenocortical response to azaperone-metomidate anesthesia. During the 4- to 6-wk experimental period, behavioral activity was observed and adrenocortical reactivity was analyzed after stimulation with synthetic ACTH(1-24), azaperone-metomidate anesthesia, insulin-induced hypoglycemia and neostigmine-atropine. Although no difference was found in general activity between groups, tethered pigs revealed a significantly higher cortisol increase after stimulation with ACTH(1-24) in both experiments and after insulin stimulation in the second experiment. Similarly, the area below the cortisol response curve after ACTH stimulation was significantly larger in tethered pigs in the second experiment. The individual reaction pattern was positively correlated between tests, indicating this pattern is a relatively constant, individual characteristic. In contrast, no correlation was found between behavior or adrenocortical reaction pattern and sensitivity to halothane. The results suggest that tethering on a partially slatted floor constitutes a chronic stressor which changes the adrenocortical response to an additional acute stressor. This increased reactivity is revealed most clearly after stimulation with ACTH(1-24) when individual responsiveness is taken into consideration.

Leg health and performance of broiler chickens reared in different light environments

1. The effects of light source and intensity on leg health and performance of female ROSS 308 broiler chickens were investigated in a 2 × 2 experimental design (8 groups of 275 chicks) of two light sources (Osram biolux and Osram warm-white) and two light intensities (5 and 100 clux, adjusted to fowl-perceived illuminance). 2. At 41 d of age, body weight, gait-score, footpad dermatitis and hock-burn were measured on 50 birds from each light environment. In addition, weekly feed intake and body weight were determined on a group basis and mortality was recorded continuously. 3. The light environment did not affect the severity of the gait-score or hock-burns. The risk of moderate to severe lameness and hock-burns increased with body weight. Birds weighing more than 2400 g had an increased probability of moderate footpad lesions in biolux light. 4. Weight and gait-score, as well as gait-score and hock-burn were positively correlated. Podo-dermatitis was weakly correlated with hock-burn, which contradicts earlier findings. The light environment did not affect feed intake, body weight or mortality. 5. The light sources and intensities employed in this study did not adversely affect production or leg health of broiler chickens reared semi-commercially.

The effect of irregular feeding times on the behaviour and growth of dairy calves

The objective of this study was to examine the effects of predictable vs. unpredictable management routines on the behaviour, production and health of dairy calves. Three different feeding schedules for milk-fed dairy calves were compared. All calves received milk twice a day, and had free access to concentrate, hay and water. Three groups of 12 calves (divided on two trials) were exposed to one of the following treatments from the age of 5 days to 9 weeks: group C (control) received milk at the same time every day, at 0700 and 1400. Group OD (occasional deviation) received the milk at the same time every day except on treatment days, one in week 5 and one in week 8, where they were fed 3 h later. Group IR (irregular schedule) received milk at irregular times throughout the experimental period. The first daily feeding took place between 0600 and 1300 and the second one between 1300 and 2100. When the calves were 5 and 8 weeks old, the behaviour of eight calves from each group was videorecorded for two days (48 h). The following behaviour was recorded: frequency and duration of lying bouts and frequency of comfort behaviour (defined as licking or scratching own body), eating, drinking, other oral behaviour and extending the head through the feeding barrier (HTB). The milk and concentrate consumption of the calves was measured and the calves were weighed weekly. Diseases were recorded.The results showed that at the age of 5 weeks, the calves in group IR differed from the control group C by performing more eating behaviour both on the control day (27.5 vs. 15.5; p<0.05) and the treatment day (28.8 vs. 18.3; p<0.05). At the age of 8 weeks, no differences were found in the behaviour between groups IR and C. When the OD calves were 5 weeks old, they responded to the delayed feeding by increasing drinking behaviour (14.5 vs. 9.0; p<0.05). When they were 8 weeks old, they showed increased frequency of comfort (195 vs. 122; p<.05), eating (37.5 vs. 27.9; p<0.05) and HTB behaviour (19.8 vs. 7.4; p<0.001) on the treatment day compared to the control day. The IR group did not respond to the same treatment except for a slight increase in drinking behaviour (9.6 vs. 6.5; p<0.05) at the age of 8 weeks. No differences were observed in the frequency or length of lying bouts, nor health or production parameters between the three groups.It is concluded that a predictable feeding schedule may not be very important for milk-fed dairy calves. However, when the calves are customised to predictable feeding times, occasional deviations from that schedule may cause frustration when their expectations are not fulfilled.

Using the cross point of demand functions to assess animal priorities

We developed a method to assess the substitutability of two reinforcers by using the divergence of the cross point of two demand functions. Two kinds of water were used as reinforcers, namely distilled water and quinine water. We tested 16 rats, Rattus norvegicus, from two strains in a closed economy. A single demand function for each kind of water was established. Then, two reinforcers were presented on concurrent fixed-ratio schedules. Finally, a control condition with distilled water for both responses was run. Demand functions were generated on scales with fixed-ratio values on the X axis and number of reinforcers obtained on the Y axis. The cross point of the functions differed significantly between the two strains of rats in both conditions within each condition. Furthermore, there was a significant difference within strains between the conditions. On evaluating the single demand functions, we found a significant difference between the slopes of the two demand functions, but no strain differences in demand. In addition, the results revealed a disagreement between demand assessed by using the slope of the single demand function and the results using the double demand function, with the results of the double demand function being in accordance with simple choice behaviour of the rats in their home environment. Using the cross point of two demand functions provides a measure of substitutability and, furthermore, the method appears to be a more sensitive measure of animal priorities than single demand functions.

Effects of interrupted social contact on the social behaviour of calves and piglets

The use of traditional operant conditioning techniques to assess the behavioural needs of farm animals has been criticised because presenting short rewards repeatedly may interrupt bouts of behaviour and thereby devalue the reward. The two reported experiments (one including 12 calves and one including 12 piglets) aimed to investigate if interruption of social contact affects social behaviour. In both experiments, animals were housed in pairs (one test animal and one companion animal) in large pens with solid sides. The experiment included three periods: a pre-test period, a test period and a post-test period. Animals were separated for 24 h and then reunited for 24 h in each period. In the test period, the first 42 min of contact after reunification comprised 12 successive 3.5 min long periods separated by gaps, whereas in the pre- and post-test periods, the contact was continuous. Calves sniffed and licked each other more when social contact was interrupted (P<0.01), but no effects of interrupting social contact were found for social or locomotor play. In piglets, the test animals performed more flank pushing of the companion (P<0.01), and avoided the companion more (P<0.05), when social contact was interrupted, while no effects of interruption were found for parallel pressing, bites and head knocks, sniffing or locomotor play. The results suggest that if social contact is interrupted in an operant conditioning set up, some elements of aggressive behaviour may be stimulated in piglets.

The adrenal response to chronic stress is modified by individual differences in adrenal function of pigs

The aim of this investigation was to quantify the intensity of stress induced by various housing systems. The stress intensity was measured by an adrenal function test, in which the cortisol secretion of the corticoadrenal glands was stimulated, and the resulting pattern of cortisol secretion was used as a stress indicator. The function of the adrenal cortex was tested following direct and indirect stimulation. The direct stimulation consisted of an intravenous injection of adrenocorticotrophic hormone (ACTHl_24). The indirect stimulation was done in three ways: by insulin induced hypoglyeaemia; neostigmine/atropine-induced muscle contraction; metomidat-induced anaesthesia. Earlier experiments with pigs showed that large individual differences in behavioural and physiological responses make it difficult to determine the effects of environmentally induced changes alone. Therefore, before analysing the chronic effect of various housing systems on the adrenal reactivity, the reaction pattern of the experimental animals was analysed prior to the experiment. Thirty-six pigs were anaesthetised and their plasma cortisol concentration 3 h later was determined. Based on these measures, the animals were assigned to four different groups (high, middlehigh, middle-low and low reacting). Half of each group was tethered on partially slatted floors and the remaining animals were kept as controls in groups of six animAh on straw. After 6 weeks the animals were subjected to the four different adrenal function tests. The adrenal function was established by radioimmunoassay determination of the plasma cortisol concentration over a 5-h period after stimulation, and a response curve was plotted for each animal. Within each reaction group, tethered animals showed a higher eortisol increase than control animals. However, this environmentally induced increase in adrenal reactivity was considerably smaller than the variation between groups. The duration of behavioural activity (standing and walking) of all pigs over a 24-h period was recorded. There was a significant negative correlation between activity and adrenal reactivity following ACTH-stimulation for the tethered animals. Is was shown that the effect of the environment on adrenal function can be seen more clearly when individual responsiveness is taken into account.

How to live in a variable world: keep your mind flexible

Hardly any situation in life is black or white. Most situations are various shades of grey. (One exception is pregnancy: either you are pregnant or you are not. A little bit pregnant doesn’t go!) To deal with these shades of grey, however, we are all forced to establish categories according to some characteristic, simply in an attempt to create some degree of order in the chaos. We people categorize our body size in small, medium, large and extra large. How else could we find a piece of clothing in the department store that would fit us? We distinguish between animals and plants, Sheep distinguish between food and non-food. All in order to deal with practical problems, with life in a variable world. But categorization not only helps us deal with chaos, there also are disadvantages to categorization. One of them is that the cut-off points between the categories are often arbitrary, maybe decided by some irrelevant factor, sometimes completely haphazardly. (Some of us, for instance, should actually wear clothes that are a large small or a small medium.) Another disadvantage is that some items may not fit in any of the categories or in two neighboring ones (e.g. some simple organisms have the characteristics of both plants and animals). But a third, much more problematic disadvantage is that categorization tends to entice us to develop ‘steel trap minds’ or ‘tunnel vision’: once we have succeeded in finding the ‘right’ category for a phenomenon, we would like it to stay there. We do not want to go through the hassle of having to re-categorize it or, worse yet, having to redefine the categories and the cut-off points between them, should it turn out that our first system appears faulty. Michael Appleby’s article is a heroic attempt at discussing a problem with which we all are confronted, animals and man alike. He emphasizes how important it is to take more than one factor into consideration when establishing categories. We all need to be told regularly that the difference between ‘natural’ and ‘artificial’, between ‘food’ and