Most studies on environmental enrichment in farm animals have looked at pig environments. Some studies have measured behavior and others both behavior and enhancing animal productivity (a goal of food animal production). Pedersen et al. (1992) found that feed efficiency was higher in pigs housed in enriched pens than in nonenriched pens. The enriched pens included a mezzanine tier with ramp, two hole self-feeder and operant waterer, maze hiding area, wheelbarrow wheel filled with concrete, suspended rubber hose mobile, and steel rings connected to a liftable wheelbarrow wheel. No immunological differences among animals were found in this study. Environmental enrichment (chains, football, tire, concrete block, straw) for group-housed gilts has also been shown to increase daily weight gain (Horrell 1992). For newly weaned pigs, environmental enrichment (tire hung from chain) reduced aggression (Schaefer et al. 1990). Questions remain, however, as to the appropriateness of enrichment devices and the standards by which we evaluate such devices. Only one study on dairy calf enrichment appears in the literature, and the goal of this work was not specifically environmental enrichment but how sucking on an artificial nipple alters digestive hormone concentration (Rushen and de Passille, 1995).
Under typical management practices, dairy calves are weaned from the dam within 24 hours of birth and then housed in individual pens of varying design. Dairy calves are not group-housed because these animals tend to look for something to suckle on or nurse on after being removed from the cow. Nonnutritive sucking is a common occurrence in young mammals (Rushen and de Passille 1995) and is normal except for the fact that one calf sucking on another (cross sucking) can result in disease transmission, hairball formation, and other management problems (Albright et al. 1991).
Is group housing an acceptable method for raising dairy calves? Certainly, it enhances the social environment of the calf and thus constitutes an enriched environment. But what about the problems encountered in this type of system such as cross sucking and disease transmission. To find a system that alleviates cross sucking, studies were conducted to determine dairy calf preferences for different environmental enrichment devices and how provision of such devices might influence cross sucking.
Housing and animal care for both experiments were consistent with the Guide for Care and Use of Agricultural Animals in Agricultural Research and Teaching (Consortium 1988), and all experiments were approved by the Purdue University Animal Care and Use Committee. In the first experiment, calves were removed from their dam between 24 and 48 hours after calving (standard production practice) and were placed in a wooden pen (23 square feet per calf) with wooden slats. Behavior was continuously recorded on a time-lapse videorecorder and later quantified for three separate 24-hour periods when calves were 1, 2, and 6 weeks old. Behaviors recorded were standing, lying, walking, and social/oral behaviors including use of the environmental enrichment devices and sucking on other calves.
|Figure 1||Figure 2a||Figure 2b||Figure 3|
Environmental enrichment devices included the following: large and small Kong toys (fig. 1) similar to the ones used by primates (they were bolted to the pen with a carriage bolt), a 15-inch diameter plastic ball, smooth chain hung from the ceiling about 1 foot from the floor of the pen, a calf lollie (fig. 2a and fig. 2b), and a Braden bottle (fig. 3). The calf lollie consisted of a piece of PVC pipe that was capped at both ends. The pipe had holes drilled in it and was suspended from the wall of the pen by two U-bolts. Inside the calf lollie were molasses flakes so that as the calf turned the pipe, the molasses flakes fell out. The Braden bottle (Braden Start Dry Feed Bottles; Braden Industries, Inc., Sulpher Springs, Texas) was mounted in the corner of the pen as specified by the manufacturer. The bottles have a nipple with a large slit. They contain calf starter feed, and as the calf sucks or bites on the nipple, it receives feed particles. Figure 4 illustrates the arrangement of enrichment devices in the pen.
Figure 4. General layout of enrichment devices in the calf pen.
During this experiment (experiment 1) using six calves per group, most of the enrichment devices were used consistently throughout the 6-week study. Frequency and duration of use was highest during week 2 for the small Kong toy (P=0.03). Frequency of use of the Braden bottle was higher during week 2 than weeks 1 and 6 (P=0.001). The same trends were seen for duration of use of the Braden bottle (P=0.083). Throughout the study, the Braden bottle was filled twice daily as needed. By week 6, calves were able to empty the bottle rapidly, and it was not continuously full. The small Kong toy was used more than the large Kong toy. Neither the ball nor the chain were used much by the calves except for two individuals that regularly pulled on the chain. Cross-sucking frequency was lower in week 1 than in weeks 2 and 6 (P=0.034).
When the duration of use for the devices was ranked for each week, the Braden bottle was used most, cross sucking second, and the large Kong toy third for week 1. During week 2, calves again spent the most time with the Braden bottle followed by the small Kong toy and cross sucking. Week 6 was characterized by use of the Braden bottle, with the large Kong toy second and cross sucking third. Calves spent more time engaged in oral activity (combination of cross sucking and use of enrichment devices) during week 2 than in weeks 1 and 6 (P=0.027).
Next, we compared group housing with and without environmental enrichment devices (experiment 2). We included immunological measures in this study to determine effects of enrichment on animal health in addition to behavior. Similar housing and management conditions were in effect for experiment 2. Three calves were included in each treatment group. Behavior was continuously videorecorded as in experiment 1. Blood samples were collected during weeks 2 and 6 for analysis of immune function. Total white blood cell counts and subsets of lymphocytes were measured along with plasma cortisol levels; these are all measures that are reflective of an animal's response to stress. Changes were seen in certain populations of white blood cells as the calves got older (CD3, total T lymphocytes; CD4, T helper cells; CD8, T suppressor cells all decreased between weeks 2 and 6), but there were no differences in immunological measures between calves in the enriched versus unenriched pens.
Frequency of cross sucking was greater (P=0.011; fig. 5) for calves in pens without enrichment devices. There was no difference in total activity (walking and standing) between the two environments, nor were there any differences in total oral activity (fig. 6), which suggests that the calves want to spend a certain amount of time sucking and that this is an important behavior for them. It appears that the calf will seek out something to suck on whether it is appropriate from a calf management standpoint or not. Use of the Braden bottle also decreased (P) in this experiment, which suggests that habituation (lack of use due to the item no longer being novel) might have occurred with this enrichment device. Duration of use of the large Kong increased over time (P=0.037) and it was the device calves spent the most time with during week 6. During week 2, as seen earlier, the Braden bottle was used most. The use of all other enrichment devices was the same for weeks 2 and 6.
Calves are social animals, spending most of their time lying near another calf. It is not clear, however, if this social enrichment (group housing) is enough to enhance calf well-being in light of increases in cross sucking when enrichment devices may not be available. In our first experiments we chose to enrich the social, nutritional and physical environment in order to determine what types of enrichment dairy calves would use most. There is a real need to place more emphasis on developing enrichment devices that meet the behavioral needs of the animal rather than on our perception of what will be enriching. Especially for farm animals, enrichment studies have used methods designed more to improve the public image of animal production (Curtis 1993) than on what enrichment devices are suitable for the animal. In these calf studies, two devices (ball and hanging chain) were included to determine if items that have previously been used as enrichment devices for farm animals were favored by calves more than behavior-oriented devices. Both the ball and chain were used very little by the calves, indicating that these devices probably have little functional significance to the calf. The Braden bottle was used by calves more than other enrichment devices in both calf studies. This may be due to the design of the bottle. Since it has a nipple for sucking on, the calves are allowed to express a behavior that they are motivated to perform (Rushen and de Passille 1995). As well as satisfying a motivation, sucking on the Braden bottle had a functional consequence (nutrient intake). While we assume that reduction in use of the Braden bottle during week 6 was due to it being empty, additional studies are required to determine if its use became habitual. Cross sucking was reduced with the environmental enrichment and, while this study is preliminary, the result suggests that enrichment may be a useful tool in enhancing environments for dairy calves.
Growth of brain cells is typically measured as increases in the cell body (indicating more machinery for metabolism) or in the arborous branches, or dendrites, that leave the cell body. A typical neuron looks like a tree, with many branches. The more branches (or dendritic segments), the more surface area there is for brain cell activity. The dendrites and the spiny processes on these dendrites serve an important role in the neurochemical transmission of signals in the brain (Bedi and Bhide 1988). In this experiment, we used changes in growth of brain cells to identify differences between an outdoor housing system and a typical indoor confinement swine housing system.
|Figure 7a||Figure 7b||Figure 8|
This study was conducted in collaboration with John McGlone at Texas Tech University and Terry Powley at Purdue University. McGlone measured behavior, immune response, and cortisol levels in indoor- and outdoor-reared pigs. The design of the study was such that pigs from the same litter were raised in the two different production environments on the same production schedule. Six sets of littermate (half-sibling) female pigs were randomly assigned to one of three treatments: euthanized at birth, or crossfostered to be developed in an indoor, simple environment (mechanical ventilation and concrete floors) or an outdoor, complex environment (straw bedding on earth; fig. 7a, fig. 7b). From one day of age and through development, genetic littermate pigs were reared both inside and outside. After 8 weeks, pigs were observed for behaviors, a blood sample was collected for immune measures, then pigs were euthanized for collection of brain tissue. Behaviors recorded were chewing, rooting, standing, sitting, drinking, rubbing, walking, wallowing, and grazing. From brain tissue, the areas studied included primary auditory (involved in hearing), somatosensory (sense of smell, taste, and touch of the pigs snout), and visual neocortex after Golgi-Cox staining (fig. 8). Only certain neurons fitting an extremely strict set of standards were measured. We used neurons from a specific part of the brain (layer IV) that were completely intact (not cut by the sectioning of tissue). This was important to ensure uniformity in sampling from one brain to the next. A graduate student, Mike Jarvinen, measured 493 total neurons using a highly specialized microscope system (Eutechtics Neuron Tracing System).
In our pig environment study, neuron cell body area increased 15 percent (P<.01) in all three neocortex regions from birth to 8 weeks old, indicating that our methods were sensitive and could detect differences if present. Other developmental changes were region specific. Auditory cell dendrites decreased in length and membrane surface area and had fewer segments (all P<.001) at 8 weeks compared with pigs at birth. Cells of the visual cortex increased in dendritic length and membrane surface area (P<.05) at 8 weeks of age compared with birth.
Pigs reared in the more complex outdoor environment had more auditory dendritic segments than pigs reared in the indoor environment (fig. 9). Outdoor-reared pigs were more active (fig. 10) and showed greater oral and rooting behavior (P<.05; fig. 11) than indoor-reared pigs. Outdoor-reared pigs had more white blood cells (P<.05) than indoor-reared pigs, but lymphocyte proliferation, neutrophil chemotaxis, and NK activity were similar for pigs in each environment.
Like the dairy calves, pigs also perform a certain level of oral behavior. In a more complex environment, they showed an increase in this type of behavior. Rearing pigs in a more typical confinement system, while reducing the amount of oral behavior performed, did not alter their neurons in a manner that would be suggestive of sensory deprivation. The finding that pigs in the indoor environment, which can be very noisy, had fewer auditory dendrites than pigs reared outdoors is of great interest. The preliminary interpretation is that the pig brain is capable of adapting to a noisy environment. Hearing tests are required to prove or disprove this interpretation. What is clear, however, is that although some behaviors (oral-nasal) were different between environments, brain development for the area of the brain processing this type of sensory information (somatosensory cortex) was unaffected. This suggests that the indoor confinement environment was not a sensory-deprived environment for pigs of this age. While outdoor-housed pigs had more total white blood cells, both groups had normal ranges for this measure and neither group of pigs had altered neutrophil-to-lymphocyte ratios or lowered natural killer cell activity suggestive of a stress response induced by the environment they were housed in. The results that the outdoor and indoor environments appear to be the same, for the most part, according to brain anatomy of the pig, although as seen in the auditory cortex, adaptation may occur over time perhaps to reduce irrelevant noises found in the indoor environment.
Corresponding author: Dr. Julie Morrow-Tesch, USDA-ARS, Livestock Behavior Research Unit, Purdue University, Poultry Science Building, W. Lafayette, IN 47907. Tel: 317-494-8022, FAX: 317-496-1993.
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