Effects of social isolation and crowding upon adrenocortical reactivity and behavior in the rat.

The effects of social isolation and crowding on adrenocortical function and upon behavioral responsiveness to electric shock have been studied in male and female rats. All female experimental groups showed higher corticosterone levels and heavier adrenals than their male counterparts. The major effect of housing condition concerned the corticosterone response to stress, while basal hormone concentration was not modified. Socially housed rats showed a more intense adrenocortical response and also a greater behavioral reactivity to electric shock than the isolates.

Replacing hens in cages: effect on subsequent egg production.

Comparisons were made to determine whether replacing hens that died in multiple-hen cages would alter the subsequent well-being of such groups, as indicated by rate of egg production. In only one of four comparisons was a significantly lower rate of lay obtained from hens in cages that received replacements in the 1st 5-wk period following replacements. Differences were not detected during the 2nd 5-wk period in any of the four comparisons. Consequences of replacing vs. not replacing hens are discussed briefly.

Broiler performance under high stocking densities.

1. In two consecutive experiments a total of 4,780 broilers were reared at high stocking densities. 2. In experiment 1, the birds were housed at 10, 20, 30, 40 or 50/m2 till 6 weeks. In experiment 2 densities of 20, 40 and 50/m2 were compared; the two higher densities were reduced to 30/m2 at either 3 or 5 weeks of age. 3. In the first experiment 6-week body weight was a curvilinear function of stocking density. Average food intake over the whole experimental period declined linearly with densities above 20/m2. 4. A slight but significant improvement in the efficiency of food utilisation was recorded from birds at high densities in the first experiment only. 5. Reducing the stocking density from 40 or 50/m2 to 30/m2 at 3 weeks increased food consumption and body weight gain and led to a recovery in their body weight by 6 weeks. 6. No significant differences were observed in mortality as a result of high stocking densities in either experiment. 7. Profit margin per m2 increased almost linearly in experiment 1, by about 65 p for every bird/m2 increase in stocking density. 8. The implications for poultry welfare are briefly discussed.

Population size, cage area, and dominance rank effects on productivity and well-being of laying hens.

The effect of two cage population sizes (four vs. six/cage) and two cage area treatments (316 cm2 vs. 406 cm2/bird) were compared in a nonconfounded design while maintaining feeder space constant (8.9 cm/bird) for egg production performances and behavioral and physiological indicators of well-being of laying hens. Egg production rates were determined for all members of each cage group (palpations at 48 to 50 wk) and on a cage group basis (20 to 60 wk). Heart weights, plasma corticosterone levels, durations of tonic immobility (TI), and plumage conditions were compared for top and bottom birds in the dominance ranks. Significant reductions in egg production were observed for low ranking hens in the high density (4 and 6/316-cm2) treatments. In addition, high ranking hens of the 6/316-cm2 treatment produced fewer eggs than high ranking hens in the 4/316-cm2 treatment. When high and low ranking individuals were housed in single-hen cages, egg production was improved relative to performances in the social environments. Heart weights of hens, as a percentage of body weight, were increased in the low ranking hens and for hens in the smaller cage size. Plasma corticosterone did not prove to be a useful indicator of well-being. Low ranking individuals had greater durations of TI but differences in feather condition were not detected. The results support the contention that appropriate population sizes and cage space allocations can be determined that will optimize the performance and welfare of layers in cage environments.

Effects of population size and cage area on agonistic activity and social structure of White Leghorn layers.

Four caging environments consisting of two population sizes (4 vs. 6 birds/cage) and two cage area allocations (316 vs. 406 cm2/bird) were evaluated for their effects on agonistic activity, social structure, and egg production of Single Comb White Leghorn layers. Wire battery laying cages were designed and constructed to study these effects in a nonconfounded approach while maintaining feed trough space constant. Agonistic activities and dominance structure for the treatment groups were assessed during Weeks 23 to 26 and 37 to 40; egg production was obtained for Weeks 20 to 40. Cage groups demonstrated a high degree of linearity (K) for dominance hiearchies during both observational periods. Values for K ranged from a low of .69 during Period 1 to as high as .91 during Period 2. Cage groups were also very stable over observation periods; correlation coefficients for dominance ranks between Periods 1 and 2 averaged .95 and .89 for the four and six-bird groups, respectively. Greater cage area and population size resulted in more agonistic activity during Period 1, but only in the 6/406 cm2 treatment during Period 2. The alpha individual was responsible for the most aggressive acts committed in all cage groups (40 to 50%). Aggressive activity was observed to decline in a linear manner with declining dominance rank. Egg production was significantly affected by population and density treatments during Period 2; however, correlations between aggressive acts per cage and egg production were not generally significant.

Behavioral and physiologic effects of early nutrition and social factors in the rat.

Two experimental methods to provoke caloric restriction during suckling were used. Each of the methods utilized two different rat groups: Low Growth (LG) and High Growth (HG). In one method, the groups also differed in a social factor, litter size: crowded (Cr) and control (Co). Growth differences and high levels of social competition were found among pups of the crowded group with Low Growth (CrLG) compared to the group with High Growth and small litters (CoHG). Both methods resulted in growth differences between respective groups from the first week of suckling. Differences in animal groups persisted forty days after weaning. LG animals had higher defecation scores with lower activity in the open-field test, higher susceptibility to restraint ulcers and adrenal hypertrophy than HG rats, in litters of equal size. However, early stimulation from social competition among pups in larger different litters in CrLG group counteracted nutritional factor effects. Elevated open-field defecation and ulceration scores with adrenal hypertrophy were found in CoHG rats.

Density and group size effects on caged hens of two genetic stocks differing in escape and avoidance behavior.

Hens of two moderately inbred White Leghorn stocks, known to differ significantly in escape and avoidance behavior, were compared for productivity traits, nervousness, and feather loss when housed four or eight per cage at densities of 348 (high), 464 (medium), and 580 (low) cm2/bird. Differences were found between stocks in sexual maturity, egg production traits, body weights, nervousness, and feather loss. The more nervous strain lost more feathers. Highest density housing depressed performance and increased nervousness and feather loss, but differences were generally lacking between the medium and lowest density housing. Group size effects were not detected for productivity traits, but hens kept in groups of eight had increased nervousness and feather loss. No interactions were detected between stocks and density, stocks and group size, or density and group size.

Crowding-induced changes in basal and stress levels of thyrotropin and somatotropin in male rats.

The effects of crowding on thyrotropin (TSH) and somatotropin (GH) secretion were studied in two-month-old male rats. Crowded rats (9-10 per cage) showed lower serum GH levels than controls (3 per cage). Likewise, serum GH was lower in crowded rats after acute exposure to stress. However, percentage inhibition of GH secretion induced by acute stress was similar in crowded and control rats. Crowding reduced the TSH response to acute stress. The results found with the administration of hypothalamic regulatory factors suggest that the impaired GH and TSH secretion observed in crowded rats was not likely to be at the pituitary level. Therefore, altered neuroendocrine control of GH and TSH secretion appears to exist in crowded rats. Preliminary results obtained in rats crowded from weaning to adulthood suggest that food restriction only partially accounts for the changes observed in crowded rats.

Effects on productivity and aggressive behavior of laying hens of solid versus wire cage partitions and bird density.

The effects of solid metal cage partitions or wire mesh cage partitions and two cage densities (5 or 7 birds/60.9 cm X 35.6-cm shallow cage) on production performance traits, aggressive behavior, and feather covering of White Leghorn layers were assessed from 20 to 60 wk of age. Type of cage partition had no significant effects on any of the traits measured. Higher cage density, however, was associated with significantly lower hen-day egg production, feed usage, final body weights, and feather covering. No differences were observed for egg weights, egg loss, mortality, or aggressive head pecking activity of birds housed in the two cage densities.

Feeding behavior characteristics of intact male lambs as affected by number of lambs in a pen with restricted access to the feed stall.

To investigate the effect of number of animals housed in a pen upon feed intake, 72 intact male lambs were randomly assigned to treatments consisting of 3, 7, 11 or 15 animals/pen in each of two trials. For each animal's feeding event, length of feeding (s) and feed consumption (g) were recorded through use of an automatic feeding system. This system allows one animal to feed at a time. Pens were treated as experimental units with observations repeated daily for 21 d. Response variables were feed consumption (g), time (s) and rate of feed consumed (g/s) per visit and feed consumption (g), average time (s) and number of visits per animal daily. Number of animals/pen was significant for most feeding behavior characteristics. As number of lambs within a pen increased, feed consumption/visit increased linearly in both trials. For Exp. 1, rate of feed consumption/visit increased at a decreasing rate, while in Exp. 2 only the linear effect of lamb numbers on this trait was significant. Daily feed consumption/lamb was greatest for intermediate lamb numbers, and the number of visits and time spent feeding/lamb decreased as the number of lambs within a pen increased. Results suggest that the feeding behavior of ram lambs with restricted access to a feeding stall can be modified by the number of lambs housed in a pen.

Effect of animal density on endocrine development in gilts.

A study was conducted to determine the effect of social crowding on the development of endocrine organs involved in the reproductive process in growing and finishing gilts. One hundred four littermate gilts weighing approximately 30 kg were randomly assigned to treatment groups of either 8 or 16 pigs/pen. Gilts raised in pens of eight were allotted 1.06 m2 per pig from 30 to 65 kg and 1.25 m2 from 65 to 100 kg; whereas, one-half the area was provided for gilts raised in pens of 16. Littermate gilts raised in pens of 8 and 16 were slaughtered on the same day when the average weight of pigs reached 100 kg. At slaughter, the brain, adrenals, pituitary, uterus and ovaries were removed and weighted. The brain was lyophilyzed and reweighed to yield dry brain weight. Gilts raised in the low-density groups had heavier adrenal (P less than .01), pituitary (P less than .08), brain (P less than .11), dry-brain (P less than .02), uterine (P less than .09) and ovarian (P less than .07) tissues. Furthermore, significantly more gilts in the low-density, compared with the high-density groups, had ovulated at slaughter. In a second study, eight littermate gilts raised in pens of 8 or 16 and weighing approximately 100 kg were moved to individual pens and fitted with a jugular vein catheter. Following blood sample collection at 15-min intervals for 2 h, 200 IU of adrenocorticotropin (ACTH) were infused into the cannula. Blood samples were collected at 15-min intervals for an additional 2 h. There were no differences between basal or ACTH-stimulated concentrations of plasma cortisol between treatment groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of pullet-stocking density on performance of laying hens.

Effects of cage-stocking density during the rearing period on three commercial strains housed in open and closed rearing and laying houses were examined in two experiments. Stocking densities in Experiment 1 were 311, 259, and 239 cm2 per bird and in Experiment 2 were 311, 259, and 222 cm2 per bird. In the rearing period, greater stocking densities significantly reduced feed intake and 18-wk body weight and increased age at 50% production. In the second experiment, mortality to 20 wk was higher among birds reared at 222 cm2 per bird compared to the less dense treatments. In the laying phase of the experiments, there were no differences among the treatments in number of eggs per bird housed, layer mortality or kilograms of feed consumed per kilograms of egg produced. Final (499 days) body weight of hens reared at 222 cm2 per bird was significantly less than that of those in the other treatment groups. Egg weight of birds reared at 22 cm2 per bird was significantly greater than that of birds reared at 311 cm2 per bird in Experiment 2. Calculated incomes over feed and chick costs were not different among the treatments in either experiment. A less rapid decline in egg production was noted among birds reared at the highest stocking density over the time of the experiment.

Effect of cage height and area on the behaviour of hens housed in battery cages.

Medium hybrid hens were housed as pairs and observed at three cage heights: 30.0, 42.5 and 55.0 cm, and at three area allowances per bird: 570, 807 and 1045 cm2. With increased height, head stretching, head scratching and body shaking were performed at a higher rate and feeding and cage pecking at a lower rate. There was also an increase in the time spent sitting. With increased area, head scratching, body shaking and feather raising were performed at a higher rate and cage pecking at a lower rate. It is concluded that spatial restriction may increase the cost of performing certain 'comfort' activities, resulting in the reductions in performance rate observed in the above experiments. Welfare implications are briefly discussed and considered to depend on the motivational state of the birds.

Effect of dietary supplementation with vitamin C or carbadox on weanling pigs subjected to crowding stress.

A 2 X 3 factorial arrangement was used in each of two trials with two levels of floor space allowance (.25, .13 m2/pig) and three dietary treatments (basal, basal + 660 ppm vitamin C, basal + 55 ppm carbadox). The reduction in floor space allowance was achieved in trial 1 by doubling the number of pigs/pen from eight to 16 and in trial 2 by reducing the size of pens by half. An 18% protein starter diet was used as the basal diet. Total numbers of pigs used were 216 in trial 1 and 144 in trial 2. Pigs were weaned between 4 and 5 wk of age (7.5 kg average wt) and fed ad libitum for 28 d. Reducing floor space allowance caused a (P less than .05) reduction in weight gain of weanling pigs in both trials. When the reduction of floor space allowance was done by increasing number of pigs/pen (trial 1), pigs responded with a significantly reduced feed intake with no change in efficiency of feed utilization. However, when floor space allowance was reduced by changing the size of the pen (trial 2), feed intake of pigs was not affected but efficiency of feed utilization was reduced significantly. Neither form of crowding affected vitamin C concentration in adrenal glands and weights of adrenal glands, spleen and thymus. Dietary supplementation of carbadox, but not vitamin C, produced significantly greater weight gain, feed efficiency, and spleen weight of pigs in both trials. Although there was no interaction between crowding and dietary treatment in affecting the performance of pigs, supplemental carbadox improved the performance of crowding-stressed pigs by maintaining an adequate level of feed intake and improving feed efficiency, whether crowding was caused by increased pig density or by reduced pen size. No significant differences in phytohemagglutinin (PHA) skin test response or in the neutrophil-to-lymphocyte ratio (N/L) were observed among treatments in trial 1, while a significantly reduced response to PHA and a higher N/L were detected in crowding-stressed pigs in trial 2.

Effect of floor area restriction upon performance, behavior and physiology of growing-finishing pigs.

Fifteen groups of eight pigs were allocated .34, .68 or 1.01 m2 lying area per pig between 25 and 100 kg live weight. These values were chosen in accordance with Petherick's model to prevent all pigs from lying in full recumbency (.68 m2/pig) or on their sternum and belly (.34 m2/pig). Productivity decreased in the groups of pigs allowed only .34 m2/individual from 20 wk following the beginning of the experiment (70 to 80 kg). Behavioral changes were observed as early as 8 wk after the beginning of the experiment (60 to 70 kg). Severe area restriction increased time spent at the feeder. Aggression did not vary as a linear function of area allocation. Analysis of the main behavioral activities over a 10-h observation period revealed higher feeding time and lower social activity in pigs kept at .34 m2/pig. Sternum resting was more frequent than resting on the side when body weight reached 60 to 70 kg. Pigs that were submitted to the lower area allocation displayed enhanced resistance of their pituitary-adrenal axis to the dexamethasone suppression test and enhanced reactivity to adrenocorticotropic hormone injection. These findings demonstrate that behavioral and physiological responses are earlier and more sensitive indicators of adaptation to the environment than productivity.

Rat cortical morphology following crowded-enriched living conditions.

This experiment studied cerebral cortical morphology in rats living in a crowded-enriched condition. Three groups of 60-day-old, male Long-Evans rats were divided accordingly: 12 rats, 3 per small cage (32 X 20 X 20 cm), standard colony condition; 12 rats in a single, large, enrichment cage with "toys" (70 X 70 X 45 cm), enriched condition; and 36 rats in a large, single, enrichment cage with "toys", crowded-enriched condition. Matched toys for the two enriched cages were changed twice a week at the time of cage cleaning. Measurements on 20-micron, transverse brain sections showed that in both the crowded-enriched and enriched groups the thickness of the medial occipital cortex increased by 4 to 6% compared with the cortex from animals in the standard colony condition. In addition, the crowded-enriched group demonstrated a 4% (P less than 0.05) increase in thickness in area 39 in the left hemisphere compared with the standard control. However, the thickness in area 39 in the crowded group was not significantly different from that of the enriched area 39. These results indicate that the cortex increases in thickness as much with "crowding" and enrichment as with enrichment alone. We hypothesize that diversion through interaction with "toys" mitigates the stress of crowded conditions.