Growth and the plasma concentrations of growth hormone and prolactin in chicks: effects of "environmental enrichment", sex and strain

Growth hormone and growth?

Pituitary GH is obligatory for normal growth in mammals, but the importance of pituitary GH in avian growth is less certain. In birds, pituitary GH is biologically active and has growth promoting actions in the tibia-test bioassay. Its importance in normal growth is indicated by the growth suppression following the surgical removal of the pituitary gland or after the immunoneutralization of endogenous pituitary GH. The partial restoration of growth in some studies with GH-treated hypophysectomized birds also suggests GH dependency in avian growth, as does the dwarfism that occurs in some strains with GHR dysfunctions. Circulating GH concentrations are also correlated with body weight gain, being high in young, rapidly growing birds and low in slower growing older birds. Nevertheless, despite these observations, there is an extensive literature that concludes pituitary GH is not important in avian growth. This is based on numerous studies with hypophysectomized and intact birds that show only slight, transitory or absent growth responses to exogenous GH-treatment. Moreover, while circulating GH levels correlate with weight gain in young birds, this may merely reflect changes in the control of pituitary GH secretion during aging, as numerous studies involving experimental alterations in growth rate fail to show positive correlations between plasma GH concentrations and the alterations in growth rate. Furthermore, growth is known to occur in the absence of pituitary GH, as most embryonic development occurs prior to the ontogenetic appearance of pituitary somatotrophs and the appearance of GH in embryonic circulation. Early embryonic growth is also independent of the endocrine actions of pituitary GH, since removal of the presumptive pituitary gland does not impair early growth. Embryonic growth does, however, occur in the presence of extrapituitary GH, which is produced by most tissues and has autocrine or paracrine roles that locally promote growth and development. The role of GH in avian growth is therefore still unclear.

Effects of auditory and physical enrichment on 3 measurements of fear and stress (tonic immobility duration, heterophil to lymphocyte ratio, and fluctuating asymmetry) in several breeds of layer chicks

The purpose of this study was to analyze the effect of auditory enrichment (by means of classical music) or physical enrichment (by means of hanging colored string bunches and barley grains on the floor) on tonic immobility duration, heterophil to lymphocyte ratio, and fluctuating asymmetry (FA) in chicks of several layer breeds. In experiment 1, 192 chicks from 8 Spanish breeds and 1 White Leghorn population were reared in cages with or without music auditory enrichment until 8 wk of age. The effect of music auditory enrichment was significant for heterophil to lymphocyte ratio (P < 0.05). The ratios were higher in chicks reared without music than in those reared with music, suggesting that auditory enrichment from classical music reduces stress in chicks. There were significant differences in morphological trait measurements (relative asymmetry of wing length, leg width, and combined asymmetry; P < 0.05), being greater in chicks reared without music. This result suggests that FA is a good indicator for stress level in chicks, given that it follows the same trend as that found for heterophil to lymphocyte ratio. There was a significant treatment by breed interaction (P < 0.05) for tonic immobility duration, indicating no consistent effect by auditory enrichment on tonic immobility duration across breeds. In experiment 2, 180 chicks from 3 Spanish breeds were housed in pens with or without physical enrichment (colored plastic string bunches and barley grains on the floor) until 6 wk of age. The effect of physical enrichment on tonic immobility duration, heterophil to lymphocyte ratio, and FA was not significant, indicating no effect on fear and stress in layer chicks. In conclusion, auditory enrichment by means of classical music is a reliable method for reducing stress levels in several breeds of layer chicks. However, music auditory enrichment was not effective in reducing fearfulness in any of the layer breeds. Physical enrichment by means of colored plastic string bunches and floor barley grains does not appear to be an effective method for reducing stress and fear in layer chicks.

Differential effects of 4 types of environmental enrichment on aggressive pecking, feather pecking, feather loss, food wastage and productivity in Japanese quail

1. We examined the effects of 4 types of environmental enrichment (foraging opportunities, structural complexity, sensory stimulation/novelty, and social companionship) on aggressive and feather pecking, feather condition, food wastage, body weight, feed conversion, and egg production in adult Japanese quail. Sex differences were examined where possible. 2. GLM analysis was used to evaluate the effects of enrichment and housing, while test-retest reliability and the stability of measures over 18 d were assessed using partial correlation. 3. Foraging enrichment reduced food wastage. 4. Body weight, feed conversion, and egg production were not affected by enrichment. Rates of aggressive and feather pecking were also not significantly affected, but these behaviours were observed very infrequently in this study. 5. Socially-housed birds had poorer feather condition, lower body weight and less efficient feed conversion than singly-housed birds. Social housing did not affect food wastage. 6. There were not sex differences in feather pecking, feather condition, food wastage, or feed conversion. 7. All measures except feather pecking were reliable over 24 h, but only feather condition and body weight were stable over 18 d. The instability f the behavioural measures over time suggest that enrichment effects may vary with age.

The effects of behavior and environmental enrichment on disease resistance of turkeys

Turkey poults were provided with environmental enrichment for the first 14 days after hatch. At 2 days of age each bird was tested for the speed in which it would cross a T-maze. At 5 weeks of age birds were treated with dexamethasone and challenged with Escherichia coli. Enriched birds had higher body weights and incidence of disease and mortality and lower numbers of leukocytes when challenged. Challenged and enriched birds that tested FAST had higher mortality and air sacculitis scores and lower body weights than SLOW birds. Non-enriched, SLOW birds were the only ones to respond to challenge with increases in leukocyte counts and heterophil/lymphocyte ratios. These data suggest that environmental enrichment during the first 2 weeks after hatch may be detrimental to those birds with a FAST T-maze response, and that poults with a FAST response in the T-maze may be more susceptible to experimental bacterial infection.

Environmental Enrichment for Laying Hens - Spherical Objects in the Feed Trough

The welfare of caged laying hens could be improved by placing objects in the feed trough. Such objects might (a) simulate general ground-litter thus promoting more normal foraging activity and (b) give hens the opportunity to work ‘for feed - a behaviour usually thwarted in conventional cages. Spherical objects with various characteristics were placed in the feed trough of a tier of caged laying hens (n = 16). The hens pecked frequently at the objects, moving them to the trough space of adjacent cages. The mean proportion of hen heads over the trough containing these objects was significantly greater than before the objects were present (35.3 cf 32.9%) and significantly greater than the proportion of heads over a similar trough containing no objects (33.6%). Thirty days later, the mean proportions were still significantly different (33.5 cf 31.0%) showing that there was little habituation. Daily manual scattering of the objects increased the distance they were subsequently moved by the hens (23.0 cf 19.3 cm/day) indicating increased pecking activity. In a second study 12 hens were given a choice of feeding from troughs containing 0, 12 or 36 spherical objects. There was no overall preference to feed from any of the troughs. All the hens fed from troughs containing the objects, possibly indicating that the opportunity to move the objects and forage or work for feed was desired on occasions. Brightly coloured spherical objects are considered to be a promising method of successful environmental enrichment for caged laying hens. Their use to improve the welfare of caged laying hens appears to be practical and reasonably inexpensive.

An enrichment object that reduces aggressiveness and mortality in caged laying hens

The effect on aggressive pecking activity and mortality by an environmental enrichment device was examined. In this study, 2955 White Leghorn chickens from three different lines were used in six separate experiments. Experiments were conducted with chickens during their first or second laying period. Half the cages in each experiment were equipped with colored key rings or an enrichment object manufactured by Gallus Ltd. (Israel). Experimental and control groups of cages were distributed in an alternate serial order for each experiment which lasted for 3, 4, 5, 8, 9, and 10 months. The enrichment devices significantly reduced aggressive head-pecking behavior and significantly decreased the mortality rate from 1.06% per month among the controls to 0.57% among the experimental groups.

Lipogenesis and lipolysis in fed and fasted chicks from high and low body weight lines

Lipogenic and lipolytic capacities were examined in fasted and nonfasted 28-day-old chicks from high-weight (HW) and low-weight (LW) selected lines. Lipogenesis was assessed in liver and bone (sternum) tissues through the activities of malic enzyme (EC 1.1.1.40), citrate cleavage enzyme (EC 4.1.3.8), and acetyl coenzyme A carboxylase (EC 6.4.1.2), as well as through the in vitro incorporation of acetate-1-14C into liver and bone lipid fractions. Lipolysis was estimated through the in vitro release of free fatty acids (FFA) from abdominal adipose tissue and through plasma FFA. Fasting depressed lipogenesis and increased lipolysis. Regardless of the feeding state, LW chicks exhibited higher lipogenic and lipolytic capacities than their HW counterparts, suggesting that lipid degradation may be relatively more important than synthesis in determining net fat deposition. In addition, the incorporation of radioactive acetate into bone lipid was associated with detectable activity of lipogenic enzymes, providing further evidence that the skeleton is an important site of lipogenesis in the chicken.

Lipogenesis and lipolysis in normal and dwarf chickens from lines selected for high and low body weight

Lipogenic and lipolytic comparisons were made among normal and dwarf adult males from both high-weight (HW) and low-weight (LW) selected lines. Six nonfasted birds from each of the four populations were sacrificed, and in vitro lipogenesis and lipolysis were measured in liver, adipose, and bone tissue. Also determined were activities of acetyl CoA carboxylase (E.C.6.4.1.2), NADP-malate dehydrogenase (E.C.1.1.1.40), ATP-citrate lyase (E.C.4.1.3.8), and plasma-free fatty acids (FFA). In comparison with the HW chickens, the LW males tended to exhibit higher activities of lipogenic enzymes, a greater capacity to incorporate acetate-1-14C into liver slices, an increased mobilization of FFA from adipose tissue, and high concentrations of FFA in plasma. The results indicated that the maintenance of increased postmaturational body fat associated with selection for high body weight was primarily the result of decreased lipolysis rather than enhanced lipogenesis. Effects of the dwarf allele on lipogenesis and lipolysis were not clear. Acetate incorporation into bone tissue was substantially higher than for adipose tissue, suggesting that bone may be an important site of lipogenesis in the fowl.