No abstract

The purpose of this study was to analyze the effect of housing system and cold stress on the heterophil-to-lymphocyte ratio, the fluctuating asymmetry, and the tonic immobility duration of chickens. In experiment 1, hens (n=120; 36 wk old) from 5 Spanish breeds and a White Leghorn population, which had been housed in pens with or without access to an outdoor area from 20 wk of age, were used. The effect of housing system on heterophil-to-lymphocyte ratio varied from breed to breed, differences between housing systems being significant (P<0.05) in 2 breeds. In these breeds (Red-Barred Vasca and Birchen Leonesa), heterophil-to-lymphocyte ratio was significantly greater in hens housed in deep litter. Housing effect was significant for the relative asymmetry of leg length (P<0.01), wattle length (P<0.05), and the combined relative asymmetry (P<0.05), the relative asymmetry of hens housed in deep litter being larger. There was no significant difference for the duration of tonic immobility between hens housed in deep litter or free range. Thus, hens with access to an outdoor area were less stressed than hens without access to an outdoor area, although the fearfulness was similar in both groups of birds. In experiment 2, cocks (n=120; 36 wk old) from 4 Spanish breeds, a synthetic breed, and the White Leghorn population, which had been housed in cages with or without a cold stress (0 to 10 degrees C) from 24 wk of age, were used. Cold x breed interaction was significant for heterophil-to-lymphocyte ratio (P<0.05), differences between cold-stressed and control birds being significant in 2 breeds. In these breeds (Red-Barred Vasca and Buff Prat), heterophil-to-lymphocyte ratio was significantly greater in cold-stressed birds. Cold stress effect was significant for the relative asymmetry of toe length (P<0.001) and the combined relative asymmetry (P<0.05), the relative asymmetry of birds with cold stress being larger than that of control birds. Thus, cold stress seriously negatively affects the welfare of cocks.

The objectives of the current study were to estimate the heritability of the heterophil to lymphocyte ratio and to evaluate the effects of age, sex, and crossing on that ratio. There were three different experiments. In Experiment 1, we used a total of 711 birds from two generations with complete pedigree of a Spanish breed of chickens (Quail Castellana) to estimate the heritability for the leukocyte ratio at 36 wk of age by restricted maximum likelihood. The estimated heritability (0.59 +/- 0.09) indicated that leukocyte ratio should easily respond to selection. Heritabilities for heterophil and lymphocyte numbers were also high (0.56 +/- 0.07 and 0.65 +/- 0.07). In Experiment 2, leukocyte ratio differences among ages and sexes were investigated at 8, 12, 16, 20, 24, 28, 32, and 36 wk, in 576 birds from the same breed. Males showed significantly greater heterophil to lymphocyte ratios than females at the onset of sexual maturity and as adults. Significant variations with age for leukocyte ratio were observed in both sexes, which were mainly related to onset of sexual maturity, from which the leukocyte ratio increased more or less continuously. In females, the effect of age was also significant on heterophil and lymphocyte numbers. Finally, in Experiment 3, crossing effects were evaluated in 96 birds from a cross between the Quail Castellana and a White Leghorn population at 8 wk of age. The negative heterosis percentages found in the F1 and F2 generations were significant (-26% and -36%, respectively).

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.

The purpose of the present study was to analyze the effect of perches and footpad dermatitis on stress and fear levels of chickens. In experiment 1 heterophil to lymphocyte ratio and tonic immobility duration were measured in 36-wk-old hens (36 birds) from 2 Spanish breeds of chickens (Black Menorca and Quail Castellana) housed in pens with or without perches from 20 wk of age. There was a significant difference in the heterophil to lymphocyte ratio between perch treatments (P < 0.05), the ratio of hens with perches being lower than that of hens without perches. Hens with perches had significant lymphophilia (P < 0.05). There was no significant difference for the duration of tonic immobility between hens with or without perches. Thus, hens with perches were less stressed than hens without perches, as indicated by the heterophil to lymphocyte ratio. Heterophil to lymphocyte ratio and heterophil number for Black Menorcas were significantly smaller (P < 0.001) than for Quail Castellanas, whereas lymphocyte number was greater in Black Menorcas. The Black Menorca hens had significantly (P < 0.01) shorter tonic immobility duration. In experiment 2 heterophil to lymphocyte ratio and tonic immobility duration were measured in 52-wk-old cocks (36 birds) of each of two different Spanish breeds of chickens (Black Barred Andaluza and Red Barred Vasca) housed in cages from 36 wk of age and showing or not showing footpad dermatitis. There was no significant effect of footpad dermatitis on the heterophil to lymphocyte ratio, its numerator, or its denominator, whereas there was significant effect on tonic immobility duration (P < 0.05) with tonic immobility of cocks with footpad dermatitis being longer than that of cocks without footpads. Thus, cocks with footpad dermatitis were more fearful than cocks without footpad dermatitis, as indicated by the tonic immobility duration. Heterophil to lymphocyte ratio and heterophil number were significantly smaller (P < 0.05) for Black Barred Andaluzas than for the Red Barred Vascas.