W. B. Gross

Food restriction early or later in life and its effect on adaptability, disease resistance, and immunocompetence of heat‐stressed dwarf and nondwarf chickens

1. Dwarf and nondwarf chickens placed under 60% food restriction from either 4 to 6 (early) or 24 to 26 (late) days of age were exposed to high ambient temperatures (35 +/- 2 degrees C) from 36 to 43 d of age. 2. As measured by heterophil/lymphocyte (H/L) ratios, stress response to food restriction was similar at both ages for dwarfs while less at the younger than the older age for nondwarfs, resulting in a significant food restriction interaction of genotype by age. 3. Nondwarf chickens food restricted at the younger age had smaller increases in H/L ratios, improved resistance to marble spleen disease infection and greater growth than those restricted at the older age or fed ad libitum in response to the high ambient temperatures. 4. For dwarf chickens feeding regimen had no influence on response to the environmental insults. 5. Antibody response to sheep erythrocyte antigen was not affected by genotype or feeding regimen.

Inhibition of adrenal steroidogenesis, food restriction and acclimation to high ambient temperatures in chickens

1. White Plymouth Rock chickens placed under 60% food restriction or ad libitum feeding, with or without metyrapone treatment, from either 4 to 6 (early) or 24 to 26 (late) d of age were exposed to high ambient temperatures (35 +/- 2 degrees C) from 36 to 43 d of age. 2. Stress attributable to fasting was not manifested through leucocytic alteration when food-restricted chicks were supplemented with an adrenal blocking chemical, metyrapone. 3. Provision of metyrapone during the fasting period resulted in inferior compensatory growth during refeeding. 4. Exposure to high temperatures from 36 to 43 d of age did not cause an elevation in the heterophil:lymphocyte (H/L) ratios of chicks that had eaten metyrapone-treated food ad libitum during the neonatal stage. 5. During heat exposure, chicks that had been subjected to early 60% restriction with non-metyrapone-treated food had lower H/L ratios and improved resistance to marble spleen disease infection.

Factors affecting chicken thrombocyte morphology and the relationship with heterophil: Lymphocyte ratios

1. Thrombocytes were observed in a haemocytometer chamber and cells were classified into 5 morphological groups which were related to the extent of environmental stress. Thrombocyte morphology scores (TMS) were calculated for each blood sample. 2. Following exposure to social stress, chilling, or the injection of killed Escherichia coli, both TMS and heterophil:lymphocyte (H:L) ratios were increased. From maximum values 1 d after chilling H:L and TMS values returned to normal within 2 and 11 d respectively. 3. The addition of corticosterone (200 mg/kg) to the food resulted in increased H:L ratios whereas TMS were not affected. 4. The injection of an adrenal blocker, 1,1-dichloro-2,2 bis p-choro-phenyl ethane, resulted in decreased H:L values whereas TMS were not affected. 5. Resistance to E. coli challenge infection was not affected by TMS.

Effects of dietary corticosterone in young leghorn and meat‐type cockerels

1. Cockerels from meat-type (MT) and Leghorn (LG) stocks were fed on diets containing 0, 20, or 30 mg corticosterone/kg from 1 to 22 d after hatching. 2. Within MT and within LG stocks, responses to dietary corticosterone inclusion rates were similar; however, patterns differed between these major classes resulting in stock X diet interactions. 3. Traits responding to different inclusion rates of corticosterone in a dissimilar manner for MT and LG chickens included: immunoresponsiveness, body weight, efficiency of food utilisation, feathering; relative weights of liver, spleen, bursa, testes, breast and abdominal fat pad, as well as the proportion of liver lipid. 4. No differential responses occurred for relative adrenal weight, plasma xanthophyll concentrations, proportion of breast lipid and abdominal fat, or surface and cloacal temperatures. 5. Results indicated genetic differences in thresholds for response to corticosterone and in degree of response once thresholds were reached. Within populations, sensitivities varied between target organs.

Genetic and environmental effects on the response of chickens to avian adenovirus group II infection.

The effects of husbandry procedures on an intravenous challenge with avian adenovirus group II were studied in lines of White Leghorns selected for high (HH) and low (LL) antibody response to sheep erythrocytes and their reciprocal crosses (HL and LH). Husbandry procedures were deprivation or no deprivation of water during the first week after hatching (ES), habituation or no habituation to humans throughout life, and flock stability or instability (LS) 24 hours prior to an intravenous challenge with avian adenovirus group II. Spleens of chickens were weighed 6 days after challenge. HL chicks were most susceptible and LH chicks were most resistant to avian adenovirus group II. Chicks subjected only to ES or no stress responded similarly and were less affected than those subjected to LS or to both ES and LS. There were major genetic-environment interactions which affected spleen size.

Interfacing genetics, behavior and husbandry in White Leghorns presented with E. coli challenge

Abstract Adult females from the S 3 and the S 4 generations of lines which had undergone previous selection for persistence and non-persistence of antibody production to sheep red blood cells, were placed in the following situations: (1) one-third remained in the same cages they were placed in at the time of caging, (2) one-third were moved to other but essentially identical single cages, and (3) one-third were paired in neutral but essentially identical cages with females from the other line. Characteristics measured were: “fear”, head shaking, social rank, comb size, body weight, antibody titers, plasma corticosterone levels, and the number and size of heterophils and lymphocytes. Although differences between lines were not significant for most of the characteristics measured, the pullets from the persistent line exhibited significantly less “fear”, had smaller lymphocytes and lost less body weight when moved than those from the non-persistent line. Temporal comparisons among pre-movement, one-day post-movement and seven-day post-movement times revealed significant differences for plasma corticosterone levels, antibody titers, number and size of lymphocytes, and size of heterophils. Significant differences were noted among movement treatments for changes in body weight and for number of air sac lesions to an E. coli challenge. It appeared that the physical and social effects were cumulative for most of the traits in both lines.

Sex‐linked feathering alleles (k, k+) in chickens of diverse genetic backgrounds

Chicks were produced for this experiment by mating males from a broiler parent stock that were heterozygous (K/k+) at the sex-linked feathering locus with early feathering (fc+/w) females. Dams were from three diverse lines - White Plymouth Rocks selected for high or low 8-week, body weight and White Leghorns selected for high antibody response to sheep erythrocytes. Escherichia coli (E. coli) were injected into the caudal air sac of some chickens and others were maintained as uninoculated controls. Body weights were obtained immediately before inoculation and at subsequent 24-hour periods until 5 days after inoculation, at which time air sac and heart lesions were scored. Chicks were less affected by E. coli if they were maintained in warmer environments, younger at time of inoculation, or from the low weight dam line. Lesion scores suggested that chicks with only allele fc+ were slightly more resistant to E. coli inoculation than those with the K allele.

Population development of Ornithonyssus sylviarum (Canestrini and Fanzago) on leghorn roosters inoculated with steroids and subjected to extremes of social interaction

Abstract High levels of social interaction or dietary administration of corticosterone or desoxycorticosterone were shown to increase resistance of roosters to Ornithonyssus sylvarium infestation. The concentration of steroid in the feed which produced this effect was critical, and increasing concentrations past this level did not appear to augment resistance. Roosters maintained under low levels of social interaction were more affected by steroids in the feed than were their high stress counterparts as measured by weight gain and selected organ weight. No difference in antibody production against horse erythrocytes was noted between birds under high and low levels of social stress, or between birds receiving different steroid treatments. Histologic examination of tissue dorsad to the cloaca indicated that mite population differences in response to stress or steroid treatment may be linked to capillary density at the skin surface.