Responses of dwarf and normal chickens to feed restriction, Eimeria tenella infection, and sheep red blood cell antigen

Temporary feed restriction partially protects broilers from necrotic enteritis

The objective of this study was to investigate the effect of feed restriction on the intestinal ecosystem and on the pathogenesis of experimental necrotic enteritis in broiler chicks. To induce subclinical necrotic enteritis, an experimental challenge model using a specific diet formulation, Gumboro vaccination, oral inoculation of broilers with a 10-fold dose of attenuated anticoccidial vaccine and multiple oral inoculations with a specific strain of Clostridium perfringens was adopted. Two hundred and forty 1-day-old Cobb 500 broilers were randomly allocated to four groups: feed restricted, challenged, both feed restricted and challenged, and negative control. At 21, 22, 23 and 24 days of age, the intestines, gizzard and liver were collected from 15 birds in each group and scored for gross lesions. The intestinal digesta was collected for pH and viscosity determination. One caecum from each bird was taken for microbiological analysis. The application of feed restriction in birds challenged with C. perfringens reduced the necrotic enteritis lesion score significantly (P ≤ 0.05) and feed restriction significantly reduced (P ≤ 0.05) pH in the small intestine, the viscosity of the jejunum digesta as well as the C. perfringens counts in the caeca compared with the controls. In conclusion, feed restriction of broilers has a positive effect on the intestinal ecosystem and a significant protective effect against necrotic enteritis in the subclinical experimental model.

Review of human-animal interactions and their impact on animal productivity and welfare

Humans and animals are in regular and at times close contact in modern intensive farming systems. The quality of human-animal interactions can have a profound impact on the productivity and welfare of farm animals. Interactions by humans may be neutral, positive or negative in nature. Regular pleasant contact with humans may result in desirable alterations in the physiology, behaviour, health and productivity of farm animals. On the contrary, animals that were subjected to aversive human contact were highly fearful of humans and their growth and reproductive performance could be compromised. Farm animals are particularly sensitive to human stimulation that occurs early in life, while many systems of the animals are still developing. This may have long-lasting impact and could possibly modify their genetic potential. The question as to how human contact can have a positive impact on responses to stressors, and productivity is not well understood. Recent work in our laboratory suggested that pleasant human contact may alter ability to tolerate various stressors through enhanced heat shock protein (hsp) 70 expression. The induction of hsp is often associated with increased tolerance to environmental stressors and disease resistance in animals. The attitude and consequent behaviour of stockpeople affect the animals’ fear of human which eventually influence animals’ productivity and welfare. Other than attitude and behaviour, technical skills, knowledge, job motivation, commitment and job satisfaction are prerequisites for high job performance.

Changes in heat shock protein 70, blood parameters, and fear-related behavior in broiler chickens as affected by pleasant and unpleasant human contact

An experiment was conducted to determine the effects of combining both pleasant and unpleasant contacts with human beings on physiology and behavior of broiler chickens. Birds were subjected to the following treatments: (i) received no physical or visual contact with humans (control); (ii) from d 1 to 28, chicks were individually stroked gently for 30 s once daily (PL); (iii) from d 1 to 28, chicks were picked up individually, suspended by both legs, exposed to recorded noise, and swung gently for 15 s once daily (UNPL); (iv) from d 1 to 14 and from d 15 to 28, chicks were subjected to PL and UNPL, respectively (PL-UNPL); and (v) from d 1 to 14 and from d 15 to 28, chicks were subjected to UNPL and PL, respectively (UNPL-PL). On d 42, birds from each treatment group were road-transported for 3 h. Heat shock protein (hsp) 70 expression, plasma levels of corticosterone, serum creatine kinase concentration, heterophil/lymphocyte ratios (HLR), and tonic immobility duration were determined pre- and posttransit. There were significant (P < 0.05) duration of transportation × human contact treatment interactions for HLR and hsp 70 density. Following transit, the PL chicks had significantly (P < 0.05) lower HLR and greater hsp 70 density than the other groups. The corticosterone of PL and UNPL chicks were lower than their control, PL-UNPL, and UNPL-PL counterparts. The PL and PL-UNPL treatments were effective in shortening tonic immobility duration significantly (P < 0.05). Except for UNPL-PL, the serum creatine kinase activity of PL was significantly lower than the other groups. In conclusion, subjecting birds to pleasant human contact reduced stress and fear reactions to transportation by enhancing the ability to express hsp 70 in the brain. Unpleasant human contact had adverse effect on the birds' response to transportation. Early age pleasant experience with humans failed to negate the adverse effects of subsequent unpleasant contact.

Physiology and behavior of the hen during induced molt

Feed deprivation has been adopted by the commercial egg industry to induce molt because it is the easiest method to apply and produces the best results. Feed deprivation, however, raises concerns about animal welfare. Birds respond to long-term feed deprivation in three phases. The first phase lasts at most a few days, during which physiological and behavioral adjustments ultimately reduce protein catabolism and energy expenditure. A temporary increase in plasma corticosterone may be observed at this time. Corticosterone promotes gluconeogenesis, helping to maintain plasma glucose levels in the initial stage of the fast. The corticosterone increase may also be linked to increased activity in feed-deprived birds. Hens have been observed to manifest temporarily increased levels of alertness and activity during the first 48 h of feed deprivation. Aggressive behavior of hens also has been observed to increase briefly during the first day of feed deprivation. The second phase is the longest, during which proteins are spared and lipids are catabolized to provide energy. This phase may last several months in some species; in the chicken it can continue more than 20 d. Hens show increasing amounts of resting behavior during this phase. The third phase begins when protein catabolism accelerates. A pathological stage eventually is reached when the bird will cease activity and no longer eat. The phased response to feed deprivation optimizes a tradeoff between the need to maintain constant levels of plasma glucose to sustain activity and the need to preserve critical body structures such as muscles and organs. Hens are capable of vigorous activity throughout feed deprivation periods typical of induced molts, which do not appear to take birds beyond the second phase of fasting. Hens having undergone extended fasts may also have improved livability. Alternative induced molting methods are being sought to reduce animal welfare concerns. The methods of current interest involve alteration of feeding regimen and cause at least some body weight loss. These alternative methods should be evaluated to ensure that they do not actually make aspects of hen welfare worse compared to feed withdrawal, which might happen if hens perceive feed restriction without being allowed to progress fully into the second phase of adaptation to feed deprivation.

Effect of naked neck gene (NA) and frizzle gene (F) on immunocompetence in chickens

1. A total of 98 birds belonging to 4 genetic groups from two specialised populations--heterozygous naked neck (NA*NA/NA*N) and normally feathered (NA*N/NA*N) from one specialised population and heterozygous frizzle (F*F/F*N) and normally feathered (F*N/F*N) from another specialised population--were evaluated for general immunocompetence by assessing antibody response to SRBC, haemolytic complement level in the serum, in-vivo cell mediated immune (CMI) response to Concanavalin-A (Con-A) and a phagocytic index at 10-12 weeks of age. 2. The naked neck gene did not seem to influence the antibody response to SRBC, CMI to Con-A or the phagocytic index. However, significantly higher haemolytic complement level in serum was observed in birds carrying a copy of the NA mutation as compared to the normally feathered birds. 3. Similar trends were observed for the frizzle gene.

Genotype-by-Environment Interaction with Broiler Genotypes Differing in Growth Rate: 2. The Effects of High Ambient Temperature on Dwarf Versus Normal Broilers

High ambient temperatures (AT) reduce feed consumption (FC) and BW in broilers, thereby leading to lower efficiency and profitability of poultry meat production in hot climates. These negative effects have been found to be more pronounced in chicken lines with high BW. The effects of high AT were investigated in a broiler population segregating for the Dw gene and, thus, consisting of normal-sized and dwarf broilers, which differed markedly in BW but had the same genetic background. All chicks were reared under normal AT (constant 22 C) up to Day 44, when AT was gradually raised, over 24 h, to 32 C and then held constant to Day 49. The dwarf chicks had 23% lower BW and BW gain (WG) at all ages until Day 44. During the first 24 h at 32 C, FC of the dwarf broilers was reduced by 35% and their average WG was 7.6 g/d, whereas FC of their normal-sized counterparts was reduced by 46% and they lost BW (average WG: -42.1 g/d). Thereafter, however, the dwarf and normal broilers adapted similarly to the chronic heat stress, with FC and WG of both phenotypes averaging 72 and 35%, respectively, of the corresponding means at normal AT. The two phenotypes had similar body temperatures at normal AT, but following its increase, body temperature in the normal-sized broilers rose by 1.14 C, whereas in the dwarf ones it rose by only 0.47 C. This finding suggested better thermoregulation during acute heat stress, apparently due to the latter's smaller body size. Under chronic heat stress, however, FC and WG were similarly reduced in the dwarf and normal broilers. We concluded that the dwarf gene has no value with regards to broiler tolerance to chronic heat stress, either for production or as a model.

The effect of early age feed restriction on subsequent response to high environmental temperatures in female broiler chickens

This study was conducted to determine whether early age feed restriction improves heat tolerance in female broiler chickens. Chicks were brooded for 3 wk and then maintained at 24+/-1 C. On Day 0, chicks were assigned to one of four feeding regimens; each regimen was applied to four cages of chicks. The feeding regimens were 1) ad libitum feeding (ALF); 2) 40% feed restriction at 4, 5, and 6 d of age (F40); 3) 60% feed restriction at 4, 5, and 6 d of age (F60); and (4) 80% feed restriction at 4, 5, and 6 d of age (F80). From 35 to 41 d of age, all birds were exposed to 38+/-1 C for 2 h/d. Serum concentrations of glucose were elevated by the heat challenge, but were not affected by the feeding regimen. The heat treatment resulted in hypocholesteremia among ALF and F80 chicks, whereas the concentrations increased and remained constant in the F60 and F40 birds, respectively. Subjecting chicks to F60 improved growth and survivability and reduced heterophil to lymphocyte ratios (H/L) in response to the heat treatment as compared with the ALF and F80 regimens. The survivability rate and H/L of F40 chicks were similar to those attained by chicks on other regimens. Newcastle disease antibody titer of ALF birds declined with duration of heat treatment. It is concluded that the F60 regimen is beneficial for alleviating, at least in part, the detrimental effects of heat stress in female broiler chickens.

Anticoccidial vaccination of broiler chickens in various management programmes: relationship between oocyst accumulation in litter and the development of protective immunity

Paracox anticoccidial vaccine was administered to a 7-day-old flock of commercial broiler breeder stock subsequently reared to point-of-lay in the same house. For comparison, three subgroups of another flock of broiler breeders were also vaccinated with Paracox at 7 days of age, reared to 42 days and then transferred to new litter on another farm until point-of-lay. The first subgroup received no further treatment, but the second and third each received a second vaccination with Paracox, either immediately after transfer to the new litter or 42 days after transfer. Using an Eiomeria necatrix model, protective immunity was demonstrated by virulent challenge of samples of birds from all groups by the age of 37-40 days (30-33 days after the first vaccination), and was maintained to at least 122-125 days of age, whether the birds remained on the same litter or were transferred to another farm, and whether they received one or two anticoccidial vaccinations. Therefore, there is no disadvantage in transferring birds onto new litter 35 days after a single Paracox vaccination, nor is there any advantage in giving a second vaccination after such a transfer. Vaccinated birds seeded the new litter with oocysts, despite being clinically immune to coccidiosis. A supplementary laboratory experiment showed that birds vaccinated at 8 days of age passed almost no oocysts after a second vaccination at 43 days of age. This indicated that they were not only protected against clinical coccidiosis, but were almost solidly immune to a homologous infection 5 weeks after a single vaccination. Nevertheless, oocysts appeared in the litter of all four groups of commercial breeders throughout the trial, showing that wild-type heterologous infections occurred whether the birds were transferred to new litter or not, but these did not overwhelm the acquired protective immunity and cause clinical coccidiosis.

Effects of dietary protein on restrict-fed broiler breeder pullets during a coccidial challenge

In each of two experiments with young, feed-restricted broiler breeder pullets, the effects of differences in dietary protein intake on intestinal development and growth were studied. All pullets were restrict-fed either a 15 or 19% CP diet to see whether differences in dietary protein would influence intestinal growth in the face of controlled exposure to coccidiosis. In each experiment, pullets were vaccinated with one of three dilutions of Coccivac (control, 1X, 4X), each level representing a different proportion of the manufacturers' suggested dosage level. Experiment 1 was conducted in battery cages with wire floors, and no infection was established, most likely because of a lack of oocyst recycling. The pullets that were restrict-fed the 19% CP diet had a significantly heavier Pectoralis major breast muscle weight at 14 and 21 d postvaccination (PV) and heavier BW at 21 d PV. Experiment 2 was conducted in floor pens with litter. In this experiment, coccidiosis was successfully established as coccidial oocysts invaded the mucosal cells of the villi in the upper small intestine. Pullets fed the 19% CP diet had significantly heavier BW at 14, 28, and 35 d of age. There were, however, no significant effects caused by level of dietary protein or vaccination dose on intestinal development (villus height and crypt depth). In conclusion, mild coccidial infections induced via the administration of commercial anticoccidial vaccines do not warrant changes in dietary protein during the onset of feed restriction in young broiler breeder pullets.

Influence of body weight restriction in a body-weight-selected line of turkeys on response to challenge with Pasteurella multocida

Previous research has shown that a line (F) of turkeys selected long-term for increased 16-wk BW was more susceptible to challenge with washed Pasteurella multocida (PM) than a randombred control line (RBC2), the base population of the F line. Published research indicated that the mortality of the F line following challenge with PM was similar to that of two commercial sire lines. The purpose of the present study was to determine the influence of reducing BW of the F line to that of the RBC2 line by nutrient restriction on resistance to PM. Four challenge trials were conducted over a 2-yr period. The BW of a group of F line birds was restricted to that of the RBC2 line by limiting access to feed from 1 to 6 wk of age. The F line restricted birds and full-fed RBC2 and F line birds were challenged with a field isolate of washed PM (1.2x10(7) organisms/bird of capsular serogroup A and somatic serotype 3, 4) at 6 wk of age. Birds were checked twice daily for 14 d. Resistance to PM was measured by days to death of those that died and percentage mortality. The BW of the restricted group of the F line did not differ from full-fed RBC2 birds for males or females. In males, the restricted F line birds had similar mortality (48.0%) to the full-fed RBC2 line birds (44.3%), and the mortalities in both groups were significantly lower than that observed for the full-fed F line birds (81.3%) following challenge with PM. The mortality following challenge in females did not differ significantly among groups, even though mortality of the full-fed F line birds (64.1%) and restricted F line birds (63.3%) was more than 9% higher than that (54.2%) observed for the full-fed RBC2 line birds. Days to death was not a sensitive indicator of resistance to PM, as no differences among the three groups of birds were observed for either sex.

Effect of feed withdrawal or challenge with Pasteurella multocida on growth, blood metabolites, circulating growth hormone, and insulin-like growth factor-I concentrations in eight-week-old turkeys

The daily effects of feed withdrawal or a bacterial disease (Pasteurella multocida; PM) challenge was studied in a slow-growing line of turkeys. The following groups (n = 6 birds/group) were sampled for up to 13 d: untreated control (CON), 4-d feed withdrawal followed by refeeding (FAST), a group that succumbed within the first 2 to 3 d after PM challenge (E-DEAD), a group that succumbed 8 to 9 d after PM challenge (L-DEAD), a group that survived the PM challenge (SUR), and a group treated with both PM challenge and 4-d feed withdrawal followed by refeeding (FAST/CHAL). Daily feed intake and BW gains were markedly reduced in the E-DEAD and L-DEAD groups immediately and 3 d after PM challenge, respectively. Feed intake and BW gain between CON and SUR groups of turkeys were not different throughout the trial. The turkeys in the FAST group followed the expected feed withdrawal and refeeding patterns for feed intake and BW loss or gain. The FAST/CHAL turkeys consumed the minimal amount of feed to maintain BW after refeeding. Plasma uric acid sharply increased 1 d prior to death in both E-DEAD and L-DEAD groups of turkeys. Plasma uric acid also increased each consecutive day during fasting in the FAST and FAST/CHAL groups of turkeys. Plasma growth hormone was measured in only the CON and FAST groups and increased from about 40 to 85 ng/mL in the FAST group during fasting but returned to control levels within 1 d of refeeding. Circulating plasma insulin-like growth factor-I (IGF-I) decreased from about 17 to 5 ng/mL in the PM-challenged (E-DEAD, L-DEAD, and FAST/CHAL groups) and FAST groups. The concentration of IGF-I returned to prefeed withdrawal levels within 3 d of refeeding the FAST group of turkeys. It was concluded that 1) turkey poults that were not susceptible to the PM challenge generally maintained physiological functions at control bird levels, 2) susceptible turkey poults generally exhibited depressed feed intake and BW gains, and 3) poults challenged with both feed withdrawal and PM treatment responded differently than poults challenged with either feed withdrawal or challenge with PM. The depletion of energy intake and mobilization of energy stores in susceptible poults might have contributed to the rate at which PM caused the poults to die.

Dietary modulation of avian coccidiosis

During the past several years, our laboratory has been investigating the anticoccidial activities of various natural products that have potential use as dietary supplements for coccidiosis control. Sources of fats containing high concentrations of n-3 fatty acids such as menhaden oil and flaxseed oil and flaxseed, when added to starter rations and fed to chicks from one day of age, effectively reduce lesions caused by the caecal parasite Eimeria tenella, but not lesions caused by Eimeria maxima. Our results are consistent with reports of effects of diets high in n-3 fatty acids on other protozoan parasites which suggest that the state of oxidative stress induced by these diets in the cells of both host and parasites is responsible for their parasitic actions. Artemisinin, a naturally occurring (Artemisia annua) endoperoxide and effective antimalarial significantly lowers lesions from E. tenella when given at low levels as a feed additive. The mechanism of its action is also considered to involve induction of oxidative stress. Diets supplemented with 8 p.p.m. gamma-tocopherol (abundant in flaxseeds) or with 1% of the spice tumeric, reduce mid-small intestinal lesion scores and improve weight gains during E. maxima infections. These compounds may exert their anticoccidial activity because they are effective antioxidants. Betaine, a choline analogue found in high concentrations in sugar beets, improves nutrient utilisation by animals under stress. When provided as a dietary supplement at a level of 0.15% it has enhanced the anticoccidial activity of the ionophore, salinomycin. Betaine may act as an osmoprotectant whereby it improves the integrity and function of the infected intestinal mucosa. In in vivo studies, betaine plus salinomycin significantly inhibit invasion of both E. tenella and E. acervulina. However, subsequent development of E. acervulina is inhibited more effectively with this combination treatment than development of E. tenella.

Comparison of outbred lines of chickens for resistance to experimental infection with coccidiosis (Eimeria tenella)

Coccidiosis causes dramatic economic losses in the poultry industry. Next to the extensive use of anticoccidial drugs, improving genetic resistance of birds to this parasitic disease represents an attractive alternative. An experiment was run in order to identify lines of chickens resistant and susceptible to coccidiosis as a tool to search for genetic markers of resistance. Five outbred lines were used: two Egyptian lines (Mandarah and Fayoumi), a Rhode Island Red line, and two White Leghorn lines (WLB21 and WLDW). The WLDW line segregated for three MHC haplotypes, B15, B19, and B21, and for the sex-linked dwarf gene, DW. Chicks were challenged at 4 wk of age with a high dose of Eimeria tenella (150,000 oocysts) and slaughtered 8 d postinoculation. Innate resistance was assessed individually by measures of lesion score, mortality, and body weight gain at slaughter, and plasma coloration 4 d postinoculation. Large differences in resistance to E. tenella were observed between lines. The Fayoumi line appeared clearly as the most resistant line, showing no mortality, less severe lesions than other lines, and a 30% reduction of growth as compared to control birds. The WLDW line was the most susceptible, with 27% mortality and a 85% reduction in growth. No major effect of MHC or dwarfism on resistance to E. tenella was found.

Impact of cage density on pullet performance and blood parameters of stress

The effects of cage density on pullet live performance and blood indices of stress were evaluated in two commercial White Leghorn strains housed at 38, 32, 26, and 20 birds per cage from Day 1 to 6 wk of age, and 19, 16, 13, and 10 birds per cage from 6 to 18 wk. Cage densities of 26 and 13 birds per cage represent a U.S. standard of 142 and 284 cm2 per bird that is often applied in commercial pullet rearing. Cage density treatments include confounding cage, feeder, and drinker spaces per bird as might be encountered in commercial practice when growing more pullets per cage. Body weight was significantly reduced at greater bird densities in both strains; however, one strain was affected as early as 6 wk of age, whereas in the other strain, body weight was not reduced significantly until 18 wk. Feed intake was increased by more than 13% in both strains at the lowest density treatment (20 birds per cage) from Day 1 to 2 wk but reduced by more than 9% by higher cage densities during the remainder of the study. Feed conversion (FC) ratio was similarly improved (i.e., reduced) when more pullets were housed per cage, and increased when fewer birds were placed per cage compared to the standard. Despite a significant reduction in feed intake and a corresponding loss of body weight, cage density treatments had no significant affect on hemagglutinin titers to sheep red blood cell antigen, percentage heterophils (H), lymphocytes (L), or the H:L ratio. However, pullet age and strain differences were observed for all blood parameters. Overall, treatments allowing more cage, feeder, and drinker spaces per bird than the U.S. commercial standard provided no body weight advantage, and allowed for greater feed intake and poorer FC at several ages.

Immunoresponsiveness of fast-growing chickens as influenced by feeding regimen

1. Immunoresponsiveness and disease resistance were measured in broiler males maintained on ad libitum feeding throughout or on alternate-day feeding. Alternate-day restrictions were started 1 and 2 d after hatch so that on any one day there were chicks fed and fasted. 2. Severity of response to E. coli challenge as measured by lesion scores, and mortality was greater for chicks fed ad libitum than those fed on alternate days. For chicks fed on alternate days, lesion scores were lower for those without access to feed for the 24-h period immediately after challenge. 3. Spleen weights, the indicator of response to marble spleen disease virus challenge, were higher for chicks fed ad libitum than those fed on alternate days. 4. Antibody response to sheep red blood cell antigen was not affected by feeding regimen. 5. Ratios of heterophils to lymphocytes were higher for chicks given access to feed for the previous 24-h period than for those fasted during the previous 24-h or those that had been fed ad libitum. 6. Results of this experiment suggest that for alternate-day feeding programs, vaccination be administered on the day that chicks are not fed.

Feeding regimen by sire family interactions on growth, immunocompetence, and disease resistance in chickens

Progeny from matings of 12 sires from a White Plymouth Rock line selected for high juvenile BW and 96 dams from a White Leghorn line selected for low antibody production to SRBC were reared under alternate-day (AD) or ad libitum (AL) feeding regimens. Within a feeding regimen males were heavier than females, and within a sex, chicks fed AL were heavier than those fed AD. Feeding regimen by sire family interactions were significant for BW at 21 d of age for both male and female progeny. The interaction was due to differences among sires in the magnitude of the AD: AL relationship. Product moment correlation coefficients between feeding regimens for male and female progeny of sire families for 21-d BW were essentially zero, which was consistent with the sire family by feeding regimen interactions observed at this age. At 41 d of age, relative to BW, weights of empty esophagus plus crop and of crop contents were greater for AD than AL chicks. There were differences among sire families for crop content and breast weights relative to BW. Lesion scores to Escherichia coli challenge were lower and antibody titers to SRBC antigen were higher in AD than in AL chicks. Sire families differed in antibody titers to SRBC antigen. Feeding regimen by sire family interactions were significant for percentage change in BW 144 h after E. coli challenge and lesion scores were greater for AL than AD chicks.

Growth, immunoresponsiveness, and disease resistance of diverse stocks of chickens reared under two nutritional regimens

Growth, immunocompetence, and disease resistance were measured in a commercial broiler stock (BC), a commercial white-egg-layer stock (LC), and a White Plymouth Rock line selected for high juvenile BW (HW) under dietary regimes differing in protein and energy content. Diet E had 20% more protein and 17% more ME than Diet A. Stock by sex interactions were significant for BW at 28 and 36 d of age because sexual dimorphism occurred at younger ages in the meat than in the layer stocks. When inoculated with .1 mL of a .25 or 2.50% suspension of SRBC, diet by stock interactions were significant for antibody titers 6 d postinoculation (PI) at the lower dosage. Interactions were not present at the higher dosage or for either dosage 13 d PI. Diet by stock interactions were significant at both dosages for change in SRBC titers from 6 to 13 d PI. The interactions resulted from a significantly smaller decline in BC than HW or LC chicks fed Diet A, whereas all stocks responded similarly when fed Diet E. A significant decline in rate of BW gain was observed in chicks inoculated with marble spleen disease virus (MSDV), with the increase in relative weight of spleen significantly greater for LC than HW or BC chicks 6 d PI. When heterophil to lymphocyte ratios were used as an assay of response to MSDV challenge, rations were significantly higher for HW chicks fed Diet A than for chicks fed Diet E and for LC chicks fed Diet E than for chicks fed Diet A, but not different for BC chicks on the two diets.

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.

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.