S. Özkan

Responses to heat stress in commercial and local broiler stocks. 1. Performance traits

1. This study investigated effects of conditioning at 5 d of age and food restriction during a hot period on responses to prolonged heat stress of two fast (G1 and G2) and one slower-growing (G3) broiler stocks. 2. Chicks from each stock were divided into 3 groups: control, conditioned (chicks exposed to 36°C for 24 h at 5 d of age) and food restricted (during the heat stress food was withdrawn 2 h before the hot period and chicks were fed between 17.00 and 08.00 h). Prolonged heat stress was induced daily from 28 to 49 d by heating until the ambient temperature reached 32° to 35°C between 10.00 and 17.00 h. 3. Body weights, mortality and rectal temperatures were lower and food conversion higher for stock G3 than G1 or G2. 4. Management procedures used in this study improved food conversion and lowered mortality without affecting body weight. Rectal temperatures of the treated groups were similar to those of the controls.

Effect of dietary methionine on performance, carcase characteristics and breast meat composition of heterozygous naked neck (Na/na+) birds under spring and summer conditions

1. Heterozygous naked neck (Na/na+) birds and their normally feathered counterparts (na+/na+) were fed from 0 to 7 weeks on 3 diets differing in methionine concentrations. From 0 to 3 and 3 to 7 weeks, respectively, the concentrations were: low containing 4.3 and 3.3 g/kg; optimum containing 5.0 and 3.8 g/kg and; high with 5.7 and 4.4 g/kg under spring (optimum ambient temperature) and summer conditions (high ambient temperature). Performance, carcase characteristics and breast meat chemical composition were determined. 2. Summer rearing resulted in a decrease in body weight, body weight gain, food consumption, and yields of carcase and breast. The summer temperature effect was more pronounced in males. Under summer temperatures, the protein content of the breast decreased while the fat content increased compared to birds reared in spring. 3. By 7 weeks of age, both genotypes reached similar body weights in the spring experiment while, in summer Na/na+ birds were 3.3% heavier and gained more in the period from 3 to 7 weeks than na+/na+ birds. Carcase and breast yields of Na/na+ birds were greater than in na+/na+ birds. 3. Second order polynomial coefficients of the dietary methionine effect were found to be significant for body weight at 3 and 7 weeks. Daily body weight gain between 3 and 7 weeks was linearly affected by the dietary methionine concentration. There was no interaction between genotype and methionine. 4. Methionine had no significant effect on carcase yield. Second order polynomial coefficients of the dietary methionine effect were found to be significant for breast yield while the methionine effect on abdominal fat was linear. Na/na+ females fed on the low methionine diet had lower protein content than the Na/na+ males. 5. It is concluded that the methionine requirement of Na/na+ birds did not differ from that of their normally feathered counterparts under either spring or summer ambient temperature conditions.

The effect of short-term fasting on performance traits and rectal temperature of broilers during the summer season.

1. The present study was conducted to determine if detrimental effects of high temperature on broiler performance could be overcome by short-term fasting and to examine the effect of food withdrawal on the responses of two commercial strains (S1 and S2). 2. An experimental design was used with three feeding groups and two strains. Birds in the control (C) group were fed ad libitum during the experimental period (0 to 6 weeks), while feed was withdrawn in the other groups between 10:00 and 16:00 h during weeks 5 and 6 (F1) or week 6 (F2), respectively. After standard brooding for the first 3 weeks temperature and humidity varied according to outside climate between 4 and 6 weeks of age. 3. Feeding strategy significantly affected body weight at week 6 (BW6) and daily weight gain during week 6 (DWG5-6). F2 gave the best results in BW6 and DWG5-6. Strain effect was significant on DWG4-5 and DWG5-6; S1 had higher DWG4-5 and S2 gained more at the last stage. S1C broilers had greater BW6 than S2C but the S2 strain gave a better response to short-term fasting compared with S1 and this resulted in significant strain by feeding interaction effect on BW6 and DWG5-6. 4. It was shown that short-term fasting was an effective method for controlling rectal temperature (RT) of broilers at 5 and 6 weeks of age. 5. Total food consumption (FC0-6), food conversion ratio (FCR0-6), mortality, and carcase characteristics were not affected by short-term fasting in the experimental conditions. 6. In conclusion, it can be recommended that broiler producers may practise 6 h of fasting during the hot period of the day without any adverse effect on slaughter weight and FCR when the birds are close to the average slaughter weight and a heat wave is expected. Strain differences in RT measurements also indicate the importance of choosing strains to be used in hot and warm climate conditions with attention to the thermoregulation ability of broilers.

Dietary vitamin E (α-tocopherol acetate) and selenium supplementation from different sources: performance, ascites-related variables and antioxidant status in broilers reared at low and optimum temperatures

1. This study compared the effect of dietary supplementation with organic or inorganic selenium (Se) sources plus control amounts or large amounts of vitamin E (α-tocopherol acetate) in broilers raised at control (20 to 24°C) or low (14·5 to 16·8°C) temperatures after 2 weeks of age. 2. The following dietary treatments were used from one day old. Diet 1, the control diet, comprised a commercial diet containing 0·15 mg/kg inorganic Se and 50 mg vitamin E/kg feed. Diet 2 was the same as diet 1, supplemented with 0·15 mg/kg inorganic Se. Diet 3 was the same as diet 2 but was supplemented with 200 mg/kg vitamin E. Diet 4 was the same as diet 1, but inorganic Se was replaced with 0·30 mg/kg organic Se. Diet 5 was the same as diet 4, supplemented with 200 mg/kg vitamin E. 3. Low temperature reduced the growth rate of broilers; however, at 6 weeks, there were no differences in the body weights of birds fed on organic Se supplemented diets housed at low or control temperature. The feed conversion ratio was significantly affected by low temperature but not by diet. The heterophil/lymphocyte ratio was higher in chicks after one week in the cold, indicating mild stress. Blood triiodothyronine levels were significantly higher in birds after 1 and 4 weeks in the cold but thyroxin was not affected. 4. Organic Se supplementation increased relative lung weight at the control temperature, which might lead to greater respiratory capacity. Relative spleen weight significantly decreased in broilers fed diets supplemented with inorganic Se under cold conditions, a possible indication of chronic oxidative stress. 5. At the low temperature, supplementation with organic Se alone, or with inorganic Se and vitamin E increased glutathione peroxidase (GSHPx) activity and glutathione (GSH) concentration in the liver of broilers, which may indicate increased activity of birds’ antioxidant defence against suboptimal environments.

The effects of feed restriction and ambient temperature on growth and ascites mortality of broilers reared at high altitude

The development of ascites was investigated in broilers at low versus high altitudes, cold versus normal ambient temperatures (AT), and 3 feeding regimens. One-day-old chicks obtained at sea level were reared at high altitude (highA; 1,720 m; n = 576) with 2 AT treatments, low AT from 3 wk onward at highA (highA/cold) and normal AT from 3 wk onward at highA (highA/norm), or at sea level (normal AT from 3 wk onward at low altitude, lowA/norm; n = 540). Under highA/cold, AT ranged between 16 to 17 degrees C in the fourth week, 17 to 19 degrees C in the fifth week, and 19 to 21 degrees C thereafter. Under highA/norm and lowA/norm, AT was 24 degrees C in the fourth week and ranged between 22 to 24 degrees C thereafter. Broilers in each condition were divided into 3 groups: feed restriction (FR) from 7 to 14 d, FR from 7 to 21 d, and ad libitum (AL). Ascites mortality and related parameters were recorded. Low mortality (0.4%) occurred under lowA/norm conditions. Under highA/norm, mortality was lower in females (8.6%) than in males (13.8%) and was not affected by the feeding regimen. The highA/cold treatment resulted in higher mortality but only in males; it was 44.2% among highA/cold AL-fed males and only about 26% under the FR regimens, suggesting that FR helped some males to better acclimatize to the highA/cold environment and avoid ascites. However, mortality was only 13.3% in AL-fed males at highA/norm and FR did not further reduce the incidence of ascites under these conditions. Thus, avoiding low AT in the poultry house by slight heating was more effective than FR in reducing ascites mortality at highA. Compared with FR from 7 to 14 d, FR from 7 to 21 d did not further reduce mortality and reduced growth. At 47 d, the majority of surviving broilers at highA had high levels of hematocrit and right ventricle:total ventricle weight ratio (>0.29), but they were healthy and reached approximately the same BW as their counterparts at low altitude. This finding may suggest that in broilers reared at highA from day of hatch, the elevation in hematocrit and in right ventricle:total ventricle weight ratio happens gradually and therefore is not necessarily indicative of ascites development.

Influence of dietary energy on bird performance, carcase parts yields and nutrient composition of breast meat of heterozygous naked neck broilers reared at natural optimum and summer temperatures.

1. Heterozygous naked neck birds were raised under natural spring (average 21.2 degrees C) and summer temperatures (average 27.1 degrees C) to investigate the influence of dietary energy on broiler performance, carcase yield and nutrient composition of breast meat. 2. Birds were fed on a low energy diet of 12.12 MJ ME/kg, a medium energy diet of 12.96 MJ ME/kg and a high energy diet of 13.79 MJ ME/kg with 2 protein concentrations per energy treatment, 230 and 200 g/kg, from 0 to 3 and 3 to 7 weeks of age, respectively. 3. Summer rearing resulted in a decrease in body weight, body weight gain, carcase weight and carcase part yields of birds. 4. Increasing dietary energy from 12.12 to 13.79 MJ ME/kg increased body weight at 3 and 7 weeks, body weight gains from 0 to 3 and 3 to 7 weeks, carcase weights and relative abdominal fat weights of birds in a linear manner. There was no effect of dietary energy on the nutrient composition of breast meat. 5. It was concluded that there was no differences in dietary energy requirements of heterozygous naked neck birds when grown under natural optimum (21.2 degrees C) and summer temperatures (27.1 degrees C).

Photoperiodic lighting (16 hours of light:8 hours of dark) programs during incubation: 1. Effects on growth and circadian physiological traits of embryos and early stress response of broiler chickens

This study was conducted to evaluate the effect of a 16L:8D photoperiod during incubation, either during the whole incubation period (Inc(0-21d)) or the last week of incubation (Inc(14-21d)), on embryo growth, incubation performance, and light:dark rhythm of plasma melatonin and corticosterone in relation to early stress responses of newly hatched chicks to the posthatching environment. A dark incubation condition (Inc(Dark)) served as control. Three batches of eggs (n = 1,080, 1,320, 720) from Ross 308 broiler breeders were used in the experiment. Embryos from Inc(0-21d) presented a daily rhythm of melatonin at internal pipping and hatching, but Inc(Dark) embryos did not. The Inc(14-21d) group had rhythmic plasma melatonin at hatching only. A L:D rhythm of corticosterone was apparent at hatching. A significant incubation × sampling time interaction suggested that a lower increment in blood corticosterone level in Inc(0-21d) at 8 h posthatching (light period), as compared with hatching (dark period) values, might be associated with probable changes in the hypothalamic-pituitary-adrenal axis in Inc(0-21d) through incubation lighting. This finding may also suggest improved adaptation to the posthatching environment. Incubation lighting did not consistently affect brain malondialdehyde concentration; the only difference between groups was higher concentrations at hatching in Inc(14-21d), whereas incubation groups at the internal pipping stage had similar values. Mean relative asymmetry (RA) did not differ with incubation lighting. The malondialdehyde and RA results indicate that neither lighting nor darkness during the overall incubation exacerbated embryo oxidative and developmental stress. An increased breast muscle weight was observed at hatching only in Inc(14-21d). The Inc(0-21d) group had increased embryo weights relative to egg weight and decreased residual yolk but had no effect on chick weight, relative heart and liver (% of embryo weight), hatchability, embryo mortality, incubation time, oxidative stress, or mean RA. In conclusion, these results provide further evidence that photoperiodic lighting during incubation (Inc(0-21d)) may improve adaptation of chicks to a novel environment at hatching, possibly giving birds a better start for early posthatching development.

Responses to heat stress in commercial and local broiler stocks. 2. Developmental stability of bilateral traits.

1. Developmental stability of bilaterally symmetrical traits was measured in two fast (G1 and G2) and one slower growing (G3) broiler stocks when conditioned (chicks exposed to 36°C for 24 h at 5 d of age) or food restricted (food withdrawn 2 h before the hot period and chicks fed between 17.00 and 08.00 h) during heat stress administered daily from 28 to 49 d of age. 2. Length of face, length, width and weight of shanks, weights of P. major and P. minor muscles, and weights of lung and caeca were chosen as bilateral traits representative of skeletal, muscle, respiratory and digestive systems. 3. Development of skeletal bilateral traits was affected primarily by genotype and sex. The heart:lung ratio decreased with conditioning in stocks G1 and G2 at 21 d. Face length, shank length and shank weight exhibited antisymmetry, whereas shank width and weights of P. minor , lung and caeca exhibited fluctuating asymmetry and antisymmetry. For P. major weight, there was directional asymmetry. 4. In general, relative asymmetry of skeletal traits was lower than for traits associated with muscle and with respiratory and digestive systems. Relative asymmetry of P. major weight was lower in conditioned and G3 broilers than in their respective counterparts. 5. If relative asymmetry is a valid indicator, item heat stress may be less in slower growing and conditioned broilers.

Photoperiodic lighting (16 hours of light:8 hours of dark) programs during incubation: 2. Effects on early posthatching growth, blood physiology, and production performance in broiler chickens in relation to posthatching lighting programs

Photoperiodic incubation lighting might improve bird adaptation to a novel environment at hatching for a better start in early posthatching development. We evaluated the effect of 16L:8D lighting for either the whole incubation period (Inc(0-21d)) or the last week of incubation (Inc(14-21d)) on early posthatching growth, blood melatonin, and corticosterone at 6 d as well as malondialdehyde levels in brain tissue, relative asymmetry, and overall broiler performance as an interaction with the posthatching lighting programs. Dark incubation conditions (Inc(Dark)) served as control. There were 3 incubation batches in the experiment. Chicks from 2 of 3 batches were reared either at 16L:8D or under continuous lighting (24 h) through 6 d posthatching. Batch 3 chicks were reared to 35 d under either 16L:8D or 23L:1D. The main finding was a significant incubation × posthatching lighting interaction for 35-d BW in broilers. Although groups had similar BW under continuous lighting, Inc(0-21d) and Inc(14-21d) broilers were respectively 94 and 78 g heavier than Inc(Dark) birds under 16L:8D at 35 d. Lighted incubation groups increased 0 to 6 d of gain and had higher d-6 breast muscle weights with no effect on other traits measured. Posthatching 16L:8D reduced the gain and d-6 breast muscle. Significant incubation × posthatching lighting and posthatching lighting × sampling time interactions for blood melatonin may indicate that Inc(0-21d) affects melatonin diurnal rhythms even at 6 d under continuous light. Lower blood corticosterone levels on d 6 in Inc(0-21d) chicks reared under 16L:8D posthatching may support our hypothesis that incubation lighting can modify the bird stress response, probably affecting the hypothalamic-pituitary-adrenal axis during ontogeny, and may improve adaptation to a similar environment posthatching. The lower malondialdehyde concentration in brain tissue of Inc(0-21d) birds on d 6 may indicate lower lipid peroxidation and thus lower oxidative stress compared with Inc(Dark). These results provide further evidence that Inc(0-21d) may improve both bird adaptation to a similar photoperiodic environment and growth, probably through early entrainment of circadian physiology.

Effect of dietary protein regime on meat quality traits and carcase nutrient content of broilers from two commercial genotypes

1. The present study aimed to evaluate breast muscle quality and muscle myofibre density in two broiler genotypes given three dietary protein feeding regimes. 2. A total of 1440 Ross 308 and 708 broilers (720/genotype) were given one of three dietary protein regimes (Low: 192, 166 and 155 g/kg, Control: 229, 199 and 182 g/kg and High: 266, 235 and 207 g/kg for starter, grower and finisher diets respectively). On d 21 and 42, initial protein solubility, DNA and myofibre density were determined. On d 42, breast meat samples were collected for meat quality analyses. 3. There were no genotype effects on pH24, L*, a* or b* values. Thawing loss was higher in meat from the 708 than the 308 genotype. 4. Broilers given the low protein feeding regime had highest carcase fat, lowest pH24 and palest meat. The low regression coefficients between dietary protein content and changes in pH24 and lightness, however, demonstrated that dietary protein was not the principal factor influencing these traits. 5. Although sarcoplasmic protein solubility was similar among protein feeding regimes on d 21, the highest sarcoplasmic protein solubility on d 42 was in broilers on the high protein regime. 6. Myofibre density was highest in meat from broilers given the low protein regime. 7. It was concluded that dietary-protein content contributes significantly to both protein solubility and myofibre density.