Consequences to chicks hatched from Escherichia coli-inoculated embryos.

An Escherichia coli causing negligible mortality in embryonated chicken eggs was adapted to grow in media containing nalidixic acid. This isolate (EcNAL) was inoculated into 12-day-old embryonated eggs. Additional embryos inoculated with tryptose phosphate broth (TPB) served as controls. Six days later, all surviving eggs were moved to hatching units. One hatcher contained half of the TPB-inoculated eggs; the chicks hatching from these eggs served as negative controls. The EcNAL-inoculated eggs and the remaining TPB-inoculated eggs were moved to a second hatcher and allowed to hatch together; chicks hatching from these TPB-inoculated eggs served as contact controls. On day of hatch and at intervals thereafter, chicks from each of the treatment groups were sampled. Their body and yolk weights were recorded, and various tissues were cultured for the presence of the EcNAL bacterium. Hatchability of the EcNAL-inoculated embryos was markedly lower than that of either control group. Chicks from EcNAL-inoculated embryos also had low but detectable levels of mortality, lowered body weights, and increased yolk-to-body weight ratios. These same chicks had persistently high levels of EcNAL in the yolk and lower but detectable levels of the organism in the lungs and tracheas, which lasted a few days. The contact controls, on the other hand, were similar to the negative controls as far as having negligible mortality, steadily increasing body weights, and declining yolk-to-body weight ratios. However, in contrast to the negative controls, EcNAL was recovered primarily from the respiratory tract of the contact controls for a brief period of 3-4 days after hatch.     

Influence of hatching order and brood size on growth in jackass penguins

Jackass penguins Spheniscus demersus hatch two different-sized eggs asynchronously: the second-hatched chick, being, on average, 59% of the weight of the first-hatched chick on hatching. We examined the effect of hatching order on growth rates of mass, culmen length and culmen depth by comparing: (i) growth rates of first-and second-hatched chicks, and (ii) chicks from experimentally synchronized broods to chicks from normal asynchronous broods. Only growth rates in mass showed significant variation. Within a brood, B chicks grew more slowly than A chicks. The effect of synchronizing a brood was to lower the growth rate of both chicks to that of a B chick, suggesting that equal-sized siblings feed less efficiently. Chicks hatching from larger A eggs, that had been synchronized for age and size with chiçks from B eggs, did not grow faster, indicating that chicks hatching from A and B eggs do not have intrinsically different growth rates. Single-chick nests result usually from egg infertility. Singletons showed only a non-significant trend towards faster growth in mass than offspring in two-chick broods, even though food availability in one-chick nests should be better than in two-chick nests. Overall, hatching order had more impact on growth rates of mass than did brood size or egg dimensions.     

开食时间对雏鸡早期生长和内脏器官发育的影响

本试验旨在研究不同开食时间对雏鸡早期的生长性能及内脏器官发育的影响.试验选取1080只0日龄、体重相近的新扬州鸡雏鸡,根据开食时间不同,随机分成6个组,每个组3个重复,每个重复60只(30只公鸡,30只母鸡).出壳后一周内,每天从每个重复中随机挑选8只雏鸡(4公4母),分别称其活重后致死,取卵黄囊、肝脏、心脏、胰腺、法氏囊和小肠分别称重,测量小肠长度.结果表明,出壳后禁食36h对7日龄鸡体重没有显著负面影响,出壳后最长禁食时间不应超过60h.     

Lack of effect of oviposition time and parental age on chick weight when egg weight remains constant

1. An experiment was conducted utilising 480 eggs from broiler breeder hens to determine the effect of oviposition and parental age on 1-d-old chick weight when egg weight remained constant. 2. Neither the age of the breeder flock nor the time of oviposition had a significant effect on egg weight loss during the 18 d of incubation. Nor was there any effect on chick weight: egg weight ratio and 1-d-old chick weight when chicks were removed and weighed at the same time. 3. Hatching time was significantly affected by time of oviposition and age of parents. Afternoon eggs or eggs from older hens tended to hatch earlier than morning eggs or eggs from younger ones.     

Inter-relationship between egg weight, parental age and embryonic development

A clear positive correlation was evident between egg weight at setting and embryo weight at 18 d of incubation for eggs laid at or after 32 weeks of age. The weight of embryos from the same size eggs were found to depend upon a curvilinear function of the age of parent flock, with the largest increase in embryo weight occurring between 28 and 32 weeks of age. Hatching weight was highly correlated with egg size at setting. Flock age had no effect on hatching weight from a particular sized egg. Within any of the five ages studied, chicks from smaller eggs tended to hatch slightly (but not significantly) earlier than those from larger eggs.     

Effects of egg weight on the egg quality,chick quality,and broiler performance at the later stages of production (week 60) in broiler breeders

The objective of the present study was to determine the effect of broiler breeder egg weight on egg quality, chick quality, and broiler performance using Hubbard Classic broiler breeder flock. Hatching eggs from a commercial broiler breeder flock (Hubbard classic strain) were obtained at the age of 60 wk and divided into 3 egg-weight categories, namely small, medium, and large. For this purpose, 930 eggs having weights 63.09 ± 0.21, 68.85 ± 0.23, and 74.81 ± 0.11g were divided into 3 egg categories labeled small, medium, and large respectively. We further divided these eggs into 2 categories, eggs for quality parameters and eggs for incubation and posthatch performance parameters. Eggs from the small egg category had greater proportion of the shell weight and more shell strength. Egg weight did not significantly affect the albumen and yolk weight percentage. Egg weight affected the shape index and specific gravity for which lower values were observed for large eggs. Egg weight positively affected the chick weight, chick yield, and chick length (P < 0.05) of both male and female chicks. Results of the body weight gain showed that effect of egg weight on the posthatch performance of chick diminishes with the age of broilers. Egg weight significantly affected the body weight gain of male and female chicks up to 3 wk of age. Egg weights did not significantly affect the feed intake and mortality of broiler. Different egg-weight categories significantly affected the feed conversion ratio of female chicks at wk 2 and 3 of age and did not affect the feed conversion of male and female chicks at the end of wk 5. In conclusion, egg weight positively affected the chick characteristics (e.g., chick weight, chick length) and did not affect the final live body weight, feed conversion ratio, feed intake, and mortality in broilers.     

Effect of oxygen supplementation in the hatcher at high altitude on the incubation results of broiler eggs laid at low altitude

1. The object of this research was to investigate the effects of high altitude with supplementary oxygen during the last stage of incubation of broiler eggs laid at low altitude and incubated at low and high altitude. We analysed thyroid hormones and haematological variables. 2. The treatment groups were: low altitude (LA), high altitude with oxygen supplementation in the hatcher (HA-OX) and high altitude non-oxygen-supplemented (HA-NOX). 3. High altitude affected relative egg weight loss and early embryonic mortality. The hatchability of fertile eggs was lower at high than at low altitude. 4. Oxygen supplementation into the hatcher cabinet during the last stage of incubation decreased late embryonic mortality ratio (LEM(1)) and improved survival rates of embryos incubated at high altitude. 5. Eggs incubated at low altitude had a higher hatched chick weight and relative chick weight than those incubated at high altitude. Hatched chick weight and relative chick weight did not change with oxygen supplementation at high altitude. 6. High altitude caused an increase in plasma T(3) and T(4) concentrations as well as in the ratio of T(3):T(4) in embryos. High altitude newly hatched chicks showed a higher T(3):T(4) ratio than low altitude chicks; this ratio decreased with oxygen supplementation at high altitude. Altitude and oxygen supplementation did not affect the mean plasma T(4). 7. Newly-hatched chicks incubated at high altitude showed a higher plasma haematocrit (PCV) than the newly-hatched chicks from eggs incubated at low altitude. High altitude without supplementation increased haemoglobin (Hb), while oxygen supplementation returned the value to low altitude values.     

Effect of pre-incubation storage conditions on hatchability,chick weight at hatch and hatching time in broiler breeders

1. Eggs were stored for two different times at varying temperatures. The effects on hatchability, chick weight at hatch and hatching time were examined in two broiler breeder lines from 33 to 58 weeks of age. 2. Short storage (1 to 3 d). Storage at 20 degrees C compared with 16.5 degrees C reduced hatchability of all eggs set. No effect was observed on hatchability of fertile eggs, hatching time or chick weight. 3. Long storage (9 to 11 d). Storage at 16.5 degrees C compared with 10 degrees C decreased both hatchability of fertile eggs and chick weight at hatch. Incidence of early embryonic death increased and incubation time decreased at 16.5 degrees C compared with 10 degrees C. 4. Chicks from morning eggs were heavier than those from afternoon eggs irrespective of storage conditions. 5. Hatchability (all eggs set and fertile eggs) and chick weight varied with hen age irrespective of storage conditions. During long storage, hatching time varied with hen age independently of breeder line, storage temperature or egg laying time. 6. Hatchability (all eggs set and fertile eggs) was higher in line A than in line B. Line B eggs hatched later and produced heavier chicks than line A eggs irrespective of storage time.     

Relationship between the weight of hatching eggs and subsequent early performance of broiler chicks

1. The effect of egg weight on the subsequent performance of individual growing chicks was studied. Eggs from commercial broiler breeder hens were collected at 52, 55 and 57 weeks of age and incubated. The chicks were reared for 18 d. 2. Egg weight and hatched chick weight were not affected by the age of the hens during the 52 to 57-week period, but there was a close correlation between egg weight and hatching weight, irrespective of the age of the hens (r = 0.89). Chick:egg weight ratio at hatching was about 0.71 and independent of hen age. One d after hatching, chick weights had decreased by about 1.5 g. 3. The initial high correlation between egg weight and chick weight decreased markedly during post-hatching growth, becoming insignificant 5 d after hatching. At 18 d of age, however, chicks from eggs of older hens tended to be heavier than those from younger birds. The greater 18-d weights appeared to be associated more with higher food intake during that period, than with greater egg weight. 4. It was concluded that, in individual broiler chicks, the advantage of the initially higher weight attributable to a larger egg diminishes rapidly after hatching, and the main factor affecting final body weight is food intake.     

Development in culture of the chick embryo from cleavage to hatch

1. Early uterine embryos were obtained from hens by induced oviposition 7.5-8.0 h after the preceding egg was laid. They were cultured in vitro and then in recipient shells to hatch. As controls, embryos from freshly laid eggs were cultured in recipient shells to hatch. 2. For embryos cultured from uterine eggs, the hatch rate was 22.5%, and for embryos cultured from laid eggs, the hatch rate was 62.5%. 3. The weight of the chicks hatched from culture was about 60% of the weight of the preceding egg, or donor egg. Male and female chicks reached maturity and have produced viable offsprings. 4. The results show that it is possible to grow chick embryos in culture from the early cleavage stage (stage II) to hatch. They extend earlier findings on the culture of embryos from the blastoderm stage (Stage X) to hatch. The technique provides a basis for investigations on chick embryo cryopreservation.     

Effects of breeder age and egg weight on morphological changes in the small intestine of chicks during the hatch window

1. The objective of the study was to investigate the effects of breeder age and egg weight on hatching performance and morphological changes in segments of the small intestine of broiler chicks during a 21 h hatch window.

2. Eggs from Ross broiler breeder flocks aged 29 (young) and 48 weeks (old) were classified as light (LE) or heavy (HE) and incubated at the same conditions. At 475 h of incubation, eggs were checked every 3 h to determine time of external pipping and hatching. The first 42 chicks to emerge from each group were weighed and chick length was measured and 14 chicks from each group were sampled to collect residual yolk and intestine segments. The rest of chicks were placed back in the incubator and chick weight and length were measured individually at 9, 15 and 21 h after chicks hatched. At the end of 21 h, 14 chicks from each group were sampled again and the same procedure was followed.

3. The HE chicks pipped and hatched later than LE, regardless of breeder age. From hatch to the end of the hatch window, chick weight, but not yolk-free chick weight, gradually reduced. Relative residual yolk weight of chicks from both egg weights was similar at hatch, however, yolk sac utilisation was higher for LE chicks during the 21 h post-hatch period. At hatch, jejunum and ileum villus development was very similar for HE and LE chicks but greater development was observed for villus area with an increase in the jejunum villus length, width and goblet cell numbers in HE chicks.

4. The longest jejunum villus and the widest duodenum and jejunum villus were obtained for HE chicks from old breeders indicating that HE chicks from old breeders would have a greater surface area for nutrient absorption.     

胚蛋注射L-精氨酸对蛋雏鸡孵化性能、1~14日龄肠道发育及血清生化指标的影响

本试验旨在研究胚蛋注射L-精氨酸(L-Arg)对蛋雏鸡孵化性能、1~14日龄肠道发育和血清生化指标的影响。选取47周龄京红1号蛋鸡种蛋1080枚,随机分为3组,分别为未注射对照(NC)组、生理盐水注射对照(SC)组和L-Arg注射(Arg)组,每组8个重复,每个重复45枚种蛋。在孵化第17.5天时,Arg组每枚蛋注射0.1 mL 10%的L-Arg溶液(0.85%生理盐水作溶剂,10 mg L-Arg/枚蛋),SC组注射相同剂量的0.85%生理盐水。出壳后,每组选取体重相近的健康母雏120只,随机分为8个重复。试验期14 d。结果表明:1)与NC和SC组相比,胚蛋注射L-Arg对1日龄蛋雏鸡的孵化率和出孵重无显著影响(P>0.05),但显著降低卵黄囊重(P<0.05)。2)与NC和SC组相比,胚蛋注射L-Arg显著提高1日龄蛋雏鸡的空肠长度、3日龄时的十二指肠长度和14日龄时的空肠和回肠长度(P<0.05),对3日龄蛋雏鸡空肠内容物脂肪酶活性有增加趋势(P=0.084)。3)与NC组相比,胚蛋注射L-Arg显著提高14日龄蛋雏鸡的空肠上皮细胞增殖指数(P<0.05)。4)与NC组相比,胚蛋注射L-Arg显著降低3和14日龄蛋雏鸡的血清甘油三酯(TG)含量(P<0.05),显著增加3和14日龄时的血清总胆固醇(TC)和低密度脂蛋白(LDL)含量(P<0.05)。与SC组相比,胚蛋注射L-Arg显著增加14日龄蛋雏鸡的血清高密度脂蛋白(HDL)和葡萄糖(GLU)含量(P<0.05)。由此可见,胚蛋注射10 mg L-Arg对蛋雏鸡的孵化率和出孵重等孵化性能无不良影响;胚蛋注射10 mg L-Arg促进蛋雏鸡的脂质代谢和糖代谢,为早期肠道发育提供更多能量,提高空肠上皮细胞增殖指数,增加肠道长度,促进早期肠道发育。     

Relationship between food consumption and energy and nitrogen utilisation by chicks given varying amounts of standard and leucine-, isoleucine- and valine-deficient diets

The effect of different amounts of food, varying from below to above the rate of voluntary intake, was studied in chicks using a standard diet and diets containing only half the recommendation concentrations of leucine, isoleucine or valine. Irrespective of diet the body weight gain of the chicks increased with increasing food consumption. The body weight gain of chicks given the leucine-deficient diet was similar to that of chicks given the same amount of the standard diet. In contrast, the body weight gains of chicks given either the valine- or isoleucine-deficient diet were significantly less than that of chicks given the same amount of the standard diet. When the food intakes of the birds were similar the differences in body protein and water contents of the birds fed the different diets reflected differences in body weight gains, whereas body fat content was affected in the reverse manner. Retention and retention rate of dietary energy increased as food consumption increased. This was particularly evident in chicks given the isoleucine-deficient diet, followed by those given the valine-, leucine-deficient and standard diets. For all diets, the amounts of nitrogen retained and nitrogen retention rate (N retained/N consumed) increased in line with body weight gain. The metabolisable energy values of the diets were similar, except for the isoleucine-deficient diet which had a significantly higher metabolisable energy value than the standard valine-deficient diets.     

鸡胚胎期及生长发育早期对孵化绿光强度的反应

试验旨在探究孵化期单色绿光不同光照强度对鸡孵化和早期生长发育的影响。选用810个大小均匀的新浦东鸡种蛋,随机分为3组（n=270）,孵化期1~18.5 d分别在黑暗、低照度（20~50 lux）和高照度（200~300 lux）的LED单色绿光（λ=525 nm）条件下孵化,每天光照24 h,各组种蛋于第18.5天转至同一台无光出雏器中,各组温度和湿度等其他孵化条件始终保持一致。检测各组受精蛋孵化率、死胚率、初生重、10周龄体重、初生雏鸡及3周龄公鸡的血清激素浓度（甲状腺素、降钙素、生长激素、褪黑激素和骨钙素等）和血液生理生化指标（碱性磷酸酶、胰岛素样生长因子和钙等含量）。结果表明：各组种蛋的死胚数和死胚率差异较小;孵化的20.5 d低照度组和高照度组的受精蛋孵化率分别为黑暗组的2.3倍和5.2倍;孵化的21.5 d黑暗组的受精蛋孵化率为82.8%,低照度组和高照度组的孵化率分别比黑暗组高6.5%和1.9%;黑暗组的健雏率为98.6%,低照度组的健雏率比黑暗组低0.4%,而高照度组与黑暗组的健雏率接近;高照度组公雏初生重显著低于黑暗组（P<0.05）,而低照度组与黑暗组无显著差异（P>0.05）。母雏初生重趋势与公雏基本一致,高照度组母雏初生重显著低于其他两组（P<0.05）,其他两组之间无显著差异（P>0.05）;在10周龄,各组公鸡和母鸡体重无显著差异（P<0.05）;各组1日龄公雏血液生理生化和激素指标无显著差异（P>0.05）,3周龄公鸡高照度组和低照度组褪黑激素含量显著高于黑暗组（P<0.05）,其他指标无显著差异（P>0.05）。综上,在种蛋的孵化过程中,与黑暗条件下相比,给予适宜强度的单色绿光能够促进鸡胚发育,在不影响雏鸡健康的前提下使出雏时间提前,孵化期光照对后期生长发育影响较小。     

Studies on reducing the crude protein content of feeds fed to chicks and young hens (laying stock)]

2 rearing trials were carried out on a total of 8550 hybrid chicks (White Leghorn) to investigate in which way food mixtures containing reduced levels of crude protein (supplemented or unsupplemented with amino acids) might influence the growth of chicks and young hens. Decreases from 21.5% to 16.5% in the crude protein content of chicken feed and from 15% to 13% in feeds feed to young hens (greater than 8 weeks of life) did not reduce the live weight of birds at the end of the rearing period to any appreciable extent. No clearly defined differences were found to exist between the different types of feed tested concerning the amount of food and energy consumed per unit of weight gain and the mortality rate among the birds; it was shown, however, that the demand for crude protein per unit of weight gain was clearly reduced in birds reared at the lower crude protein level. For young hens receiving the diet poorer in protein the date when the birds began laying was slightly delayed. Otherwise, no statistically significant differences were found to exist between the young birds fed varying levels of crude protein, concerning the age at 50% laying performance and other parameters that are characteristic of the entire laying period (laying performance, weight of individual eggs, food consumption, mortality, fertilization of hatching eggs, hatchability of eggs). It appears that the feeding of a reduced protein diet to chicks and young hens (laying stock) did not have any detrimental effect on the growth and later laying performance of the birds. Apart from the fact that the demand for protein feeds is considerably reduced during the rearing period the costs of feeding per bird can also be cut down.     

蛋形指数对拉萨白鸡种蛋孵化效果的影响及相关分析

为了研究蛋形指数对拉萨白鸡种蛋孵化效果的影响,在相同孵化条件下,选用3世代47周龄拉萨白鸡种蛋,按蛋形指数分组进行孵化,并对蛋形指数与孵化效果的相关性进行了分析。结果表明,蛋形指数(横径/纵径)在0.68~0.72时,0胚龄蛋重、纵径均值、头照(第11日胚龄)蛋重、二照(第20日胚龄)蛋重最大,分别为:(51.92±5.27)g、(57.71±1.97)mm、(48.95±4.67)g、(45.47±3.97)g;蛋形指数(横径/纵径)在0.73~0.77时,入孵蛋孵化率、受精蛋孵化率和雏鸡的初生重最大,分别为:82.65%、86.60%、(36.31±4.71)g;蛋形指数(横径/纵径)在0.78~0.82时,头照(第11日胚龄)失重、头照(第11日胚龄)失重率、二照(第20日胚龄)失重、二照(第20日胚龄)失重率最大,分别为:(3.35±0.93)g、(6.64±1.54)%、(6.70±1.47)g、(13.47±2.56)%;蛋形指数(横径/纵径)在0.83~0.87时,橫径均值、受精率、健雏率、雏鸡初生重占入孵蛋重的百分比最大,分别为:(42.82±1.23)mm、97.26%、95.96%、(70.23±3.58)%;雏鸡初生重与雏鸡初生重占入孵蛋重的百分比呈极显著正相关(P<0.01)。该研究为拉萨白鸡今后的选育提供了理论依据。     

Response of Chickens’ Embryo and Early Growth and Development to Different Intensities of Green Light Stimulation During Incubation

The purpose of this experiment was to investigate the effects of different intensities of monochromatic green light on hatching,embryo development,and early growth and development of chickens during incubation.810 New Pudong chicken eggs with similar size were randomly divided into 3 groups (n=270).The eggs were hatched in dark,low illumination (20~50 lux),or high illumination (200~300 lux) LED monochromatic green light (λ=525 nm) respectively during 1~18.5 days of incubation period,with 24 h light per day.From 18.5 days of incubation,the eggs of 3 groups were transferred to the same hatcher without light.Incubation temperature and humidity conditions were consistent among groups.The hatchability of fertile eggs,percentage of early dead embryo,body weight (BW) at birth and 10 weeks of age,serum hormones (thyroid hormone,calcitonin,growth hormone,melatonin and osteocalcin),and blood physiological and biochemical indicators (alkaline phosphatase,insulin-like growth factor and calcium of one-day-old and 3-week-old chicks) were examined.The results showed that 3 groups had similar early dead embryo number and percentage.At the 20.5 d after incubation,the hatchability of fertile eggs in the low illumination group and the high illumination group was about 2.3 times and 5.2 times of that in the dark group.At the 21.5 d after incubation,the hatchability of fertile eggs in the dark group was 82.8%.This parameter of the low illumination group and high illumination group was 6.5% and 1.9% higher than that of the dark group.The percentage of healthy chicks of dark group was 98.6%,this parameter of the low illumination group was 0.4% lower than that of dark group,while high illumination group and dark group was almost the same.The birth BW of males of the high illumination group was lower than that of the other two groups (P<0.05),but there was no difference between the low illumination group and the dark group (P>0.05).The trend of birth BW of females was basically consistent with that of males.The birth BW of female chicks in the high illumination group was lower than those of other two groups (P<0.05),and there was no difference between other two groups (P>0.05).At 10 weeks of age,there was no difference in BW between males or females of 3 groups (P<0.05).For the day-old chicks,there was no difference in blood and hormones indicators among groups (P>0.05).For the 3-week-old New Pudong roosters,the serum melatonin level(P<0.05)in the high and low illumination groups were higher than that in the dark group,and there was no difference in other indicators (P>0.05).In conclusion,compared to the dark condition,providing proper intensity of monochromatic green light during the incubation could promote the development of chicken embryo,and advance the hatching process without impairing chicks’health and following growth performance.     

Development of the chicken as a model for prenatal stress

Exposing a pregnant mammal to stressors causes behavioral and physiological alterations in her offspring ("prenatal stress"); however, elucidation of the underlying mechanism is hindered by an inability to control maternal compounds that may affect the fetus. We designed this experiment to determine if the autonomously developing chicken embryo could be developed as a model for prenatal stress. On d 16 of incubation, eggs were treated with: 1) 60 ng corticosterone (CORT), 2) elevated incubation temperature (40.6 degrees C) for 24 h (HEAT), or 3) no treatment (Control). Chicks from all three treatments hatched at similar weights; however, HEAT chicks weighed less by 100 d of age and remained lighter until the end of the study (P < 0.05). At 8 d post-beak trimming, adrenal gland weight was not different (P > 0.20) among treatments, basal plasma corticosterone concentrations tended (P < 0.06) to be greater for CORT chicks than either the Control or HEAT chicks, and CORT chicks were heavier than HEAT chicks (P < 0.005) but not Control chicks (P > 0.20). At 11-wk, HEAT birds had heavier adrenal glands than did Control birds (P < 0.01). At 16 wk of age, Control cocks performed more (P < 0.01) pecking aggression than either HEAT or CORT cocks, whereas CORT cocks were chased more often and chased another cock less often than either HEAT or Control cocks (P < 0.01). Treatments did not alter the behavior of the hens (P > 0.10). Administration of corticosterone during incubation replicated some, but not all, of the effects seen in prenatal stress in mammals.     

Delayed replication of Marek's disease virus following in ovo inoculation during late stages of embryonal development

Several oncogenic and non-oncogenic isolates of Marek's disease virus (MDV) were inoculated into embryonated eggs on embryonation day (ED) 16 to 18, and embryos or chicks hatching from inoculated eggs were examined for infectious virus and viral internal antigen (VIA) in lymphoid organs. There was no evidence of extensive replication of MDV in any of the embryonic tissues examined. Levels of VIA peaked 4-5 days after chicks hatched. This indicated that MDV remained inactive during embryonation and did not initiate pathogenic events until chicks hatched. Because HVT replicated rapidly in the embryo but MDV did not, in ovo inoculation of HVT simultaneously with oncogenic MDV or several days after MDV resulted in significant protection (P less than 0.025) of hatched chicks against Marek's disease (MD). Little protection was obtained if HVT was given simultaneously with MDV or after MDV to chicks already hatched. The relative susceptibility of the embryo to extensive replication of the vaccine virus but not the challenge virus apparently accounted for protection against MD in chicks hatching from dually infected eggs.     

Studies on some feed additives and materials giving partial protection against the suppressive effect of ochratoxin A on egg production of laying hens

The protective effects of various feed supplements against the harmful effect of ochratoxin A on egg production and sexual maturation of two-weeks old Plymouth Rock female chicks designed for laying hens were studied. A significant protective effect of the feed additives or materials: water extract of artichoke (WEA), sesame seed (SS), Roxazyme-G (RG) and l-β phenylalanine (PHE) against the suppressive effect of ochratoxin A (OTA) on egg production of laying hens was found. A similar protection was also seen on the toxic effect of OTA on various internal organs of the same hens. A significant protection was found against the decrease of the weight or the quantity of eggs as well as against the delay of the beginning of the laying period of chicks, both of which were provoked by ochratoxin A. These protective effects were strongest in chicks treated with SS or WEA, but were slightest in chicks treated with l-β PHE.