The response of egg weight to the inclusion of different amounts of vegetable oil and linoleic acid in the diet of laying hens

1. Four diets containing different amounts of vegetable oil and linoleic acid were fed to White Leghorn hens throughout a full laying year.

2. Egg weight was poor with the low fat basal diet but increased in relation to the amounts of maize oil (4 and 30 g/kg) included in the diet.

3. With a diet containing 30 g olive oil/kg, egg weight was similar to that obtained with the diet containing the same amount of maize oil.

4. Rearing the birds on diets containing low or moderate amounts of linoleic acid did not affect the response to fatty acid content of the layer's diet.

5. It is concluded that the requirement of the laying hen for linoleic add is not higher than 9 g/kg but that egg weight does respond to higher dietary amounts of readily absorbable fatty acids.     

Effect of diet and natural variations in climates on the performance of laying hens

1. Laying hens raised in 3 natural tropical environments were fed on 2 series of diets with a view to defining the optimum combination of climate and dietary energy.

2. A combination of 3 growing climates, 3 laying climates (temperate, hot dry, hot humid), and 2 dietary energy concentrations (10.03 and 11.70 MJ ME/kg with protein concentrations proportional to energy) were tested for 46 weeks using 432 point‐of‐lay pullets.

3. Both growing and laying climates significantly affected most traits measured during the laying period. The patterns of egg production showed good persistency in all environments and differences observed reduced with age.

4. The difference between the high and low energy intake reduced at high ambient temperatures. Feeding low energy diets did not affect mean age at first egg, rate of lay or the egg output in the hot dry environment, nor egg weight in either hot dry or hot humid climates. Rather, feeding low energy diets resulted in improved body weight change in all 3 laying environments.

5. The growing climate and diet interacted significandy on body weight change, while highly significant interactions between laying climate and diet occurred on rate of lay, food and energy intake and egg weight during the laying period.     

Response of egg weight to the inclusion of various fats in layer diets

1. Brown egg layers were fed diets differing in oil content, oil source and linoleic acid concentration and the effect on performance from 22 to 69 weeks of age was studied.

2. The birds responded with an increasing mean egg weight up to a linoleic acid intake of 2.75 g/bird d.

3. Increasing the intake of readily absorbable oil without increasing linoleic acid concentration did not increase mean egg weight.     

Effect of dietary inclusion of ascorbic acid and palm oil on the performance of laying hens in a hot tropical environment

1. Two experiments were conducted to evaluate the effects of including ascorbic acid (AA), palm oil or a combination of both in the diets of laying hens during the hot months in a tropical environment.

2. The inclusion of AA improved egg production, food intake and efficiency of utilisation, and decreased the cost of food per kg egg. The addition of 400 mg AA/kg diet gave the most efficient performance.

3. Palm oil inclusion reduced the effect of heat stress and increased egg production, egg weight, food intake and efficiency of utilisation.

4. When 200 mg AA and 50 g palm oil/kg were used, additive responses were obtained with further improvements in egg production, food cost and efficiency.

5. Ascorbic acid and palm oil when fed alone or in combination reduced the incidence of cracked eggs.

6. Thus, 400 mg ascorbic acid/kg of diet, 50 g palm oil or 200 mg AA plus 50 g palm oil/kg diet ameliorated the effects of heat stress in laying hens.     

The use of rapeseed meals and a mustard seed meal as a protein source in diets for laying pullets

1. Three experiments with laying pullets were carried out in which rapeseed meals (B. napus and B. campestris) and a mustard seed meal (B. juncea) formed 12% of the diet.

2. Dietary rapeseed had no effect on the onset of lay when fed from 17 weeks of age but caused a delay when fed from 10 weeks of age: changing to a control soyabean diet for the laying period resulted in normal egg production.

3. Diets containing B. napus but not B. campestris consistently depressed egg production and reduced egg weight in one experiment. Mustard seed meal did not affect performance.

4. Significant number of eggs with a “fishy” taint were laid by brown‐egged birds fed on a diet containing rapeseed.

5. Thyroids of birds fed on rapeseed meal diets during the laying period were significantly heavier than those of birds fed on diets containing mustard seed or soyabean.

6. The enlargement of the thyroid gland is probably related to the oxazolidinethione content of the rapeseed.     

The influence of three rapeseed meals and a mustard seed meal on egg and broiler production

A mustard seed meal free of oxazolidinethione and three rapeseed meals of low (C), medium (D) and high (E) oxazolidinethione contents were included at a rate of 12% in the diets of laying birds and of broilers. The control diets contained a similar quantity of protein as soyabean meal. In each experiment a further control group was given a suitable commercial diet.

The mustard seed meal and rapeseed meals D and E caused large and significant mortalities among laying birds. Macroscopic observations suggested that the main cause of death was probably liver haemorrhage.

Egg production, after correction for mortality, was significantly decreased by rapeseed meals D and E, and egg weight by the mustard seed meal. There were no significant treatment effects on food intake and therefore the weight of food needed for each egg produced followed fairly closely the pattern of egg production.

Overall egg production was depressed by mustard seed meal and by rapeseed meals D and E. Rapeseed meal C decreased production but not significantly.

Liver weights were not influenced by treatment, but thyroid weights of groups given rapeseed meals were significantly increased.

Broiler production was not significantly influenced either by mustard seed meal or by any of the rapeseed meals.     

Use of field beans (Vicia faba L) in diets for laying hens

1. Most samples of field bean, irrespective of their genetic origin, induced a decrease in the mean egg weight when included in the diet at a rate of 300 g/kg: the relative sizes of yolk, albumen and shell were unchanged.

2. Lipoxygenase was not involved in this phenomenon since addition of linoleic acid to the diets containing field beans did not improve egg weight.

3. The depressing effect of the field beans was proportional to the proanthocyanidine content of the seed extracted with absolute methanol.

4. In a longer trial (252d) field beans rich in these kinds of tannin decreased laying rate, efficiency of food utilisation and tended to increase mortality.

5. The removal of the hulls from the field beans did not prevent the reduction in egg weight.     

Comparison of nutritive values of groundnut oil cake and Niger oil cake for laying pullets

1. The nutritive value of Niger oil cake (Guizotia abyssinica, Cass.) as a protein supplement for layers’ diets has been assessed.

2. Replacing groundnut oil cake (GNC) by Niger oil cake (NC) on an isonitrogenous basis, did not affect egg production, egg weight or the amount of food required per dozen eggs.

3. The percentage retention of nitrogen from diets containing 30% GNC or 30% NC was similar.

4. The ME value of NC used was 3025 kcal/kg.

5. It is concluded that NC can replace GNC in layers’ diets.     

Phosphorus requirements of poultry. V. The effects during the subsequent laying year of feeding growing diets containing no animal protein or supplementary phosphorus

Pullets reared to 18 weeks of age on diets containing no feeding stuffs of animal origin and without phosphorus supplementation showed no significant difference in egg yield compared with similar pullets fed rearing diets containing animal protein and added phosphorus.

During the laying stage, diets in commercial use at this centre gave significantly higher egg yields, better average egg prices due to superior grading results and a higher margin over food cost than the same diets modified to conform with the nutrient recommendations of the National Research Council of America (1960).

Where the supplementary protein in both types of layers' diet was of vegetable origin, egg yield, food cost and margin of income over food cost were all significantly inferior to groups fed comparable diets containing supplementary protein of both vegetable and animal origin.

Soyabean meal and sunflower seed meal gave significantly poorer results when used in combination as the sole protein supplement compared with soyabean meal plus methionine.     

The nutritional value of algae for poultry. Dried chlorella in layer diets

1. The nutritional value of a sample of algae meal, mainly Chlorella, was assessed in an experiment with laying hens. The algae meal was that described by Lipstein and Hurwitz (1980).

2. Diets formulated by linear programming contained up to 120 g algae meal/kg with supplementary DL‐methionine.

3. There were no significant effects of dietary algae meal on egg output, food conversion or egg‐shell quality. Thus algae meal at the concentrations tested can be a useful substitute for soyabean meal in diets for laying hens.

4. High concentrations of dietary algae meal caused a deep yellow yolk colour of acceptable appearance.     

Dietary rapeseed meal and the incidence of tainted eggs

1. Incorporating 0, 3, 6 or 9% rapeseed meal in the diet of brown‐egg laying birds for 28 d resulted in the production of 0, 1.2, 19.3 and 20.9% tainted eggs respectively, the first tainted eggs being laid on the fifth day.

2. During the second and third weeks the incidence of tainted eggs exceeded 20% but fell to 11.4% during the final week.

3. Omission of the rapeseed meal from the diets halted the production of tainted eggs.

4. Neither egg production nor the health of the birds was adversely affected by the treatments.

5. The taint was described as “ fishy ” or “ crabby ” and was distinctive, but the source was not identified.     

Whitening of brown shelled eggs: Individual variation and relationships with age,fearfulness, oviposition interval and stress

1. Fearfulness, shell colour, incidence and degree of shell whitening and the interval between ovipositions were studied in two populations of 30 brown egg laying hens with family histories of a low or a high incidence of egg shell whitening.

2. Hens of the population with the high incidence of whitening appeared to be more fearful than hens of the population with the low incidence of whitening.

3. Brown colouration of the egg shell and the incidence and degree of shell whitening declined as the hens aged.

4. Brown colouration and egg shell whitening were most pronounced on the blunt ends of the eggs.

5. A large part of the variation in egg shell whitening was attributable to the individual (hen) component of variance.

6. Differences in egg shell whitening, between the two populations, were detectable throughout the 26 weeks of the experiment.

7. Oviposition intervals were similar for normal and coated eggs when birds were not exposed to disturbance.

8. Disturbance of hens increased oviposition intervals and the incidence and degree of shell whitening, to a similar extent, in both populations.

9. It is concluded that stress‐related egg retention is not the sole factor responsible for abnormal egg shell whitening. Shell whitening may occur as a consequence of the premature termination of shell pigmentation as well as a consequence of the retardation of oviposition which occurs when hens are disturbed.     

Effects of an induced pause in egg production and supplementation of the diet with iron on egg shell colour,quality and performance of brown egg layers

1. A pause in egg production was induced in brown‐egg laying hens, aged 68 weeks, by feeding them whole oats for 7 d. Subsequently, these hens, together with control groups, were given laying diets with either 400 or 600 mg/kg iron. The 200 mg/kg of supplemental iron was added in the form of either ferrous sulphate or iron proteinate (chelated iron).

2. The feeding of whole oats halted egg production in 5.7 ±0.22 d and the duration of the pause was 8.3 ±0.78 d.

3. The induction of a pause improved the subsequent rate of egg production, egg output, efficiency of food utilisation, albumen quality, egg specific gravity and shell colour. It also increased food intake and body weight gain but neither egg weight nor the rate of mortality were affected.

4. Neither supplementation of the diet with iron nor its source had any significant effect on laying performance, egg quality or shell colour.     

Effects of heat-treated hempseed supplementation on performance,egg quality,sensory evaluation and antioxidant activity of laying hens

1. This study was conducted to determine the effects of raw and heat-treated hempseed (HHS, Cannabis sativa L.) on performance, egg quality and antioxidant activity in laying hens.

2. A total of 108 laying hens, aged 36 weeks, were divided into three treatment groups with 12 replicates and each replicate contained three laying hens. The treatments were as follows: (1) Control (no hempseed), (2) 15% raw hempseed (RHS) in diet and (3) 15% HHS in the diet. Experiments lasted for 12 weeks.

3. Feed intake of the RHS group was lower than those of the control and HHS groups. Egg weight, egg mass, shell weight, shell surface area and shell thickness of the HHS group were significantly (P < 0.05) higher than that of the RHS group. Roche (DSM) colour fan values of the RHS group were higher than that of the HHS group (P < 0.01).

4. Palmitic, palmitoleic and oleic acids of egg yolk were significantly (P < 0.05) decreased in the RHS and HHS groups; however, linoleic, α-linolenic and docosahexaenoic acids (DHA) of egg yolk increased (P < 0.05) for both treatment diets compared to the control group.

5. Both RHS and HHS supplementation to layer diets did not influence malondialdehyde (MDA) and superoxide dismutase (SOD) activity and blood lipid profile.

6. It was concluded that HHS was superior in improving the egg quality of laying hens as compared to the RHS.     

Effects of feeding deoxynivalenol‐contaminated oats on reproduction performance in white leghorn hens

1. The effect of feeding trichothecene‐contaminated diets with graded concentrations of deoxynivalenol ranging from 120 to 4900 μg/kg to groups of laying hens was investigated.

2. Food intake, weight gain and egg production were not affected by mycotoxin administration. No significant differences were found between groups.

3. The overall results from the hatching tests did not reveal any significant differences in fertility, hatchability or perinatal mortality, which could be explained by the mycotoxin content in the diets.

4. Body weight at hatching and viability of the chicks were not affected by the mycotoxin concentrations in the diets.

5. The incidence of chick developmental anomalies was increased in the mycotoxin‐administered groups compared to controls. Minor malformations were the dominating anomalies and included unwithdrawn yolk sac and delayed ossification. The most frequent major malformations were cloacal atresia and cardiac anomalies.     

Influence of dietary calcium and phosphorus on metabolism and production in laying hens

1. The effects of different dietary concentrations of calcium (24 to 56.9 g/kg) and phosphorus (4.5 to 14.2 g/kg) on production and some aspects of metabolism were studied in laying hens.

2. Treatments did not affect egg numbers, food consumption, conversion efficiency of food to egg, bodyweight gain or mortality.

3. Increasing dietary calcium (Ca) significantly increased plasma Ca and inorganic phosphorus (P), breaking strength at the radius and egg specific gravity and significantly decreased plasma alkaline phosphatase and egg weight.

4. Increasing dietary phosphorus increased plasma P and decreased egg specific gravity significantly.

5. Plasma Ca, P and alkaline phosphatase and radius breaking strength were suitable indices of the Ca status of the hens.     

Influence of dietary magnesium content on laying performance and egg shell magnesium content in the domestic hen

1. The effects of feeding diets containing various amounts of magnesium on laying performance in the domestic hen were investigated.

2. A reduction in egg number, egg mass, egg shell thickness and egg shell magnesium content occurred in birds receiving diets containing either 207 or 132 mg Mg²⁺/kg even though the duration of egg formation was unaffected.

3. The progressive increase in magnesium content normally observed towards the outer surface of the hen's egg shell was not present in birds receiving a diet containing 207 mg Mg²⁺/kg.     

Comparison of wheats of high or conventional protein content with added lysine in diets for layers

1. High‐protein wheats (196 or 210 g/kg) were compared with conventional wheat (163 or 162 g/kg) in layers’ diets in three experiments.

2. In diets of 160 g protein/kg without added lysine, high‐protein wheats caused lower rates of production and egg size than conventional wheats in White Leghorns. Lysine supplementation of the former diets eliminated these differences.

3. The improvements in egg production and egg weight were significant with 1 g additional lysine/kg and egg production tended to improve further with 2 g additional lysine/kg, as did egg weight with all subsequent additions, but not significantly so.

4. With diets containing high‐protein wheats supplemented with lysine, high egg production and egg weight could be obtained without a protein supplement (e.g. soyabean meal).

5. In broiler‐breeders egg production was lower and food conversion poorer with high‐protein wheat despite added lysine.     

Regulation of plasma oestrogen by dietary fats in the laying hen: Relationships with egg weight

1. Feeding a diet supplemented with maize oil was found to elevate plasma oestradiol concentration in laying hens.

2. In a larger‐scale experiment, isoenergetic and isonitrogenous diets containing 10, 20, 40 or 60 g/kg supplemental maize oil, tallow, coconut oil or fish oil were fed for 5 weeks.

3. Egg weights showed very different responses to the different fats. The responses could be described by quadratic functions that all gave optimum responses with supplemental dietary fat concentrations of about 40 g/kg. Egg weight increased the most with maize oil and was decreased with fish oil at the highest inclusion rate.

4. Measurements of egg components showed a relatively larger increase in albumen weights with maize oil than with other fats.

5. Across treatments, mean plasma oestradiol concentrations were very highly correlated (r = 0.96) with the changes in egg weights over the experimental period.

6. It is concluded that oestrogen is important in controlling egg weight and that the effect of dietary fats in influencing egg weight is mediated by an effect of the fats on oestrogen metabolism.     

Diets for laying hens containing unusual ingredients and varying concentrations of cereals including no cereals

1. Light‐ and medium‐hybrid laying hens received one of six diets (A, B, C, D, E and F) containing decreasing amounts (758, 560, 374, 270, 185 and 0 g/kg) of cereals and increasing amounts of unusual ingredients, from 22 weeks of age.

2. The diet containing no cereal and 225 g dried poultry manure/kg (diet F) caused a severe reduction in performance and was discontinued at 27 weeks of age; the other treatments were continued until 48 weeks of age.

3. In the case of medium hybrids, rate of lay (number of eggs/100 hen d) was similar with diets A, B and C and about 2 percentage points lower with diets D and E; egg output (g per hen d) tended to decrease slightly as dietary cereal concentration decreased.

4. In the case of light hybrids, rate of lay was about 5 percentage points lower with diets B, C and D and about 13 percentage points lower with diet E than with diet A.

5. Mortality was similar on each diet.

6. The effect of diet on live‐weight gain was inconsistent and statistically not significant.