Short‐term effects of food protein content on subsequent diet selection by chickens and the consequences of alternate feeding of high‐ and low‐protein foods

1. Growing male chickens of broiler and layer strains were allowed to eat either a high‐protein food (HP) or a low‐protein food (LP) for 10 min after an overnight fast and then offered a choice between HP and LP. During the next hour they ate significandy more of the food other than die initial meal. Similar results were obtained when there was a gap of 45 min without food between the initial meal and the choice period.

2. When the initial meal was given by tube into the crop, followed by 45 min without food, there was no significant effect on subsequent diet selection. These results show that it is necessary for the birds to eat the food themselves for it to exert its effect on subsequent choice.

3. Birds with experience of eating two foods identical in nutrient composition but different in colour did not select either food in preference to the other following an initial meal of one alone. This is evidence against the possibility that neophagia accounts for the results of the first two experiments. When an initial meal of low protein food was followed by a choice of high and low protein foods, birds ate a greater proportion of the high protein when it was placed on the opposite side of the cage from that in which the initial meal was given. Thus they are not choosing a food simply by its position within the cage.

4. To see the extent to which broilers can extend their ability to compensate for protein content over several weeks, male broilers were given one of 4 treatments from 5 to 10 weeks of age: (A) HP and LP concurrendy; (B) HP and LP on alternate days; (C) HP in the morning and LP in the afternoon, (D) LP in the morning and HP in the afternoon. There was no significant effect of treatment on food intake, body weight gain or carcase protein content but carcases were significantly less fat after treatment (B) than treatment (D).

5. It is concluded that growing broiler chicks can compensate well for periods of access to only a low‐protein food, by subsequent intake of a high‐protein food, and lice versa, as long as they are able to gauge the sensory properties of the foods. Offering two complementary foods in alternating half‐day periods is an effective method of choice‐feeding, allowing birds to select a diet to meet the requirements for growth.     

L‐aspartic acid and urea supplementation of low‐protein layer diets1

1. Urea supplementation of low‐protein (125 g/kg) conventional‐type diets for layers, whether containing fish meal or not, did not appear advantageous.

2. Supplementation of the low‐protein diet with aspartic acid did not affect egg production rate or efficiency.

3. Soyabean meal supplementation of the low‐protein diet increased egg weight significantly whereas aspartic acid did not.     

Urea and aspartic acid supplementation of low‐protein broiler diets1

1. L‐Aspartic acid does not seem useful as a protein surrogate in conventionally formulated low‐protein diets for broiler chicks.

2. Urea as a protein substitute does not enhance the value of conventional broiler diets.

3. Urea does not improve broiler diets that have been supplemented with fish meal or crystalline amino acids to satisfy requirements for all indispensable amino acids.

4. Urea is absorbed into the bloodstream, but is not assimilated into body proteins.     

Evaluation of methanol‐grown bacteria as a source of protein and energy for young chicks

1. The inclusion of 100 or 200 g/kg spray‐dried methanol‐grown bacteria in unpelleted semi‐purified diets reduced growth rate and efficiency of food conversion of young chicks over a 14 d period.

2. Classical metabolisable energy values for the spray‐dried product, at relatively low inclusion rates, ranged from 9.55 to 10.92 MJ/kg dry‐matter (DM) and nitrogen‐corrected values ranged from 8.95 to 10.16 MJ/kg DM.

3. Inclusion of 96 g/kg flash‐dried methanol‐grown bacteria in unpelleted semi‐purified diets marginally increased growth rates, efficiency of food conversion and nitrogen utilisation of chicks, but higher inclusions of up to 290 g/kg caused adverse effects.     

Time course of oxidative phosphorylation in liver mitochondria of chickens fed on high‐protein diet

1. Progressive alterations in oxidative phosphorylation of liver mitochondria were followed for 14 d in growing chickens fed on either semi‐purified low (7%) or high (61%) protein‐energy diet. Hepatic mitochondrial oxidative phosphorylation rates were assessed polarographically with pyruvate + malate as substrates.

2. The ADP:O values were reduced significantly 4 d after the feeding of a high‐protein‐energy diet, when compared with those in chickens fed on a low‐protein‐energy diet, whereas the state 3 oxidation rates in chickens fed on a high‐protein‐energy diet from day 6 to 14 were significantly lower than those in low‐protein‐fed chickens.

3. No changes in sensitivity of mitochondrial ATPase activity to oligomycin, expressed as % of total ATPase activity, were observed among chickens fed for 21 d on diets with various protein concentrations though the FoF₁‐ATPase activity, expressed per mg protein, tended to decrease in chickens fed on high‐protein‐energy diet.

4. These results suggest that the reduced ADP:O values for liver mitochondria in the high‐protein‐fed chickens may not be involved in the degrees of integrity of the FoF₁‐ATPase.     

Responses of laying hens to a low‐protein diet supplemented with essential amino acids,l‐glutamic acid and/or intact protein

1. Three sequential experiments, each lasting 8 weeks, were carried out on 576 singly‐caged light hybrids.

2. In experiment 1 egg production was 84% using a conventional control diet, 61% with a basal low‐protein diet, and 79% with the basal diet supplemented with 10 essential amino acids + L‐glutamic acid (GA).

3. In experiment 2 supplementation with lysine and methionine (L + M) alone increased egg production significantly from 54 to 72%, compared with 83% with the conventional diet.

4. In experiment 3 egg production was 55% with the basal diet, 71% with the basal diet + L + M, 75% with a diet containing 141 g protein/kg + L + M, and 73% with the conventional diet.

5. In all three experiments supplementation with GA alone either gave no significant response or a depression in production.

6. Daily intakes of 1.24 g nitrogen as non‐essential amino acids and 13 to 14 g total crude protein per bird resulted in good egg production. Supplementation of the basal diet with L + M resulted in a daily intake of 413 mg methionine/bird day which was considered adequate, and a daily intake of 710 mg lysine which was considered slightly inadequate.     

The effect of feeding low‐protein diets to pullets from hatch to point‐of‐lay and the quantitative restriction of food during the subsequent laying period

Pullets from two commercial breeds were fed on diets of similar energy content but with 19% or 16% crude protein to 8 weeks of age and from 8 to 20 weeks of age on one of three isoenergetic diets containing either 12, 14 or 16% crude protein. At 20 weeks the birds were offered a conventional layers’ diet containing 16% crude protein either ad libitum or on a daily food intake of 100 g for a further 32 weeks.

The results indicate that with certain breeds the dietary protein levels can be lowered to approximately 16% during the o to 8‐week period and to approximately 12% during the 8 to 20‐week period without adversely affecting egg production. However, variations in the laying performance of the different breeds appear to be dependent on the amount of protein fed in the first eight weeks of life. Significant breed effects were observed throughout the experiment and although restricted feeding during the laying period substantially reduced the food intake it also had a detrimental effect on the rate of egg production and on the total weight of eggs produced.     

Effects of oven‐drying tubers of two high‐protein sweet potato varieties at different temperatures on their feeding value in broilers

1. Unpeeled tubers from 2 high‐protein varieties of sweet potato (white‐fleshed Bosbok, and orange‐fleshed Carmel) were chipped and oven‐dried at 40, 60, or 80°C, to examine the effects on nutritive value. The dried ground chips were substituted for maize at 500 g/kg and the diets fed to day‐old, Ross‐1 broiler chicks for 3 weeks.

2. Compared with Carmel, Bosbok had a lower crude protein content (90 v. 138 g/kg DM) and trypsin inhibitor activity (TIA) (3 v. 5 mg of trypsin inhibited per g flour). Processing did not significantly affect TIA, but the lysine and cystine contents were lowered and the starch content raised as the drying temperature increased. However, whereas this was reflected in increased reducing sugars in Carmel, there was no trend in Bosbok.

3. The results of in vitro pancreatin digestibility and total dietary fibre assays showed variety and processing temperature to be significant factors influencing the nutritive value of sweet potato tubers, with a variety X temperature interaction also being indicated. The interaction was also observed for weight gain, dry matter intake, water: food intake ratios, excreta water content, presence of bile in excreta and liver weights. The best growth was obtained with Bosbok dried at 60°C, for which liveweights at 21 d were 11% lower than for the maize controls.     

Effects of restricting the amounts of medium or low‐energy diets fed to laying hens in different colony sizes

1. Light hybrid hens between 32 and 68 weeks of age kept 4, 5 or 8 birds to the cage received one of three energy intakes, from a medium‐ or low‐energy diet.

2. Ad libitum fed birds laid more and heavier eggs than any of those restricted. A decrease in daily egg output of about 5 g was associated with each 100 kJ decrease in daily intake of metabolisable energy.

3. For the same energy intake, egg output of birds fed on the low‐energy diet was markedly greater than that associated with the medium‐energy diet.

4. The mortality of birds receiving restricted quantities of the medium‐energy diet was two to three times greater than that associated with similar rationing of the low‐energy diet.     

The effect of low‐protein grower diets on the subsequent response of pullets to quantitative food restriction during lay

1. The laying responses of pullets fed from 8 weeks of age on a 12.5% protein grower diet and subsequently subjected to food restriction commencing at various times between 20 and 40 weeks of age were compared with those of pullets reared on diets containing 12.5 or 16% protein and given access to food throughout lay.

2. Restricted feeding during lay of pullets reared on the low‐protein diet substantially improved laying performance, the best results being obtained from pullets fed the low‐protein grower diet and restricted from 20 weeks. The laying responses of pullets restricted after peak‐lay at 40 weeks of age were not significantly different from those of birds restricted prior to peak‐lay.

3. Maximal egg production of 81 % over the 48weeks of the experiment was attained on an average daily ME intake of 270 kcal (1130 kJ) and a FCR of 2.06 : 1.

4. It is suggested that food restriction of laying pullets previously reared on low‐protein diets may be successfully utilised prior to peak‐lay provided such restriction is not so severe as to retard the rate of attainment of mature weight and a continued slight gain in weight thereafter.     

Transfer of 125I to eggs in hens fed on diets containing high‐ and low‐glucosinolate rapeseed meals

1. An experiment was designed to evaluate the effect of the gluco‐sinolate content of rapeseed meal on the transfer of dietary iodine to eggs.

2. The experimental diets, containing two concentrations (50 or 100 g/kg) of high‐ or low‐glucosinolate rapeseed meal and a diet, devoid of rapeseed meal, all supplemented with 0.3 mg I/kg were given to laying hens for 6 weeks before oral administration of ¹²⁵I daily for 11d.

3. The percentage of ¹²⁵I transferred to egg yolk was significantly reduced by the inclusion of high‐glucosinolate rapeseed meal but not by low‐glucosinolate meal.

4. Determination of the total iodine content of egg yolk indicated that there was some reduction in the transfer of dietary iodine to eggs even with the low glucosinolate rapeseed meal.     

Response of broiler chickens to well‐balanced protein mixtures

1. Four experiments were conducted on broiler chickens between one and three weeks of age to determine their response to dietary protein concentrations.

2. Diets prepared by serial dilution of a concentrated protein mixture, well‐balanced with respect to all essential amino acids, were fed in three experiments, while in a fourth experiment, a lysine‐deficient protein mixture was used.

3. Response curves relating body‐weight gain to increasing concentrations of protein and of lysine intake are presented.

4. A table is presented from which optimum protein intakes can be calculated according to changes in input and output costs and changes in growth potential of the chickens.     

Relationship between energy and protein intakes and laying characteristics in individually‐caged broiler breeder hens

1. Individually‐caged broiler hens, which had been reared on an advised rationing programme, were fed allowances of 1.88, 1.61, 1.32 or 1.13 MJ apparent metabolisable energy/bird d at four different protein intakes (27, 23, 19.5 or 16.5 g crude protein per bird d) from 21 to 60 weeks of age.

2. Age at first egg, body‐weight gain and egg production were affected by energy allowance. Birds on the lower energy allowances came into lay later than birds on the higher energy allowances and at a lower body weight.

3. Body‐weight gain decreased with decreasing energy allowance. The decrease in egg output in response to decreasing energy allowance resulted from more birds ceasing to lay and fewer birds laying on more than 3 d per week. Similar changes in the distribution of rates of lay were observed on each treatment as the flock aged.

4. The relationship between body‐weight gain and egg number on each treatment was negative from 21 to 36 weeks, but became less consistent with age.

5. Protein intake had little effect on body weight. At the lowest energy allowance, egg number and egg weight decreased with increasing protein allowance. This effect was not observed on the higher energy allowances.     

Genotype‐level of protein interaction for growth rate in broilers

1. Two groups of White Plymouth Rock which were related to each other as half‐sibs were fed on diets containing either a normal or reduced amount of protein.

2. Compared with the normal diet the low‐protein diet caused a decrease in growth rate which at 38 d was 37% and 25% for male and female chickens, respectively.

3. A genotype‐level of protein interaction was demonstrated for weight at 38 d. Expressed as a genetic correlation for the same trait and measured in the two feeding environments the values were about 0.33.

4. In estimating the genetic correlation the interaction as well as the covariance method were used. The two methods did not give the same estimates.

5. Heritabilities for weight at 38 d tend to be larger in the low‐protein environment.     

The use of n‐paraffin‐grown yeast as the main source of protein in diets for chicks

1. n‐Paraffin‐grown yeast and a mixture of soyabean meal and fish meal were compared in the net protein utilisation (NPU) test, and as protein supplements in diets for broilers up to 4 weeks of age.

2. The difference between the NPU values, 0.66 for yeast and 0.80 for the soyabean meal and fish meal mixture, could largely be attributed to the high nucleic acid content of the yeast.

3. Chicks given the diet containing yeast (190 g/kg) did not grow as rapidly as those given the soyabean meal and fish meal reference diet, and the reduced growth could only partly be explained by a marginal deficiency of methionine.

4. Food conversion efficiency with the yeast diet was improved by maize oil while responses to α‐tocopheryl acetate and sodium selenite were inconsistent.

5. Chicks grew well when yeast replaced fish meal in the mixture of soyabean meal and fish meal, and when fish meal (194 g/kg diet) was the sole protein supplement.     

A test for photorefractoriness in high‐producing stocks of laying pullets

1. Pullets of 2 high‐producing commercial stocks (both brown‐egg layers) were exposed to 5 different lighting patterns between 18 and 72 weeks to test the hypothesis that photoperiods used in commercial lighting programmes early in the laying year may be unnecessarily long and, by accelerating the development of photorefractoriness, may contribute to the decline in egg production observed after the initial peak. Two rooms of 288 pullets were allocated to each treatment.

2. The rate of lay observed with a Step‐Up treatment which gave increases in photoperiod from 8L:16D at 18 weeks to 15L:9D at 27 weeks of age was not significantly different from that of treatments which held the birds on 11L:13D during peak egg production but gave increments up to 15L:9D later in the laying year.

3. A control group maintained on 11L:13D from 20 to 72 weeks laid 295 eggs per bird housed and a further group held on 8L:16D from 0 to 72 weeks laid 284 eggs per bird. These yields were lower than the Step‐Up treatment (299 eggs) but show the potential of modern hybrid stocks to lay prolifically even without light stimulation.

4. It is concluded that the stocks tested in this experiment showed no advantage when given lighting programmes in the first laying year which were designed to minimise the adverse effects of photorefractoriness.     

Differential response of sex‐linked albino (s al ) and silver (S) hens to high and low light intensity

1. Sex‐linked albino (s ^al ) and S (Silver) female chicks were hatched from heterozygous sires from a brown egg‐type line. They were raised in a windowless house and at 17 weeks of age were caged individually in 4 rooms with white fluorescent tubes: two rooms had a “low” light intensity (less than 10 lux) and two had a “high” intensity (average near 400 lux). In total, 157 females completed the experiment.

2. Body weight, sexual maturity, egg weight, the number of abnormal and cracked eggs, efficiency of food utilisation and mortality were not affected either by lighting treatment or by genotype.

3. The genotype X treatment interaction was highly significant for egg number, laying percentage and clutch length to 362 d. The S females were not affected by light intensity. Albino hens of “high” light intensity were superior to the other 3 groups, laying 12 per cent more eggs than non‐albino hens; but their egg production was moderately depressed by “dim” light relative to others.     

Influence of protein concentration on the sulphur‐containing amino acid requirement of broiler chickens 1

1. Two experiments were conducted with male broiler chickens from 3 to 6 weeks of age to determine the effect of dietary protein content on the requirement for sulphur amino acids (SAA). In experiment 1, 0, 0.5, 1.0 or 1.5 g DL‐methionine/kg were added to diets calculated to contain 200, 240 or 280 g protein/kg. In experiment 2, 0, 0.6, 1.2 or 1.8 g DL‐methionine/kg were added to diets calculated to contain 160, 180 or 200 g protein/kg.

2. In experiment 1, the SAA requirement for body weight gain increased as dietary protein content increased. Regression analysis indicated a requirement of 38 g SAA/kg protein.

3. In experiment 2 in which lysine supplementation provided a minimum of 10 g/kg, the requirement for SAA per unit of diet increased only slightly as protein concentration increased indicating that below 200 g protein/kg of diet, the SAA requirement increases per unit of protein with supplementation of the second‐limiting amino acid.

4. Abdominal fat percentage declined in a linear manner with each increment of SAA added to diets containing 160 to 200 g protein/kg. Adding methionine to diets containing 240 or 280 g protein/kg did not affect abdominal fat content. A lower limit of abdominal fat was achieved with a protein concentration of 240 g/kg.

5. It is concluded that the requirement for SAA of finishing broiler chickens is directly related to protein content at concentrations of 200 or more g protein/kg but increases per unit of protein at lower protein concentrations when a minimum lysine concentration is specified. Abdominal fat content reaches a minimum between 200 and 240 g protein/kg of a maize‐soyabean meal diet regardless of SAA content.