Bacterial contamination on eggs during incubation and hatching,and of fluffs of newly‐hatched chicks

1. Average numbers of bacteria on clean and dirty eggs produced from a specified‐pathogen‐free chicken flock were 10^3.0 and 10^4.5, respectively. When the eggs were washed with running tap water at about 40°C, the respective bacterial counts were reduced to 10^2.0 and 10^2.7, the latter difference being not significant.

2. After fumigation with formaldehyde from 40 ml formalin (372 g formaldehyde/1) and 20 g potassium permanganate/m³ for 1 h, no bacteria were recovered from clean eggs by agar plate culture, while a small number of bacteria were detected in three out of five dirty eggs.

3. Average numbers of bacteria detected in clean fumigated eggs were 10^0.8 to 10^1.1 during the first 19 d of incubation and 10^1.2 and 10^1.4 were recovered on days 20 and 21 of incubation, respectively. At the end of hatching, eggs containing dead embryos were highly contaminated with 10^3.8 organisms on average.

4. Fluffs of newly‐hatched chicks scattered inside the hatcher were contaminated with bacteria at 10^4.0 to 10^8.4 organisms/g. Water in the basin placed in the hatcher and floating fluffs in water were highly contaminated with bacteria.     

Response of broiler chicks to threonine‐supplemented diets to 4 weeks of age

1. Two experiments were carried out to determine the response of broiler chicks to threonine‐supplemented diets between 10 and 28 d and 7 and 21 d of age, respectively.

2. In the first experiment female broiler chicks were fed on 11 experimental diets. Two iso‐energetic basal diets (diets 1 and 2) were prepared with 200 and 160 g CP/kg and 7·6 and 6·0 g threonine/kg respectively. Both diets contained 11·5 g lysine and 8·7 g sulphur‐containing amino acids/kg. Diet 3 was composed of diet 2, supplemented with all essential and non‐essential amino acids (EAA and NEAA, respectively) except threonine, to the concentrations of the amino acids in diet 1. The NEAA were added as a combination of glutamic acid and glycine. Diets 4 to 11 had the same compositions as diet 3, but contained increasing amounts of threonine.

3. For birds fed on diet 2, gain was significantly lower and food/gain ratio was significantly higher than for birds fed on diet 1. Supplementation with EAA, NEAA and threonine to the same concentrations in diet 1 resulted in a performance similar to that found on diet 1.

4. In experiment 2, male and female broiler chicks both received 10 experimental diets. Diet 1 contained 220 g CP/kg and 8.5 g threonine/kg, diet 2 contained 160 g CP/kg from natural raw materials and 6 g threonine/kg. Both diets contained 12·4 g lysine and 9·3 g sulphur‐containing amino acids/kg. Basal diet 2 was supplemented with all EAA and NEAA to the concentrations of basal diet 1, except for threonine. Diets 3 to 10 had the same compositions as the supplemented diet 2, but contained increasing amounts of threonine.

5. For male and female chicks on diet 2, gain was significantly lower and food/gain ratio significantly higher than those on diet 1. Diet 10 (160 g CP/kg plus all EAA, including threonine, and NEAA supplemented to the concentrations of diet 1) resulted in the same performance as diet 1.

6. The results indicate that, when low protein maize‐soyabean meal diets supplemented with EAA and NEAA with 13·31 MJ ME/kg were fed to male and female broiler chicks until 21 d of age, improvements in gain and food/gain ratio were obtained when the dietary threonine content was increased to 7·25 g/kg. When female chicks were fed threonine‐supplemented diets to 28 d of age, improvement in gain and food/gain ratio was obtained when the threonine concentrations were increased to 6·32 g/kg diet.

7. Curves have been fitted to the data, from which a cost‐benefit analyses can be made and an optimum threonine dose calculated, using local prices.     

Influence of diet on the intestinal microflora and meat flavour of intensively‐reared broiler chickens

1. An attempt has been made to modify the composition of the gut flora of broiler chickens by dietary means in order to determine any concurrent changes in meat flavour.

2. Birds given a diet containing an increasing proportion of whole wheat supplemented with fresh green vegetable matter (special diet) were compared with conventionally‐fed controls. At 12 weeks of age those receiving the special diet had 10 to 100‐fold higher counts of Escherichia colt and faecal streptococci in the duodenum and lower small intestine and showed differences in the intestinal incidence of species and biotypes of lactobacilli.

3. Evaluation of cooked breast‐meat samples by a trained sensory panel showed a significant difference in flavour (P < 0.01) between conventional and special‐diet birds which varied from perceptually very slight to slight. The main terms used in distinguishing special‐diet birds from conventional controls included ‘richer’, ‘meatier’ and ‘sweeter’.

4. Storage of plucked, uneviscerated birds at 4 °C for 8 d maintained the flavour difference between the dietary groups but the effect of storage on flavour was greater in both groups of birds than the influence of diet alone. The likely influence on flavour of autolytic changes occurring in the muscle during storage of the birds is discussed.     

Attempts to achieve low‐weight broiler breeder hens by severe growth depression during various periods up to 6 weeks of age and food allocation below the recommendations thereafter

1. Three experiments were carried out with White Rock (Anak) female chicks to evaluate the possibility of obtaining low‐weight breeder hens and to assess their reproduction potential. Such hens were obtained by early growth depression induced by either severe food restriction (SFR) from 1 or 2 to 3 or 4 weeks of age, or a low‐protein diet (LPD) fed from 0 to 6 weeks of age, or the use of diets containing 0·7 or 0·8% zinc as ZnO from 1 to 3 weeks of age, followed by food allocation below recommendation up to 22 or 67 weeks of age.

2. Body weights (BW) of the birds whose growth had been depressed were consistently and at time significantly lower than those of the control birds throughout the experiments. Age at first egg was delayed in hens previously fed the LPD and the diet containing the higher concentration of ZnO, and in those exposed to SFR from 2 to 4 weeks of age. BW at that time tended to be lower in birds whose growth had been depressed, although a significant effect was observed in only one experiment.

3. Egg production and egg size were not significantly affected by the various treatments, except for the lower production in hens fed the LPD at an early age.

4. Negative regressions (on an individual basis) were consistently observed between BW at 22 weeks of age and age at first egg, and between age at first egg and number of eggs laid. Positive regressions were observed between age at first egg and BW at that time. The regressions between BW at 22 weeks of age and number of eggs laid were positive but not always significant.

5. Severe growth depression at an early age (produced by food restriction or ZnO supplemented diet, but not LPD) followed by decreased allocation of food afterwards, could provide a means for reducing BW of broiler breeder hens without adversely affecting egg production. This procedure may save 2·5 to 6·6% of the food consumed during the life span of the birds.     

Plasma growth hormone and insulin‐like growth factor‐I (IGF‐I) concentrations at the onset of lay in ad libitum and restricted broiler breeder fowl

1. Plasma concentrations of growth hormone (GH) and insulin‐like growth factor I (IGF‐I) were determined in individually caged broiler breeder females from 17 to 30 weeks of age. The birds were fed ad libitum or restricted during rearing in a randomised block design. Restricted birds were fed ad libitum after laying an egg and egg production was recorded to 54 weeks.

2. GH concentrations were higher in restricted compared with ad libitum‐fed birds at 17 to 21 weeks of age and were similar thereafter. Plasma IGF‐I concentrations were higher in restricted compared with ad libitum‐fed birds throughout the sampling period of the experiment.

3. The age at first egg was delayed by about two weeks in restricted birds. At 54 weeks of age they had laid 114 compared with 67 eggs in birds fed ad libitum throughout and had produced less than half the number of eggs with defective shells.

4. It was suggested that differences in egg production between ad libitum and restricted broiler breeder females could be related to changes in the pattern of GH and/or IGF‐I secretion.     

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.     

Effects of male body weight,strain and dietary protein content on fertility and musculo‐skeletal disease in naturally mated broiler breeder males

1. The effects of male body weight at mating and different rates of gain on overall fertility were studied in two strains of broiler breeder males fed on a diet containing 160 or 120 g crude protein/kg. Sexual activity, musculo‐skeletal disease and culling were also assessed.

2. There were no differences in early fertility between males weighing 3–0 or 3–5 kg at the start of the mating period, or between males gaining 1.0 or 1.5 kg body weight from mating to 60 weeks of age.

3. There were no differences in fertility between males fed on the two diets differing in crude protein content.

4. One strain of male had lower fertility than the other and this was associated with a greater weight of breast muscle, lower frequency of observed copulations and a higher number of incompleted matings.

5. Sexual activity declined and the number of spermatozoa trapped on the perivitelline membrane increased with age.

6. There were no differences among the treatments in the prevalence of musculo‐skeletal lesions (destructive cartilage loss). As a proportion destructive cartilage loss occurred in 0^‐67 of the males at 66 weeks of age. Degeneration of the antitrochanter was present in 3 of 50 females examined and a cartilage flap in the medial condyle of the tibiotarsus occurred in 15 of these birds.

7. Beak lesions were the most important cause of male culling which averaged 0–24 as a proportion of the males at the start of the experiment.     

Effect of restricted feeding during the rearing period and a “forced moult” at 40 weeks of production on the productivity of Pekin breeder ducks

1. Six males and 24 female Cherry Valley Pekin ducklings were randomly allocated to each of 12 pens to test the effects of quantitative food restriction during the rearing period on the subsequent reproductive performance. At the end of the laying period (60 weeks) a “forced moult” was introduced and its effect on a further 40 weeks production investigated.

2. The 3 rearing treatments were 50% of ad libitum intake from 3 to 20 weeks; 75% of ad libitum intake from 3 to 20 weeks and ad libitum intake throughout. During the laying period (20–60 weeks) and post forced‐moult period (60–100 weeks) duck breeder pellets were fed ad libitum to all groups.

3. Highly significant (P ≤ 0.01) differences in favour of the restricted groups over the ad libitum‐fed groups were observed in most of the responses studied. The following were the main advantages of food restriction: lower lifetime food intake, lower carcase fat content at 20 weeks, delay in sexual maturity, higher egg production, higher peak and terminal production, higher fertility, higher hatchability of eggs set and lower mortality. Egg mass and hatchability of fertile eggs was not influenced by food restriction in this experiment. The use of a “forced moult” showed that it could be of economical importance.

4. Differences between treatments in respect of absolute and relative visceral masses were also investigated. The absolute masses of the intestine, heart, gizzard and liver all decreased as the degree of food restriction increased. The relative visceral masses showed the opposite trend with the exception of the heart which showed no significant differences between treatments.     

Differential effect of age on metabolisable energy content of high protein‐low energy and low protein‐high energy diets in young broiler chicks1

1. An experiment was carried out with 6‐d old male broiler chicks in an attempt to understand better the effect of age on dietary AME_n of high protein‐low energy (HPLE) and low protein‐high energy (LPHE) diets which are used in the determination of the AME_n content of grains when substituted for the entire diet. The experiment was carried out in a split‐plot design in which the effects of 2 diets (HPLE‐reference and LPHE‐test, containing maize) on food intake, faecal excretion, dietary AME_n and the utilisation of the nutrients were evaluated in 3 age periods (A = 11–13, B = 15–17 and C = 20–22 d of age).

2. Chicks fed on the HPLE diet consumed significantly less food than those fed on the LPHE diet during periods A and B, but not in G. They also produced a significantly larger amount of droppings during periods B and C. Food‐to‐droppings ratio, which was consistently and significantly lower in chicks fed on the HPLE diet, decreased markedly in period C only in these birds.

3. Absolute and relative retention (RR) of dry matter (DM) and starch, and RR of nitrogen (N) from birds fed on the HPLE diet, were consistently and significandy lower than from those fed on the LPHE diet, but fat retention (absolute and relative) was higher. RR of DM and of N in period C was significantly lower than in periods A and B, while RR of fat and of starch was not affected by age. The effect of age on RR of N was observed only with the HPLE diet.

4. AME_n of the HPLE diet, but not of the LPHE diet, in period C was significandy lower than in periods A and B, resulting in a significant interaction between age and diet and a general reduction with age. The calculated AME_n contents of the maize in periods A and B were essentially the same (14.91 and 14.85 MJ/kg, respectively), and lower than in period C (15.28 MJ/kg). It is concluded, therefore, that because of its effect on AME_n of the HPLE reference diet in chicks older than 17 d, bird age is of considerable importance in the determination of AME_n in grains when substituted for the entire diet.     

Comparative development of digestive organs,intestinal disaccharidases and some blood metabolites in broiler and layer‐type chicks after hatching

1. Body weight, digestive organ weights, and activities of disaccharidases (maltase and saccharase) activities were determined from day of hatch to 21 d of age in meat‐ and egg‐type chickens. Blood plasma was analysed for enzyme activities and metabolite concentration.

2. In meat‐type chickens food intake and growth rate were about 3‐fold those in egg‐type chickens. Food efficiency was superior in meat‐type chickens throughout the experimental period.

3. Meat‐type chickens hatched with disaccharidase activities exceeding those found in their egg‐type counterparts 2‐ to 5‐fold. From 7 d of age on, this trend reversed, i.e. activity was much higher in egg‐type than in meat‐type chickens.

4. Blood plasma amylase activity increased gradually in meat‐type chickens and was higher than in egg‐type chickens to 14 d of age. No breed differences were observed for alkaline phosphatase or lactate dehydrogenase activities during the experimental period.

5. Blood plasma concentrations of total protein, albumin, glucose, and calcium, were lower in meat than in egg‐type chickens.     

Effect of oiling on internal quality of eggs stored at 28 and 12°G

1. The effects of spraying linseed oil on naturally clean eggs, subsequently stored for 24 d at 28 °C were studied.

2. Oiling slowed the decline in albumen height (Haugh units) to that which occurred in unoiled eggs stored at 12 °C.

3. Oiling slowed the increase in albumen pH equally at 28 and 12 °C.

4. Oiling markedly decreased the weight loss of eggs stored at either temperature.

5. Oiling and temperature of storage were without effect on the whipping volumes of either albumen or unseparated albumen and yolk.     

Effects of structure and xylanase treatment of brewers’ spent grain on performance and nutrient availability in broiler chickens

1.?A factorial (2 × 3) feeding trial was set up to investigate the effects of coarse or finely ground brewers’ spent grain (BSG) and xylanase treatment, either with no xylanase, top-dressed with xylanase or pre-treated with xylanase.

2.?The experimental diets shared the same basal formulation and were fed to male broiler chickens (Ross 308) housed in individual cages from 12 to 29 d of age.

3.?Xylanase pre-treatment reduced the dietary concentration of arabinoxylan by 15–30%. Pellet durability increased when BSG was ground.

4.?Feed utilisation was significantly higher (6%) when the birds were given coarse BSG rather than ground BSG, whereas there was no significant effect of enzyme treatment. Apparent metabolisable energy was unaffected by the dietary treatments.

5.?The overall starch digestibility was high (99%), with no dietary differences, whereas ileal protein digestibility was low (57%). Xylanase top-dressing tended to improve ileal protein digestibility but, in general, xylanase treatment had no major effect on overall performance in male broilers given diets with BSG.     

Correlations between body measurements and tissue composition of oat-fattened White Kołuda geese at 17 weeks of age

1.?The aim of the present study was to evaluate the yield and tissue composition of carcases from White Ko?uda® ganders (males) and geese (females), and to determine the relationships between body measurements and carcase tissue composition.

2.?The experiment was carried out on 200 geese (100 males and 100 females) reared to 14 weeks of age and then fed with oats for the next 3 weeks. Live body weight and body dimensions, slaughter yield, weight and percentage of muscles and skin with fat in carcase were measured and correlation coefficients were calculated between body measurements and slaughter values and carcase tissue composition.

3.?White Ko?uda® geese reared to 17 weeks of age were characterised by high body weight (6705 g) and good muscle yield (29·9%). Males had greater body weight, musculature and fatness than females. Sternum length and breast circumference, width and depth were good indicators of carcase muscle weight in 17-week-old geese.

4.?Negative coefficients of correlation between sternum length and weight of skin with subcutaneous fat indicate that increased selection pressure in pedigree flocks of geese on sternum length should be paralleled by reduced carcase fatness in these birds.     

The choline and sulphur amino acid requirements of broiler chickens fed on semi‐purified diets

1. Growth and food conversion efficiency of broilers were reduced at low dietary choline concentrations. These effects were accentuated by low dietary total sulphur amino acids (TSAA).

2. Increased mortality, perosis and other pathological changes involving a number of tissues were observed in birds fed on a low‐choline diet.

3. Methionine replaced part of the dietary requirement for choline at low dietary choline concentrations.

4. High dietary concentrations of choline (> 1 750 mg/kg) increased the requirement for dietary TSAA.

5. Increasing the dietary choline while maintaining the TSAA at an inadequate level may decrease performance.     

Effects of ascorbic acid and 1, 25‐dihydroxycholecalciferol on alkaline phosphatase and tibial dyschondroplasia in broiler chickens

1. The effects of graded amounts of dietary ascorbic acid with or without 10 μg/kg dietary 1,25‐dihydroxycholecalciferol on performance, blood and bone variables were measured in broiler chicks.

2. 1,25‐Dihydroxycholecalciferol prevented the tibial dyschondroplasia and rickets caused by feeding a low calcium diet. Gain:food was decreased, but body weight was not affected by feeding 10 μg/kg 1,25‐dihydroxycholecalciferol. Phytate phosphorus retention was increased by dietary 1,25‐dihydroxycholecalciferol.

3. Dietary ascorbic acid did not influence the incidence of tibial dyschondroplasia, but did reduce the incidence of rickets at a dietary concentration of 250 mg/kg. Gakv.food was increased when 250 or 500 mg ascorbic acid/kg diet were added along with 10 μg/kg 1,25‐dihydroxycholecalciferol in one of two experiments.

4. Alkaline phosphatase activity and plasma 1,25‐dihydroxycholecalciferol were not affected by the dietary treatments. Plasma 25‐hydroxycholecalcif‐erol concentration was decreased by dietary 1,25‐dihydroxycholecalciferol.

5. Ascorbic acid had no synergistic effects with 1,25‐dihydroxycholecalciferol on the blood and bone variables investigated in broiler chickens at the dietary concentrations of 1,25‐dihydroxycholecalciferol used in this work.     

Influence of ante‐ and peri‐mortem factors on biochemical and physical characteristics of turkey breast muscle

Summary

The course of post‐mortem breakdown of glycogen and ATP in turkey pectoralis major muscle was markedly influenced by several ante‐ and peri‐mortem variables. Application of a proper stunning procedure was highly effective in preventing peri‐ and post‐mortem muscle stress reactions.

The physiological level of glycogen and ATP was not significantly affected by road transportation covering 260 km. Birds which rested for 24 hrs following transportation had lower glycogen and ATP levels at the moment of slaughter than non‐rested birds.

According to the changes in the rate and extent of post‐mortem biochemical reactions, several meat characteristics such as water‐holding capacity, colour, and tenderness were significantly changed.

Furthermore, the results also indicate that turkey breast muscle is susceptible to a PSE‐like condition as described in pork.     

Effect of dietary protein,essential and non‐essential amino acids on the performance and carcase composition of male broiler chickens

1. The present study was conducted to determine the possibility of using low‐protein broiler diets supplemented with synthetic amino acids. The effects on performance, carcase composition and nitrogen retention were evaluated.)

2. A starter diet was given, ad libitum, from 7 to 21 and a finisher diet from 21 to 42 d of age. Body weight, weight gain, food intake and food conversion (FC) were determined at 3 and 6 weeks of age. Abdominal fat deposition (AFD), carcase yield, carcase fat and protein and nitrogen retention were determined at 6 weeks of age. During the starter period chicks were given a 231 g/kg crude protein (CP) diet and a low protein diet supplemented with synthetic amino acid, a: to National Research Council recommendations, b: to the concentration of the control diet, and c: in agreement with the pattern of body composition. Glutamic acid and glycine were added to some diets as sources of non‐essential amino acids (NEAA). All diets contained 12.62 MJ metabolisable energy (AME_n)/kg. The diets administered between 3 and 6 weeks were comparable to the starter diets, except that they contained more AME_n (12.85 MJ/kg) and less protein.

3. Performance equal to that of high protein controls was obtained with birds fed a low protein diet supplemented with synthetic essential and NEAA to the amounts in the control diet or based on the amino acid profile of body protein. This was not achieved with low protein diets supplemented with synthetic amino acids to the amounts recommended by NRC.

4. Without altering performances, the efficiency of protein utilisation of birds fed on low protein diets was superior to that of birds fed on the commercial control diet and their nitrogen excretion was reduced by 26%. The percentage carcase yield and protein was unaffected by the dietary regimen but carcase fat content and AFD increased as the protein content of the diet decreased.

5. These results show that it is possible to obtain the same performances with low protein diets supplemented with synthetic amino acids, using an ideal amino acid balance. However, low protein diets result in a higher carcase fat content.     

Studies on the toxic effects of crambe meal and two of its constituents, 1‐cyano‐2‐hydroxy‐3‐butene (GHB) and epiprogoitrin,in broiler chick diets

1. Studies were undertaken to determine a safe inclusion rate for crambe (Crambe abyssinica) meal in broiler chick diets, and to determine the mechanism for adverse effects by investigating its constituents; l‐cyano‐2‐hydroxy‐3‐butene (CHB) and 3‐butenyl glucosinolate (epi‐progoitrin, E‐PG).

2. Crambe meals were prepared to differ in E‐PG (19, 36 and 40 g/kg) and CHB contents (0.1, 0.7 and 1.9 g/kg), and with either active or inactive thioglucosidase.

3. Meals were fed to 7‐d‐old broiler chicks at 50 or 100 g/kg of the diet for 12 or 13 d. In separate studies, isolated E‐PG or CHB were mixed into the diet or administered by gavage to 7‐d‐old broiler chicks in amounts equivalent to 50 or 100 g/kg crambe meal diets for 10 and 12 d, respectively.

4. Weight gain decreased (P<0.05) in chicks fed on the high glucosinolate crambe diets or isolated E‐PG. Food consumption decreased (P<0.05) in chicks fed on the diet containing the high E‐PG meal with active enzyme.

5. Mild liver lesions and increased serum aspartate aminotransferase were found in chicks fed on the diet containing the high glucosinolate meal with active enzyme. Other organs, including thyroids, were normal.

6. Commercially‐processed crambe meal appeared safe at an inclusion rate of 50 or 100 g/kg diet, but could not be recommended at this point for long term feeding.     

Effects of dietary sulphur‐containing amino acids on performance and breast meat deposition of broiler chicks during the growing and finishing phases

1. Two growth trials were performed to measure the effects of dietary methionine and cystine (SAA) on growth rate, food conversion efficiency and breast meat deposition in male broilers.

2. In experiment 1, broilers were grown on 6 experimental diets covering a range from 6.9 to 9.6 g SAA/kg. The diets were fed from 15 to 33 d of age. Similarly, in experiment 2, 6 diets containing 6.0 to 8.5 g SAA/kg were fed to finishing broilers 33 to 43 d of age. In each experiment 60 birds per treatment were processed, and carcase yield and breast meat percentage were determined.

3. Significant responses in weight gain, efficiency of food conversion and breast meat percentage were detected, which could be described well by exponential regression curves. Dietary SAA requirements to obtain maximum efficiency of food utilisation and maximum breast meat deposition were estimated to be about 9.0 g/kg from 15 to 33 d of age, and about 8.0 g/kg from 33 to 43 d of age.

4. Economic aspects were considered to calculate optimum SAA specifications from the results. In both trials, the dietary optimum of SAA was found to be higher for birds to be further processed than for birds to be marketed as whole carcases.     

Influence of period of deferment before stocking spring‐burnt sourveld on sheep performance and veld productivity

Spring‐burnt sourveld was stocked with Merino lambs after three different periods of deferment from the time of start of growth in spring. During three seasons, average seasonal livemass gains on veld which was stocked shortly after the start of growth were some 80% higher than on veld stocked two to three weeks later. Using veld from which grazing was excluded by means of exclosure cages as a control, the residual effects of the deferred grazing treatments on yields of grasses classified as palatable, intermediate or unpalatable were estimated in the next season. Deferring grazing in spring was of negligible value in preventing loss of vigour of the palatable grasses. The respective yields for the three classes were on average for three seasons, 57, 101 and 144% of those for the controls. The findings indicate the need for drastic revision of current recommendations with regard to the management of sourveld for sheep production.