Search

SUMMARYIn a 2 × 4 factorial experiment, the laying performance of hens given diets with or without blood meal and four concentrations (0, 5·71, 11·43 and 17·14 g/kg) of added magnesium chloride was measured for 280 days. The inclusion of 50 g/kg blood meal in the laying diet reduced the rate of laying (P < 0·05), egg weight (P < 0·01), egg output (P < 0·01), food intake (P < 0·01), body weight gain (P < 0·01) and body weight at 457 days (P < 0·05). It increased the height of albumen (P < 0·05), Haugh unit score (P < 0·01) and shell colour intensity (P < 0·05) of fresh eggs. The inclusion of increasing dietary concentrations of magnesium chloride reduced (P < 0·01) the specific gravity of eggs but had no significant effect on any of the other egg quality or production characteristics. The dietary treatments had no significant effect on Haugh units of stored eggs.

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.

White Leghorn × Australorp hens were given 4 layer diets containing 0, 5.79, 12.19 and 18.97% of undecorticated, oil-extracted sunflower seed meal (SSM) either with or without added sunflower oil (SO) and 4 other diets containing either 2.35% full-fat sunflower seeds (FSS) or 1% sunflower hulls (SH) or 1% SH + SO or 2.0% sunflower kernels (SK). The laying performance of these hens was measured from 24 to 64 weeks of age. The dietary level of SSM either with or without SO had no significant effect on either the rate of egg production or egg mass. There was a tendency for egg weight and food intake to be increased and Haugh units to be decreased by the diets containing 12.19% and 18.97% SSM. The SH reduced egg weight and FFS reduced Haugh unit score. None of the dietary treatments had a significant effect on the rate of lay, egg mass, food conversion efficiency, body-weight gain, mortality, egg specific gravity or faecal moisture content.

A simulation model was constructed to compare the profitability of feeding high- and low-protein diets when rearing pullets for egg production. Low-protein diets were found to be more profitable if laying adult birds were subsequently retained beyond 58 weeks of age, although predictions of the model were shown to be very sensitive to some of the inputs and production parameters incorporated in the model. The optimum length of lay for the data being analysed extended beyond 84 weeks of age. This model may be simply modified to study other genotypes and diets than those considered in this paper.

The productivity of heavy-, medium- and light-weight White Leghorn x Australorp pullets (216 of each strain) was established on three feed restriction regimes. The pullets were either restricted from 6 to 21 weeks of age to 80% of feed intake of pullets fed ad libitum, restricted in feeding time to 6 hours in every 48 from 6 to 21 weeks, or fed a diet containing 10% protein from day-old to 16 weeks of age. All restricted pullets ate between 19 and 37% less feed during rearing, were between 11 and 34% lighter at 21 weeks of age, and attained 50% production by 10 to 32 days later than pullets fed ad libitum. Strains differed in their responses to feed restriction as measured by mean body weight at 21 weeks, feed intake during lay, and feed per dozen eggs. Strain x rearing interactions were not observed for rate of lay, mean egg weight, total egg mass or rate of mortality. The biological responses were analyzed in economic terms using a computer simulation model. Restricting the feed intake of the heavy strain by any of these methods was more profitable, at ruling 1976 prices, than ad libitum feeding, because of the saving in feed cost and marked improvement in productivity. Performances were not improved by restriction in the light strain pullets, but feed cost was reduced by all three methods. With the medium strain, limiting the quantity of feed was more profitable than the other two methods.

The effects on body weight and laying performance of restricting the feeding time of medium weight crossbred pullets to 6 or 8 hours in every 48 hours from 6, 9 or 12 to 20 weeks of age were studied in a factorial experiment. Before the start of the restriction programme, half of the pullets were fed ad libitum; the other half were not fed on Wednesday and Sunday of each week from three weeks of age. The control birds were fed ad libitum throughout the rearing phase. The feed intake and the weight of pullets at the end of the restriction programme at 20 weeks were reduced by between 17 and 40 per cent and between 18 and 33 per cent, respectively, compared with the control, depending on the early feeding regime and the duration of restriction. The average age at 50 per cent production of the restricted treatments was delayed by 15 days compared with the controls. No significant difference was found in the laying performance of the restricted birds or between any of these and the controls. The restricted birds however were less efficient in converting their feed to eggs than the control birds. Rearing and adult mortality were not affected by restriction. The results suggested that for maximum economic return the restriction programme should not be delayed beyond 6 weeks and should continue to 20 weeks of age. Delaying the start of the restriction programme beyond 6 to 9 or 12 weeks of age will reduce the saving in feed intake from approximately 35 to about 29 and 17 per cent of feed consumed by full-fed birds at 20 weeks respectively.

The deposition of dietary oxycarotenoids in egg yolks of 576 hens was studied in a factorial experiment where diets contained three levels (0, 2 and 4 per cent) each of animal tallow and sunflower oil. The diets were isocaloric and isonitrogenous and supplemented with 22 mg kg-' of synthetic pigment. The deposition of oxycarotenoids in egg yolks was determined by both visual and colorimetric methods. Supplementing the diet with either or both fats increased the visual score of the yolk colour compared with the unsupplemented control. The colorimetric method showed a similar increase in yolk colour with all supplements except 2 per cent sunflower oil. When the two fats were mixed, yolk colour was deeper when the level of tallow was higher than that of sunflower oil.

Three of five groups of White Leghorn x Australorp hens aged 73 weeks, housed in cages, were fed a laying diet containing zinc (23.7 g/kg), or iodine (4.1 g/kg), or calcium (1.0 g/kg). The fourth group of hens was given only whole-grain barley while a fifth group given a normal laying diet served as the control. All groups were fed their respective diets until rate of lay dropped to 0% or less than 2%, and they were then given a normal laying diet until 97 weeks of age. Water was available at all times and 15.5 h of constant light was provided daily to all treatments throughout the experiment. Hens given the zinc and the whole-grain barley diets ceased egg production within 1 week and remained out of production for about 10 days. The hens in both of these treatments reached peak egg production (67%, on a hen day basis) 8 weeks after the initiation of treatments, after which they continued to lay at a higher rate than those given iodine, calcium and control treatments. Hens given the diets with either iodine or calcium reached their lowest rate of lay (1.6%) after 15 and 7 days of feeding the two diets respectively. They resumed laying immediately after the resumption of feeding the normal laying diet and reached peak egg production (59%) at 8 and 12 weeks after feeding the iodine and calcium diets respectively. The treated hens laid eggs with higher Haugh units and specific gravity values than those eggs of the controls. The lowest rate of decline in both those traits, from the pre-treatment values, was in the zinc and barley treatments. These treatments also had the lowest percentage of cracked eggs. There was no significant difference among treatments in mean rate of lay, egg weight, or rate of mortality from 73 to 97 weeks of age. The present results suggest that feeding wholegrain barley can be used successfully to extend the productive life of laying hens beyond the first year of egg production if such an extension is desirable in a given economic situation. It is a simpler technique than the conventional method of induced moulting and the method of feeding a high level of zinc.

A diet containing 10 per cent protein and 11.31 MJ M.E. kg-1 was fed to six groups of eggtype pullets from either day old or four weeks for 8, 12 and 16 weeks in both summer and winter. The same diet was also fed to another group from 8 to 20 weeks of age in both seasons. During the rest of the rearing period of each treatment a diet containing 16 per cent protein was fed to 20 weeks of age. The control group was fed a diet containing 20,16 and 12 per cent protein and 12.1 5 MJ M.E. kg-1 from day old, 6 and 14 weeks of age respectively. In both seasons, feeding the restrictive diet resulted in a reduction in the cost of feeding and in body weight gain to 20 weeks of age; and a delay in maturity compared with the control without adversely affecting egg production traits or increasing food consumption during the laying phase. Pullets fed the restrictive diet from day old ate less food during rearing, matured later and tended to lay smaller eggs throughout the laying period than their counterparts which were restricted from four to eight weeks of age in both experiments. Food consumption was not affected by the duration of restriction in either rearing season. However, feeding costs and body weight of pullets at the end of both rearing seasons were reduced progressively by increasing the duration of restriction. Rate of mortality was not affected by the rearing treatments when the birds were reared in summer, whereas in winter pullets restricted from day old for 12 to 16 weeks had the higher rate of mortality. Mortality during laying was not affected by the rearing treatments in either season. The results of both experiments suggest that for maximum return the optimum age for feeding the low protein diet is from 4 to 20 weeks of age in either season.