NUTRITION ▶▶▶
WG = daily weight gain, grams, EM = daily egg mass, grams and T = °C below 26°C. This equation has been evolving over the last 20 years or so and was recently updated for applica- tion with 2020 broiler breeder genetics and productivity. Maintenance needs are calculated based on metabolic body weight, since both surface area and weight influence basal metabolism. The coefficients for weight gain and egg mass production are quite ‘similar’, meaning that both require com- parable quantities of feed to fuel production of either 1g of egg or 1g of body tissue . The ‘energy’ estimates are then di- vided by the energy level of the feed, in this case 2.85 kcal/g. Finally, the effect of low environmental temperature is recog- nized, being +1g feed for each -10°C below the thermoneu- tral temperature of 26°C. Using these components that drive feed intake, the following calculations show estimated feed intake from 24-65 weeks of age (Table 1). In this example, estimates of feed intake are at a thermoneu- tral temperature of 26°C. Table 2 shows a breakdown of these components in relation to feed intake. Maintenance is always clearly the dominant use of feed at 60-70% which equates to anywhere from 100-120 g/b/d. Feed needs for growth are quite significant up to peak production but, hopefully, tail off to less than 3% of needs, assuming ideal control of body weight during the post-peak period. Requirements for daily egg mass never exceed 30%, declining to only 20% at the end of the breeder cycle. Interestingly, the peak feed needs for egg mass are maximised at around 36 weeks of age, then declin- ing very little until 45 weeks of age. This latter effect is predi- cated by the slowly increasing egg size off-setting the decline in egg numbers and suggests caution in the degree of feed withdrawal that often starts as early as 35 weeks of age.
Restricted-fed breeder hens When there is a limited supply of nutrients, as always occurs with restricted-fed breeder hens, the bird needs to prioritise their use. Maintenance needs are the main priority and nutri- ents are only available for growth or egg production after
these needs have been met. As has been suggested. It would be convenient to accept this assumption, yet it may be a naïve assumption, especially when it comes to amino acid utilization. Since maintenance is such a large component of nutrient needs, then feed allocation must closely mirror changes in body weight. Simply stated, if birds are ‘over- weight’ then they have even greater maintenance needs and this is given priority in energy partitioning. Consequently, when breeders are heavier than standard it is essential to feed correspondingly more feed to meet maintenance needs, rather than the often adopted commercial approach of giving less feed in an attempt to ‘control’ escalating weight gain. If breeders are underweight then we can judiciously give more feed than standard in an attempt to standardise weight for age (making more energy available for growth). Consequent- ly, both heavy and light birds need more feed than normal and it will only be the bird on target weight that receives the standard allocation. Such predictions are obviously greatly in- fluenced by uniformity of body weight, since we must react to flock mean metrics.
Beyond thermoneutral The equation for calculating feed needs includes a component to account for colder environmental temperatures beyond the thermoneutral temperature of around 26°C. While there is an obvious global trend towards controlled environment housing, significant numbers of flocks are still maintained in open-sided houses. With colder seasonal temperatures, maintenance ener- gy needs may increase by as much 10%. In estimating the need for increased feed, it is potentially not straightforward to consider ‘average’ temperature in such calculations. In regions where this adjustment is most critical there are invariably sig- nificant differences between day and night-time temperatures. With floor-managed breeders, birds usually ‘huddle’ together at night-time on the litter or slats to insulate themselves from the effects of the colder temperatures. In effect, colder night- time temperatures are perhaps not as harmful as might be pre-
Table 2 – Breakdown of feed used for maintenance, growth and egg production. Proportional use of feed (%)
Daily feed (g)
Weeks age Predicted intake (g) Maintenance 24 28 32 36 40 45 50 55 60 65
101 153 164 163 163 163 160 158 156 154
10 ▶ POULTRY WORLD | No. 7, 2022
85 61 63 67 69 70 72 74 76 77
Growth 13 12 8 3 3 1 1 1 1 2
Eggs 1
27 29 30 28 28 26 24 23 21
Maintenance 86 94
103 110 112 115 116 117 118 119
Growth 14 18 14 5 5 2 2 2 2 3
Eggs 1
42 47 49 46 46 42 38 36 32
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