65. The Code of Recommendations ("Welfare Code") for turkeys issued by the Agriculture Departments provides guidance on the minimum available floor area per bird which is acceptable in most circumstances for different housing systems. These recommendations aim to provide turkeys with sufficient space to stand normally, turn round and stretch their wings, and also to sit down without interference from other birds. The recommended minimum available floor area per bird for turkeys reared in conventional (enclosed) housing is 260cm² per kg which equates to a maximum stocking density of 38.5kg/m².
66. We have seen turkeys of a wide range of weights and ages, stocked at a variety of densities in different production systems. We have visited farms with conventional (enclosed) houses stocked with turkeys of advanced ages at densities of 40-60kg/m². These densities exceed the maximum recommended in the Welfare Code. However, the birds' requirements for ventilation, litter quality and temperature were met by careful management and sophisticated technology and we observed that the turkeys made use of shared space to stretch, wing flap and squat. We believe that most needs, including many of those to show particular behaviours, are met at these levels. However, it is essential that the house is properly equipped with effective environmental control systems. Our investigation did not discover scientific evidence concerning the effect of stocking density on behaviour. Therefore, our observations lead us to the conclusion that a stocking density of greater than 38.5kg/m² is acceptable for large birds kept in conventional houses.
67. We found that turkeys were marketed at a wide range of weights (5kg-20kg) and believe that a more sophisticated rule than a simple limit on weight per square metre is required for houses with modern environmental control systems. We believe that big turkeys require, weight for weight, less space than small ones, because as turkeys grow their size increases in three dimensions (length, width and height), whilst the floor area they occupy increases in only two dimensions.
68. In order to calculate the area occupied by a bird of any particular weight stocking densities should be scaled as a two-thirds power of liveweight (two dimensional floor area divided by a three dimensional turkey). The use of such mathematical scaling has a long tradition in biology (e.g. D'Arcy Thomson 1932). Certain complications with scaling have become apparent such as the slight change in density as animals grow and change in shape. However, these differences are relatively insignificant and, in order to establish a method of measuring area, they have been discounted. Indeed, it is the view of FAWC that studies of livestock space requirements have revealed no evidence that a two-thirds power scaling factor applied to weight should be modified in any way to provide a better relationship between body size and floor space requirement. It is therefore our conclusion that, when dealing with turkeys of different sizes, stocking densities should be scaled according to a two-thirds power of liveweight.
69. This scaling factor shows how stocking density varies with turkey liveweight; in other words, given the stocking density for one liveweight of bird, the stocking densities for other liveweights can be calculated. The two-thirds power scaling factor does not, however, in itself establish the stocking density. To do so we need to introduce a co-efficient (k) so that:-
Floor space = k x liveweight ²/³
where floor space is in m², liveweight is in kg and k is the coefficient.
The value of this co-efficient k will vary depending upon which units
stocking density and liveweight are measured. More importantly, it is also determined by the level of stocking density considered sufficient for one liveweight of bird for subsequent scaling to other liveweights.
70. Using the above principles a co-efficient value of 0.0121 would give the area required by each turkey to stand on the floor whilst in contact with other birds on all sides. This is clearly unacceptable. It is therefore necessary to establish how much additional space is required to allow the birds to behave satisfactorily. In the absence of scientific evidence on the effect of any particular stocking density, we have used the existing recommendation of the Turkey Welfare Code (38.5kg/m²) at a weight of 5.5kg (the point at which the first birds are usually removed for killing and therefore when the houses are most heavily stocked). This is the equivalent to 7 birds/m² or 0.14m² per bird. In terms of liveweight to the power of two-thirds, 38.5kg/m² is equal to a co-efficient [k] of 0.0459. With this value of k, the formula allows 20kg turkeys to be stocked at up to 59.1kg/m² (see Appendix D). During our visits to commercial firms we viewed various stocking densities and concluded that turkeys stocked at this density can behave satisfactorily provided there is an adequate system of environmental control.
71. Producers should plan to stock their houses at no more than the stocking density calculated from A = 0.0459 W ²/³ where A is in m² and W is liveweight in kg. However, in the latter stages of the production period and in circumstances such as lower than expected mortality, higher than expected growth rate or where birds are removed from the house later than planned, we accept this may be slightly exceeded for a short period. Birds can be successfully stocked at these rates only if the house has sophisticated, efficient environmental control systems. The onus should rest on the person responsible for the birds to demonstrate that the stocking density of any one flock is appropriate and that person should take expert advice to assess the capability of the house.
72. Whilst we recognise that parts of the industry allow birds to be stocked above 0.0459 W²/³, we call for research to show whether or not turkeys' needs to show particular behaviours are satisfied at these higher densities.
73. The preceding paragraphs relate to turkeys kept in conventional (enclosed) housing systems. Turkeys are also reared in pole barns and on the range; and breeding stock is often kept in pole barn type housing. These systems seldom incorporate sophisticated, automatic environmental control systems of the kind described in paragraph 18, and lower stocking densities are necessary. The densities outlined in the current Turkey Welfare Code should continue to apply (i.e. 24.4kg/m² for meat birds in pole barns and 19.4kg/m² for breeding hens).
74. There is an urgent requirement for research to determine the relationship between stocking density and turkeys' needs, including those to show particular behaviours. This work should be completed by the year 2000 at which time our stocking density recommendation should be reconsidered, with a view to the introduction of a legislative control.
75. Meanwhile the Turkey Welfare Code should be amended to make it clear that in conventional (enclosed) housing systems the maximum stocking density should be calculated on the basis of the formula A = 0.0459 W2/3 where A is in m2 and W is liveweight in kg. It should be recognised that there are unavoidable circumstances, which can arise in the latter stages of the production cycle, that can lead to slightly higher stocking densities. Producers should be allowed to stock at densities in excess of 38.5kg/m2 only where the house environment is controlled, in line with our recommendations in paragraphs 30-34. Otherwise, the present maximum of 38.5kg/m² should continue to apply to conventional (enclosed) housing systems.
76. The person responsible for the turkeys should be able to demonstrate that the stocking density is no higher than the maximum recommended in this report and is appropriate for the design of the building, its locality and the relevant predictable environmental conditions for the time of year. That person should also be responsible for taking expert advice to ensure that the house is capable of supporting turkeys at these densities and should keep records which enable the stocking density to be easliy verified at any time (see paragraph 135). To assist this calculation the internal floor area available to the birds in each house should be clearly and permanently displayed at the entrance to the house.