Body condition at slaughter of hens from five maternal strains used as breeders for the production of free-range broilers

As a desirable genotype for the organic or ecological poultry production, dual purpose populations have been proposed that include males for meat production and females for egg production as primary objective and the potential of culling hens for meat production (Bassler, 2005). The drawback of this objective is the negative effect of the growth rate and body weight increase on the reproductive characters both of males and females (Chambers, 1990) which needs to be considered when designing strategies to improve this type of systems. INTA free-ranging broiler (Bonino & Canet, 1999) is a bird that grows slower than traditional broilers, destined to a less intense poultry system, and not only represents an alternative for small-scale growers but, through the Pro-Huerta program, it is distributed to low-income families for self-consumption and sale of remaining parts. The possibility of consuming the culling hens depends on their body condition once they are no longer used as laying hens. The body condition of hens at the end of their first laying cycle can be categorized by palpating the keel and the breast muscles.  Gregory & Robins (1998) applied a scale of this type and concluded that birds with a smaller condition have a poor development of the breast muscles.  The same authors suggest that such technique could be a subjective way to determine the level of body reserves in this particular type of birds. The scale proposed is based on evidence obtained from pheasants (Reynolds, 1997) which suggests that the breast development may be a useful indicator of the protein mobilization for egg production with the subsequent muscle atrophy.  In addition to this objective, the technique also allows to evaluate the potential value of such laying hens as birds for meat, under the framework of a dual purpose production system. The determination is made by keeping the bird alive, individually holding it by the two legs and head down and with the other hand palpating and evaluating the protuberance of the keel and the concavity or convexity of the breast muscle contour.  Based on this assessment, the condition of each bird is categorized in a discreet scale from 0 to 3, where 0 means a prominent edge of the keel with a limited muscle coverage and breast muscle concavity along the keel; 1 means greater development of the breast muscle with a flat edge; 2 means the breast muscle is slightly convex and 3 means a well developed and convex breast. The objective of this paper was to characterize the body condition of hens from five maternal strains of breeders used for the production of free-ranging broilers, at the end of their first laying cycle, by using the above scale.  

The evaluation consisted of birds of five maternal strains (A, E, CE, DE y ES) used for the production of free-ranging broilers at the end of the first laying cycle (54 weeks of age). The birds (n = 25 per group) were randomly selected from their own populations, their individual body weight was recorded and their body condition was determined. The effect of the group of belonging on the body weight was evaluated through a variance analysis followed by a Tukey multiple comparison test. The distribution differences of birds of each strain in all four body condition categories, were analyzed with the homogeneity test based on chi-square statistics (Sokal & Rohlf, 1979).

Table 1 summarizes the values (average ± standard error) of body weight at 54 weeks of age for all five strains.

Table 1. Body weight (average ± standard error) of maternal strains of free- ranging broilers at 54 weeks of age  

Birds from strain A showed the highest average body weight at the age considered; birds from strain E showed the lowest and birds from the three remaining strains showed intermediate values with no statistically significant differences among them. The average weight of birds from the heaviest strain received a value of 100, birds from strain E had an average weight of 83.6%, birds from strain DE,ES and CE 90.8% , 92.5% and 93.0% respectively.

Table 2 shows the relative frequency of birds from each strain discriminated by body condition category:  

Table 2. Relative frequency of birds discriminated by body condition category based on strain

The behavior of the five strains was not homogeneous (X² = 48,04; P < 0,0001). No birds from category 0 were observed in any of the five strains.  Strain E, with the lowest body weight, had the highest amount of birds in Category 1, similar amount of birds in Category 2 as strain A, no birds qualified for Category 3. Strain A, with the highest body weight, had the same amount of birds in Category 1 (12%) as the three strains of intermediate body weight (DE, ES y CE) and the highest amount of birds in Category 3. The strains of intermediate body weight had a similar behavior among them and the highest amount of them were in Category 2.

Based on the body weight, three groups of birds were identified: high weight (strain A), intermediate weight (strains DE, ES and CE) and low weight (strain E). The body condition accompanied such behavior.  Birds from strain A, high weight, differed both from DE, ES and CE birds, intermediate weight (X² = 15,92; P = 0,0142) and from birds with the lowest average body weight (strain E - X² = 19,05; P < 0,0001). Birds from strain E, lowest body weight, differed (X² = 24,82; P = 0,0004) from the three intermediate body weight strains (DE, ES y CE). Among the intermediate body weight strains (DE, ES y CE), no differences were observed (X² = 0,3196; P = 0,9885).

We conclude that females of the five strains not only can be used as breeders for the production of free-ranging broilers, but they have a significant potential for meat production when no longer used as laying hens.  Such value is closely related to their body weight at the end of the first laying cycle, which coincides with the observations made on free-ranging layers (Canet et al., 2008).

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