Analysis of the reproduction of two genetic lines of Campero-INTA hens

The domestic hens lay eggs in series, by following a production pattern that accompanies the follicular maturation - process controlled by the circadian rhythm and the physiological systems linked to reproduction (Etches, 1996).  Although little is known about the exact way in which the various factors converge to determine the laying rate, it is known that the genetic potential, nutrition, health, body weight, social position and environmental conditions regulate the laying cycle (Spies, 2000). The comparison of the egg production between the laying hens and the heavy breeder hens highlights the importance of genetics in order to determine the reproductive capacity  (Robinson & Wilson, 1996).
In our country, the Instituto Nacional de Tecnología Agropecuaria (INTA) has had for some decades a pyramidal-type production structure (similar to that of the poultry industry), whose scheme begins with a genetic core from the city of Pergamino (Province of Buenos Aires), where different breeds are crossed.
From this place, the breeding parents are sent to reproduction farms located in sites across the country, where crossings are made of heavy stocks for the production of poultry for meat ("Campero-INTA" chicken). Due to its rustic nature, these birds adapt much better to the local conditions, than the hybrid commercial ones -  as they have greater production rates than non-selected native birds - thus becoming a significant economic alternative (local consumption or sale of products)  (Bonino & Canet, 1999).
In this paper, an evaluation is made of the reproductive behavior of two genetic types of Campero-INTA breeding hens, for long-cycle poultry for meat (Campero-INTA chicken).

The study was carried out at the Birds Reproduction Center of the INTA Agricultural & Livestock Experimental Station at Corrientes, located at National Highway 12, km 1008, El Sombrero - Corrientes, Argentina. The reproductive behavior of two genetic lines (E and T) of hens for the production of Campero-INTA chicken was analyzed. The two genetic lines were placed under similar experimental conditions. Upon the breeding and re-breeding phase, the birds were taken to the reproduction house where they were placed in three boxes of equal characteristics per genetic line. Each box acted as a simple repetition of the independent variable (genetic line), thus each treatment had three repetitions in a fully random design. From the time the hens were moved, the egg production was evaluated in terms of laying percentage, eggs per hen housed and egg weight and mass, considering the Body Weight (BW) of the birds at the beginning of the analysis period.  A variance analysis was applied to a fully random design as well as Pearson's Correlation.

The BW analyses after 21 weeks are shown in table 1. Differences in favor of line T are observed, which were significant in the variance analysis (p<0,05).

Table 1. Body weight average and standard deviation according to each line

Generally speaking, the end of the re-breeding stage represents a critical moment in the bird's life, as it is the end of the photo-sensitivitation period and the beginning of the photo-stimulation and sexual maturity; it is a transition age in which the dynamics of the body weight evolution  (specially between weeks 20 and 25) becomes relevant to determine the reproduction status of the batch (Robinson et al., 2007). Such period is critical in the life of birds belonging to heavy stocks, as significant physical and physiological changes take place affecting the reproduction skills of the hens, starting the development of the primary and secondary sexual organs with the expected weight gain (Leeson & Summers, 2000).

The laying curve is shown in Figure 1, where we see that in general terms, both lines have a similar shape, although under further analysis, differences are shown at different ages.  At week 24 values of 9.41 and 6.24 % of laying rates for E and T were seen respectively (p>0,05). Later we see a first phase of quick increase, until reaching the production peak at week 29 with 88% laying rate for line E and at week 34 for line T, with 81% laying rate. If we remember that the literature mentions that a 5-week period is needed, from the sexual maturity age, to reach the laying peak in breeders (Leeson & Summers, 2000), we can point out that birds from line E adjusted their age better to the peak, as compared to line T, which took them 10 weeks.  Based on findings by Hudson et al. (2001), the relative differences of age vs production peak, help explain (partly at least) the huge difference in the number of eggs per bird, which is a variable that will be discussed later.  So, if we take the theoretical framework as reference and we make a comparison at 29 weeks of age, in numeric terms we will see, the highest laying percentage reached by line E. Indeed, at that age, the variance analyisis for the production percentage showed significant differencies in favor of line E (p<0,05).

Figure 1. Laying curve per genetic line down to week 64 of the cycle

The average percentages of egg production during the cycle were statistically different, with values of  66,39 ± 4,32 and 56,96 ± 4,14 for lines E and T respectively, similar to what happened with the number of eggs produced by bird housed for 64 weeks (p<0,05), with averages of 189 ± 11 and 162 ± 12 eggs/bird (lines E and T respectively). These values represent a total of 27 eggs/bird in favor of line E. These results (that relate the body weight with egg production) ratify the findings of several works developed on parental lines for the production of hybrid broilers (Thorsteinson, 1999; Leeson & Summers, 2000).

The analysis of the correlation between egg production and body weight at different ages after re-breeding, shows a different behavior based on the genetic line. It was possible to detect a significant positive correlation for line E, among such variables at some points of the curve.    Thus,  at week 23, the body weight had a correlation with the total amount of eggs/bird  (r=0,99; p=0,008); also the body weight at week 25 and the production of eggs at week  54 (r=0,99; p=0,03), and BW at week 27 with the production of eggs at week 35 (r=0,99; p=0,007).

A behavior opposite to the one shown in lineT, where the BW variables and egg production have not had a correlation or have had a negative one.  In this genetic line a, the BW at week 36 had a negative correlation with the total egg production (r= -0,99; p=0,03). In this case, the relationship between body weight and a smaller egg production in the line of the heavy breeders of broilers, is ratified  (Bruggeman et al., 2005)

On the other hand, the analysis of the evolution of the average weight of eggs, discriminated by genetic line, indicated greater weight in favor of line T.  At week 25 of age, the averages were 48,53 ± 1,47 and 49,45 ± 0,89 (p>0,05); however, at week 29 significant differences were seen in favor of line T, with averages of 53 ± 0,49 and 56 ± 0,81 (E and T respectively). The average values of this variable during the cycle, significantly favor line T, with 61,52 ± 0,14 and 58,97 ± 0,28.

Regarding the egg mass, the evolution analysis of this variable showed variations during the cycle, irrespective of the line. The egg mass averages during the cycle were 40,48 ± 2,46 and 36,39 ± 2,56 for lines E and T respectively.

Based on the results obtained, we can conclude that the Campero-INTA breeders from line T, whose body weight  was higher than that of those from line E at the end of the re-breeding period, showed smaller egg production and negative correlations.  This coincides with what was observed in other lines of heavy breeders.

We thank Darío Ortíz and Carlos Escobar for the support provided for this paper.

Bonino MF & Canet ZE. 1999. Producción de pollos y huevos camperos. Boletín Técnico editado por la Dirección de Comunicaciones INTA. 39 pp.

Bruggeman V, Onagbesan O, Ragot O, Metayer S, Cassy S, Favreau F, Jego Y, Trevidy J, Tona K, Williams J, Decuypere E, Picard M. 2005. Feed allowance-genotype interactions in broiler breeder hens. Poultry Science 84:298-306.

Etches RJ. 1996. Reproducción aviar. Ed. Acribia S.A. Zaragoza, España. 339 p.

Hudson BP, Lien RJ, Hess JB. 2001. Effects of body weight uniformity and pre-peak feeding programs on broiler breeder hen performance. J. Appl. Poultry Res. 10:24-32.

Leeson S & Summers JD. 2000. Broiler breeder production. Published by University Books. Guelph, Ontario. Canada.

Robinson FE, Renema RA, Zuidhof MJ. 2007. The pullet to hen transition: Why this is the most critical time in female broiler breeder management. URL:http://www.poultryindustrycouncil.ca
/pdf/HC%2007%20PDF/Robinson%20-%20PIC%202007.pdf. Acceso: 05/02/09.

Robinson FE & Wilson. 1996. Reproductive failure in overweight male and female broiler breeders. Animal feed Science Technology 58:143-150.

Spies A. 2000. Reproductive efficiency of broiler breeder females as influenced by post peak feed allocation and long ahemeral days. Master of Science Thesis. Department of Agricultural, Food and Nutritional Science. Edmonton, Alberta.

Thorsteinson KA. 1999. Effects of maternal trains, feeding program and photostimulation program on eggs quality, chick quality and broiler growth and carcass characteristics. Master of Sciencie Thesis. Edmonton, Alberta, Canadá. 91 p.