Table 4.
Prevalence of various diseases and disorders by production systems (%)
| Production system |
||||||
|---|---|---|---|---|---|---|
| Disease | Conventional | Volwaard | Better Life 1*/ Puur & Eerlijk | Better Life 2* | Better Life 3*/Skal | Organic |
| IB1 | 0 | 0 | 0 | 0 | 0 | 0 |
| IBD | 02 | 03 | 03 | 03 | 03 | 03 |
| Coccidiosis | 34.44 | 61.65 | 62.16 | 62.16 | 65.57 | 65.57 |
| E. coli | 1008 | 1009 | 1009 | 1009 | 10010 | 10010 |
| Necrotic enteritis | 12.311 | 15.712 | 15.712 | 15.712 | 15.712 | 15.712 |
| Leg problems (gait score >3) | 11.3513 | 0.614 | 0.614 | 0.614 | 015 | 015 |
| Ascites | 3.316 | 1.717 | 1.717 | 1.717 | 018 | 018 |
| SDS | 0.819 | 0.420 | 0.420 | 0.420 | 021 | 021 |
No change in disease prevalence across systems due to vaccination of 1-d-old chicks and a lack of research with regard to risk factors (Cook et al., 1999; Lopez et al., 2006). Re-vaccination is assumed to provide a protection level of 100% against the infectious bronchitis (IB) virus. In case of no vaccination, morbidity in the flock is 90% (Cook et al., 1999; Cavanagh, 2003).
Although Homer et al. (1992) found a prevalence rate of 13.3%, the present study assumed that birds have been vaccinated against infectious bursal disease (IBD), indicating that IBD does not occur on the farm. Cavanagh (2003) suggested that vaccination against IBD provides 100% protection. According to Voeten (2000), vaccination is necessary to prevent loss due to IBD. In this study, IBD vaccination is assumed to provide 100% protection.
No literature has been found indicating an increase in prevalence due to wild birds (Gilchrist, 2005). In the present study, IBD vaccination is assumed to provide 100% protection.
Infection level >50,000 oocysts (Haug et al., 2008).
Free-range area and lower stocking density: 59.1% (Williams et al., 1996). Increase due to a longer daylight period (6 h): a small increase in coccidiosis is expected due to a longer daylight period, which results in more activity in this period and, in turn, increases the likelihood of picking up oocysts from the environment (Henken et al., 1992). Therefore, the estimated increase in prevalence is 2.5%.
Free-range area and lower stocking density: 59.1% (Williams et al., 1996). Increase due to a longer daylight period (8 h): a small increase in coccidiosis is expected due to a longer daylight period, which results in more activity in this period and, in turn, increases the likelihood of picking up oocysts from the environment (Henken et al., 1992). Therefore, the estimated increase in prevalence is 3.0%.
Free-range area, use of prevention drugs prohibited, and lower stocking density: 62.5% (Williams et al., 1996). Increase due to a longer daylight period (8 h): a small increase in coccidiosis is expected due to a longer daylight period, which results in more activity in this period and, in turn, increases the likelihood of picking up oocysts from the environment (Henken et al., 1992). Therefore, the estimated increase in prevalence is 3.0%.
Escerhichia coli is assumed to colonize the intestines of all chickens, among other organ systems. The number of chickens in the flock that suffer from symptoms is unknown.
No change in prevalence assumed due to a decrease of cfu in the environment, a lower stocking density, and less dust; however, they do result in a lower impact of the disease.
The number of E. coli bacteria increases due to stagnant water in the free-range area, which results in a greater impact of the disease.
Free-range area: 28% of the wild birds’ feces is infected (Craven et al., 2000). Therefore, the estimated increase compared with the situation without free-range area is 28%.
Free-range and lower stocking density (Van Horne et al., 2003).
Slow-growing breed and outdoor access (Fanatico et al., 2008). Effect of daylight is ignored, because leg problems decrease even further due to a longer dark period (Knowles et al., 2008). The effect of stocking density is ignored because the likelihood of having leg problems decreases even further due to a lower stocking density.
The prevalence in case of slow-growing breed is 0. The prevalence in case of a slower-growing breed is assumed to be between 0 and the value of fast-growing breed used in conventional system (1.7). Effect of free-range access: unknown. Natural day-night regimen: increase of 0.6% (Maxwell and Robertson, 1998).
Slow-growing breed: no occurrence of ascites in case of a slow-growing breed (Scheele et al., 2005).
Free-range access results in a decrease in mortality due to sudden death syndrome (SDS; Van Horne et al., 2003). The prevalence of SDS is assumed to decrease as well due to the provision of free-range area.
No SDS in case of slow-growing breed. Natural day-night regimen and provision of free-range area reduces the prevalence of SDS even further (Havenstein et al., 1994; Van Horne et al., 2003; Brickett et al., 2007).