ESCALA DE APOYO FAMILIAR DE LA MADRE ADOLESCENTE

The plasma concentrations of muscle enzymes in the chickens did not change as expected. In other studies with wild birds, capture and handling has resulted in the rapid elevation of these enzymes in plasma associated with leakage of the enzymes from damaged myocytes (Bollinger et al., 1989; Dabbert & Powell, 1993; Bailey et al., 1997). Within week one, chickens did not respond to capture with significant elevations in plasma CK or AST, although the CK concentrations in the control group were highly variable especially at 24 hour. This suggests at least one bird responded to the event with a CK response indicative of muscular damage. The reason for the lack of muscular response in both groups was not determined but a possible explanation for the difference between the chickens in my study and the previously published studies on other species (Bollinger et al., 1989; Dabbert & Powell, 1993; Bailey et al., 1997) could include the low overall muscle mass of these birds which were sourced as end-of-lay caged hens and therefore had lower enzyme activities. Alternatively the handling treatment may not have been severe enough to cause muscle damage compared to other studies. It is unlikely that the catheters used in week one were the cause of the observed elevated plasma CK and AST concentrations as then the treatment group in week one would be expected to exhibit the same trend.

In week one the differences in plasma CK and AST concentrations between control and treatment groups were significant and since these enzymes did not change significantly over time it suggests that the control group started with higher concentrations of these enzymes which they maintained throughout. The most likely hypothesis to explain this difference is that the some or all birds in the control group experienced some type of muscle damage prior to the sampling that the treatment birds did not. The results of week two would lend support to this hypothesis. The treatment group from both week one and two and the control group from week two respond much more similarly to each other compared to the control group in week one.

The cause of the elevation of plasma CK concentrations in the control group in only week one is unclear but may have been due to fighting between individuals. When layer hens are kept in small groups they form a dominance hierarchy (Schjelderup-Ebbe, 1922;Wood-Gush,

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1971; Rushen, 1982; Syme et al., 1983 as cited in D’Eath & Keeling, 2003) and show aggression towards unfamiliar birds (Guhl and Allee, 1944; Maier, 1964; Craig et al., 1969; Bradshaw, 1992; Dawkins, 1995; D’Eath and Stone, 1999 as cited in D’Eath & Keeling, 2003). When the membership of a group is changed aggression between birds is high (Guhl

and Allee, 1944; Craig et al., 1969 as cited in D’Eath & Keeling, 2003). Since the birds in my

study were taken from a range of cages at the poultry farm, they would have had to establish a new hierarchy and there was likely fighting between individuals that could have resulted in muscle damage in the day between obtaining the birds and sampling. By chance the control group of chickens in week one could have been made up of hens with similar competitive ability resulting in more fighting between individuals in this group to establish dominance and therefore a higher level of muscle damage in this group prior to sampling. However, it should also be noted that I observed no fighting in the group and there were no injuries present that would suggest such intra-specific aggression.

While not observable in week one the changes in plasma CK and AST over the sampling period were significant in week two. There was a gradual increase in plasma CK concentration up to a low peak at 24 hours after which it decreased. This aspect of the

chickens’ muscular physiology response to capture and handling is similar to other studies on

birds which have shown plasma CK to peak at 24 hours following capture (Bailey et al., 1997; Ward et al., 2011). Plasma AST responded similarly but peaked around 24-48 hour and was still elevated at 72 hours. This would agree with the studies that have found circulating AST concentrations persist longer then CK in the bloodstream (Lumeij et al., 1988). However, as previously mentioned, the physiological changes observed in the chickens are significantly attenuated compared to other species. The cause of the peak in CK and AST at 24-48 hours may also have been a result of the cumulative effect of repeated blood sampling in a relatively short period of time. Although if this is a potential cause of the increase the samples at 24, 48 and 72 hours do not appear to cause additional increases in the responses. What is apparent from these results is that the layer hens in this study in both weeks had baseline concentrations of plasma CK and AST that were much higher than is considered normal for other avian species (Franson et al., 1985) and were at levels which could be considered to be indicative of clinical myopathy (Bollinger et al., 1989). The starting values in my study were also much higher than has been reported in chickens in another study which showed baseline concentrations of plasma CK at 143±71 IU/L and AST 49±31 IU/L (mean±SD) in 25 week old layer hens (Macrae et al., 2006).

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These high values of baseline CK and AST and attenuated response to capture and handling could be due to a number of factors such as the physical condition of the birds, including the reduction of total muscle mass associated with their confined caging, metabolic conditions associated with extended periods of egg-laying, the transportation process or fighting to establish dominance. The rate of egg production required of layer hens puts a level of demand on their bodies that is not seen in wild birds, and is detrimental to their health as shown by the high rate of fractures in layer hens, particularly at the end of lay (Nicol et al., 2006; Sherwin

et al., 2010). Some evidence of this poor health was observed in the hens in my research with three of the hens in my study having broken wings and one showing elevations of GLDH in plasma indicating acute liver disease. Post mortem examination was not extensive and focussed on obtaining muscle samples, a higher incidence of current or historic injury may have been observed on closer inspection. This may have affected the physiology of the birds which were included in the results and thus affected my findings.

There are a number of metabolic diseases in commercial chickens that are associated with high egg production or rapid growth causing a body system to fail because of the demand placed on the organ or system (Julian, 2005). Some of these diseases such as ‘deep pectoral

myopathy,’ ‘sudden death syndrome’ and nutritional myopathy have the potential to cause

muscle damage in the birds (Julian, 2005). However these conditions are largely due to the highly developed muscles in birds bred for meat rather than layer hens (Soike & Bergmann, 1998). The high metabolic demands placed on the birds used in my study when they were commercial layer hens may have caused the abnormal physiology and therefore affected the results (Nicol et al., 2006).

Another factor that may have caused muscle damage in the birds prior to sampling and thus elevated starting CK and AST concentrations could have been the handling of the birds at the poultry farm and subsequent transport to the study site. The birds may have experienced physiological muscle damage or capture myopathy during their removal from the cages at the poultry farm and/or the potentially altered health of the layer hens used in this experiment may have led to the birds being physical injured during this process. The starting concentrations of plasma CK and AST observed during sampling may have been elevated due to these events a day prior to sampling. The effect of transport may have been compounded by the previously mentioned health condition of the layer hens used.

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2.4.1.1 Pathology Findings

The pathological findings indicate similar results to the muscle enzymes; some of the hens in this study were experiencing muscle damage. Unlike biochemistry which cannot indicate the location of muscular damage the histology shows the damage occurred in both cardiac and skeletal muscle. The pathology reflects recent muscle damage but it cannot show whether this was caused during the sampling protocol or just before it started. The pathology also did not find any differences in the frequency of occurrence of muscle lesions between control and treatment groups. The common finding of cardiac and skeletal muscle neoplasia in these birds suggests a high prevalence of retroviral infection in the poultry sheds, adding further evidence to the conclusion that these birds are not suitable as physiological models for wild species.