Relationship between early finishing and reduced prevalence of cysticercosis in cattle

Article history This study aimed to group cattle carcasses with similar characteristics to assess the group-specific prevalence of cysticercosis using data from the slaughter of 15,002 cattle. The following variables were recorded: carcass weight, cover fat, individual age, and prevalence of cysticercosis. A k-means clustering method was used to examine the relationship between carcass characteristics and the prevalence of cysticercosis. We did not specify the number of clusters before the analyses but used automatic methods based on a cross-validation to select the best-fitting clusters. One of the three produced clusters included carcass weight, cover fat, and age, as desired by the Brazilian meat industry. This cluster showed a reduced prevalence of cysticercosis (P = 0.0147) and earlier finishing compared with the other groups. In conclusion, earlier finishing seems to be associated with a lower prevalence of bovine cysticercosis. Received 08 October 2018 Received in revised form 04 January 2019 Accepted 22 January 2019


Carcass Traits
Subcutaneous Fat

INTRODUCTION
The bovine taeniasis-cysticercosis complex can be defined as a set of pathological alterations caused by adult and larval forms of Taenia saginata.This zoonosis can show two distinct forms: taeniasis, which affects humans; and cysticercosis, which is caused by the presence of Cysticercus bovis (the larval stage of Taenia saginata) in bovine tissues (MAGALHÃES et al., 2017).This disease has an impact on animal production and public health (PADILHA et al., 2018).
Infection of humans with T. saginata is common in areas where sanitation is inadequate (USIP et al., 2011;ACEVEDO-NIETO et al., 2012).This parasite is commonly found in South America, North America, and Africa (USIP et al., 2011), with high prevalence in several regions of Brazil (PANZIERA et al., 2017) and mainly in economically impoverished areas.
Information on the prevalence of bovine cysticercosis is important for the implementation of control programs (ACEVEDO-NIETO et al., 2012).Anatomopathological diagnosis is the most important instrument in veterinary diagnostics as identification of cysticercosis at the time of slaughter is crucial for the success of programs to prevent the spread of taeniasis to humans (CORTÊS, 2000;LARANJO-GONZÁLEZ et al., 2018).
Age may be one of the factors that increase the prevalence of bovine cysticercosis, and a respective positive correlation has been reported previously (DORNY et al., 2000).However, due to the diversity of environments and the associated phenotypical differences in cattle of the same genotype (LOPES et al., 2008), age at the time of slaughter is variable.
The age at which animals are slaughtered depends on several factors such as carcass weight and composition.Typically, animals that reach a body composition that is appropriate for slaughter at a young age (i.e.early finishing) are desired.In general, cattle are slaughtered when they reach about 50% of the weight of the corresponding adult non-castrated male genotype (LANNA, 1997).The large slaughterhouses in Brazil use a grading manual that targets carcasses weighing 240 to 330 kg, with a fat cover of 3 to 10 mm, and maturity indicated by 0 to 6 permanent incisor teeth; animals meeting these criteria are considered desirable.
Thus, we hypothesized that animals with carcass traits desirable for meat industry also show a lower prevalence of cysticercosis.The aim of this study was to group carcasses with similar characteristics (weight, age, and fat cover) in order to assess the group-specific prevalence of bovine cysticercosis.

MATERIAL AND METHODS
This study is based on data from the slaughter of 15,002 Zebu cattle from the year 2010.Males and females aged between 20 and 60 months were slaughtered in a slaughterhouse under federal inspection, located in Janaúba, State of Minas Gerais.
After fasting for 12 h, cattle were slaughtered after stunning with a bolt gun, as commonly done in the meat industry.Inspection work on the slaughter lines was carried out by a team of inspection agents duly trained to carry out the post-mortem inspection under the supervision and responsibility of an official veterinary doctor of the Federal Inspection Service, as described by Ferreira et al. (2014).
The recorded variables were hot carcass weight, subcutaneous fat cover (using a scoring system), age (according to the number of permanent incisor teeth), and prevalence of cysticercosis.
The weight of the hot carcasses was obtained by adding weight of the half-carcasses weighed in the inspection line.The number of incisor teeth of each animal was determined by inspecting the dental arch.Subcutaneous fat from the carcasses was assessed visually during the passage of the carcasses in the inspection line.We followed a previously published scoring system for carcass fat cover with scores from 1 to 5 (FELÍCIO, 2011), where 1 corresponded to the absence of fat (zero to 1 mm); 2 indicated scarce fat (> 1 to < 3 mm); 3 indicated a moderate amount of fat (3 to 6 mm); 4 indicated a considerable amount (> 6 to 10 mm), and 5 indicated an excessive amount of fat (> 10 mm).
Carcasses with lesions that indicated cysticerci were sent to the Department of Final Inspection for parasite detection as described by Ferreira et al. (2014).
A k-means clustering method was applied to examine a potential relationship between animals with cysticercosis and their carcass characteristics.The number of clusters was not specified before the analyses.The software Statistica (version 8.0) was used with automatic methods based on a cross-validation in order to determine the best-fitting clusters.This methods serially assigns each object to different clusters in order to minimize the variance within groups and maximize the variance between groups.With this approach a potential correlation of desired carcass traits and the prevalence of bovine cysticercosis can be examined.For the dissimilarity measure, a Euclidean distance was used, which is a coefficient that produces the degree of dissimilarity based on the distance between clusters.A chi-square test was used to test the difference between clusters based on a significance level of P < 0.050.

RESULTS AND DISCUSSION
Three clusters were formed according to carcass traits and the prevalence of cysticercosis (Table 1).Cluster 1 showed a significantly higher prevalence of cysticercosis than the other clusters (P = 0.0147), and carcasses in this cluster had lower proportions of subcutaneous fat and higher age at slaughter.Cluster 2 showed lower a prevalence of cysticercosis and lower age at slaughter.Cluster 3 showed a significantly higher prevalence of cysticercosis than the Cluster 1 and carcasses in this cluster had lower proportions of subcutaneous fat.Among the three clusters, cluster 2 contained carcasses of the earliest finishing cattle.Comparing the prevalence of cysticercosis of cluster 2 and the average of clusters 1 and 3, the prevalence was reduced in cluster 2 by 35.71%.Therefore, besides information on risk factors for cysticercosis such as those listed by Laranjo-González et al. (2016), investment in improved management schemes may indirectly help to fight this disease.
To ensure early finishing, the diet of cattle should contain high energy levels (SILVA et al., 2008).Thus, to achieve the desirable fat scores in regions of low-energy forage, it is necessary to confine the animals and supplement their diets with concentrates.Moreover, confinement may also result in lower contact of cattle with human feces owing to restricted access to swards and river water.

CONCLUSIONS
Early finishing in cattle may reduce the prevalence of bovine cysticercosis.

Figure 1 -
Figure 1 -Patterns of normalized means of bovine carcass traits according to the prevalence of cysticercosis per cluster.

Table 1 -
Numbers of animals (Sample N), prevalence of cysticercosis per cluster, and traits of carcasses in each cluster.