Beef Cattle Welfare Topic: Castration
Humans have been using cattle to aid in agricultural enterprises since the 4th millennium BC, and castration as a means of physiologically taming cattle has existed for nearly as long (Bogucki 1993; Clutton-Brock 1992). Animal welfare is growing increasingly important in the developed world. Consumers, agricultural producers, and those within the animal health industry are focussing attention on the practice of castration as it relates to animal welfare. By researching castration methodology, pain, and analgesia, the optimal means of castrating bulls will hopefully be uncovered. This paper explores some of these issues and reviews the past and current research being done in the area of bovine castration.
Within the beef industry, castration of male calves is an extremely common management practice with numerous benefits. In addition to the beneficial behavioral effects of castration (ie. decreased aggression, mounting behaviours, and fewer resultant injuries), it has also been shown to increase meat quality with respect to marbling and tenderness (Field 1971). Slaughter of steers versus bulls results in fewer dark cutting individuals (Tarrant 1981). In addition, better control of breeding is possible, as genetically inferior males can be prevented from reproducing, and comingling of sexes is possible without unwanted pregnancies (Stafford and Mellor 2005).
Bovine castration methods may generally be classified as physical, chemical, or hormonal. The most commonly utilized of these fall into the physical category. Surgical castration, whereby the scrotum is cut with a scalpel blade and the testicles are exteriorized and cut (surgery-cut,) or manually pulled out (surgery-pull), are two means of physically castrating animals. Clamping (with a Burdizzo), and banding (placing either a rubber ring or latex band/elastrator around the testicles, causing them to necrose and slough off) are two other physical castration methods. Chemical castration is achieved by injection of a caustic substance such as lactic acid into the testes (Fordyce et al.,1989). Detractors of this method have cited pain, inconsistent success rates, and operator safety as factors contributing to its unpopularity (Coventry and McEwan 1989). Finally, hormonal castration (also known as immunocastration) involves injection of a substance which immunizes bulls against gonadotropin-releasing hormone, thereby reducing testosterone and testosterone-associated behaviours (Adams et al., 1993). The need for repeated injections, as well as concern for operator safety, has made this method non-viable at the present time.
All types of castration cause the animal a significant amount of acute pain (Marti et al., 2010). Quantification of a subjective experience such as pain proves difficult within the human realm, where patients are able to communicate. Within the animal realm it is even more difficult, and it becomes necessary to rely on other indices to help quantify pain. Physiological markers of stress, pain-related behaviors, and growth/performance are three means by which pain has been evaluated in castrated bulls.
Plasma cortisol levels as an indicator of post-castration pain dates back to the 1970s (Johnston and Buckland 1976). Since that time assays for cortisol levels in both saliva and hair have also been developed (Fell et al., 1986, Schwartzkopf-Genswein et al., 1997). Immunosuppression secondary to pain has also been examined, by monitoring animals’ susceptibility to pathogens/disease (ie. bovine respiratory disease), blood profiles (ie. leukograms), and total fecal E. coli shedding (Coetzee et al., 2012; Gonzalez et al., 2009;Macauley et al., 1986).
Behaviorally, animals in pain have been documented to exhibit one or more of the following behaviors: vacant staring, vocalization, decreased socialization, decreased grooming, repeated attempts at lateral recumbency, abnormal gait, licking at the castration site, loss of mobility, and inappetance (George 2003; Molony et al., 1995). It has also been argued that increased activity (ie. increased walking) after castration may be observed, as animals use this behaviour as a coping mechanism to deal with the pain (Chapman et al., 1985). Changes in posture, such as displaying a sawhorse stance, swishing of the tail, treading of the feet, and looking back at the castration site have also been used as pain-related behaviours (Molony et al., 1995; Stafford and Mellor 2005). Behaviour is a notoriously difficult parameter to assess, as it is affected by many variables. Some argue the subtlety of behaviour detracts from its significance as an indicator of pain. However, it is important to recognize that cattle are a prey species which have evolved behavioral mechanisms over millions of years of evolution in order to mask pain and minimize the chances of being singled out of a herd and attacked. Certain behaviours may only be expressed when the animal feels it is safe to do so or the pain is extremely intense.
It has also been hypothesized that pain adversely affects rate of growth in beef animals. Performance indices such as feed intake and average daily gain (ADG) have been used to reflect pain experienced by castrated animals. Given the economic nature of the commercial beef industry, altered growth as a result of castration- induced pain has the potential to be extremely powerful. Many studies report loss of body weight, or a decrease in average daily gain, post-castration (Bretschneider et al., 2005; Coetzee et al., 2012; Gonzalez et al., 2010; Massey et al., 2001). These findings are complicated, however, by other research demonstrating reduced ADG is age-dependent, and in some cases is corrected for by compensatory gain later in the feeding period (Bretschneider 2005; Coetzee et al., 2012). In some instances more painful animals have been shown to have greater feed intake than less painful animals, but lower ADG. This may perhaps be explained by increased metabolic rates associated with the stress of pain (Gonzalez et al., 2010).
While it is irrefutable that castration induces pain, significant differences exist between the methods with respect to severity and duration of pain. As surgical castration and rubber banding are the two most commonly used methods in bovine production today (Coetzee et. al, 2010), they will serve as the focus here. The vast majority of the literature suggests surgical castration to be superior to banding from a pain and animal welfare perspective. However, due to the high level of acute pain it induces, from the vantage point of the operator it may appear that surgical castration is in fact more invasive and painful than banding. Real differences arise, however, in the period of time following castration via these two methods. Following surgical castration the lesion on average appeared most severe in the 24 hours following the procedure and required 10 days to resolve. By comparison, the lesion resulting from banding peaked at 15 days post procedure, and took 48 days to resolve (Molony et al., 1995). In many cases long standing inflammation and necrosis have been observed proximal to the rubber ring, especially in instances where the rings were improperly applied (Molony et al., 1995). Other studies have demonstrated comparable results, in that 28-35 days are required for the scrotum to detach following banding, and 49 days for full healing (Stafford and Mellor 2005). By examining behaviours, physiological indicators of stress, and growth parameters it appears that chronic pain builds over several weeks in banded animals, and peaks around 4 weeks (Gonzalez et al., 2010). This has been demonstrated by an increase in abnormal standing postures (ie. sawhorse stance), abnormal gait (ie. short-stepping), and licking at the lesion in banded animals as compared to surgically castrated (Gonzalez et.al 2010; Molony et al., 1996). Physiologically, cortisol levels peak at a higher level in banded versus surgically castrated animals (Coetzee et al., 2010). With respect to growth parameters, evidence indicates banding is more painful than surgery as well, as banded animals may gain less weight and/or have suppressed growth (Coetzee et al., 2010; Fisher et al., 2001; Gonzalez et al., 2010; Lentz et al., 2001). While one study completed on feedlot bulls demonstrated that banded animals had lower occurrences of undifferentiated fever and improved ADG (Booker et al., 2009), the vast majority of evidence indicates that surgical castration is superior from a pain perspective.
At present, the Canadian Veterinary Medical Association’s position statement regarding castration of farm animals recommends that it be performed within the first week of life (CVMA website). The belief that neonates do not feel pain dates back to a single study performed on human infants in the 1940s (McGraw 1941). Based on the observations that human babies display only diffuse movements or no response at all to a noxious pin prick during the first 10 days of life, it was concluded that anesthesia and/or analgesia was not necessary during or after painful procedures. It has since been shown that this is not the case. Neonates do indeed perceive pain differently, owing to broader receptive fields and a lack of descending neural inhibition. However, despite these differences, they do experience the same hormonal and metabolic responses to pain (Wolf 2012). The administration of local anesthetics prior to circumcision of neonates prevented tachycardia and reduced crying, suggesting these children felt less pain (Williamson and Williamson 1983). Extrapolation of this knowledge from human medicine suggests that castrated cattle experience pain no matter the age at which the procedure is performed.
From an animal health and welfare standpoint it is imperative that safe, effective, and easily administered analgesia be provided to address the pain associated with castration in cattle. To that end, many different analgesic techniques have been explored. Local anesthetics, sedation, epidural anesthesia, and systemic administration of non-steroidal anti-inflammatories (NSAIDs) are all possible means of providing analgesia to castrated cattle. Local anesthesia involves injection of lidocaine into the scrotal skin and the testes, with or without infiltration of the spermatic cord. When this is carried out prior to band castration, cortisol response is abolished (Stafford et al., 2002). Local anesthesia prior to surgical castration appears to be less effective, especially if the site of injection is distal to where the spermatic cord tears and breaks (Stafford et al., 2002). Allowing the lidocaine sufficient time to take effect as well as infiltrating as proximally as possible are important in ensuring maximal analgesia is obtained. Intravenous sedation reduces behavioral indicators of pain as well as plasma cortisol when administered prior to castration (Coetzee et al., 2010). Similar results have been observed for epidural xylazine (Gonzalez et al., 2010). Prolonged sedation post-castration, the controlled nature of the drugs, as well as the technical nature of these methods make them less than ideal for widespread use in the cattle industry. By comparison, administration of systemic anti-inflammatories is comparatively simple and easy to perform, and results in lengthy post-castration analgesia (Anderson and Muir 2005). While there are several available anti-inflammatory drug options (ie.ketoprofen, flunixin meglumine, and sodium salicylate) intravenous routes of administration and short half-lives are disadvantages of these drugs. Injectable (subcutaneous or intramuscular) meloxicam (Metacam®) has become increasingly popular in recent years for treating pain and inflammation associated with respiratory disease, diarrhea in calves, and mastitis. By creating a new formulation of the drug that may be given orally, this drug has the potential to be the drug of choice in treating post-castration surgical pain. Oral NSAIDs are convenient to administer and well absorbed in ruminants(George 2003). Oral meloxicam also provides lengthy analgesia owing to its 27 hour half life (Coetzee et al., 2012). While more research is needed to fully investigate the benefits of oral meloxicam, thus far it has been shown to be beneficial in decreasing post castration stress and illness in bulls (Coetzee et al., 2012).
Within the food animal industry veterinarians are in the position of having to provide the best possible care for animals in their charge, within certain economic restraints. All of the analgesic techniques discussed above come at a cost. It has been shown that when veterinarians perceive their client is unable or unwilling to afford analgesia they are more likely to rationalize the procedure is non-painful (Hewson et al., 2007). It is common for those working within the industry to become habituated to the pain induced by practices such as castration. As the public grows increasingly concerned with animal health and welfare issues these defenses may no longer be adequate. It is important that veterinarians take a leadership role in guaranteeing proper analgesia is an inherent part of the protocol when painful procedures are carried out.
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