The population of interest for this scoping review was beef cattle (i.e., fed beef cattle), and the studies of interest were included if they investigated pre-slaughter management factors and indicators of animal welfare. While bulls and cows are not considered as fed beef cattle in the United States, several of the studies from other geographic regions reported mainly processing bulls and cows and therefore these animal types were included in the population when they were considered primarily beef animals. Pre-slaughter management factors were defined as any procedures adopted by workers, slaughter facilities or companies during loading, transportation, unloading, lairage and the actual slaughter process. Other factors present during the pre-slaughter period that were considered relevant included animal characteristics (e.g., breed), environmental characteristics (e.g., temperature and humidity), handling, water and/or feed access, and additives fed one month prior to slaughter were also included in analysis. All types of slaughter facilities, stunning methods, and pre-slaughter management strategies were included to ensure there was a comprehensive list to catalog pre-slaughter management factors that may impact fed beef cattle welfare at the time of slaughter. Including all slaughter facility types, pre-slaughter management strategies and slaughter methods in the discussion also provides a comprehensive catalog of strategies and methods to identify potential areas of the pre-slaughter process that may warrant further research attention. Welfare outcomes were broadly defined as any measure related to one of the three conceptions of animal welfare as outlined by Fraser et al. (1997): biological functioning, affective states, and natural living. For example, biological functioning included cattle health and condition and physiological parameters; affective states included reactivity, head posture, emotional states, and vocalizations; natural living included social and sexual behaviors, eating, drinking and lying down. The outcomes of pre-slaughter management investigated were categorized as: behavior; health, injury and disease; physiological; and stunning and sensibility.

Only papers written in English were included. Research articles covering alternative slaughter types (e.g., religious slaughter, on-farm slaughter, mobile slaughter, and slaughter without captive bolt stunning first) were included in the discussion, but not included in the final analysis. Due to the differences of slaughter methods and systems’ possible impact on welfare outcomes, the decision was made to discuss these papers separately.

A librarian knowledgeable in systematic reviews was consulted when identifying databases for the literature search. Three data bases were ultimately selected for this scoping review: PubMed, CAB Abstracts (EBSCO; including a filter for peer-reviewed articles), and Web of Science. The concepts used in the database searches were the population of interest (i.e., fed beef cattle), the location in the supply chain (i.e., pre-slaughter), pre-slaughter management factors, and welfare outcomes. Other livestock species (e.g., dairy) not of interest were excluded in the searches. The final searches were performed on August 2^nd, 2022.

Initial search strategies were tested on PubMed against a few core references to verify that the core studies were present in the search results. After consultation with the librarian and other research members, a final search string was developed. The same search string was used for all three databases, and peer-reviewed was selected as a filter when available, which was only for CAB abstracts. The final search string and information on the databases searched is available in Table 1 .

All sources from the three databases were collated, uploaded to Zotero, an open-source citation management software (Zotero, Fairfax, VA), and software tools were used to remove duplicates. One reviewer performed the first level of screening of titles to remove any sources that were not relevant to the concepts. For the second level of screening, abstracts and full-text articles were reviewed by two independent reviewers to further exclude sources according to the inclusion criteria. If there was disagreement between the reviewers, each paper was then reviewed together and discussed until an agreement was made. Only primary studies, written in English that covered the inclusion criteria were included in this study. One additional article was discovered post-database searches after reviewing the bibliographies from the original database search results and was included in the final analysis.

After reviewing the 69 studies, a total of 37 unique predictor variables were categorized into the following categories: animal characteristics, environmental characteristics, handling, lairage, transportation or water/feed. The number of studies including a predictor within each category were recorded and are displayed in Figure 3 . Some studies explored more than one predictor, therefore, the total number of transportation predictors (n = 71) reported in Figure 3 exceeds the total number of studies included in the final analysis (n = 69). Out of these five categories, transportation was studied the most (n = 71) in papers reviewed for this scoping review. Within transportation, distance and duration of transportation was measured the most, followed by the mention of general transportation. General transportation in this case meaning the study transported animals and looked at downstream effects of this factor, but no other specific characteristics of the experience were evaluated. The second most studied factor was handling (n = 56). Within handling, general handling was measured the most frequently. General handling, similar to general transportation, meaning the study observed animal handling and downstream effects of this factor, but again, no other specific characteristics of the experience were evaluated. The handling category also included slaughter practices such as stun to stick time (i.e. the time from being stunned to exsanguinated) and stun quality (e.g., missed stuns or number of stuns to render the animal unconscious). The evaluation of animal characteristics was included in 43 studies and the most commonly measured animal characteristic was origin of cattle prior to being transported to the slaughter facility. Environmental characteristics (n = 33) included temperature and humidity, noise levels and facility design and condition. The most measured lairage predictors (n = 32) were lairage duration and density. The least measured factor across the studies was water and feed (n = 6). This category included measures such as fasting duration, water consumption and alternative feeding systems or feed additives prior to transport for slaughter.

After reviewing the 69 studies, a total of 69 outcome variables were measured and categorized into the following categories: behavior; cattle health, injury and disease; physiological or stunning and insensibility, and the number of studies measuring each category were recorded and are displayed in Figure 4 . Out of these categories, physiological parameters were evaluated the most (n = 68) in studies reviewed for this scoping review. Within physiological parameters, blood parameters were measured substantially more than others such as vital measurements or urine parameters. Cattle behaviors were the next commonly measured indicators of welfare (n = 40), with the most frequently measured being the frequency of falls, vocalizations and slips. Cattle health, injury and disease (n = 12) was commonly assessed by recording injuries, mortality and mobility or lameness at the slaughter plant. The final category, stunning and insensibility indicators (n = 7), were measured as post-stunning behaviors or checking for signs of insensibility and bleed out time. Frequently measured behavioral signs to check for insensibility were the lack of corneal reflex (n = 5) and rhythmic breathing (n = 4).

Transportation and handling were the most highly researched pre-slaughter factor categories found in this collection of papers. The effects of transportation on beef cattle welfare are extensively researched and reviewed (Fike and Spire, 2006; Huertas et al., 2010; Schwartzkopf-Genswein et al., 2012; Schwartzkopf-Genswein et al., 2016) as transportation presents a period in the pre-slaughter phase that is considered one of the most stressful events that cattle must experience during their lifetime (Chambers and Grandin, 2001; Schuetze et al., 2017). For some cattle, depending on the production system they have been raised in, transport to the slaughter plant may be the first time they have been in a trailer. Livestock transportation regulations and policies vary greatly across areas of the world (e.g., Twenty-Eight Hour Law, 1994; CARC, 2001; European Council, 2005a) as do cattle production systems and associated infrastructure (i.e., pasture-based vs. feedlot; Gonzalez et al., 2022) which can all shape transportation logistics and thus impacts on welfare. There are many different components to transportation as well, including but not limited to, transportation duration and distance, the microclimate in the trailer, and driver experience, which have all been incorporated into the studies included in this review (e.g., Tarrant et al., 1992; González et al., 2012; Chulayo et al., 2016; Valadez-Noriega et al., 2018). Animal handling was also highly represented as a pre-slaughter management factor of interest. There have been considerable efforts in educating stakeholders about low-stress handling techniques as the benefits to reducing animal stress are clear (Grandin, 2012; Grandin, 2014). Additionally, animal handling is a component of pre-slaughter management that can be more easily controlled and manipulated as compared to other factors such as the environment or facility design and thus a target area to identify improvements. Lastly, many of the industry regulations and guidelines globally highlight the need to have trained employees that understand the basic principles of low-stress animal handling (Government of Canada, 2018; OIE, 2018; GRSB, 2021) and thus this area has perhaps received more attention in relation to cattle welfare at slaughter.

To assess the relationships between pre-slaughter management factors and outcome indicators of welfare for fed beef cattle, the following discussion will be arranged by the categories of outcomes and a discussion on each one’s relationship with pre-slaughter management factors. Main factors and outcomes will be highlighted throughout this discussion. Relationships between variables with less research or no significant impact will be limited in discussion.

Allowing an animal to perform natural highly-motivated behaviors has been a foundational component of many animal welfare frameworks (e.g., the Five Freedoms, FAWC, 1993; Fraser’s Three Circles, Fraser et al., 1997; the Five Domains Mellor et al., 2020). Additionally, current frameworks for welfare assessment encourage both the promotion of positive experiences and the reduction of negative experiences (Green and Mellor, 2011). Even though the pre-slaughter phase represents a relatively short period within the animal’s lifetime, it is still important to provide cattle with the opportunity to express positive natural behaviors such as lying, exploring, and ruminating. Upon arrival at a slaughterhouse, the state of the animal will depend upon the nature and duration of their experience from their place of origin, and the new physical and social environment is likely to affect the ability of the cattle to rest and relax (Cockram, 1990). In several studies, the frequency of both positive (e.g., ruminating, eating or drinking) and negative (e.g., aggression or vocalizing) behavioral states were measured (Cockram, 1990; Jarvis et al., 1996b; Njisane and Muchenje, 2014; Njisane and Muchenje, 2017b; del Campo Gigena et al., 2021). Lying time can be an important welfare indicator in cattle (Haley et al., 2000; Tucker et al., 2021). In a slaughter plant, lying behavior would most commonly occur during lairage as cattle experience a period of inactivity (i.e., no handling) during holding. Studies have shown that lying behavior tended to increase with lairage duration, where 26% of focal animals were lying down by 3 hours in lairage (Jarvis et al., 1996b), however, this is highly influenced by time of day, activity within the pen and origin of cattle (Cockram, 1990; Cockram, 1991; Jarvis et al., 1996a). Cockram (1990) reported that the mean number of head alert reactions to external stimuli in cattle originating from a market decreased with time in lairage and occurred the least in steers over heifers with a space allowance of greater than 5m² per animals, a sign that cattle were acclimating to the new environment. One study comparing cattle that did not experience transportation or lairage with ones that were transported and held for durations up to 24 hours, found reduced aggression frequency (0.00 compared to 0.57 at 24 hours) (e.g., butting) with conspecifics in the group that went straight to slaughter (Özdemir et al., 2022); this is a logical finding as there were reduced opportunities for animal-to-animal interactions in the direct slaughtered group.

Cattle are also motivated to spend time eating and drinking (Schütz et al., 2018); the availability of food and water for cattle during this pre-slaughter phase varies across production systems. The origin of the cattle (i.e., market vs. farm) has been shown to influence drinking time; cattle from markets drank for significantly longer and more often at the plant than cattle coming from farms (Jarvis et al., 1996b). This may be indicative of an extended period of water deprivation for cattle originating from markets. Related, cattle being transported from farms over 80 miles away from the abattoir drank significantly more than cattle transported for shorter distances (Jarvis et al., 1996a) from the extended water deprivation period. Cattle ruminate while resting, and time spent ruminating is a direct indicator of animal welfare status in ruminants (del Campo et al., 2021). del Campo et al. (2021) reported that as lairage time increased (from 3 to 15 hours), the frequency of rumination decreased from approximately 40% to 15% of time; one study reported that rumination decreased by as much as 34% when cattle were held for over 12 hours (Mach et al., 2007), a finding that was likely partially related to gut fill. In summary, many factors can influence the expression of behaviors during the pre-slaughter phase, however, past research does show that cattle still have the ability to express highly motivated behaviors at different points in the pre-slaughter period.

Movement behaviors, such as slipping, falling, jumping, and loss of balance were frequently measured throughout multiple studies. Studies have demonstrated that these types of behaviors are impacted by both animal handling techniques (Cockram and Corley, 1991; Hemsworth et al., 2011; Huertas et al., 2018; Cevallos-Almeida et al., 2021) and facility condition or type (Grandin, 1996; Disanto et al., 2014; Romero et al., 2017; Willson et al., 2021) and many of them can negatively impact animal welfare by increasing the risk of injury to the animal. Generally, these movement behaviors are observed during periods of animal handling which can occur at multiple times throughout the pre-slaughter period allowing for assessment at a variety of locations and stages. Additionally, these types of behaviors are relatively easy to observe and quantify and are thus practical methods of assessing welfare in a slaughter plant environment. Loading and unloading of cattle are activities during the pre-slaughter period in which handling intensity increases and thus several studies have evaluated the impacts on welfare outcomes from these events (Jarvis et al., 1996b; von Holleben et al., 2003; Hagenmaier et al., 2017). Loading has been shown to be more stressful for cattle than unloading, as the frequency of falls (approximately 33%) and balking (approximately 50%) was greater during loading than unloading (approximately 15% and 10%, respectively; María et al., 2004), possibly due to the cattle being moved into an unfamiliar environment. However, unloading can be more difficult when temperatures are lower, when the duration of transportation is longer, and if cattle are mixed immediately before loading (Mounier et al., 2006), demonstrating the interactive effects of multiple pre-slaughter factors. Once cattle are loaded onto a trailer there are limited opportunities to assess behavior without the use of technology (i.e., cameras in the trailer, accelerometer on the cattle) but it has been reported that during transport, cattle frequently lose their balance with sudden stops or on roads with curves and gravel portions (Tarrant et al., 1988; Wikner et al., 2003). Additionally, increases in transportation duration (60 minutes versus 180 minutes) and greater Temperature-Humidity Index (THI) classes (<60, ≥60<70 and ≥70) have been associated with increased restlessness frequency (7.0% during 60 minutes of transportation and 11.8% during 180 minute transportation duration, and 8.1% in THI class <60, 9.8% in ≥60<70 and 10.8% in ≥70) in cattle on trailers during transport (Costa et al., 2003). Within the slaughter plant cattle have the potential to slip and fall in areas where active handling occurs such as the holding pens, the single-file alley, or moving into the stun box or restrainer system (Costa et al., 2006).

Vocalization is another behavior that is measured as a welfare indicator in research studies focusing on pre-slaughter management; similar to the movement behaviors, vocalization can be measured at a variety of time points throughout the pre-slaughter period and is relatively simple to quantify. Cattle have been observed to vocalize at the plant from aversive and novel events such as prodding with electric prods, slipping at or near the stunning box, missed or inadequate stuns, sharp edges from poor facility conditions, being moved through holding pens to the single-file, or excessive pressure from restraint devices (Grandin, 1998b; Grandin, 2001; Cevallos-Almeida et al., 2021). Due to these events, measuring vocalizations is a valuable indicator of animal welfare and it can be compared across animal handling facilities (Grandin, 2017). Increased vocalizing has been observed more in cattle being moved after overnight lairage (number of vocalizations ranged from 0-29 per group) compared to cattle being moved after a shorter lairage duration (ranged from 0-4 per group; Cockram and Corley, 1991), likely because cattle housed overnight had time to rest and recuperate. Again, there are many factors that impact cattle behavior during the pre-slaughter phase and vocalization is a welfare indicator that is responsive to changes in handling and the environment that cattle experience.

Many of the above descriptions of behavioral outcomes include some component of animal handling. The impact of human-animal interaction on animal welfare is well-documented (Mota-Rojas et al., 2020; Acharya et al., 2022). As noted above, animal handling during this pre-slaughter phase can have negative impacts on welfare outcomes; most of the research found focused on negative actions of the animal handlers during intense animal handling events (e.g., loading, movement at the plant) and the subsequent cattle behavioral responses (e.g., balking, falling, vocalizing; Cockram and Corley, 1991; Grandin, 2001; Hemsworth et al., 2011; Doyle et al., 2016). Probst et al. (2013) took a different approach and explored positive handling interactions prior to the commencement of the pre-slaughter period. In their study, Probst et al. (2013) discovered that gentle touching and increased interactions with handlers in the few weeks prior to slaughter decreased avoidance distances in cattle at the abattoir, suggesting that positive human handling prior to being transported for slaughter can reduce an animals’ fear of humans. While gentle touching of each animal is not practical in most commercial settings, these results do raise the question of whether increased animal handler interactions of other manners (e.g., walking through the pens or moving cattle) may be a plausible solution to decreasing stress responses in cattle prior to slaughter.

There are several pre-slaughter management factors that impact the prevalence of cattle injury and health outcomes. Previous literature has identified relationships between pre-slaughter management factors specifically during transport and welfare outcomes, including weight loss, traumatic lesions and even death, for both cattle and other livestock species (Knowles et al., 1993; Knowles et al., 1994; Villarroel et al., 2001; Gallo et al., 2003). Overall health and well-being can be impaired and the onset of severe stress can be observed in animals being transported (Minka and Ayo, 2010). A survey of transporters commercially hauling cattle for long durations reported that cattle condition was good (98.66% of journeys), fair (1.28%) and poor (0.05%) at time of loading, but the prevalence of journeys with ‘fair’ or ‘poor’ conditioned cattle increased 2.7-fold and 4.2-fold upon unloading (96.3% good, 3.49% fair and 0.21% poor) as a result of transportation stress (González et al., 2012). Another survey of livestock haulers reported that almost half of its participants (48.6%) observed up to five animals with injuries inflicted during transportation to the plant, however, this could be a low estimate as drivers have been documented to have limited ability to recognize pain and injuries in animals (Valadez-Noriega et al., 2018).

An animal’s ability to move through the pre-slaughter phase and navigate the different transport and handling systems is critical. Cattle mobility and lameness are important considerations and have been focused on significantly more in recent years within the fed cattle industry, particularly in the United States (Edwards-Callaway and Calvo-Lorenzo, 2020). Mobility is a multifactorial issue impacted by not only weight, THI, sex, and days on feed (DOF; (González et al., 2012; Edwards-Callaway et al., 2017; Martinez et al., 2021; Mijares et al., 2021), but also transportation (e.g., distance hauled) and lairage factors (e.g., lairage duration; Hagenmaier et al., 2017). One study within this review, however, reported a rather low prevalence of lameness (0.7%; Burgstaller et al., 2022) compared to other studies ranging from as low as 1.1% to 54.8% of cattle reported as clinically lame (Dudley, 2017), likely because the sample size of this study consisted of mostly young bulls and calves rather than older cattle. Older cattle are typically more prone to mobility issues due to age-related variations in their physiological status (Gavrilova and Sementovskaya, 2021). Individual animal characteristics (e.g., horned or different weight categories), truck flooring conditions, falls during loading or unloading, and trailers with inadequate conditions such as loose or protruding boards, screws or nails have also been shown to be associated with increased injury and lesions in cattle at the abattoir (Lee et al., 2017; Brito et al., 2019).

Studies in this review included several physiological measures ranging from vital parameters to metabolites measured in biological samples, however, blood metabolites were the most commonly measured within this category, comprising approximately 65% of studies. Hematological blood indicators are known to be the primary determinants of an animal’s ability to adapt to its environment and thus are useful parameters to include in welfare assessment (Anderson et al., 1999). Specific hematological parameters such as neutrophil/lymphocyte ratios, cortisol, adrenaline and noradrenaline are commonly used to measure the stress response to pre-slaughter management in cattle (Warriss, 2010; Cucuzza et al., 2014; Mirzad et al., 2018). Adrenal hormones in particular, such as cortisol, represent one of the most important physiological parameters to measure the stress response as various stressors can result in its release, and is used in several studies assessing the impact of pre-slaughter management on cattle welfare (Mitchell et al., 1988; Ndlovu et al., 2008; Burdick et al., 2010; Tarantola et al., 2020). Common blood parameters measured in studies included in this review included cortisol, creatine kinase (CK) and catecholamines such as epinephrine and norepinephrine but the selection of physiological parameters measured varies substantially between studies. As cattle attempt to maintain homeostasis, adaptive responses such as these physiological changes attempt to restore that balance (Carrasco-García et al., 2020).

Generally, regardless of the pre-slaughter predictors assessed, most studies have found that physiological parameters change in response to management manipulations (Rulofson et al., 1988; Tarrant et al., 1988; Chacon et al., 2005; Tadich et al., 2005; Romero et al., 2014). For example, transportation effects on blood parameters were highly researched in studies included in this review. Transportation has been shown to induce changes in the composition of blood along with other parameters such as heart rate, hormones, metabolites, enzymes and even skin dehydration (Fazio and Ferlazzo, 2003; Gregory, 2008), however, these effects will vary based on transportation duration, road conditions, and age, breed, and previous experiences of the cattle. Several studies discovered that transportation stress was substantial enough to elevate blood concentrations of antidiuretic hormone (Ballarin et al., 2006), epinephrine and norepinephrine concentrations (Mitchell et al., 1988; Rulofson et al., 1988), glucose (Jarvis et al., 1996a), lactate (Chacon et al., 2005; Gruber et al., 2010), cortisol (Villarroel et al., 2003; Romero et al., 2014; Bertoloni et al., 2016; Capra et al., 2019), LDH (Birhanu et al., 2019), and creatine phosphokinase (CPK, i.e., creatine kinase or CK; Tarrant et al., 1992; Tadich et al., 2005). Cattle can be transported in various ways across the globe and thus transport conditions vary greatly; in the US, cattle are transported using livestock trailers, whereas other geographic regions such as Oceania may export cattle for slaughter overseas via ship. Cattle transported by sea are usually subjected to longer transport times and extended periods of feed withdrawal (Phillips, 2008). Route of transportation has also shown differences in plasma CK levels as cattle transported by sea and road experienced mean plasma CK levels of 1,137.86 (IU/L) compared to cattle subjected to only road transportation and a saleyard pathway (596.79 IU/L; Loudon et al., 2019), however, both transportation pathways resulted in cattle with elevated plasma CK levels as published normal basal concentrations range from 35 to 280 IU/L (Radostits et al., 2000).

Lairage at the slaughter plant presents a particularly challenging period prior to slaughter as several factors such as lairage duration, mixing with unfamiliar cattle, stocking density and temperature microclimates differ in severity at each plant and offer their own varying degrees of stress for cattle (Edwards-Callaway and Calvo-Lorenzo, 2020). Several studies explored the impact of varying lengths of time spent in lairage on physiological outcomes (Tadich et al., 2005; Liotta et al., 2007; Giannetto et al., 2011; de Marchi et al., 2022). Allowing animals to rest in lairage for longer durations has shown a reduction in: CK and LDH activity (Chulayo and Muchenje, 2017), glucose, lactate and protein blood levels (Pighin et al., 2015) and cortisol concentrations (Liotta et al., 2007; Chulayo et al., 2016). Grosskopf et al. (1988) reported that blood parameters such as total plasma cortisol decrease in value as time in lairage increased (203 nmol/L immediate slaughter, 128 nmol/L after 3 hours of lairage and 85 nmol/L after overnight lairage), however, plasma CK was greater in cattle with a lairage period of 3 hours (513 U/L) compared to cattle slaughtered immediately upon arrival to the abattoir (372 U/L), with a decrease in values in cattle held overnight (112 U/L). Differing results between studies likely are partially due to differences in other pre-slaughter management practices, such as transportation time. The stress impacts of mixing non-familiar groups of cattle is a highly researched area (Šímová et al., 2016; Hubbard et al., 2021), particularly during the pre-slaughter phase. Warriss et al. (1984) found that when mixing unfamiliar cattle during lairage, those that exhibited the most animal-to-animal interactions compared to other animals had greater levels of CPK and free fatty acids (FFA) concentrations and decreases in plasma lactate, indicating that liver and muscle glycogen was depleted from the stress of social mixing.

The pre-slaughter process involves several instances where cattle will be moved to different locations (e.g., loading or unloading, moving from holding pens to the drive alley and through the single file) all of which present a challenge if facilities and handling techniques are suboptimal (Disanto et al., 2014). High levels of cortisol can be attributed to inadequate handling of cattle during the pre-slaughter and slaughter phase (Mitchell et al., 1988; Carrasco-García et al., 2020; Guarnido-Lopez et al., 2022). Cattle exposed to low-stress slaughter conditions (i.e., less time being transported and moved through the slaughter process at the abattoir) resulted in lower heart rates and stress hormone concentrations (Reiche et al., 2019). Cattle that fell from slippery flooring or improper handling, were lame, or were injured during transportation showed mean levels of CK and cortisol increasing by 43U/I and 8 ng/ml, respectively, compared to those without injury (von Holleben et al., 2003). When stunning animals, it has been discovered that animals needing to be stunned more than once had increased blood cortisol concentrations compared to those that only required one stun to be rendered unconscious (Chulayo et al., 2016; Njisane and Muchenje, 2017b). Studies such as the ones presented here offer further evidence on the importance of animal handling and stunning training, and how they are essential in improving efficiency and animal welfare (Ceballos et al., 2018; Večerek et al., 2021).

Potential relationships between behavior and blood parameters have also been explored (Burdick et al., 2010; Stockman et al., 2012). Temperamental cattle have been reported to have greater cortisol and epinephrine concentrations compared to calmer cattle post-transportation (Burdick et al., 2010). Stockman et al. (2012) found that cattle scored as ‘nervous’ or ‘anxious’ prior to being slaughtered had greater plasma lactate concentrations than those that were calmer; this effect was also associated with the amount of time waiting to be slaughtered (i.e., end of the queue vs. the beginning of the queue). Other animal characteristics such as breed, which also could influence temperament, have also been explored (Doornenbal et al., 1988; Prisacaru, 2014). In one study examining the relationships between Bonsmara, Nguni and Angus breeds and physiologic parameters, Bonsmara cattle were reported to have the greatest concentrations of adrenaline, noradrenaline and dopamine and Nguni had the greatest serum cortisol concentrations suggesting that both breeds had increased responses to the stress associated with the pre-slaughter period (Ndlovu et al., 2008). In a similar study, Angus cattle had lower levels of urinary creatinine compared to other breeds such as Limousin and Blond d’Aquitain, suggestive of a lesser stress response to slaughter events such as transportation and stunning (Bourguet et al., 2015). Results from these studies suggest the possible need for breed specific pre-slaughter management strategies, however, further research is warranted in this area, specifically investigating differences between breeds underrepresented in current research.

Vital parameters such as heart rate were also commonly measured as indicators of welfare after particularly stressful events during the pre-slaughter phase. Heart rate variability in cattle can be used to quantify stress from physical, emotional and pathological origins (von Borell et al., 2007), all of which can be caused by events in the pre-slaughter phase. For example, cattle recovered resting heart rates during longer journeys compared to those only transported for thirty minutes where all cattle maintained elevated heart rates (Chacon et al., 2005), suggesting that time to recuperate during transportation may be beneficial. Also, cattle that showed more resistance to handling during human exposure prior to transport for slaughter have also shown to have faster heart rates during loading (Terlouw et al., 2012).

The actual act of slaughter can have a significant impact on animal welfare and thus is an important consideration when evaluating the pre-slaughter period. In non-religious slaughter systems, an animal will be stunned prior to further processing, required by law (e.g., The Humane Methods of Slaughter Act, USDA-FSIS, 1978), in order to render the animal insensible to pain. Despite the significance of ensuring effective stunning to overall welfare, few studies in this review measured post-mortem behaviors of cattle following stunning (Grandin, 1998a; Miranda-de la Lama et al., 2012; Mpamhanga and Wotton, 2015; Romero et al., 2017; Cevallos-Almeida et al., 2021). These studies were primarily assessing behaviors indicative of return to sensibility which included eye reflexes, blinking, rhythmic breathing and righting reflexes (Grandin, 1994). Agitation just prior to stunning, such as using a pre-slaughter crush restraint for the purpose of cattle identification, have resulted in a less effective stun as rhythmic breathing, rotation of the eyeball and limb movement at sticking in stunned cattle was significantly reduced when crush restraint was not used (Mpamhanga and Wotton, 2015). A notable point to consider is employee behavior related to the stunning and exsanguination process; stunning operators can become fatigued, resulting in cattle that are not efficiently stunned and the need for multiple stunning attempts to render the animal unconscious (Grandin, 1998a). The single study measuring pre-slaughter effects on bleed-out times did not find any significant effects of genotype, transportation groups or durations of lairage on bleed out times (Njisane and Muchenje, 2017b).

Several pre-slaughter factors and indicators of fed beef cattle welfare have been identified in this review; however, some underrepresented welfare-friendly practices and useful indicators of welfare should be investigated further. While factors such as transportation, handling, animal and environmental characteristics, and lairage factors have been extensively measured in studies assessing pre-slaughter management on welfare outcomes, factors related to water and feed provision have not been thoroughly researched in this space. Fasting duration for both feed and water have been studied (Jarvis et al., 1996a; Jarvis et al., 1996b; Clariget et al., 2021), but little information is known about the implications of these factors on the welfare of cattle. Analyzing the interactions between fasting durations and water deprivation on both cattle condition and cattle responses to stressful experiences would be beneficial to understand.

Behavioral and physiological parameters were included in the majority of studies in this review, however indicators of welfare related to cattle health, injury and disease and stunning and insensibility were underrepresented. Although in the United States there has been considerable attention paid to cattle mobility at the slaughter plant (Eastwood et al., 2017; Lee, 2017), mobility and lameness were measured in less than 5% of papers in this review. Heat stress is another area of concern particularly for cattle in the finishing and pre-slaughter phases of the industry as climate change continues to impact both cattle welfare and production efficiency (Berman, 2019; Lees et al., 2019). Several recent studies have been conducted exploring the implementation of heat mitigation strategies and their benefits for cattle in the beef supply chain (Mitlöhner et al., 2002; Rusche et al., 2021; Davis et al., 2022). Heat stress behaviors such as open-mouth breathing was only measured in one study in this review (Hagenmaier et al., 2017). Surprisingly, the impacts of heat mitigation on cattle welfare during the pre-slaughter phase was not measured in any of the studies included in this review.

The welfare of animals during religious slaughter has been extensively discussed (Adams and Sheridan, 2008; Anil, 2012; Downing, 2015; Farouk et al., 2016). Due to the nature of religious slaughter (i.e., in most instances, no stun delivered prior to exsanguination), welfare concerns have been identified including an increase of stress for the animals (Bozzo et al., 2018), casting procedures (Ahsan et al., 2014), incorrect knife use (i.e., dull or small; Ahsan et al., 2014; Alam et al., 2020) and sensibility (Alam et al., 2020). Some of the studies in this category explored different aspects of religious slaughter impacts on cattle welfare, such as: a general focus on welfare outcomes during the religious slaughter process (i.e., not treatment comparisons; Ahsan et al., 2014; Alam et al., 2020); a comparison of welfare outcomes in cattle experiencing religious slaughter as compared to conventional slaughter (e.g., stunning with a captive bolt stunner prior to exsanguination; Bourguet et al., 2011; Bozzo et al., 2018); and a comparison of different restraint devices used during religious slaughter on welfare outcomes (Imlan et al., 2021). All of these studies included one or more of the following measurements to aid in welfare assessment: blood parameters, electroencephalography (EEG) analysis, post-exsanguination animal responses (e.g., signs of insensibility), behavioral reactions to lairage conditions, electrical prod use, pre-slaughter handling (e.g., slipping and falling), and characteristics of the neck cut that could impact welfare (e.g., cuts and stabs). The last study in this category examined the relationship between transport distance and stocking density on the trailer and cortisol response and EEG parameters of animals slaughtered using religious methods (Abubakar et al., 2021). Several of the same or similar welfare outcomes were measured as those found the formal analysis portion of this review. For example, antemortem behaviors and blood parameters were measured frequently throughout these studies and the studies included in the review.

Although a direct comparison between welfare outcomes in studies utilizing religious slaughter methods as compared to non-religious methods was not performed, it is worth noting that some of the results reported in these studies did cause concern for animal welfare. For example, religiously slaughtered animals had an increase in blood parameters such as cortisol (Bozzo et al., 2018) indicating increased stress, and observed corneal reflex (Bourguet et al., 2011) indicating sensibility post-slaughter as compared to conventionally slaughtered cattle. Some pre-slaughter handling techniques of animals during the religious slaughter process also raises welfare concern due to practices such as casting; Ahsan et al. (2014) observed animals pushed onto hard concrete, dragging by tails, bounding of all four legs for several minutes’ pre-slaughter, and vocalization during casting and post-cut. Consideration should be given to how the actual slaughter method (e.g., stunning and exsanguination, exsanguination only, etc.) could impact results when exploring other pre-slaughter management practices.

On-farm and mobile slaughter has become an area of interest, mainly due to the stress transportation induces on cattle which is avoided in on-farm scenarios, and it is anticipated that more research will be conducted in this area as this type of processing becomes more popular (Johnson et al., 2012; Friedrich et al., 2015; Hultgren et al., 2020; Hultgren et al., 2022). Hultgren et al. (2022) studied slaughter by rifle from a distance (ranging 6-12 m), focusing on blood parameters and pre and post slaughter behaviors (e.g., walking, exploring, sniffing, and vocalizing) as indicators of stress. Hultgren et al. (2020) conducted a study to assess the stress related behaviors in a mobile slaughter scenario compared to a stationary slaughter plant. The measurements recorded in this study focused on the actions of the animal handlers (e.g., touching, hitting, prodding, and tail-twisting) and subsequent animal responses (e.g., slipping, backing up, and vocalizing). The study concluded that more handling actions by stockmen, such as during the transportation process, increased stress behaviors in animals (Hultgren et al., 2020).