A Review of Animal-Based Welfare Indicators for Calves and Cattle

Simple Summary

Animal welfare monitoring indicators in cattle (Bos taurus and Bos indicus) and calves can be used to assess and ensure animal welfare. Many types of animal welfare monitoring indicators exist in the literature; however, there is yet to be an ideal and comprehensive collection of animal-based welfare indicators for calves and cattle. A review of calf and cattle animal-based indicators across scientific and grey literature was conducted. The results of this literature review aim to provide a selection of indicators for use in the development of animal welfare assessments and/or schemes. The indicators identified in this review have the potential to inform future research priorities, improve animal welfare assessment, and support uplift in animal welfare in cattle production and research to better meet societal expectations of animal care and use.

Abstract

As the human population continues to rise, so does the consumption of animal proteins and products. To meet this demand, animal agriculture has intensified. Simultaneously, there are increased public concerns related to improving calf and cattle welfare to ensure ethical and sustainable livestock production. To meet these expectations, it is essential to maintain high standards of cattle (Bos taurus and Bos indicus) welfare. The use of animal-based welfare indicators is critical when assessing and developing assessments for animal welfare. A review of calf and cattle animal-based individual and herd health indicators in the scientific and grey literature was conducted. Indicators were initially grouped into the categories of behavioral, physiological, or physical indicators and further analyzed to determine potential affective states, ease of training, cost, special equipment, time, and current use as herd health indicators. The indicators identified in this review have the potential to inform future research priorities, improve animal welfare assessment, and support uplift in animal welfare in cattle production and research to better meet societal expectations of animal care and use.

1. Introduction

As the human population continues to rise, so does the consumption of animal proteins and products [1]. Animal agriculture has subsequently intensified [1]. Simultaneously, public concern is increasingly focused on improving sustainability and animal welfare in the cattle and research industries [2]. To meet public expectations, maintain the social license of animal industries, and ensure high standards of production, the assessment and monitoring of cattle welfare (Bos taurus and Bos indicus) are essential [3,4]. Basic principles in farm animal welfare assessment include the disciplines of physiology, behavior, physical, and affective states [5]. The use of affective (emotion-like and mood-like) states [6] is fundamental to determining mental states and welfare states [both short and long term] of animals [6,7]. Using animal-based welfare indicators offers the potential to assess the affective states of livestock welfare [8] and evaluate changes or interventions to animal care and management [9].

Several frameworks for assessing animal welfare have been established over the years. The Welfare Quality (WQ) protocol was created from the principles of the Five Freedoms and has been used to assess welfare in dairy cattle [10]. The WQ protocol was one of the first protocols that focused on the integration of animal-based, resource-based, and management-based indicators. More recently, the Five Domains have served as a holistic foundation for multiple animal welfare assessment schemes [11,12] and offer a potentially more comprehensive approach to evaluating animal welfare [7]. It is a framework that moves beyond animals being free of negative experiences and advocates for the active inclusion of positive experiences to support opportunities for animals to thrive. For the purposes of this review, good animal welfare is defined to be when an animal is healthy, comfortable, well nourished, safe, able to express behaviors to support positive physical and mental states, and overall attains positive experiences to promote a life worth living [7,13,14].

The use of appropriate monitoring and indicators in calves and cattle is a critical component in assessing and promoting good animal welfare. The welfare of cattle and other animals should always be assessed with a combination of animal-, management-, and resource-based indicators [2,15]. Although resource- and management-based indicators are important in assessing the environment and husbandry practices of animals, they may not reflect the animal’s emotional or affective state [16]. Affective states can be defined as an animal’s feelings, emotions, or mood and encompass behavioral, physiological, and cognitive components based on arousal and valence [17]. Different experiences can lead to positive, neutral, or negative changes in affective states and can fluctuate in intensity and duration. The aim of many animal welfare assessments is to determine the likely affective states of an animal to infer or make inferences on their potential welfare status. Therefore, a collection of animal-based indicators (and resource or management-based indicators) is needed to provide an assessment of animal welfare and to indicate how an animal might be responding to its experiences (e.g., environment).

In the literature, there are numerous types and kinds of monitoring indicators for calves and cattle. Specifically, animal-based indicators play a vital role in welfare assessment, and their use in animal monitoring and assessment schemes is strongly encouraged [18]. To support the use of animal-based indicators in animal care, management, and assessment, a review of peer-reviewed, grey, and selected key literature was conducted to identify animal-based welfare indicators for potential use in calves and cattle. To facilitate appropriate selection, indicators were sorted into the categories of behavioral, physiological, or physical [14,19] and reviewed against the variables of potential affective state, ease of training, cost, equipment, time, and current use in herd health management. This review aims to provide a selection of potential indicators for animal welfare assessments and to promote better animal monitoring to enhance animal welfare, improve production, support research, and maintain public expectations.

2. Materials and Methods

A population (calves and cattle), exposure (animal welfare assessment), and outcome of interest (animal-based indicators) also known as a ‘PEO’ approach was utilized in this review. Databases were searched to align with the ‘Preferred Reporting Items for Systematic Reviews and Meta-Analyses’ (PRISMA) guidelines [20]. Keywords were entered into database search engines, and articles found were screened, reviewed, and selected based on specified inclusion and exclusion criteria (

Table 1. Inclusion and exclusion criteria for databases searched on 5 April and 18 September 2023, for potential calf and cattle animal welfare indicators as the population, exposure, and outcome of interest (PEO).

Databases	CABI	Web of Science	PubMed
Dates	1986–2023
Search terms:	‘Animal welfare’ AND ‘Monitoring indicators’ AND ‘Cattle OR Calves’ AND ‘Assessments’
Inclusion criteria:	Focused on cattle or calves Peer reviewed or primary research Published or translated in English Focused on assessing animal-based welfare indicators Studies focused on the development of methods to assess welfare in calves and cattle
Exclusion criteria:	Studies not relevant to the PEO Not in English Duplicates Abstract only Studies that did not focus on animal-based indicators to assess welfare

).

Three independent electronic databases were searched for the review (CABI, Web of Science, and PubMed) from the years 1986 to 2023. Literature searches were performed on 5 April and 18 September 2023. PRISMA flow charts of database search results are described in Figure 1 and Figure 2. The first search was completed using the keywords: “animal welfare” and “monitoring indicators” and “cattle” or “calves” (Figure 1). The second keyword search was undertaken to attempt to improve and refine the literature search using the keywords “animal welfare” and “monitoring indicators” and “cattle” or “calves” and “assessments”; however, the addition of the term “assessment” did not find any additional articles matching the article selection criteria for selection (Figure 2).

Screening and review were undertaken using the selection and inclusion criteria outlined in Table 1. Original articles were reviewed first, and then review articles were included to determine if any additional indicators could be identified. The literature focusing only on resource or management indicators was excluded; however, publications that included both animal and/or resource and/or management indicators were retained. Studies were also excluded if animal welfare assessment and/or related indicators were not a key focus of the publication (e.g., feed trial using body condition score).

Animal-based welfare indicators were extracted from the remaining eligible literature reviewed. Indicators were assigned to the category of physiological, physical, or behavioral to avoid duplication. An indicator was first assessed and determined if it was ‘physiological’ if it was primarily physiological and/or involuntary in nature and origin and/or used to detect (or quantify) potential stress responses (e.g., biomarkers). Indicators were then categorized [14] as ‘physical’ if primarily assessed via physical examination and/or observed physically and/or were physical or anatomical in nature and origin (e.g., discharges). An indicator was categorized as ‘behavioral’ if it was primarily observed as behavioral in nature and origin (abnormal or normal). If an indicator fit multiple categories or did not clearly easily fit the categories, it was discussed further amongst the authors and was classified based on consensus into the category it was most closely aligned with and how it was likely to be used across veterinary, animal productions, and research industries.

Categories were further grouped based on inductive thematic qualitative review techniques of body system, body part, or another thematic descriptor. The category of physiological was subdivided into cardiovascular, circadian rhythm, endocrine, gastrointestinal, hydration status, lactation, metabolic disease, post-mortem changes, respiratory, temperature, and urogenital. The category of physical was grouped into the digestive system, eyes, head, integument, neck, nutritional status, nervous system, thorax, musculoskeletal, reproductive, mortality, oral cavity, and dentition. The category of behavioral was separated into behaviors of concern, general behaviors, human-animal interactions, resting behaviors, and social and exploratory behaviors.

Indicators were extracted from articles, assessed, and analyzed against six variables. Variables included were affective state, time, special equipment, costs, ease of training, and current use in herd health assessments for each indicator. Affective states were classified as negative, positive, and/or neutral. Time was categorized as ‘no or yes’ if the assessment would likely take five minutes or less to complete by animal care staff. Any requirement for special equipment (e.g., stethoscope) was indicated as ‘no or yes’. Ease of training was denoted by a ‘no or yes’ if it was thought it could be taught without difficulty to a lay person within a standard 15- to 20-min veterinary consult. Cost was categorized ‘no or yes’ if the technique would typically cost more than AUD 100 to perform or for any special equipment required. It should be noted that any indicator that required veterinary or other specialist care was categorized as a high-cost method due to the cost of standard veterinary or similar specialist farm consultations (>AUD 100). If indicators were known to be currently in use for commercial herd health on-farm assessment, this was indicated as a ‘no’ or ‘yes’. The total number of physiological, behavioral, and physical indicators for ‘adult cattle and calves’, ‘calves only’, and ‘adult cattle only’ in

Table 2. Summary of the number of animal-based welfare indicators for calves and cattle found via systematic review of the available literature grouped into physiological, physical, or behavioral indicators. Some indicators are applicable to both calves and cattle. The total numbers of indicators outlined demonstrate more than twice the number of indicators for adult cattle than calves.

Category of Animal-Based Indicators	Total for Calves and Cattle	Total for Calves	Total for Cattle
Physiological	58	32	55
Physical	70	20	69
Behavioral	42	20	30
Total number of indicators	170	72	154

was generated via the results of

Table 3. Physiological calf and cattle animal-based welfare indicators identified via systematic review. Indicators were assessed for potential affective state, ease of training, cost (>100$ or requiring a veterinary or specialist visit as denoted by an asterisk (*)), special equipment required, time to assess (<5 min), and known current herd health indicators on-farm. Indicators specifically described for calves in the literature are denoted with a double asterisk (**).

Descriptor	Indicator	Affective State	Easy to Train	Cost (>$100)	Special Equipment	Time   <5 Min	Herd Health Indicator	References
Cardiovascular system	Heart auscultation	Positive,	No	Yes	Stethoscope	Yes	No	[21,22,23,24,25,26,27,28]
	(rate and rhythm) **	Neutral,
		Negative	Yes	Yes	Digital heart rate monitor	Yes	Yes
	Heart noises (muffling,	Negative	Yes	Yes *	Stethoscope	Yes	No	[21,22]
	murmurs, extra beats) **
	Heart palpation (’thrill’)	Negative	No	Yes *	Stethoscope	Yes	No	[21]
	Pulse rate and quality **	Neutral,	Yes	No	No	Yes	No	[22,25]
		Negative
	Capillary refill time	Neutral,	Yes	No	No	Yes	No	[22]
	(<2 s) **	Negative
	Heart rate variation (HRV) **	Neutral,	No	Yes	Electronic	No	No	[23,25,26,29]
		Negative			recorders
			No	Yes	Monitors	No	No
Gastrointestinal	Rumen status ** and	Neutral,	No	Yes	Stethoscope	Yes	Yes	[18,21,22,24,28,30,31,32]
system	rumination rate/time	Negative,
		Positive	No	Yes	Observation	No	No
	Faecal glucocorticoid	Negative	No	Yes	11-oxoaetiocholanolone	No	No	[29,30,33,34]
	Concentrations				enzyme
					immunoassay
Endocrine system	Plasma or serum cortisol **	Negative	No	Yes	ELISA kit	No	No	[24,35,36,37]
	Catecholamines **	Negative	No	Yes	Laboratory test	No	No	[24]
	Glucose **	Negative	No	Yes	Biochemistry	No	No	[22,25,37,38,39]
			No	Yes	Urine Dipstick	Yes	No
	Creatine phosphokinase	Negative	No	Yes	Chemistry	No	No	[35]
					analyser
	Aspartate	Negative	No	Yes	Chemistry	No	No	[35,38,39]
	aminotransferase **				analyser
	Non-esterified fatty acids **	Negative	No	Yes	Chemistry	No	No	[24,35,36,38]
					analyser,
					colorimetric assay
	Free fatty acids **	Negative	No	Yes	Laboratory test	No	No	[24]
	Glycogen	Negative	No	Yes	Laboratory test	No	No	[24]
	Creatine Kinase **	Negative	No	Yes	Biochemistry,	No	No	[24,36,38,39]
					colorimetric assay
	B-hydroxybutyrate **	Negative	No	Yes	Laboratory test	No	No	[18,24,37,38]
	Lactate **	Negative	No	Yes	Laboratory test	No	No	[36,37,38]
	Lactate dehydrogenase **	Negative	No	Yes	L-Lactate fluorescence assay	No	No	[24,39]
	Packed cell volume **	Negative	No	Yes	Haematology	No	No	[24]
	Total serum protein **	Negative	No	Yes	Haematology	No	No	[24,37,39]
	Haematological Parameters	Negative	No	Yes	Haematology	No	No	[22,24,25,39,40]
(e.g., Hematocrit, red/white				analyser, flow
blood cells,				cytometry
haemoglobin, neutrophils to
lymphocytes ratio) **
Acute phase proteins	Negative	No	Yes	Urine dipstick, ELISA kit,	No	No	[22,24,29,35,36]
(haptoglobin, serum amyloid A,				colorimetric assay
fibrinogen) **
Hair, saliva, or milk	Positive, Negative	No	Yes	ELISA kit,	No	No	[25,29,30,34]
cortisol **				Laboratory test
Serotonin	Positive, Neutral	No	Yes	Laboratory test	No	No	[29,38]
Magnesium	Negative	No	Yes	Biochemistry	No	No	[38]
Sodium (Na)	Negative	No	Yes	Biochemistry	No	No	[38]
Chloride (Cl)	Negative	No	Yes	Laboratory test	No	No	[25]
β-endorphin	Negative	No	Yes	ELISA kit	No	No	[25]
Fructosamine	Negative	No	Yes	Laboratory test	No	No	[25]
Thyroxine (T4)	Negative	No	Yes	Chemi-luminescence	No	No	[25]
				immunoassay
Albumin **	Negative	No	Yes	Biochemistry	No	No	[18]
Creatinine **	Negative	No	Yes	Laboratory test	No	No	[37,39]
Cholesterol **	Negative	No	Yes	Biochemistry	No	No	[28,31]
Triglyceride **	Negative	No	Yes	Laboratory test	No	No	[37,39]
Ketones **	Negative	Yes	No	Urine dipstick	No	No	[39]
			Yes	Wearable sensors	Yes	Yes	[39]
Urea	Negative	No	Yes	Biochemistry	No	No	[22]
Pro-brain derived neurotropic	Negative	No	Yes	Laboratory test	No	No	[37]
factor [BDNF]
Lipid plasma profiles	Negative	No	Yes	Laboratory test	No	No	[41]
(phosphatidylcholines)
Peripheral kynurenine pathway	Negative	No	Yes	Laboratory test	No	No	[41]
(KP) activation
Respiratory system	Respiratory rate and/or	Neutral,	Yes	Yes	Stethoscope	Yes	No	[21,22,24,26,31,34,42,43,44]
	effort **	Negative
			No	Yes	Infrared	No	No
					thermography
			Yes	Yes	Video recordings	No	No
			Yes	No	Observation	Yes	Yes
			Yes	Yes	Wearable sensors	Yes	Yes
	Respiratory noise **	Negative	No	Yes *	Stethoscope	Yes	No	[21,22,31,39,43,44,45]
	Chest percussion **	Negative	No	Yes *	Stethoscope	Yes	No	[21,22]
Temperature	Body temperature **	Negative	Yes	No	Thermometer	Yes	No	[18,21,22,23,28,34,36,38,40,46]
			Yes	Yes	Infrared	No	Yes
					thermography
			No	Yes	Implantable	No	No
					microchip
			No	Yes	Reticulorumen boluses	No	Yes
			Yes	Yes	Wearable sensors	Yes	Yes
	Ocular surface	Neutral,	Yes	Yes	Infrared	No	Yes	[27,46]
	temperature **	Negative			thermography
Lactation	Somatic cell count (above	Negative	No	Yes	Milk records	No	Yes	[2,18,28,42,43,45]
	200,000 cells/mL)
	Milk composition	Neutral, Negative	Yes	Yes	Milk processors	No	No	[18]
	(fat:protein)
Hydration Status	Dehydration (tacky mucous	Neutral,	Yes	No	No	Yes	No	[18,21]
	membranes, sunken eyes, skin tent)	Negative
Metabolic Disease	Milk Fever	Negative	No	Yes	Yes	Yes	Yes	[18]
	Ketosis	Negative	No	Yes	Yes	Yes	Yes	[18]
Post-mortem	Meat quality	Neutral,	No	No	Yes	No	No	[27,47]
		Negative
Urogenital system	Changes in urination,	Negative	Yes	No	No	Yes	No	[21]
	output and appearance
	Urine pH **	Negative	No	Yes	Urine dipstick	Yes	No	[22]
Circadian rhythm	Periodicity intensity of the	Neutral,	Yes	Yes	Wearable Sensor	Yes	No	[48,49]
	circadian rhythm **	Negative
	Sleep patterns (REM, non-REM) **	Neutral,	Yes	Yes	Wearable Sensor	Yes	No	[48,49]
		Negative

,

Table 4. Physical calf and cattle animal-based welfare indicators identified via systematic review. Indicators were assessed for potential affective state, ease of training, cost (>100$ or requiring a veterinary or specialist visit as denoted by an asterisk (*)), special equipment required, time to assess (<5 min), and known current herd health indicators on-farm. Indicators specifically described for calves in the literature are denoted with a double asterisk (**).

Descriptor	Indicator	Affective State	Easy to Train	Cost (>$100)	Special Equipment	Time <5 Min	Herd Health Indicator	References
Nutritional status	Body weight **	Negative,	Yes	Yes	Weigh scales	Yes	Yes	[22,24,25,28,30,36,42,50]
		Neutral,
		Positive	Yes	Yes	Body girth tapes	Yes	Yes
			Yes	Yes	Thermal infrared	Yes	Yes
					cameras
	Weight distribution **	Neutral,	Yes	Yes	Thermal infrared	Yes	No	[48]
		Negative			cameras
	Body size **	Neutral,	Yes	Yes	No	Yes	No	[46]
		Negative
	Body condition score **	Negative,	Yes	No	No	Yes	Yes	[2,18,21,24,25,28,39,42,43,44,51,52,53]
		Neutral,
		Positive
Thorax	Palpation **	Negative	Yes	No	No	Yes	No	[21,22]
	Respiratory distress, collapse	Negative	Yes	No	No	Yes	Yes	[18]
Gastrointestinal system	Distended abdomen/bloat **	Negative	Yes	No	No	Yes	No	[21,39,44]
	Faeces output and	Neutral, Negative	Yes	No	No	Yes	Yes	[2,18,21,22,44]
	consistency **
	Diarrhoea **	Negative	Yes	No	No	Yes	Yes	[22,39,42,44,45]
	Rectal examination	Neutral,	No	Yes *	No	Yes	No	[21]
		Negative
	Faecal egg count **	Neutral,	No	Yes	Yes	No	Yes	[22]
		Negative
Integument system	Coat and skin	Negative	Yes	No	No	Yes	Yes	[18,21,34]
	Swellings or similar	Negative	Yes	No	No	Yes	Yes	[18,21,42,45,52,53]
	abnormalities
	Lesions	Negative	Yes	No	No	Yes	Yes	[18,21,42,45,52,53]
	Dirt on legs, udder, perineum	Negative	Yes	No	No	Yes	Yes	[18,21,42,45,52,53]
	Carcass quality or bruising	Negative	Yes	Yes	Abattoir	Yes	Yes	[47,54]
Head	Discharges	Negative	Yes	No	No	Yes	Yes	[21,22,39,42,43,44,45]
	(e.g., ocular or nasal) **
	Restricted nostril airflow	Negative	Yes	No	No	Yes	No	[21]
	Sinus and facial palpation	Negative	Yes	No	No	Yes	No	[21]
	Submandibular lymph node	Negative	Yes	No	No	Yes	No	[21]
	enlargement
	Facial swellings, masses,	Negative	Yes	No	No	Yes	Yes	[21,22]
	submandibular oedema or
	similar **
	Nostril mucosa	Negative	Yes	No	No	Yes	No	[21]
	Nostril odour (sickly sweet, foetid)	Negative	Yes	No	No	Yes	No	[21]
Neck	Larynx palpation	Negative	No	Yes *	No	Yes	No	[21]
	Jugular vein (engorgement, pulse)	Negative	No	Yes *	No	Yes	No	[21]
	Enlargement of prescapular lymph node	Negative	No	Yes *	No	Yes	No	[9]
	Oesophagus palpation	Negative	Yes	Yes *	No	Yes	No	[21]
	Trachea palpation	Negative	No	Yes *	No	Yes	No	[21]
	Neck lesions	Negative	Yes	No	No	Yes	No	[18]
Eyes	Eyelids (blepharospasm, swelling,	Negative	No	No	No	Yes	No	[21]
	third eyelid protrusion
	Cornea, ocular opacity,	Negative	No	Yes *	Yes	Yes	No	[21]
	Ulceration **
	Eye globe position (exophthalmos	Negative	No	Yes	No	Yes	No	[21]
	or enophthalmos) and eye
	movement (strabismus or
	nystagmus)
	Internal chamber of eye (e.g., hypopyon,	Negative	No	Yes *	No	Yes	No	[21]
	cataracts, pupillary light reflex)
	Conjunctiva (e.g., icteric, pale,	Negative	No	Yes	No	Yes	Yes	[21]
	inflamed, conjunctivitis
Nervous system	Head-tilt **	Negative	Yes	No	No	Yes	No	[21,22]
	Opisthotonos	Negative	Yes	No	No	Yes	No	[21]
	Ataxia **	Negative	Yes	No	No	Yes	No	[22]
	Circling **	Negative	Yes	No	No	Yes	No	[22]
	Suckle reflex absent **	Negative	Yes	No	No	Yes	No	[22]
Musculoskeletal	Foot and claw disorders	Negative	No	Yes	No	No	Yes	[18,47,53,55,56,57]
	Joint lesions and swelling **	Negative	No	Yes	Infrared thermography	No	No	[18,21,22]
			Yes	No	Observation	Yes	Yes
	Gait (Lameness, locomotion) **	Negative	No	Yes	Automated system	No	No	[18,21,22,24,36,42,43,44,46,48,52,53,58]
			No	No	Gait/mobility score	Yes	Yes
			No	Yes	Force plates	No	No
			Yes	Yes	Wearable sensor	Yes	Yes
	Limbs (e.g., symmetry,	Negative	Yes	No	No	Yes	Yes	[18,21,22,53]
	conformation, lesions) **
	Abnormal posture	Negative	Yes	No	No	Yes	No	[18,21,28,48]
	Downer cow	Negative	Yes	No	Observation	No	Yes	[8,9,14,36]
			Yes	Yes	Wearable sensors	Yes	Yes	[18,45]
	Laminitis or white line disease	Negative	No	No	No	Yes	Yes	[18]
	Falls, slips	Negative	Yes	No	No	Yes	Yes	[18]
	Difficulty changing position	Negative,	Yes	No	Observation	Yes	Yes	[18,37]
	(standing up, lying down)	Neutral,
		Positive	Yes	Yes	Wearable sensors	Yes	Yes
	Posture in cubicle (lying with legs	Negative,	Yes	No	Observation	Yes	Yes	[18]
	extended to another	Neutral,
	cubicle) **	Positive	Yes	Yes	Wearable sensors	Yes	Yes
Reproductive system	Milk yield	Neutral	Yes	No	Automated milking systems	No	Yes	[21,25,28,33,48]
	Residual milk	Negative	No	Yes	Yes	No	Yes	[18]
	Navel (e.g., enlargement, red) **	Negative	Yes	No	No	Yes	No	[22]
	Mammary gland & teats	Negative	Yes	No	No	Yes	Yes	[18,21]
	(e.g., colour, swellings, lesions)
	Mammary vein	Neutral,	Yes	No	No	Yes	No	[21]
		Negative
	Internal examination of reproductive	Negative,	No	Yes *	Ultrasound (+/-)	Yes	No	[18,21]
	organs (e.g., abnormalities)	Neutral
	External examination of reproductive	Negative,	No	No	No	Yes	No	[18,21,43,45]
	organs (discharges, swellings,	Neutral
	ulceration, injuries)
	Dystocia	Negative	Yes	No	No	No	Yes	[21,42,45]
	Mastitis	Negative	No	Yes	Yes	No	Yes	[21,46]
	Fertility	Negative,	No	Yes	No (farm records)	No	Yes	[21]
		Neutral
Mortality	On-farm mortality	Negative	Yes	No	No	Yes	Yes	[18,42,44,45]
Oral cavity	Tongue (e.g., protrusion, tone,	Negative	No	Yes *	Yes	Yes	No	[21]
and Dentition	mobility, erosions, vesicles,
	ulcers, swellings)
	Mucosa (e.g., pallor, inflamed,	Negative	No	Yes *	Yes	Yes	No	[21]
	icteric, haemorrhages, necrosis,
	vesicles, erosions, ulcers)
	Teeth (e.g., sharp edges,	Negative	No	Yes *	Yes	Yes	No	[21]
	alignment, diastema, abscess,
	fracture)
	Pharynx (e.g., swelling, foreign	Negative	No	Yes *	Yes	Yes	No	[21]
	bodies, flaccidity of mucosa)
	Hypersalivation	Negative	Yes	No	No	Yes	No	[21]
	Cud/food dropping	Negative	Yes	No	No	Yes	No	[21]

and

Table 5. Behaviourial calf and cattle animal-based welfare indicators identified via systematic review. Indicators were assessed for potential affective state, ease of training, cost (>100$ or due to veterinary or specialist visit), special equipment required, time to assess (<5 min), and known current herd health indicators on-farm. Indicators specifically described for calves in the literature are denoted with a (**).

Descriptor	Indicator	Affective State	Easy to Train	Cost (>$100)	Special Equipment	Time <5 Min	Herd Health Indicator	References
General Behaviours	Standing **	Positive,	Yes	Yes	Wearable sensors	Yes	Yes	[18,23,24,28,30,31,33,36,42,48,59]
		Neutral,
		Negative	Yes	No	Observation	No	Yes
			Yes	Yes	Video recording	No	Yes
	Feeding behaviour (intake, frequency &	Positive,	Yes	Yes	Automated or electronic feeders	Yes	Yes	[18,22,23,24,28,36,40,48,59,60]
	duration of food consumption) **	Neutral,
		Negative
			Yes	Yes	Wearable sensors	Yes	Yes
			Yes	Yes	Radio frequency ear tags	No	No
			Yes	No	Observation	Yes	Yes
	Grazing	Positive	Yes	Yes	Wearable sensors	Yes	Yes	[30,32]
			Yes	No	Observation	Yes	Yes
	Water intake **	Positive,	Yes	Yes	Wearable sensors	Yes	Yes	[18,23,30,45,48]
		Neutral,
		Negative	Yes	No	Observation	Yes	Yes
	Locomotion (e.g., activity, gait) **	Positive,	Yes	Yes	Wearable sensors	Yes	Yes	[18,23,24,25,28,30,31,33,36,48,49,61]
		Neutral,
		Negative	Yes	No	Observation	Yes	Yes
	Vocalisations **	Positive,	Yes	No	No	No	Yes	[21,22,24,28,37,44,62]
		Negative
	Eye white:iris ratio	Neutral,	Yes	Yes	No	No	No	[28,29,34,46]
		Negative
Resting behaviours	Lying time and frequency **	Positive,	Yes	Yes	Wearable sensors	Yes	Yes	[18,23,24,28,30,31,36,40,42,45,48,58,59,61,63]
		Neutral,
		Negative	Yes	No	Observation	Yes	Yes
			Yes	Yes	Video recordings	No	Yes
	Absence of normal resting	Negative	Yes	Yes	Wearable sensor	Yes	Yes	[18]
			Yes	No	Observation	Yes	Yes
			Yes	Yes	Video recordings	No	Yes
Other behaviours	Aggression (e.g., head butts, chasing, fights) **	Negative	Yes	No	Observation	Yes	Yes	[18,21,24,25,37,40]
			Yes	Yes	Video recording	No	Yes
	Freezing	Negative	Yes	No	No	Yes	Yes	[24,30]
	Isolation **	Negative	Yes	No	No	Yes	Yes	[18,22,24]
	Stereotypies (e.g., tongue rolling,	Negative	Yes	No	No	Yes	Yes	[21,22,34,59]
	naval or ear sucking, head
	shaking) **
	Altered attitude (e.g., dull,	Negative	Yes	No	No	Yes	Yes	[18,21,22,36]
	depressed) **
	Facial grimace score **	Negative	Yes	No	No	Yes	Yes	[22]
	Flinch, step, kick (FSK) response	Negative	Yes	Yes	Wearable sensors	Yes	No	[26]
	Tail flicking **
		Negative	Yes	No	No	Yes	Yes	[40]
	Foot stamping **	Neutral,	Yes	No	No	Yes	Yes	[40]
		Negative
	Reversing	Neutral,	Yes	No	No	Yes	Yes	[37]
		Negative
	Jumping **	Neutral,	Yes	No	No	Yes	Yes	[37,40]
		Negative
	Mounting	Negative	Yes	No	No	Yes	Yes	[37]
	Cows interfering with	Negative	Yes	No	No	Yes	Yes	[18]
	calving
	Mismothering **	Negative	Yes	No	No	Yes	Yes	[18]
	Kicking milking clusters	Negative	Yes	No	No	Yes	Yes	[18]
	Lying in passage, standing in	Negative	Yes	No	No	Yes	Yes	[18]
	water/slurry
	Time to enter milking area	Neutral,	Yes	No	No	No	Yes	[18]
		Negative
	Stopping and turning	Neutral,	Yes	No	No	Yes	Yes	[18]
		Negative
	Hypersensitive to touch	Negative	Yes	No	No	Yes	Yes	[18]
	Discomfort when standing (e.g.,	Negative	Yes	No	No	Yes	Yes	[18]
	paddling, resting a foot)
	Abnormal social interactions and	Negative	Yes	No	No	Yes	Yes	[18]
	activity
	Baulks	Negative	Yes	No	No	Yes	Yes	[37]
Human animal interactions	Large flight zones or avoidance	Neutral,	Yes	No	No	Yes	Yes	[2,18,24,25,30,34,39,45,52,53]
	distance of humans **	Negative
	Negative reactions to humans	Negative	Yes	No	No	Yes	Yes	[18]
Social and exploratory behaviours	Grooming (allogrooming, self-grooming) **	Positive	Yes	No	No	No	Yes	[18,25,28,34]
	Play behaviour (running, bucking) **	Positive	Yes	Yes	Wearable sensors	Yes	Yes	[22,23,34,48,59]
	Social interactions **	Positive	Yes	No	No	No	Yes	[22]
	Agonistic behaviour **	Positive	Yes	No	No	No	Yes	[18,25,28,42,44,45,52]
	Antagonistic behaviour	Negative	Yes	No	No	No	Yes	[37]
	Exploring	Positive	Yes	No	No	No	Yes	[24]

.

3. Results

A total of 366 articles were found by the authors in the first search. Duplicate articles and articles not in English were first removed. There were a total of 299/366 articles retained for screening. Next, the title and abstract of each manuscript was assessed for initial eligibility based on the inclusion and exclusion criteria (Table 1). A total of 41/299 articles were retained and progressed to further evaluation using full-text reading. After full-text reading, a total of 29/41 relevant manuscripts matched all the inclusion criteria for analysis (Table 1).

The inclusion of the term “assessment” reduced the number of initial articles found to 69 articles. Five duplicate articles, and two not written in English were eliminated. A total of 62/69 articles were kept for screening of the titles and abstracts. After screening, 38/62 of the same articles from the original search (n = 41) were selected and still deemed to be eligible for full-text reading. Of these 38 articles, the same 29 articles were eligible for complete classification and analysis. Two additional articles were hand-picked to be analyzed and met the relevant inclusion and exclusion criteria. For the final review, a total of 32 articles were classified and analyzed (Table 2, Table 3 and Table 4).

A total of 170 animal-based welfare indicators were found (Table 5). Physical indicators had the highest number of indicators when compared to the other categories with 70 identified. Physiological indicators totaled 58, and behavioral indicators had the least number with a total of 42. Overall, there were fewer indicators denoting positive affective states (n = 17) in comparison to negative or neutral affective state indicators (n = 160) of animal welfare. There were more than twice as many indicators identified during the literature review for cattle (n = 154) in comparison to calves (n = 72).

4. Discussion

4.1. General Discussion

Various frameworks have been created to assess animal welfare states including Five Domains, Five Freedoms, and the WQ protocol for dairy cattle [13,64]. The use of systematic reviews and analyses of indicators could be beneficial to animal welfare assessment frameworks. This review particularly focuses on the use of animal-based indicators, which are essential to the assessment of animal welfare and affective states [65]. While resource- and management-based indicators can have benefits (e.g., easy to measure pen size) [45] and add value to animal welfare assessments (e.g., assess husbandry) [18], there is increasing recognition and emphasis on utilizing a combination of animal and resource-based indicators to assess animal welfare [8,15]. There is also an emphasis on selecting and validating positive (and negative) animal-based indicators to offer greater insights into the affective states of animals [66]. The analysis from this review has highlighted a relatively low number of positive indicators available for calves and cattle. This can pose issues when attempting to demonstrate positive welfare states and/or incorporate positive welfare indicators into assessments. It is therefore strongly encouraged that further work is undertaken into the discovery, development, validation, collation, and application of specifies- and affective state-specific animal-based welfare indicators to address this gap.

Animal welfare assessments can be used and form the basis of animal welfare assurance, standards, certifications, and audits (internal and external). These techniques and tools can help to inform stakeholders [e.g., farmers, consumers, researchers] on the potential or likely welfare status of farmed animals. Many of these schemes may utilize a number of indicators as well as multiple types of animal welfare indicators. However, there can be practical challenges when attempting to select the ideal combination [number and type] of indicators. Research into addressing these challenges by outlining which indicators are available and offering insights into their potential use, pros, cons, and likely affective state may be of interest and benefit to the greater animal care and use industry. Farmers, researchers, veterinarians, trainers, teachers, industry groups, government bodies, non-governmental animal welfare organizations, as well as the public/consumers may find the outcomes from this study useful both personally and professionally as well as across the wider industry to improve calf and cattle welfare. Some of the indicators outlined in this review should be considered for use in animal welfare assessments to improve animal welfare, monitoring, and management on farms, in research, and across the wider animal care industry.

The information generated from this review (Table 2, Table 3, Table 4 and Table 5) highlighted indicators that can be used in identifying calf and cattle welfare (n = 170). The category of ‘physical’ had the highest number of indicators (n = 7). This could have been related to the search terms; however, it could also perhaps reflect the integral importance of physical observation and examination when assessing animal welfare. There was also a much lower number of calf specific animal-based indicators (n = 72) regardless of the category (physiological, physical, or behavioral). While many of the indicators could potentially be used in both calves and cows (e.g., heart rate variability, body weight, lying time), others were clearly only for adult cattle (e.g., milk production, rumination rate) or calves (e.g., navel checks). Of the available calf-specific research publications, many are not explicit for affective states or specific for animal welfare assessments [67]. These publications instead appear to focus on experimental or production-specific outcomes rather than animal welfare outcomes. While specific assessments of cattle welfare based on life stage (e.g., pregnancy, lactation, heifers) is essential, calf-specific welfare indicators could be seen as particularly important due to their vulnerability and unique conditions (e.g., infected navels, single housing). The prospective lower availability of indicators specific for life stage in cattle, and especially calves, requires further investigation to ensure animal welfare can be assessed and maintained.

All indicators were evaluated against the six variables of potential affective state, ease of training, cost, requirement for special equipment, assessment time (<5 min), and current known use in herd health assessments in research and commercial farms. Each of these variables was included to evaluate the suitability and practicality of these indicators for use in routine animal monitoring and welfare assessments on the farm and/or in experimental studies. By determining factors such as speed, cost, ease of training, the need for special equipment or skills, suitability for herd health monitoring, and the potential to identify affective state, stakeholders can select the most suitable suite of indicators for their requirements. Further work needs to be undertaken to validate and research which indicators, and/or combination of indicators, are most accurate and beneficial. Findings from this work also outlined that many of these indicators can be monitored using multiple methods. For example, lying time and activity levels can be monitored using video recordings, wearable sensors, or observation. With the advent, commercialization, and increasing use of wearable sensors and other livestock precision technologies, some indicators may become easier and more feasible to use by animal care managers and staff. In terms of herd management, many of these indicators could be combined to form herd health and individual animal assessments, especially when applying the right technologies, strategies, and veterinary support.

4.2. Physiological Indicators

Physiological indicators are often measured using laboratory tests but can also include basic vital signs examination (e.g., heart rate, temperature) to detect potential states of compromised welfare [25,27,68]. Physiological stress responses can include alterations to heart rate, temperature, and glucocorticoid release. These types of indicators can be used to denote both negative (e.g., distress, pain) and positive stress (e.g., eustress, pleasure) [34]. Factors such as sampling technique, animal handling, lactation stage, disease status, and endotoxins may all affect physiological indicators [24]. The sample type and chronicity of stressors may also influence indicator values [25,34,69]. Therefore, careful interpretation is required [23,25,26], and multiple indicators should be used to avoid inaccurate assessments of animal welfare states [29]. Less commonly used laboratory-based physiological indicators were also found in this review and included acute phase proteins, neutrophil/lymphocyte ratio, haptoglobin, creatine kinase, glucose, B-hydroxybutyrate, packed cell volume, insulin, and free fatty acids [24]. These were more frequently found in experimental animals but are available for on-farm individual animal and herd health assessments. Drawbacks for some of these laboratory tests can be increased costs, increased time, special equipment requirements, invasiveness of sample collection, and limited availability in some locations.

The use of non-laboratory low-impact physiological indicators (e.g., temperature, heart rate) can also be used to assess calf and cattle welfare. These can be rather reliable if animals are accustomed to people or if sensors or wearable technologies are applied. Wearable sensors and other technologies may also permit more frequent and remote monitoring [26]. However, these technologies can have high entry costs and may cause injury to animals [26]. Other techniques such as remote non-invasive infrared thermography (IRT) can be used for respiration rate and body temperature but again have high entry costs and are affected by ambient temperatures [23,29,38,46].

Overall, physiological indicators play an important role in the assessment of animal welfare, but results must be interpreted with caution and with other indicators prior to inferring animal affective state [66]. These techniques can be suited to herd, individual, on-farm, and experimental animal welfare assessments but may often require specialized equipment, more time, higher cost, and context-specific skilled interpretation of results.

4.3. Physical Indicators

Generally, physical indicators are non-intrusive, easy to train, quick, and low cost as they commonly employ visual observation or physical examination. These indicators are often assessed or measured using techniques such as body condition score, lameness score, body weight, and observation of external abnormalities including swellings, masses, lesions, and/or discharges [18,21,22,24,25,28,30,39,42,43,44,45,46,52,53,58]. Observation of an abnormal posture, such as an arched back, or the display of a facial grimace can be used to detect pain [16,18,21,22,28]. Other scoring systems can be used to identify welfare issues using numerical scoring systems to evaluate gait, lameness, and body condition score [16,24,25]. These kinds of indicators are common to welfare assessments but can be prone to subjectivity as they rely on human visual evaluation, and subtle differences can be difficult to detect [24]. The concurrent use of automated equipment/systems, such as wearable sensors (e.g., accelerometers), cameras, and video recordings or software applications, may reduce subjectivity errors [16,42,70]. Other indicators such as rectal or oral examination may require handling, restraint, extra time, and specialist skills or equipment. Some physical indicators are specific for life stage, such as milk yields, residual milk, mastitis, somatic cell counts, dystocia, fertility status, mammary gland issues, or other reproductive system abnormalities [68].

4.4. Behavioral Indicators

Behavioral indicators can be assessed directly or via recorded observations [27]. These observations can be relatively low cost, do not require complex technology, and can be performed by animal care staff [27,34]. Time and timing may be an issue as many indicators, such as allogrooming and play, may occur irregularly requiring long periods of observation [34,59]. Additionally, the presence of humans may disrupt the display of natural behaviors [16,27,59]. Remote technologies using wearable sensors, accelerometers, automated systems, and other technologies (e.g., video) can be used to monitor feeding intake, locomotion, lying, feeding, drinking, rumination, and play [16,23,59]. These devices offer the benefits of ongoing animal monitoring and reduce disruptions to animal behavior and inter-observer variations but can have higher costs and/or maintenance [27].

Negative welfare states such as fear can be expressed as aggression, jumping, reversing, mounting, baulking, and other agonistic behaviors [24,44], while stereotypic and repetitive behaviors can denote states of distress and boredom [27,34]. These behaviors can occur more frequently if animals are stressed, in resource-limited environments (e.g., food), or when social groups are disrupted [27]. Other behaviors such as standing, lying time, vocalizations, and feed and water intake can also be used as indicators for identifying illness, pain [16,44], or other negative welfare states [58]. Alterations to these behaviors can be alerting indicators to identify welfare issues [16,44,61,62,63].

Some indicators are less clear in their interpretation. The presence or relative ratio of the eye’s white to iris can indicate both positive and negative aspects of welfare in cattle [34]. Conversely, lying down, ruminating, and vocalizations at appropriate frequencies and sound levels (hertz) can signify a positive affective state [62]. Other behaviors such as appropriate play, exploration, and allogrooming can be important indicators of positive affective states [23,34,59]. Similar to other categories, indicators of both positive and negative states should be incorporated into welfare assessments [30,59,66].

4.5. Limitations

This study aimed to review some of the available animal-based indicators for use in welfare assessments and/or welfare assessment schemes. A potential limitation of this study is that not all the indicators described have been validated [limited research], and validation itself was not considered a variable. There are always potential risks with utilizing non-validated indicators; however, there is still limited research in validating many available animal welfare indicators [71,72,73]. While evidence-based indicators are and can still be used in animal welfare assessments, care and caution are required along with further future research.

Several of the reviewed experimental studies utilized animal-based indicators to assess negative stress, pain, and health status in response to specific treatments, transport, and various environments such as abattoirs or feedlots [30,31,33,35,36,37,38,40,47,51,54,55,56,57,58], which could be a limitation. Furthermore, not all cattle life stages were included in this study (only divided by calf or adult cattle). It is quite likely that the search methodology did not locate all known published articles on animal-based welfare indicators in calves and cattle. This could be due to the keywords or electronic databases used. Some indicators were only found in grey literature or through hand selection of the known literature. Alternatively, some indicators may not have been published and/or were not explicitly developed for animal welfare assessment. These publications may have focused on other experimental (e.g., faster growth rates) or animal management (e.g., breeding for fertility) outcomes. However, the study focus was limited to ensure that the most prominent animal welfare indicators were captured, to encourage discussion, and to identify indicators of pragmatic value for animal welfare assessment for calves and cattle at the individual and herd health level.

4.6. Future Research

There were a greater number of indicators pertaining to negative (n = 160) versus positive affective states (n = 16) found in this study. Animal-based indicators and many animal welfare assessments primarily rely on the absence of negative welfare states [e.g., disease], resource availability [74,75], or neutral states (absence of physical abnormalities). Modern animal welfare science acknowledges that animal welfare occurs on a spectrum from very poor to very good, and good welfare occurs when animals experience primarily positive states and a life worth living [13]. Animal welfare schemes and standards should aim to be comprehensive in their approach and include (when possible) validated indicators for both positive and negative states to promote and provide opportunities for animals to thrive and experience consistent states of good animal welfare. However, the indicators collated and analyzed highlighted that there is a relatively low number of indicators specific and/or suitable for the assessment of positive welfare states. More research should be encouraged to explore and expand the availability of positive animal welfare-specific indicators in calves and cattle.

Given that so many indicators were identified in this first review (n = 170), training and further extension materials could support context-specific selection and assessment of animal welfare. Reviewing the application and appropriateness of wearable sensors, cameras, and other similar technologies to support animal welfare assessments is another key area for more research. With the more recent increase in these livestock precision technologies, there are opportunities to utilize this technology for better welfare when used appropriately in conjunction with other modalities. However, stakeholders should be mindful that challenges and animal welfare issues can arise when there is an overreliance on technology in lieu of in-person real-time monitoring and oversight of animals.

Additionally, a database or similar collection of key welfare assessment parameters could be collected, curated, and applied to animal welfare assessments and framework (e.g., Five Domains). Indicators can also be mapped and organized based on the animal’s environment, purpose, life stage, and other similar conditions to facilitate ease of choice. Information on the validity, practical application, and affective state of indicators can also be included. More work should be undertaken to validate existing indicators and to investigate the possible interplay between different indicators. Further classification and validation can be undertaken to identify when special specific indicators based on life stage, purpose, or environment should be used [e.g., beef, calves, lactating females]. Where possible, the interrelatedness of some indicators could be further acknowledged (e.g., BCS and weight). The current selection of indicators identified and assessed in this, and other reviews ideally will offer impetus and preliminary information for future research.

In the future, determining when and which indicators should be utilized and under which circumstances may also allow for more tailored assessments of animal welfare. Currently, there is no optimal combination of indicators that can be used in animal welfare assessment frameworks (e.g., Five Domains, WQ). However, these frameworks and assessments rely on good decision-making and choice of indicators to promote good animal welfare. Further analyses are needed along with industry and expert consensus in animal welfare indicators. Together these insights and research can improve the robustness and accuracy of animal welfare assessments, enhance animal monitoring, improve training, and ultimately enhance the welfare of calves and cattle in our care.

5. Conclusions

With increased interest in providing better animal welfare across all animal industries, identifying appropriate animal-based welfare indicators for animal welfare assessments, certifications, audits, research, and animal care and management is paramount. Many of these indicators identified in this study can be helpful for on-farm and experimental work to provide objective and subjective data to inform welfare assessments. For most indicators (physiological, physical, and behavioral), it is important to monitor absolute values as well as changes over time. Critically, the absence of an abnormality does not necessarily indicate an optimal state of welfare. As such, it is vital that multiple types of animal-based indicators as well as resource- and management-based indicators are utilized to ensure good animal welfare monitoring and appropriate assessment.

The results from this research can be used by stakeholders to identify a selection of animal-based welfare indicators suitable for calf and cattle welfare assessment. The information provided in this review outlines practical considerations when implementing these indicators in on-farm settings, experimental studies, and animal welfare assessments. This analysis also highlights potential gaps in positive welfare indicators for calves and other life stage-specific animal-based welfare indicators in calves and cattle. As indicators are vital to holistic animal welfare assessments, further research is needed to ensure the availability of validated, life stage-specific indicators for both herd health and individual calves and cattle. Finally, more work should be done to determine potential ideal combinations of indicators and to outline caveats and considerations for all calf and cattle animal welfare assessments throughout the animal care and use industries.