Hunger and thirst Adroaldo J. Zanella ANS 305

Introduction 4 Freedom from hunger and thirst features as the first requirement that has to be satisfied in animal welfare codes/laws in many parts of the world. –Extreme –Mild deprivation

Background 4 Extreme nutrient and water deprivation causes death. 4 Failure to satisfy the animal’s requirement for essential nutrients leads to illness, poor performance and death.

Background 4 Mild deprivation of water and nutrients has little effect on health and vigor. 4 Ad libitum feeding of animals may lead to increase incidence of disease and poor reproductive performance.

Hunger & feeding motivation 4 The state of the animal in which it is stimulate to eat –Nutritional properties of the food –Physiological state of the animal –External factors

Problems I 4 Animals need to be hungry or thirsty in order to eat or drink. 4 Aristotelian concept of ‘telos’: –“All animals desire or strive to reach the functional end for which they were designed”.

Problems II 4 A) Malnourished: conditions are limiting by being inappropriately balanced in relation to the animal’s requirements 4 B) Undernourished: conditions are limiting by being insufficient in relation to the animal’s requirements 4 A & B

Conditions 4 Harsh environments 4 Hot temperatures 4 Competitive environment 4 Lack of feeder and drinker space 4 Inadequate drinker & feeder design

Eating behavior 4 Sensory cues 4 Nutrients in the diet 4 Hormonal factors

Feeding strategies 4 Decision making processes are often overlooked. –Pigs are capable of balancing their diets –Food avoidance is common in many species –Grazers will not eat in a random fashion. Plant chemicals Feces Nutritional contend

Feeding patterns 4 Cows may graze from 4-14 h day and bite rates may vary from minute. 4 Periods of high ingestive intake –Shortly prior to sunrise –Mid-morning –Early afternoon –Near dusk

Feeding patterns 4 Horse grazing behavior is affected by –Early experience –Quality of the pasture –Social facilitation –Temperature

Feeding patterns 4 Eating behavior in pigs is affected by: –Social hierarchy –Food quality –Temperature –Age –Genetic background

Measurements 4 A) Monitor food intake, rate of eating & time spent in food-directed activity. 4 B) Animal’s response to operant methodologies (e.g. the animal needs to work. 4 C) Trade food acquisition with aversive stimulus.

Sources of malnutrition 4 Unintentional: –Poorly balanced diets 4 Intentional –Veal calves are sometimes fed on liquid diet deficient in iron.

Sources of undernutrition 4 Intentional: –Quantitative restriction Sows & boars (60%) Broiler breeders (25%) –Qualitative restriction Sows & boars Ruminants

Sources of undernutrition 4 Unintentional –Negative energy balance (poor grazing conditions) –Restrictions imposed by other group members –High temperature Amount eaten Feeding pattern

Thirst 4 Definition: It is a subjective sensation aroused by lack of water (Rolls & Rolls, 1982) –Physiological state –Diet –Temperature –Access to water –Water quality

Water=nutrient 4 Adjustment of body temperature. 4 Maintenance of mineral homeostasis. 4 Excretion of end products of digestion & anti nutritional factors. 4 Achievement of satiety. 4 Satisfaction of behavioral drives

Secondary drinking 4 Hunger induced 4 Schedule-induced polydipsia

Measurement 4 A) Monitor water intake, rate of drinking & time spent in drinking-directed activity. 4 B) Animal’s response to operant methodologies (e.g. the animal needs to work. 4 C) Trade water acquisition with aversive stimulus.

Water restriction 4 Intentional –Liquid & wet feeding (pigs) –Restricted to periods (broilers & pigs) –Premarin farms

Water restriction 4 Unintentional –Blocked pipes –Inadequate flow rates –Drinker design –Water quality –Social competition

Welfare problems 4 Sheep will walk more than 25 km (16 miles) a day foraging 4 Free range sows will spent over 50% of their time foraging

Welfare problems 4 Expression of foraging behavior 4 Failure to meet requirements (stress) 4 Secondary illness associated with nutrient (including water) deprivation

Behavioral problems 4 Abnormal behaviors –Tail biting –Wool-stripping 4 Redirected behaviors –Activity levels –Exploratory behavior 4 Food related stereotypies –Sham-chewing