Jeremy N. Marchant-Forde

USDA-ARS, Livestock Behavior Research Unit

The Ethology of Sow Aggression

Overview of the Talk

Introduction to social behavior

Natural behavior of pigs

oCompare and Contrast – “Natural” vs “Farmed”

Why and when does aggression occur?

The detail within sow aggression

Management factors influencing aggression

Take home message

Being social is good, right?

Reduces predation

Improves successful foraging

Improves rearing of offspring

Increases chances of mating

Helps thermoregulation

But….

Increases conspicuousness

Increases risk of infectious disease

Decreases access to resources

Competition!

Social Behavior

“those patterns of behavior that involve two or more members of a species.”

Social Behavior

“those patterns of behavior that involve two or more members of a species.”

Natural Social Behavior

To better understand how to manage thepig‟s behavior in our current systems, weneed to take a step back….

Wild boar - social group

2-4 adult females – related

Mother-daughters or Siblings

Un-weaned juveniles

Sub-adults – previous litters

Boar(s) – breeding season

Group size will vary according to season and available resources

Groups distribute around resources

Boars distribute around groups

Wild boar - social group

Sows are dominant to allother members

Overt aggression in coregroups is rare

Dominant sows will displace subordinates from choice feeding sites

Litters are introduced to the group gradually

Home ranges can overlap, but groups won‟t interact

Where‟s the relevance?

•Not the same animal?

Domestic pig - social group

Studies on feral pigs and pigs in semi-natural enclosures show that:

Domestic pigs behave like Wild Boar

Social behavior

Domestic pigs form „family‟ groups

Small core groups of related females + progeny

Solitary males, associate with groups at mating

Domestic pig – social behavior

Groups may share common space in home ranges but do not merge

Groups maintain distance from each other when foraging in the same area

When foraging, average distance between group members is 4 m

Aggression in core groups is rare = 1 every 2h per animal

Strategy is avoidance

Contrasting Features

Natural FarmedGroup size Small Single to Large

Social structure Stable Unstable

Relatedness Related Variable

Age/Size profile Wide Narrow

Space Unlimited Restricted

Behavioral repertoire Complex Constrained

Activity Active - foraging Inactive

When & why does aggression occur?

Two major opportunities for aggression in sows:

Mixing

Feeding

Mixing

Formation of social hierarchy

Feeding

Access to, and defense of, scarce resources

Reinforcement of social hierarchy

Factors Impacting Aggression

Housing

Groups vs. stalls

Mixing

How many times

How many pigs

Feeding

Method

Quantity

Ingredients

Space

Amount

Quality

Impact of Aggression for the Pig

Activation of sympathetic-adrenal-medullary axis Catecholamines

Increased heart rate/blood pressure

Activation of hypothalamic-pituitary-adrenal axis Cortisol

Health Skin lesions/Leg injuries

Immunity

Productivity Feed intake/Growth/Body condition

Pregnancy

Litter size

Life cycle of breeding sows

Gestation

Lactation

Service

Gilts

Cull

Gilts

MIX

MIX

MIX

Getting to know you…..

Sequencing Aggressive Behavior

Break

Ano-genital nosing

Bite

Follow/Approach

Head over body/threat

Knock

Mount

Nose to nose

No Response

Other

Push/lift

Withdraw

Walk

NN

NRP

OTH

PU

WD

WLK

BRK

AGN

BT

F/A

HO/T

K

MO

Markov analysis to distinguish meaningful pairs from randomly occurring pairs

Break

AGN

BT

Fo/Apr

HO/T

K

MO

NN

NRP

OTH

PU

WD

WLK

AGN

BT

Fo/Apr

HO/T

K

MO

NN

NRP

OTH

PU

WD

WLK

Break

AGN

BT

Fo/Apr

HO/T

K

MO

NN

NRP

OTH

PU

WD

WLK

0.47

0.23

0.19

0.15

0.37

0.16

0.10

0.29

0.24

0.18

0.31

0.05

0.03

0.02

0.06

0.18

0.06

0.23

0.02

0.36

0.20

0.49

0.32

0.42

0.65

0.45

0.08

0.10 0.20

0.13

0.11

0.19

0.29

0.12

0.10

0.25

0.17

0.42

0.16

0.12

0.23

0.09

0.04

0.43

0.17

0.60

0.28

0.29

0.06

0.26

0.35

0.17

0.30

0.42

0.37

0.18

0.38

0.50

0.30

0.36

0.13

0.17

0.21

0.03

0.02

0.17

0.20

0.14

0.60

0.15

0.14

0.42

0.14

0.19

0.07

0.13

TO FROMBreak

Mixing Aggression - Scenarios

We investigated four different scenarios:

Indoors – 11 pairs at 3.0 m2/sow (n=11)

Outdoors – 15 pairs at 2500 m2/sow

Indoors – 7 × 2 sub-groups of 3 sows at 3.2 m2/sow

Outdoors – 14 × 2 sub-groups of 3 sows at 833 m2/sow

Similarities and differences….

Mixing Aggression - Scenarios

In all 47 mixings, social interactions occurred

In 45 mixings, aggressive interactions occurred

2 outdoor pairs did not engage in aggression

More aggressive actions in indoor groups

0

100

200

300

400

500

600

Indoor Group Indoor Pair Outdoor Group Outdoor Pair

Num

ber

of

actions

a

b b

c

Mixing Aggression - Scenarios

In indoor pairs, aggression ramped up gradually

In all other scenarios, aggression was immediately high intensity

0

20

40

60

80

100

120

Indoor Group Indoor Pair Outdoor Group Outdoor Pair

Num

ber

of

actions

Pushes

Knocks

Bites

a

x

x

y

xm

n

mn

m

ab

a

b

Mean number of actions before first push, knock and bite

Mixing Aggression - Scenarios

In groups, 9 possible unacquainted pairs, 6 acquainted pairs

Mean number of pairs interacting in groups

0123456789

101112131415

Interacting socially Interacting non-aggressivelyInteracting aggressively Fighting

Nu

mb

er

of p

airs

Indoor all

Indoor between sub-groups

Indoor within sub-groups

Outdoor all

Outdoor between sub-groups

Outdoor within sub-groups

Mixing Aggression - Scenarios

Space especially affects how the sows behave at mixing

When space is „limitless‟, strategy quickly involves avoidance

When space is limited, avoidance is difficult – same behavior can have different results

In Pair

In Group

Out Pair

Out Group

„Break‟ preceded by „Withdraw‟ 11.7 % 15.6 % 44.8 % 61.1 %

„Break‟ preceded by „No Response‟ 46.0 % 51.6 % 35.7 % 18.4 %

„Bite‟ preceded by „No Response‟ 32.3 % 39.7 % 18.4 % 8.5 %

„Nose-to-Nose‟ or „Ano-Genital Nosing‟ followed by „Bite‟,„Knock‟, „Push‟

4.3 % 6.3 % 12.4 % 6.5 %

Mixing and Aggression

Methods tried to reduce aggression at mixing

• Get-away areas

• Chemical intervention /

• Time of day /

• Fresh bedding

• Ad libitum food

• Boar presence /

• Sub-groups

• Space /

• Pre-exposure /(Marchant-Forde & Marchant-Forde, 2005)

Space

(Edwards et al., 1993)

6.1 m2/sow 3.7 m2/sow

barriers

3.7 m2 6.1 m2

No. of interactions (0-12h) 187 324

Damage scores 13.5 8

Space

Little evidence for optimum space allowance to reduce aggression

Aggression may be reduced at high density conditions (1.4 m2 v 3.4 m2) but only initially

1.4 m2 3.4 m2

No. of interactions (0-1.5 h) 5.9 6.6

No. of interactions (d 2) 2.6 1.9

No. of interactions (d 3-10) 13.7 8.7

(Barnett et al., 1993)

Space

Limited space in the longer term may result in increased aggression and higher lesion scores

(Weng et al., 1998)

0

50

100

150

200

250

300

350

2 2.4 3.6 4.8

Aggressive interactions Lesion scores

Pre-exposure pen

Pre-exposure

• Can we let the sows get to know each other

without letting them fight?

Pre-exposure

**

0

20

40

60

80

100

120

140

Bites Knocks Threats Total

Control

Pre-exposed

*

**

*

• Aggression was reduced at day of mixing, +1d, +1wk, +2wks

(Kennedy, 1997)

Pre-exposure

• These results are telling us that vocal, olfactory, visual and limited physical cues are conveying important information:

• „Familiarity‟?

• Relative social rank?

• Relative fighting ability?

• When we mix, not all possible combinations of pigs fight, yet hierarchy is established

Pre-exposure

Pre-selecting your group out of the farrowing house

Next to each other

Randomly separated

Housed in service crates

7d post-service

35d post-service

Pre-exposure

Grouped after 7 days in service crates

5

6

7

8

9

10

11

12

13

14

15

Grouping 24h 2wk 4wk 5wk 6wk 8wk 12wk

Time relative to moving to gestation pen

Le

sio

n S

co

re

Grouped

Random

Pre-exposure

Grouped after 35 days in service crates

5

6

7

8

9

10

11

12

13

14

15

Grouping 24h 2wk 4wk 5wk 6wk 8wk 12wk

Time relative to moving to gestation pen

Le

sio

n S

co

re

Grouped

Random

What if we keep sows in crates

• Crate housing is not trouble-free

• Inter-sow aggression can be high

• But physical consequences are reduced

(Barnett et al., 1987; Broom et al., 1995)

Agonistic interactions – groups vs. stalls

0

0.5

1

1.5

2

2.5

3

1st Parity

Nu

mb

er o

f in

tera

ctio

ns

per

h

• Agonistic interactions start higher in groups

(Broom et al., 1995)

0

0.01

0.02

0.03

0.04

0.05

0.06

1st Parity

Pro

po

rtio

n w

hic

h e

sca

late

Crates

Small Group

Large Group

Agonistic interactions – groups vs. stalls

0

0.5

1

1.5

2

2.5

3

4th Parity

Nu

mb

er o

f in

tera

ctio

ns

per

h

• Over time, numbers same, escalation higher

(Broom et al., 1995)

0

0.05

0.1

0.15

0.2

0.25

0.3

4th Parity

Prop

orti

on

wh

ich

esc

ala

te

Crates

Small Group

Large Group

Take Home Message

A thorough understanding of social behavior is critically important when housing pigs in groups

Commercial practice conflicts with „natural‟ social behavior

Where system design or management is inadequate, aggression can be problematical

May have “low impact” overall, but “high impact” on some individuals

Take Home Message

Still a great many unknowns

Many types of “Group Housing”

Feeding system/group size/space/stability/flooring etc.

Genetics – influence on behavior

Research tends to focus on individual components

How do all these components interact?

Husbandry is key!

The act or practice of breeding and raising livestock

Farming, especially the care of farm animals

Farming, especially when regarded as a science, skill, or art

Invest in your people!

Questions?