MÍNIMO COMÚN MÚLTIPLO Y MÁXIMO COMÚN DIVISOR

.sso

644

4)6

8.52

ter

(1954)

J'V88

that

hill

ehe are ore

e

than p duritlc the

hours f4 ciayllpt.

o

ta

wer avaUable on the

nipt

'b

ot

bUl beep but Bun r

136

(who worked in S cotland ) believes it quite probable that they are more active

than

lowland sheep. The .following data (Table

16 )

are

presented by this author :

Table

16.

Percentage time spent resting in the hours

7 : 00

a .m.

-

7 : 00

p .m. by lowland and

bill

sheep , April - September

(Huntet" 19.54) .

Apr . May June July Aug . Sept .

Lowland

(Tribe ' s Cheviots

1949 )

32

32

40

45

45

47

Hill

( Hunter• s Scotch Black

.faced sheep

1954)

13

13

21

26

Hunter overlooks the fact that he is comparing not types of

sheep but locations , !or the Cheviot is not a lowland type . This

kind of contusion of the sheep breeds can only be deplored.

23

In a comparative study of the grazing habits of sheep carried

out by

Van

Rensburg in South A1'rica

(1956 )

the .following results were obtained (Table

17 ) :

the technique is not specified.

T

17.

Breed

Merino

The average daily distance walked by four she p breeds

(Van

Rensburg

1956 ) .

Averag daily distance walked (yards )

r.man Merino X Merino Cross

449.5

6532

4845

4980

Blackhead Persian Dorper

137

Tribe

{Hammond 1955 )

reviews the literature on grazing behaviour

studies. Excerpts from the review are now presented in order that the present work can be assess ed in the light of this modern summary.

Tribe writes , that valid and standardised techniques are the

prerequisite of any s cientific investigation. and it is an important

criticism of grazing behaviour studies in all parts of the world

that there is no standardised technique of observation , and no

oomparisbn has yet been made of the accuracy of the many different

methods used . There is , for instanc , no uniformity concerning

even the period during whi ch observations should be made . Some

workers have mistakenly assumed that during the hours o! darkness

animals will remain at rest and have therefore only recorded their

observations during th hours of daylight .

Tribe continu a--similarly the methods of recording vary

considerably . Some workers record the behaviour of individual ani.Dlals

while others record the behaviour of flocks or herds . Some workers

make a continuous recording while others record o

nly

ob ervations

taken at regular and frequent intervals . Some

records

are the work

of singl observ rs while others are ade by several observers

working on a shift syst Tribe further remarks that in an effort to increase the accuracy o! behaviour records a number of automatic

and semi-automatic oorders hav been volved•

and 1n

use with

anim.als penned or in stalls the

e

auto-r co:rding ebtnes have

proved very suce s _f'ul. However,· according t o Trib , the difficulties

much greater and have not yet been overcome. He mentions that Burton and Castle

(1950 )

have described the construction _and u e

of a portable infra-red ray equipment for _animal observation in ·

lJ8

the field. For watching from a stationary position not more

than

four animals at a rang of ten �o fifteen yards on a clear dark night the equipment was ideal . \1/hen using it to observe a large number of animals either in the field or in the cowshed the obs rver was liable to miscount the animals owing to the limited field of the screen . Also, the constant wearing of the equipment which weighed

21

pound was very tiring and, when the weather was misty, the lense qui ckly clouded over .

Tribe considers that the differences between the animal behaviour patterns describ by various workers are not surprising• In addition to the differences in observational technique, there is a complex

of environmental factors which must be expect d to influence a normal pattern of behaviour. For example, such variable factors as th climate. the density and quality of the sward, the ize of paddock, th system of grazing managem nt _.and of cours , the in­ dividuality of the grazing animal may

v

ry significantly influ nee

the times devoted to different acti _vi ti s .

Tribe discusses these and other factors a they affect many functions of th grazing animal. A thi project is primarily

concerned w1 th activity • further diseu

si

on will be limited to the stated effect of various factors on this

item,

139

Bot weather causes animals both to graze for a shorter time than normal and to increase the proportion of time that is

spent grazin at night ,

When

idling under these conditions

the animals app ar agitated and in consequence the distances

traveled tend to increase .

During cold windy or rainy weather grazing times are again shortened. and the normal overall pattern may be radically altered, When a storm begins animals will usually cease

grazing and walk to shelter if such is close at hand. otherwise

they will stand with their heads down,..wind , Under such conditions

hiU sheep and cattle will move to higher ground,

It has been shown on several occasions that the size of

the pasture available to the grazing animal will influence

its: behaviour and in particular the daily cftstance it tr v ls ,

In

general one can

say,

the bigger the area of pasture the

farth r will an a.ni.mal walk, Shepherd

(1921 )

reported that

beef cattle on

a

JO acre pasture walked one and fiv eighth

miles between

4 : 00

a.m.

and 8 : 00

p.m. whereas simUar cattle

throughout the same p riod traveled three and on sixteenth

mil s on a

lOO

acre pastur and

ti

v and

a halt

_miles on a

640

acre pasture . There must obviously be limits to thi

tendency

at both ends of the seal , but so tar they have not

140

Perhaps the greatest and most imponderable problem which

besets the animal watcher is the degree to which recorded

behaviour may be due to environmental f

ac

tor

s

_and how far

merely to the pers

o

nal whim of the animal.

Hancock (1950 ) using

six sets of monozygotic cattle twins in a one acre paddock showed that inherited variability in

razing behaviour was by far the largest source of variation due to individuality.

A

part of thes inherited differenc s could be explained by relating them to differences between the ph

y

siological requirements of individual animals. It seems

reasonable to argue that increased nutritional requirements during growth, pregnancy, or lactation, result in an increased

food intake and there

f

ore in increased grazing and ruminating times .

In approaching the problem of measuring sheep activity, as expressed in miles t�aveled per w ek, certain difficulties had to

be idered '

(1)

Work on the other divisions of the overall project would limit tb amount or time available .

(2)

It was n

oes

ary t o measure

th

ranging mi l age o f th

sheep und r

natural

conditions on hill and lowland arazings.

techn1.que

(1v

alla.c

e

and Kenn

edy 1944) .

Even

where the terrain would

permit

subdivision, no

time

was

available

£or

24

hour observation shi£ts.

141

( ) ) Radio

control , pedometers and other such devices £or tracking movemen

t were all

too

compl

i

ca

ted or

impossible

to use satisfactorily on the

grazing sheep.

The restrictions

thus imposed on

the work

subsequently

led to the

dev

e

l

opmen

t

of an

e

n

t

irely

new device. This device t

oo

k

the i"orm of

a ma chine

which it

has b

e

e

n

proposed shall b

known

as a

Rangemeter.

The

Rangemeter consists of

a

ight harness,

two

metal

In document 1 MATEMATICAS I (página 35-42)