Research Programme - usaid

Legend
1Beca
8 1 3
2
E]6
-5
99 9
10
1 and 3 resistant paddocks
2 and 4 susceptible paddocks
5 stockade
6 tent
7 ecology arena
8 crush
9inner fence and sub-divisions
10 outer fence
11gate
Iigti rr3. I.; .itutit r,twriu.mintal i), Lt.k at itlhmia r nth
weeks and collections every 6months, and inthe pastures by
bhlanket draggings at monthlily intervals. Monthly can half'-
body counts on the difflrent experimental groups are
luescntet inligite-1.
.6
z
300/
200 =
S40 Susceptible
T! 400-1
J\+. Resistant
100- &-A rexperiment.
Period. Period Period 'Per
,1:;12 ±
Oc De Fe Ap Ju Au Oc De
1984 1985
,
I~iguart' . "I',tut lit'k o'p il *lsc , t't~llith. oncIrvssiclai catliv, IvricI I
io4 atInima rantch.
26
use tile animals are innmu niscd against theilcriosis
prior to the introduction in the paddocks, deaths due to this
disease have been rare ( I case). However, 13 tick-naive and
2 tick-resistant cattlt have succumbed, primaily to tick
toxicosis with occasional concurrent heartwater.
1he development of naturai tick resistance inthe animals
has been as,,cssed jepeatedly vby the application of 10)
nymphs of R.al)jentliChmOIt in tie cars of the cattle (de
6astro, Twelfth Annual Report, 1984). In this way, the
tick-rcsistance status of the animals under continuous
challenge has been monitored since May 1984. The mean
dailv weight gain for the 3 groups of ani mals is shown in
Figurc 5. It should be noted that when total tick counts
(1 igut .1)in the rcsistatt group of antimals losec above 300)
ticks per ainial, daily weight gains tell to 0 and
subseq uen tly the ani itals lost weight daily as the tick counts
rose to over (0 per animal. Su:ceptible animals lost weight
steadily throughout the experiment.
300
20
20
100
0.­
" -100iit
--30C
- A Dtpp
0 O
Susceptile
-400 Period Period PerKod Perbd
-600 -500­
0 ..
Oc eFe Ap Ju Au Oc De
1984 1985
Iigir s. M an(lalld %trii gains during peri ds I Ii-t for Ihrtegrmuils
The population of R.aplwntdi'uhtus,A. cohaerens, and
A. variegalumt, ias risen steadily throughout the entire
B3.ho/orattl have decreased to negligible
itnubers on the cattle, particularly oni the resistant groups.
Conclusion
The experiment isstill inprogress and it istoo early to draw
Firm conclusions. However. it does appear that under the
conditions otlined resistance to R. [pi'tndicUtlatuv,
induced by irradiated ticks and reinforced by natural
cx posite, is inadequate to control productivity losses front
a heavy field tick challenge.