the effect of experience on twin-care in new zealand romney sheep
TRANSCRIPT
Applied Animal Behaviour Science, 12 (1984) 363--372 363 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
T H E E F F E C T O F E X P E R I E N C E O N T W I N - C A R E IN N E W Z E A L A N D
R O M N E Y S H E E P
G. ALEXANDER, R. KILGOUR, D. STEVENS and L.R. BRADLEY
CSIRO, Division of Animal Production, P.O. Box 239, Blacktown, N.S.W. 2148 (Australia)
(Accepted for publication 25 October 1983)
ABSTRACT
Alexander, G., Kilgour, R., Stevens, D. and Bradley, L.R., 1984. The effect of experience on twin-care in New Zealand Romney sheep. Appl. Anita. Behav. Sci.., 12: 363--372.
Behaviour of ewes at lambing was observed in a flock of N.Z. Romney sheep com- posed of selected (or "el i te") ewes that had produced litters of 2 or more lambs at least twice previously, and 2-year-old ewes that had produced 0, 1 or 2 lambs at 12 months of age. The observations concentrated on twin-bearing ewes.
Only 6% of twin-bearing elite ewes became separated from a twin compared with 16% of primiparous ewes. Conflicts between elite and younger ewes over ownership of twin lambs were won by elite ewes in 6 of 7 cases, and elite ewes gathered their twin lambs together more quickly after artificial separation than primiparous ewes.
Irrespective of litter size, primiparous ewes remained within 20 m of their birth-site for a mean of 11 h compared with 7 h for elite ewes, and the incidence of separation from a twin in primiparous ewes was higher with ewes that moved from the birth-site within 6 h of birth than in those that remained for more than 6 h. Also, primiparous ewes appeared more reluctant than elite ewes to leave one twin to recover the other that had been deliberately separated.
The behaviour towards twins in the small number of 2-year-old ewes that had pro- duced twins at 12 months of age was similar to that of the elite ewes in several respects, but contrasted with behaviour of primiparous mothers of the same age. This indicates that twin care improved with experience rather than age. The behaviour towards twins in 2-year-old ewes that had previously produced a single only tended to fall between that of primiparous ewes and ewes that had produced twins when 12 months old.
INTRODUCTION
T h e ab i l i t y o f ewes t o ca re f o r t w i n s d u r i n g t h e f i r s t d a y o r t w o o f l i fe
va r ies w i d e l y b e t w e e n f locks . F o r e x a m p l e , in f ine w o o l M e r i n o sheep
l a m b i n g o n sparse p a s t u r e s , b u t r e c e i v i n g a d e q u a t e s u p p l e m e n t a r y f eed ,
a b o u t h a l f o f t h e t w i n - b e a r i n g e w e s b e c a m e p e r m a n e n t l y s e p a r a t e d f r o m
a t l eas t o n e t w i n d u r i n g t h e f i r s t d a y a f t e r b i r t h ( A l e x a n d e r e t al., 1 9 8 3 b ) ,
a n d e v e n u n d e r g o o d p a s t u r e c o n d i t i o n s , 25% o f t w i n - b e a r i n g e w e s in a
f l o c k o f m i x e d M e r i n o s t ra ins l o s t c o n t a c t w i t h a t w i n s o o n a f t e r b i r t h
0168-1591/84/$03.00 © 1984 Elsevier Science Publishers B.V.
364
(Alexander et al., 1983a). In both instances, poor maternal behaviour was a major factor in the loss. By contrast, in the study of Alexander et al., (1983b), separation from a twin occurred in only 8% of twin-bearing New Zealand Romney ewes selected for their ability to rear twins (Hight et al., 1975). In all instances precipitating factors other than poor maternal behav- iour were identified.
Since all of these Romney ewes had reared twins previously, the ques- tion arises whether superior twin-care by these sheep is innate or is the results of previous lambing experience.
This paper presents evidence on this question, and is concerned with a comparison of aspects of peri-natal behaviour between 2-year-old N.Z. Romney ewes that had not lambed before, similar ewes that had produced either a single or twins at 12 months of age, and older ewes that had pro- duced at least 2 sets of twins previously.
METHODS
Flock and experimental site
The study was done with the Romney flock of the New Zealand Depart- ment of Lands and Survey, in spring (8--25 September 1981) on the Depart- ment 's Waihora block in the Mangakino district on the North Island. The flock and its "drif t"-management at lambing are described elsewhere (Hight et al., 1975). Briefly, the unlambed ewes were separated from the lambed ewes each morning and moved into another paddock, disturbance to ewes with new lambs was avoided. The paddocks and the weather experienced were similar to those described previously (Alexander et al., 1983b).
The experimental flock of approximately 1200 ewes, carrying numbered neck tags, included 200 ewes aged 3--8 years from the Department 's "el i te" flock of selected ewes; each had previously produced at least 2 sets of "multiples", mostly twins. The remainder were 2-year-old ewes, comprising 680 that had not lambed previously, 250 that had produced a single lamb at their first lambing at 12 months of age, and 70 that had produced twins at this age. Among the 2-year-old ewes, 17% that had produced a single at 12 months were known to have lost the lamb prior to weaning and 56% of the ewes that had produced twins had lost at least one lamb. However, since the ages at which the lambs died were not known, distinction was not made between these and ewes that reared all their lambs, except in regard to movement from the birth site of ewes that had produced singles at their first lambing.
To facilitate observations, the flock was randomly divided into 2 sub- flocks for the first 13 days of the observation period, and each was drifted through a separate set of paddocks. The sub-flocks were pooled for the remainder of the period of observation. The observations continued for 19 consecutive days, during the peak of the 9-week lambing period; and data were obtained on 880 ewes.
365
Observations
The observation routine was similar to that repor ted previously (Alex- ander et al., 1983b). In brief, each sub-flock was kept under surveillance from dawn to dusk (06.00--18.00 h) by 2 observers who walked through the paddocks for most of the observation period. As reported for similar studies (Stevens et al., 1982; Alexander et al., 1983b), the sheep rapidly habi tuated to the presence of observers and scarcely moved unless the observer came within 10 m, but almost all ewes with newborn lambs showed a zero flight distance.
Birth-sites were identified by direct observation of birth or from the presence of blood and foetal fluids spilled on the ground; these sites were marked by numbered pegs as soon as the newborn lamb(s) was seen. With twin births, the site of the second birth was regarded as the birth-site; twins were usually born within 1--2 m of each other. The time which ewes then took to move more than 20 m from the birth-site was recorded to the nearest 0.5--1 h for most ewes. Interference by ewes at the birth of others and noticeable difficulties of birth were noted, together with any other factors obviously contributing to permanent separation of ewes from their lamb(s). Ewes giving birth overnight without identifiable birth- sites were not observed further. Lambs of ewes under observation were identified (i.e. ear tagged, weighed, sexed and assessed for vigour) only after the ewe had moved more than 20 m from her birth-site, except that when this had not occurred by late af ternoon on the day of birth, some lambs were tagged just prior to the end of the day's observations.
The sub-flocks were drifted between 08.30 and 10.30 h daily.
Separation tests
The response of ewes to the deliberate separation of one twin was also examined in most twin-bearing ewes at a convenient time, usually at tag- ging, within the first 2 days after birth. One twin, selected at random, was tethered by the hind-leg to a peg driven into the ground 20 m from the ewe and her other twin. Their behaviour was then observed for at least 5 min and the time taken for the ewe to reach the tethered lamb was re- corded.
Statistical analysis
Times for ewes to move were logl0-transformed to reduce skewness of distribution and were then examined by conventional "t" tests and analyses of variance. Non-paramatric data were examined by Fisher's exact test.
366
RESULTS
Incidence o f permanent separation o f ewes from lambs
Among all ewes giving birth to single lambs, separation of ewes from their lambs was observed only in ewes lambing for the first t ime (5/229 v. 0/167, P = 0.07) (Table I), but within the 2-year-old ewes, numbers were insufficient to reveal whether the apparent differences between the groups were real.
Among 2-year-old twin-bearing ewes, separation from at least one twin was also highest (15.9%) in ewes that had not lambed before; it was lowest (5.0%) in the ewes that had produced twins at their first lambing, and at an intermediate level (12.1%) in the ewes that had produced a single lamb only at their first lambing (Table I); but again numbers were too small to show whether the apparent differences within groups of 2-year-old ewes were real. However, the incidence of separation from a twin among the older (elite) ewes (5.8%) was significantly lower than among the ewes that had not lambed before (15.9%) (P --- 0.003). Similarly, the incidence of separation was lower in ewes that had previously produced twins (2-year- old and elite ewes pooled) than in the 2-year-olds that had previously pro- duced a single only or no lamb at all (P = 0.003), and similar trends were seen where poor maternal behaviour or interference by other sheep at the birth was the only obvious contr ibuting factor (P = 0.009 and 0.008, res- pectively).
Time that ewes remained within 20 m o f their birth-site
The mean times that ewes remained near the birth-site were similar for single and twin-bearing ewes in 3 of the 4 lambing-history groups (Table II).
In the fourth group, the 2-year-olds that had produced twins previously, the difference was statistically significant, but in view of the very low standard error for the few single births amongst these ewes, it is questionable whether the result was representative.
There were clear differences between the lambing-history groups (Table II) within both single-bearing and twin-bearing ewes and the groups pooled, irrespective of litter size (in analysis of variance P <~ 0.001, P ~ 0.05 and P ~ 0.001, respectively). In the pooled data, ewes that had not lambed before remained on the birth-site for longer than ewes in any of the other 3 groups, and ewes that had previously produced a single only remained for longer than the "e l i te" ewes.
There were too few ewes that had given birth to twins at 12 months of age to provide evidence about the time to move from the birth-site at the second lambing in relation to whether the ewe reared 0, I or 2 lambs at the previous lambing. However, among ewes that had given birth to
TA
BL
E I
Inci
den
ce o
f p
erm
an
en
t se
par
atio
n o
f si
ng
le a
nd
tw
in-b
eari
ng
ew
es f
rom
th
eir
lam
bs
No
. in
N
o.
of
lam
bs
in
No
. o
f S
epar
atio
ns'
M
ajo
r c
on
trib
uti
ng
fac
tors
pre
sen
t p
rev
iou
s li
tter
s ew
es
litt
er
ob
serv
ed
"No.
%
B
irth
In
terf
ere
nc
e
Po
or
pro
ble
ms
mo
the
r
2-y
ear-
old
ew
es
Sin
gle
0
22
9
5 2
.2
2 2
1 1
11
2
0
0
--
--
--
2
12
0
0
--
--
--
'Eli
te'
ewes
Sin
gle
>~
2
(mo
re t
ha
n
on
e li
tter
) 4
3
0 0
2-y
ear-
old
ew
es
Tw
ins
0 2
01
3
2
15
.9
5 1
10
7
13
1
2.1
0
2 2
0
1 5
.0
0
10
6 0
14 5 0
'Eli
te'
ewes
Tw
ins
>/ 2
(m
ore
th
an
on
e li
tter
) 1
56
9
5.8
4
' N
o.
of
ewes
fro
m w
hic
h a
t le
ast
on
e la
mb
be
ca
me
sep
arat
ed.
Po
or
vig
ou
r o
f la
mb
s
i
Mis
c.
50
O~
TA
BL
E I
I
No
. o
f la
mb
s in
p
rev
iou
s li
tter
s
Tim
e th
at e
wes
rem
ain
ed w
ith
in 2
0 m
of
the
bir
th-s
ite
Sin
gle
bir
ths
No
. o
f G
eo
me
tric
me
an
ew
es
tim
e (h
) 1
2-y
ear-
old
ew
es
0 9
7
1 6
3
2 7
'Eli
te'
ewes
/>2
(m
ore
th
an o
ne
litt
er)
10
.9
(NS
**
) 81
(
1.0
4
± 0
.03
)
8.5
(N
S*
*)
41
(0
.93
÷
0.0
4)
4.2
(P
<
0.0
01
"*)
10
0
.63
± 0
.02
)
30
6
.1
(NS
**
) 0
.78
±
0.0
7)
Sig
nif
ican
ce o
f d
iffe
ren
ces
(P)
by
"t"
tes
t
0 v.
1
<: 0
.05
0
v. 2
<
0
.01
0
v. "
elit
e"
<
0.0
01
1
v. 2
<
0
.05
1
v. "
elit
e"
<
0.0
5
2 v.
"el
ite"
N
S
Tw
in b
irth
s P
oo
led
No
. o
f G
eo
me
tric
me
an
G
eo
me
tric
me
an
ew
es
tim
e (h
) 1
tim
e (h
) 1
10
.8
10
.9
( 1
.03
±
0.0
4)
( 1
.04
± 0
.02
)
8.9
8
.7
( 0
.95
÷
0.0
5)
( 0
.94
± 0
.03
)
10
.1
7.1
( 1
.00
± 0
.08
) (
0.8
5 ±
0.0
7)
67
7.
5 7
.0
(0.8
8
± 0
.04
) (0
.85
±
0.0
4)
NS
=
0
.01
N
S
<
0.0
5
<
0.0
1
<
0.0
01
N
S
NS
N
S
=
0.0
5
NS
N
S
Mea
ns
calc
ula
ted
usi
ng
log
10 t
ran
sfo
rma
tio
ns;
mea
ns
and
SE
's i
n t
he
tra
nsf
orm
ed
dat
a ar
e sh
ow
n i
n p
aren
thes
es.
**
Sig
nif
ican
ce o
f d
iffe
ren
ce b
etw
ee
n s
ing
le-
and
tw
in-b
eari
ng
ew
es.
369
singles a t 12 m o n t h s , the m e a n t ime t h a t t hey r ema ined nea r the bir th- site a t the i r n e x t ( second) l ambing appea red to be i n d e p e n d e n t o f w h e t h e r one l a m b or no l a m b was reared a t the first lambing. A m o n g s t these ewes, the respect ive d e - t r a n s f o r m e d m e a n s for those p roduc ing singles a t the i r second l ambing were 8.5 h ( t r a n s f o r m e d 0.93 + 0.04, n = 51) and 8.2 h {0.91 ± 0.08, n = 12) (NS), and for ewes p r o d u c i n g twins at this second lambing , the means were 8.6 h (0.93 + 0.05, n = 33) and 10.3 h (1.01 ± 0 .12, n = 8) (NS).
Incidence o f separation o f ewes from a twin in relation to the time spent on the birth-site
There were insuf f ic ien t animals to examine this re la t ionsh ip e x c e p t a m o n g ewes l ambing for the first t ime. In this group, the inc idence of separa t ion a m o n g those t h a t m o v e d f r o m the bir th-si te in 6 h or less (9 /20) was higher than in those t h a t m o v e d a f te r 6 h (6 /61) (P = 0 .001) ; and there was a similar d i f fe rence when the c o m p a r i s o n was con f ined to cases of separa t ion in which there were no o the r obv ious c o n t r i b u t i n g fac tors than ma t e rna l behav iou r (5 /20 versus 2/61, P = 0 .009) .
Interference by ewes at the birth o f another
In 13 /23 cases o f in t e r fe rence t h a t resul ted in l ambs being cared for b y alien ewes, there was clear c o m p e t i t i o n for the one l a m b b e t w e e n a ewe t h a t had jus t p r o d u c e d twins and a ewe in l abour or a r ecen t ly l a m b e d ewe whose l amb(s ) had been bo rn dead. Six o f the conf l ic ts were be tween 2 y o u n g ewes; o f the 7 be t ween a y o u n g ewe and an o lder eli te ewe, 6 ended in the o lder ewe rear ing a l a m b o f the y o u n g e r ewe, and there was one exchange of l ambs be t ween a y o u n g ewe tha t had n o t l a m b e d be fo re and an eli te ewe. The o the r 10 cases resul ted f r o m m u t u a l confus ion , when ewes l a m b e d in close p r o x i m i t y , and o f t en ended in l a m b sharing.
The re was no e f f ec t o f age of ewe on the incidence of i n t e r f e rence wi th or b y o the r sheep; all g roups showed a similar incidence.
Separation test
T h e p r o p o r t i o n o f ewes t h a t fai led to reach the t e t he r ed l a m b wi th in 5 min , and the m e a n the t ime (log~0 t r a n s f o r m a t i o n ) of those t ha t m o v e d were e x a m i n e d in re la t ion to the t ime since bi r th , r o u n d e d to the neares t h o u r (~< 6 h, 7 - -12 h, 13 - -24 h, > 24 h and u n k n o w n bir th t ime) . A m o n g s t el i te ewes, all 16 t h a t had l a m b e d wi th in 6 h of the tes t m o v e d to the te th- e red l amb , bu t on ly 16 o f the r ema in ing 72 did so (P = 4 × 10-9); this e f f e c t o f t ime since bi r th was n o t f o u n d in the p r imipa rous ewes or ewes t h a t had l a m b e d once before . A m o n g s t ewes t h a t m o v e d to the t e t h e r e d l a m b wi th in 5 min there was no s ignif icant e f f ec t o f t ime since b i r th on the
O
TA
BL
E I
II
Sep
arat
ion
tes
ts o
n t
win
-bea
rin
g e
wes
(o
ne
lam
b t
eth
ere
d 2
0 m
fro
m o
the
r ew
e an
d l
amb
)
No
. o
f la
mb
s in
N
o.
No
. n
ot
mo
vin
g t
o
pre
vio
us
litt
ers
test
ed
teth
ere
d l
amb
in
5
min
Ew
es m
ov
ing
to
te
the
red
lam
b
No
. G
eo
me
tric
me
an
tim
e (h
) 1
2-y
ear-
old
ew
es
0 9
3
34
(3
6.6
%)
59
1
.4(
0.14
+_
0.0
5)
1 4
7
15 (
31
.9%
) 3
2
1.6
( 0
.19
-+
0.0
6)
2 1
2
4 (3
3.3
%)
8 0
.6 (
-0.2
2
± 0
.13
)
"Eli
te"
ewes
/>2
(m
ore
th
an o
ne
litt
er)
88
16
(1
8.2
%)
72
0.9
(-0
.05
±
0.0
5)
6 (6
.8%)
1 Mea
ns
calc
ula
ted
usi
ng
log
10 t
ran
sfo
rma
tio
ns;
mea
ns
and
SE
's i
n th
e tr
an
sfo
rme
d d
ata
are
sho
wn
in
par
enth
eses
.
No
. o
f ew
es w
aiti
ng
fo
r u
nte
the
red
lam
b
18 (
19.4
%)
6 (1
2.8%
) O(
0%)
Sig
nif
ican
ce o
f d
iffe
ren
ces
(P)
by
"t"
tes
t
0 v.
1
NS
N
S
NS
0
v. 2
N
S
<
0.0
2
NS
0.
v.
"eli
te"
0.0
08
<
0
.01
0
.00
1
.1 v
. 2
NS
<
0
.01
N
S
1 v.
"el
ite"
0
.09
<
0
.01
N
S
2 v.
"el
ite"
N
S
NS
N
S
371
mean time to reach the lamb. On the other hand, there were significant differences among the 4 lambing-history groups in both the propor t ion reaching the lamb (P = 0.038 by Fisher's exact test) and in the mean time to reach it (P < 0.01 in analysis of variance) (Table III). The "e l i te" ewes and the 2-year-old ewes that had produced twins at the previous lambing at 12 months of age reached the te thered lamb significantly more quickly than either the primiparous ewes or the ewes that had produced a single lamb at their first lambing, and a smaller propor t ion of elite ewes (18.2%) failed to move than in the other groups (31.9--36.6%) combined (P = 0.007).
Of the ewes that reached the te thered lamb in 5 min, the propor t ion that clearly waited for the unte thered lamb was also lower in the elite ewes (6.8%) and younger ewes that had produced twins at 12 months (0%) than in the other 2 groups (12.8 and 19.4%) (P = 0.001 for the pooled data) (Table III). In addition, the behaviour of a small number of ewes was observed after release of the te thered lamb. The propor t ion of ewes that had left the unte thered lamb behind but were observed to bring the 2 lambs together immediately after the te thered lamb was released was higher in the elite ewes (10/14) than in the primiparous ewes (1/11) (P = 0.O02).
DISCUSSION
The results reveal differences in behaviour associated with twin-care between experienced ewes that had produced at least 2 sets of "mult iples" previously ("e l i te" ewes), and inexperienced ewes producing twins for the first time. For example, 2--3 times as many inexperienced ewes as experienced ewes became separated from at least one twin, conflicts be- tween experienced and inexperienced ewes over ownership of twin lambs were almost always won by the former, and experienced ewes gathered their lambs together after artificial separation more readily than inexpe- rienced ewes.
Other differences indicate that experienced ewes are less constrained in their care of twins than inexperienced ewes. Thus, the latter remained near the birth-site for 1.5 times as long as the former, and more inexpe- rienced ewes waited for the unte thered lambs in the separation tests than experienced ewes.
While these differences are clear, it is less clear whether they result from differences in age or in parity, because the number of 2-year-old ewes that had produced twins previously was small. However, their behaviour was consistently similar to that of the older elite ewes. There were few separa- tions f rom twins, in the pooled data they remained near the birth-site for a mean time similar to that of the elite ewes, and they moved quickly to a deliberately separated twin wi thout waiting for the other twin to follow.
The consistency of the results also indicates that the experience of having a single lamb previously modifies the behaviour of ewes at their next
372
lambing. These ewes remained on the birth-site for significantly less time than ewes that had not lambed before, they tended to experience fewer separations from a single lamb or from a twin than primiparous ewes, and in some respects their twin-recovery after artificial separation tended to be superior to that of primiparous ewes.
These results indicate that the ability of ewes to care for twins improves with experience rather than age. However, the incidence of twin-separation in the inexperienced primiparous N.Z. Romneys (16%) was low by com- parison with that in mixed-age Merinos of various strains lambing under similar good pasture conditions (Alexander et al., 1983a). This confirms previous evidence of a major difference between sheep breeds in the ability of ewes to care for twins (Alexander et al., 1983b).
In conformity with previous results, the incidence of separation from twins, in this case by inexperienced ewes, was high with animals that moved from their birth-site soon after giving birth. Hence, the traditional tendency of shepherds to intensively manage ewes lambing for the first time could aggravate the loss of lambs through precipitating premature movement from the birth-site, where the bonds between mother and young are established.
ACKNOWLEDGEMENTS
This study was made possible by the cooperation and assistance of Mr. Peter Roberts, manager of the Waihora flocks. Thanks are also due to the Department of Lands and Survey for permission to study the flock, and to Henk de Langen for assistance with the observations.
REFERENCES
Alexander, G., Stevens, D. and Mottershead, B., 1983a. Problems in accurate recording of lambing data. Aust. J. Exp. Agric. Anim. Husb., 23: 361--368.
Alexander, G., Stevens, D., Kilgour, R., de Langen, H., Mottershead, B.E. and Lynch, J.J., 1983b. Separation of ewes from twin lambs: incidence in several sheep breeds. Appl. Anita. Ethol., 10: 301--317.
Hight, G.K., Gibson, A.E., Wilson, D.A. and Guy, P.L., 1975. The Waihora sheep im- provement program. Sheep Farming Annual 1975, pp. 67--89.
Stevens, D., Alexander, G. and Lynch, J.J., 1982. Lamb mortal i ty due to inadequate care of twins by Merino ewes. Appl. Anita. Ethol., 8: 243--252.