Fostering in sheep. I. Facilitation by use of textile lamb coats

Applied Animal Behaviour Science, 14 (1985) 315--334 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

FOSTERING COATS

315

I N SHEEP. I. FACILITATION BY USE OF TEXTILE LAMB

G. ALEXANDER, D. STEVENS and L.R. BRADLEY

CSIRO Division of Animal Production, P.O. Box 239, Blacktown, N.S. W. (Australia) (Accepted for publication 16 January 1985)

ABSTRACT Alexander, G., Stevens, D. and Bradley, L.R., 1985. Fostering in sheep. I. Facilitation by use of textile lamb coats. Appl. Anita. Behav. Sci., 14: 315--334. Transfer of odour between lambs less than I week old was attempted by the use of rectangular coats of hessian (a jute textile) worn for 24 h by a ewe's own lamb and then transferred to a potential foster lamb. In the absence of their own lamb, 50--60% of ewes accepted the foster lamb immediately and more than 90% accepted the foster after confinement together over the next 2 days. Without exchange of coats, 12% of ewes accepted alien lambs immediately, and 50% after confinement. Breed differences in the success of fostering were observed, and a higher proportion of primiparas than multiparas accepted foster lambs. Foster lambs of similar appearance to the ewe's own lamb were more readily accepted than lambs of different appearance, and lambs 1--2 days old were more readily accepted than older lambs. There was a low level of success with fostering several weeks after lambing. Ewes that had accepted a foster lamb and then had their own lamb returned within 24 h of fostering initially tended to favour their own lamb. The success of the fostering method used in these studies appears to depend on both transfer and masking of lamb odour. The method should prove useful as an experimental tool, and as a practical means of saving lambs.

INTRODUCTION F o s t e r i n g o f l a m b s is u s e f u l as a n e x p e r i m e n t a l t o o l in s t u d i e s o n l a m b g r o w t h ( L a n g l a n d s , 1 9 7 2 ) , a n d as a p r a c t i c a l m e a n s o f r e d u c i n g m o r t a l i t y of lambs from large litters (Holmes, 1976) or of orphaned or abandoned l a m b s , a n d t h e p r o c e d u r e is l i k e l y t o b e a m o r e e c o n o m i c a l m e a n s o f p r o viding lambs with adequate nutrition than artificial rearing. Ewes can be readily induced to accept lambs that are not their own ( " a l i e n " l a m b s ) p r o v i d e d t h e l a m b is n e w l y b o r n a n d is p r e s e n t e d a t , o r very soon after, birth of the ewe's own lamb, before specific olfactory r e c o g n i t i o n o f t h e l a m b b y t h e e w e h a s d e v e l o p e d ( P o i n d r o n e t al., 1 9 8 0 ) . After birth, the willingness of recently lambed ewes to accept alien lambs declines rapidly, and within a few hours most ewes will vigorously resist

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316 advances to the udder by lambs that are not their own. In practice, fostering is usually attempted 12 or more hours after birth, and sheep producers use a variety of methods, mostly based on an a t t e m p t to disguise the odour of the foster lamb. Such procedures include placing the skin of a ewe's dead lamb on a substitute foster lamb, or smearing lambs with strongsmelling substances, in the hope of overcoming rejection of aliens (Lamond, 1949; Close, 1979). The effectiveness of these methods has not been well documented. Fostering methods that have been studied include restraint of the ewe and close confinement of the ewe and lamb (Hersher et al., 1963), induction of temporary or permanent anosmia in the ewe (Poindron and Le Neindre, 1980), tranquillization of the ewe (Neathery, 1971; Tomlinson et al., 1982), and washing of lambs coupled with confinement (Alexander et al., 1983a). This paper reports on aspects of the first of a series of studies that represent a search for a simple fostering method. The approach was based on attempts to transfer the odour of the ewe's own lamb to a potential foster lamb by means of a coat of hessian or other fabric, previously worn by the ewe's natural lamb for about 24 h. The essentials of the method and some of the initial results have appeared in a preliminary account (Alexander et al., 1984) which showed that about 50% of Dorset ewes accepted the foster lamb immediately, and that a higher proportion of primiparous than multiparous Dorsets accepted foster lambs. The procedure was shown to be less successful with cross-bred ewes (Border Leicester X Merino), but confinement for up to 2 days resulted in a high acceptance rate in both types of sheep. Of the various types of coat tested (wool, cotton, nylon and polyethylene), none was shown to be more effective than hessian, especially when this was combined with the use of a hood that had been held in contact with the donor lamb's rump for about 24 h. The present paper extends these findings to 10 distinct studies done over a 2-year period (1981--83) and covering a range of breeds held under a variety of conditions. It also examines a number of variables that could influence the success of fostering. METHODS Outline The investigation consisted of 10 separate studies and involved approximately 600 ewes and their lambs, of 16 breeds or crosses, at 6 sites (Table I). Two sites were near Sydney, Australia (CSIRO Division of Animal Production), and the other four were in the United Kingdom at Bangor (University College of North Wales), "Glensaugh", Scotland (HFRO field station), Roslin, Scotland (ABRO field station) and Babraham, England (ARC Institute of Animal Physiology). Procedures varied from site to site according to availability of animals, facilities and management constraints.

317

At each site, new fabric coats that had been worn for approximately 24 h were exchanged between ewes' own lambs and alien foster lambs and the effect on the ewes' acceptance of the aliens was observed in pen tests. At some sites, acceptance during confumment o f the ewe and foster alien over the next 1--3 days was also examined (Table I). Results were compared with those in control tests with the same or other lambs that wore their own c o a t s or no coats at all {Table I). Other differences in procedures, such as the breed used, are also indicated in Table I. Most ewes and lambs were penned prior to fitting the lambs with coats, but in Series 3 and 4, coats were fitted in the lambing paddock and the ewes were penned at the same time of coat exchange. While the principal aim was to test the effectiveness of the coat-exchange procedure for fostering lambs under a variety of conditions and with a variety of sheep, the studies also provided information, either from retrospective analysis or by design, about other factors which could influence the acceptance of alien lambs {Table II). Procedures Coat design and use Coats were rectangular pieces of fabric, ranging from approximately 650 X 450 mm for 2--3-kg lambs to 800 X 600 mm for 5--6-kg lambs. Coats were held in place by passing the head and legs through slits approximately 100--120 mm long, and the tail through a 30°mm slit (Fig. 1 of Alexander et al., 1984). Except in Series 6, in which various coat materials were tested {Alexander et al., 1984), coats were made of heavy-grade hessian; a coarse woven material of jute fibres. In both Series 5 and 6, tubular hoods that covered the head and neck and had holes for the eyes and ears were used in conjunction with hessian coats; these were 200-mm lengths o f an elastic "tubular support bandage" (Tubigrip -- Seton, Oldham, England), with a circumference of 140 ram. Both hood and hessian coat from a ewe's own lamb were placed on the potential foster lamb. Coats were fitted to lambs mostly within 1--3 days of birth. In the few instances (< 5%) where a ewe showed signs of rejecting her own lamb with its newly fitted coat, the coat was temporarily reflected forward to expose the lamb's hindquarters by placing the front legs through the slits for both fore- and hind-legs. The occasional ewe that failed to accept its lamb after an hour or two of this treatment was discarded. The ewe's acceptance of a " f o s t e r " lamb wearing her own lamb's coat was usually tested after her own lamb had worn its coat for 22--30 h; for these tests the foster lamb wore the coat inside-out and its tail was not drawn through the tail slit.

St. MalTs (N.S.W.)

Bangor (N. Wales)

Cambridge (England)

Glensaugh (Scotland)

Roslin (Sco~and)

2

3

4

5

Site/ country

1

Series

Llyn Welsh Mt. Suffolk X Welsh crosses

Llyn ~ Welsh Mt. Welsh crosses (W X C a m b . ) ( W X BL) (W X Llyn)

{ S. B l a c k f a c e \ M u l t i p a r o u s Cheviots |

Dam l i n e 3

Darn l i n e

Mixed

Nth. C o u n t r y { C h e v i o t s Cheviot S. b l a c k f a c e | Greyface G r e y face | (BL X B,face) (BL X B.face)J

Scottish Blackface

Primiparous Multipaxous Multiparous Primtparous Multipaxous

Soay } Mixed Jacob Clun Forest Dalesbred

Cambridge

Soay Jacob Clun Forest Dalesbred

Parity of ewe Treatments

Transfer of hessian coats or c o a t s p l u s hoods. Ewe given own lamb plus foster lamb

Transfer of hessian coats. S o m e foster lambs w a s h e d before c o a t s transferred

Transfer of hessian coats

Transfer of hessian coats

Dorset X B L Primiparous I T r a n s f e r of × Merino hessian Merino Multiparous coats

Foster lambs

Cambridge I

Merino

B L X Merino

Ewes

Sheep b r e e d or cross

S u m m a r y of m e t h o d s and d e s i g n o f the 10 s t u d i e s

TABLE I

No. of ewes tested

32 18 5 f 2 i 18

8 18 10 21 20

Different (control lambs with coats)

24

Different 24 (control 17 lambs with coats) 14 17 18

Same (control lambs with coats)

Different (control lambs without coats)

Both 18 (control l lambs with ] 12 or without ~ 4 coats) {

Different ewes or same ewes w i t h different lambs

Controls

1--4 (lambs 1--13 days old)

1--5

Pen

Field

Field

Pen

Pen

In pen or field until c o a t exchange 4

171 1--7 1--2 1--6 11 - - 2 2

1--3

1--5 2O

1--3 !

Lamb age a n d time since ewe lambed (days)

Pen

Pen

Open field

Pen

Open field

Test situation 4

Both

Both

Pen

Pen

Both

Pen or confinement tests 4

24--51

23--79

24--120

19--48

19--31

24--27 24

24--29

Time coats worn before transfer (11)

Merino

Merino

St. Marys (N.S.W.)

St. Marys (N.S.W.)

Prospect (N.S.W.)

St. Marys (N.S.W.)

7

8

9

10

Corriedaie

Multiparous

Multiparous

~14 |

hessian c o a t s | w i t h coats) I at various ~ ]32 times after /

Transfer of /Same hessianc o a t s | ( c o n t r o l

26 Same (control lambs with coats)

Transfer of hessian coats w o r n for various periods before transfer

I Mer. X Mer. t Multiparous BL X Mer. f

}

l

Pen

Pen

10--15

2--4

2--4

Pen

Pen

3--6 f Pen 10--15 27--49

2--4

2---6

(0 (4.75-5.75 (22--24.5

18--24

Pen

Pen

Pen

Pen

23--51

22--25.5

16--55

Both

Pen

Pen Open field

Pen

Pen

IA recently-developed synthetic breed based on Clun Forest; characterized by prolificacy a n d rapid growth rates (Owen, 1976). 2A fecund strain of Welsh Mountain sheep. 3A fecund " s y n t h e t i c " breed based on Finn sheep (McClelland, 1975). 4See text. 5Second lambing of ewes in Series 8.

Corriedaie

Same 35 (control lambs with coats)

9

{ 6

46

66

Transfer of hessian coats at various times after lambing

1 Transfer of Nil f coats or Multiparous coats plus hoods. Some ewes given own lamb plus foster lamb

Mixed

Both (control lambs with or without coats)

Primiparous

Dorset X BL Mar.

BL X Met.

Merino

Dorset

Mixed

~ Transfer of I coats of difDorset X BL Multiparous ferent types, X Merino or transfer of hessian coats plus hoods

Dorset

Dorset

BL X Mer.

Dorset

St. Marys (N.S.W.)

6

~D

320 TABLE II Ancillary information, provided by the studies, on factors that could influence success of fostering

the

Effect of treatment, other than standard coat transfer, on fostering Use of other coats and coats plus hoods Confinement of ewes and fosterlambs Washing lambs before transferof coats

Series 5, 6, 7 Series 1, 4, 5, 7 Series 5

Effect of procedural variables on fostering with coats Period for which coats worn before transfer Period for which lambs were separated from ewes Order in which lambs were tested

Series 4, 9 Most series Series 1, 3, 6

Effect of characteristics of the ewe on fostering Breed Time since lambing Parity Litter-size of foster

ewe

Series 1--10, especially 2 and 3 Most series, especially 1, 3, 8 and 10 Most series, especially 6 Most series

Effect of characteristics of the lamb on fostering Age Sex Appearance

Most series All series Series 3, 4

Management of sheep L a m b s w e r e b o r n o n p a s t u r e o r in i n d o o r p e n s ( T a b l e I), b u t all ewes w e r e t r a n s f e r r e d t o p e n s ( a p p r o x i m a t e l y 2 m × 1 m ) p r i o r t o tests. In Series 3 a n d 4, ewes a n d t h e i r l a m b s w e a r i n g c o a t s w e r e left o n p a s t u r e until t h e y w e r e p e n n e d j u s t p r i o r t o t h e tests, b u t in t h e o t h e r series, ewes w e r e held in p e n s f r o m t h e t i m e t h e c o a t s w e r e f i t t e d (i.e. f o r 2 3 - - 3 0 h). L a m b s w e r e r e t u r n e d to t h e i r o w n m o t h e r s a f t e r t h e tests, e x c e p t in Series 1, 4, 5 a n d 7, w h e r e a t t e m p t s at p e r m a n e n t f o s t e r i n g w e r e p e r m i t t e d . In these series, ewes a n d f o s t e r l a m b s w e r e k e p t in small p e n s (2 m × 1 m ) f o r 1--3 d a y s f o l l o w i n g t h e initial tests, a n d w e r e o b s e r v e d at least o n c e daily to c h e c k f o r a c c e p t a n c e . T h e l a m b s w e r e w e i g h e d daily, a n d w e r e initially p r o t e c t e d f r o m aggression b y t h e ewe b y m e a n s o f a h o r i z o n t a l b a r a t l a m b h e i g h t n e a r o n e e n d o f t h e pen. With s o m e ewes in t h e s e series, t h e e w e ' s o w n l a m b was r e m o v e d f o r u p t o 24 h a n d f e d b y s t o m a c h t u b e ; it was r e t u r n e d t o its m o t h e r a f t e r she h a d a p p a r e n t l y a c c e p t e d t h e f o s t e r l a m b , a n d t h e ewe a n d t w o l a m b s w e r e o b s e r v e d f u r t h e r f o r a c c e p t a n c e . C o a t s w e r e rem o v e d a n d t h e a n i m a l s released to p a s t u r e w h e n f o s t e r i n g a p p e a r e d c o m p l e t e ; release was d e l a y e d f o r an h o u r or t w o w i t h t h e f e w ewes t h a t ap-

321 peared hesistant to accept the foster lamb after its coat had been removed. T h e p e r m a n e n c e o f fostering was de t e r m i ne d during additional observations. Rejected lambs were r em ove d f or artificial rearing.

Acceptance tests Ewes were tested in sets of 2 or 3, with each ewe's own lamb being used as a foster lamb for a n o t h e r ewe of the same set. Lambs were removed fr o m ewes for 2--8 h prior to t he tests. In some series, ewes were also tested with the foster lamb wearing its own coat or with a n o t h e r alien, either immediately before or immediately after the test in which the coat of the ewe's own lamb was worn. Tests with the ewes' own lambs wearing an alien's coat were also included in Series 1 and 3. Acceptance tests were either in an " o p e n - f i e l d " or in a pen (Table I). In the open-field test, a ewe and lamb were released simultaneously from opposite ends o f a 13 m X 8 m enclosure and were observed until their responses could be classified as acceptance or rejection, or for up to 5 min (Alexander, 1977). In the pen test, the ewe was held in a 2 m X 1 m pen and was observed for a p p r o x i m a t e l y 5 min after the test lamb had been placed with her. The ewe was regarded as having accepted the lamb if sucking was permitted, or where the lamb did not a t t e m p t to suck, if the ewe showed c o n t i n u o u s o l f a c t o r y interest, usually accompanied by soft bleats. L o u d bleats, circling to avoid the lamb, and butting were taken as indicative of rejection.

Washing lambs In Series 4, some lambs were washed during the period of separation f r o m the ewe immediately prior to the tests. A warm, dilute solution o f wool-scouring detergent was used, and lambs were scrubbed for approxim a t ely 10 min (Alexander et al., 1983a); after rinsing t hey were allowed to d r y in th e sun or in f r ont of a blow-heater. Coats from these lambs were stored in sealed plastic bags while the lambs were washed and dried.

Statistical comparisons Fisher's exact test was used in all comparisons. RESULTS

Effect o f transfer o f standard hessian coats on fostering In 25 o f 26 separate comparisons (Table III), more alien " f o s t e r " lambs were accepted b y ewes than control aliens, although the differences were significant in only 8 of the comparisons. Overall, 49% (135/ 253) of test lambs were accepted c om par e d with 10% (29/243) control lambs, as defined at f o o t o f Table III.

322 TABLE Effect

III of transfer

Ewe breed o r croSS l

Merino

of hessian coats on acceptance

Series

1 and9

Time since birth (days). Range (median)

of alien lambs:

Proportion

results from

16 breeds or crosses

of alien lambs accepted 2

Multipsxas

P

Primiparas

Control

Test

Control

Test

1--5 (2)

1/32

16/32

--

--

0.00003

3--6 3--5 3--6 2--4 1--3 2--4 3--5 2--5 1--2 1--3 1--2

-0]32 -2/14 -1/8 -1/7 -0/94 1154

-3]32 -5114 --

4/33 -0/S -219

9/33 -4]8 -7/9 --

NS NS 0.04 NS 0.057 NS NS NS NS NS NS

1 - - 2 (2) 1 - - 2 (2)

-2/104

-7/10

--

--

4/32 (22) s --

22/32 (22) -3 / 1 4 (Ii) --

(pooled)

8 10 Corriedale BL X Met. 3 Dorset 3 Cambridge Llyn Welsh Mt. Welsh crosses Soay

10 1 6 6 2 2 2 2 3

(5) (4) (4) (3) (2) (3) (3) (3)

(2) (2) (2)

118

--

--

2/4

4]4

3/8

--

--

-2/9 4/5

0/24 - -

-

-

1/114

3/6 - -

- -

7/10 --

0.008 0.07

3/10

10/10

0.003

-0/10 (7)

-4/10 (7)

0.00001 0.09

-0/1

-1/1

NS NS

--

Jacob

3

1--6 (3) 1--7 (3) 1--6 (3)

Clun

3

1 - - 7 (3) 1 - - 2 (1)

0/14 --

Dalesbred Scottish Blackface Nth. Country Cheviot BL X B.Face (Grey face) Dam line

3 4

1--2(1) 1--6 1--3 (2)

1/5 (4) 0/4 (2) 0/10 (8)

3/5 (4) 4/4 (2) 6/12 (8)

----

----

NS 0,029 0.015

4

1--5 (2)

1/10 (6)

9/10 (6)

--

--

0.001

4

1--3 (2)

3/13 (8)

4/10 (i0)

--

--

NS

5

1--4 (2) 1--4 (3)

-0/1

-1/4

I/3 --

4/7 --

ILambs were mostly of same breed as ewes, 2Test lambs were aliens wearing the coat of same alien or a twin of the same allen wearing 3 E x t r a c t e d f r o m A l e x a n d e r e t al., 1 9 8 4 . 4Control groups tested without coats. $Figures in parentheses show the number of ewes.

(11)

(2)

(7)

NS NS

but some were sired by rams of another breed (Table I). the ewe's own lamb. Control lambs were frequently the its own coat.

ewes tested, where more than one test was done on some

In addition, many ewes recorded as failing to accept test aliens showed more interest in the alien when it was wearing the coat from the ewe's o w n lamb than w h e n wearing its own. For example, in Series 8, where 9 / 3 3 ewes accepted the test alien, a further 10 showed a clear increase in interest. In Series 1 and 3, some ewes in the control situation were presented with t w o alien lambs with or w i t h o u t coats in succession, or with the same alien lamb wearing different alien coats; very few ewes (7--12% or 1 / 1 5 - 4 / 3 4 ) accepted one alien and n o t the other. In addition, 74 ewes were tested with their o w n lamb wearing an alien lamb's coat; only 8 (including 5 / 1 8 Jacobs) rejected the lamb.

323 T A B L E IV E f f e c t o f c o n f i n e m e n t f o r u p t o 3 d a y s f o l l o w i n g transfer o f c o a t s , or c o a t s plus h o o d s

Series (breeds pooled)

Treatment

1

Control (no coats) Coat exchanged

4

Control (coats)

Proportion of alien lambs accepted I Within 5 rain

Coats exchanged L a m b s w a s h e d and c o a t s e x c h a n g e d

3/15 10]15

After confinement

6]15 12]15

NS NS

2 days 2 days

1120 (14)

12]20 (14)

0.0004

23]46 (34) 16/32 (24)

42]44 (32) 30]31 (23)

9 X 1 0 -7 3 X 1 0 -s

overnight (~--- 1 6 h) ( 2 1 6 h) ( 2 16 h)

0.07

3 days

NS

2 days

5

Coats exchanged

5]11

72

Coats exchanged

12/15

Totals

Control

Others

Period o f confinement

8]9 15/15

4/35

66/119

18/35

/

107/114}'

1.7 X 10-9

1Figures in p a r e n t h e s e s i n d i c a t e t h e n u m b e r o f e w e s t e s t e d . 2 I n c l u d e s D o r s e t s a n d B L X M e r i n o c r o s s e s ; h e s s i a n c o a t s i m p r e g n a t e d w i t h w o o l fat, a n d h e s s i a n coats with hood from the rump of the ewe's own lamb were used.

Effect of other treatments on fostering Confinement o f ewes and foster lambs Confinement of ewe and foster lamb together, for periods ranging from 16 h (overnight) to 2 days following pen tests of acceptance after transfer of coats, increased the proportion of ewes accepting the foster lamb in all 7 groups in which confinement was tested (Table IV). In the pooled data for control groups, confinement increased acceptance from 11 to 51% (4/35 v. 18/35, P = 0.0006) and for coat-transferred groups from 55 to 94% (66/119 v. 107/114, P = 6 × 10-13). In Series 1, in which the ewe's acceptance of her own lamb was tested subsequent to her confinement with the foster lamb, acceptance of own lamb decreased, during the 1--3 days of confinement with the alien lamb; from 15/15 to 10/15 in a control group in which coats were not used. Similarly, a decrease from 15/15 to 8/15 occurred in the group confined after exchange of coats. However, after a further week during which ewes and lambs ran in a c o m m o n paddock, acceptance of own lamb was unchanged in the control group (9/14), compared with a marked decrease in the coat-exchanged group (from 8/15 to 1/13, P = 0.016).

Washing foster lambs before transfer o f coats In Series 5, using Scottish Blackface and North Country Cheviot ewes and lambs, ewes tested with freshly washed lambs wearing the coat from the ewe's own unwashed lamb accepted a similar proportion of alien lambs to other ewes tested with unwashed lambs (14/36 v. 16/32 in the pooled data).

Merino

Merino or Merino × BL

Blackface N.C. Cheviots Blackface N.C. Cheviots Greyface

Lambs

4/23 (15%)

------

(18) 3 (13) (10) (10) (14)

9] 23 (39%)

30/91 (33%)

8/25 7/18 3/14 7/15 5/19

Shorter period (24--36 h, Series 4) (4.75--5.5 h, Series 9} Control' Test

Proportion of alien lambs accepted

'Lambs wearing their own coats. Control tests were not done in Series 4. 2At 0 h, 26 ewes accepted 3 alien lambs in 52 tests. 3Figures in parentheses indicate the number o f ewes tested.

92

Total

Blackface Blackface N.C. Cheviots N.C. Cheviots Greyface

Series Ewes

Effect of period for which coats were worn prior to transfer to foster lamb

TABLE V

1/26 (4%)

D

m

m

Control' (6) (4) (7) (4) (4)

13/26 (50%)

17130 (57%)

6/9 2]4 4/8 3]5 2/4

Test

Longer period (37--79 h, Series 4) (22--24.5 h, Series 9)

text

S e e

0.03

NS NS NS NS NS

P

325

Effect o f procedural variables on fostering with coats Period for which coats were worn before transfer In Series 4, coats were fitted to lambs at times ranging from 24 to 79 h prior to the test of acceptance. A higher proportion of acceptances was found in all five groups (Table V) in which coats had been worn for > 36 h ( 2 1 - 4 7 % v. 50--67%). In Series 9, the proportion of acceptances also tended to be higher after coats had been worn by the ewe's own lamb for 24 h than after they had been worn for only 5 h (5/19 v. 12/25, P = 0.21, for ewes that did n o t accept the alien lamb wearing its own coat). Period for which lambs were separated from ewes In the overall series, the proportion of acceptance of foster lambs wearing the coat of the ewe's own lamb, at tests after 2--3, 4--5 or 6--8 h of separation were 77/147 (52%), 129/288 (45%) and 20/34 (59%), respectively; these proportions are not significantly different. Order in which lambs were tested In routine pen tests of acceptance, a control alien or potential foster alien wearing its own coat was presented to the ewe shortly before the test with the foster wearing the transferred coat, b u t in Series 6, many tests were done in the reverse order, with the test coat being removed and the foster lamb's own coat being replaced for the control test. Amongst Dorsets, the lamb presented first tended to have a lower chance of being accepted than the lamb presented second (20/63 (32%) v. 17/42 (40%) NS for aliens, and 32/63 (51%) v. 23/42 (55%) NS for the foster lambs), and the same trends were found amongst the crossbreds (1/34 (3%) v. 3/34 (12%) NS for aliens, and 2/34 (6%) v. 8/34 (24%), P = 0.08 for foster lambs). In the open-field tests of Series 1 and 3, ewes were usually tested with sets of 3 lambs, or less frequently 2 lambs, including the ewe's own lamb, prior to and after transfer of coats. The proportion of lambs accepted showed no obvious relationship with the test order; the proportions of foster lambs accepted in the 1st, 2nd and 3rd tests were 14/21 (67%), 13/20 {65%) and 8/15 (53%), and the proportions of other alien lambs accepted were 11/53 (21%), 13/53 {25%) and 12/55 (22%), respectively. Effect o f characteristics o f the ewe on fostering Breed There was wide variation between breed groups across the series, b o t h in proportion of control aliens and test aliens accepted (0--50 and 9--100%, respectively) (Table III); significant differences were also observed within series. For example, amongst multiparas of Series 3, a higher proportion of Soay ewes accepted foster lambs than Jacobs (P = 0.02), and in Series 2, a higher proportion of Welsh-cross ewes accepted foster lambs than

326

Cambridge ewes (P = 0.07). However, sample size was often small and breed comparisons were usually confounded by uncontrolled variables such as parity of ewe and previous management, as well as undefined site differences.

Time since lambing In all pen tests where this was not deliberately varied, acceptance was examined within 1 week of lambing and with lambs up to 7 days old. There was no clear relationship in any series between acceptance and time since the foster m o t h e r lambed, except in Series 4 in which a higher proportion of lambs was accepted by ewes that had lambed 3 or more days previously than by ewes that had lambed for only 1 or 2 days (19/30 (65%) v. 17/71 (24%), P = 0.0003); this trend occurred within each of the 5 groups of ewes in Series 4. However, time since lambing was c o n f o u n d e d with time for which coats were worn before transfer. In pooled data for all the other series, the difference was in the reverse direction (95/228 (42%) v. 92/151 (61%), P = 0.0003). Tests were also done in four series with ewes and lambs more than 1 week post-partum (Table VI). The acceptance rate clearly decreased with increasing time post-partum. No control lambs were accepted by any of the ewes t h a t had lambed more than 1 week previously. At each of 3 times since birth in Series 8, some of the ewes that failed to accept the " f o s t e r " lamb showed more interest in the l a m b after coat exchange than before the exchange (10/33, 16/33 and 13/32 at 3--6, 10--15 and 27--40 days, respectively). This t o o k the form of low bleats and prolonged sniffing at the lambs. TABLE VI Proportion of foster lambs accepted in tests more than 1 week post-partum Series

Type of ewe

Proportion accepted at various time post-partum

1 and 9 Merinos-- multiparous

Days post-partum Proportion accepted

1--5 16[32

2

Dalesbred -- mixed parity Days post-partum Proportion accepted

1--6 4/4

11--22 4/26

8

Merinos -- primiparous

Days post-partum Proportion accepted

3--6 9/33

1 0 - - 1 5 27--40 3/33 0/32

Days post-partum -- primiparous t, Proportion accepted -- multiparous J

3--6

10--15

10

Merinos

Pooled 1After confinement together overnight.

20 1/4(4/4) 1

418

o18

• 3/32

0/32

36/109

8/103

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Parity of foster ewe The proportions of Dorset ewes (Series 6) accepting alien lambs wearing the coat (or coat and hood) of the ewes' own lamb were significantly higher amongst those that had not lambed before than amongst those that had lambed previously (26/36 v. 31/72, P = 0.005) (Table VII); a similar difference was seen in the Merinos of Series 10 (4/8 v. 3/32, P = 0.02) (Table III). The same trend was apparent in the pooled data from other breeds. The primiparous ewes also accepted a higher proportion of control alien lambs than the multiparas, and the difference was again significant amongst the Dorsets (Table VII). Nevertheless, a 15% parity difference appeared to remain in b o t h sets when the proportions of test lambs accepted were adjusted to allow for acceptance of controls (Table VII, footnote), although in neither case was the difference statistically significant in the adjusted data. Litter size of foster ewe The proportion of foster lambs accepted b y twin-bearing ewes whose lambs had b o t h survived b e y o n d birth was about 20% above that by singlebearing ewes (110/211 v. 87/203, P = 0.062).

TABLE VII Effect of parity of foster mother Parity

Primiparas

Proportion of alien lambs accepted Various breeds ~ (Table III)

Dorsets (Alexander et al., 1984)

Control

Control

Test Observed

Adjusted 2

4[34

26]42

17]30

(12%)

(21/34) 3 (62%)

34]96

Multiparas 5/93

Observed

Adjusted 2

20/36

26/36

6/16

(57%)

(56%)

(72%)

(38%)

28]88

17169

31]72

13156

(33]93) 3

P

Test

(30/69) 3

(5%)

(35%)

(32%)

(25%)

(44%)

(23%)

NS

NS

NS

0.0025

0.005

NS

'Includes only breeds for which data on both primiparas and multiparas were available in the same series -- Dorset excluded. 2Adjusted by excluding ewes which also accepted aliens in control tests. 3Proportion adjusted to equalize numbers in test and control groups.

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Effect o f characteristics of the lamb on fostering Age There was no clear relationship between age of foster lamb and proportion of lambs accepted by foster ewes in the individual series, but in the pooled data, lambs 3--7 days old were less readily accepted than lambs 1--2 days old (110/266 (41%) v. 120/227 (53%), P = 0.011). Sex o f foster lamb The proportions of ewes accepting male and female lambs wearing their own lamb's coat were similar (112/294 (38.1%) v. 129/299 (43.1%), respectively, in the pooled data). Likewise, lambs of the same sex as the ewe's own lamb were accepted as readily as lambs of the opposite sex (137/339 (40.4%) v. 98/259 (37.8%) in the pooled data). However, in the test groups of Series 4, more ewes accepted a foster lamb of similar than dissimilar sex to that of their own lamb(s) (33/58 (57%) v. 10/30 (33%), P = 0.044). Appearance of foster lamb Some Soay and Jacobs ewes in Series 3 were tested with foster lambs whose heads were judged by the observers to differ markedly in appearance from that of the ewe's own lamb; in Series 4, the Blackface and Cheviot ewes were tested with lambs of the other breed (Table VIII). In pen tests, ewes accepted a smaller proportion of lambs that were dissimular to their own than similar lambs (Table VIII). However, the differences were significant only for the Cheviots (7/22 v. 9/10, P = 0.005) and in the pooled data (27/71 v. 61/73, P = 2.3 × 10-s). In tests after confinement overnight (Series 4), the only 3 lambs not accepted were different in appearance from the ewe's own lamb. Attempts to foster lambs on to ewes rearing a lamb o f their own (Series 5 and 7) In tests with Dam Line ewes held in pens, lambs were separated for 4--6 h and 9 ewes were then given a foster lamb wearing their own lamb's coat or coat and hood; 5--24 h later, their own uncoated lamb was returned, and acceptance of both lambs was assessed for 1 week. One ewe accepted b o t h lambs immediately and 8/9 had accepted both lambs within 4 days, compared with 3/5 controls in which coat transfer was not used. In Series 7, two Dorsets and two crossbreds, also held in pens, all accepted their own and a foster lamb within 1 day after being presented with the foster lamb wearing " o w n " lamb's coats impregnated with wool fat, or own lamb's coat and hood from the rump; the ewe's own lamb was presented approximately 18 h after the foster. Prior to full acceptance in both series, the foster lamb was permitted to suck only when the ewe's own lamb was also sucking.

9/10

Cheviots 2 (83.6%)

(90.0%)

(58.3%)

(50%)

(77.4%)

27/71

7/22

9/22

3/16

8/11

(38.0%)

(31.8%)

(40.9%)

(18.8%)

(72.7%)

Lamb different from own

~Tested with own breed. 2Tested with lambs of other breed in series.

61/73

14/24

4/8

Jacob'

B. Face ~

34/31

Lamb similar to own

Proportion of alien lambs accepted

Soay'

Pooled data

4

3

Series E w e breed

Effect of appearance of foster lamb

TABLE VIII

2.3 ×

0.005

NS

NS

NS

P

1 0 -s

Black with white nose and muzzle White

Brown with or without white patches White with various amounts of black, especially round eyes

Appearance of lamb's head

C~ tO

330

Permanence of fostering Observations of ewes at pasture with foster lambs in Series 1, 4, 5 and 7, indicated that the fostering was permanent. DISCUSSION

The results (Tables III and IV) show that on average about 12% of ewes in the test situation readily allow sucking b y a substitute lamb during the first few days after lambing, and that the proportion can be increased to around 60% if the alien lamb is wearing a textile coat that has previously been worn b y the ewe's own lamb. The additional finding that close confinement of the ewe with the foster lamb, overnight or for a further 1--2 days, increases the acceptance rate of alien lambs, with or without the transfer of textile coats, b y 33--40% is consistent with previous studies (Alexander et al., 1983a) in which confinement alone resulted in 8/22 (36%) ewes accepting alien lambs. The observations indicating that the fostering was permanent were confirmed by subsequent studies (Alexander and Stevens, 1985). Despite the opportunistic nature of the study and the likely presence of confounding influences, the results point to a number of factors that have some influence on the success of fostering attempts, and that will contribute to differences, which can be considerable, in the success rate b e t w e e n flocks. Breed of sheep is clearly important (Tables III, VI and VIII, and Alexander et al., 1984), and breed differences may be partly explained b y differences in the appearance of lambs (Table VIII); the ewe's recognition of her lamb has been shown to depend in part on the appearance of the lamb's head (Alexander and Shillito, 1977). This may explain the low acceptance rate in Jacob and Cambridge sheep, whose lambs have distinctively marked faces. On the other hand, acceptance rate was high in the Soays, Welsh-crosses and in the few Dalesbreds, flocks in which lambs are also distinctively marked. Perhaps some breeds rely more heavily on visual cues for recognition than others. The consistent trend for primiparous ewes to accept a foster lamb more readily than multiparas (Tables III and VII) was unexpected in view o f the reputation of primiparous ewes to display poor maternal behaviour (Alexander, 1960). It appears that the ability of ewes to discriminate between alien lambs improves with increasing parity. The trend (P = 0.06) for ewes rearing more than one lamb to accept a foster lamb more readily £han ewes rearing a single appears logical, b u t requires confirmation; the more cues involved in recognition, the more likely the ewe is to become confused. Throughout the series, the period b e t w e e n the foster mother lambing and the a t t e m p t at fostering was closely related to the age of the foster lamb. However, the evidence a b o u t the success of fostering in relation to

331 the time-since-lambing was conflicting,, whereas the success rate appeared to decrease as the age of the foster lamb increased. This is consistent with other evidence that ewes tested 12 h after lambing are more likely to accept 12-h-old lambs than lambs 1 or 2 days old (Alexander et al., 1983b), and with suggestions arising from work with goats that distinction between own and alien is aided by a specific olfactory labelling of the young by the m o t h e r through her saliva or milk (Gubernick, 1981). Some success was achieved with periods greater than 1 week, but the rate clearly declined with increasing period since lambing (Series 8). In contrast to age and appearance of the foster lamb, the lamb's sex appeared to be unimportant, except in a single series (4) in which acceptances were more frequent when the foster lamb had the same sex as the ewe's own lamb(s) than when the sexes differed. The result in Series 4 is consistent with the frequent observation that ewes sniff at the genital orifices of both male and female lambs. Procedural variables also had an influence on acceptance. The period for which lambs were separated from the ewes had no apparent effect on acceptance. In pen tests, lambs that were presented second had more chance of being accepted than lambs presented first, but this trend also requires confirmation. Success rate appeared to increase with the period for which the coat had been worn by the ewe's own lamb, and there appeared to be some facilitation of fostering after a period as short as 5 h. This effect may explain w h y the success rate increased with time-since-lambing in Series 4, in which lambs were fitted with coats soon after birth. Attempts to improve the success rate above that obtained with the use of hessian coats have not been successful (Alexander et al., 1984). Washing lambs and the use of hoods was introduced following observations of apparent acceptance of a lamb wearing the transferred hessian coat, followed by its vigorous rejection after the ewe had sniffed at the head and/or legs. Washing lambs w i t h o u t other treatment apart from confinement has facihtated fostering in other studies (Alexander et al., 1983a), but in Series 4, the only series in which lambs were washed, there was no obvious improvement due to washing. Likewise, any improvement due to the use of hoods was small. The facilitation of fostering by the use of coats appears to be only partly due to the transfer of own lamb's odour to the foster lamb. Significant facilitation also appears to result from the mere wearing of some types of coats or coats plus hoods (Alexander et al., 1984), but how this decreases the ewe's perception that a lamb is an alien is not clear. It may be that the ewe recognizes the odour of the coat material, or the alien odour is masked or muted. However, the mechanism whereby the use of coats facilitates fostering is obviously an olfactory one. The reasons, other than those already discussed, for variations between ewes in acceptance of alien lambs are not clear and are unlikely to become clear until more is known about the nature of lamb odour(s). It is possible

332

that there are degrees of difference between lamb odours, and that fostering fails where differences are large; for example, some ewes appeared to distinguish between two apparently similar alien lambs. Alternatively, some ewes m a y have a less acute sense of smell, or rely more on the other senses, or be slower to learn the odour of their own lamb than other ewes, and may therefore be more readily deceived than other ewes. Ewes might also differ in their criteria for acceptability of lambs, some requiring the presence of their own lamb's odour and others the absence of an alien odour; for example, only some ewes will readily accept washed aliens (Alexander et al., 1983a). The low acceptance rate in ewes with lambs more than 1 week old could be due to any of these factors, or to an increase in the strength or specificity of their own lamb's odour; olfaction certainly appears to be involved as judged from the apparent increase in olfactory interest by m a n y ewes in potential foster lambs or washed older lambs (Alexander et al., 1983a). While the use of transferred coats facilitates acceptance of alien lambs, the a t t a c h m e n t of the ewe to the foster lamb appears to be less strong, at least for the first day or two, than the attachment to her own lamb, as shown in the attempts to foster a lamb on to a ewe already rearing a lamb of her own (Series 1 and 5); although the foster lambs were permitted to suck initially in the absence of the ewe's own lamb, the foster was apparently less readily accepted after return of the ewe's natural lamb. However, acceptance increased with time. The concept of incomplete bonding is consistent with field observations on ewes with twins (Kilgour et al., 1983). The use of transferred coats appears to create a firmer attachment than confinement alone, as shown in Series 1 in which ewes with a coat-fostered lamb come to reject their own lamb fostered on to another ewe, sooner than ewes with a lamb fostered by confinement alone. In summary, the use of cheap textile coats coupled with confinement appears an effective practical means of fostering lambs, and could be of practical economic use on farms where pens and labour for fostering are available. The m e t h o d would be useful both for transferring lambs between ewes for experiments on lamb growth or development, as well as saving orphaned or abandoned lambs, or lambs from large litters whose mortality is high and growth slow. The maintenance of a small flock of recentlylambed single-bearing ewes with their lambs wearing coats could provide a reservoir of potential foster mothers. ACKNOWLEDGEMENTS

These studies originate from a suggestion made by Mr. Bob Elwin, of CSIRO Armidale, based on his experience of,fostering calves on a cattle property at T a m w o r t h N.S.W.; we are particularly grateful to him. The senior author is grateful to Mr, G w y n Williams, Dr. Elizabeth Walser, Dr. Jeff Maxwell and Dr. J o h n Slee who are responsible for the provision of animals and facilities at the four United Kingdom Institutions at which

333

studies were done. The authors are also grateful to the various people who assisted with the observations and sheep management: Miss Rosalind Hughes at Bangor, Dr. Elizabeth Walser and her assistants at Babraham, Messrs. John Senior and Andrew Alexander at Glensaugh, Mr. Bruce Wilson at Roslin, and Mr. Bill Dwyer and Miss Joanne Innes at St. MalTs.

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