Small Ruminant Research, 2 (1989) 119-132 119 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

Feeding Behaviour of Milk-fed Lambs at Pasture

G. BECHET, M. THERIEZ and S. PRACHE

I.N.R.A. - - Theix, Laboratoire de la Production et du Mdtabolisme Mindral des Petits Ruminants, 63122 Ceyrat (France)

(Accepted 30 November 1988 )

ABSTRACT

B~chet, G., Th~riez, M. and Prache, S., 1989. Feeding behaviour of milk-fed lambs at pasture. Small Rumin. Res., 2: 119-132.

Four groups of Ile de France lambs were fed milk at pasture either by their dam (mother-fed lambs, single or twins: SMR and TMR) or artificially {high or low level of milk: HAR and LAR) during two experiments. A fifth group of artificially reared lambs was used during the first year. They grazed with foreign ewes and were fed at the high level (FHAR). All lambs had free access to concentrate (maize). Concentrate consumption and growth rate of lambs were measured and their grazing behaviour was monitored by visual appraisal or with electronic devices.

SMR and HAR lambs had very similar performances and gained more weight from birth to weaning, at 120 days, than TMR and LAR animals whose performances were close. Weaning weight was 39 kg for the SMR and HAR lambs, 35 kg for the TMR and LAR lambs. Maize consumption by creep feeding differed by type of suckling (10.7 for SMR and 5.4 kg for TMR) but not with level of milk offered to artificially reared lambs (29.1 kg for HAR and 29.4 kg for LAR ). This is an important dam's effect on lambs' behaviour and performance, and has practical implications.

Lambs always remained close to their mother (5 to 10 m) and mother-fed lambs spent more active time grazing than artificially reared ones (417 min/day vs. 259 rain/day). Active time spent grazing was higher for twin suckling ewes than for single suckling ones (112 rain/day). Similar differences were observed between twins and single lambs (44 rain/day) or between artificially reared lambs at H or L level (36 rain/day) but the former spent 158 min more grazing per day than the latter.

INTRODUCTION

M a n y au thor s have d e m o n s t r a t e d a negat ive cor re la t ion be tween milk in- t ake by young lambs and the i r c o n s u m p t i o n of grass ( Joyce and Ra t t r ay , 1970; Lang lands , 1972; P e n n i n g and Gibb, 1979; D o n e y et al., 1984). General ly, a reduc t ion of milk c o n s u m p t i o n induces an increase of grass in take bu t com- pensa t ion is no t sufficient, and as l ambs ' energy ba lance is lowered, the i r daily gain declines. In order to sus ta in h igh growth rate, l ambs are of ten provided

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with concentrated feeds. However, we observed that, when concentrates are fed ad libitum, single suckling lambs consumed more than twins (15 kg and 10 kg in 10 weeks; unpublished results).

This difference in feeding behaviour could result from mother-offspring re- lationships which are very important in sheep. During the first month of life, the lamb remains within 4 m of its mother and within 20 m until 3 months (Arnold and Dudzinski, 1978). It continues to suckle approximately 10 times in 12 h during its second month (Ewbank, 1967 ). Further, copying phenomena are frequent in sheep (Arnold and Dudzinski, 1978). It appears likely that the longer grazing periods of twins compared with single lambs, correspond not only to compensation of a nutritional deficiency but also to copying of the mother. Ewes nursing two lambs spend more time grazing than those nursing only one (130 min more, Dulphy et al., 1979), and their offspring may mimic them. Further, when concentrate is offered in small paddocks, lambs have to move away from their mother to consume it. Twins, which suckle more fre- quently than singles, remain closer to their dam and their access time to the creep feeder is more limited.

These hypotheses were tested in the trials described here. Comparisons were made between twin and single lambs nursed by their mother or artificially reared with two levels of milk supply.

MATERIAL AND METHODS

Animals and feeds

Animals were assigned to their experimental group according to their rearing status.

(1) Mother reared lambs (MR) nursed as singles (SMR) or twins (TMR). Groups were composed of 6 ewes and 6 or 12 lambs.

(2) Artificially reared lambs (AR) fed at a High level (HAR) or at a Low level (LAR) and grazing alone: 8 lambs per group.

(3) Artificially reared lambs, fed at a High level but grazing with foreign dry ewes (FHAR): 8 lambs and 6 ewes.

The experiment was carried out twice: with five experimental groups (42 lambs and 18 ewes ) during the first year (1984), and with four only (34 lambs, 12 ewes) during the second (1985), the FHAR group being omitted.

All experimental groups composed of pure Ile de France animals, with an equal number of male and female lambs, were constituted two weeks after lambing. The animals were fed indoors until they were turned out to grass in mid April when the lambs were 6-7 weeks old.

The lambs fed artificially with ewe milk replacer (25% CP, 25% fat in DM and 17.6% DM in liquid reconstituted milk) received their daily milk allow- ance once a day at 8.30 a.m. Milk was offered ad libitum up to 15 days of age

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and in restricted quantities thereafter to simulate differences between singles and twins. Overall quanti ty was progressively reduced up to the end of the trial (140 days of age). Average quantities fed at pasture each year were 1.1 kg/ lamb/day for groups HAR and FHAR and 0.75 kg/ lamb/day for group LAR during the first month and then 0.43 and 0.25 kg/ lamb/day, respectively, dur- ing the second month.

From age 15 days, all lambs were provided with high-moisture whole grain maize treated with propionic acid. This maize was offered ad libitum in creep- feeders to which the ewes did not have access.

The animals grazed rotationally a fescue, rye-grass and white clover pasture. Each group of six ewes and their lambs used three paddocks of 1500 m 2 while the paddocks of AR lambs were smaller: three paddocks of 700 m 2 for HAR and for LAR lambs and three of 1100 m 2 for FHAR lambs and dry ewes. Sheep were moved to the next paddock when grass height was reduced to 6-7 cm.

Measurements

Lambs were weighed every two weeks. Total milk (AR lambs) and maize intakes of each of the experimental groups were recorded daily.

Animal behaviour was monitored by two methods: (1) Visual observation of all animals. On four occasions in 1984 and twice

in 1985, the animals were observed every 30 min, from sunrise to sunset (15 h/day) . At each observation, the animals' position in the pasture and their activity were recorded. This provided information about synchronisation of activities of different types of animals (i.e. percentage of observations when two animals, ewes or lambs, had the same activity: grazing, resting, lying, mov- ing) and estimated distances between them.

Synchronisation of activities and distances between animals were deter- mined for different groups of animals. These couples were defined by their age (Lambs: L or Ewes: E) or by their relationship (Mothers: M or Twins: T). Synchronisation of activates for couple L-M means for example: percentage of lambs having the same activity as their mothers (grazing, resting, etc.). Distance between couples L-E or T - T means distances between lambs and ewes (other than their mothers) or between twins from the same mother.

Feeding behaviour (grazing by ewes and by lambs, concentrate intake by lambs) was also recorded. These visual appraisals were completed during the first year by taking photos of lambs at the maize creep-feeder every minute during daylight in three and four 48 h periods for AR and MR groups, respectively.

(2) Automatic recording. In 1985, all jaw movements of different animals from each group were recorded (six ewes and six male lambs for SMR and TMR, four male lambs for HAR and LAR). Recordings (for 17-days periods) were carried out twice (in May and June ) with electronic recorders.

The recorders were made of an elastic conductor surrounding animals'

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mouths and whose resistance varied when elongated by spacing of jaws. Each 2.5 seconds, elementary data were stored in a RAM memory: 0 if the animal had kept its mouth closed during the previous time unit; 1 if it had opened it once or more. The memory was emptied each fourth day and data analysed with a computer (Brun, unpublished).

The following parameters were used for the description of the animals' feed- ing behaviour: duration of meals or rumination periods, time spent grazing or ruminating. A meal or a rumination period was a period exceeding 7 min, and during which the animal had the same activity. This might include short pauses, less than 7 min. According to whether pauses made up less or more than 50% of meals' duration, two types of meals were distinguished: intensive or idling meals. Mastication time represented true mastication time, when pauses were excluded from meals or rumination periods.

RESULTS

Lamb weight gain

Different periods corresponding to change of diet can be considered: birth to 30 days: milk alone; 30 days to turning out: milk and concentrate; turning out to weaning: grass, concentrate and milk. Rearing method (MR vs. AR) induced significantly different growth rates between experimental groups from birth until turning out to pasture (Table 1 ). Most differences disappeared at

TABLE1

Effect of rearing method, number of lambs suckled or level of milk offered on lambs' growth rate (average values for both years)

Period Experimental groups 1 Level of significance of differences between 2

SMR TMR HAR LAR rearing number level of method of lambs milk

Birth to 30 days 300_+ 23 220_+ 46 325 _+ 46 273 __ 42 ** ** ** 30 days to transfer 231_+35 201_+59 283_+51 274_+49 ** * NS

to pasture Transfer to pasture 330_+47 263_+45 291_+38 269_+52 NS ** NS

to weaning

~SMR, single mother-fed lambs; TMR, twin mother-fed lambs; HAR, high milk level artificially reared; LAR, low milk level artificially reared. 2NS = not significant; *denotes significant differences, P < 0.05; **denotes highly significant dif- ferences, P < 0.001.

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that time and, during the true experimental period, only the SMR group's growth rate was different from others.

When lambs' live weights at weaning are compared, it appears that SMR and HAR lambs, weighing 39 kg at four months, were comparable, as were TMR and LAR lambs, weighing only 35 kg at the same age. These two groups corresponded to differences in milk supply.

Maize consumption

Maize intake by suckling lambs was consistently higher for singles than for twins {10.7 vs. 5.45 kg DM/lamb, average value for both years). Artificially reared lambs consumed 29.25 kg DM/lamb without any difference between groups (29.1 kg DM for HAR vs. 29.4 kg DM for LAR, average values for both years).

Animal behaviour (visual observations)

Lambs and ewes each formed homogeneous groups (L-L and E-E couples) with good cohesion (high percentage of synchronisation and short distances between animals, Tables 2 and 3 ). In the same way, ewes and their own lambs formed couples with a strong social a t tachment as shown by synchronisation of activities and particularly short distances between animals of the same cou- ple: 6.4 to 7 m for L-M when grazing and 2.8 to 3.4 m when resting. The bond between twins was also very strong (more than 70% of synchronisation and very short distances from one to the other). Mature and young animals formed social groups which mixed but remained loosely associated: lowest synchroni- sation of activities and greatest distances between animals were observed for the L-E couples. Couples with the strongest cohesion were observed with AR animals for lambs as well as for ewes (FHAR experimental group in 1984). In the last group, mature and young animals, which were not related, never mixed.

Distances between lambs and their dams during grazing changed with age in 1984 for singles as well as for twins and increased from 5 m when animals were transferred to pasture to almost 10 m before weaning. On the other hand these distances remained fairly constant in 1985 (Fig. 1). Distances between lambs and other ewes were on average twice the former distances and followed the same pat tern during the grazing period.

For adults, time spent grazing increased regularly from dry ewes (31%, FHAR group) to single and twin suckling ewes (39.4% for SMR and 44.6% for TMR on average). The rearing status had a considerable effect on lambs' feeding behaviour. The AR lambs spent 12 to 19% of their time grazing, with no dif- ference between animals fed high or low milk level, whereas MR lambs spent nearly twice as long grazing: 33.1% on average for single and 37.8% for twins. On the other hand, AR lambs spent nearly 8% of their time consuming maize,

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T A B L E 2

Visua l o b s e r v a t i o n s o f l a m b s ' a n d ewes ' b e h a v i o u r a t p a s t u r e (year: 1984)

Coup le s 1 R e a r i n g m e t h o d 2

M a t e r n a l Ar t i f ic ia l

S M R T M R H A R L A R F H A R

( C ) 3 ( G ) 3 (C) (G)

S y n c h r o n i s a t i o n o f L - M 64 ~ a 66 a ac t iv i t i e s (%) (all L - E 56 b ~ 53 b b

ac t iv i t i e s pooled) L - L 65 a a 56 ¢ b

T - T - 71 E - E 66 a ~ 59 d b

(G) (G) (C) (G)

- - 4 8 ~

69 c 63 ~ 74 b d

- - 7 9 c c

D i s t a n c e s ( m ) L - M 7.0 a ~ 7.1 ~ a _ _ _ b e t w e e n L - E 10.6 b ~ 13.1 b b _ - 14.4 ~ ¢ i nd iv idua l s d u r i n g L - L 9.0 ~ ~ 12.3 b b 4.4 c 5.9 d 5.2 b cd

g raz ing T - T - 6.3 a _ _ _ E - E 9.4 ¢ a 12.0 b b _ - 7.7 c

D i s t a n c e s ( m ) L - M 2.8 a a 4.6 a a _ _ _ b e t w e e n L - E 4.7 b a 8.8 b b _ - 12.2 a i nd iv idua l s d u r i n g L - L 4.1 c ~ 7.1 c b 1.9 ¢ 2.3 c 2.5 b

r e s t i ng T - T 3.5 ~ - - - E - E 4.7 b a 8.3 b~ b _ - 3.7 c

I n t a k e ac t iv i t i e s (%)

Ewe 41.6 42.8 - - 31.4 L a m b

C o n c e n t r a t e 2.1 1.8 6.8 6.9 7.7 G r a s s 31.5 38.8 18.6 16.0 15.6 To t a l 33.6 40.6 25.4 22.9 23.3

1L, l ambs ; E, ewes; T , twins ; M, m o t h e r s ; T - T , t w i n s f r o m t h e s a m e m o t h e r . 2SMR, s ingle m o t h e r - f e d l ambs ; T M R , t w i n m o t h e r - f e d l ambs ; H A R , h i g h mi lk level ar t i f ic ia l ly reared; L A R , low mi l k level ar t i f ic ia l ly reared; F H A R , l a m b s g raz ing w i th fore ign ewes ar t i f ic ial ly reared on h i g h m i l k levels. 3Sta t i s t ica l i n t e r p r e t a t i o n : (C ) , d i f fe rences b e t w e e n couples ( L - M , L - E , etc. ), a,b,cp < 0.05 in t h e

s a m e co lumn ; (G ) , d i f f e rences b e t w e e n g roups ( S M R , T M R , etc. ) a,b,cp < 0.05 on t h e s a m e line.

b u t 1 - 2 % o n l y f o r M R l a m b s . T h e s e r e s u l t s o b t a i n e d b y v i s u a l o b s e r v a t i o n a r e

i n g o o d a g r e e m e n t w i t h e s t i m a t i o n s o b t a i n e d f r o m p h o t o s ( 8 . 4 a n d 1 . 6 % o f

t i m e s p e n t c r e e p - f e e d i n g f o r A R a n d M R , r e s p e c t i v e l y ) . T h e A R l a m b s w h i c h

c o n s u m e d m o r e m a i z e t h a n t h e M R , r e m a i n e d a l s o c l o s e r t o t h e c r e e p - f e e d e r

t h a n t h e l a t t e r ( F i g . 2 ) . D i s t a n c e f r o m c r e e p - f e e d e r v a r i e d w i t h a g e b u t r e -

T A B L E 3

Visual observat ions of lambs ' and ewes' behaviour a t pasture (year: 1985)

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Couples 1 Rearing method 2

Mate rna l

S M R T M R

Artificial

HAR LAR

Synchronisa t ion of L - M activit ies (%) (all L - E activit ies pooled) L - L

T - T E - E

Distances (m) L - M between L - E individuals during L - L grazing T - T

E - E

Distances (m) L - M between L - E individuals during L - L rest ing T - T

E - E

(C) a (G) 3 (C) (G) 79 a " 71 a b 71 b " 56 b b 77 ~ " 60 ¢ b

- 7 5

72 b " 61 ¢ b

6.4 a " 8.2 a b 9.3 b " 12.7 b b 7.4 " " 10.9 c b

- 8 . 6 "

9.9 b " 13.6 b b

3.4 ~ " 4.7 " b 5.2 b . 8.5 b b 4.5 ¢ " 6.5 "~ b

- 4.4 "¢ 5.3 b a 7.6 b~ b

76

4.0

3.8

(G) (G)

" 6 8 c

4.2 ¢

" 2 . 8 ¢

Intake activit ies ( % ) Ewe 37.2 46.4 - Lamb

Concent ra te 0.1 1.1 6.8 10.2 Grass 34.7 36.9 11.6 11.7 Total 34.8 38.0 18.4 21.9

1L, lambs; E, ewes; T, twins; M, mothers ; T - T , twins from the same mother . 2SMR, single mother-fed lambs; TMR, twin mother-fed lambs; HAR, h igh milk level artificially reared; LAR, low milk level artificially reared. 3Statistical in terpre ta t ion; (C) , differences between couples (L -M, L-E , etc.), a'b'cP< 0.05 in the

a b c same column; (G) , differences between groups (SMR, TMR, etc.), ' • P < 0.05 in the same line.

m a i n e d s i m i l a r f o r e w e s a n d t h e i r l a m b s w h i c h d i d n o t a p p e a r t o l e a v e t h e i r

m o t h e r s t o e a t m a i z e .

Animal behaviour (automatic recording)

Lambs. F o r b o t h p e r i o d s o f m e a s u r e m e n t , a n d t h u s f o r l a m b a g e s o f t w o a n d

t h r e e m o n t h s , t h e d u r a t i o n o f i n t e n s i v e m e a l s w a s g r e a t e r f o r s u c k l i n g l a m b s

t h a n f o r t h o s e f e d a r t i f i c i a l l y ( 2 7 5 m i n m o r e p e r d a y i n M a y a n d 1 7 9 i n J u n e ) ,

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20

15

E 10

u~

121

1984 1985

~0

// / O / / /

"... ~%> • .s- / ~

s " % . ~ /

T . . . . . . . . T

S - - S

- - : l amb-mother S: S M R

. . . . . : l a m b - e w e T: T M R

O: F H A R

io ¢2 8's ,~o ~o ~2o Lambs age (days)

Fig. 1. Distance separating lamb and mother or other ewe during grazing.

1984 1985

40

30

~ 2 0 -

'° i

T /

Z •

S: S M R

- - : lamb T: T M R

. . . . : ewe H: H A R

L: L A R

o: F H A R

v ~m

~o ¢2 & ~o ~o 40 L a m b s age (days )

Fig. 2. Changes in distances between lambs or ewes and the maize distributor.

whereas the reverse was true for idling meals ( 130 and 138 rain/day less) (Ta- ble 4 ). The duration of mastication time during grazing was also much longer (170 rain/day on average) for suckling lambs than for artificially reared ones in May as well as in June. Differences in time spent ruminating were more limited (30 to 60 rain less per day for AR than for MR lambs). Among suckling lambs, the duration of meals varied little with age but there was significant increase in rumination time. In contrast, the artificially fed lambs modified their feeding behaviour with age (intensive meals were longer, at the expense of idling meals) which resulted in a significant increase in grazing time without

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TABLE 4

Feeding activities of lambs according to season and source of milk (min/day) i

Maternal period effect M / J

May June

Maternal Mode Artificial Maternal Mode Artificial effect effect M / A M / A

Artificial period effect M / J

Number of 24 11 31 30 days, lambs

Total t ime Intensive

meals NS 491_+73 ** 216-+114 496_+86 ** 317_+109 * Idling meals * 80-+99 ** 210_+91 31_+50 ** 139_+115 NS Rumination ** 348_+ 76 NS 314_+ 81 425_+ 78 ** 355_+ 91 NS

Mastication t ime During grazing NS 406_+61 ** 216_+80 427_+72 ** 275_+69 * During

ruminating ** 299_+ 75 NS 261 _+ 68 365_+ 75 ** 307_+ 86 NS

1NS -- not significant; M/A, comparison of maternal vs. artificial rearing; MJ, comparison of May vs. June; *P< 0.05; **P< 0.01.

any marked alteration in rumination patterns. The ratio of durations of the two kinds of mastication (grazing and ruminating) varied with rearing method. Suckling lambs spent less time ruminating than feeding and this ratio in- creased with age {from 0.74 to 0.84) whereas for those fed artificially there was an opposite effect: rumination was always longer than feeding and the ratio decreased with age {from 1.2 to 1.1).

Ewes. Ewes nursing twins had always longer intensive meals and shorter ru- mination periods than those suckling only one lamb (Table 5). However, while the former reduced their intake time from May to June (66 min/day less in- tensive meals, 50 rain/day less grazing mastication time), the duration of daily mastication during grazing of ewes nursing one lamb increased slightly (20 min/day) as an effect of longer idling meals ( + 41 min/day) without any change of intensive meals. Rumination time increased from May to June mainly for ewes nursing twins.

Comparative behaviour of ewes and lambs. The durations of intensive meals for ewes and lambs were not significantly different (500 and 494 min/day, respec- tively; Table 6) but the former had shorter idling meals than the latter (19 min/day vs. 51 ) and total daily mastication time during grazing was the same for lambs and their dams.

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TABLE 5

Average feeding activities of ewes according to season and number of lambs suckled (min/day)

May June

Group S Group T Group S Group T

Number of days, ewes 13 8 7 16

Total time Intensive meals 434 +__ 64 a 598 _+ 50 b 440 _+ 78 ~ 532 _+ 60 ¢ Idling meals 8_+ 15 a 26 +_ 33 ab 49 _+ 58 b 11 ___ 16 ~ Rumination 481 _ 83 a 378 _+ 47 b 500 _+ 87 ~ 453 ___ 62 ~

Mastication time during grazing 369 _+ 57 ~ 521 _+ 33 b 390_+ 36 a 471 _+ 52 c

1Group S, ewes nursing a single lamb; Group T, ewes nursing twins; ~,b,cp< 0.05.

TABLE 6

Feeding activities of lambs and ewes according to litter size (rain/day)

Lambs Ewes Type of animal

Group S Group T Group S Group T effect

Number of days, animals 29 26 20 24

Total time Intensive meals 480 +_ 86 a 510 +__ 71 a 436 +_ 67 b 554_+ 64 ¢ NS 1 Idling meals 72 _ 98 ~ 30 +_ 41 b 22 ___ 40 b 16___ 24 b * Rumination 365___ 102 ~ 421_+ 48 b 487___ 83 c 428___ 67 b **

Mastication time during grazing 397_+ 62 a 441_+ 68 b 376_+ 51 a 488_+ 52 c NS

a'b'cValues followed by different letters are significantly different (P< 0.05). 1NS = not significant; *P < 0.05; **P < 0.01.

L i t t e r size m o d i f i e d l a m b s ' f e e d i n g b e h a v i o u r ; t w i n s s p e n t m o r e t i m e g r a z i n g

a n d r u m i n a t i n g t h a n s i ng l e s b u t t h e y h a d s h o r t e r i d l i n g mea l s . H o w e v e r , e v e n

i f m a s t i c a t i o n t i m e d u r i n g g r a z i n g of t h e f o r m e r w a s s i g n i f i c a n t l y l o n g e r t h a n

t h a t of t h e l a t t e r , d i f f e r e n c e s r e m a i n e d l i m i t e d i n a b s o l u t e t e r m s (44 m i n /

d a y ) .

I n t h e s a m e way, ewes n u r s i n g two l a m b s s p e n t m o r e t i m e g r a z i n g pe r day,

w i t h l o n g e r i n t e n s i v e m e a l s a n d s h o r t e r i d l i n g m e a l s t h a n m o t h e r s of s ing le

l a m b s , a n d t h e i r m a s t i c a t i o n t i m e d u r i n g g r a z i n g w a s 112 m i n l o n g e r p e r da y

t h a n t h a t o f t h e l a t t e r .

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TABLE 7

Average feeding activities of artificially fed lambs according to level of milk supply (min/day)

Milk level Milk level effect (H/B)

High Low

Number of days, lambs 25 16

Total time Intensive meals 266 __ 127 327 _+ 94 NS 1 Idling meals 168__ 120 142 +_ 103 NS Rumination 334 _+ 101 358 +_ 68 NS

Mastication time during grazing 245 _+ 87 281 _+ 50 NS

1NS = not significant.

Effects of milk level on feeding behaviour of artificiaUy reared lambs. Time spent grazing and ruminating by artificially reared Iambs was not significantly af- fected by milk level. If LAR lambs had longer intensive meals and shorter idling meals than H A R ones, differences were not significant and on average their mastication t ime during grazing was only 36 min longer per day (Table 7).

DISCUSSION AND CONCLUSIONS

The results obtained in the present s tudy agree with most data in the liter- ature. Distances between animals tha t we observed (9 to 13 m between alien animals) were smaller in absolute terms than reported by Arnold and Dudzin- ski (1978). But paddocks grazed in our experiments were very small (1500 m 2 ) and we used Ile de France animals which are Merinos crossbred and are known for their strong group cohesion. Distances between ewes and lambs are similar to those reported by Morgan and Arnold (1974) and Arnold and Grassia (1985).

The greater distances between adults among the T M R and, to a lesser extent SMR, than in the F H A R group may be due, according to Arnold and Dudzinski (1978), to progressive reduction in the amount of grass available. The pastures provided to each group were identical but since requirements of ewes feeding two lambs were higher, these sheep had to explore a greater proport ion of their area. They thus spread out away from each other. In spite of this increased tendency to group dispersion in the M R group compared with AR, the lambs always remained close to their mothers, even in the case of twins, and could learn from them how to graze (Mat thews and Kilgour, 1979). This close rela- t ionship between adult and young existed only with the mother; the F H A R

130

lambs, which remained separate from alien adults, behaved in the same way as other AR lambs: same mean distance between lambs, high synchronisation of activities, very short distance to the creep-feeder and the same maize intake.

The short distance between mother and offspring resulted in synchronisa- tion of activities among individuals, much greater in our study than observed by Morgan and Arnold (1974). Once again, animal breed and pasture size which led to a reduction in distances between individuals may explain this result. It is particularly true for maize intake; when ewes exploited their whole field, they were often at a considerable distance from the maize distributor and lambs who remained close to their mothers consumed much less maize than the AR group. For the latter, the maize distributors constituted a point of attraction for the lambs, due to the maize but also as windbreaks; and consumption by these groups became considerable (400 to 500 g/day on average) while grazing time was correspondingly reduced.

Close to the mother during her movements and activities, suckling lambs based their activities on those of their dams. Their mastication time during grazing was very similar to that of their mothers (397 and 376 min/day for lambs and ewes in the SMR group, 441 and 488 min/day in the TMR), 60% more than the corresponding values observed with AR lambs. Grazing time of ewes increased with their level of production (152 min more for ewes with 2 lambs compared with singles in May, 81 min in June). These values are higher than given by Arnold and Dudzinski (1978) (0.6 to 1.3 h/day) but are similar to those we obtained earlier (Dulphy et al., 1979:2 h/day). The differences between lambs are smaller, 44 min intake mastication more for twins than for singles and the same level as those observed between the HAR and LAR groups (36 min).

The lamb's grazing behaviour thus does not depend only on the level of sat- isfaction of its requirements. If the lambs which had little milk available con- sumed more grass, this resulted from different factors such as metabolic reg- ulation or social behaviour.

Doney et ai. (1984) and Penning and Gibb (1979) observed an increase of grass DM intake when milk supply was reduced and from their results one can consider this difference as a regulation: the lambs eat more grass because they are hungry. In fact, if we observed such a difference (LAR lambs spent 40 min more per day grazing than HAR, and TMR 36 min more than SMR ) it was not sufficient to allow lambs fed at low milk level (LAR and TMR) to com- pensate the energy deficit. Then, in both situations, this regulation seemed inefficient and, moreover, did not appear for maize consumption (same amount for LAR and HAR lambs and less for TMR than for SMR).

Much more important were differences between MR and AR lambs (150 to 190 rain/day). The first ones were led by their mothers, while the latter had no model to copy even in the FHAR group. Moreover, if twins spent more time

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graz ing t h a n s ingles t h a t could also resu l t f r o m ewes ' b e h a v i o u r d i f fe rences ( the twin-suck l ing ewes spend ing more t i m e grazing t h a n s ingle-nurs ing ewes ).

D i f f e r e n t p rac t i ca l conc lus ions can be d r a w n f r o m these results: (1) W h e n l a m b s a t p a s t u r e are c reep- fed , the t r oughs m u s t be p laced n e a r

c a m p i n g s i tes or w a t e r i n g po in t s , or d i spersed over t he p a d d o c k in o rder to reduce the i r ave rage d i s t ance f r o m the ewes a n d the i r l a m b a n d to m a k e con- c e n t r a t e c o n s u m p t i o n easier .

(2) C o n t r a r y to conc lus ions b y Z y g o y a n n i s e t al. (1982) a n d D o n e y et al. (1984) , ar t i f ic ia l ly fed l a m b s are no t good mode l s for s tudies on graz ing l a m b m a n a g e m e n t .

REFERENCES

Arnold, G.W. and Dudzinski, M.L., 1978. Ethology of Free-ranging Domestic Animals. Elsevier, Amsterdam, xii + 198 pp.

Arnold, G.W. and Grassia, A., 1985. Spatial relationship between ewes and lambs. Appl. Anim. Behav. Sci., 14: 253-261.

Doney, J.M., Smith, A.D.M. and Sim, D.A., 1984. Milk and herbage intake of suckled and artifi- cially reared lambs at pasture as influenced by lactation pattern. Anim. Prod., 38: 191-199.

Dulphy, J.P., Raymond, B. and Theriez, M., 1979. Ingestive behaviour and related activities in ruminants. Proc. 5th Int. Syrup. Rumin. Physiol., Clermont-Ferrand, Ch. 5, pp. 103-122.

Ewbank, R., 1967. Nursing and suckling behaviour amongst Clun Forest ewes and lambs. Anim. Behav., 15: 251-258.

Joyce, J.P. and Rattray, P.V., 1970. The intake and utilization of milk and grass by lambs. Proc. N.Z. Soc. Anim. Prod., 30: 94-105.

Langlands, J.P., 1972. Growth and herbage consumption by grazing Merino and Border Leicester lambs reared by their mothers and fostered by ewes of the other breed. Anim. Prod., 14: 317- 322.

Matthews, L.R. and Kilgour, R., 1979. Learning and associated factors in ruminant feeding be- haviour. Proc. 5th Int. Syrup. Rumin. Physiol., Clermont-Ferrand, Ch. 6, pp. 123-144.

Morgan, P.D. and Arnold, G.W., 1974. Behavioural relationships between Merino ewes and lambs during the four weeks after birth. Anim. Prod., 19: 169-176.

Penning, P.D. and Gibb, M.J., 1979. The effect of milk intake on the intake of cut and grazed herbage by lambs. Anim. Prod., 29: 53-67.

Zigoyannis, D., Sim, D.A., Smith, A.D.M. and Doney, J.M., 1982. The behaviour of suckled and artificially reared lambs at pasture. Scientific Yearbook, Vet. Faculty, Thessaloniki, 21, pp. 2- 12.

RI~.SUMI~

Bechet, G., Th&iez, M. and Prache S., 1989. Feeding behaviour of milk-fed lambs at pasture. Small Rumin. Res., 2:119-132 (en anglais).

Une exp&ience a ~t~ conduite, deux armies successives, au p~turage avec quatre lots d'agneaux Ile de France allaitSs soit par leur m~re (SMR et TMR: un ou deux agneaux sous la mbre), soit artificiellement avec deux niveaux de lait (HAR et LAR pour haut et bas niveau). La premiere annie la comparaison comprenait un cinquibme lot compos~ d'agneaux au lait artificiel haut ni-

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veau et des brebis dtrang~res (FHAR). Les agneaux avaient libre acc~s ~ du ma'is. La consom- mation de ce ma'is et la vitssse de croissance des agneaux furent mesurdes. On a observ~ les activitds des diffdrents types d'animaux durant le p~turage et on a enregistrd avec un appareil dlectronique leurs activitds alimentaires.

Les agneaux des lots SMR et HAR ont montr~ des performances similaires, et des gains de poids de la naissance au sevrage ~ 120 jours, supdrieurs ~ ceux des lots TMR et LAR. Le poids au sewage rut de 39 kg pour les premiers et de 35 pour les seconds.

La consommation de maYs a varid selon le type d'allaitement pour les maternels (10,7 kg pour SMR contre 5,4 pour TMR) mais non selon le niveau de lair pour les artificiels (29,1 kg pour HAR contre 29,4 pour LAR).

Les agneaux ~levds par leur m~re restent pros de celle-ci et pr~sentent plus de temps actif fringes- tion d'herbe que ceux ~levds artificiellement (417 min/jour contre 259 min/jour). Les brebis al- laitant 2 agneaux passent plus de temps actif d'ingestion clue celles n'en aUaitant qu'un (+ 112 min/jour) et les agneaux doubles ~galement plus de temps actif que les simples ( + 44 min/jour). Pour les artificiels il y a ~galement influence du niveau de lait sur le temps actif d'ingestion ( + 36 min/jour pour le bas niveau) mais dans rensemble ils passent 158 rain de moins ~ p~turer par jour que les maternels.

L'influence de la m~re sur le comportement alimentaire de l'agneau au p~turage est ainsi raise en 4vidence et discutde.