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Effect of slope of lambing site on lambsslipping and lamb mortalityT .W. Knight b a , W. H. McMillan a , deceased R. Kilgour c , H. -U.P. Hockey d & D.R.H. Hall da Whatawhata Hill Country Research Station , MAFTech , PrivateBag, Hamilton , New Zealandb Flock House Agricultural Centre , Ministry of Agriculture andFisheries , Private Bag, Bulls , New Zealandc MAFTech Ruakura Agricultural Centre , Private Bag, Hamilton ,New Zealandd Whatawhata Hill Country Research Station , MAFTech , PrivateBag, Hamilton , New ZealandPublished online: 30 Jan 2012.

To cite this article: T .W. Knight , W. H. McMillan , deceased R. Kilgour , H. -U. P. Hockey & D.R.H.Hall (1989) Effect of slope of lambing site on lambs slipping and lamb mortality, New ZealandJournal of Agricultural Research, 32:2, 199-206, DOI: 10.1080/00288233.1989.10423454

To link to this article: http://dx.doi.org/10.1080/00288233.1989.10423454

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New Zealand Journal of Agricultural Research, 1989, Vol. 32: 199-206 0028-8233/89/3202-0199 $2.50/0 © Crown copyright 1989

199

Effect of slope of lambing site on lambs slipping and lamb mortality

T .W. KNIGHT*

W. H. McMILLAN

MAFfech Whatawhata Hill Country Research Station Private Bag, Hamilton, New Zealand

*Present address: Flock House Agricultural Centre, Ministry of Agriculture and Fisheries, Private Bag, Bulls, New Zealand

R. KILGOUR (deceased)

H. -U. P. HOCKEY

MAFTech Ruakura Agricultural Centre Private Bag, Hamilton, New Zealand

D.R. H. HALL

MAFfech Whatawhata Hill Country Research Station Private Bag, Hamilton, New Zealand

Abstract Two experiments were carried out to determine the effect of slope on lamb mortality. In Experiment 1, 166 Marshall Romney (MR), 170 conventional Romney (CR), and 59 MR X CR ewes were allocated to one of 17 lambing areas of 0.2-0.4 ha and uniform slope. Mean slopes ranged from 3 to 44 ° and each area was surrounded by electric netting fences. Ewes entered their respective lambing areas 2 days before the expected lambing date and remained there for 4-5 days. In Experiment 2, two 1 ha plots selected on the basis of conformity of slope (36--44°) and 100-120 m long were each divided into three equal lambing areas by fences down the slope. Barriers either 15 or 30 m apart were constructed of 33-cm-high woven polyethylene mesh across the

Received 29 August 1988; accepted 27 February 1989

slope on two of the three lambing areas in both plots. Lamb mortality in Experiment 1 was not affected by slopes up to 30° but there was a large increase in lamb mortality with slopes of 36--44° (19.4% lamb mortality for less than 30° versus 50.1 % lamb mortality for more than 30°). In Experiment 2, 83-90% of lambs slipped off the birth site and 68-70% of ewes followed their lambs down the slope. The barriers stopped only 60% of the lambs encountering them. The other 40% passed under or over the barriers. Barriers increased separation of twin lambs (39% no barriers versus 65% barriers). The incidence of ewes rearing both twins when the co-twins were separated soon after birth by 0-1 m, 2-4 m ,or greater than 4 m was 15/16, 1/5, and 0/18, respectively. MR ewes had a lower lamb mortality than CR ewes (17 versus 43%). Although there were no differences in the incidence oflambs slipping off the birth site (83% MR versus 89% CR), the MR ewes had a lower incidence of abandonment of lambs (20% MR versus 41% CR).

Keywords lambing; behaviour; Romney; Marshall Romney; slopes; lambs slipping; birth sites, lamb mortality; sheep; ewes

INTRODUCTION

Slipping of more than 80% of single- and twin-born lambs up to 35 m from their birth site has been observed on steep hill country (Kilgour& de Langen 1980; Kilgour et a1. 1982). Ewes followed many of these lambs down the slope but 40% of lambs were abandoned (Kilgour etal. 1982). However, the degree of slope on which a ewe can lamb without the lamb slipping from the birth site is unknown.

Loss of lambs is also affected by breed. Marshall Romney (MR) ewes have been selected for lamb survival on hill country (Mackereth 1979). Knight et a1. (1988) found MR ewes had higher lamb survival than conventional Romney (CR) ewes. These workers, however, lambed their ewes on slopes less than 24° to facilitate recording and collection of

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dead lambs. Based on a small number of ewes (10 MR and 13 Romney) Kilgour & de Langen (1980) reported a superior perinatal behaviour of MR compared with Romney ewes on steep hill country. Thus differences in lamb survival between MR and CR ewes may be greater for ewes lambing on steep hill country.

The aims of the two experiments reported in this paper were to determine lamb mortality and slipping of lambs from their birth sites with increasing slope of the lam bing paddocks, to determine if barriers 15 or 30 m apart across the slope would reduce the distance lambs slipped and increase lamb survival, to compare the lamb survival of MR and CR ewes lambing on steep slopes, and to obtain further information on the effects of slope on the behaviour over lambing of both the ewe and lambs.

MATERIALS AND METHODS

Animals

The 3- to 7-year-old MR and CR ewes and the 2-year-old MR x CR ewes have been described by Knight et aI. (1988). Oestrous cycles were synchronised using vaginal pessaries containing 60 mg medroxyprogesterone acetate. MR and CR ewes were mated with rams of t)1eir respective strains and MR x CR ewes were mated with CR rams. Only ewes conceiving over a 2-3 day period were selected for the experiments. All ewes were X-rayedat95-120 days of gestation to determine the number of foetuses each ewe carried (Owen & Armstrong 1985). Those with three or more foetuses were excluded.

Lambing areas

Lambing areas were selected for their uniformity of slope, although on the steeper slopes (i.e., above 30° slope) there were sheep tracks, flat areas of up to 1.5 m wide, and vertical drops of 1 m. Slopes were measured using a clinometer. Electric netting fences were used to enclose the lambing areas. All streams and flat banks of streams at the bottom of the slopes were excluded from the lambing areas.

Observations

Lambing areas were cleared of scrub and could be clearly viewed from vantage points outside the lambing areas. Photographs and diagrams of each lambing area facilitated marking of lambing sites and plotting of where lambs slipped. White pegs, placed 10 m apart along the perimeter fences and down the middle of each lambing area, assisted in

the estimation of distances. Observations commenced at dawn and continued until dusk each day. The birth sites and slipping oflambs born overnight could not always be determined, but by using the information on the expected number of lambs born to each ewe, it was possible to allocate lambs to dams.Lambing observations continued for 4-5 days by which time most ewes had lambed. Ewes and lambs remained in their lambing areas for another 4-5 days. Checks for dead lambs were made 3 times a day. At the end of each lambing period ewes and lambs were gathered together into one flock.

Lambing

In Experiment 1, ewes entered their respective lambing areas 2 days before the expected peak of lambing (i.e., Days 146-148 of gestation, Knight et al. 1988). In Experiment 2, lambing was induced by the intramuscular injection of 16 mg of dexamethasone (Dexadreson; Intervet), when the ewes were 142-144 days of gestation (Bosc 1972). Ewes entered their respective lambing areas on the day before the expected peak of lambing.

Ewes were coded using large stripes of coloured raddle sprayed across their head, shoulders, and rump. Ewes lambing, location of birth site, and number of lambs born were recorded. Lambs that had not sucked for at least 4 h and had no ewe, either their own dam or another ewe, showing an interest in

Table 1 Mean slope and size, and number of ewes lambing on the 17 lambing areas included in the three periods of Experiment 1.

Lambing Mean Size No. area slope (ha) ewes

Period 1 1 3° 0.28 22 2 15° 0.21 17 3 15° 0.40 29 4 24° 0.25 19 5 27° 0.20 13 6 44° 0.24 22

Period 2 7 18° 0.40 33 8 22° 0.30 25 9 27° 0.30 24

10 36° 0.32 27 11 38° 0.36 29 12 40° 0.20 22

Period 3 13 5° 0.30 22 14 15° 0.33 24 15 15° 0.40 29 16 28° 0.30 19 17 44° 0.24 19

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Knight et al.-Effect of slope of lambing site on lamb mortality 201

them were removed and artificially reared. Lambs slipping under or getting entangled in the surrounding flexi-net fences were returned to their mothers when the ewe had followed the lamb down to the fence or were removed and artificially reared when the ewe had made no attempt to retrieve the lambs. Lambs which were taken away to be artificially reared were recorded as being dead with cause of death being mis-mothering. Dead lambs were removed each day and autopsied to assess the cause of death. At the end of each day's observations, lambs which had been accepted by a ewe were weighed, ear-tagged, and marked with a coloured raddle. Recently born lambs were left until the next day so as not to disturb the ewe-lamb interactions.

Experiment 1 One hundred and sixty-six MR, 170 CR, and 59 MR X CR ewes, which were mated over three periods, were randomly allocated within strain and age of ewe and number of foetuses to one of 5-6 lambing areas in each lambing period. Each of the 17 lambing areas varied in slope and each area was used once. Table 1 presents the slope and size of each lambing area, and the number of ewes in each area. Slopes

ranged from 20 to 60 m long. Peak lambing for Periods 1,2, and 3 were respectively 31 August-2 September, 14-16 September, and 16-18 September.

Experiment 2 Two 1 ha plots of uniform slope were divided into three equal-sized lambing areas. Plot 1 had an easter! y face with a slope of 38-44°and 100 m long. Plot 2 had a northerly face with a slope of 36-400 and 120 m long. Barriers 15 and 30 m apart were erected across the slopes in two of the lambing areas in each plot. These were constructed of 33-cm-wide woven polyethylene mesh which was stapled to wooden pegs 1 m apart, along sheep tracks which ran across the slopes.

On 30 August, 24 MR and 23 CR ewes, and on 14 September, 18 MR and 28 CR ewes, were randomly allocated within strain and age of ewe and number of foetuses to one of the three lambing areas in Plots 1 and 2, respectively. The peak of lambing in Plots 1 and 2 were 2 and 15 September, respectively, and because of the dexamethasone injection, most of the ewes lambed over an 18-h period.In addition to the recording of lamb deaths and slippage of lambs, records were kept of the

Table 2 Number of lambs in analysis of each trait recorded in Experiment 2 and mean values from regression models for lambs born to Marshall Romney (MR) and conventional Romney (CR) ewes, and singles and twin lambs.

No. of Slrain of ewe Birth rank lambs MR CR single twin

% lamb mortality 127 17 43 30 34

** % lambs observed to slip 71 83 89 90 83 % of lambs abandoned

by dams at birth 127 20 41 14 40

*** *** % of co-twins separated 50 44 87

SED 0.1 0.1 Birth weight (kg) 136 4.3 4.0 4.8 3.5

SED 0.1 0.1 Mean distance slipped (m) 59 13 16 14 15

SED 3.1 3.3 Mean distance separating

lamb and dam (m)a 40 14 30 27 18 SED 7.2 10.2

Mean distance syparating co-twins (m)b 30 12 12

loge 2.49 2.48 SED 0.2

a only includes lambs separated from their dams. b only includes co-twns that were separated. ** = P<O.Ol; *** = P<O.OOI.

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202 New Zealand Journal of Agricultural Research, 1989, Vol. 32

A B 70 60

60 50

~ 50 OJ

~ .§ 40 OJ

g 40 ro t:: 0 E

.r: 0 E .~ 30

E .0 30

E ~

20

I c ·220 ro 2: b'l

10 10

0 0

0 10 20 30 40 50 0 10 20 30 40 50

Slope (0) Slope (0)

Fig. 1 Effect of slope of the lambing area on (A) lamb mortality and (B) starvation-mismothering. The raw mean for each of the 17 lambing areas is indicated by open circles and curves are fitted from logit models.

incidence of lambs being abandoned at birth, of lambs being adopted by other ewes, of ewes following lambs down the slopes, of lambs being permanently separated from their dam and/or their co-twin, and whether or not the ewe had an adopted lamb with her at the birth of her own lamb. Lambs were considered to be permanently separated from their dam and/or co-twin when the observer judged that the two would not get together again because of the large distance between the lambs and/or ewe, or because a lamb was being cared for by another ewe.

Statistical analysis All data were analysed using either linear regression or logit models. First-order interactions were tested in the initial models but were then excluded if they were not significant. Values for the various traits in the tables are fittedmeans from the respective models which include all the main effects.The percentage lamb mortality was calculated from the number of lambs dead at weaning per 100 lambs born and the percentage starved-mismothered was calculated from the number of lambs diagnosed as dying from starvation-mismothering per loo lambs born. In Experiment 2, there were different numbers of lambs present for each trait because of incomplete records on some lambs born overnight or just before dusk. Table 2 presents the number of lambs included in each analysis. The distance between co-twins was analysed after the natural log transformation of the data.

Meterological data Information on temperatures, wind speed, and rainfall was collected twice dail y from the Research Station's meterological unit.Over the period of Experiment 1, the weather was mild. The daily average (± SD) minimum, maximum, and mean temperatures were 4.9 ± 2.9°C, 13.8 ± 1.8°C, and 9.3 ± 1.9°C, and the wind speed averaged 5.5 ± 2.0 km/h. There was only 1 day of rain, when 6.5 mm fell. The weather was warmer over the period of Experiment 2 but it was also wetter and windier. The average (± SD) minimum, maximum, and mean temperatures were 6.9 ± 3.4°C, 14.5 ± 1.1°C, and 10.7 ± 2.l oC, respectively. The 24-h wind run averaged 14.8 ± 5.4 km/h and 1.8 ± 4.3 mm rainfall fell per day.

RESULTS

Experiment 1 Over the three periods of lambing, the birth of 355 lambs was recorded on the 17 plots. The raw unadjusted mean lamb mortality and starvation­mismothering are presented for each of the 17 plots in Fig. I. Lamb mortality included lamb deaths from dystocia, infection, and pre-natal deaths which may not have been directly affected by slope of the lambing area. Deaths from starvation-mismothering were more likely, however, to be directly attributed to the effects of slope where slipping of the lamb from the birth site resulted in lambs failing to be reared. There were significant (P<O.OOI) effects

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Knight et al.-Effect of slope of lambing site on lamb mortality 203

Table 3 Response of Marshall Romney (MR) and conventional Romney (CR) ewes to lambs slipping off the birth site.

Single lambs Twin lambs One sliEs Both slip

MR CR Total MR CR Total MR CR Total

Total no. ewes 9 11 20 6 3 9 8 8 16 Ewe follows lamb 8 6 14

Abandons co-twin 2 1 3 1 5 6 Does not abandon co-twin 2 0 2" 4 2 6

Ewe does not follow lamb Lost sight of lamb 0 2 2 0 0 0 1 1 2 Ewe has pirated lambs 1 3 4 0 0 0 2 0 2 Stays with co-twin on birth site 2 2 4

" One ewe gave birth to second lamb after moving down to slipped lamb while the other ewe moved the slipped lamb back to the birth site.

(quadratic) of slope on lamb mortality and starvation­mismothering, with an additional significant (P<0.05) negative effect of birth weight on the latter trait.

It is apparent from Fig. 1 that slope only affected lamb mortality and starvation-mismothering at slopes greater than about 30°. When the data were reanalysed with the plots grouped into those with slopes greater than or less than 30°, there was no further effect of slope (linear or quadratic). Lamb mortality was 19.4% for lambing areas with. slopes less than 30° and 50.1 % for lambing areas with slopes greater than 30° (P<O.OOI). The respective values for starvation-mismothering were 4.8 and 38.5% (P<O.OOI). Despite suggestions from observations over lambing that the effects of slope on lamb mortality should be greater in twin-born than single­born lambs, the interaction between slopes greater or less than 30° and birth rank was not significant (19 and 20% lamb mortality for single- and twin-born lambs on slopes less than 30°, and 46 and 63 % for slopes greater than 30°).

After including slope in the analysis, there were no significant effects of the 17 lam bing areas or three lambing periods on lamb mortality or starvation­mismothering. Differences in lamb mortality between strains of ewes (25% for MR, 33% for CR, and 22% for MR X CR ewes) and birth rank of the lambs (25% for single and 33% for twin lambs) were not significant. Similarly for % starvation-mismothering, there were no effects of strain of ewe (13% for MR, 20% for CR, and 7% for MR X CR ewes) or birth rank (14% for single and 17% for twin lambs).

Experiment 2 There were no differences in the results between the two plots and data for the plots have been combined for the rest of the analyses.

Lamb mortality and slippage

Twenty-three of 42 MR and 26 of 51 CR ewes lambing produced twins and the remainder produced singles. MR lambs were 0.3 kg heavier (P<0.05) than CR lambs and single-born lambs were 1.3 kg heavier (P<O.OOI) than twin-born lambs.

The barriers were ineffective at stopping lambs from slipping. Only 60% of lambs coming into contact with the barriers were prevented from slipping further down the slope. Most of the remaining 40% oflambs wriggled under the barriers, although a few went over the top of the barriers, and continued sliding down the slope. Barriers failed to reduce the incidence and distance the lambs slipped and had no effect on percentage lamb mortality (24 % no barriers, 27% for 15 and 30 m barriers). The only effect they had was to increase (P<0.05) the proportion of co­twins that became separated from 39% on the control slopes to 65% on the slopes with barriers.

Lamb mortality was 17 and 43% for MR and CR ewes, respectively (P<O.OI) and 30 and 34% for single- and twin-born lambs, respectively (P>0.05) (Table 2). This included one single MR and five CR (four single-and one twin-born) lambs which died at birth. These deaths were unlikely to have been associated with the slopes and when they were excluded from the analysis, the mortalities were 15 and 37% forMR andCR ewes, respectively (P<O.OI) and 19 and 33% for single- and twin-born lambs, respectively. At these steep slopes there was no relationship between lamb mortality and birth weight.

Eighty-seven percent of lambs slipped off their birth site but there were no differences between MR and CR lambs or between single- and twin-born lambs in the incidence or distance lambs slipped off the birth site (Table 2). Although most ewes followed

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their lambs down the slope, the incidence of permanent separation of the lambs from their dams as a result of slipping from the birth site and abandonment at birth was significantly higher (P<O.OOI) for CR than MR ewes and it was higher (P<O.OOI) for twin- than single-born lambs (Table 2). Of those lambs abandoned at or after birth by their dam, 74% died or would have died if not assisted compared with 6% of lambs not abandoned at birth (P<O.OOI). The mean distance separating lambs and their dams at the end of the slippage process in CR was approximately twice that for MR (P<0.05). For twin lambs separated at birth by slipping off the birth site, the mean distance between co-twins was 12 m and in both MR or CR lambs.

Ewes' response to lambs slipping Incidents involving lambs slipping were closely monitored for 20 single- and 25 twin-bearing ewes (Table 3). In 70% of situations of slippage of single lambs and 68% for twin lambs, the ewe followed at least one of the lambs down the slope. The main reasons for ewes not following the lamb was where a ewe was already rearing another ewe's lamb or the ewe lost sight of the slipped lamb and stayed on the birth site (Table3). In 419 of the instances of one twin lamb slipping off the birtil site, the ewe stayed on the birth site with the co-twin.

For six ewes in which both twin lambs slipped off the birth site, the lambs ended up close together and the ewes followed the lambs down the slope and mothered both lambs. One twin-bearing MR ewe followed her first-born lamb down the slope and gave birth to the second lamb close to the final resting site of the slipped lamb. Another twin-bearing MR ewe shepherded its lamb, which had slipped 4 m down the slope, back up to the birth site where the co-twin had been born.

The numbers of ewes of each strain were too small to detect any difference in the response of MR and CR ewes to slipping of the lamb (Table 3).

Separation of co-twins by more than 1 m usually resulted in the abandonment of one of the lambs. There were 39 twin-bearing ewes which had one or both lambs slipped off the birth site but the ewes reared at least one of the lambs. When the co-twins were separated by 1 m or less, 15/16 ewes reared both lambs; when co-twins were separated by 2-4 m, 1/5 ewes reared both lambs; and for co-twins separated by more than 4 m none of the 18 ewes reared both lambs. Where the co-twins were separated by 2-4 m it appeared to the observers that the ewes were generally aware of the presence of their

separated lamb but usually would not attempt to get the twins together; they appeared to be satisfied with the one lamb.

Stealing of other ewes' lambs Most un lambed and newly lambed ewes showed initial interest in lambs which slipped close to them. In some instances ewes walked 10-15 m to investigate a slipped lamb, especially if the lambs were vocal. The ewes sniffed and nudged the lambs. In tum the lambs showed interest in these ewes and if the lamb's own dam did not come down to retrieve it, the lamb followed these ewes. Most of these ewes soon lost interest in the slipped lambs and forcibly discouraged the lambs' attention.

Six ewes (three MR and three CR) adopted lambs up to 24 h before lambing themselves. Another three ewes (one MR and two CR) adopted or exchanged lam bs immediately after the birth of their own lambs. Of the 11 lambs adopted by these nine ewes, 4 died. In tum, these nine ewes gave birth to 12 lambs and 9 died (75%) compared with 20% of lambs dying for those born to ewes not adopting a lamb (P<O.OI).

DISCUSSION

Slipping of lambs from the birth site would be a major factor contributing to lamb mortality in flocks of ewes lambed on slopes greater than 30°. The lack of lambing areas with slopes between 28 and 36° prevented a more exact determination of when slope influenced lamb survival and whether there was a linear increase in lamb mortality as the slope increased above 28°.

The weather conditions were mild with little rain during the experiments. Although wet conditions may make the slopes more slippery, it is unlikely to decrease the slopeatwhich slipping oflambs becomcs a major problem. This is because most of the slipping of the lambs is associated with the lamb rolling and tumbling down the slope rather than sliding down the slope.

On slopes of greater than 36°, up to 87% of lambs slipped off their birth site. In both experiments, a large proportion of the ewes followed their lambs down the slope and the ewes and lam bs were reuni ted. These results are consistent with those of Kilgour et al. (1982) and Kilgour & de Langen (1980). The main reasons for ewes not following their lambs down the slope were that they had lost sight of their lambs, they had already adopted another lamb, or in

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Knight et al.-Effect of slope of lambing site on lamb mortality 205

the situation of twin lambs, the ewe stayed on the birth site with the co-twin that had not slipped. A major problem occurred with twin lambs where the ewe would follow one lamb and abandon the other. In Experiment 2, 44-87% of twin lambs became separated from their co-twin.

The barriers in Experiment 2 failed to completely stop the slipping oflambs down the slope. In fact, the separation of twins was higher in the areas with the barrier. This, together with the observation that the ewe will not follow a lamb down the slope if it loses sight of the lamb, suggests that lamb deaths could be higher on slopes covered with bracken and scrub than on cleared slopes. Even if barriers were completely effective at stopping the slipping of lambs, the results in Experiment 2 suggest the barriers would have to be 1-2 m apart. With separation of twins by more than 1-2 m, the ewe was unable or unwilling to bring the twins together again.

MR ewes were no better than CR ewes at preventing lambs slipping off the birth site but MR ewes were more willing to follow their lambs down the slope as indicated by the lower percentage of abandoned lambs and the smaller distance between the dam and lamb for the lambs that did become separated from their dams. Lamb mortality in Experiment 1 was only 8% lower for MR compared with CR ewes, which was simnar to the differences reported by Knight et al. (1988). In Experiment 2 where all the slopes were steeper than 30° and longer than in Experiment 1, the lamb mortality was 22% lower for MR than CR lambs, even when lambs dying from dystocia were excluded. The incidence of lambs dying from starvation-mismothering in Experiment 1 decreased with increasing birth weight. This, however, did not account for the difference in lamb mortality between MR and CR lambs despite the MR lambs being heavier than CR lambs at birth.

Observations of single- and twin-born lambs on the slopes suggested the difference in lamb mortality would be greater in twins on the steeper slopes because of the separation of co-twins and the inability of the ewe to mother both lambs. The lack of a significant interaction between slope and birth rank in Experiment 1 possibly arose because of the overall low number of twins born (106) especially on the five steeper plots (42). The 14% difference in the mortality of single- and twin-lambs after exclusion of lambs dying of dystocia was not significant in Experiment 2 but the incidence of separation from their dam and of abandonment of the lamb was 26% lower for single- than twin-born lambs.

Further experiments are needed to determine if steep slopes have a more detrimental effect on the

survival of twin- than single-born lambs. With the identification of single- and twin-bearing ewes using ultrasound being commercially available in New Zealand (Owen & Armstrong 1985), it may be possible to increase overall lamb survival by lambing the single-bearing ewes on the steeper paddocks and the twin-bearing ewes on the flatter paddocks (i.e., slopes less than 30°.

Only 26% of the lambs permanently separated from their own dam survived. These lambs were reared by other ewes which had adopted the lambs at or before lambing themselves. Although the survival rate of the adopted lambs was high (7/11), the survival rate of the lambs born to the ewes adopting a lamb was low (3/12). The worst situation was where a twin-bearing ewe adopted a lamb before parturition had started and subsequently abandoned her own lambs.

Adoption of lambs by ewes appeared to be higher on the steep slopes. This was because of the number of unmothered lambs wandering about the slopes and their bleating attracted unlambed ewes or the lambs had ended up on the birth site of a ewe in the process oflambing. This suggests a lower stocking rate oflambing ewes may be necessary on steep hill country than on the flat lambing areas to reduce the stealing of lambs by ewes.

Although no measurements were made of the time it took for lambs to be able to move about the slopes it appeared from observations over the two experiments that slopes were only a problem to lambs in the first 6-12 h oflife. McMillan & Knight (1985) found no effect of slope on lamb survival when the ewes and lambs were transferred to 36-40° slopes 24 h after birth of the lambs.

ACKNOWLEDGMENTS

We acknowledge the technical assistance of Miss K Bremner, and Messrs P. R. Lynch, I. Kitney, and A. Richards; and the patience of other staff of the Whatawhata Hill Country Research Station and the Ruakura Agricultural Research Station who assisted with the 0 bserv ations under difficult conditions.

REFERENCES

Bose, MJ. 1972: The induction and synchronization of lambing with the aid of dexamethasone. Journal of reproduction andfertility 28: 347-357.

Kilgour, R.; Alexander, G.; Stevens, D. 1982: A field study of factors interrupting bonding of ewes and twins. Proceedings of the Second Asia-Oceania Congress of Perinatology: 118-123.

Kilgour, R.; de Langen, H. 1980: Neonatal behaviour in sheep. pp. 117-121 in: "Reviews in rural science IV", Wodzicka-Tomaszewsks, M., Edey, T. N., Lynch, 1. 1. ed.

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McMillan, W.H.; Knight, T.W.; 1985: Effect of slope on lamb mortality. Proceedings of the New Zealand Society of Animal Production 45: 163-165.

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