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Journal of Veterinary Behavior 9 (2014) 132e135

Journal of Veterinary Behavior

journal homepage: www.journalvetbehavior .com

Short Communication

A note on the effect of number (single or twin) and sexof contemporary siblings on male-like play behavior of lambs(Ovis aries)

Reyes Vázquez, Agustín Orihuela*, Virginio AguirreFacultad de Ciencias Agropecuarias, de la Universidad Autónoma del Estado de Morelos, Cuernavaca, Morelos, México

a r t i c l e i n f o

Article history:Received 22 November 2011Received in revised form31 January 2014Accepted 31 January 2014Available online 12 February 2014

Keywords:social interactionsjuvenilesexual behaviorSuffolk sheepmounts

* Address for reprint requests and correspondenceultad de Ciencias Agropecuarias, de la Universidad Aelos, Av. Universidad 1001, Colonia Chamilpa, CuernaTel: þ52 777 3297046.

E-mail address: aorihuela@uaem.mx (A. Orihuela)

1558-7878/$ e see front matter � 2014 Elsevier Inc.http://dx.doi.org/10.1016/j.jveb.2014.01.003

a b s t r a c t

This study evaluates the effect of the number and sex of contemporary siblings on male-like playbehavior of Suffolk lambs (Ovis aries). Fourteen males and 14 females, all single born, plus 26 ram lambsborn co-twin to another male (n ¼ 14) or female (n ¼ 12) as well as 26 ewe lambs born co-twin toanother male (n ¼ 12) or female (n ¼ 14) were observed daily for 7 weeks from 1 week of age. Twoobservers sitting outside a sand-bedded pen (10 � 5 m) recorded received and performed behavior(butts, nudging, attempts to mount, and mounts) by the lambs in the pen from 08:00 to 09:00 and 16:00to 17:00 hours. Animals were in the pen only during the observation periods; the rest of the day theyremained with their mothers in individual pens. Male-like play behavior patterns were displayed by bothmale and female lambs. Males were more active (P < 0.05) than females. Butting was the most frequentactivity and performed mostly by ram lambs, recipients were generally males, and most resulted inreciprocal simultaneous encounters (sparring). Single males performed most of the nudging activity,which was the least frequent of the observed behaviors. Males with twin brothers mounted significantly(P < 0.05) more than males with twin sisters, and females with twin sisters performed the lowestamount of gutting and nudging. Lower (P < 0.05) levels of activity were found during the first 2 weeks.Overall, it was concluded that male lambs performed and received more male-like play behaviors thanfemale lambs and the influence of sex of contemporary sibling was restricted to some behaviors: buttingand nudging in females and mounting in males.

� 2014 Elsevier Inc. All rights reserved.

Introduction

Male-like play behavior has been reported in both male andfemale lambs (Thwaites, 1982; Orgeur, 1995). The fetal brain is atarget site for circulating steroid hormones (Roselli et al., 2006),suggesting that in sheep, some masculinization occurs normally inthe female during development.

Male domestic sheep have significant prenatal levels of circu-lating androgen (Kauffman, 2009), sufficient to masculinize notonly their own phenotype but also in some cases that of their fe-male twins (Szatkowska and Switonski, 1996) although their ju-venile behavior has yet to be described. Masculinization may reach

: Agustín Orihuela, PhD, Fac-utónoma del Estado de Mor-vaca, Morelos 62210, México,

.

All rights reserved.

the female tubular reproductive tract by way of vascular connec-tions between the placentas of the developing heterosexual twinfetuses XX/XY chimeras progresses. These so-called freemartinewes may show genital and other morphological virilization, aswell as masculine social behavior in adulthood (Short, 1974). Theincidence of ovine freemartins has been reported as approximately1% (Parkinson et al., 2001; Padula, 2005).

The purpose of the present study was to generate quantitativedata on the male-like play behavior of Suffolk sheep while evalu-ating the possible effect of the number and sex of contemporarysiblings on performed and received activities during early life.

Materials and methods

The experiment was conducted in a research center in Morelos,Mexico, located at 18� 370 N and 99� 190 W. Observations weremadeduring the natural lambing season in ewes whose parturitions hadbeen synchronized.

Table 1Mean (�standard error) number of acts (mounts, mount attempts, butts, and nudging)/animal/hour of observation

Behavior Twins Singles

Female with twinbrother (n ¼ 12)

Female with twinsister (n ¼ 14)

Male with twinbrother (n ¼ 14)

Male with twinsister (n ¼ 12)

Female (n ¼ 14) Male (n ¼ 14)

MountsPerformed 5.0 � 1.8a,B 9.0 � 7.0a,A,B,C 37.7 � 11.7b,D 20.0 � 5.5a,C 2.0 � 0.6a,A 34.2 � 8.2a,D

Received 17.0 � 4.3b,B,C 7.8 � 1.9a,A 13.0 � 1.7a,B 20.0 � 4.1a,C 10.6 � 1.9b,A,B 27.9 � 10.6a,C

Attempts to mountPerformed 2.0 � 0.5a,A 5.0 � 4.0a,A,B 16.0 � 5.0a,C 11.0 � 2.5a,B,C 2.3 � 0.5a,A 21.9 � 5.4a,C

Received 12.0 � 2.5b,B 7.0 � 2.4a,A 9.0 � 5.0a,A,B 5.3 � 0.9b,A 6.8 � 1.4b,A 12.9 � 2.9a,B

ButtsPerformed 20.5 � 9.6a,B,C 6.5 � 3.2a,A 41.3 � 7.0a,C 38.8 � 14.9a,C 13.0 � 2.9a,A,B 70.2 � 18.2a,D

Received 26.3 � 11.7a,B,C 13.0 � 3.1a,A 39.7 � 3.3a,C 37.8 � 5.3a,C 22.2 � 3.1b,B 51.9 � 8.7a,C

NudgingPerformed 2.0 � 0.5a,B 1.0 � 0.0a,A 3.5 � 2.5a,A,B 4.0 � 1.3a,B 2.0 � 0.6a,B 15.1 � 6.3a,C

Received 5.5 � 2.1a,A,B 4.0 � 1.8a,A,B 3.0 � 0.0a,A 8.0 � 4.0a,B 7.3 � 2.3b,B 6.8 � 1.8a,B

Different superscript letters indicate statistical effect (P < 0.05) between performed and received activities.Different superscript capital letters indicate statistical effect (P < 0.05) among values in the same row.

R. Vázquez et al. / Journal of Veterinary Behavior 9 (2014) 132e135 133

Eighty ewes were housed in individual pens (2.0� 3.0 m) wheretheir offspring were born. Lambs were marked with large identi-fying numbers on their flanks and kept in the pens with theirmothers and siblings until weaning (60 days). When the ewe had 2offspring, only 1 (always the same) was used in the experiment.Fourteen males and 14 females, all single born, and 26 ram lambsborn co-twin to another male (n ¼ 14) or female (n ¼ 12) as well as26 ewe lambs born co-twin to another male (n¼ 12) or female (n ¼14) were used for the study.

Two observers sitting outside the sand-bedded pen (10.00 �5.00 m) recorded spontaneously occurring interactions from 08:00to 09:00 and 16:00 to 17:00 hours, daily for 7 weeks, beginningwhen lambs reached 1 week of age. Observer 1 dictated the activityto the observer 2, whowrote it down. In this way, observer 1 did notmiss any detail of the behavior performed at any time. All lambswere taken from their mothers’ pen to the observation enclosureand returned to their mothers’ pen after each observation period.This procedure was followed because release from confinement,social stimulation, and floor bedding are known to encourageplaying activity (Brownlee, 1984).

Activity was recorded for each animal and characterized aseither active or passive. These 2 categories were further subdividedinto the following activities: butting, nudging, attempting tomount, and mounting, defined as follows:

Butting involves hitting another lamb with the front and top ofthe head (Hurnik et al., 1995). Reciprocal butts were almostinvariably a frontal contact between the foreheads of the 2 lambs.No attempt was made to interpret which animal initiated the ac-tion. One-way butts were unreciprocated butts, usually directedtoward the head, but sometimes toward the shoulder, side, or,rarely, the rear of another lamb. Both reciprocal and 1-way buttswere considered in the same category.

Mounting involves the action of the lambs raising the front partof their body generally onto the posterior part of another lamb(Hurnik et al., 1995). Occasionally, mounts were directed to the sideor to the front of another lamb. However, all mounts observed wereincluded in the same category. The mounted lamb rarely stood stillfor the mounter. Hence, mounts were not maintained for long andthrusting or erection was not seen, although Górecki and Kieltyka(2012) reported occasional erection events.

Attempts tomount were similar to previously reported behaviorexcept that the mounter did not raise the front legs high enough tosupport themselves on the rump of the recipient.

Nudging consisted of 1 or more kick (forefeet used in a pawingmotion while standing parallel to other lamb), rubbing (the lamb

rubs head and shoulders along or under the partner’s flank), andlow stretch of the neck (Lynch et al., 1992).

The present study was carried out in accordance with The Codeof Ethics of the World Medical Association (Declaration of Helsinki,2013) for experiments.

Data were analyzed with the least square methods of theGeneralized Linear Model procedure using SAS/STAT (version 9.1;SAS Institute, Inc., Cary, NC) by SAS (1988) fitting a split plot withblocking of subjects (split block) model (Gill, 1978), under themodel:

Yijk ¼ mþ ai þ Dj þ ðaDÞij þ bkj þ ðabÞij þ ðabÞik þ ðDbÞjkþ ðaDbÞijk þ EðijkÞ:

The 80 lambs were paired (a) according to the type of birth(single or twin), the effect of sex on performing or receiving eachbehavior (D), and the effect of male-like play recorded daily andpooled by week for 7 weeks (b). In addition, a 1-way analysis ofvariance was used only with twin lambs to analyze for the effect ofsex of the sibling (Gill, 1978).

Results

Table 1 summarizes the results of the present study. Patterns ofmale-like play behavior were seen in both male and female lambs,although in general males weremore active (P< 0.05) than females,regardless of being single or twin and the sex of their sibling. Singlemales were found to be the most active generally.

Butting was the most frequent activity and performed pre-dominantly by ram lambs, and recipients were generally malesbecause most of them resulted in reciprocal butting encounters(sparring). Single males performed the bulk of the nudging activity,which was the least frequent of the behaviors observed (P < 0.05).

The proportion of female twins of males that mounted andattempted to mount was similar (P > 0.05) to that of the femaletwins of females. However, they differed (P < 0.05) in butts andnudging performed. Furthermore, females with a male twinreceived more (P < 0.05) mounts than females with a twin sister.

Although in general, males with twin brothers did not performmore activities than single males, and females with twin sisters didnot receive the highest number of behaviors as expected, maleswith twin brothers mounted significantly (P < 0.05) more thanmales with twin sisters, and females with twin sisters performedthe lowest amount of butting and nudging.

0

2

4

6

8

1 2 3 4 5 6 7

Acts

/ani

mal

/h

Butts

0

2

4

6

8

1 2 3 4 5 6 7

Acts

/ani

mal

/h

Weeks

Mounts

0

2

4

6

8

1 2 3 4 5 6 7Weeks

Attempts mount

0

2

4

6

8

1 2 3 4 5 6 7

Nudging

b

a

bb

b

bb

b

b

b b

aa

b

b

bb

b

aa

b

a

a

a

a

a

a

a

Figure 1. Mean (�standard error) frequencies of mounts, butts, attempts to mount, and nudging displayed by Suffolk lambs, pooled by week, during the first 7 weeks of age.

R. Vázquez et al. / Journal of Veterinary Behavior 9 (2014) 132e135134

Significant differences (P < 0.05) regarding the male-likebehavioral patterns recorded were found among the experimentallamb groups over time. Data pooled by week for 7 weeks areillustrated in Figure 1, where lower frequencies (P < 0.05) wereobserved during the first week (attempts to mount) and during thefirst and second weeks (nudging and mounts) compared with thefollowing weeks, in 3 of the behaviors evaluated. However, lambsdisplayed similar (P > 0.05) high frequencies of butting activityfrom the first week until the end of the study.

Discussion

In the present study, forms of male-like behaviors wereobserved in lambs of both sexes, which is consistent with previousfindings (Orgeur and Signoret, 1984; Orgeur, 1995; Górecki andKieltyka, 2012). Also male lambs performed more activities thanfemales, confirming the behavioral dimorphism reported previ-ously in domestic and wild sheep (Sachs and Harris, 1978; Berger,1980; Guilhem et al., 2006). It has been suggested that playbehavior contributes to the development of several functional skillsin the adult, with a delayed positive effect on individual fitness(Fagen, 1981). According to this hypothesis, coincident differencesin male-like play behaviors would be expected in those species inwhich sexual selection has led to substantial behavioral differencesbetween sexes. Interestingly, Guilhem et al. (2006) stated thatmouflon lambs of both sexes directed more interactions towardmales, whereas Górecki and Kieltyka (2012) did not observe apreference in either sex. Dissimilarities in these findings could beexplained at least in part by breed differences (Górecki andKieltyka, 2012) or by different approaches used to analyze andclassify behaviors.

Inwild and domestic sheep (Berger, 1980; Schubert and Scheibe,1993), sex-linked differences in social behavior are discernible asearly as the first day of life and are undoubtedly related to physi-ological differences (Le Pendu et al., 2000). Fetal and neonatalsteroids are involved in the differentiation of sexual behavior and

determine what behavior male or female will display at adulthood(Vom Saal, 1990). Furthermore, the fact that male patterns of playbehavior spontaneously exist in female lambs might be a result ofmaternal secretion of testosterone via the placenta (Orgeur, 1995).However, during the present work, the females born co-twin withmales showed no significant behavioral evidence of virilization.

Male-like play behaviors in lambs might be hormone dependentas has been demonstrated in rats (Hotchkiss et al., 2003), but if so,no obvious relationship appears to exist between these behaviorsand the secretion of testosterone during infancy in this species.Indeed, in male lambs, circulating levels of testosterone are verylow during the first weeks postpartum, a period when intensemale-like play behaviors are generally observed (Cotta et al., 1975).Nevertheless, it has been proposed that fetal testicular secretionsthat mediate sexual behavior differentiation (Vom Saal, 1990) couldexplain the higher frequencies of male-like play behaviors in malelambs. Taking this finding into consideration, it could be hypothe-sized that males born co-twin with another male would havedouble levels of testosterone in their prenatal environment whencompared with male lambs born single or co-twin with a female,whereas females born co-twin with males will also have higherlevels of testosterone than females born co-twin with females orfemales born single. This theoretical difference in hormone con-centrationmight affect male-like play behaviors during a number ofweeks postpartum.

According to the literature, the presence of a twinmalewould beexpected to increase the number of activities performed, whereasthe presence of a female would decrease the amount of behaviorsexhibited or perhaps increase the behaviors received. However, thiswas not the case in our study because single males performedmorebutts and nudging than males with twin brothers and females withtwin sisters did not receive the highest number of behaviors,although they tended to perform the lowest amount of activities,thus no clear evidence of influence of the sex of the sibling wasobserved. This apparent discrepancy might be because of at least 3factors; first, the development of strong preference for certain play

R. Vázquez et al. / Journal of Veterinary Behavior 9 (2014) 132e135 135

partners. Thompson (1996) found that 47% of infant sable antelopeshad 1 strongly preferred play partner regardless of the sex of thepreferred animal. This preference could mask other possible effectson play behavior, particularly those related with the sex of theselected partner and the frequencies of the activities displayed. Asecond possibility is based on physical characteristics. Single-bornram lambs are more vigorous as a result of their larger size andweight than twin-born sheep and therefore more active anddominant. This difference could help to explain our finding thatsingle male lambs were the most active animals. In addition, Hassand Jenni (1993) found that lambs of bighorn sheep preferred toplay with other juveniles close in age, probably as a result of similarstrength and skills. A third factor could be that although the sand-bedded pen and the congregation of all lambs were strong moti-vations to play, single-born male lambs could be more active alsobecause the observation period was for them the only opportunityto play with other lambs, whereas twins could play with theirsiblings at anytime.

In conclusion, circulating hormones possibly do not contributeto the sex differences or the development of male-like play be-haviors in lambs.

It was also found that encounters between individuals were notrandom because ram lambs tended to perform and receive morebutts and mounts than females. These results agree with Orgeurand Signoret (1984) who found that during infancy aggressiveinteraction was directed mainly toward males (64%). However,these authors also found that a higher proportion of nudging andmounts were directed toward females (57%), compared with males.This latter finding was not confirmed in the present study in whichfemales tended to receive less mounts than males, and there wasnot a clear tendency for nudging. Moreover, present findings do notagree with Orgeur (1995) and Guilhem et al. (2006) who found thatmale lambs were the only ones that “nudged.” However, in thepresent study, single males were found to perform most of thenudging activity. Also these earlier studies used different sheepbreeds that varied in their prolificacy and libido performance.Furthermore, former studies did not consider the effect of birthtype and sex of siblings as factors in their analysis.

Regardless of sex or the presence of a sibling, butting was thefirst and the most frequent behavior observed, followed bymounts,attempts to mount, and nudging, reaching their highest frequenciesbetween weeks 4-5 after birth. Results were similar to those re-ported by Orgeur (1995) who found that play behavior, mainlymale-like sexual behavior patterns, was observed at 4-8 weeks ofage.

Conclusion

It was concluded that male lambs performed and received moremale-like play behaviors than female lambs and the influence of sexof contemporary sibling was restricted to some behaviors: buttingand nudging in females and mounting in males. These resultscontribute to our body of knowledge on sex differences in theexpression of male-like play behaviors of lambs.

Acknowledgments

The authors are grateful to Dr. Jane Russell for her comments andcareful review of the manuscript.

Ethical considerations

The study has been carried out in accordance with The Code ofEthics of the World Medical Association (Declaration of Helsinki,

2013) for experiments, respecting animals’ life and withoutinducing any pain to the subjects.

Conflict of interest

The authors declare no conflict of interest. The idea for thearticle was conceived and the experiments were designed byAgustín Orihuela. The experiments were performed by Reyes Váz-quez. The data were analyzed by Virgino Aguirre. The article waswritten by Agustín Orihuela. The funding was provided by Uni-versidad Autónoma del Estado de Morelos.

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