Effect of sex and litter size of lamb on sucking behaviour.

Abstract

EFFECT OF SEX AND LITTER SIZE ON THE SUCKING BEHAVIOUR OF THE LAMB D.L. STAPLETON: G.N. HINCH,* C.J. THWAITES* and T.N. EDEY* SUMMARY Suckling behaviour was studied in 18 Border Leicester x Merino ewes rearing lambs by Suffolk sires (six male/female twin pairs; six each male and female singles). Observations were made during 3 h periods commencing at 0600 and 1530 h on each of two successive days when the lambs averaged 3, 14 and 28 days of age. No significant sex differences in live weight were recorded, nor were there any sex effects in the behavioural variables studied (frequency of, duration of and interval between sucklings and identity of the suckling initiator and terminator). The frequency of sucking bouts was significantly lower in twins than in singles at both 3 and 28 days of age, while the duration of sucking was longer with twins than with singles at 3 days of age (i.e. litter size x age interactions were significant). The frequency of sucklings was significantly greater in the evening than in the morning. Regardless of age and litter size, about 90% of suckings were initiated by the lamb(s). At 3 days 36% of suckings were terminated by the lamb(s) compared with 2.5% at 4 weeks. More frequent sucking was associated with poorer growth rates in lambs up to 2 weeks old. INTRODUCTION Ram lambs are commonly heavier than ewe lambs at birth and this weight advantage normally increases in absolute terms during growth (Fourie et al. 1970). Single lambs exhibit similar advantages over twins (Dun and Grewal 1963; Burfening 1972). The reasons for the post-natal growth advantages of males and singles are not fully understood. Sex hormone effects eventually favour the ram, but these are unlikely to operate until at least the second month of life (Skinner - al. 1968). Ewes rearing twins produce only 30-50% more milk than et those with singles (Wallace 1948), and hence twins are at a significant disadvantage as long as milk represents a large proportion of their intake. Litter size and sex differences in growth could also be differences in sucking behaviour and thus with the extent and intake. Sucking frequency is known to decline with time after 1956; Ewbank 1967; Morgan and Arnold 1974) and may be higher singles (Munro 1956). associated with pattern of milk parturition (Munro in twins than In the Merino, sucking frequency has been reported to be similar in male and female lambs, and to be unrelated to growth rate (Fletcher 1971). The Merino, however, is recognized as a breed with an inherently low voluntary intake of milk and pasture (Langlands 1973), and the observations reported here were made to determine the nature of the sucking-growth relationships exhibited by Suffolksired lambs born to Border Leicester x Merino ewes. MATERIALS AND METHODS Two groups of Border Leicester x Merino ewes with Suffolk-sired lambs were selected for observation from a flock of 200 ewes lambing during September 1978: a> A 'twin group' consisting of six ewes each with male/female twin pairs,and * Department of Animal Science, University of New England, Armidale, N.S.W., 2351. 333 Animal Production in Australia b) A 'singles group' of 12 ewes, half with male and half with female single lambs. within each group lambs were born within a 48 h period, but the group mean birthdates were separated by five days. Ewes and lambs, identified by ear tags and body brands, confined in a 0.5 ha paddock containing plentiful pasture, were watched by two observers located in a caravan on the perimeter. Behavioural observations were made during 3 h periods commencing at 0600 h and 1530 h on each of two successive days when lambs were a mean age of 3, 14 and 28 days. The flock to be observed was introduced into the observation paddock the previous evening and was removed two days later. The lambs were weighed every seven days. Duration of sucking, interval between suckings, frequency of sucking, and the identity of the suckling initiator and terminator were recorded throughout each 3 h period. Dry bulb shade temperature and wind speeds were measured at 30 min intervals during each observation period and at the same time a general subjective assessment of climatic conditions was made. Logarithmic transformation was used to normalize data which were then subjetted to analysis of variance. RESULTS Temperatures ranged from 0 to 15OC during the AM observations and from 5.5 to 19OC during the PM periods. Only on one AM observation on the 3-day twins did wind and rain appear to influence behaviour patterns. There were no significant differences between the sexes in either live weight or any of the behavioural parameters recorded (Table 1). TABLE 1 Means of interval between sucking bouts, number of suckings/ 3 h, duration of sucking and lamb weight according to sex of lamb (n = 12) The interval between suckings showed a significant (P < 0.01) litter size x age interaction, with twins recording a greater interval than singles at both 3 and 28 days of age (Table 2). In twins, the interval between suckings declined from a mean of 61.9 min at 3 days to 47.0 min at 14 days (P < 0.05), a similar figure to that for singles at the same age (43.9 min). The inversely related parameter, number of suckings per 3 h period, also displayed a significant litter size x age interaction (P < O.OOl), with values for singles declining progressively with age while twins showed a peak at 14 days (Table 2). The duration of sucking data interaction (P < O-01>, with twins (3.9 vs 1.3 min respectively; P < was apparent, the interval between also exhibited a significant litter size x age differing from singles only at 3 days of age 0.05). Some diurnal variation in behaviour suckings being 60.8 min in the morning 334 Animal production in Australia compared to 49.1 min in the afternoon (P < 0.01). Duration of sucking, on the other hand, did not differ. At 3 days, twins and singles weighed 3.7 + 0.2 and 4.8 f 0.5 kg respectively. This weight advantage in favour of singles-increased to 3.1 kg by the end of the experimental period (Table 2). TABLE 2 Litter size and age effects on sucking behaviour and live weight Initiation of sucking was by effect of litter size or of age of was usually terminated by the ewe, responsible for 47% and twin lambs the lamb(s) lambs. At but at the for 25% of in about 90% of cases, with little the 2- and 4-week stages sucking 3-day stage single lambs were terminations. TABLE 3 Percentage of suckings (i) initiated and (ii) terminated by lambsinewes sucked by twins or singles of three age groups Correlations between duration of sucking and weight gain during a seven day period which spanned each observation period were all negative, the correlation of -0.67 for twins at two weeks being significant (P < 0.05). The corresponding correlation for sucking frequency was also negative and significant (Table 4). TABLE 4 Correlations between weight gain and the frequency and duration of sucking 335 Animal production in Australia DISCUSSION Earlier studies of suckling behaviour (Munro 1956; Ewbank 1967) began when the lambs were about one week of age. In the present study observation at 3 days showed thattwins sucked less frequently than singles, but that sucking by the twins was very prolonged (3.9 min) and was terminated by the lambs in only 25% of cases. At this early stage the ewes tolerated extended episodes when sometimes only one of a twin pair persisted with desultory sucking. At 14 days, duration of sucking had fallen to 30 set for both singles and twins and over 90% of episodes were terminated by the ewe. Duration of sucking at 14 and 28 days was almost identical with that reported by Ewbank (1967). Unlike previous studies, (e.g. Ewbank 1967; Fletcher 1971) in which there was no clear relationship between suckling behaviour and growth rate, the present work revealed significant negative correlations between weight gain and both frequency and duration of sucking in twins at 2 weeks of age. Frequent and prolonged sucking may thus be attributed to inadequate milk supply, or to some innate characteristics of twins, or both. In the current work the low overall growth rates, particularly in twins (144 g/day), provide strong presumptive evidence of inadequate milk intake. The same low growth rates may explain the failure of ram lambs to grow faster than ewes as there is a well-established nutrition x sex interaction with respect to growth. Subsequent observations showed that it was not until 56 days of age that males significantly (P < 0.05) exceeded females in live weight. The fu.rther study of growth-behaviour relat.ionships oflambs would be greatly assi sted by con temporaneous measurements of milk intake. REFERENCES BURFENING, P.J. (1972). Anim. Prod. 15: 61. DUN, R.B. and GREWAL, R.S. (1963). Aust. J. Exp. Agric. Husb. 3: 235. = EWBANK, R. (1967). Anim. Behav. 15: 251. FLETCHER, 1-C. (1971). Anim. Behav. 19: 108. FOURIE, P.D., KIRTON, A.H. and JURY, K.E. (1970). N.Z. J. Agric. Res. 13: 753. LANGLANDS, J.P. (1973). Anim. Prod. 16: 285. MORGAN, P.D. and ARNOLD, G.W. (1974). Anim. Prod. 19: 169. MUNRO, J. (1957). Br. J. Anim. Behav. 2: 34. SKINNER, J.D., BOOTH, W.D., ROWSON, L.E.A. and KANG, H. (1968). J. Reprod. Fert. 16: 463. WALLACE, L.R. (1948). 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