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To Butt or Not to Butt: Suck l ing Tactics in Lambs

IAN HORRELL, NICOLA WILSON and JANE HODGSON

Department of Psychology, University of HuU, Hull, HU6 7RX (Gt. Britain)

ABSTRACT

It is generally assumed that milk ejection has to be actively elicited and that actions such as udder massage and butting achieve this. However, although the broad outlines of suckling in sheep and its development with time have been described (Ewbank, 1967), no attempt has been made to develop a quantitative description of the individual acts and their distribution in time within a suckling period. Observations were therefore made on indoor-reared crossbred ewes and their lambs, both at 24 h of age when penned individually and at 7-10 days of age with 20 ewes per 5.0 × 8.4-m pen. Starting and stopping time of sucking, the teat involved, movement between teats and each udder-butt were recorded.

Typically, suckling periods begin with a bout of 1-5 butts of the udder followed by a sustained period of sucking (usually lasting 10-60 s). The lamb may then re-stimulate the udder or move to the other teat before another period of sustained sucking. Individual butts and brief breaks from the teat may be interspersed within the prolonged sucking phase (breaks of greater than 6 s were regarded as the end of a suckling period). A whole suckling period generally consists of a number of cycles of this kind, each cycle comprising a period of stimulation (which may be absent for the first cycle) and/or (for the second and subsequent cycles) a switch to the other teat, followed by a period of sustained sucking. Successive cycles within a period tended to be shorter and to involve more initial stimulation. The particular characteristics of individual suckling periods vary a great deal - 29% of periods began without initial butting and the number of cycles ranged from I (48% of periods) to 9.

The number of cycles within a period tended to be larger in the older lambs, and switching between teats within a period only emerged in these animals. The mean duration of periods, the number of cycles and the extent of each bout of butting were all greater in twins than in singles. Switching between teats only occurred in twins when one lamb was suckling alone. In 7-10-day singles and in twins suckling alone, the duration of successive cycles did not reduce as much, nor the extent of successive butting bouts increase as much, as in twins suckling together. These facts suggest that switching to the other teat (when it is available) is a more productive method of maintaining milk flow than udder stimulation. The data provide other suggestive insights into the role of these events in eliciting and maintaining milk flow.

REFERENCES

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