Abstract:
THE EFFECTS OF PADDOCK SIZE, LIVEWEIGHT CHANGE AND FLOCK DISPERSION ON FERTILITY OF MERINO EWES NICHOLLS, P.J., FOWLER, D.G. and KEARINS, R.D. Paddock size (Inkster 1957) and liveweight change (Coop 1966) can influence fertility in sheep. While readily accessible to managerial control, their mode of action is not yet understood. Six hundred Merino ewes were randomised into six groups of equal size. Two groups (C,D) were joined in large, and two (E,F) in small paddocks. Two groups were joined in paddocks designed to restrict ramewe-contact. One (A) was large, irregular in shape and topography and almost devoid of feed, while the other (B) was small with abundant feed and contained a radial maze. Liveweight changes for each group are shown in the table. Joining began in May, known to be late in the breeding season of these ewes, and lasted 34 days. Each group was joined with one inexperienced ram, and rams were moved to another group every three days. When liveweight fell, fertility (percentage of ewes which lambed) in small paddocks (E,F) was higher (P < 0.01) than in large (A). When liveweight increased the reverse held, fertility in large paddocks (C,D) being higher (P < 0.01) than in small (B). In large paddocks, fertility was lower (P < 0.05) when liveweight fell (A) than when it increased (C, ' D) I but in small paddocks the reverse held, fertility being higher (P < 0.001) wh en liveweight fell (E,F) than when it increased (B). The conflicting effects of paddock size and liveweight change can be reconciled by the effect of flock dispersion: where it was low (C,D, E,F) t fertility was greater (P < 0.001) than where high (A,B). Dispersion may affect fertility by influencing contacts realised between ram and ewe. Reduced contact, as indicated by higher dispersion indices and fewer ewes marked, reduced fertility. Poor nutrition and large paddocks have combined to reduce contact but poor contact also occurred on good nutrition where there was a maze. The results suggest that paddock size . and liveweight change affect fertility in Merinos by influencing dispersion and thereby the contact realised between rams and ewes. Effects of paddock size, liveweight change and dispersion on fertility REFERENCES COOP, I.E. (1966). J. Agric. Sci. Camb. 67: 305. TFOWLER, D.G. and JENKINS, L.D. (1976). ? appl. Anim. Ethol. (in press) INKSTER, IIJ. (1957). Sheep farming annual N.Z. p. 163. N.S.W. Department of Agriculture, C.S.I.R.O., Prospect. 2P
