The effects of age, year and lambing performance on liveweight of Merino ewes in north west Queensland.

Abstract

460 Proc. Aust. Soc. Anim. Prod. Vol. 17 THE EFFECTS OF AGE, YEAR AND LAMBING PERFORMANCE ON LIVE WEIGHT OF MERI NO EWES IN NORTH WEST QUEENSLAND MARY ROSE and R.A. YOUNG* Live weight is an important criterion in a breeding flock because of its phenotypic correlation with wool production and its high genetic correlation with reproduction rate (Turner and Young 1969). It is also the chief determinant of the value of cast-for-age animals so age-specific data are important in deciding the profitable age structure of a breeding flock. Estimates were made of the effects of age, year and lambing performance on live weight in Merino ewes aged 2.5 tc 10.5 years for the period 1966-70. Tk: e The nalysis Figure 1 shows that live weight increased with age till 5.5 years and thereafter declined rapidly. Differences between years were very marked. The maximum between-year difference of 6.3 kg (1967 and 1969) was equivalent to 17.3% of the mean for all years. The effects of Preg nanc y and lactation were -1.9 and -1.0 kg ( 5.0 and 2.8% less than the mean for fSWf?S which failed to lamb). These data differ frcJm those of Merino ewes at Cunnamulla in ScmtkJ west Queensland (Brown et al. 1966). The Toorak ewes were generally much lighter at However, at both 2.5 years and showed a smaller rise in live weight with age. locations the live weights of aged ewes declined steeply. The effect of pregnancy was greater and o f lactaticn less than that for Cunnar::~:lla ewes. These data and earlier ones (Pose 1972, 1974, 1982) reveal aged ewes show a dramatic decline in reproductl.ve performance, wool producticn, wool quality and live weight. If a market could be found for aged ewes it. may be pos,cible to enhance the producticn of a ma3 1 er fJ ock by improved husbandry. BROWN, G.F., TURNER, HELF:h: NEWTON, YOUNG, S.S.Y., Aust. J. Agric. Res. 17:557. ROSE, MiR?- 1972),--Pr& --- - '2 Soc --e-m 2 SW.- - 2 me 2 &t -2. Anim Prod RC>SF, MARY (1974). B-B.- 2 -m-m 2 Soc s--.-m 2 Prod Proc Aust --a,' Anim -.-s-2 ROSE:, PAW (1982). -,,' ,-L-,.2 W-BSoc Anim Prod Proc Aust 2 -s-s ,,' --- - 2 TURNER., HE;lJI\! IGEWOE, mii YOUNG, S.S.Y. (1969). Sheep Breeding' (Macmillan: KeJkourne). and DOLLING, C.&S. $48. (1966). 10:367. -.14:463. -'Quantitative Ger;eti.cs in OrlcJ& illy, Q. 41C5. i c-11 CJgy Lab0 ratory, Depa I-t n-lent of Fr imaq Industries, Yeer ` t ry Er anch, Animal Ecs;e ar ch I nstitute, Ycerorqpilly, Q. 4 105.