Wool growth of wethers grazing Acacia aneura – Triodia pungens savanna and ewes grazing Triodia pungens hummock grass steppe in the Pilbara district, W.A

Abstract

Seasonal variations in wool growth, fibre diameter, and body weight were estimated at six weekly intervals in the period 1962-1964 in the north-west of Western Australia. These measurements were made on (a) Merino wethers grazing on Acacia aneura-Triodia pungens shrub savanna on a commercial pastoral holding, 'Mulga Downs', Wittenoom Gorge, and (b) fertile and sterile Merino ewes grazing Triodia pungens hummock-grass steppe on Abydos Pastoral Research Station, Port Hedland. The period of maximum wool growth-rate occurred in summer and, together with the extensive trough in the dry autumn through to mid-summer, produced a characteristic pattern which may be modified by occasional autumn-winter rainfall. Wool growth-rates at both Abydos and Mulga Downs rose and fell following the onset and cessation of summer rain. The response in wool growth at Abydos was prompt, and that at Mulga Downs somewhat delayed, possibly due to their differences in soil moisture characteristics and botanical composition. This pattern of summer maximum and winter minimum wool growth-rates differs substantially from the three patterns described previously for southern Australia, and the general level of the maximum rates in the north-west of Western Australia is well below those attained on sown pasture and semi-arid grasslands in the south. Further, periods of comparatively low wool growth-rates were of longer duration in the north than in the south, and clean fleece weights were lower. The nutritional inadequacies of the environment were further confirmed in the study of fertile and sterile ewes at Abydos. By comparison with the sterile group, the fertile ewes suffered a reduction of 24 per cent in wool growth in late pregnancy, 44 per cent in early lactation, and 26 per cent over the whole lactation. Following lactation, there was a long delay before fibre diameter and body weight reached parity for the fertile and sterile ewes.