R.G. WALKER¹, R.T. COWAN², W.N. ORR² and B.A. SILVER²

¹Queensland Department of Primary Industries, Kairi Research Station, Kairi; and
²Mutdapilly Research Station, Peak Crossing, Queensland, Australia

Abstract

The effect of the area of irrigated temperate grass pasture available to cows during autumn and spring on milk composition was measured using autumn-calving Holstein-Friesian cows. The irrigated pasture (Lolium multiflorum) was used in conjunction with a raingrown tropical pasture (Panicum maximum, Setaria sphacelata cv. Narok and Neonotonia wightii cv. Tinaroo) pasture at the levels of 0, 0.1 and 0.2 ha/cow. Mean overall stocking rate in each treatment was 1 ha/cow, and cows were confined to treatments from May 25–December 22.
Differences in animal production between treatments developed progressively during the experiment. During winter (May 25–July 27), there were no differences in milk yield, milk composition or liveweight gain. During late winter-early spring (July 28–September 29), milk yield and milk protein concentration for cows with 0, 0.1 and 0.2 ha/cow of irrigated ryegrass were 21.6L at 2.99%, 22.8L at 3.11% and 22.6L at 3.16%, respectively. Liveweight gain was also increased at 0.2 ha/cow of irrigated ryegrass pasture. During late spring (September 30–December 1), milk yield, and fat and protein concentrations were all affected by amount of irrigated pasture.
Following storm rains in late November, responses in milk yield were inversely related to amount of irrigation, and differences in milk protein concentration persisted for at least 5 weeks following rainfall. The soluble carbohydrate concentration of the tropical grasses was similar to levels in ryegrass (14% DM) for only 3 weeks following rainfall, after which it declined to 7% DM.
Results show that irrigated temperate grasses were effective in maintaining both protein and fat percentages during winter and spring.