Published online by Cambridge University Press: 27 March 2009
The growth, development, chemical composition and nutritive value of sunflower (cv. Fransol), was examined from the flower-bud (12 July) to milky-ripe seed (late September) stages. Dry-matter yield increased from 2·1 to 14·1 t/ha over the period. Drymatter content was low (100–110 g/kg) up to flowering, early in August, and then increased to 193 g/kg. Crude protein content declined after flowering and ether extract values were low throughout the period. Organic-matter digestibility in vitro and derived metabolizable energy values declined rapidly with the onset of flowering. Gross energy values, calculated from the proximate constituents, increased to 17·6 MJ/kg D.M. at the end of the period. Calcium to phosphorus ratios varied from 5·6 to 7·4:1.
Sunflower was cut and fed to eight Friesian heifers over 3 weeks from the onset of flowering. Average daily D.M. intake was 63·5 g/kg W0·76 and the organic-matter digestibility was 0·684. Average live-weight gain was 0·79 kg/day.
Fresh sunflower was successfully ensiled without an additive 2 weeks after flowering and the silage (pH 4·0) was fed to three cross-bred wethers in a feeding trial. The organic-matter digestibility was 0·649, the metabolizable energy 8·0 MJ/kg D.M. and the average D.M. intake 6·73 g/kg W0·75. In a metabolism trial, with four fistulated sheep, the organic-matter digestibility was 0·718, the metabolizable energy 9·4 MJ/kg D.M. and the D.M. intake 43·1 g/kg W0·75. Rumen pH decreased and total volatile fatty acid concentration increased markedly within 2 h of feeding the silage. Molar proportions of acetic and propionic acid (0·539 and 0·381), 1 h after feeding, were typical of cereal-based diets. Ammonia-nitrogen concentration increased to a maximum of 216 mg/1 within 2 h of feeding.
The good yield and animal performance from fresh sunflower make it a possible annual crop for zero-grazing in late summer in northern Britain. Satisfactory results from feeding sunflower silage suggest that the crop has potential for ensilage if the problem of effluent can be overcome.