The nutritional evaluation of Italian ryegrass cultivars fed as silage to sheep and cattle

Three feeding trials with big bale silage were carried out to determine whether previously established intake differences between artificially dried Italian ryegrass cultivars could be repeated under differing conditions of food preparation and presentation. The silage was prepared in 2 consecutive years from the same field crop and fed to groups of cattle in both years. The second year silage was also fed to sheep indoors. All animals were fed ad libitum and the voluntary intakes recorded for groups of cattle and individual sheep. Chewing activity was also recorded on all groups of sheep.
The chemical composition of the two cultivars as fresh grass was similar in 1984 but there were small differences in 1983 with Tarquin showing slightly higher organic matter digestibility (DOMD) and lower dry matter and water-soluble carbohydrate compared to RvP. The only consistent differences in silage composition between cultivars was a slightly higher level of modified acid detergent (MAD) fibre in RvP compared to Tarquin. Despite these small differences the voluntary intake of cattle fed Tarquin was 19% higher than RvP in the first year and 35% in the second, while sheep showed a similar difference of 40% with the second year silage.
Recording of jaw activity with sheep showed that animals spent 40% more time eating and 27% more time ruminating RvP than Tarquin per unit of food eaten. This suggested that the intake differences, which were independent of digestibility, were related to the physical resistance of the feed to breakdown by chewing. These differences depend on the structural characteristics of the plants and were associated with differences in leaf/stem ratios and MAD-fibre content. These are less likely to be affected by the method of conservation or feed presentation and, although the degree of difference between the cultivars changed with the different procedures, the inherently higher intake of Tarquin persisted.