No abstract

Pure swards of S22 Italian ryegrass, H.I hybrid ryegrass, SI70 tall fescue, S48 timothy, S2f5 meadow fescue and Germinal cocksfoot were each harvested at several stages of maturity during first growth in the spring, and in the subsequent regrowths. Each batch of herbage was fed to sheep in a digestion trial under conditions of voluntary intake. Results from the first growth herbages showed the expected fall in digestibility with increasing maturity. However, the digestibility of S22, H.I, S170 and S48 began to fall well before ear emergence, whereas the digestibility of Germinal fell only slowly up to the time of ear emergence, as had been found previously with S24 and S23 ryegrass and S37 cocksfoot. The rate of fall of digestibility in H.I and S48 (0-4 units/day) also appeared to be lower than with the perennial ryegrasses and cocksfoot (0-5 units/day). The monthly regrowths within each herbage were of similar digestibility, but the mean digestibility of regrowths differed between herbages, being highest for S215 and lowest for Germinal and S170. The grasses with highest digestibility in the early Spring, in particular S22 ryegrass, were not, however, always the most digestible in the subsequent regrowths. The numbers of sheep fed on each herbage were insufficient to show whether there were significant differences in voluntary intake between different herbage species of the same digestibility. It is suggested that an intake/digestibility relationship, based on data from more animals, should be developed for each herbage species. Only if different relationships are found can it be concluded that factors other than level of digestibility have an effect on intake.

SUMMARYThe free-acid content of grass silages was reduced by the addition of sodium bicarbonate to the silage and increased by additions of lactic acid. In each of four comparisons the addition of sodium bicarbonate to increase pH from about 4·0 to about 5·4 resulted in significant increases in intake of dry matter which ranged from 9·7 to 20·7%. Intake of organic matter was consistently increased by this partial neutralization treatment, but the increases were not significant in all experiments. The addition of sodium as sodium chloride rather than sodium bicarbonate did not alter the intake of a highly acid silage. Addition of lactic acid to reduce the pH of a silage feed from 5·4 to 3·8 resulted in a decrease in dry-matter intake of 22%. The correlation between dry-matter intake and the silage characteristics: titratable acidity, total organic-acid content, lactic-acid content and pH were all significant.It is concluded that the acids produced during the normal silage fermentation can limit the intake of the silage and it is suggested that chemical treatments to preserve wet grass without the presence or formation of large quantities of acids be investigated.

This paper presents the results of 125 digestion trials with sheep fed herbage at different stages of growth from three clover-free pure grass swards. During 1958 and 1959, a study was made of the yield, leaf lamina, nitrogen, ash and digestible organic matter percentage (D) of first growths, of regrowths cut at monthly and two monthly intervals and of swards receiving various quantities of fertilizer nitrogen.For first growths in the spring D remained almost constant until the ears started to protrude from the leaf sheaths and then fell rapidly at approximately 0 5 per cent per day. The D values for S 23 ryegrass were three weeks later than S 24 ryegrass, which correspond with later ear emergence of the latter. S 37 cocksfoot was always less digestible than S 24 ryegrass although both were at similar stages of growth. This difference in D also occurred in the regrowths. The D of monthly regrowths tended to fall with each successive cut, although in 1959 ryegrass values improved in the autumn.Fertilizer nitrogen had little effect on D.Despite the warmer spring and drier summer in 1959 and corresponding changes in production per acre there was little effect on D.

The digestibilities of 22 herbages, and of the silages made from them, were measured with sheep: in two experiments batches of the same herbage were ensiled by several different methods. In every case the digestibilities of herbage and of the corresponding silages were found to be very similar, and no significant effect of method of ensilage on digestibility was found. The importance of using the true dry-matter content of silages (i.e. corrected for losses of volatile constituents during drying) is emphasized; a depression in the digestibility of herbage during ensilage is likely to be estimated unless this correction is made. These experiments have shown that silage of high digestibility (>80%) can be made from highly digestible herbage; however the intakes, both of dry matter and of digestible dry matter, from such silages were found to be much lower than expected. If the potential for animal production of high digestibility in silage is to be exploited, intakes must be increased; two possible measures, viz. the wilting of herbage before ensilage, and the use of high-digestibility forages of high soluble carbohydrate contents, are discussed. INTRODUCTION It is widely recognized that the digestibility of herbage decreases as it becomes more mature, and that this is reflected in a decreasing digestibility of the corresponding conserved crops. Studies at a number of centres have indicated that it should be possible to predict the digestibility of cut herbage from inforniation on the herbage species and variety, the date of cutting and the previous management (13,21). Such information would be of particular use in conservation practice if it were possible also to predict the digestibility of the conserved products made from the cut herbage.Investigations of haymaking methods (23) have shown that the digestibility of the cut herbage has a major effect on the digestibility of the resulting hay, but that the latter is also affected by the efficiency of the conservation process. Similar quantitative evidence is however lacking for silage, particularly in regard to the digestibility of silages made from highlydigestible immature herbage. Clearly two effects must be studied: first the overall relationship between the digestibility of herbages and that of the resulting silages, and second the possible modifying effect of the 204 method of ensilage. An effect of herbage digestibility was reported by Dodsworth and Campbell (9) who found that delay in the date of cutting of herbage led to lowered digestibility of silage. Sears et al. (22) found that herbages of different digestibilities gave ensiled products which also differed in digestibility. Most available evidence suggests that the effect of ensilage method on silage digestibility is not marked. Watson and Ferguson (25) found that the digestibilities of herbage ensiled without additives, or with molasses or mineral acids, were very similar, and also similar to the digestibility of the original herbage. Camburn et al. (5) found similar digestibilities for silages...