THE EFFECT OF ENSILING ON CROP DIGESTIBILITY

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 in-creased; two possible measures, viz. the wilting of herbage before ensilage, and the use of high-digestibility forages of high soluble carbohydrate contents, are discussed.     

THE EFFECT OF GROWTH-REGULATING WEEDKILLERS ON THE MORPHOLOGY OF GRASSES

A series of experiments were carried out in 1954 and 1955 designed to investigate the effects of MCPA and 2,4-D applied at different stages of growth to grasses grown for seed. Single, spaced plants were sprayed at the rate of 1·5 lb. a.e. per acre with 2,4-D amine in 1954 and with 2,4-D amine and ester and MCPA ester in 1955. The development of the grass growing point was used as a criterion of the developmental stages at which the plants were sprayed.
Some treatments caused abnormal types of growth. S.23 perennial ryegrass and S.143 cocksfoot developed ear malformations, S.53 meadow fescue had leaf and ear malformations, while S.51 timothy showed leaf, stem and ear abnormalities.
Leaf malformations developed only after spraying when the growing points showed vegetative primordia while ear abnormalities usually appeared after treatment at most early stages of development. Stem malformation in timothy occurred after spraying at all stages in 1954, but only at the vegetative stages in 1955.
The percentage of abnormal ears in a random sample of tillers in all but one case fell as the growing point developed and most damage occurred after treatment when the apex was at the vegetative stage. Normally, treatment when glume ridges were visible on the apex produced no significant difference between the number of abnormal ears in the treated and untreated plots.
The results suggest that the chemicals act on that part of the apex which is just beginning its development but is not yet visible as a protuberance on the apex.
The type of abnormalities occurring in grasses as a result of spraying with growth regulating weedkillers is similar to those found in cereals after similar treatment.
Provided that the chemicals are applied in the 4 to 5 weeks prior to ear emergence the amount of malformation occurring in the grasses will be small.     

SOURCES OF VARIATION IN THE IN VITRO DIGESTIBILITY OF TROPICAL GRASSES

The in vitro DM digestibility of four tropical pasture species, Cenchrus ciliaris, Chloris gayana, Digitaria spp., Setaria spp. and one temperate grass, Lolium perenne , were studied, using the method described by Tilley and Terry (13).
In vitro digestibility was affected by fineness of grinding, sample size, pH of original rumen fluid and size of rumen fluid inoculum. Different relations were found between the in vivo and in vitro results for the five species, with a maximum predicted difference of 3–5 digestibility units.
It was considered that the in vivo digestibility of tropical grasses could be accurately predicted by this method, provided that the procedure was standardized and samples of known in vivo digestibility similar to those being tested are included in each run.     

THE EFFECT OF DEFOLIATION ON THE SEED-PRODUCING CAPACITY OF BRED VARIETIES OF GRASSES

Leafy grass varieties S24 perennial ryegrass, S26 cocksfoot, S215 meadow fescue and S51 timothy were cut in October and at various growth stages in spring; S53 meadow fescue was grazed at similar periods. Sub-plots were given different applications of N. The control plots had similar manurial treatments but were not defoliated. The seed yield of S24 following October cutting was significantly lower than the control in the first harvest year and significantly higher in the second; the mean yields over 2 years, as a result of cutting at this stage and before ear formation in March, were very similar to those of the control treatment. The mean yields from 3 harvest years for S26, S215 and S51 were generally improved by cutting in October and before ear formation, but cutting after ear formation reduced the number of heads and the seed yields. Extra N applied in conjunction with the defoliation had no significant effect on the number of seed heads or on seed yield. Double grazing of S53 in Sept. and Dec. reduced significantly its seed production in both harvest years. Application of N in spring gave a greater response than a similar application in autumn.     

THE EFFECT OF DEFOLIATION ON THE SEED-PRODUCING CAPACITY OF BRED STRAINS OF GRASSES

A leafy strain of timothy and of perennial ryegrass showed no significant reductions in seed yields following grazing at different dates from October to January, when extra nitrogen was applied.
Spring and winter + spring grazing, together with extra nitrogen, significantly reduced the seed yield of S50 timothy for three successive harvest years.
Perennial ryegrass S101 showed no reduction after spring or winter + spring grazing when defoliation was made not later than mid-April, but when grazing was delayed until May and drought occurred there was a significant reduction in seed yield.     

THE EFFECT OF DEFOLIATION ON THE SEED-PRODUCING CAPACITY OF BRED STRAINS OF GRASSES

Two leafy strains of cocksfoot, S143 and S37 were subjected to winter, spring and winter + spring defoliation; 2 cwt. per acre of nitro-chalk was applied after each defoliation, in addition to the standard manuring for all plots.
Winter grazing of leafy cocksfoot does not appear to depress the yield of seed appreciably when extra nitrogen is applied.
Grazing of cocksfoot in mid-April is likely to depress the seed yield substantially, especially if followed by a very dry summer.
The reaction to hard defoliation by sheep may vary with the growth form of the cocksfoot strain.
Grazing appeared to be more detrimental to seed yield than defoliation by cutting.
During this investigation, prolonged frost which occurred during the early part of the year appeared to have an adverse effect on cocksfoot seed yield.     

THE DIGESTIBILITY OF STRUCTURAL CARBOHYDRATES OF GRASSES BY RUMEN MICRO-ORGANISMS IN VITRO

In vitro digestion of grass samples has shown that the amount of digestible cellulose, hexosan or pentosan is not greatly affected by species or by stage of maturity. A survey of published data on crude fibre and cellulose digestibility has confirmed these findings. Marked differences between grasses and legumes were observed. The rate of digestion has also been shown to be independent of the total amount of structural material present. The relevance of these observations to the selection of herbage varieties with greater intake by ruminants is discussed.     

THE NORMAL-ACID FIBRE CONTENT OF SPFCIES AND VARIETIES OF HERBAGE GRASSES

Normal-acid fibre content has been suggested as a useful indication of the digestibility of herbage. The changes in fibre content were therefore recorded during the spring and early summer of 1957 and 1958 to see whether regular differences occurred between species and varieties of herbage grasses.
All species showed an increase in fibre content during spring and early summer, but considerable year-to-year fluctuations occurred: fibre content was also influenced by manuring and spacing. Regular differences between species and varieties have been detecled and, in perennial ryegrass, differences between individual genotypes. It should be possible to select breeding material for high or low fibre content if required.     

FURTHER STUDIES ON THE RELATIONSHIP BETWEEN SHOOT AND ROOT SYSTEMS OF GRASSES

In young grass plants it is possible to relate the weight of the root to that of the shoot through the allometric formula y = bx ^k . Using this formula it was found that flower formation was associated with an increase in shoot growth relative to that of the root. Within varieties of Lolium , the greater the intensity of heading the more was the growth of the shoot relative to that of the root. Perenniality was associated with a high rate of root growth relative to that of the shoot. A decrease in the light intensity or soil water reduced the growth of the plant as a whole, but light decreased root growth more than that of the shoot while water supply had the opposite effect.     

A MODIFIED METHOD FOR THE IN VITRO DETERMINATION OF HERBAGE DIGESTIBILITY IN PLANT-BREEDING STUDIES

In plant–breeding studies large numbers of samples, often taken from single plants, are assessed for digestibility. A modified in vitro method for such estimations, which has proved accurate and less time-consuming than other methods, is described and results obtained for some grasses are presented.     

SOME FACTORS CAUSING DIFFERENCES IN DIGESTIBILITY OF GRASSES MEASURED BY AN IN VITRO METHOD

Stage of growth, leafiness and the accumulation of dead material were evaluated as factors causing differences in digestibility between varieties of perennial ryegrass, cocksfoot and timothy. In first growth these factors only partly accounted for the variation in digestibility between species but almost entirely accounted for the variation between varieties within each species. In the regrowths, heading behavior and leafiness were not closely associated with digestibility, which indicated that the variation between grasses following first growth may be a result of inherent differences.     

STUDIES ON THE HEIGHT/WEIGHT RELATIONSHIP IN DESERT RANGE GRASSES OF INDIA

Studies on height/weight relationship of the key grass species of Western Rajasthan ranges, India, were undertaken so as to form concepts which will guide the assessnient of the extent of their utilization by the livestock. Regression studies of the data obtained indicated that the relationship between the percentage of height clipped and the percentage of weight removed is quadratic. A graph has been drawn for each of the 5 species to relate the percentage of height removed with the percentage of weight utilized. The studies have shown that the weight distribution in respect of height is different in different species.     

THE EFFECT OF COMPANION GRASSES ON TIMOTHY PRODUCTION IN SWARDS CUT FOR CONSERVATION

To assess the effect of companion grasses on timothy productivity, swards of timothy sown alone or with one of eight companion grasses were harvested as for silage four times per year for two years. The companion grasses were: diploid perennial ryegrasses S24 and S23; tetraploid perennial ryegrasses Reveille and Taptoe; meadow fescues S215 and S53 and cocksfoots Trifolium and S143. Averaged over the N application rates (226, 339 and 452 kg N/ha per year) the total herhage yields of timothy/companion-grass mixtures were all significantly superior to that from timothy alone in the first year. Only perennial ryegrass S24 and the cocksfoot mixtures significantly outyielded timothy alone in the second year. Winterkill hecame evident in April of the second year and pure timothy and timothy/meadow-fescue swards were least affected. Over all swards, timothy DM increased hy a mean of 19% from the first to the second year, compared with a fall of 20% in total herhage DM. The contrihution of timothy herhage to the mixtures was very low with companions other than meadow fescue. Late-heading varieties were more compatihie than early-heading varieties, and tetraploid ryegrasses were more compatihie than diploid ryegrasses. It is concluded that if the inherently valuahle characteristics of timothy are to he exploited, it should not he sovm with aggressive companion grasses.     

EFFECT OF SOME GREEN-CROP-DRYING PROCESSES ON THE DIGESTIBILITY AND VOLUNTARY INTAKE OF HERBAGE BY SHEEP

The effect of artificial drying under commercial conditions on the digestibility and voluntary intake of herbage by sheep was studied, using either van den Broek (900°C inlet temperature) or Swiss Combi (1100°C inlet temperature) triple-pass drum-type driers. Organic-matter digestibility of chopped dried herbage was 8·3, 5·8 and 5·3% lower than that of fresh herbage in Experiments 1, 2 and 3, respectively. Packaging chopped dried grass into ‘cobs’ caused a further reduction in OM digestibility of up to 2·8%. Pre-milling plus packaging (i.e. ‘pelleting’) depressed OM digesti bility of chopped dried grass by 5 to 6 percentage units. Digestibility of dried grass in its various physical forms was further reduced when offered ad lib.; the greatest fall (9·4%) occurred with pellets and the smallest fall (0·8?1·3%) with loose chopped material; cobs were intermediate at 4·3?7·0%.     

THE INFLUENCE OF THE QUANTITY OF HERBAGE OFFERED AND ITS DIGESTIBILITY ON THE AMOUNT EATEN BY GRAZING CATTLE

Six calves, six heifers and six dry cows grazed a mature sward (treatments A and B) and a leafy aftermath (treatment C) in succession. The yields of herbage on the two swards were 7100 lb and 1950 lb DM per acre (7950 kg and 2180 kg per ha), respectively. The amounts of herbage offered daily were 47 lb (21–5 kg) DM per head (treatment A), 70 lb (32 kg) (treatment B), and 60 lb (27 kg) (treatment C), Two estimates of herbage organic–matter intake (O,M,I,) were made on each treatment; records of grazing behaviour were made on treatments B and C, The digestibility of the diet selected on treatment C was higher than that selected on treatments A and B, and the animals ate significantly more O,M, on treatment C, The total grazing times on treatments B and C were similar, but the animals found it more difficult to graze on treatment B
Herbage O.M.I. increased significantly from treatment A to treatment B, even though the quantity of herbage offered per day on treatment A greatly exceeded the amount eaten. The increase in O,M,I, was found to be associated with an increase in faecal 0,M, output, but the digestibility of the diet did not change.