THE FEEDING OF SUPPLEMENTARY CONCENTRATES TO DAIRY COWS GRAZING GOOD PASTURE

In an experiment on the effect of feeding concentrates to spring-calved Ayrshire cows grazing leafy pasture 2 treatments were compared. On the control treatment the sole feed of the cows from M ay to October was grazed herbage. On the supplement treatment the cows grazed the same pasture as the control animals, but in addition were fed concentrates at an average rate oi 21 lb per 10 lb milk. Milk yields on the two treatments were not significantly ditferent, either during the summer feeding period or for the complete lactation. The lengths of the lactations and the fat and S.N.F. contents of the milk were not significantly affected by the treatments. The margin between the value of the milk and the cost of the concentrates was reduced significantly by £13 per cow for the complete lactation as a result of feeding the supplements. It is concluded that at the present price of concentrates and value of milk there are no economic advantages to be gained by feeding supplementary concentrates to spring-calved cows if ample herbage of leafy quality is available.     

AN ELECTRONIC INSTRUMENT FOR PASTURE YIELD ESTIMATION

This is a preliminary report on an instrument being developed for the measurement of pasture yield in situ . In essence the instrument is an electrical capacitance measuring unit in which the introduction of herbage to a measuring head causes a change in the electrical capacitance of the system. This capacitance change is measured at a radio frequency and used as an indicator of the mass of herbage contained within the measuring head.
The development and construction of the instrument is described and data are presented for 15 calibration series in which frequency change has been related to pasture yield.
Within series the instrument accounts for approximately 90% of the variation in pasture sample yield measured either as wet, dry or organic matter. However, significant differences exist between series. These differences would give rise to bias if pasture yield were estimated from a prediction equation derived from the pooled data.
Possible sources of the differences between series are discussed and avenues for further development indicated.     

THE EFFECT OF INCLUDING DRIED GRASS IN THE SUPPLEMENT GIVEN TO LACTATING COWS AT PASTURE

An investigation into the effect of including dried grass in the supplement given to dairy cows at pasture is reported. Supplements containing 0, 50 and 100% dried grass were used in the investigation which was carried out in two parts. In the first part 12 high-yielding cows with unrestricted access to pasture were used in an experiment with a change over design to assess the effects of feeding 5 kg/day of each supplement on milk yield and composition. In the second part 8 steers, housed in stalls and given cut herbage from the same sward as that grazed hy the cows, were used in a change over experiment to assess the effects of the three supplements on herhage and total DM intake. No significant differences in milk yield between supplements were ohtained, the mean yields being 23·9, 24·5 and 23·9 kg/day for the supplements containing 0, 50 and 100% dried grass, respectively. Milk composition was also not significantly affected by including dried grass in the supplement. In the indoor feeding trial using the steers, the addition of 3·5 kg DM from the supplement resulted in an increase in total DM intake of only 1·3 kg/day. There was no significant difference hetween supplements on herbage and total DM intake.     

SOME ESTIMATES OF THE AREAS OF PASTURE FOULED BY THE EXCRETA OF DAIRY COWS

Observations were made of the areas of herbage receiving the faeces of grazing dairy cattle and of the areas and relative palatability of herbage whose growth was affected by faeces and urine. The average area covered by faeces was 7·3 sq. ft./cow/day. Faeces dropped during grazing had a negligible affect on the utilization of herbage at that grazing, but each dung-pat probably affected the growth and palatability of an area of herbage about six times as great at the next grazing. The area of herbage whose growth was affected by urine was equal to that affected by faeces, but unlike faeces, urine improved the palatability of the herbage to dairy cows. The data were used to calculate approximate areas of herbage likely to be affected by excreta at different levels of stocking, and it appeared that excreta return plant nutrients to a given pasture acreage more quickly than some other estimates suggest.     

THE RELATIONSHIP BETWEEN COMPETITION AND DEFOLIATION IN PASTURE

Field trials were carried out on a downland permanent pasture at the Grassland Research Institute, Hurley, between 1953 and 1955, to investigate the factors involved in competition in pasture undergoing periodic defoliation. Response to competition was estimated by comparing the yield of species units (either individual plants or close groups of shoots) growing normally in the pasture with the yield of matched units from which the surrounding herbage had been removed. The species studied were cocksfoot, red fescue, creeping bent, plantain, ox-eye daisy and bulbous buttercup. In addition to the estimation of normal competition for environmental resources in pastures of differing height, two special effects upon species due to the presence of surrounding herbage were investigated following unusual results from competition tests in swards under periodic defoliation. First, the influence of surrounding herbage in modifying the growth habit of a species, causing it to grow in a more erect manner, and consequently to suffer more on defoliation at a specific height than in the absence of competition. Secondly, a decreased yield after defoliation, not associated with changes in the growth habit of the species, which was ascribed to an increase in top/root ratio brought about by shading during the preceding period of competitive growth. The effect of selective defoliation of a species in relation to the herbage surrounding it was also studied. Differences in the degree of defoliation of a species and its surrounding herbage had a marked effect upon the degree of competition exerted by the latter upon the former, increasing it when the species was preferentially defoliated and decreasing it when the surrounding herbage was preferentially defoliated. The factors involved in pasture competition under periodic defoliation are listed and discussed.     

PASTURE YIELD INSTRUMENT USING A RADIO FREQUENCY BRIDGE

A single unit grass-meter has been developed to replace the twin transmitter-receiver units which have been in use since 1958. In the new design a radio-frequency capacitance bridge is mounted on top of a measuring head. Introduction of grass into the measuring head unbalances the bridge and the amount of unhalance, which is a function of the mass of the herbage, is indicated on a micro-ammeter. Two ranges are incorporated so that sheep pastures with short grass and cow pastures with long grass can be measured.     

COMPARISONS OF GRASS VARIETIES FOR SURFACE SEEDING UPLAND PASTURE TYPES

A series of experiments was laid down in 1957 on different upland vegetation types in Scotland to provide a basis of critical information on the performance of 18 herbage varieties. The present paper deals with results on areas dominated originally by Molinia and Nardus at Sourhope farm, Roxburghshire. Data obtained between 1957 and 1954 are discussal in relation to sward development, competition with remnants of native herbage and seasonal productivity.     

THE EFFECT OF A RYEGRASS COMPANION GRASS AND THE VARIETY OF RED CLOVER ON THE PRODUCTIVITY OF RED-CLOVER SWARDS

An experiment was conducted to measure the effects of differrat ryegrass companion grasses and red-clover varieties on the productivity of red-clover swards. Three silage harvests per year were taken over a 2-year period. The addition of a companion grass increased total herbage yields; S24 perennial ryegrass gave the highest herbage yield over the two years, followed by Reveille perennial ryegrass. Because of lack of persistence, Tetila Italian ryegrass yielded poorly the second year. A companion grass had little effect on red-clover yields in the mixed swards but improved percentage digestibility of the OM of the total herbage and lowered the CP percentage. Its presence also reduced the ingress of unsown species. The variety of red clover used had little effect on total herbage yields or red-clover yields in the first harvest year. In the second year, Hungaropoly and Tilo persisted better and so gave higher total herbage yields and red-clover yields than Dorset Marl or Essex. The fall in total herbage yields from the first to the second year was entirely due to a fall in red-clover yield since yields of the ‘non-red clover’ fraction of the total herbage increased. A red-clover/grass sward may have advantages over a pure red-clover sward nutritionally, for silage-making and for its effect in diluting the oestrogenic activity of a pure clover sward. A major reappraisal of the role and potential of red-clover swards in the UK is warranted because of their many valuable attributes, particularly their ability to give high herbage yields of high nutritive value without the addition of fertilizer N. The improved persistency of some of the tetraploid varieties of red clover enhances the value of the plant.     

BEEF PRODUCTION FROM PASTURE LEYS IN UGANDA*

The potential for producing beef in savanna grassland areas is discussed in relation to the results obtained from grazing trials on sown pastures at Serere Research Station, Uganda. Liveweight gains from small East African Zebu stock are used to illustrate the progress that has been made in the selection of improved pasture species and mixtures grown at various levels of fertilizer application. The utilization of herbage from selected pastures is shown to vary under different grazing management systems, grazing pressure having the greatest effect upon animal production. The need for further investigations and the integration of existing research findings into farming practice is stressed.     

THE GROWTH OF LAMBS AT PASTURE

Data on the growth rates of 'worm-free' Iambs were collected at different seasons over 4 years. In 1959 and 1960 the Iambs were set-stocked on a perennial ryegrass/white-clover sward, and in 1961 and 1962 lambs were rotationally grazed on a pure S23 perennial rye-grass sward. Although significant differences were obtained between seasons, there was no correlation between lamb growth rate and any one factor of herbage quality or environment.     

FACTORS LIMITING ANIMAL PRODUCTION FROM GRAZED PASTURE*

Animal production from intensively managed pasture (240 units N/ac or 300 kg N/ha applied annually) should in theory reach 11,000 Ib/ac (12,500 kg/ha) of milk or 1550 lb/ac (1750 kg/ha) of liveweight gain per year. The figure for theoretical milk production is achieved in experiments, although rarely approached in commercial practice; the figure for liveweight gain is never approached, either experimentally or commercially. On commereial farms in Britain, the average stocking rate for grazed lowland pasture in 1971 was about 0·74 cow equivalents/ac (l±82/ha), compared with a theoretical target of 1·9/ac; in 1969 fertilizer N application was about 48 units/ae (60 kg/ha). The main purpose of this paper is to suggest reasons for the differences between practical, experimental and theoretical levels of production. Economic factors may deter farmers from intensifying their grassland management, but the deterrent to high stocking rates may be the fear of running out of grass. In practice, ungrazed herbage is used as a buffer, but other feeds might be used for this purpose. Concentrates, pelleted roughages and even long dried grass and silage are too attractive to grazing beef cattle to be offered to appetite; but silage might be used as a long-term buffer. Fouling of pasture reduces efficiency of harvesting, but attempts to overcome this effect, by conditioning of grazing animals, spreading excreta or by alternation of grazing and cutting, have largely been unsuccessful. High production per unit area cannot be achieved without high production per animal. Legumes have often been found to increase production per animal, and a technique has been developed for growing red-clover and grass in adjoining areas and grazing them together. The clover was grazed satisfactorily by dairy cows (and caused no bloat) but failed to increase milk yield per animal. Recent calorimetric studies of grass have shown that the net energy value of digestible organic matter is variable, and in particular is low for late-season herbage.     

THE EFFECTS OF CUTTING AND GRAZING SYSTEMS ON HERBAGE PRODUCTION FROM GRASS SWARDS

Studies were made on two perennial ryegrass–dominant swards of the effects of cutting and grazing systems of herbage production. A motor scythe was used for cutting and sheep in small enclosures for grazing. In both systems, herbage production was measured by a ground-level sampling technique, using sheep shears, and the difference between pre-treatment and post-treatment herbage was expressed as ‘utilized yield’. Correction for soil contamination is ensured by quoting all results on an organic-matter basis. Grazing treatments averaged 14–16% more organic matter and 36–45% more crude protein than cutting treatments in both experiments. These differences were ascribed to recycling of N under grazing. Infrequent defoliation gave higher yields than frequent, and severe defoliation higher yields than lenient under both cutting and grazing systems. The trends shown by cutting and grazing intensities are comparable and can be quantified. There is need to examine closely the relationships between the effects of cutting and grazing techniques on herbage production, since such knowledge would allow a more accurate prediction of the relevance to the grazing situation of results obtained under cutting.     

Effects of species aggregation, habitat and season on the accuracy of double-sampling to measure herbage mass in a lowland grassland ecosystem

Double‐sampling, as a cost‐effective and sufficiently accurate method, is an acknowledged method for estimating herbage mass at the level of the plant species up to the total plant community. It was investigated whether adjusting visual estimations of double‐sampling is applicable at different levels of species aggregation when different seasons and habitats are involved. The method was used in six different habitats of the same ecosystem, a grassland nature reserve in western Belgium, based on eight sampling periods. A general linear model was used to analyse the data at four levels of species aggregation. The correlation between estimated and measured values of herbage mass was significant for the majority of graminoid species at the levels of the sub‐life‐form and total plant community but not at the level of the life‐form. Interaction of habitat type and measured herbage mass, and interaction of date and measured herbage mass, were significant for a minority of species. A significant interaction of both date and habitat with measured herbage mass was found in some cases at the level of the sub‐life‐form and total plant community. Results suggest that the double‐sampling method is reliable for most graminoids and at the sub‐life‐form level, but should be applied more cautiously for forbs species, and when different sampling periods and habitat types are involved at the level of the life‐form. To avoid producing several calibration lines at the level of the species and to overcome deficiency of observations at this level, lumping morphologically similar species from the same vegetation stratum in sub‐life‐form groups is recommended for adjusting estimated herbage mass.     

A COMPARISON BETWEEN SPRING AND AUTUMN PASTURE FOR BEEF CATTLE AT EQUAL GRAZING PRESSURES

Two comparisons between spring and autumn pasture for beef cattle were made. Animals used in all comparisons were of similar breed and weight and were subjected to the same feeding regime for 6–8 weeks before turn-out. The pastures were grazed on an equal grazing pressure basis between season comparisons. The pastures received similar rates of fertilizer N between seasons and had similar lengths of rest period for regrowth. Intakes of digestible OM were greater per unit of metabolic liveweight in spring than in autumn. Daily liveweight gains in spring were high, being 1·09 and 1·37 kg (2·4 lb and 3·0 lb), but were lower from autumn pasture at 0·98 and 0·71 kg (2·2 lb and 1·6 lb). Weather was implicated as a factor affecting daily gain from autumn pasture. Greater herbage yields in spring supported 42 and 204 more grazing days per ha which together with the greater gains per animal supported 80–120% more liveweight gain/ha.     

A FURTHER INVESTIGATION OF THE EFFECT OF NITROGEN AND STOCKING RATE ON THE PRODUCTIVITY OF PASTURE FOR BEEF CATTLE

The liveweight gain was measured of beef cattle on pastures stocked at 5.9 to 11.8 cattle/ha and receiving 50, 182 or 329 kg N/ha in a 12-week season. N levels and stocking rates were so adjusted that similar yields of herbage per animal were expected. Results showed that similar liveweight gains per animal, averaging 1.03 kg/day, occurred at all N levels. Liveweight gain/ha ranged from 547 to 1037 kg in 12 weeks and the corresponding quantities of metabolizable energy utilized were 9890 and 17590 Meal. The results confinn earlier work (4, 7).     

THE INFLUENCE OF GRAZING "IMMUNE COWS" ON THE LEVEL OF DICTYOCAULUS VIVIPARUS INFECTION ON PASTURE

At the Agricultural Research Institute, Hillsborough, Northern Ireland, during September and October, 1958, a field which was naturally infected with Dictyocaulus viviparus (lungworm) larvae was divided and one part was intensively grazed by cows which were not excreting lungworm larvae while the other part remained unstocked. Records were kept of the available herbage, total dry matter and the numbers of larvae on both areas. Grazing resulted in a marked reducuon of the larval numbers which was greater, in proportion, than that of the amount or herbage. Although severe grazing did not remove the infection, it so accelerated the decline in numbers that an infection level of one larva per lb. herbage was reached 7 weeks earlier on the grazed than on the ungrazed area. The herbage in both areas showed no larvae about 4 months after infected faeces were last voided on to it.     

THE EFFECT OF NITROGEN, STOCKING RATE AND GRAZING METHOD ON THE OUTPUT OF PASTURE GRAZED BY BEEF CATTLE

An experiment was conducted in 1971 and 1972 to study the effects of two levels of fertilizer N (50 and 504 kg/ha) on the productivity of pastures grazed by young beef cattle. Two stocking rates were imposed at the lower N level and three at the higher. In addition to rotational grazing, set-stocking and an integrated grazing-conservation system were included. The responses/kg N were approximately 1 kg live-weight gain, 19–24 Meal ME and 8–9 kg DM. Maximum yields of 1200–1300 kg live-weight gain/ha and 25,000–27,000 Meal ME/ha were recorded. Productivity of set-stocked pasture was similar to rotational grazing at the high N level, but lower at low N. The integrated system yielded comparable results to high-N rotational grazing. Performances and herbage intakes per animal reflected the stocking rates imposed.     

The use of conserved forage as a supplement for grazing dairy cows

The difficulty in matching the herbage requirements of grazing dairy cows to herbage production, due mainly to the unpredictability of the latter., causes stocking rates to be too low for maximum per hectare production and, thus, cows to be underfed at certain times in the grazing season. Conserved forage may be used as a supplement for grazing dairy cows in order to reduce variation in forage intake by the cow, to allow pasture stocking rates to be increased and to increase the efficiency of land use. The effect of offering conserved forage with herbage on intakes and production is reviewed in comparison to both ad libitum and restricted herbage. Total nutrient intakes and milk fat + protein yields are reduced for cows offered herbage and supplementary forage compared with cows offered ad libitum herbage, but increased compared with cows offered a restricted herbage level. Increasing pasture stocking rates may allow increases in utilized metabolizable energy levels from grassland but further research is needed in this area. Both grass and maize silage supplements offer potential for increasing the efficiency of land use, but in the case of grass silage this is only achieved in the best management practices.     

A COMPARISON OF THE GROWTH OF A CUT SWARD WITH THAT OF GRAZED SWARDS, USING A TECHNIQUE TO ELIMINATE FOULING AND TREADING

A technique is described whereby sward defoliation by sheep can occur in the absence of treading and the deposition of excreta. By using this technique, swards were grazed to a moderate severitj, leaving behind an amount of herbage similar to that left after cutting; the DM yields from both methods are compared. The technique was also used to study other swards which were grazed either very leniently or very severely. Within the limits tested, efficient rotational grazing (i.e. the removal of a large proportion of the herbage on each occasion) did not give the greatest DM yields, except at the first harvest. Cutting- and grazing-treatments produced differences in sward structure.     

THE EFFECT OF IRRIGATION AND STOCKING RATE ON THE OUTPUT FROM A SWARD

In view of the paucity of information on the effect of grassland irrigation on livestock production, a grazing experiment was made in 1960 and 1961 in which the response to irrigation was measured at two dairy-cow stocking rates. The method and herbage results are described.
The increases in herbage utilized as a result of irrigation were comparable with the results of cutting experiments, averaging 342 lb of ash-free organic matter per acre-inch of water used. Irrigation also increased the uniformity of herbage production.