THE RELATIONSHIP BETWEEN INTENSITY OF GRAZING AND THE HERBAGE CONSUMPTION AND GROWTH OF CALVES

Experiments were conducted in 1967 and 1968 in which HerefordXFriesian (Experiment 1) and Friesian (Experiment 2) steer calves horn in April were turned out to graze at one week or 3 months of age, respectively, and maintained at three stocking densities in the ratio 1:2:3 animals per unit area. The calves grazed paddocks of S23 perennial ryegrass in rotation, and were moved when the height of grazed stubble at the medium stocking density was reduced to 8 cm. The rate of liveweight gain and herbage intake per head declined as stocking rate increased. When the results of the two experiments were compared, the weight gain of the calves was more closely related to the weight of herbage residues than to the height of the grazed sward. The rate of liveweight gain was depressed when the amount of herhage left after grazing fell helow 2000–2500 kg OM/ha (1800–2250 Ib/ac).     

Supplementary feeding of grazing beef cattle

The effects of cereal and protein supplements on feed intake and liveweight gain were studied. In 1975, steers were continuously stocked on autumn pasture and fed no supplement or 8 g dry matter (DM) per kg liveweight (LW) per d as rolled barley (crude protein (CP) concentration 120 g kg^-1), lucerne cobs (CP concentration 190 g kg^-1) or a mixed concentrate (CP concentration 300 g kg^-1). In 1976, steers were continuously stocked or rotationally grazed in summer and fed no supplement or 7 g DM per kg LW per d as either rolled barley (CP concentration 130 g kg^-1) or a mixture of rolled barley and groundnut meal (CP concentration 210 g kg^-1). Herbage organic matter (OM) intakes in 1975 and 1976 were depressed on average by 22 and 15% respectively with supplementation, but total OM intakes were increased by 9 and 15% respectively. Daily liveweight gain was not significantly increased by supplementation in 1975 when herbage allowance was ample but was significantly increased in 1976 when herbage allowance was limited and herbage digestibility was lower. Protein concentration of the concentrate did not significantly affect daily gain in either year nor was there any difference in gain between rotational grazing and continuous stocking.     

A NOTE ON THE ZERO-GRAZING OF BEEF CATTLE

Groups of 8 steers weighing 300–400 kg (660–880 Ib) were rotationally grazed on a ryegrass-dominant pasture for 115 days. The systems compared were zero grazing (Z), field grazing conducted at the same stocking rate (FC), and field grazing conducted at a stocking rate varied with the intention of giving the same liveweight gain per uiimal as zero grazing (FV). Mean daily liveweight gains were: Z, 0.98; FC, 0.78; FV, 0.90 kg/animal (2.2, 1.7 and 20 Ib/animal), and liveweight gains/unit area were in the ratio 100:78:85. Organic-matter intake, measured on four occasions, was, on average, Z, 6.54; FC, 6.18; FV, 687 kg/head daily (14.4, 13.6 and 15.1Ib). From these results it appears that a comparison of zero grazing and field grazing made at the same stocking rate is likely to underestimate the potential of field grazing for beef production from grass.     

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 STUDY OF THE UTILIZATION OF SILAGES OF DIFFERENT DRY–MATTER CONTENT BY YOUNG BEEF CATTLE WITH OR WITHOUT SUPPLEMENTARY BARLEY

Three Uages containing 18.7, 35.2 and 51.0% DM were given to young beef cattle without supplementary barley or with a daily allowance of 1.8 or 3.6 kg air-dry fortified barley. Each diet was given to 9 individually fed animals, the mean fasted liveweight of which at the start of the experiment was 304 kg. The dafly voluntary DM intake was recorded for a 10-day period for the 9 animals on each silage without supplementary barley. The mean DM intakes per kg W^0.73 were 58.4, 94.6 and 104.1 g for Silages 1, 2 and 3 and the intakes increased curvilinearly with the DM content of the silage. The mean daily liveweight gains on Silages 1, 2 and 3 were 0.63,0.73 and 0.75 kg, respectively; the relationship was significantly linear (P <0.01). The barley supplement also had a significantly linear CP <0.01) effect on daily gains. The mean daily gains for 0, 18 and 3 6 kg fortified barley per day were 0.54, 0.74 and 0.84 kg, respectively. The DM and digestible organic matter required per kg liveweight gain were not significantly affected by the DM of the silage, but were significantly (P < 0.01) affected by supplementation. The metabolizable energy (ME) values of Silages 1,2 and 3 were 2.46, 2.52 and 2.50 Meal/ kg DM, respectively. The supplementary concentrate increased the ME concentration significantly (P < 0.05), although the overall increase was small. The mean values were 2.49, 2.54 and 2.61 Meal/ kg DM, respectively, for 0, 1.8 and 3.6 kg fortified barley per day. The digestibilities of DM and organic matter were not significantly affected by the type of silage, but there was a significant increase with increasing intake of supplementary barley.     

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

An experiment was conducted in two successire years to measure the effect of two levels of fertilizer N, 50 and 300 kg/ha (45 and 270 Ib/ac) on the productivity of pastures grazed by young beef cattle. Two stocking rates were imposed at the lower N level and 4 at the higher level. The responses per kg fertilizer N were approximately 1 kg liveweight gain, 20–24 Meal ME and 8–9 kg DM. Maximal yields of about 1000 kg gain/ha (890 Ib/ac) and 19,000 Meal ME/ha (7700 Mcal ME/acre) were recorded. Animal performance was similar on the low and the high N pastures. There was evidence that the chemical quality of pasture was lower on the low N pasture in the first year, but there was no difference in the second year. The numbers of dung pats per ha and the refusal of herbage due to fouling were reduced by Increasing the stocking rate.     

COMPARATIVE STUDIES OF PERENNIAL RYEGRASS. TIMOTHY AND MEADOW FESCUE.

Hays made, mainly in May, from pure swards of perennial ryegrass, timothy and meadow fescue were fed to 8-month old steers in 1963 and to yearling steers in 1964. High-quality hay was obtained, but no significant differences in growth rate were observed between calves fed on hays from the 3 species. In 1963, barley (1.5 kg DM/ head per day) was fed, in addition to the hays, to half the animals and resulted in a significant increase in live weight gain. The productivity, in terms of liveweight gain/ unit area, of each species when managed for hay and‘zero grazing', or hay and grazing, was calculated. On this calculation perennial ryegrass was the most productive species.     

THE EFFECT ON FATTENING STEERS OF SUPPLEMENTING SILAGE WITH DRIED GRASS OR ROLLED BARLEY

Eighteen crossbred Aberdeen-Angus and six Shorthorn steers with an average liveweight of 382 kg were given silage (DM content 22.3%) ad lib., supplemented with 0, 1.2, 2.4 and 3.6 kg artificially dried grass, or 1.8 kg rolled barley, per day. A digestibility study carried out on the silage and dried grass showed that the concentration of the metabolizable energy was 52.7 and 45.6 kcal/100 kcal of food, respectively. Live-weight gain increased with each level of supplementation. Supplementation did not significantly affect the intake of silage DM, but differences in the intake of total DM were significant. The killing-out percentages of the steers were similar. The results suggest that dried grass pellets may be a usefid supplement for a silage diet. It was shown that 1.12 kg of dried grass was equivalent to 1.80 kg rolled barley as a supplement for silage.     

THE UTILIZATION OF GRASS FED INDOORS TO YOUNG BEEF CATTLE, WITH OR WITHOUT SUPPLEMENTARY BARLEY

An experiment was carried out in which grass was cut and fed indoors, with or without supplementary barley. Seven animals were allocated to each of the following treatments: (1) grass ad lib . without supplementary barley; (2) grass ad lib . with supplementary barley at the rate of 0.5 lb/100 lb bodyweight; (3) grass ad lib . with supplementary barley at the rate of 1 lb/100 lb bodyweight. Supplementary barley increased total dry-matter intake and improved daily liveweight gain and food conversion rate. The mean daily liveweight gains for the 17-week experimental period were 1.60, 1.91 and 2.20 lb and the corresponding feed dry-matter conversion ratios were 6.18, 5.67 and 5.55 for Treatments 1, 2 and 3, respectively.
The dry-matter digestibility of the diets was slightly higher when the grass was supplemented with barley than when grass alone was given. Although barley depressed the digestibility of protein, the absolute and the proportionate retention of nitrogen was increased. This was particularly marked on Treatment 3, presumably because of the higher net energy value of the diet containing the greater amount of barley. The N-retention data corresponded to the rates of liveweight gain obtained.     

OBSERVATIONS ON THE UTILIZATION OF GRASS GRAZED BY YOUNG BEEF CATTLE WITH AND WITHOUT BARLEY SUPPLEMENTATION

A field trial was carried out in which 3 groups of cattle were grazed on a paddock system with and without supplementary barley. The cattle were 6 months old when turned out to grass and were each fed 4 lb/day of barley for one week to prevent any adverse effect from an abrupt change of diet. The trial began on 14 May and continued until 8 October. The mean liveweight gain obtained on the unsupplemented grass was only 0·97 lb/day up to 20 August and owing to the poor growth of the animals a supplement of 4 lb barley/head/day was then introduced. The daily liveweight gain for the remainder of the trial was 1·94 lb. When a supplement of 4 lb barley was provided throughout the trial the mean daily liveweight gain was 1·61 lb. When barley was fed ad lib . intake averaged 12·3 lb/head/day throughout the trial and the mean daily gain was 2·45 lb.
Indoor digestibility and nitrogen retention trials were carried out. The starch equivalents of diets on the three treatments were 63·7, 68·3 and 69·5, respectively. The respective mean daily intakes of dry matter were 11·2, 11·9 and 11·8 lb, and the mean daily retentions of N were 35·0, 35·8 and 33·6g. These results indicate that although the grass was of good nutritive value the poor performance of the animals on grass alone was mainly due to their inability to graze sufficient grass.     

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

Two successive grazing experiments were conducted over 12 weeks on perennial ryegrass pastures with 50 and 44 young cattle to study the effect of N fertilizer when applied at a daily rate of 1 or 3 kg N/ha. At each level of N two stocking rates differing hy 20% were imposed. At the liigher N level and stocking rate, three frequencies of grazing were imposed. At the stocking rates imposed N tended to reduce the daily liveweight gain per head, but increased the total liveweight gain per ha by from 0.79 to 1.58 kg/kg N. A 20% increase in stocking rate depressed gain per head in both years. In the first year it did not improve gain/ha, hut in the second year gain/ha was increased by 12–17%. There was a tendency for performance per animal and per ha to increase as the grazing cycle was lengthened. In 1969 the highest yield in the whole season was 1880 grazing days and 1260 kg gain/ha. The overall response to N fertilizer was similar to that recorded in other reports, but it is possible that a lack of K had limited pasture growth.     

The effects of cereal supplementation of grass and maize silages

Grass and maize silages were fed alone and with two levels of a barley supplement to Friesian steers of about 300 kg liveweight. The organic matter (OM) intakes of grass and maize silage were similar although the OM digestibilities of the silages were 0·722 and 0·649 respectively. For both silages, barley supplementation increased total OM intake and total digestible OM intake by 0·46·0·08 and 0·37·0·06 g per g OM of supplement respectively. Liveweight gains on grass and maize silage diets were 1·38 and 1·20 kg d^-1 respectively, but the differences were not significant (P> 0·05).     

THE INFLUENCE OF TYPE AND LEVEL OF SUPPLEMENTARY FEED ON INTAKE AND PERFORMANCE OF BEEF CATTLE ON PASTURE

Two experiments, each of 6 weeks dehydration, were conducted in 1972. In Expt 1, 24 cattle were grazed in individnal paddocks during July and August and received one of 4 treatments over a 6-weeks period: no supplements; straw ad lib; 3.3 kgj. day sugar-beet pulp; 4.0 kg/day molasses. Mean daily live weight gains were significantly increased by the sugar-beet pulp and molasses supplements; which also increased OM and DOM intake significantly. The increase in total OM intake per kg OM in the supplement was 0.48 for sugar-beet pulp and 0.67 for molasses. In Expt 2, 18 cattle grazed in groups of 3 during November and December. Two groups each received 0.5, 3.5 or 6.5 kg/day sugar-beet pulp over a 6–weeks period. There was no significant difference in live weight gain between treatments, and no significant difference in total intake. Intake from pasture declined with increasing level of supplement, so that the average increase in OM intake per kg OM in the supplement was 0.28. Hie results are discussed in relation to availability of pasture and the effects of the supplements on intake.     

EFFECT OF HIGH FERTILIZER NITROGEN AND STOCKING RATES ON LIVEWEIGHT GAIN PER ANIMAL AND PER HECTARE

The effect of increasing annual fertilizer N application rate from 400 to 800 kg/ha (357 to 714 lb N/ac) and stocking rate from 5.0 to 7.5 animals per forage ha (2.02 to 3.04 animals per forage ac) on herbage availability, digestible OM intake and live weight gain was investigated in a grazing experiment repeated in 3 consecutive years. A 21×1 day rotational paddock grazing system was used in which the grazing area was increased in the ratio of 1:1.5:3 on two predetermined occasions. Increasing the fertilizer N application rate increased herbage availability by 12% but failed to increase live weight gain. Increasing stocking rate decreased herbage availability per ha and per animal, and also live weight gain per animal, but increased live weight gain per forage ha by 17.6%.     

THE USE OF LIVEWEIGHT-GAIN TRIALS FOR PASTURE EVALUATION IN THE TROPICS

An experiment is described in which liveweight gains were measured from two grass/legume pastures using small East African Zebu animals and also progeny of small East African Zebu cows crossed with Bos taurus bulls. Significantly higher production was obtained from cross-bred stock, which averaged 706 lb liveweight gain at per annum (791 kg/ha per annum), compared with 509 lb liveweight gain/ac per annum (571 kg/ha per annum) from Zebu stock, indicating that pasture management had advanced beyond the genetic potential of the local Zebu stock. The problems of designing, conducting and interpreting the results of such grazing trials are discussed.     

The effects of dalapon and stocking rate on the species composition and animal productivity of a sown sward

Dalapon (2.8 kg ha^×1) was applied in July, either annually or biennially, to a sown sward that contained about 50%Lolium perenne measured on a ground cover basis. The sward was grazed with young beef animals at three stocking rates throughout the 4 years of the experiment. In unsprayed plots, the proportion of L. perenne declined to less than 20% (30, 14 and 16% on high, medium and low stocking rates respectively). Lolium perenne was replaced largely by Holcus lanatus and Poa spp. Annual applications of dalapon checked the decline in L. perenne. After 4 years of annual treatment with dalapon, 44%L. perenne was present on heavily stocked plots, 41% on medium stocked plots and 26% on lightly stocked plots. Biennial applications of dalapon had slightly less effect on the proportion of L. perenne. The proportion of Trifolium repens in the sward was affected by dalapon and stocking rate in much the same way as that of L. perenne. Monthly cattle weights showed that dalapon caused a slight check to individual animal performance in the month after spraying, but total liveweight gain per unit area was not significantly affected. Increasing stocking rates were inversely related to performance per animal and directly related to output per unit area. Dalapon × stocking rate interactions were generally non-significant. There was a slight tendency for higher animal gains to be associated with higher proportions of L. perenne, but this only held for the first half of the growing season. Mean maximum liveweight gain of about 1000 kg ha^?1 was achieved in 1974, by which time the proportion of Holcus lanatus had risen to a mean value of nearly 40%. The value of indigenous grasses for summer beef production is discussed.     

THE USE OF GRAZING CONTROL FOR INTENSIVE FAT-LAMB PRODUCTION

Three grazing managements (set stocking, 4-paddock rotation, 8-paddock rotation), each with an undivided lateral creep area, were studied. Each of these managements carried 2 stocking rates (6 ewes and twin lambs per acre, 10 ewes and twin iambs per acre) and the sub-divided managements were grazed at 2 severities of grazing.
Stocking rate had a major effect upon the lambs' liveweights but did not significantly affect the ewes' liveweights. Lambs on set-stocking managements had a significantly higher rate of liveweiglit gain than lambs on managements with sub-divided ewe areas. Under lax grazing, for much of the experimental period, the lambs had a significantly higher rate of liveweight gain and the ewes had significantly higher liveweights than under severe grazing.     

Concentrate supplementation of grazing dairy cows. 2. Effect of concentrate composition on herbage intake and milk production

The effect of feeding either traditional concentrates containing starch or high quality fibrous concentrates on the performance of grazing dairy cows was examined in a trial in which cows were given concentrates with either 350 g starch and sugars (kg dry matter (DM))^-1 (high-starch) or 100 g starch and sugars (kg DM)^-1 (high-fibre). The swards used consisted predominantly of perennial ryegrass and were usually aftermaths following cutting. Each area was grazed for 3 or 4 d at each grazing and a two-machine sward-cutting technique was used for estimating herbage intake.
The effect of concentrate composition on the herbage intake of grazing cows at a high daily herbage allowance of 28 kg OM above 4 cm cutting height was investigated in 1983 and 1984. With 54 kg OM d^-1 of high-starch concentrates the mean herbage intake was 11·5 kg OM d^-1 per cow while cows fed 5.3 kg d^-1 of high-fibre concentrates consumed on average 12–6 kg OM d^-1. The mean substitution rate of herbage by concentrates was reduced from 0·45 kg herbage OM (kg concentrate OM)^-1 with the high-starch concentrate to 0·21 with the high-fibre concentrates.
The effect of the treatments on milk production was studied in 1984. The cows consumed 5·5 kg OM d^-1 as concentrates and grazed at a lower herbage allowance of 19 kg OM above 4 cm cutting height. With high-fibre concentrates milk production and 4% fat-corrected milk production were 13 and 1·8 kg d^-1, respectively, higher than with the high-starch treatment. The daily live weight gain with the high-starch concentrates was 0·17 kg per cow more than with the high-fibre concentrates.     

THE USE OF LIVEWEIGHT-GAIN TRIALS FOR PASTURE EVALUATION IN THE TROPICS

A 21-acre grazing trial which ran continuously for three years to evaluate grass and grass/legume pasture with and without inorganic fertilizers is described. Techniques for conducting grazing trials where large treatment differences are expected and the interpretation of results from these trials are discussed. Good practical management of stock and pastures was shown to be necessary in these grazing trials and where it was only possible to establish one true replicate some measure of statistical control was achieved by comparing regression coefficients of cumulative animal production.
The results showed that up to 475 1b liveweight gain/acre per annum (532.48 kg/ha) could be obtained from pastures grazed by small East African Zebu steers. The addition of the legumes Stylosanthes gracilis and Centrosema pubescens to grass mixtures gave significant and economic increases in liveweight gain. Grass/legume swards receiving phosphorus and sulphur produced liveweight gains equivalent to the animai production from grass swards receiving 140 1b N/ac per annum (156.94 kg/ha).