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).     

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.     

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

A grazing experiment is described in which the liveweight gains of small East African Zebu heifers were measured from Hyparrhenia rufa/Stylosanthes gracilis and H. rufa/Centrosema pubescens swards. The design of this trial enabled animal production to be assessed from variations in liveweight gain since stocking rate was maintained at the same level on both pastures, but the overall stocking rate was varied according to seasonal changes in herbage availability.
Production was measured both by using individual animals within a group as independent units, and by true animal replication. Gains from individual animal blocks were shown to be of value for comparing pasture species, provided that the composition of the grazing group was varied. Problems of conducting and interpreting small–scale grazing trials as means for evaluating pastures are discussed.     

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).     

GRASSLAND RESEARCH ON BLANKET PEAT IN IRELAND

The results from 10 years of grassland research at the Peatland Experimental Station, Glenamoy, are summarized.
Grass and legume species were introduced by surface seeding, without cultivation or by direct seeding after rotavation, depending on the specific situation. The rate of establishment was dependent on pretreatment and the management of grazing animals before and after sowing.
The most suitable species were Trifolium repens, Lolium perenne, Festuca arumlinacea, Festuca rubra and Holcus lanatus .
A level of fertility suited to the introduced species must be reached initially and subsequently maintained. The requirements (per/ac) for Ca, P, K, N, Cu and Co were: 2240 lb (1016 kg) ground limestone, 36 lb (16 kg) P, 112 lb (51 kg) K, 20 lb (9 kg) N, 20 lb (9 kg) CuSO₄ and 2 lb (0–91 kg) CoSO₄ at sowing, with 27 lb (12–25 kg) P and 56 lb (254 kg) K annually.
Dry–matter yields of 6000 lb/ac (6720 kg/ha) were obtained from grass–clover swards without fertilizer N, and approximately twice this quantity where 400 lb N/ac (448 kg/ha) had been applied annually. A liveweight gain of 526 lb/ac (589–12 kg/ha) and a starch equivalent output of 2946 lb (3299–5 kg) were obtained with sheep. The relationship between these results and those on peat soils abroad are discussed.     

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 EFFECT OF HIGH NITROGEN LEVELS AND STOCKING RATES ON MILK OUTPUT FROM PASTURE

An experiment using 40 lactating dairy cows was conducted for 3 successive years to examine the effects of fertilizer N applied at 400 and 700 kg/ha (358 and 627 lb/ac) at stocking rates of 4.94 and 7.41 cows/ba (2 and 3 cows/ac). The animals were grazed in groups of 10 per treatment, using a fixed rotational grazing system, for 22 weeks in each year. Milk ontput/cow and/ha was significantly affected by stocking rate, the mean milk outputs being 2499 and 2218 kg/cow (5498 and 4880 lb/ cow) and 12313 and 16396 kg/ha (11032 and 14691 lb/ac) at the lower and higher stocking rates, respectively. Milk yield/cow at the lower stocking rate was not affected by N level. At tbe higher stocking rate, increasing the amount of N resulted in a 7.4% increase in milk output/cow and/ha. This response to N declined from 1.7% in the first year of the trial to 2.4% in the third year. The response in milk yield to N appeared to he greatest during the first part of the grazing season. Milk composition, liveweight change, and herbage availahilities and intakes were also recorded.     

THE EFFECT OF NITROGENOUS FERTILIZER ON THE RATE OF GROWTH OF ITALIAN RYEGRASS

In an experiment described earlier (13), the N content of Italian ryegrass in spring reached a high value one or two weeks after applying N and then fell quickly at first and then more slowly. After 10 weeks average N content (in DM) was 0.6% from an application of 25 lh N/ac (28 kg/ha), 0.9% from 75 lb N (84 kg/ha), and 12% from 125 lb N (140 kgJha). Nitrate-N content fell more abruptly and tben remained fairly constant. Percentage nitrate–N (in DM) fell below 0.10% during the second week after an application of 25 lb NJac, during the third week after 75 lb N, and during the fifth week after recciriag 125 lb N. The yield of N increased during the first 5 or 6 weeks, remained fairly constant for 3–5 weeks, and then hegan to fall. During the ninth and tenth weeks, the crop lost an average of 9 lb N/ac per week (10 kg/ha) after an application of 75 Ib N/ac and 12 lb N/ac per week (13 kg/ha) after 125 Ib N.     

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.     

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.     

A COMPARISON BETWEEN A PADDOCK SYSTEM AND A 'WYE COLLEGE' SYSTEM OF GRAZING FOR MILK PRODUCTION

Two grazing systems, a paddock system and a ‘Wye College’ system, were compared in two 20-week experiments nsing 16 and 20 spring-calved Ayrshire cows in 1970 and 1971, respectively. A sward of S23 perennial ryegrass was used, and an average of 342 kg N/ha (305 lb N/ ac) was applied per annum. The paddock system had 28 separate paddocks; one paddock was grazed each day in rotation and occasionally topped in mid-season. The Wye College system had 4 plots of equal size and the cows were offered 1/7 of one plot each day; no back fence was used and surplus herbage was neither cut nor topped. The stocking rate on hoth systems was 1 cow per 0.20 ha (0.49 ac) in 1970 and per 0.16 ha (0.40 ac) in 1971. The mean daily milk yields per cow on the paddock and the Wye College systems were 16.2 and 15.3 kg (35.7 and 33.7 lb), respectively, in 1970; and 18.1 and 18.4 kg (39.9 and 40.6 lb) in 1971. The average annual output of milk was 13,500 and 13,150 kg/ha (1200 and 1170 gal/ac) on the paddock and Wye College systems, respectively. The fat and solids-not-fat (S.N.F.) contents of the milk were not significantly affected by the grazing system. It is concluded that the Wye College system was as effective as the paddock system in producing a high output of mUk per ha, but at a lower cost and with far fewer management decisions.     

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).     

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.     

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%.     

Effect of virginiamycin supplementation on the performance of young grazing cattle

Three experiments have been conducted to study the effect of virginiamycin in young grazing-bulls (Experiment 1) and heifers (Experiments 2 and 3). Rotational grazing on permanent grassland was practised and animals were supplemented with 1 kg dried sugarbeet pulp per head daily. Control groups did not receive virginiamycin via the supplement, while it was incorporated at 120, 300 and 200 mg kg⁻¹ for the treatment groups in Experiments 1 to 3 respectively.
Average daily liveweight gain was significantly increased from 0·59 to 0·72 kg in Experiment 1 and from 0·73 to 0·81 kg in Experiment 3, but was not affected in Experiment 2 (0·51 vs 0·55 kg). Virginiamycin also increased liveweight gain per ha by 12, 7 and 13%, respectively, for the three experiments. Grazed area per animal was not enlarged to the same extent as the calculated daily energy allowances, which may suggest an improved digestibility and/or rumen fermentation.     

THE EFFECT OF NITROGEN APPLICATION TO PASTURE ON BEEF PRODUCTION

Five grazing experiments each lasting 2 or 3 years were made between 1955 and 1967, all starting in the first year of ryegrass/cocksfoot/clover or ryegrass/clover leys. A high and a low rate of N, 235 and 45 Ib/ac on average (263 and 51 kg/ha) were compared for beef production. High- and low-N treatments gave mean clover contents for the grazing season of 8 and 24 % on a dry-weight basis, respectively. High N consistently gave a smaller liveweight gain/animal than low N, on average 1±92 and 2±08 Ib/day (0±87 and 0±94 kg/day), respectively. Liveweight gain/ac was 20% greater for high N than for low N, and in terms of net energy the production from high- and low-N, respectively, was 18,500 and 15,000 MJ/ac (45,700 and 37,100 MJ/ha). Data from these experiments, together with published results, were used to calculate a regression of liveweight gain response on N rate and an equation was derived from this to express the output in terms of profit. At 1971 prices profit was maximal at λ0±9/ac (λ2/ha) with 112 Ib N/ac (125 kg N/ha); it was considerably greater at 1973 prices when higher rates of N were justified.     

RESPONSE OF GRASSLAND TO NITROGENOUS FERTILIZER IN THE WEST OF ENGLAND

Extensive replicated plot experiments were carried out at Henley Manor Farm from 1956–1961 to obtain accurate measurements of herbage production and response to nitrogenous fertilizers under West of England conditions. 356 plots were used; use of the herbage by both cutting and grazing was studied. The principal results are: Grass/ clover swards (containing approx. 35% clover) grown without nitrogenous fertilizer averaged 75 cwt dry matter per acre per annum. Application of nitro-chalk to initially grass/clover swards reduced the clover content of the herbage. About 133 lb N/annum was required by an all-grass sward to equal the production of a grass/clover sward without N. Attempts to increase production of grass/clover swards by using N for early growth and relying on clover for mid-season growth were unsuccessful in 2 out of 3 years. Swards (initially grass/clover) gave significant increases in total dry-matter production from regular use of the lowest level of N (26.0 or 34.7 lb N/acre/cut or graze) in 44 out of 49 cases. Extremely high yields were obtained from the heaviest use of N (104.2 lb N/acre/silage cut). 52.1 lb N/acre/cut or graze was the optimum rate of application on ail-grass and grass/clover swards. Up to about 350 lb N/acre/annum the dosage-response curve was very nearly straight for all-grass and grass/clover swards. On the grazed plots herbage left ungrazed amounted on average to only 6% of the total. The health of all stock on the high nitrogen plots (as well as all others) was excellent.     

THE EFFECT OF SUPPLEMENTARY BARLEY UPON GROWTH AND EFFICIENCY OF FOOD CONVERSION IN CALVES KEPT AT HIGH GRAZING INTENSITY

Three groups of Hereford × Friesian steer calves, bom in early January 1969, were strip-grazed on eqoal areas of a sward of S321 perennial ryegrass from May to September inclusive, and received kibbled barley at the rate of nil, 3/4% or 1 1/2% of liveweight per day. Adjustments were made to the number of animals per group in order to maintain the same high grazing intensity (defined as 8 cm stubble height in grazed areas) on all treatments. The animals receiving supplementary barley gained weight at a rate 17–19% higher than the controls, but there was no significant difference in growth rate between the high and low levels of supplementation. The effficiency of conversion of barley was only 5–12 kg per animal liveweight gain/100 kg barley OM. The high level of supplementation resulted in an increase in stocking rate of 36 % over that of the control group, and an increase in liveweight gain per unit area of land grazed of 63%. The additional liveweight gain due to supplements, expressed per unit area of land grazed, was relatively constant at 21–24 kg liveweight gain/ 100 kg barley OM consumed.     

The performance of beef animals on a permanent pasture*

Between 1967 and 1975, 416 beef animals were grazed rotationally on an indigenous pasture (11.65 ha) containing Festuca rubra, Holcus lanatus, Poa trivialis and Agrostis spp. and dicotyledonous plants, but little Lolium perenne or Trifolium repens. Part of the land received fertilizer nitrogen at rates varying between 120 and 200 kg h^?1 each year and part did not; some of the land was grazed only and some was cut and then grazed. The winter gains of the animals (approx. 45 kg) were more variable and less than the summer gains (approx. 155 kg). Summer gain was inversely correlated with winter gain. An increase in initial weight of animals purchased from 1973 onwards did not increase either winter or summer gain. Friesians gained more than Hereford-cross animals during the winter, but there was no difference in summer gain. During 9 years the average animal weight per grazed ha in April was increased from 1260 to 2122 kg. The mean total gain on 1165 ha of grass was 6486 kg per annum in the first 3 years and 7266 kg per annum in the last 3 years. The average annual production was 590 kg live-weight gain and 1.01 t hay or 2.33 t silage per ha. The output of fertilized grass in 1975 was calculated as 842 Livestock Unit Grazing Days (LUGD) per ha and that from unfertilized grass as 360 LUGD per ha. The overall output of utilized metabolizable energy in 1975 was 59–7 GJ h^?1, with 69.3 GJ h^?1 from fertilized grass and 29.8 GJ h^?1 from unfertilized grass.