A NOTE ON THE LIVEWEIGHT CHANGE OF SHEEP GRAZING AT THREE STOCKING RATES AND TWO LEVELS OF NITROGENOUS FERTILIZER

The liveweight changes of sheep grazing at 3 stocking rates and 2 levels of N fertilizer were recorded. The results are discussed in relation to the model proposed by Owen and Ridgman (1) for short–term periods of grazing.     

THE EFFECTS OF WINTER GRAZING ON SUBSEQUENT PRODUCTION FROM PASTURE

The eflFects of various systems of winter-grazing management on pasture production in the following spring and summer were studied in four trials in the Pentland Hills, Scotland. Winter grazing reduced the yield of herbage in spring, but growth in May and June was primarily influenced by the level of nitrogen application in spring, irrespective of winter-grazing treatments.     

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.     

EFFECTS OF DIFFERENT GRAZING ROTATIONS ON PASTURE PRODUCTION

Different grazing treatments applied to pastures in which perennial ryegrass was dominant had little influence on DM production during the main reproductive growth period in late spring and early summer. Lax and infrequent grazing at this time did, however, reduce tiller density. During the dry summer period lax infrequent grazing increased production by 20%, while in the vegetative growth period in autumn those pastures which were alternately lax- and hard-grazed outyielded those which were hard grazed by 63%. In all treatments, initial recovery growth resulted almost exclusively from the production of leaf tissue. The rate of leaf growth declined three to five weeks after grazing, depending on treatment and season, and subsequent yield increase was dominated by sheath and stem growth.     

THE EFFECT OF STOCKING RATE ON ANIMAL PRODUCTION FROM CONTINUOUS AND ROTATIONAL GRAZING SYSTEMS

Liveweight and wool production data are presented from a grazing management experiment in which continuous stocking was compared with a four-paddock rotational system at three stocking rates on a sown pasture. Significant differences were recorded in liveweight and wool production between stocking rates. The overall effect of management was non-significant but its interaction with stocking rate and year were both significant. At the intermediate stocking rate (8 wethers/ac, 20 wethers/ha) increases in both liveweight and wool production were recorded for the rotational management system; in this treatment there was also less need for supplementary feeding. Greater wool production was recorded from the continuously grazed treatments at both the high and the low stocking rates but there was little effect on liveweight or the need for supplementary feeding.     

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.     

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 EFFECTS ON DAIRY COWS OF GRAZING PASTURE CONTAINING HIGH LEVELS OF NITRATE-NITROGEN

Two paddocks each received a total of 412 kg N/ha (371 lb/ac) between April and July in four equal applications. The paddocks were grazed four times for four days by two groups of 5 Friesian cows starting 14 and 21 days after each N applica tion. The nitrate-N content of the herbage DM reached a peak of 0·76 % in the third grazing 14 days after N application. There was a significant (P < 0·001) correlation (r =0·67) between water soluble carbohydrates and nitrate-N in the herbage DM. No marked changes occurred in eitber the methaemoglobin or packed cell volume of the blood samples from either group. No detrimental effects on animal health or production were recorded during the experiment.     

A COMPARISON OF TWO HAYS FOR BEEF PRODUCTION

A medium quality barn-dried hay and a poor quality field-cured hay were each supplemented with 3 levels of concentrate in the diet of young beef cattle, averaging 313 kg liveweight. The supplement was given on predetermined hay concentrate metabolizable energy (ME) ratios based on the determined ME of the hays and an assumed ME of 3·0 McalsAg DM for the supplement. The hay concentrate ratios used were 1:1, 1:2 and 1:3, the aim being to provide a reasonable rate of growth (0·7 kg/day) with the poorer hay. It was necessary to include urea in the concentrate mixtures used on the 1:1 and 1:2 ratios with the field-cured hay. The urea appeared to have an adverse effect on the intake and utilization of DM on the 1:1 ratio. The range of mean intakes of supplement DM was 3·02 to 4·41 kg/day for the barn-dried hay and 2·23 to 4·61 for the field-cured hay. Mean daily liveweight gains with the barn-dried hay were 0·76, 0·89 and 0·85 kg for the 1:1, 1:2 and 1:3 ratios, respectively, with no significant difference between ratios. The mean daily gains with the field-cured hay were 0·39, 0·77 and 0·75 for the three ratios, the mean gain on the 1:1 ratio being significantly lower than those of the other ratios. The ME conversion ratios were not significantly affected by either ratios or hay type, except on the 1:1 ratio with field-cured hay. There were significant differences between the barn-dried hay and field-cured hay diets in the digestibilities of DM, organic matter, crude protein and energy; the mean coefficients for DM being 74·5% and 65·6%, respectively.     

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 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 EFFECT OF WINTER GRAZING BY SHEEP ON SPRING AND EARLY SUMMER PASTURE PRODUCTION

Studies were made in S.W. Scotland of the effect of winter grazing (October to March) by sheep on subsequent spring and early summer pasture production from a sward in its first harvest year and from a permanent pasture. Averaged over the two swards, DM yields in April, May and June were reduced by 38%, 8% and 5%, respectively, as a result of various times and frequencies of grazing, compared with no grazing. Reductions were greatest after grazings in the January to March period, especially grazings involving the month of March. In a trial in which fertilizer N was used to compensate for March grazing, 50 kg NJha raised DM yields in April to the level of those from no grazing, while only 15 kg NJha were needed to raise June yields to parity. Controlled winter grazing of sheep and the use of fertilizer N to restore production losses after early spring grazing are justified.     

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.     

RESEEDING AND SURFACE TREATMENT-A COMPARISON OF TWO METHODS OF IMPROVING HILL GRAZINGS

Two methods of improving hill land for sheep grazing have been compared on a Festuca/Agrostis pasture in mid-Wales. Ploughing and reseeding, following a pioneer crop, resulted in an excellent sward which remained productive at the end of the 8-year trial period. Surface seeding with light cultivation gave only a fair establishment of white clover, but no sown grass, during the same period. The production and financial results point to the superiority of the former technique where conditions are suitable and where increased grass production can be met by increased sheep stocking. Any worthwhile method must produce real improvement to the herbage.     

SOME FACTORS AFFECTING THE OUTPUT OF STARCH EQUIVALENT FROM GRAZING LAND ON UPLAND DAIRY FARMS

Grazing records and cost records have been analysed from 19 dairy farms, all situated at least 400 feet above sea level, in order to determine the effect of height and of increased expenditure on the level of output of starch equivalent, and to investigate whether these farms have special problems not met with on lowland farms. The analysis shows a very marked influence of height on output and a low, statistically non-significant, correlation between costs and yields. The low correlation between costs and yields is reviewed and reasons are suggested why a higher correlation was not found. Finally the fall in output with increasing height of farm is related to costs in order to quantify the economic disability of the upland dairy farm.