FURTHER COMPARISONS BETWEEN A RIGID ROTATIONAL WYE COLLEGE' SYSTEM AND OTHER SYSTEMS OF GRAZING FOR MILK PRODUCTION

In two 20-week grazing experiments, a rigid rotational system of grazing termed the ‘Wye College’ system was compared with a flexible paddock-grazing system in 1972 and with strip grazing and set-stocking in 1973. Eight spring calved Ayrshire cows were used on each treatment at a stocking rate of 5 cows/ha (2 cows/ac). The mean daily milk yields per cow were 17·7 and 17·0 kg(39·0 and 37·5 Ib) on the Wye College and the paddock systems, respectively, in 1972; and 17·9, 17·7 and 16·4 kg (39·4, 38·9 and 36·2 Ib) on the Wye College, strip, and set-stocking systems in 1973. The average annual output of milk varied from 11,500 kg/ha (1030 gal/ac) on the set-stocking system to 12,500 kg ha (1120 gal/ac) on the Wye College system, but none of the differences was significant. The most rapid decline in daily milk yield occurred on the set-stocking system in August and September as the amount of available herbage declined. This system requires further investigation. It is concluded that the Wye College system, with its rigid and pre-determined grazing cycle was as effective as either a one-day paddock or a daily strip-grazing system in producing high yields of milk.     

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.     

A STUDY OF THE INTAKE OF DRINKING WATER BY DAIRY COWS AT GRASS

The average daily intake of drinking water of two groups of 10 spring-calved Ayrshire cows, one gronp on a paddock and the other on a Wye College system of grazing, was measured on 4 days/week for 20 weeks. Trends in water intake were similar on both systems, the average daily intake being 23.0 ±8.5 kg (5.1 ± 1.9 gal)/cow. The average DM content of the herbage was 17.8% and the mean air temperature 134°C (56 1°F). The weight of water drunk was positively related to the daily milk yield and the DM percentage of the herbage, and negatively related to daily rainfall and relative humidity. All of these relationships were significant. Possible changes in the provision of water for dairy cows at grass are discussed.     

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.     

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%.     

A NEW GRAZING SYSTEM FOR BEEF CATTLE—THE TWO FIELD SYSTEM

A new simplified grazing management system has been devized for spring- or antumn-born calves scbednled for beef production at 18 months of age on a grass/cereal system. The new system which can be conveniently described as the two-field system obviates the need for paddock fencing and paddock water installations, is simple to operate and is giving results in terms of liveweight gain performance and stocking rates per acre which are comparable with those from paddock systems. The new system employs the old practice of set-stocking. Two fields are used, however, and these are alternately set-stocked and cut for silage, or vice-versa. It has been found that by using N fertilizer to the same extent as in intensive paddock systems, i.e. around 250–350 units N/ac, it has been possible to achieve similar stocking rates/ac and performance has been unimpaired. No bealth upsets have occurred as a result of applying fertilizers on fields in the presence of grazing cattle over a period of four years at two centres, Jealott's Hill and The Leaths, in trials involving hundreds of beef cattle and dairy cows. This new system of grazing management for beef cattle is now well proven and can now be recommended to farmers as an alternative to paddock grazing.     

DAIRY PRODUCTION FROM PASTURE; A COMPARISON OF TWO METHODS OF CONTROLLED GRAZING AT TWO RATES OF STOCKING

An experiment was started in 1957 that compared the production from dairy cows on daily strip-folding with that from a system of rotational grazing where the cows were given a fresh allocation of pasture about once or twice a week. Management was so arranged that equal areas of pasture were grazed off by the same number of cows in a similar period of time. The experiment was carried out at two rates of stocking, one about 20% greater than the other, the lower rate considered to be equivalent to good close folding practice and the higher rate therefore somewhat restrictive. No supplementary food was given during the grazing season.
At the high rate of stocking, rotational grazing gave an average milk yield of 40 lb./cow/day whilst daily strip-folding yielded 38 lb./cow/day. At the low rate of stocking production was 42 lb./cow/day for both methods.
At the high rate milk yield/acre from the rotational grazing was 1007 and from the strip-folding 977 gals. At the low rate comparable results were 881 and 874 gals.
There was no general trend in yield per cow or per acre in favour of either the rotational grazing or daily strip-folding systems of management. Increasing cow days/acre by 21% decreased yield/cow/day by 7% but significantly increased milk yield/acre, by 13%.     

INTENSIVE SET-STOCKING OF DAIRY COWS

Farm-scale trials with Ayrshire dairy cows were conducted in South-West Scotland over two seasons to compare set-stocking and paddock grazing at similar stocking rates and N fertilizer rates. At a stocking rate of 1±9–2±0 cows/ac throughout the grazing season and a fertilizer N rate of about 400 units/ac, milk production per head from set-stocked cows was equal to that from paddock-grazed cows. No health problems arose as a result of applying fertilizer to the fields which were set-stocked. These trials hare established that set-stocking is a viable system for the intensive management of dairy cows on grassland in the UK, but further work is necessary to determine whether paddock-grazing has a higher potential for milk production than set-stocking.     

THE INTAKE OF DRINKING WATER BY GRAZING DAIRY COWS. THE EFFECT OF WATER AVAILABILITY

In a 16-week grazing experiment with six spring-calved Ayrshire cows, drinking water was available to the animals in three different ways, and the effect on milk prodnction was studied. The water was available from a water howl in the cowshed for 2.8 h/day in Treatment A, from a trough in the field for 21.2h/day in Treatment B, and from hoth sources for a total of 24 h/day in Treatment C. The cows on all treatments were grazed in individual plots of intensively-managed perennial ryegrass, stocked at the rate of 1 cow/0.22 ha (0.54 ac). The mean daily intakes of drinking water were 10.1, 15.3 and 15.5 kg (2.23, 3.37 and 3.42 gal)/cow, and the mean daily milk yields were 17.0, 17.2 and 16.8 kg (37.5, 37.9 and 37.0 lb)/cow in Treatments A, B and C, respectively; milk yields were not significantly different The herbage had an average DM content of 17.3%, and contained 19.6% crude protein and 66.5% digestible organic matter in the DM. The weight of water drunk was significantly and positively related to the DM percentage of the herbage, the air temperature and the daily hours of sunshine, and negatively related to daily rainfall. It is concluded that when dairy cows are grazing leafy herbage of high digestibility as their sole feed, the time during which drinking water is available may safely be restricted.     

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 effect of grazing intensity on the performance of high‐yielding dairy cows

The study evaluated the impact of High, Moderate and Low grazing intensities throughout the grazing season, within a rotational stocking system, on the performance of high‐yielding dairy cows receiving a high level of concentrates. Sixty‐three Holstein‐Friesian dairy cows, 21 at each grazing intensity, were rotationally grazed. Average paddock size, post‐grazing sward heights and seasonal grazing stocking rates within the High, Moderate and Low grazing intensities were 0.143, 0.167 and 0.200 hectares, 5.2, 6.1 and 6.8 cm and 7.8, 6.7 and 5.6 cows ha^?1 respectively. Grazing intensity had no effect on milk fat and protein content, end‐of‐study body condition score or end‐of‐study live weight although the latter tended towards significance (p = .057). Average daily milk yield per cow was higher within the Low grazing intensity (33.2 kg day^?1) than High grazing intensity (30.5 kg day^?1), and average daily fat‐plus‐protein yield was higher for Low and Moderate than High. Milk output per hectare was higher for the High grazing intensity than Low grazing intensity (33,544 and 26,215 kg ha^?1 respectively). Grazing intensity had no effect on grazing bite number, blood metabolites or concentrations of milk fatty acids or on sward morphological components, although dead matter increased with time across all grazing intensities. Herbage utilization efficiency (above 1,600 kg DM ha^?1) was 52%, 74% and 87% for Low, Moderate and High respectively. It is concluded that high‐producing dairy cows can graze at high levels of utilization when they are receiving high rates of concentrates. Although cow performance will be reduced, milk yield per ha will increase.     

Pasture‐based dairy farm systems increasing milk production through stocking rate or milk yield per cow: pasture and animal responses

A 2‐year whole‐farm study compared pasture‐based systems increasing milk production per ha by increasing either stocking rate (from 2·5 to 3·8 cows ha^?1) or milk yield per cow (from 6000 to 9000 kg cow^?1 lactation^?1) or both. Four treatments (systems), comprising 30 cows each, were compared under the same management and grazing decision rules. The diet was based on grazed pasture, whereas pellets and conserved fodder were fed when deemed necessary. Milk production per ha increased by 0·49, 0·1 and 0·66 in the systems that increased either stocking rate, milk yield per cow or both respectively. Cows in the ‘high milk yield per cow’ systems had a significantly higher body condition score throughout the lactation, but reproductive performance was similar among all groups. Total pasture utilized (11 t DM ha^?1 year^?1) and pasture nutritive value were similar across all systems. This was associated with the grazing rules applied and the ability of accurately supplementing to meet deficits in available pasture. At the whole‐system level, there was a higher marginal efficiency of supplement use when increasing stocking rate than when increasing milk yield per cow or increasing both (0·18, 0·07 and 0·12 kg milk MJ^?1 of metabolizable energy of supplements respectively).     

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 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.     

THE EFFECT OF STOCKING RATE AND SUPPLEMENTARY CONCENTRATE FEEDING ON MILK PRODUCTION

The effect of stocking rate and of feeding a supplement of barley on milk yield and quality was studied in an experiment with 18 spring-calved Ayrshire cows grazing from early May until early September in 1964 and 1965. Three treatments were compared: (A) grazing at a normal stocking rate with no supplements fed (the control); (B) grazing at a high stocking rate with no supplements fed; (C) grazing at a high stocking rate, as on treatment B, with a supplement of 8 Ib rolled barley per cow daily. On treatment A, 0.92 ac/cow was used for grazing, plus some conservation, and on treatments B and C, 0.70 and 0.58 ac in 1964 and 1965, respectively. The average daily milk yields were 35.4, 32.9 and 37.0 Ib (16.1, 14.9 and 16.8 kg), respectively, on treatments A, B and C in 1964, and 39.1, 32.3 and 38.8 Ib (17.8, 14.7 and 17.6 kg) in 1965. Milk production/ac was 24 and 32% higher on treatment B than on treatment A in 1964 and 1965, respectively.
The response to the barley feeding on treatment C was equivalent to an extra 1 gallon milk from 20 Ib barley in 1964 and from 12 Ib barley in 1965 (10 litres of milk from 20 and 12 kg barley). The total-solids content of the milk from the three treatments was not significantly different. It is concluded that, at the present price of barley and the price received for milk, an increase in stocking rate, with a consequent increase in the milk yield per acre, was more profitable than feeding barley.     

A short-term comparison of the performance of four grassland-based systems of milk production for autumn-calving dairy cows

Eighty winter‐calving dairy cows of mixed parity were managed in four grassland‐based systems of milk production (F‐F, F‐C, C‐F and C‐C) over a full lactation (year 1) and during the winter period of the subsequent lactation (year 2). During the winter periods cows on systems F‐F and F‐C were offered silages of high feeding value, supplemented with 6·0 kg d^?1 of concentrate [crude protein (CP), 307 g kg^?1 dry matter (DM)] through an out‐of‐parlour feeding system, while cows on systems C‐F and C‐C were offered silages of medium feeding value, supplemented with c. 12·8 kg d^?1 of concentrate (CP, 204 g kg^?1 DM), in the form of a complete diet. After 25 February in year 1, cows on systems F‐F and C‐F were given access to grazing for periods of increasing duration, achieving full turnout on 17 April. Thereafter, until 21 October, these cows were offered a high daily allowance of herbage within a flexible grazing system (23·0 kg DM per cow, measured above a height of 4·0 cm), supplemented with 0·5 kg d^?1 of a ‘high magnesium’ concentrate. Cows on systems F‐C and C‐C (year 1) commenced grazing on 1 April, achieving full turnout on 17 April. Thereafter, until 20 October, these cows were managed on a restricted allowance of herbage in a rotational paddock grazing system, with concentrates (average allocation, 3·9 kg d^?1) being offered according to yield. In year 2, cows on systems F‐F and C‐F were given access to grazing for periods of increasing duration, from 11 March to 8 April, at which point the study was terminated. With systems F‐F, F‐C, C‐F and C‐C, mean feed inputs and milk outputs (per animal) during year 1 of the study were as follows: total concentrate DM intakes [881, 1272, 1729 and 2171 kg (s.e.m. 96·1)]; total silage DM intakes [1722, 1713, 1047 and 1154 kg (s.e.m. 70·7)], total grass DM intakes (3245, 2479, 3057 and 2481 kg) and total milk outputs [7541, 7527, 7459 and 7825 kg (s.e.m. 305·8)] respectively. Stocking rates associated with each of the four systems were 2·2, 2·5, 2·6 and 2·9 cows per hectare respectively. Performance of dairy cows on the systems during the winter of year 2 was similar to that recorded during year 1. The results of this study indicate that similar levels of milk output, DM intakes, tissue changes and plasma metabolite profiles can be achieved from grassland‐based systems involving very different combinations of grass silage, grazed grass and concentrate feeds.     

Effect of frequency of application of inorganic nitrogen fertilizer within a rotational paddock-grazing system on the performance of dairy cows and inputs of labour

As herd sizes and labour costs increase, and the availability of skilled labour decreases, efficient use of available labour becomes more important in dairy cow systems. Two experiments were conducted to examine the effect of reducing the frequency of application of inorganic nitrogen (N) fertilizer on inputs of labour and performance of dairy cows. Experiments 1 (duration of 169 d) and 2 (duration of 179 d) involved fifty-eight and forty multiparous Holstein–Friesian dairy cows, respectively, in mid-lactation. In each experiment, in the 'infrequent' treatment fertilizer was applied to all paddocks on a single occasion at the start of each grazing cycle, while in treatment 'frequent', fertilizer was applied on three occasions each week, within 2 or 3 d of each paddock having been grazed. The experimental treatments were started from 30 March and 29 March in Experiments 1 and 2 respectively. Total N application rates were approximately 360 and 250 kg N ha⁻¹ in Experiments 1 and 2 respectively. Concentrate feed (4·0 kg per cow) was offered daily in both experiments. With the 'infrequent' treatment, highest concentrations of crude protein and nitrate in herbage were observed in swards grazed approximately 10 d after N fertilizer was applied. Treatment had no significant effect on milk yield, milk fat and protein concentrations, and final live weight and body condition score of cows in either experiment. Milk urea and plasma urea concentrations were not significantly affected by treatment. Calculated application times of fertilizer for a herd of 100 dairy cows were 107 and 83 min week⁻¹ for the 'frequent' and 'infrequent' treatments respectively.     

Some effects of herbage composition, as influenced by previous grazing management, on milk production by cows grazing on ryegrass/white clover pastures. 1. Milk production in early spring: effects of different regrowth intervals during the preceding winter period

Two experiments (1a and 1b) were carried out to examine the effects of differences in pre-grazing herbage mass and composition on milk production by cows grazing in early spring. Swards with high (5 · 1t DM ha⁻¹) or low (2 · 9 t DM ha-1) pre-grazing masses in early spring were created by either long or short periods of regrowth during the preceding winter.
The low-mass swards contained lower concentrations of grass stem and senescent material, but higher concentrations of clover, than the high-mass swards. Herbage from the low-mass swards was also more digestible.
Cows were offered common daily herbage allowances from both swards (26 and 22 kg DM cow⁻¹ in Experiments la and lb respectively). The cows grazing on the low-mass swards produced significantly greater yields of milk, milk fat and milk protein.
The results show that herbage from the lowmass swards was of higher feeding value for lactating cows in early lactation. The practical implications for milk production per cow and per hectare are discussed.     

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.     

The effects of offering a range of forage and concentrate supplements on milk production and dry matter intake of grazing dairy cows

An experiment was undertaken to examine the effect of supplement type on herbage intake, total dry matter (DM) intake, animal performance and nitrogen utilization with grazing dairy cows. Twenty‐four spring‐calving dairy cows were allocated to one of six treatments in a partially balanced changeover design with five periods of four weeks. The six treatments were no supplement (NONE), or supplementation with either grass silage (GS), whole‐crop wheat silage (WS), maize silage (MS), rapidly degradable concentrate (RC) or slowly degradable concentrate (SC). Cows were rotationally grazed with a mean herbage allowance of 20·5 kg DM per cow per day, measured above 4 cm. Forage supplements were offered for approximately 2 h immediately after each morning milking, with cows on NONE, RC and SC treatments returning to the grazing paddock immediately after milking. Cows on treatment MS had a significantly higher supplement DM intake than the other treatments but a significantly lower grass DM intake than the other treatments, resulting in no significant difference in total DM intake when compared with cows on treatments WS, RC and SC. Concentrate type had no significant effect on herbage intake, milk yield, milk composition or yield of milk components. The yield of milk fat and milk protein was significantly higher on treatments MS, RC and SC compared with treatments NONE, GS and WS. The results indicate that despite a relatively high substitution rate, maize silage can be a useful supplement for the grazing dairy cow.