Sodium fertilizer application to pasture. 2. Effects on dairy cow production and behaviour

Fifty-four lactaling dairy cows were grazed for 24 weeks on pasture receiving 0 (Nil), 32 (Low) or 64 (High) kg Na ha^-1 yr^-1 and with (+) or without (-) 100g NaHCO₃ buffer included in a maize gluten concentrate supplement. Cattle grazed the Na-fertilized pasture to a lower height, particularly in the High treatment. Cows grazing pasture with Na fertilizer produced more milk, and milk fat concentration increased in direct proportion to amount of Na fertilizer applied and with NaHCO₃. This increase was greatest in early season. Milk protein concentration was not affected by Na fertilizer application or NaHCO₃ buffer addition. Milk lactose concentration was increased by Na fertilizer application but not by NaHCO₃ supplementation. Cows in the Na-applied treatments gained more live weight but there was no effect of treatment on condition score change. Grazing time and drinking frequency increased linearly with increasing pasture Na. Ruminating time and biting rate were similar at the Low and High treatments and greater than the Nil treatment. NaHCO₃, supplementation increased drinking frequency and decreased the rate of concentrate intake. Cow reproductive performance was not significantly affected by Na fertilizer application. During the residual period, cows that had previously grazed the Na-fertilized pasture had reduced milk fat and protein contents.     

Effect of stocking rate on the grazing behaviour and faecal output of lactating dairy cows

Information about the grazing behaviour and the return of dung to pasture by lactating dairy cows was collected from stocking rate experiments in northern Victoria. Grazing behaviour was observed for 24-h periods in mid-summer in two years. Grazing time increased as herbage allowance decreased to about 32 kg DM cow⁻¹ d⁻¹ but as herbage allowance decreased further grazing time also decreased. A herbage allowance of 32 kg DM cow⁻¹ d⁻¹ corresponded to a stocking rate of about 5.5 cows ha⁻¹. This effect of herbage allowance on grazing time may have been confounded by herbage mass, however. Rumination time of the cows increased by 003 h for each kg increase in herbage allowance while resting time was not affected by treatment.
The effects of stocking rate on some of the characteristics of faecal output were measured for a 3-d period in mid-summer. The number of pats deposited per cow daily declined by 0.66 for each unit increase in stocking rate. The fresh weight of dung also declined as stocking rate increased by 0.16 kg per unit of stocking rate. While the values for the amounts of dung deposited on the pasture by the cows at the lower stocking rates are similar to many of those reported in the literature, this study has quantified the way in which stocking rate may influence this in one instance. Furthermore, provided that some measure of herbage intake is made when measurements of dung excretion are performed, it is suggested that estimates of in vivo digestibility can be obtained.     

How does protein supplementation affect the selectivity and performance of Charolais cows on extensively grazed pastures in late autumn?

Management of beef cows grazing extensively grazed semi-natural pastures in temperate regions in late autumn can require supplements to be offered. The effects of supplementation with soya bean meal on the diet selected by Charolais cows and on their subsequent performance were examined for an 8-week period in late autumn in 2 years. Three groups of eight cows were compared: non-supplemented dry cows (D), non-supplemented (L) and supplemented (LS) lactating cows. The amount of soya bean meal supplement offered per cow was 250 g d⁻¹ in year 1 and 800 g d⁻¹ in year 2. Dietary choices were measured by direct observations and herbage intake was estimated in year 2. Supplementation affected neither diet selection (L: 0·42 vs. LS: 0·43 for the proportion of bites on green patches in year 1; 0·24 vs. 0·22 in year 2) nor daily organic matter intake of herbage (L: 15·6 vs. LS: 15·9 kg d⁻¹), which may have resulted from an adequate crude protein concentration of herbage. The higher total dry matter intake by cows offered the supplement reduced losses in live weight (L: −1212 vs. LS: −828 g d⁻¹; P  < 0·01) rather than increased milk production (L: 5·1 vs. LS: 5·0 kg d⁻¹). This may be linked to the low milk yield potential of the Charolais cows. The use of lactating cows rather than dry cows for pasture management in late autumn would increase the utilization of herbage but a reduction in liveweight losses of cows by supplementation is unlikely to be economic.     

Effects of application of nitrogen fertilizer on concentrations of P, K, S, Ca, Mg, Na, Cl, Mn, Fe, Cu and Zn in perennial ryegrass/white clover pastures in south-western Victoria, Australia

Effects of timing and rate of N fertilizer application on concentrations of P, K, S, Ca, Mg, Na, Cl, Mn, Fe, Cu and Zn in herbage from perennial ryegrass/white clover pastures were studied at two sites in south-western Victoria, Australia. Nitrogen fertilizer (0, 15, 25, 30, 45 and 60 kg ha^–1) was applied as urea in mid-April, early May, mid-May, early June and mid-June 1996 to pastures grazed by dairy cows. At Site 1, N fertilizer resulted in a linear increase in P, K, S, Mg and Cl concentrations in herbage and a linear decrease in Ca concentration. For all times of application, concentrations of P, K, Ca, Mg and Cl in herbage increased by 0·0048, 0·08, −0·010, 0·0013 and 0·053 g kg^–1 dry matter (DM) per kg N applied respectively. For S concentration, maximum responses occurred in mid-May (0·012 g kg^–1 DM per kg N applied). At Site 2, N fertilizer resulted in a linear increase in P, S and Na concentrations in herbage, a linear decrease in Ca concentration and a curvilinear increase in K and Cl concentration. The maximum responses for P, S and K concentrations in herbage occurred for the N application in mid-June and were 0·015, 0·008 and 0·47 g kg^–1 DM per kg N applied respectively. For Cl concentration, the maximum response occurred for the N application in early June and was 0·225 g kg^–1 DM per kg N applied. Overall, applications of N fertilizer up to 60 kg ha^–1 did not alter herbage mineral concentration to levels that might affect pasture growth or animal health.     

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.     

A comparison of buffer and partial storage feeding of a straw/concentrate mixture to grazing dairy cows

A straw/concentrate mixture was offered to set-stocked dairy cows over a 24-week period. The cows were offered grazed herbage only (G), or grazed herbage with a straw/concentrate supplement offered either for 45 min after each milking (B), or overnight (P). The overnight treatment involved housing the cows between afternoon and morning milking. The straw/concentrate mixture contained 0·33 long barley straw, 0·28 barley, 0·12 soya bean meal, 0·25 molaferm and 0·02 minerals. During the first 8 weeks of the experiment an average of 2·25 kg of concentrate were fed, and from weeks 9–24, 2·0 kg of concentrate were fed.
The feeding of the straw/concentrate mixture led to a decrease in estimated herbage dry matter (DM) intake, particularly for treatment P. Estimated total DM intakes were increased throughout the experiment by offering the straw/concentrate mixture. However, total metabolizable energy (ME) intakes were only increased in mid-and late season.
Milk yield was higher in early season for treatment G; 28·1 kg d⁻¹ compared to 26·8 kg d⁻¹ and 25·5 kg d⁻¹ for treatments B and P respectively. In late season the cows in treatment G had lower milk yields; 13·3 kg d⁻¹ compared to 15·5 kg d⁻¹ and 16·8 kg d⁻¹ for treatments B and P respectively. Milk fat content was increased in early season in treatment P, and milk protein content tended to be reduced throughout the experiment for cows offered the straw/concentrate mixture overnight. Over the whole experiment there were no differences in yield of milk solids.     

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.     

Supplementary feeding of forage to grazing dairy cows, 3. The effect of three daytime stocking rates on the performance of cows offered grass silage overnight

Over a 24-week period, three groups of dairy cows were continuously stocked at 8, 10 or 12 cows ha^-1 between morning and afternoon milkings, and overnight were housed and offered grass silage ad libitum. Due to a prolonged drought, sward heights only averaged 4·1 cm.
The increase in daytime stocking rate led to a decline in herbage intake, and increases in silage intake. At the highest stocking rate (12 cows ha^-1), the silage intake failed to compensate for the reduced herbage intake. Consequently the total dry matter and estimated metabolizable energy intakes were lower than for the 8 and 10 cows ha^-1 treatments. Milk yields and milk composition were not significantly affected by treatment but the 12 cows ha^-1 stocking rate gave the lowest milk and milk solids yields.
The utilized metabolizable energy (UME) on the grazed swards was greatest for the 10 cows ha^-1 treatment. The sward cut to provide the silage had a UME level (GJ ha^-1) 32% greater on average than the grazed swards during the same growth period. The total areas utilized for grazing and silage production for 8, 10 and 12 cows ha^-1 were 0·240, 0·224 and 0·215 ha respectively. Fat and protein yields per unit area were greatest for the 10 cows ha^-1 group.     

The herbage intake and performance of set-stocked suckler cows and calves

Groups of eight Hereford × Friesian cows and their South Devon cross calves were set stocked over a 24-week grazing season at 3·23 (low), 3·21 (medium) or 4·24 (high) cows ha^-1 together with their calves. For the first 8 weeks only two-thirds of the total area was grazed. Increasing the stocking rate from low to medium reduced daily milk yield and cow and calf liveweight gains by 1·2, 0·24 and 0·29 kg d^-1 respectively, and from medium to high by 1·2, 0·24 and 0·23 kg d^-1. The main sward factor influencing faecal output and herbage intake was the quantity of organic matter on the pastures but the digestibility of the herbage selected also exerted a significant effect on the intake of cows. Major depressions in the herbage intake of cows occurred once the average sward height fell below 7 cm. Output of calf live weight was 628, 658 and 743 kg ha^-1 for the 3 stocking rates from low to high, and for cows 246, 179 and 30 kg ha^-1. It was concluded that decisions on pasture management should be taken in relation to the cow rather than the calf on set-stocked swards.     

Some challenges and opportunities for grazing dairy cows on temperate pastures

Grazing plays an important role in milk production in most regions of the world. In this review, some challenges to the grazing cow are discussed together with opportunities for future improvement. We focus on daily feed intake, efficiency of pasture utilization, output of milk per head, environmental impact of grazing and the nutritional quality to humans of milk produced from dairy cows in contrasting production systems. Challenges are discussed in the context of a trend towards increased size of individual herds and include limited and variable levels of daily herbage consumption, lower levels of milk output per cow, excessive excretion of nitrogenous compounds and requirements for minimal periods of grazing regardless of production system. A major challenge is to engage more farmers in making appropriate adjustments to their grazing management. In relation to product quality, the main challenge is to demonstrate enhanced nutritional/processing benefits of milk from grazed cows. Opportunities include more accurate diet formulations, supplementation of grazed pasture to match macro- and micronutrient supply with animal requirement and plant breeding. The application of robotics and artificial intelligence to pasture management will assist in matching daily supply to animal requirement. Wider consumer recognition of the perceived enhanced nutritional value of milk from grazed cows, together with greater appreciation of the animal health, welfare and behavioural benefits of grazing should contribute to the future sustainability of demand for milk from dairy cows on pasture.     

Influence of some sward characteristics on the consumption of irrigated pastures grazed by lactating dairy cattle

Pasture variables measured in eight experiments at Kyabram, Victoria were used to quantify factors influencing the consumption of irrigated pastures grazed by dairy cows. In addition, whether intake prediction equations based on sward characteristics could be developed and applied in the field was also considered.
Herbage intake (DMI) was positively related to herbage allowance (HA) in all cases; however, the increase in daily DMI achieved for every additional kg herbage offered to a cow ranged from 015 to 0·35 kg. Herbage intake was also consistently related to residual herbage (RH). For every additional tonne herbage dry matter (DM) ha⁻¹ remaining after grazing, each cow consumed increased daily amounts of herbage ranging from 3·2 to 5·1 kg DM. However, of the other pasture variables, herbage mass (HM), pasture type (P_T) and digestibility of the herbage DM on offer (DMD) influenced herbage intake less consistently.
When the data from all experiments were included together, DMI was influenced by sward characteristics in the following manner: where LW = live weight of the cow (kg) and DE = duration of experiment (d).
When RH was considered instead of HA, only 61% of the variability in intake was accounted for compared to 80% when HA was considered:
In both of these equations, two variables other than the sward characteristics were significant; these were LW and DE. The significance of these variables in these relationships are discussed together with the possibility of using them for predicting DMI in other environments. However, it is concluded that they do not have general applicability and it is suggested that they may be useful only in the environment in which they were generated.     

Milk-production potential of different sward types in a temperate southern Australian environment

The milk-production potential of different sward types was measured in each of the four seasons of the year in a replicated experiment in south-west Victoria, Australia. Dairy cows were offered ad libitum allowances of a 'short-term winter' sward, based on Italian ryegrass (treatment STW), a 'long-term winter' sward, based on a winter-active tall fescue (treatment LTW), a 'long-term summer' sward, based on a summer-active tall fescue (treatment LTS) and a Control sward (perennial ryegrass) in four seasons (days in milk in parentheses): spring (November dairy cows, 124), summer (February, 227), autumn (May, 234) and winter (August, sixty-four). A 'short-term summer' sward, based on chicory and white clover (treatment STS), was also included in summer. There was a significant season × treatment interaction caused by a more gradual decline in milk yield from peak for cows grazing treatment LTS compared to the Control treatment in the transition period from spring to summer. In summer, cows grazing treatment STS produced more milk (1·41 kg fat plus protein per cow d⁻¹) than cows grazing all other treatments (0·92 kg per cow d⁻¹) because of the superior nutritive value of herbage of pre-grazing pasture and higher apparent dry-matter intakes. Swards based on alternative species to perennial ryegrass are capable of supporting milk production that is at least comparable over an annual cycle.     

Silage and milk production: studies with molasses and formic acid as additives for grass silage

In two separate feeding experiments using a total of twenty-four individually housed Ayrshire cows six silages made from perennial ryegrass were offered ad libitum with supplements of concentrates. In Experiment I herbage with a dry matter (DM) concentration of 225 g kg⁻¹ received either formic acid ('Add-F') at the rate of 2·0 litres t⁻¹ or undiluted cane molasses at rates of 10, 20 and 30 litres t^−l; the mean daily silage intakes were 9·54, 908, 9·27 and 9·49 kg DM per cow and the daily milk yields, corrected to 40 g fat kg⁻¹, were 23·2, 22·3, 22·8 and 22·9 kg per cow respectively but none of the differences between the four treatments was significant. In Experiment 2 herbage with a DM concentration of 269 g kg⁻¹ received formic acid at a uniform rate of 2·6 litres t⁻¹ either with or without an additional application of molasses at 20 litres t⁻¹; the mean daily silage DM intakes were 8·70 and 9·28 kg per cow and the daily fat-corrected milk yields were 22·2 and 21·9 kg per cow respectively and were not significantly different. In both experiments the effects of the treatments on milk composition were small and not significant. It is concluded that there were no advantages in applying molasses to herbage treated with formic acid, and that the rate of application of molasses to untreated herbage which equated with the formic acid application was 20·30 litres t^−l when assessed on the basis of silage composition, intake and milk production.     

The combined use of fertilizer nitrogen and white clover on grazed ryegrass swards

A 1-year grazing experiment with dairy cows is described in which the milk yield and herbage intake from a sward of S23 perennial ryegrass alone receiving fertilizer N at an annual rate of 360 kg ha⁻¹ were compared with those from a ryegrass-white clover var. Blanca sward given a total N application of 180 kg ha⁻¹. Both treatments gave virtually the same total milk yield of about 12500 kg ha⁻¹ over a 20-week grazing season.     

The effect of herbage allowance upon the herbage intake and performance of suckler cows and calves

Twenty-four Hereford × Friesian cows and their South Devon cross calves were allocated to three herbage allowances allotted daily for three periods of 8 weeks in a Latin square design. The daily allowances were 17, 34 and 51 g dry matter per kg cow plus calf live weight. Milk production was depressed by 0·2 and 1·2 kg d^-1 at the medium and low allowances. The corresponding falls in liveweight gain were for cows 0·26 and 0·25, and for calves 0·27 and 0·24 kg d^-1. Residual sward height after grazing gave a better indication of the animals' reaction to sward conditions and the management imposed than actual herbage allowance. The quantity per unit area and the composition of material present were important factors influencing intake. Calves were unable to compete with their dams to maintain herbage intake at the lower allowances and therefore are likely to benefit from additional feeding or creep grazing when residual sward height falls below 6cm for periods in excess of 1–2 weeks.     

Effect of stocking rate in early season on dairy cow performance and sward characteristics

A comparison was made of stocking rates of 4·7, 5·6 and 6·4 cows ha^-1 during the first 7 weeks (period 1) of the grazing season. Each group of British Friesian cows was continuously stocked on a day and a night field. In the subsequent periods 2 and 3 (each lasting 7 weeks) the three groups were maintained at the same stocking rate within periods (4·2 and 31 cows ha^-1, respectively). The differential stocking rates were achieved by the addition and removal of cows.
The stocking rates applied in period I had no significant effects on milk yield, milk composition, liveweight change or condition score, in any period. Milk production ha^-1 over the three periods totalled 12390,13 978 and 14986 kg, and the estimated utilized metabolizable energy totalled 773, 81·5 and 86·6 GJ ha^-1 for low, medium and high stocking rates, respectively.
Increased stocking rate in period I was associated with a decrease in sward height in periods 1 and 2. This led to an increase in herbage metabolizable energy, and crude protein contents, and to an increase in tiller population density. The lowest stocking rate gave greater live individual tiller weights throughout the experiment and a longer interval between defoliation of individual tillers in period 1.
The results indicate that high stocking rates in the spring are not necessarily detrimental to overall summer performance of spring calving dairy cows. However, high stocking rates in the early season ensure a high level of herbage utilization and milk output ha^-1 in that period. Although this practice leads to a reduced sward height in mid season, the sward has less rejected area, a higher tiller population density and a higher digestibility than swards stocked at a lower level.     

The effect of calving date and stocking rate on the performance of spring-calving dairy cows

A 3-year experiment on milk production systems was set up in 1989 to investigate the effect of calving date and stocking rate on the performance of spring-calving dairy cows. An early-calving herd (System A) with a mean calving date of 23 January and stocked at 2·9 cows per hectare was compared with two later calving herds (Systems B and C) with a mean calving date of 15 March. System B had a similar stocking rate to System A (2·9 cows ha⁻¹), while System C had a stocking rate of 2·6 cows ha⁻¹. The average lactation yields (kg) over the three years were as follows: 5872, 5444 and 5584 (milk)210, 204 and 215 (fat), 187, 184 and 189 (protein) and 261, 245 and 250 (lactose) for Systems A, B and C respectively. The average milk composition (gkg⁻¹) was: 36·0, 37·6 and 38·7 (fat), 31·9, 33·7 and 33·8 (protein) and 44·5. 45·1 and 44·8 (lactose) for Systems A, B and C respectively. Delaying calving date to coincide with the beginning of the grass-growing season (System B compared with System A) reduced milk yield per cow significantly (P < 0·05) in all three years of the experiment. However, fat and protein concentration were increased, resulting in no significant difference in the yield of fat or protein per cow. Reducing the stocking rate from 2·9 cows per hectare to 2·6 cows per hectare for cows calving in mid-March (System C compared with System B) increased milk yield per cow significantly (P < 0·05) in only one of the three years (1990). Milk fat content was increased significantly in 1990. Stocking rate had no other     

Mineral concentrations in herbage and soil in a Pinus radiata silvopastoral system in north-west Spain after sewage sludge and lime application

Silvopastoral systems in north-west Spain can reduce the risk of fires and promote multi-purpose forest land use. Fertilizer application is important for optimal pasture and tree production. The application rate of sewage sludge as a fertilizer is regulated and is based on its nutrient concentration, especially nitrogen. The aim of this study was to assess the effect of three consecutive years of application of different application rates of sewage sludge and inorganic fertilizer, with or without lime (2·5 t CaCO₃ ha⁻¹) on the ammonium, nitrate and exchangeable K, Ca and Mg contents in soil, and on the crude protein (CP), K, Ca and Mg concentrations in herbage in a silvopastoral system established under a 5-year-old Pinus radiata D. Don plantation with a density of 1667 trees ha⁻¹. The experiment was started in autumn 1997, when a pasture mixture was sown (25 kg ha⁻¹ Lolium perenne , 10 kg ha⁻¹ Dactylis glomerata and 4 kg ha⁻¹ Trifolium repens ). Changes in ammonium and nitrate content in the soil in response to liming and sewage sludge application reflected the initial pH of the soil. In general, liming increased the available Ca and Mg content in soil, and CP and Ca concentrations in herbage, but reduced exchangeable K content in the soil in the first year. Application of sewage sludge increased all of the measured nutrients in both soil and herbage.     

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.     

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.