Herbage intake and milk production by grazing dairy cows 1. The effects of variation in herbage mass and daily herbage allowance in a short-term trial

Twenty-four British Friesian cows were allocated between six grazing treatments (two levels of herbage mass x three levels of daily herbage allowance) in a balanced change-over design with four periods of 12 d each at monthly intervals. Herbage OM mass ranged from 3790 to 5770 kg ha^-1 measured to ground level and daily herbage DM allowances were 30, 60 and 90 g per kg animal live weight. Herbage OM intake was lower at high than at low herbage mass (24·6 vs 26·3 g per kg LW), and was 26·9, 26·6 and 22·9 g per kg LW respectively at daily herbage DM allowances of 90, 60 and 30 g per kg LW. Milk yield was not affected by herbage mass but was depressed at the low herbage allowance.     

Allowance-intake relations of cattle grazing vegetative tall fescue†

Herbage allowance is one of the important pasture factors in the determination of intake by grazing livestock. Ingestive behaviour of 12 adult Angus cows (Bos taurus) was measured over a range of allowances (0·25 to 0·72 kg dry matter (DM) per 100 kg live weight (LW) for a 1-h period) of vegetative tall fescue (Festuca arundinacea Schreb.). A balanced change-over design was used to estimate direct, residual and permanent effects of herbage allowance on rate of DM intake, rate of biting and herbage DM intake per bite. In Experiment 1, herbage DM intake per meal increased linearly from 0·68 to 1·72 kg (100 kg LW)^?1 as DM allowance increased from 0·25 to 0·72 kg (100 kg LW)^?1 h^?1. Cows grazed at ·30 kg (100 kg LW)^?1 h^?1 and stopped grazing when the sward was reduced to a height about 10 to 12 cm above the soil surface, approximately defined by the tops of pseudostems. In Experiment 2, herbage DM intake rates of 0·29, 0·47 and 0·42 kg (100 kg LW)^?1 h^?1 were recorded as cows grazed allowances of 0·43, 0·70 and 0·90 kg (100 kg LW)^?1 h^?1 for most of the 1-h grazing period. Limiting herbage DM allowances in Experiment 2 were associated with small reductions in rate of biting and herbage DM intake per bite as allowance declined. Sward DM density (>5 cm) was an important variable in the determination of herbage DM intake rates at lower herbage allowances.     

The effect of initial spring grazing date and subsequent stocking rate on the grazing management, grass dry matter intake and milk production of dairy cows in summer

The objective of this study was to investigate the effects of an early (February; F) or delayed (April; A) primary spring grazing date and two stocking rates, high (H) and medium (M), on the grazing management, dry matter (DM) intake of grass herbage and milk production of spring‐calving dairy cows grazing a perennial ryegrass sward in the subsequent summer. Sixty‐four Holstein‐Friesian dairy cows (mean of 58 d in milk) were assigned to one of four grazing treatments (n = 16) which were imposed from 12 April to 3 July 2004. Cows on the early spring‐grazing treatment were grazed at 5·5 cows ha^?1 (treatment FH) and 4·5 cows ha^?1 (treatment FM) while cows on the late‐grazing treatment were grazed at 6·4 cows ha^?1 (treatment AH) and 5·5 cows ha^?1 (treatment AM). The organic matter digestibility and crude protein concentration of the grass herbage were higher on the early‐grazing treatment than on the late‐grazing treatment. The cows on the FM treatment had significantly (P < 0·001) higher milk (24·5 kg), solids‐corrected milk (22·5 kg), fat (P < 0·01, 918 g) and protein (831 g) yields than the other three treatments. Cows on the FM treatment had a higher (P < 0·001) DM intake of grass herbage by 2·3 kg DM per cow per day than cows on the AH treatment, which had a DM intake significantly lower than all other treatments (15·2 kg DM per cow per day). The results of the present study showed that grazing in early spring has a positive effect on herbage quality in subsequent grazing rotations. The study also concluded that early spring‐grazed swards stocked at a medium stocking rate (4·5 cows ha^?1; FM) resulted in the highest DM intake of grass herbage and milk production.     

Effect of grazing severity on grass utilization and milk production of rotationally grazed dairy cows

Two experiments were carried out to examine the effects of grazing severity on the performance of January/February calved British Friesian dairy cows. In Experiment 1, three groups of cows were rotationally grazed across twenty-four one-day paddocks with high (H), medium (M) or low (L) herbage allowances. Cows on treatment M were offered a daily herbage allowance designed to achieve a residual sward height of 50 mm, assessed by a rising-plate sward stick. The daily herbage allowance (g organic matter (kg live-weight)^-1 on treatments L and H were 0.30 below and above that for M, respectively, to give residual sward heights of 42 and 59 mm. In Experiment 2, three groups of cows were grazed across twenty-four one-day paddocks to obtain residual sward heights of 50 mm (severe), 60 mm (moderate) and 80 mm (lax). Average milk yields on the L, M and H treatments in Experiment 1 were 11.8, 14.6 and 14.5 kg d,^-1 and in Experiment 2 they were 13.7, 16.0 and 17.0 kg d^-1 on the severe, moderate and lax treatments, respectively. The results indicate that the critical herbage height below which milk production per cow declines may vary with the production potential of the animal. There were no significant treatment effects on milk composition. Milk output ha^-1 and utilized metabolizable energy ha^-1 were greatest with the low herbage allowance in Experiment I and the moderate treatment in Experiment 2. Net herbage accumulation on the severe treatment in Experiment 2 was 30% lower than that on the lax treatment, as a result of treading damage in early season. It is concluded that, in a rotational grazing system, a reasonable compromise between sward utilization and animal performance can be achieved by grazing January/February calved cows to a residual sward height of 60 mm as assessed by a rising-plate sward stick. This is equivalent to a sward surface height of about 80 mm.     

The effects of a flexible grazing management strategy and leader/follower grazing on the milk production of grazing dairy cows and on sward characteristics

An experiment was carried out during 1984 to examine the effects of three alternative grazing strategies for January/February calved British Friesian dairy eows on sward and animal production. Cows were rotationally grazed across 1 d paddocks without concentrate supplementation from 30 April to 1 October. A flexible grazing (EG) treatment involved manipulating residual herbage height, as assessed by a rising-plate sward stick, with cows initially grazing to 80 mm, reducing to 60 mm when milk yield declined below 20 kg d^?1 and finally to 50 mm when milk yield declined below 15 kgd^?1. Control (C) cows grazed to a constant residual herbage height of 60 mm throughout the season (a 60-inm rising-plate sward stick height is equivalent to a sward surface height of approximately 80 mm). On a further treatment a leader/follower (LF) approach was used, with cows paired for calving date and parity and within pairs allocated to either a high-(leader) or a low-yielding (follower) group, according to milk yield at turnout, with the leader group grazing 1 d ahead of the follower group. Overall stocking rates on C and LE treatments were identical but herbage allowances differed as a result of treatment effects. Animal performance data for the FG, C and LE treatments, respectively, were: milk yield (kg d^?1) 14·5, 14·7 and 16·0 (s.e. 0·59); milk fat yield (g d^?1) 577, 571 and 637 (s.e. 29); milk protein yield (g d^?1) 528, 527 and 576 (s.e. 19); and liveweight gain (kg d^?1) 0·09, 0·20 and 0·14 (s.e. 0·04). Overall, there was no benefit in animal production following lax grazing in spring even with high-yielding cows, and this approach resulted in the accumulation of stem and senescent material in the sward in mid-season. However, preferential treatment of high-yielding cows by grazing as a leader group in a leader-follower system resulted in higher milk production, particularly in late season, with an overall improvement in milk yield for the LF treatment of 9% relative to treatment C.     

Concentrate supplementation, and the herbage intake and milk production of heifers grazing Cenchrus ciliaris

Friesian heifers grazing Cenchrus ciliaris cv. Biloela were supplemented with 0, 3 or 6 kg concentrates daily during weeks 10–34 (±1·7) of lactation during either the rainy or the dry season. The overall responses to concentrate were identical between seasons at 0·27 kg extra milk and solids corrected milk per kg. Supplementation increased total feed intake and modified the grazing behaviour of cows. For each kg concentrate organic matter eaten, herbage organic matter intake was reduced by 0·64 and 0·42 kg in the rainy and dry seasons respectively and the time spent grazing by 11 min. Higher intakes in the dry season were the result of an increased rate of biting and were reflected in liveweight change but not milk yield.     

A comparison of two grassland-based systems for autumn-calving dairy cows of high genetic merit

A full lactation study compared the performance of autumn‐calving dairy cows of high genetic merit under two contrasting systems of milk production: high forage (HF) and high concentrate (HC). During the winter, animals on system HF were offered a silage with a high feeding value characteristics, supplemented with 5·5 kg of concentrate [crude protein content of 280 g kg^?1 dry matter (DM)] through an out‐of‐parlour feeding system. From 14 March, these animals were given increasing access to grazing, achieving 24‐h turnout on 15 April. Thereafter, until day 305 of lactation, these animals were offered a large daily herbage allowance (23·0 kg grass DM cow^?1, measured above a height of 4·0 cm), supplemented with 0·5 kg d^?1 of a ‘high‐magnesium’ concentrate. During the winter, animals on system HC were offered a silage of medium feeding value, mixed with ≈14·0 kg of concentrate d^?1 (crude protein content of 202 g kg^?1 DM) in the form of a complete diet. These animals commenced grazing on 9 April, achieving 24‐h turnout on 18 April. From 18 April until 9 June, daily herbage allowances and concentrate feed levels were 17·0 kg DM and 5·0 kg respectively; thereafter, and until day 305 of lactation, these daily allowances were reduced to 15·0 kg of herbage DM and 4·0 kg of concentrate. Animal performance during the first 305 days of lactation for systems HF and HC, respectively, were as follows: total concentrate DM inputs, 842 and 2456 kg; total silage DM intakes, 2205 and 1527 kg; total grass DM intakes, 3019 and 2044 kg; total feed DM intake, 6061 and 6032 kg and total milk output, 7854 and 8640 kg. Total milk output per cow with system HF was 786 kg lower than for system HC, despite similar total DM intakes, suggesting a greater total nutrient requirement with the former to support a given milk production. However, the study confirms that relatively similar levels of animal performance can be achieved from systems based on very different sources of nutrient supply.     

Concentrate supplementation of grazing dairy cows

Two experiments are described in which twenty-four spring-calving Dutch Friesian cows were allocated between six grazing treatments (two levels of daily herbage allowance × three levels of daily concentrate intake) in a 2 × 3 factorial design. The swards consisted predominantly of perennial ryegrass. A two-machine sward-cutting technique (with correction for herbage accumulation during grazing) was used for estimating herbage intake by cows which grazed swards for 3 or 4d. Experiment 1 was carried out for 16 weeks of the grazing season of 1981 and experiment 2 for 18 weeks in 1982.
Daily herbage OM allowances in both experiments were 16 and 24 kg per cow above 4 cm cutting height. Daily concentrate OM intake ranged from 0.8 to 5.6 kg per cow. The effect of concentrates on herbage intake differed significantly between allowances. At the low allowance level and at daily concentrate OM intakes of 0.8, 3.2 and 5.6 kg per cow daily herbage OM intake was 10.9, 10.6 and 10.4 kg per cow respectively and the mean substitution rate of herbage by concentrates was only 0.1. At the high allowance level and at daily concentrate OM intakes of 0.8, 3.2 and 5.6 kg per cow daily herbage OM intake was 14.8, 13.6 and 12.4 kg per cow respectively and mean substitution rate was 0.5 kg herbage OM (kg concentrate OM)⁻¹.     

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.     

GrazeIn: a model of herbage intake and milk production for grazing dairy cows. 3. Simulations and external validation of the model

GrazeIn is a model for predicting herbage intake and milk production of grazing dairy cows. The objectives of this paper are to test its robustness according to a planned arrangement of grazing and feeding scenarios using a simulation procedure, and to investigate the precision of the predictions from an external validation procedure with independent data. Simulations show that the predicted effects of herbage allowance, herbage mass, herbage digestibility, concentrate supplementation, forage supplementation and daily time at pasture are consistent with current knowledge. The external validation of GrazeIn is investigated from a large dataset of twenty experiments representing 206 grazing herds, from five research centres within Western Europe. On average, mean actual and predicted values are 14·4 and 14·2 kg DM d^?1 for herbage intake and 22·7 and 24·7 kg d^?1 for milk production, respectively. The overall precision of the predictions, estimated by the mean prediction error, are 16% (i.e. 2·3 kg DM d^?1) and 14% (i.e. 3·1 kg d^?1) for herbage intake and milk production, respectively. It is concluded that the GrazeIn model is able to predict variations in herbage intake and milk production of grazing dairy cows in a realistic manner over a wide range of grazing management practices, rendering it suitable as a basis for decision support systems.     

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 performance of summer-calving cows grazing perennial ryegrass swards

The objectives of this experiment were to study the effects of different grazing managements in spring on herbage intake and performance of summer-calving dairy cows and to examine the effects of regrowth in early June on herbage intake and cow performance. Four spring-grazing treatments were applied to predominantly perennial ryegrass swards: Control (C), sward grazed by cows to 6–8 cm sward surface height (SSH); CG16, sward grazed by cows to 3–4 cm SSH in May and allowed to regrow to a target SSH of 16cm in early June; CG8, sward grazed by cows to 3–4 cm SSH in May and allowed to regrow to 8cm in early June; and SG8, sward grazed by sheep to 2–3 cm SSH in May and allowed to regrow to 8 cm in early June, All swards were continuously stocked by summer-calving (May and July) primiparous and multiparous cows from 16 June to 7 September, to a target SSH of 8–10cm. Spring treatments bad marked effects on herbage intakes and milk production. Estimated in July by n alkane analysis, the mean herbage intake ± s.e.d. of cows on each treatment were 1·8, 1·4, 1·4 and 3·0 ± 0·31 kg dry matter (DM) 100 kg live weight (LW)^?1 d^?1 (P < 0·01) for treatments C, CG16, CG8 and SG8 respectively. Measured in August, intakes were 1·8, 20, 2·1 and 2·4 ± O·33kg DM 100kg LW^?1 d^?1 respectively. Severe spring grazing led to increased milk yield and reduced milk fat content from summer-calving cows fed 5·2 kg d^?1 of a proprietary concentrate. Average milk yields for the eleven experimental cows on each treatment were 24·3, 23·4, 26·2 and 29·0 ± 1·20 kgd^?1 (P < 0·01) for C, CG16, CG8 and SG8, and average milk fat contents were 45·4. 42·4, 43·9 and 40·9 ± 1·02gkg^?1 (P<0·05) respectively. The results suggest that severe grazing of swards in early season could improve herbage intake and milk yield of summer-calving cows in mid- and late season. The most favourable spring treatment in this respect was severe grazing by sheep. However, this advantage could be negated in midseason by lax grazing at that time.     

Continuous and rotational grazing of dairy cows – the interactions of grazing system with level of milk yield, sward height and concentrate level

An experiment was conducted to test the hypothesis that for cows with high levels of milk yield, rotational grazing produces higher milk yields than continuous grazing. The comparison of grazing systems was made at two levels of milk yield (initially 20·3 and 32·5 kg d^?1), and interactions with sward height and concentrate level were also examined. The study used 48 multiparous Holstein Friesian cows over a period of 62 d. Mean milk yield, its persistency and composition, live weight, body condition score and liveweight gain were not significantly affected by grazing system at either level of milk yield. There were no significant interactions between grazing system and sward height or concentrate level for any milk production measurement. Mean estimated herbage and total dry matter (DM) intake (P < 0·01), grazing time (P < 0·05) and ruminating time (P < 0·01) were significantly greater on the continuous grazing system. The cows in the higher milk yield group and those grazed at the higher sward height had a significantly (P < 0·05) higher estimated daily herbage DM intake and rate of herbage intake on the continuous grazing system than those on the rotational grazing system. There was no evidence to support the hypothesis that rotational grazing systems support higher levels of milk production than continuous grazing for cows of high milk yield. The shorter grazing time on the rotational grazing system indicated that cows may anticipate the timing of the daily movement of the electric fence, and this reduces their time spent grazing residual herbage.     

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.     

Herbage intake and milk production by grazing dairy cows. 3. The effect of grazing severity under continuous stocking

The effects of severity of grazing on the herbage intake and milk production of continuously stocked British Friesian cows calving in February–March were examined in three experiments conducted in the years 1976–78 (experiments 1–3 respectively) using a put-and-take technique. In experiment 1 four grazing severities were imposed by maintaining swards with different herbage masses (2500, 3000, 3500, 4000 kg OM ha^-1); in experiments 2 and 3 there were two severities of grazing maintained by keeping swards canopies at constant heights of 5 and 7 cm (experiment 2) and 5 and 7·2 cm (experiment 3). Cows were reallocated to treatment every 8 weeks in experiments 1 and 2 and there were three periods, whereas they all grazed throughout a 23-week period on the same treatment in the final trial.
A decrease in the quantity of herbage on offer or in sward height reduced herbage intake and milk production in all experiments. Mean daily herbage OM intakes were 11·2, 12·2, 12·2 and 12·2 kg respectively in experiment 1, 12·2 and 13·2 kg respectively in experiment 2 and 12·2 and 152 kg respectively in experiment 3. Mean daily solids–corrected milk yields were 14·2, 15·2, 15·2 and 16·2 kg respectively in experiment 1, 14·2 and 16·2 kg respectively in experiment 2 and 12·2 and 17·2 kg respectively in experiment 3. It was apparent from the data obtained in the first two trials that grazing at a sward canopy height of 7 rather than 9 cm had little effect, but that at 5 cm there were significant depressions in both herbage intake and milk production. Milk yield was depressed to a greater extent when cows were kept on the same treatment for the whole season.     

The manipulation of grass swards for summer-calving dairy cows

Two experiments examined the effects of different defoliation treatments in spring on sward morphology and animal performance in mid-season and late season. Three treatments were applied in both experiments: Control (C), sward grazed by cows in spring to 6–8 cm grass height. Grazed Aftermath (GA). sward grazed by cows in spring to 3–4cm and allowed to regrow before being grazed by summer-calving cows, Silage Aftermath (SA), sward not grazed in spring, but a primary cut taken and the sward allowed to regrow before being grazed by summer-calving cows. The aim of treatment GA was to produce a sward with a high tiller density and high intake characteristics to meet the forage intake requirements of continuously grazed summer-calving cows, without resorting to offering forage buffers. Experiment 1 was conducted in 1989 on a sandy loam soil and Experiment 2 in 1990 on a heavy loam soil. In both experiments the GA treatment led to high live tiller density and live: dead tiller ratios compared with the C and SA treatments. Differences in sward morphology were also detected by applying double normal distribution analyses to measurements of grass height. The GA treatment also increased sward herbage mass and, to a limited extent, herbage metabolizable energy and crude protein contents. The results from Experiment 1 suggested that these sward effects lead to increased herbage dry-matter intake (as estimated by the n-alkane technique) and milk yield in cows grazing the GA sward. However, in Experiment 2, where conditions for grass growth in mid-season were more favourable than in Experiment 1, the differences in sward morphology produced in spring were quickly lost in June and July. There were therefore no differences in herbage intake or milk yield in the second experiment. Herbage intakes (kgDMd^?1± s.e.d) estimated in July for cows on treatments C, GA and SA were 11·0, 13·4, 10·1 ± 2·16 for Experiment 1 and 10·7, 11·1, 11·2 ± 2·32 for Experiment 2. Average milk yield (kgd^?1± s.e.d.) for cows on treatments C, GA and SA were 26·1, 28·0, 25·6 ± 0·31 (Experiment 1) and 28·5, 27·3, 28·4 + 0·58 (Experiment 2). The results suggested that acceptable milk yields can be obtained from grazing summer-calving cows, without offering forage buffers, by applying high stocking rates (low grass heights) in spring. However, the benefits of this manipulation could be lost by lax grazing in mid-season.     

Nitrogen flows and balances in four grassland‐based systems of dairy production on a clay‐loam soil in a moist temperate climate

This study examined productivity, nitrogen (N) flows and N balances in grassland‐based systems of dairy production in Ireland. There were four stocking densities of dairy cows on grass/white clover pastures and four inputs of N as fertilizers, concentrates and biological fixation over 2 years; 2001 and 2002. Annual stocking densities were 1·75, 2·10, 2·50 and 2·50 cows ha^?1. Associated N inputs were 205, 230, 300 and 400 kg ha^?1 respectively. There were eighteen cows per system. Cows calved within a 12‐week interval in spring with a mean calving date of 28 February and lactation extended until mid‐December in each year. There were no differences in annual milk yield (6337 kg cow^?1; s.e.m. 106·1), live weight or body condition score. Pre‐grazing N concentrations in herbage increased (P < 0·001) with increasing N input, whereas there were no differences in N concentrations in silage reflecting optimum N inputs for silage production. Grazed herbage accounted for 0·64, silage 0·26 and concentrates 0·10 of annual dry matter consumed by the cows. Annual intakes of N ranged from 144 to 158 kg cow^?1 and were mostly influenced by N concentration in grazed herbage. Annual output of N in milk and liveweight change was 38 kg cow^?1 and was not different between systems. Annual N surpluses increased with increasing N inputs from 137 to 307 kg ha^?1, whereas the proportion of N inputs recovered in products declined from 0·34 to 0·24. More efficient N use was associated with lower N inputs and in particular lower N concentrations in grazed herbage.     

A comparison between barley and groundnut as supplements for dairy cows at pasture

In two 12-week grazing experiments using twelve and eighteen spring-calved cows in 1976 and 1977 respectively, the effects of feeding either a barley or a groundnut concentrate supplement were investigated. The mean yield of herbage DM on offer was 2330 and 2030 kg ha^-1, with crude protein concentrations of 192 and 193 g per kg DM in 1976 and 1977 respectively. Grazed herbage was the sole feed in the control treatment. In the other two treatments the herbage was supplemented with 3 kg per cow per d of a concentrate containing either 82·2% barley or groundnut with mean crude protein concentrations of 109 and 409 g per kg DM respectively. Similar results were obtained in both experiments with average daily milk yields of 18·3, 19·8 and 19·9 kg per cow on the control, barley and groundnut treatments respectively. The supplements had no significant effects on either milk composition or liveweight change. It is concluded, that with an ample supply of herbage of high crude protein concentration, a supplement of groundnut had no advantages over one of barley.     

Effects of post‐grazing herbage height and concentrate feeding on milk production and major milk fatty acids of dairy cows in mid‐lactation

Milk fatty acids (FA) were compared in mid‐lactation dairy cows in four feeding systems combining grazing management and supplementation. The four treatments were factorial combinations of compressed herbage grazed to 3·7 or 4·6 cm post‐grazing height, with or without concentrate feeding (3·6 kg cow^?1 d^?1). Milk yield and composition were measured for four groups of eight Friesian × Jersey dairy cows over 3 weeks in mid‐lactation for cows that had grazed treatments for 64 d from early spring. Milk yield was higher in cows fed concentrate plus herbage (23·9 kg d^?1 cow^?1) than cows fed herbage only (20·3 kg d^?1 cow^?1). Milk fat percentage was higher in cows fed herbage only (5·5%) than that fed herbage plus concentrate (5·1%). Milk protein percentage was higher in cows fed herbage plus concentrate (4·0%) than that fed herbage only (3·7%). The concentrations of conjugated linoleic acids c9, t11, C18:0, C18:1 t11 and C18:2 t9, c12 FA were lower where concentrate was fed. The concentrations of C18:1 t10, C18:1 t5, t8 and C18:2 c9, c12 FA were higher where concentrate was fed. The concentrations of C18:1 c6, C18:1 c9, C18:1 t9 and C18:3 c6,9,15 were unaffected by concentrate feeding. Post‐grazing herbage height had no significant effect on milk yield or concentration of milk FA. Provided dairy cows are harvesting leafy material of similar nutrient and FA concentration, post‐grazing herbage height does not appear to alter milk FA and the supply of high energy concentrates is more influential on milk FA profiles.     

Effect of replacing time available for grazing with time available for eating maize silage and soyabean meal on milk yield and feeding behaviour in dairy cows

Low rates of herbage dry matter (DM) intake impose limits on total daily DM intake in grazing dairy cows. The objective of this study was to increase total daily DM intake and milk production by restricting daily time available for grazing (TAG) and replacing it with time available for eating a maize silage/soyabean meal (TAMS) diet indoors. The treatments (TAG + TAMS) were 20 + 0, 19 + 1, 10 + 10 and 5 + 15 h. Measurements were made of milk production, intake and feeding behaviour. The interactions of TAG + TAMS treatments with sward height (SH) and concentrate level (CL) were also examined. Two experiments, each lasting 42 days, were carried out in spring ( Experiment 1 ) and autumn ( Experiment 2 ) using forty‐eight and twenty‐four Holstein‐Friesian cows respectively. Treatments were arranged in a factorial design with TAG + TAMS treatments, SH ( Experiment 1 only) and CL as the independent variables and a TAG + TAMS of 20 h. Reducing TAG and increasing TAMS significantly reduced estimated herbage DM intake and significantly increased maize silage/soyabean meal intake in both experiments, but there were no significant main effects of TAG + TAMS treatments on milk yield (mean, 27·4 and 25·5 kg d^?1 for Experiments 1 and 2 respectively), and yield of milk constituents. Increasing SH ( Experiment 1 ) and CL ( Experiments 1 and 2 ) significantly increased milk yield. In Experiment 1 , there was a significant interaction between TAG + TAMS treatments and SH with the taller sward height of 8–10 cm and the 20 + 0 treatment having the highest milk yield (29·7 kg d^?1) and the 5 + 15 treatment the lowest (27·2 kg d^?1), whereas at the lower sward height of 4–6 cm, milk yield was lowest on the 20 + 0 treatment (25·5 kg d^?1) with the other three treatments being higher (mean, 26·9 kg d^?1). Replacing TAG with TAMS significantly increased liveweight gain in Experiment 1 but not in Experiment 2 . Estimated rates of intake of herbage were lower in the autumn experiment ( Experiment 2 , 9·6 g DM min ^?1) than in the spring experiment ( Experiment 1 , 29·4 g DM min ^?1) but rates of intake of maize silage were higher in the autumn (112·4 g DM min^?1) than in the spring (72·5 g DM min^?1). In conclusion, in spring the response to replacing TAG with TAMS was dependent on sward conditions with the highest milk fat plus protein yield being on the 20 + 0 treatment at the high sward height and on the 19 + 1 treatment at the low sward height. The high liveweight gain of the 5 + 15 treatment could be an important means of restoring body condition in grazing lactating cows. In autumn, intakes of herbage were low in spite of its high estimated nutritive value with all treatments having a similar level of performance.