Grass Intake of Dairy Cows

Maximum grass intake is a critical component to efficient dairy cow output in terms of milk production and reproductive performance.

Of recent concern is the very poor reproductive performance of high genetic merit dairy cows. Due to very conflicting reports and a general confusion, a topical question is “what is the average daily grass intake capacity of cows in the dairy herd?”

It is important for Irish dairy farmers to realise the grass intake capacity, so that cows are not underfed thus leading to poor performance. This is especially so as cow genetic merit and milk output, thus, cow nutrient requirement, increase. A conference was organised by the Irish Grain and Feed Association with researchers at Teagasc, Moorepark to cover these issues. The conference title was “The production of high quality milk from grass and other feeds”.

It gave a comprehensive review of Moorepark research, focusing on the type of cow, production systems, grassland management, supplementation and winter nutrition. This bulletin covers aspects of the conference, but primarily focuses on, scientific evidence available on the grass intake of dairy cows, as well as, summarising recent research on high genetic merit cows and strategies for feeding them.

Grass Production and Intake

Grazed pasture is notoriously variable in yield and nutritive value (Clark and Jans, 1995) due to components, some of which are unpredictable and/or uncontrollable, such as, climate, weather, soil fertility, drainage, herbage varieties and grassland management. Grass growth in Ireland can vary by up to 70% from year to year.

The main factors, which affect production and intake of grazing dairy cows, are:

  • Pasture quality/digestibility
  • Pasture allowance
  • Ground Conditions

Sward characteristics that determine bite size are an important component of grass intake. Bite size is optimised with tall, dense, leafy swards, which are best achieved on rotational grazing systems (McGilloway and Mayne, 1996).

The main periods of grass deficit are:

  • Early spring period after turnout
  • Mid Summer period during silage conservation
  • Autumn-September onwards during declining growth rates

Adverse weather conditions e.g. “late springs” and drought often exacerbate these deficit periods.

What is the Daily Herbage Intake Capacity of the Grazing Dairy Cow?

Research results (primarily from Ireland) on dairy cow herbage intakes with and without concentrate supplementation are summarised in the Table. The average intake values on grass alone range from 10.9 to 20.7 kg dry matter (DM) per day with the majority of results falling between 12 and 17 kg DM per day. Surprisingly, grass intakes in many recent studies are similar to intakes recorded in the eighties (with much lower genetic merit cows). As cow genetic merit is very much a relative term, to put some of the results into perspective, the current national RBI is around 105. A number of things such as, time of year, lactation stage, cow genetic merit, cow age profile, grass allowance, grass quality and whether the intakes obtained were for grazed or zero-grazed animals need to be considered when interpreting the results in the Tables.

In a detailed study, McGilloway (unpublished) measured herbage intake of grazing dairy cows over two consecutive years (1992 and 1993) in Moorepark. Pastures were grazed to either 4cm (severe grazing), 6cm (optimum grazing) or 8cm (under grazing). This study had individual intake points over the entire grazing season for each year. Results showed that for each of the treatments, grass intake was HIGHLY VARIABLE over the grazing season. For the three treatments combined, the average grass DM intakes in 1992, at the first, fourth, seventh and ninth (final) grazing cycles were approximately 14.7, 12.2, 13.7 and 14.3 kg respectively. Corresponding intakes for the 6cm post grazing sward height treatment (which is well established as the optimum for grassland management – see later on) were approximately 15.7, 12.4, 13.0 and 14.7kg. In 1993, the average DM intakes for the three treatments combined at grazing cycles 1, 2, 3, 6 and 9 were approximately 13.6, 16.1, 14.2, 14.8 and 13.1kg respectively while corresponding intakes for the 6cm post grazing height treatment were approximately 13.8, 15.6, 13.3, 14.6 and 12.5kg. These two detailed experiments demonstrate that the average grass DM intake of a dairy cow under ideal grazing management conditions ranges from 12.0 to 16.5 kg across the grazing season.

This range in grass DM intake is CONSISTENT with values obtained from nearly all published Moorepark experiments (Table 1) carried out at various times of the year, from the 1980’s right up to the present day, with cows under optimum grazing management (Stakelum 1986a, 1986b, 1986c; Stakelum and Dillon, 1988, 1989a and 1989b; Dillon et al., 1997; Maher et al., 1997) and also with zero-grazed cows (Stakelum and Morgan, 1983; Stakelum and Connolly, 1987; Keady and Murphy, 1993; O’Mara et al., 1997), as well as being consistent with research data from Northern Ireland (Cushnahan and Gordon, 1993; Cushnahan and Mayne, 1994; Cushnahan et al., 1995; Sayers and Mayne, 1998) and elsewhere (See Table 2). The fact that these published grass intake figures under Irish conditions, are available almost annually for well over a decade, thus including good and bad years for grass performance, demonstrates realistically what’s actually happening and/or possible at Irish farm level.

To say “average cow intake of X kg are/or can be achieved” can be misleading. Does it mean intake for the whole grazing season or just when grazing conditions are ideal? Does it mean herd intakes which include primiparous cows or just multiparous cows? etc. For example, it must be noted that the “widely cited”, highest average reported grass intake figures of 18.6 to 20.7 kg DM per day obtained with high genetic merit cows (Buckley et al., 1998) were:

  • From a herd that did NOT include primiparous (which have lower capacity and normally constitute 10 to 20% of a herd).
  • Recordings obtained during the summer months when grazing conditions are more favourable.
  • From a time period when the peak intake capacity of the cow was attained.

In addition, the highest average intake figure in the latter study was obtained on a daily herbage allowance of 27kg DM per cow which is much higher than recommended for practical grassland management, (in terms of subsequent herbage quality – see later on). This is similar to the study of Orr et al. (1998) where herbage intakes of 18 kg DM were obtained but at an herbage allowance of 32kg DM per cow, which again, is not practical.

The intake studies of Stakelum (1986a and c) and Maher et al. (1997) for example, only contained multiparous cows which is not directly applicable to average herd intakes at farm level.

Very few studies have recorded grass intake during the early spring (March/April) period. Intake will be generally lower during this period for three main reasons.

Firstly, the DM content of grass can significantly effect herbage intake at pasture (Forbes, 1995; McGilloway and Mayne, 1996). The grass nutrient content will be markedly diluted by the presence of water, which is predominantly intra-cellular in nature and thus makes a large contribution to the bulk of the diet (McGilloway and Mayne, 1996). The water content of fresh herbage includes both the internal and surface water. Verite and Journet (1970) feeding the same grass, fresh or dried, reported that the water content limits voluntary intake of dairy cows below a DM concentration of 18%, with a decrease of 0.34kg DM for each percentage drop in DM. In an experiment with zero-grazed dairy cows they found that herbage intake decreased by 0.21kg DM for each percentage drop in DM below 15%. Average dry matter content of pasture can vary from 15% in spring to 25% in mid-summer (McGilloway and Mayne, 1996) but can fall to, as low as 10-12% during wet weather. Reasons suggested for the decrease in intake at low dry matters include, physical limitations from excess water in the rumen or from water content entrapped in the cell structure, behavioural limitations related to rate of intake or simply reduced palatability from herbage surface water (Demment et al., 1995).

Secondly, this decrease in DM intake is compounded by the interaction of “adverse grazing conditions” during wet weather. These include, poaching effects, grass soiling etc and occur frequently during the early spring and especially during “late springs”. These latter effects increase in importance, the further north and west you go in Ireland. Dillon et al. (1997) attributed the low daily grass intakes to poor grazing conditions and inclement weather in the early part (May) of their study.

Thirdly, the fact that cow voluntary intake is minimal at calving and then increases slowly (a lag relative to milk yield) until it peaks during the third month of lactation (Coulon et al., 1989) or between 10-16 weeks after calving (Murphy and Fitzgerald, 1998) means that grass intake capacity of spring-calving cows is relatively lower during this period, all else being equal.

It can be suggested that grass intake in the early part of the year is the most important factor in terms of energy balance and reproductive performance of the spring-calving dairy cow, especially with high genetic merit animals.

Increased Grass Allowance

Stakelum et al. (1995) reported that for each additional 1 kg of fat-corrected milk that a cow can produce daily, she would need to consume between 0.4-0.5 kg of extra grass DM daily. Increases in food intake with high merit cows on grass and grass silage based diets are relatively small (5-8%) (Mayne and Patterson, 1995; Dillon and Buckley, 1998).
The allocation of extra grass in order to improve performance has been questioned (Gordon, 1996). The problem here is that at high grass allowances, very small additional increases in daily intake are got from further increases in daily allowance (Stakelum, 1996) or simply, the additional grass consumed by the cow is only a fraction of the additional grass offered. This was evident from the work of Maher et al. (1997) who found that the allocation of an extra 4kg herbage DM daily (24 v. 20 kg) to low-medium merit cows (RBI 107) only resulted in an increase in grass dry matter intake of 0.7kg. Similarly, Dillon and Buckley (1998) reported that the allocation of an additional 3kg herbage DM daily (27 v. 24 kg) to high merit cows (RBI 117 & 134) only resulted in an increase in grass dry matter intake of 0.5kg.

If grass is not grazed sufficiently, this obviously results in an inefficiency of grass use at time of grazing. However, it also leads to additional problems in terms of poor pasture regrowth quality in the following grazing rotation, thus resulting in sward deterioration as the year progresses (Stakelum et al.,1995; Stakelum, 1996) and from year to year. This deterioration may be offset somewhat, by topping (Stakelum and Dillon, 1989) or possibly by using a leader-follower system but essentially it means severe grassland management difficulties. As sward digestibility is one of the main factors affecting output of the dairy cow (Stakelum and Dillon, 1989; Stakelum and O’Donovan, 1998), maintenance of sward quality is critical. For example, a one unit decrease in digestibility of grazed pasture will decrease daily intake by an average of 0.60kg DM, the magnitude of the decrease increasing at lower digestibilities (Stakelum, 1996).

Maher et al. (1997) reported that a daily herbage allowance of 20 kg DM per cow per day (from May to late August) was capable of supporting 22.2 kg (~5.0 gallons) of milk production per day (RBI 107) and optimum pasture utilisation and that a higher pasture allowance of 24 kg DM resulted in only a small increase in milk yield and under-utilisation of pasture. In addition, there were no significant differences in cow liveweight or body condition score changes between the grass allowances.

In a series of subsequent, short-term experiments using higher genetic merit (RBI 112) cows, Maher et al. (1998) found a milk yield and component response up to 23 kg DM daily herbage allowance with spring calvers over a grazing period from late April to Mid-June but only a milk yield response up to 20 kg DM daily herbage allowance with autumn calvers over the same period and with spring calvers from late July to late August. Similarly Dillon and Buckley (1998) found that the allocation of extra grass (3 kg DM) to medium (RBI 117) and high (RBI 134) genetic merit dairy cows only resulted in a small increase of 190 kg in milk production, most of which was achieved during the autumn period of the grazing season. Seemingly, an additional grass allowance is not the answer.

Firstly, high intakes are not achieved, especially, the intakes required by high merit cows to express their full genetic potential. These cows end up mobilising excessive body reserves or “milking off their backs” to meet their requirements.

Secondly, pasture quality decreases due to poor utilisation.

Thirdly, milk yield response to additional daily grass allowance (above 20-24kg DM depending on genetic merit and time of year) is small or absent.

Supplementation

Excessive mobilisation of body reserves in high forage systems can have major implications on the incidence of metabolic and/or reproductive disorders thus animal survivability. The positive effect of concentrate supplementation in spring, on milk production and reproductive performance of the grazing dairy cow has been clearly demonstrated (Dillon et al., 1997).

Even in optimal grazing conditions, high merit cows will require supplementation with concentrates of high nutrient concentration in order to fully exploit their genetic potential for milk production (Mayne and Gordon, 1995; McGilloway and Mayne, 1996). Gordon (1996) suggested that if high performance animals are to be grazed at pasture then a strategy of maintaining a sufficiently tight stocking rate, coupled with supplementation, is likely to be most effective. Murphy and Fitzgerald (1998) reported that a high level of crude protein (obtained in spring and autumn) in grass is insufficient (75% is rapidly degraded in the rumen) to maximise microbial protein production and that a source of undegradable protein may be required with high yielding cows.

Attention must also be drawn to the fact, that the limited research available, examining the effect of concentrate supplementation of silage and pasture on dairy cow performance, has been carried out using cows of low to moderate milk yield potential (relatively low RBI). Thus, extreme caution is required in applying these results to cows with high RBI or high milk production potential.

Up until now, concentrates only had a role under special circumstances, where supply of grass was limiting, in achieving high intakes (Stakelum and Dillon, 1995). Early research with concentrate supplementation at pasture demonstrated large substitution rates and established that supplementation is unlikely to have a reasonable effect on total nutrient intake unless pasture is being tightly grazed. However some major findings and changes have occurred in recent years.

It has been demonstrated that high starch diets, such as barley, have high substitution rates (close to 1.0), while high digestible fibre diets, such as beet pulp, citrus pulp, corn gluten, distillers grains, soya hulls, have much lower substitution rates (frequently in the range 0.15 to 0.25) thus giving much better milk yield responses (Stakelum and Dillon, 1995)

Research has established that high genetic merit cows respond better to additional concentrates than medium or lower merit cows (Ferris et al., 1996; Chalmers et al., 1997; Dillon and Buckley, 1998).

Patterson and Ferris (1997) reported that with high concentrate diets fed indoors, medium merit cows gained condition whereas there was little change in tissue deposition with high merit cows, who instead, partitioned the additional energy towards milk production. They calculated that milk production responses to increases in concentrate feed level were 50% higher with high merit relative to medium merit cows. Mayne (1997) concluded that at present silage and concentrate costs and current milk price, high merit cows could be economically fed an additional 2kg of concentrate per day above medium merit cows during the winter period. Similarly Murphy and Fitzgerald (1998) recommended feeding an additional 2-3kg of supplement to high yielding herds (1300-1600gallons/lactation) compared to lower yielding herds (900-1250 gallons/lactation).

In addition, Patterson and Ferris (1997) reported that at pasture, there was a residual or carry-over effect of level of indoor concentrate feeding to the high merit cows, but this did not occur with the medium merit cows. The high merit cows produced an additional 0.21 kg of milk at pasture per kg of concentrate offered during the winter. Hoden et al. (1991) reported a greater response to concentrate supplementation at pasture by higher yielding dairy cows. Similarly, Dillon and Buckley (1998) reported a large response in milk production to concentrate supplementation at pasture in both medium (0.9 kg milk/kg of extra concentrate) and high (1.12 kg milk/kg of extra concentrate) genetic merit dairy cows due to very low substitution rates (0.2).

Table 1. Grass dry matter intakes of dairy cows in Moorepark experiments
Author Calving Time (Merit) Cow “age” Conc Level kg Herbage “allowance” Herbage Digestibility g/kg Recorded Grazing period Milk yield kg/day GRASS DM INTAKE kg/day
MOOREPARK
Stakelum and Morgan 1983 Autumn Zero-grazed 13.7
Stakelum 1986a Spring Mature 0 16 kg DM September 14.4
3.3 16 13.4
0 24 18.2
3.3 24 16.2
Stakelum 1986b Spring 90% mature 0 16 kg DM April 12.9, 13.8
4.5 16
0 24 11.5, 12.4
4.5 24 16.1, 17.8
14.9, 15.5
Stakelum 1986c Spring Mature 0 16 kg DM August 15.3 12.6, 13.6
3.9 16 14.2
0 24 14.3 11.6, 12.0
3.9 24 13.9 14.8, 18.1
12.0, 15.4
Stakelum and Connolly 1987 Zero-grazed May 16.7
June 17.3
July 16.9
August 16.2
Stakelum et al. 1987 Strip-grazed 807 OMD June 21.7 17.9
30 kg DM
Stakelum and Dillon 1988 Spring x 0 22 kg OM 853 OMD 4-12 week of lactation x 14.8, 14.3
3
3 12.5, 10.6
3 12.9, 12.9
13.2, 13.8
Stakelum et al. 1989 Spring Zero-grazed 13.8, 10.9
Stakelum and Dillon 1989a Spring x x 14 kg DM 830 OMD April-July ~27 12.6
22 808 16.3
Stakelum and Dillon 1989b July-Sept
~804 OMD Grazing cycle 1 ~19.5 15.0
~790 ~18.3 14.8
~782 ~17.2 12.6
Grazing cycle 2 15.3
14.7
12.6
Grazing cycle 3 14.6
13.8
12.0
Grazing cycle 4 14.4
13.7
13.0
McGilloway
(unpublished)
4cm PGSH Grazing season of 13.6
6cm 14.0
1992+1993
8cm 14.8
Keady and Murphy 1993 Zero-grazed April/May 12.8 12.7
Stakelum et al. 1995 25-27 ~17.5
Dillon et al. 1996, 1997 Spring 0 18.5 kg DM 832 DMD/ May 24.2 14.2
2 18.5 824 OMD 25.8 13.2
4 18.5 26.0 12.9
0 19.0 June 24.2 13.5
2 19.0 25.8 13.3
4 19.0 26.0 12.6
Spring 0 19.0 kg DM 833 DMD/ May 24.0 13.5
2 19.0 826 OMD 25.0 13.8
4 19.0 26.6 13.1
0 23.2 June 24.0 17.1
2 23.2 25.0 16.5
4 23.2 26.6 16.8
O’Mara et al. 1997 0 Zero-grazed x 13.6
3 11.5
Maher et al. 1997 (Stakelum and O’Donovan, 1998) Spring Multi-parous 0 16 kg DM May-Aug 20.6 15.3
RBI 107 20 22.2 16.4
24 22.9 17.1
Dillon and Buckley 1998 Spring
RBI 135 Primi-parous 1.0 May-Nov 14.2
1.0 13.4
RBI 117
RBI 135 Primi-parous 3.5 May-Nov 13.9
3.5 13.5
RBI 117
RBI 135 Primi-parous 1.0 May-Nov 15.1
1.0 14.1
RBI 117
Spring
RBI 135 2nd Lact. 0 24 kg DM June-Sept 25.4 20.3
0 21.8 18.6
RBI 117
RBI 135 2nd Lact. 3.0 21 kg DM June-Sept 26.5 19.6
3.0 23.4 18.3
RBI 117
RBI 135 2nd Lact. 0 27 kg DM June-Sept 24.8 20.7
0 22.2 19.2
RBI 117
Table 2. Grass dry matter intakes of dairy cows from experiments in Hillsborough, France and elsewhere
Author Calving Time Cow “age” Conc Level kg Herbage “allowance” Herbage Digestibility g/kg Recorded Grazing period Milk yield kg/day GRASS DM INTAKE kg/day
HILLSBOROUGH
Cushnahan and Gordon 1993 Spring 1.0 June + Aug 10.7-12.9
Cushnahan and Mayne 1994 Zero-grazed June 20.6 17.4
Cushnahan et al. 1995 Zero-grazed 786 DMD May 19.8 16.8
744 June 17.4 13.8
Sayers and Mayne 1998 0 Zero-grazed Mid- lactation 18.2 12.7
3 20.8 12.2
6 22.1 10.9
FRANCE
Wade 1991 PGSH Day
(cited by Demment et al. 1995) 29.6cm 1 850 OMD 23.2 18.3
22.4cm 2 840 23.1 18.1
18.4cm 3 830 22.6 16.7
14.5cm 4-5 810 20.5 14.6
Mambrini and Peyraud 1994 Zero-grazed 14.3
Peyraud et al. 1994 0 Strip-grazed 800 OMD 22.3 17.6
0 28 kg OM 790 17.6
2 790 18.3
Peyraud and Delagarde 1995 Strip-grazed
>20 kg OM 22.1 17.6
Peyraud et al. 1996 Autumn 40% Strip-grazed May/June
Multi-parous 0.8 21.2 kg OM 821 OMD Week 1 22.5 13.9
22.1 819 Week 2 22.6 16.1
23.6 807 Week 3 23.0 16.6
24.2 824 Week 4 21.5 16.6
22.3 816 Week 5 21.9 15.2
Autumn 50% Strip-grazed May/June
Multi-parous 0.8 34.7 kg OM 834 Week 1 23.8 18.2
29.2 822 Week 2 22.8 17.9
30.0 788 Week 3 21.3 15.3
ELSEWHERE
Meijs and Hoekstra 1984 16.9
Holden et al. 1994 Multi-parous 7.3 685 OMD Apr 30 36.0 13.9
7.2 700 May 28 30.1 15.1
5.5 677 Aug 27 19.6 14.3
4.8 700 Sept 24 17.4 15.6
Rook et al. 1994 Spring Multi-parous Set-stocked
0 4cm SH May/June 17.2 13.9
4 20.8 12.2
0 6cm SH 21.2 15.3
4 24.6 13.8
0 8cm SH 21.5 16.8
4 26.1 16.5
Set-stocked
0 6cm SH July/Aug 22.1 13.5
4 24.4 13.5
0 8cm SH 21.1 14.1
4 24.8 13.9
Fisher et al. 1995 Summer 50% Multi-parous Set-stocked
6 1.54 t DM/H July, Sept 26.1 11.0, 10.7
6 1.94 28.0 13.4, 11.1
6 1.36 25.6 10.1, 11.2
Spring/Summer Multi-parous 6 1.51 t DM/H July, Sept 28.5 12.1, 12.0
6 1.57 27.3 11.5, 13.8
6 1.50 28.4 12.8, 12.2
Berzaghi et al. 1997 0 14.1
6.4 10.6
Orr et al. 1998 Spring 4 Strip-grazed May-July 18.0
Kolver and Muller 1998 Multi-parous June 29.6 19.0

Conclusions

  • Grass Growth in Ireland can vary by up to 70% from year to year.
  • There are limitiations in grass, firstly in terms of intake capacity, secondly, in terms of advers interactions between grass allowance, ideal post-grazing sward height and subsequent sward quality and thirdly, in terms of poor or lacking milk yield responses to very high grass allowances.
  • Grass intake is highly variable over ther grazing season.
  • It is reasonable to assume that grass intakes are lower in early spring.
  • Dairy herd grass intake is between 12 and 18kg DM per cow per day.
  • Dairy herd grass intakes of >20kg DM per cow have yet to be realised.
  • Clearly there is an inadequacy in the literature at present on the management and feeding of high genetic merit dairy cows on forage based systems.
  • Trying to apply “old” research results and principles (attained with cows of lower genetic merit) to high merit cows is not possible. They cannot be treated the same.
  • Higher genetic merit cows have a superior milk yield responses to concentrate supplementation than lower merit cows.
  • Basic component research is requires to define the optimum supplementation of high merit animals on silage based diets and especially at pasture.

Main References

  • Dillon P. and Buckley F.1998. Managing and feeding high genetic merit dairy cows at pasture. In: ‘R&H Hall Technical Bulletin’. Issue No. 2, 1998.
  • Dillon P., Crosse S. and O’Brien B1997 Effect of concentrate supplementation of grazing dairy cows in early lactation on milk production and milk processing. ‘Irish Journal of Agricultural and Food Research’ 36: 145-159.
  • Mc Gilloway D.A. and Mayne C.S.1996. The importance of grass availability for the high genetic merit dairy cow. In: ‘Recent Advances in Animal Nutrition’ 1996; Eds. P.C. Garnsworthy, J. Wiseman and W. Haresign. Chp. 8, 135-169.
  • Murphy J. and Fitzgerald S.1998. Concentrate supplementation of Grass and Silage (Type of concentrate). In: ‘The production of high quality milk from gras and other feeds’, 23rd April 1998, Teagasc and I.G.F.A., Ed. S. Fitzgerald, 41-70.
  • Patterson D.C. and Ferris C.P.1997. Winter feeding of the high genetic merit dairy cow. In: ‘Managing and Feeding the High Genetic Merit Dairy Animal’, Agricultural Research Institute of Northern Ireland 12th March, 1997, 25-42.
  • Stakelum G.1996. Practical grazing management for dairy cows. Irish Grassland and Animal Production Journal 30: 33-45.

About the Author

  • Dr. Mark McGee is a Technical Executive with IAWS Group plc. Before joining the group he spent 4 years undertaking reserach on suckler cow nutrition and physiology at Grange Research Centre.