Sward Factors Influence on Pasture Dry Matter Intake of Grazing Dairy Cows: A Review

Document Type: Review Article


Centro de Investigaciones Agrarias de Mabegondo, INGACAL, Apdo 10, 15080, A Coruna, Spain


Successful pasture-based milk production systems pivot on balancing dairy cows’ feed requirements with seasonal and annual fluctuations in pasture production. In order to maximise cow production from grazing dairy systems, it is necessary to reach an efficient utilization of grazed grass for feeding cows and the development of appropriate grazing management systems designed to maximize daily pasture dry matter intake (PDMI) per cow and per hectare, while maintaining high sward quality over the grazing season by keeping high pasture levels of crude protein, water soluble carbohydrates and digestibility of organic matter and low levels of acid and neutral detergent fibers in the swards. To maximize PDMI, cows need to consume plants that have characteristics that allow rapid consumption and lead to fast rates of passage through the rumen. This review considers the role of sward factors which affect the short-term feed budget of cows at pasture and, therefore, condition cow feed requirements at grazing and influence on PDMI. Furthermore, it highlights the relevance that havefor the development of pasture-based milk production systems the study of the species of grasses and / or legumes that integrate the pastures, the changes on sward structure, the seasonality in grass production, the pasture chemical constituents, the sward botanical composition, the grass feeding value, the digestibility of pastures, the intensity of sward defoliation, and the importance of sward height and herbage mass in relation to maximizing PDMI. The amount of herbage consumed is the major determinant of cow production but it is yet one of the most difficult aspects of forage quality to predict. In this review, three methods for PDMI calculation are presented as faecal output/diet digestibility method, sward difference method and the grazing-behaviour method. Also, three equations for PDMI estimation are described considering different sward and animal variables.


Ackerman C.J., Purvis H.T., Horn G.W., Payton M.E., Vermeire L.T., Paisley S.I. and Bodine T.D. (1999). Estimation of forage mass of Old World bluestem using a visual obstruction measurement technique. Anim. Sci. Res. Rep. 973, 194-199.
Aitchison E.M., Gill M., Dhanoa M.S. and Osbourn I.D.F. (1986). The effect of digestibility and forage species on the removal of digesta from the rumen and the voluntary intake of hay by sheep. Br. J. Nutr. 56(2), 463-476.
Alberda T. (1966). The influence of reserve substance on dry-matter production after defoliation. Pp. 140-147 in Proc. 5th Int. Grass. Cong. Helsinki, Finland.
Bailey R.W. (1973). Structural carbohydrates. Pp. 157-211 in Chemistry and Biochemistry of Herbage. G.W. Butler and R.W. Bailey Eds. Academic Press. New York, USA.
BakerA.M.C. and Leaver J.D. (1986). Effect of stocking rate in early season on dairy cow performance and sward characteristics. Grass Forage Sci. 41, 333-340.
Bargo F., Muller L.D., Delahoy J.E. and Cassidy T.W. (2002). Milk response to concentrate supplementation of high producing dairy cows grazing at two pasture allowances. J. Dairy Sci. 85, 1777-1792.
Bartholomew P.W. and Chestnutt D.M.B. (1977). The effects of a wide range of fertilizer nitrogen application rates and defoliation intervals on the dry matter production, seasonal response to nitrogen, persistence and aspects of chemical composition of perennial ryegrass. J. Agric. Sci. 88, 711-721.
Barthram G.T. (1986). Experimental techniques: the HFRO sward stick. Pp. 29-30 in H. Farming Research. Biennial Report Univ. California.
Beeker W., Priess M., Berendonk C., Tholen E. and Spiekers H. (2006). 9000 Iauch mit Halbtagsweide? Top Agrar. 5, 26-29.
Beever D.E. and Siddons R.C. (1986). Digestion and metabolism in the grazing ruminant. Pp. 479-497 in Proc. 6th Int. Symp. Rumin. Physiol. Bonff, Canada.
Beever D.E. and Thorp C. (1996). Advances in the understanding of factors influencing the nutritive value of legumes. Legumes in sustainable Farming Systems. 194-207 in Proc. Occa. Symp. British Grassland.  
Beever D.E., Losada H.R., Cammell S.B., Evans R.T. and Haines M.J. (1986). Effect of forage species and season on nutrient digestion and supply in grazing cattle. Br. J. Nutr. 56(1), 209-225.
Beever D.E., Offer N. and Gill E.M. (2000). The feeding value of grass and grass products. Pp. 140-195 in Grass its Production and Utilization. A. Hopkins Ed. 3rd Ed. Blackwell Science. Oxford (UK).
Benkovi L., Uresk D.W., Schenbeck G. and King R.M. (2000). Protocol for monitoring standing crop in grasslands using virtual obstruction. J. Range. Manag. 53, 627-633.
Berzaghi P., Herbein J.H. and Polan C.E. (1996). Intake, site and extent of nutrient digestion of lactating cows grazing pasture. J. Dairy Sci. 79, 1581-1589.
Binnie R.C. (1980). The effect of initial defoliation and height of defoliation on productivity of Lolium perenne swards. Grass Forage Sci. 35, 267-273.
Binnie R.C. and Harrington F.J. (1972). The effect of cutting height and cutting frequency on the productivity of an Italian ryegrass sward. J. Br. Grassl. Soc. 27, 177-182.
Binnie R.C., Chestnutt D.M.B. and Kilpatrick D.J. (1997). The effect of altering the length of the regrowth interval in the early, mid and late season on the productivity of grass swards. J. Agric. Sci. 128, 303-309.
Blaxter K.L., Mcgraham N. and Wainman F.W. (1956). Some observations on the digestibility of food by sheep, and on related problems. Br. J. Nutr. 10, 69-91.
Braithwaite G.D. (1976). Calcium and phosphorus metabolism in ruminants with special reference to parturient paresis. J. Dairy Res. 43, 501-520.
Bransby D.I., Matches A.G. and Krauge G.P. (1977). Disk meter for rapid estimation of herbage yield in grazing trials. Agron. J. 69, 393-396.
Brereton A.J. and Carton O.T. (1986). Analysis of theseasonal changes in the structure of a perennialryegrass (Lolium perenne) sward underdifferent managements. Irish J. Agric. Res. 25, 97-110.
Burk R.F. (1978). Selenium in nutrition. Wld. Rec. Nutr. Diet. 30, 88-106.
Butler G.W. and Jones D.I.H. (1973). Mineral biochemistriy of herbage. Pp. 127-162 in Chemistry and Biochemistry. Fllerbag. G.W. Bulter and R.w. Baily Eds. London. Academic Press.
Butris G.Y. and Phillips C.J.C. (1987). The effect of herbage surface water and the provision of supplementary forage on the intake and feeding behaviour of cattle. Grass Forag Sci. 42, 259-264.
Buxton D.R. and Redfearn D.D. (1997). Plant limitations to fiber digestion and utilization. J. Nutr. 127, 814-818.
Buxton D.R., Mertens D.R. and Fisher D.S. (1996). Forage quality and ruminant utilization. Pp. 229-266 in Proc. Am. Soc. Agron. Inc., Crop Sci. Soc. Am. Inc. and Soil Science Society of America Inc. Wisconsin, USA.
Cabrera-Estrada J.I., Delagarde R., Faverdin P. and Peyraud J.L. (2003). The addition of external water to fresh grass does not affect dry matter intake, feeding behaviour and rumen characteristics in dairy cows. Anim. Res. 52, 3-16.
Cabrera-Estrada J.I., Delagarde R., Faverdin P. and Peyraud J.L. (2004). Dry matter intake and eating rate of grass by dairy cows is restricted by internal, but not external water. Anim. Feed Sci. Technol. 114 (4), 59-74.
Caird L. and Holmes W. (1986). The prediction of voluntary intake of grazing dairy cows. J. Agric. Sci. 107, 43-54.
CamlinM.S. (1997). Grasses. Pp. 2-14 in Proc. 1th Seeds of progress. Br. Grassland Soc. Occas. Symp. British Grassland.
Carton O.T., Brereton A.J., O'Keeffe W.F. and Keane G.P. (1989). Effect of turnout date and grazing severity in a rotationally grazed reproductive sward. 1. Dry matter production. Irish J. Agric. Food Res. 28, 153-163.
Charles A.H. and Haggar R.J. (1979). Changes in sward composition and productivity. Pp. 253-261 in Proc. 1th Br. Grassland Soc. Occas. Symp. British Grassland Society. Hurley, UK.
Chenais F., Seuret J.M., Brunschwig P. and Fiorelli J.L. (2001). Pour un role croissant du paturage dans les systèmes bovins laitiers. Fourrages. 166, 257-277.
Combellas J. and Hodgson J. (1979). 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. Grass Forage Sci. 34, 209-214.
Corbett J.L., Greenhalgh J.F.D. and Macdonald A.P. (1958). Paper as a carrier of chromium sesquioxide. Nature. 182,1014-1016.
Corrall A.J., Lavender R.H. and Terry C.P. (1979). Grass Species and varieties: seasonal patterns of production and relationships between Yield, Quality and Date of First Harvest. GRI Technical Report No.26. Grassland Res. Inst. Hurley, UK.
Dalley D.E., Roche J.R., Grainger C. and Moate P.J. (1999). Dry matter intake, nutrient selection and milk production of dairy cows grazing rainfed pastures at different herbage allowances in spring. Aust. J. Exp. Ag. 39, 923-931.
Delagarde R., Prache S., D’Hour P. and Petit M. (2001). Ingestion de l’herbe par les ruminants au pâturage. Assoc. Franc. Pour. Prod. Fourrag. 166, 189-212.
Dillon P. (2006). Achieving high dry-matter intake from pasture with grazing dairy cows. Pp. 1-26 in Fresh Herbage for Dairy cattle: the Key to a Sustainable Food Chain. A. Elgersma, J. Dijkstra and S. Tamminga, Eds. Springer.
Dillon P., Roche J.R., Shalloo L. and Horan B. (2005). Optimising financial return from grazing in temperate pastures. Pp. 131-147 in Proc. 10th Int. Grass. Cong. Cork, Ireland.
Dillon P. and Stakelum G. (1989). Herbage and dosed alkanes as a grass management technique for dairy cows. Irish J. Agric. Res. 8, 104-109.
Donaghy D.J. and Fulkerson W.J. (1997). The importance of water-soluble carbohydrate reserves on re-growth and root growth of Lolium perenne L. Grass Forage Sci. 52, 401-407.
Donaghy D.J. and Fulkerson W.J. (1998). Priority for allocation of water-soluble carbohydrate reserves during regrowth of Lolium perenne. Grass. Forage. Sci. 53, 211-218.
Dove H. and Mayes R.W. (1991). The use of plant wax alkanes as marker substances in studies of the nutrition of herbivores: a review. Aust. J. Agric. Res. 42, 913-952.
Ducrocq H. and Duru M. (1997). In vitro digestibility of green lamina of cocksfoot (Dactylis glomerata) in relation to water deficit. GrassForage Sci. 52, 432-438.
Duru M. (2003). Effect of nitrogen fertilizer rates and defoliation regimes on the vertical structure and composition (crude protein content and digestibility) of a grass sward. J. Sci. Food Agric. 83(14), 1469-1479.
Ferguson J.D. (1996). Diet, production and reproduction in dairy cows. 3th Amer. Nutr. Conf. Pp. 173-184.
Ferreira L.M.M., Oliván M., Celaya R., García U., Rodrigues M.A.M. and Osoro K. (2007). The use of n-alkanes to estimate diet composition of ruminants grazing on species diverse plant communities. Effect of feeding selectivity on diet composition estimates. Livest. Sci. 111, 114-123.
Fisher G.L. (1975). Function and homeostasis of copper and zinc in mammals. Sci. Total Environ. 4, 373-421.
Fleming G.A. (1973). Mineral composition of herbage. Pp. 529-566 inChemistry andBiochemistry of Herbage (Vol. 1). G.W. Butler and R.W. Bailey Ed. Acad. Press.Inc. New York, USA.
Fletcher J.E. and Robinson M.E. (1956). A capacitance meter for estimating forage weight. J. Rang. Manag. 9, 96-97.
Forbes J.M. (1993). Voluntary feed intake. Pp. 479-494 inQuanti-tative Aspects of Ruminant Digestion and Metabolism. J.M. Forbes and J. France Eds. CAB International, Oxon, UK.
Forbes J.M. (1995). Voluntary Food Intake and Diet Selection in Farm Animals. CAB International. Wallingford. UK.
Forbes T.D.A. and Hodgson J. (1985). Comparative studies of the influence of sward conditions onthe ingestive behaviour of cows and sheep. Grass Forage Sci. 40(1), 69-77.
Frame J. (1981). Herbage mass. Pp. 39-69 in Sward Measurement Handbook. J. Hodgson, R.D. Baker, A. Davies, A.S. Laidlaw and J.D. Leaver Eds. British Grassland Society. Hurley, UK.
Frame J. (1990). The role of red clover in United Kingdom pastures. Outlook. Agric. 19, 49-55.
Frame J. (1993). Herbage mass. Pp. 59-63. in Sward Measurement Handbook. A. Davies, R.D. Baker, S.A. Grant and S. Laidlaw Eds. British Grassland Society. Reading, UK.
Fulkerson W.J. and Slack K. (1995). Leaf number as a criterion for determining defoliation time for Lolium perenne: 2. Effect of defoliation frequency and height. Grass. Forage. Sci. 50, 16-20.
Ganguli A.C., Vermeire L.T., Mitchell R.B. and Wallace M.C. (2000). Comparison of four non-destructive techniques for estimating standing crop in short grass plains. Agron. J. 92, 1211-1215.
Gladstone I.S. and Loneragan J.F. (1967). Mineral elements in temperature crops and pasture plants.Aust. J. Agric. Res. 18, 427-446.
Good R.A., West A. and Fernandes G. (1980). Nutritional modulation of immune responses. Fed. Proc. 39, 3098-3104.
Gowen N., O'Donovan M., Casey I., Rath M., Delaby L. and Stakelum G. (2003). The effect of grass cultivars differing in heading date and ploidy on the performance and dry matter intake of spring calving dairy cows at pasture. Anim. Res. 52, 321-326.
Grumes D.L. (1983). Uptake of magnesium by different plant species. Pp. 23-38 in Proc. John Lee Pratt Int. Symp. Role Magnesium in Anim. Nutr. Virginia Polytechnic Institute and State University. Virginia, USA.
Hageman I.W., Lantinga E.A., Schlepers H. and Neuteboom J.H. (1993). Herbage Intake, digestibility characteristics and milk production of a diploid and two tetraploid cultivars of perennial ryegrass. Pp. 459-460 in Proc. 19th In. Grass. Cong. Palmerston North, New Zealand.
Haggar R.J. and Koch D.W. (1983). Slot-seeding investigations. 3. The productivity of slot-seeded red clover compared with all-grass swards receiving nitrogen. Grass Forage Sci. 38, 45-53.
Hall M.B. (1994). Pectin: the structural non-structural carbohydrate. Pp. 29-36 in Proc. Corn. Nutr. Conf. Ithaca, New York, USA.
HansenJ.C. and Deguchi Y. (1996). Selenium and fertility in animals and man. Acta Vet. Scan. 37, 19-30.
Harmoney K.R., Moore J.K., George J.R., Brummer A.C. and Russell J.R. (1997). Determination of pasture biomass using four indirect methods. Agron. J. 89, 665-672.
Harris S.L., Auldist M.J., Clark D.A. and Jansen E.B. (1998). Effects of white clover content in the diet on herbage intake, milk production and milk composition of New Zealand dairy cows housed indoors. J. DairyRes. 65,389-400.
Harris S.L., Clarck D.A. and Jansen E.B.L. (1997). Optimum white clover content for milk production. Proc. NZ. Soc. Anim. Prod. 57, 169-171.
Harrison J.H. and Conrad H.R. (1984). Effect of selenium intake on selenium utilization by the non lactating dairy cow. J. Dairy Sci. 67, 219.
Head H.H., Thatcher W.W., Wilcox C.J. and Bachman K.C. (1976). Effect of a synthetic corticoid on milk yield and composition and on blood metabolites and hormones in dairy cows. J. Dairy Sci. 59(5), 880-888.
Heady H.F. (1957). The measurement and value of plant height in the study of herbaceous vegetation. Ecology. 38, 313-320.
Hodgson J. (1977). Factors limiting herbage intake by the grazing animal. Pp. 70-75 in Proc. Int. Meet. Anim. Prod. Temp. Grass. Dublin, Ireland.
Hodgson J. (1986). Grazing behavior and herbage intake. Pp. 51-64. inGrazing. J. Frame Ed. British Grassland Society, Berkshire, UK.
Holden L.A., Muller L.D. and Fales S.L. (1994). Estimation of intake in high producing Holstein cows grazing grass pastures. J. Dairy Sci. 77, 2332-2340.
Holmes C.W. (1980a). Grass: its Production and Utilization. Blackwell Scientific Publications. Boston, USA.
Holmes C.W. and Hoogendoorn C. (1983). Some effects of grazing management in early lactation and topping on the growth and quality of pasture. Pp. 36-43 in Dairy Farming Annual. Massey University. Palmerston North, New Zealand.
Hoogendoorn C.J., Holmes C.W. and Chu A.C.P. (1992). Some effects of herbage composition, as influenced by previous grazing management, on milk production by cows grazing on ryegrass / white clover pastures. 2. Milk production in late spring / summer: effects of grazing intensity during the preceding spring period. Grass Forage Sci. 47, 316-325.
Horvath D.J. and Reid R.L. (1980). Soil chemistry and mineral problems in farm livestock. A review. Anim. Feed Sci. Technol. 5, 95-167.
Humphreys M.O. (1989). Water-soluble carbohydrates in perennial ryegrass breeding. II. Cultivar and hybrid progeny performance in cut plots. Grass. Forage. Sci. 44, 237-244.
Hutchings N.J., Phillips A.H. and Dobson R.C. (1990). An ultrasonic rage finder for measuring the undisturbed surface height of continuously grazed grass swards. Grass Forage Sci. 45, 119-127.
Ishack M.A. and Erickson E.D. (1986). Effects of selenium, vitamins and ration fibre on placental retention and performance of dairy cattle. J. Dairy Sci. 66, 99-106.
Jarrige R. (1989). Ruminant Nutrition: Recommended Allowances and Feed Tables. J. L. London UK.
Jewiss O.R. (1972). Tillering in grasses-its significance and control. J. Br. Grassl. Soc. 26, 65-83.
Johansen A. and Höglind M. (2007). Herbage intake, milk production and sward utilization of dairy cows grazing grass / white clover swards at low, medium and high allowances. Acta Agric. Scand. 57(3), 148-158.
John A. and Ulyatt M.J. (1987). Importance of dry matter content to voluntary intake of fresh grass forages. Proc. NZ. Soc. Anim. Prod. 47, 13-19.
Julien W.E., Conrad H.K., Jones J.E. and Moxon A.L. (1979). Selenium and vitamin E and incidence of retained placenta in parturient dairy cows. J. Dairy Sci. 59, 1954-1959.
Jung H.G. (1997). Analysis of forage fiber and cell walls in ruminant nutrition. J. Nutr. 127, 810-813.
Kemp A. (1983). The effect of fertilizer treatment of grassland on the biological availability of magnesium to ruminants. Pp. 143-157 in Proc. John Lee Pratt Int. Symp. Role. Magnesium. Anim. Nutr. Virginia Polytechnic Institute and State University. Virginia, USA.
Kennedy E., O’Donovan M., Murphy J.P., Delaby L. and O’Mara F. (2005). Effect of grass pasture and concentrate-based feeding systems for spring-calving dairy cows in early spring on performance during lactation. Grass Forage Sci. 60, 310-318.
Koketsu A.U. and King V.L. (1996). The influence of nutrient intake on biological measures of breeding herd productivity. Health Prod. 2, 85-94.
Korte C.J. (1981). Spring pasture management to improve summer pasture production. Pp. 25-27 inDairy Farming Annual. Massey University. Palmerston North, New Zealand.
Korte C.J., Watkin B.R. and Harris W. (1984). Effects of timing and intensity of spring grazings on reproductive development, tillering and herbage production of perennial ryegrass dominant pasture. NZ. J. Agric. Res. 27, 135-149.
Kotb A.R. and Luckey T.D. (1972). Markers in nutrition. Nutr. Abst. Rev. 42(3), 813-845.
Kristensen E.S. (1988). Influence of defoliation regime on herbage production and characteristics of intake by dairy cows as affected by grazing intensity. Grass Forage Sci. 43, 239-251.
Kristensen T., Oudshoorn F., Munksgaard L. and Soegaard K. (2007). Effect of time at pasture combined with restricted indoor feeding on production and behaviour in dairy cows. Animal. 1, 439-448.
Laidlaw A.S. (2005). The relationship between tiller appearance in spring and contribution to dry-matter yield in perennial ryegrass (Lolium perenne) cultivars differing in heading date. Grass Forage Sci. 60, 200-209.
Langlands J.P. (1975). Techniques for estimating nutrient intake and its utilization by the grazing ruminant. Pp. 320-332 in Proc. 4th Int. Symp. Rumin. Physiol. University New England. Sydney.
Laredo M.A. and Minson D.J. (1973). The voluntary intake, digestibility, and retention time by sheep of leaf and stem fractions of five grasses. Aust. J. Agric. Res. 24, 875-88.
Lawrence T. and Ashford R. (1966). The productivity of intermediate wheatgrass as affected by initial harvest dates and recovery periods. Can. J. Plant Sci. 46, 9-15.
Lüscher A., Fuhrer J. and Newton P.C.D. (2005). Global atmospheric change and its effect on managed grassland systems. Pp. 251-264 in Proc. 20th Int. Grass. Cong. Dublin, Ireland.
Maher J.G.S., Stakelum G. and Rath M. (2003). Effect of daily herbage allowance on the performance of spring-calving dairy cows. Irish J. Agric. Food Res. 42, 229-241.
Mangan J.L. (1982). The nitrogenous constituents of fresh forages. Pp. 25-40 in Proc. 6th Br. Soc. Anim. Prod. Occasional Publication England, UK.
Marsh R., Campling R.C. and Holmes W. (1971). A further study of a rigid grazing management system for dairy cows. Anim. Prod. 13, 441-448.
Mayes R.W., Lamb C.S. and Colgrove P.M. (1986). The use of dosed and herbage n-alkanes as markers for the determination of herbage intake. J. Agric. Sci. 107, 161-170.
Mayland H.F. and Wilkinson S.R. (1996). Mineral nutrition. Pp. 165-191 inProc. Am. Soc. Agron. Inc., CropSci. Soc. Am. Inc. Soil Sci. Society of America Inc. Wisconsin, USA.
McDowell L.R. (1985). Common salt (sodium and chlorine), magnesium and potassium. Pp. 213-235 inNutrition of Grazing Ruminants in Warm Climates. L.R. McDowell Ed. Academic Press Inc. Orlando, USA.
McFeely P.C., Browne D. and Carty O.T. (1975). Effect of grazing interval and stocking rate on milk production and pasture yield. Irish J. Agric. Res. 14, 309-319.
Mertens D.R. (1985). Factors influencing feed intake in lactating cows: from theory to application using neutral detergent fiber. Pp. 1-18 in Proc. 46th Georgia Nut. Conf. Univ. Georgia. Georgia, USA.
Michalk D.L. and Herbert P.K. (1977). Evaluation of the forage disk method in mixed rangeland in Kansas. J. Range. Manag. 40, 467-471.
Miller J.K. and Miller W.J. (1960). Development of zinc deficiency in Holstein calves fed a purified diet. J. Dairy Sci. 43, 1854-1856.
Miller W.J. (1970). Zinc nutrition in cattle: a review. J. Dairy Sci. 53, 1123-1135.
Minson D.J. (1982). Effects of chemical and physical composition of herbage eaten upon intake. Pp. 167-177 in Proc. Int. Symp. St. Lucia, Queensland, Australia.
Minson D.J. (1990). Forage in Ruminant Nutrition Animal Feeding and Nutrition Series. Academic Press.
Minson D.J. (1990b). Forage in Ruminant Nutrition. Academic Press Inc.
Minson D.J. (1990c). Forage in Ruminant Nutrition. Academic Press Inc.
Minson D.J. (1990d). Forage in Ruminant Nutrition. Academic Press Inc.
Minson D.J. (1990e). Forage in Ruminant Nutrition. Academic Press Inc.
Minson D.J., Raymond W.F. and Harris C.E. (1960). Studies in the digestibility of herbage. VIII. The digestibility of S-37 cocksfoot, S-23 ryegrass and S-24 ryegrass. J. Brit. Grass. Soc. 15, 174-181.
Moorby J.M., Evans R.T., Scollan N.D., Macrae J.C. and Theodorou M.K. (2006). Increased concentration of water-soluble carbohydrate in perennial ryegrass (Lolium perenne). Evaluation in dairy cows in early lactation. Grass Forage Sci. 61, 52-59.
Morrison J. (1980). The influence of climate and soil on the yield of grass and its response to fertilizer nitrogen. Pp. 51-57 inProc. 5th Int. Symp. Eur. Grass. Fed. The role of nitrogen in intensive Grassland Production. Wageningen, The Netherlands.
Mott G.O. (1960). Grazing pressure and the measurement of pasture production. Pp. 606-611 Proc. 8th Int. Grass. Cong. Alden Press. Oxford, UK. 
Muller L.D., Kolver E.S. and Holden L.A. (1995). Nutritional needs of high producing cows on pasture. Pp. 106-120 Proc. Cornell Nutr. Conf. Feed Manufact. Cornell University Ithaca. New York, USA.
Munro J.M.M. and Walters R.J.K. (1981). The feeding value of grass. Pp. 65-78 in Proc. 19th British Grass. Soc.Occa. Symp. England, UK.
Murphy W.M., Silman J.P. and Mena A.D. (1995). A comparison of quadrate, capacitance meter, sward stick, and rising plate for estimating herbage mass in a smooth-stalked, meadow grass-dominant white clover sward. Grass. Forage. Sci. 50, 452-455.
Newton G.L., Fontenot J.P., Tucker R.E. and Polan C.E. (1972). Effects of high dietary potassium intake on the metabolism of magnesium by sheep. J. Anim. Sci. 35, 440-445.
NRC. (1981). Effect of Environment on Nutrient Requirements of Domestic Animals. National Academy of Sciences. Washington, USA.
NRC. (1989). Nutrient Requirements of Dairy Cattle. 6th Ed. National Academy Science. Washington, USA.
NRC. (2001). Nutrient Requirements of Dairy Cattle. 7th Ed. National Academy Press. Washington, USA.
Nyfeler D., Huguenin-Elie O., Suter M., Frossard E., Connolly J. and Lüscher A. (2009). Strong mixture effects among four species in fertilized agricultural grassland led to persistent and consistent transgressive overyielding. J. Appl. Ecol. 46, 683-691.
O’Donovan M., Delaby L. and Peyraud J.L. (2004). Effect of time of initial grazing date and subsequent stocking rate on pasture production and dairy cow performance. Anim. Res. 53, 489-502.
Oliván M., Ferreira L.M.M., García U., Celaya R. and Osoro K. (2007). Application of n-alkanes as diet composition markers in grazing / browsing goats and sheep: effect of using different faecal recovery corrections and plant species grouping approaches. Aust. J. Agric. Res. 58, 1013-1022.
Parga J., Peyraud J.L. and Delagarde R. (2000). Effect of sward structure and herbage allowance on herbage intake and digestion by strip-grazing dairy cows. Pp. 61-66 in Proc. 34thGrozing Management, Occa. Symp. British Grassland.
Peyraud J.L. (1993). Comparaison de la digestion du trèfle blanc et des graminées prairiales chez la vache laitière. Fourrages. 135, 465-473.
Peyraud J.L. (1996). Managing high yielding dairy cows at pasture. Pp. 1-23 in Proc. Semin. Dep. Anim. Nutr. Management. Swedish University of Agricultural Science. Uppsala, Sweden.
Peyraud J.L. and Astigarraga L. (1998). Review of the effect of nitrogen fertilization on the chemical composition, intake, digestion and nutritive value of fresh herbage: consequences on animal nutrition and N balance. Anim. Feed Sci. Technol. 72, 235-259.
Peyraud J.L., Astigarraga L. and Faverdin P. (1996a). Digestion of fresh perennial ryegrass fertilized at two levels of nitrogen by lactating dairy cows. Anim. Feed Sci. Technol. 64, 155-171.
Peyraud J.L., Comeron E.A., Wade M.H. and Lemaire G. (1996b). The effect of daily herbage allowance, herbage mass and animal factors upon intake by grazing dairy animals, Ann. Zootech. 45, 201-217.
Peyraud J.L. and González-Rodríguez A. (2000). Relations between grass production, supplementation and intake in grazing dairy cows. Grassl. Sci. Eur. 5, 269-282.
Peyraud J.L. and Delaby L. (2001). Ideal concentrate feeds for grazing dairy cows. Responses to supplementation in interaction with grazing management and grass quality. Pp. 203-220 in Recent Advances in Animal Nutrition. P.C. Garnsworthy and J. Wiseman Eds. University Press. Nottingham, UK.
Peyraud J.L., Mosquera-Losada M.R. and Delaby L. (2004). Challenges and tools to develop efficient dairy systems based on grazing: how to meet animal performance and grazing management. Grassl. Sci. Eur. 9, 373-384.
Phillips C.J.C. and James N.L. (1998). The effects of including white clover in perennial ryegrass swards and the height of mixed swards on the milk production, sward selection and ingestive behaviour of dairy cows. Anim.Sci. 67,195-202. 
Poe J.H., Greene L.W., Schelling G.T., Byers F.M. and Ellis W.C. (1985). Effect of dietary potassium and sodium on magnesium utilization in sheep. J. Anim. Sci. 60, 578-582.
Polan C.E. (1997). Nutritional considerations when supplementing grazing lactating dairy cows. Pp. 22-36 in Proc. 2nd Mid-Atlantic Dairy Grazing Field Day. Co. Augusta, Virginia, USA.
Pollock C.J. (1986). Fructans and the metabolism of sucrose in vascular plants. New. Phytol. 83, 9-15.
Powell K., Reid R.L. and Balasko J.A. (1978). Performance of lambs on perennial ryegrass, smooth bromegrass, orchardgrass and tall fescue pastures. II. Mineral utilization, in vitro digestibility and chemical composition of herbage. J. Anim. Sci. 46, 1503-1514.
Ragsdale A.C., Thompson H.J., Worstell D.M. and Brody S. (1950). Milk production and feed and water consumption responses to Brahman, Jersey and Holstein cows to changes in temperature 50 to 105˚F. Univ. Missouri. Agric. Exp. Sta. Res. Bull. 521, 1-28.
RayburnB. (1997). An acrylic pasture weight plate for estimating forage yield. University Extension Service.Available online: http://www.caf.wvu.edu/~forage/plastplate.htm. Accessed Mar. 2011.
Rayburn E.B. (1994). Forage quality of intensive rotationally grazed pastures. West Virginia University Extension Service. Morgantown, USA. Pp. 44.
Raymond W.F. and Minson D.J. (1955). The use of chromic oxide for estimating the faecal production of grazing animals. J. Br. Grassl. Soc. 10, 282.
Reid R.L. (1983). Biological availability of magnesium from natural and supplemental sources. Pp. 121-142 in Proc. John Lee Pratt Int. Symp. Role Magnesium. Anim. Nutr. Virginia Polytechnic Institute and State University, Virginia, USA.
Ribeiro-Filho H.M.N., Delagarde R. and Peyraud J.L. (2003). Inclusion of white clover in strip-grazed perennial ryegrass swards: herbage intake and milk yield of dairy cows at different age of sward regrowth. Anim. Sci. 77, 499-510.
Robel R.J., Briggs J.N., Cebula J.J. Silvy Viers C.E. and Watt P.G. (1970a). Greater prairie chicken ranges, movements and habitat usage in Kansas. J. Wildl. Manag. 34, 286-306.
Robel R.J., Briggs J.N. and Hulbert L.C. (1970b). Relationships between visual obstruction measurements and weight of grassland vegetation. J. Range. Manag. 23, 295-297.
Roca-Fernández A.I. (2011) Sustainable milk production systems in humid areas using farm resources. European DoctoralThesis. University of Santiago de Compostela, Spain. Available online: dspace.usc.es/bitstream/10347/3373/1/9788498877274_content.pdf. Accessed Apr. 2013.
Roca-Fernández A.I., O’Donovan M., Curran J. and González-Rodríguez A.(2011). Effect of pre-grazing herbage mass and daily herbage allowance on perennial ryegrass swards structure, pasture dry matter intake and milk performance of Holstein-Friesian dairy cows. Span. J. Agric. Res. 9(1),86-99.
Roca-Fernández A.I., González-Rodríguez A. and Vázquez-Yáñez O.P. (2012). Effect of pasture allowance and cows’ lactation stage on perennial ryegrass sward quality, pasture dry matter intake and milk performance of Holstein-Friesian cows. Spanish J. Agric. Res. 10(2),393-408.
Rogers G.L., Porter R.H.D. and Robinson I. (1982). Comparison of perennial rye-grass and white clover for milk production. Pp. 213-214 in Proc. Conf. Dairy Prod. Pasture. New Zealand and Australian Soc. Anim. Prod. Ruakura Animal Research Station. Hamilton, New Zealand.
Rook A.J. (2000). Principles of foraging and grazing behaviour. Pp. 229-246 in Grass its Production and Utilization. A. Hopkins Ed. 3rd Ed. Blackwell Science. Oxford, UK.
Sanderson M.A. and Wedin W.F. (1989). Phenolical stage and herbage quality relationships in temperate grasses and legumes. Agron. J. 81, 864-869.
Sanderson M.A., Rotz C.A., Fultz S.W. and Rayburn E. (2001). Estimating forage mass with a commercial capacitance meter and pasture ruler. Agron. J. 93, 1281-1286.
Schwartz W.A. and Kirchgessner M. (1975). Experimental zinc deficiency in lactating dairy cows. Vet. Med. Rev. 20, 19-40.
Schwarz K. and Foltz C.M. (1957). Selenium as an integral part of factor 3 against dietary necrotic live degeneration. J. Am. Chem. Soc. 79, 3292-3293.
Sheldrick R.D., Lavender R.H. and Tewson V.J. (1986). The effects of frequency of defoliation date of first cut and heading date of a perennial ryegrass companion on the yield, quality and persistence of diploid and tetraploid board red clover. Grass Forage Sci. 41(2), 137-149.
Smith D. (1973). The nonstructural carbohydrates. Pp. 106-152 inChemistry and Biochemistry of Herbage. G.W. Butler and R.W. Bailey Ed. Academic Press Inc. New York, USA.
Stakelum G. and Dillon P. (1990). Influence of sward structure and digestibility on the intake and performance of lactating and growing cattle. Pp. 30-44 in Management Issues for the Grassland Farmer in the 1990's. British Grassland Society.
Stakelum G. and Dillon P. (2007a). The effect of grazing pressure in spring / early summer in rotationally grazed pastures on subsequent sward characteristics. Irish J. Agr. Food Res. 46, 15-28.
Stakelum G. and Dillon P. (2007b). The effect of grazing pressure on rotationally grazed pastures in spring / early summer on the performance of dairy cows in the summer / autumn period. Irish J. Agr. Food Res. 46, 29-46.
Steg A., Van Straalen W.M., Hindle V.A., Wensink W.A., Dooper F.M.H. and Schils R.L.M. (1994). Rumen degradation and intestinal digestion of grass and clover at two maturity levels during the season in dairy cows. Grass Forage Sci. 49, 378-390.
StobbsT.H. (1973). The effect of plant structure on the intake of tropical pastures. 2. Differences in sward structure, nutritive value, and bite size of animals grazing Setaria anceps and Chloris gayana at various stages of growth. Aust. J. Agric. Res. 24, 821-829.
Taweel H.Z. (2006). Improving dry-matter intake of perennial- ryegrass pasture by dairy cows. Pp. 159-174 inFresh Herbage for Dairy Cattle, the Key to a Sustainable Food Chain. A. Elgersma, J. Dijkstra and S. Tamminga Eds. Springer.
Thomas H. (1980). Terminology and definitions in studies of grassland plants. Grass Forage Sci. 35(1), 13-23.
Thomas H. and Norris I.B. (1981). The influence of light and temperature during winter on growth and death in simulated swards of Lolium perenne. Grass Forage Sci. 36, 107-116.
Thompson K.F. and Poppi D.P. (1990). Livestock production from pasture. Pp. 263-283 in Pastures Their Ecology and Management. R.H.M. Langer Ed. Oxford University Press, Oxford, England.
Thomson D.J. (1982). The nitrogen supplied by and the supplementation of fresh or grazed forage. Pp. 53-66 inForage Protein in Ruminant Animal Production. Occasional Publication. D.J. Thomson, D.E. Beever and R.G. Gunn Eds. British Society of Animal Production. England, UK.
Thomson D.J., Beever D.E., Haines M.J., Cammell S.B., Evans R.T., Dhanoa M.S. and Austin A.R. (1985). Yield and composition of milk from Friesian cows grazing either perennial ryegrass or white clove in early lactation. J. Dairy Res. 52, 17-31.
Tilley J.M.A. and Terry R.A. (1963). A two-stage technique for the in vitro digestion of forage crops. J. Br. Grass. Soc.31, 69-72.
Turner L.R., Donaghy D.J., Lane P.A. and Rawnsley R.P. (2006). Effect of defoliation management, based on leaf stage, on perennial ryegrass (Lolium perenne), prairie grass (Bromus willdenowii) and cocksfoot (Dactylis glomerata) under dry land conditions. 1. Regrowth, tillering and water-soluble carbohydrate concentration. Grass Forage Sci. 61, 164-174.
Ullrey D.E., Brady P.S., Whetter P.A., Ku P.K. and Magee W.T. (1977). Selenium supplementation of diets for sheep and beef cattle. J. Anita Sci. 46, 559-567.
Ulyatt M.J. (1973). The feeding value of herbage. Pp. 131-178 inChemistry and Biochemistry of Herbage. G.W. Butler and R.W. Bailey Eds. Academic Press Inc., New York, USA.
Ulyatt M.J. (1981). The feeding value of herbage. Can it be improved? New Zeal Agric. Sci. 15, 200-205.
Ulyatt M.J., Thomson D.J., Beever D.E., Evans R.T. and Haines M.J. (1988). The digestionof perennial ryegrass (Lolium perenne) and white clover (Trifolium repens) by grazing cattle. Br. J. Nutr. 60, 137-149.
Underwood E.J. (1977). Trace Elements in Human and Animal Nutrition. 4th Ed. Academic Press Inc. New York, USA.
Underwood E.J. (1979). The current status of trace element nutrition: an overview. Pp. 1-31 Proc. Int. Minerals Conf. Orlando, USA.
Van Soest P.J. (1965). Symposium on factors influencing the voluntary intake of herbage by ruminants: voluntary intake in relation to chemical composition and digestibility. J. Anim. Sci. 24, 834-843.
Van Soest P.J. (1971). Estimation of nutritive value from laboratory analysis. Pp. 106-117 in Proc. Cornell Nutr. Conf. Feed Manufact. Cornell Univ. Ithaca. New York, USA.
Vartha E.W. and Matches A.G. (1977). Use of weighted-disk measure as an aid in sampling the herbage yield on tall fescue pastures grazed by cattle. Agron. J. 69, 888-900.
Vázquez-Yáñez O.P. and Smith T.R. (2000). Factors affecting pasture intake and total dry matter intake in grazing dairy cows. J. Dairy Sci. 83(10), 2301-2309.
Vérité R. and Journet M. (1970). Influence de la teneur en eau et de la déshydratation de l’herbe sur sa valeur alimentaire pour les vaches laitières. Ann. Zootech. 19, 255-268.
Vermeire L.T. and Gillen L.R. (2001). Estimating herbage standing crop with visual obstruction in tall grass prairie. J. Range. Manage. 54, 57-60.
Virkajärvi P., Sairanen A., Nousiainen J.I. and Khalili H. (2002). Effect of herbage allowance on pasture utilization, regrowth and milk yield of dairy cows in early, mid and late season. Anim. Feed Sci. Technol. 97, 23-40.
Wade M.H. (1991). Factors affecting the availability of vegetative Lolium perenne to grazing dairy cows with special reference to sward characteristics, stocking rate and grazing method. Thèse d’Université de Rennes Ph D. Thesis.
Wade M.H., Peyraud J.L., Comerón E.A. and Lemaire G. (1995). The dynamics of daily milk production and sward height under paddock grazing conditions. Ann. Zootech. 44, 127-134.
WadeM.H., Peyraud J.L., Lemaire G. and Cameron E.A. (1989). The dynamics of daily area and depth of grazing and herbage intake of cows in a five-day paddock system. Pp. 1111-1112 Proc. 16th Int. Grassland Cong. Nice, France.
Wales W.J., Doyle P.T., Stockdale C.R. and Dellow D.W. (1999). Effects of variations in herbage mass, allowance and level of supplement on nutrient intake and milk production of dairy cows in spring and summer. Aust. J. Exp. Agric. 39, 119-130.
Walters R.J. and Evans E.M. (1979). Evaluation of the sward sampling technique for estimating herbage intake by grazing sheep. Grass. Forage. Sci. 34, 37-44.
Ward G.M. (1966). Potassium metabolism of domestic ruminants. J. Dairy Sci. 49, 268-276.
Webster A.J.F. (1976). The influence of the climatic environment on metabolism in cattle. Pp. 103-120 in Principles of Cattle Production. H. Swan and W.H. Broster Eds. Butterworths. London, UK.
Weiss W.P., Hogan J.S., Smith K.L. and Hoblet K.H. (1990). Relationships among selenium, vitamin E. and mammary gland health in commercial dairy herds. J. Dairy Sci. 73, 381-390.
Wheeler J.L. and Corbett J.L. (1989). Criteria for breeding forages of improved feeding value: results of a Delphi survey. Grass Forage Sci. 44, 77-83.
White L.M. (1973). Carbohydrate reserves of grasses: a review. J. Range. Manage. 26, 13-18.
Wilkins P.W. and Humphreys M.O. (2003). Progress in breeding perennial forage grasses fortemperate agriculture. J. Agric. Sci. 140, 129-150.
Wilkins R.J. (1997). Congress highlights from perspective of temperate regions. Pp. 581-582 in Proc. 18th Int. Grass. Cong. Saskatoon, Canada.
Wilkins R.J., Gibb M.J. and Huckle C.A. (1995). Lactation per formance of spring-calving dairy cows grazing mixed perennial ryegrass / white clover swards of differing composition and height. Grass Forage Sci. 50, 199-208.
Wilkins R.J., Gibb M.J., Huckle C.A. and Clements A.J. (1994). Effect of supplementation on production by spring-calving dairy cows grazing sward of differing clover content. Grass. Forage. Sci. 49, 465-75.
Wilman D., Daly M., Koocheki A. and Lwoga A.B. (1977). The effects of interval between harvests and nitrogen application on the proportion and digestibility of cell wall, cellulose, hemicellulose, and lignin and on the proportion of lignified tissue in leaf cross-section in two perennial ryegrass varieties. J. Agric. Sci. 89, 53-63.
Wilman D., Droushiotis D., Koocheki A., Lwoga A.B. and Shim J.S. (1976). The effect of interval between harvests and nitrogen application on the digestibility and digestible yield and nitrogen content and yield of four ryegrass varieties in the first harvest year. J. Agric. Sci. 86, 393-399.