DAIRY FARM MANAGEMENT SYSTEMS

672 DAIRY FARM MANAGEMENT SYSTEMS/Seasonal, Pasture-Based ± Dairy Cow Breeds Johnston M and Klindworth D (00) Increasing ef ciency. In: Klindworth D (ed.) Working Smarter not Harder, pp. 31±34. Ellinbank, Australia: Agriculture Victoria. Lavers M and McDougal G (1999) The Daley individual calf pen design. In: Calf Pens: Correct Design and Use for Rearing Dairy Heifers, pp. 4±7. Peak Crossing, Australia: Department of Primary Industries. Moran J (1993) Housing of calves. In: Burgi A (ed.) Calf Rearing: A Guide to Rearing Calves in Australia, pp. 179±191. Melbourne, Australia: Department of Natural Resources and Environment. DAIRY FARM MANAGEMENT SYSTEMS Contents Seasonal, Pasture-Based ± Dairy Cow Breeds Non-Seasonal, Pasture-Optimized ± Dairy Cow Breeds in the United States Non-Seasonal, Pasture-Based Milk Production Systems in Western Europe Dry Lot ± Dairy Cow Breeds Goats Sheep Seasonal, Pasture-Based ± Dairy Cow Breeds P T Doyle and C R Stockdale, Kyabram Dairy Centre, Kyabram, Victoria, Australia Copyright 02, Elsevier Science Ltd. All Rights Reserved Introduction Pasture-based dairy production systems with seasonal calving predominate in southern Australia and New Zealand (NZ). The dairy industries in both countries have grown rapidly over the last 10 years and are export oriented. This dependence on exports means that production systems must remain low-cost to be internationally competitive. The seasonal patterns of growth and nutritive characteristics of pastures interact with prices received for milk to determine the most cost-effective management systems. Milk production systems within and between regions are diverse because of variations in patterns of pasture growth and nutritive characteristics. The recognition of these differences has led to the differentiation of feed-base zones. The need to understand the interactions between pastures, conserved feed inputs, concentrate supplements and grazing cows is essential to the cost of milk production. The differences between feeding and management systems in southern Australia and NZ, and in the end uses of the milk produced, has led to differences in cow breed and type. Milk Production Patterns In 1998±99, Australia and NZ produced 10.5 and 11.1 billion litres of milk, respectively, accounting for 2.2% and 2.3% of world production. The two countries accounted for 13% and 31%, respectively, of world exports in milk equivalents. Average milk production in Australia is about 5000 l per cow compared with 3500 l per cow in NZ. Milk production in NZ is very seasonal, peaking in spring (September±November), with less than 5% of annual milk supply delivered in the `trough' quarter (May±July). Cows usually calve between

DAIRY FARM MANAGEMENT SYSTEMS/Seasonal, Pasture-Based ± Dairy Cow Breeds 673 late July and September. The industry appears to have accepted that capital investment in processing plant to handle this large variation in milk supply is unavoidable, since feeding concentrates to cows when pasture growth is slow is not an economic proposition because of the high cost of concentrate feeds. The Australian dairy industry is undergoing accelerated change following deregulation in July 00. Prior to this, seasonal calving in pasture-based systems of milk production predominated in Victoria and Tasmania, where most milk was used for manufactured dairy products. This will continue, as will the reliance on export markets, meaning that lowcost pasture-based systems of production remain essential. In New South Wales (NSW), Queensland, South Australia (SA) and Western Australia (WA), a much higher proportion of the milk produced was for domestic consumption as liquid milk or manufactured products. Hence, year-round calving was common. It is too early to predict the full impact of deregulation on these production systems. Therefore, we will only consider the seasonal pasture-based production systems of southern Australia, where over 75% of cows calve between June and September. Seasonal calving in late winter (July±August) to early spring is practised in southern Australia to match herd feed requirements with the seasonal pattern of pasture growth, although milk production in the `trough' quarter (May±July) is about 15%. This re ects the use of supplements during periods of pasture shortage and the payment of premiums in winter to encourage production of enough milk to satisfy the liquid milk sector. In the mid-1990s, the on-farm costs of milk production in NZ were about ±85% of those in Victoria and Tasmania, but less than 50% of those in NSW and Queensland. Importantly, feed costs were similar in NZ, Victoria and Tasmania. Pasture Zones The dairy industry in southern Australia is concentrated in three feed-base zones. The climatic diversity between these zones and the regions within them has a profound effect on the feeds used for milk production. The Cool Temperate zone (southern Victoria, Tasmania, south coast of NSW) generally has annual rainfall in excess of 700 mm, with a relatively long and reliable pasture-growing season. The major sown pasture species are perennial ryegrass (Lolium perenne) and white clover (Trifolium repens), but pastures vary in composition from being dominated by the sown species to heavily invaded by volunteer grasses and weeds (see Forages and Pastures: Perennial Forage and Pasture Crops ± Species and Varieties). The Mediterranean zone (WA, southeast SA, parts of Victoria) has annual rainfall in excess of 0 mm, but this is winter-dominant and the regions experience long hot summers, short growing seasons, and unreliable autumn breaks. In the truly Mediterranean regions, the long summer drought means that, in most situations, perennial ryegrass/white clover pastures cannot persist and pastures are predominantly annual ryegrass (Lolium rigidum) and subterranean clover (Trifolium subterraneum) (see Forages and Pastures: Annual Forage and Pasture Crops ± Species and Varieties). The Inland Irrigation zone (northern Victoria, southern NSW) experiences average annual rainfall of 350±550 mm. Pasture growth is dependent on irrigation. The percentage of the milking area on irrigated dairy farms sown to perennial pastures (perennial ryegrass/white clover) averages 75%, but varies from less than % to 100%. These pastures are invariably invaded by summer growing species, in particular paspalum (Paspalum dilatatum). Irrigated annual pastures also form an important part of the feed-base, as do summer fodder crops, particularly maize. In NZ, there is a 10-fold range in average annual rainfall (about 500±5000 mm), considerable variation in sea level temperature, which declines from north to south, and diverse soil types. This leads to large variations in average annual and seasonal pasture production. Over 85% of dairy farms are in the North Island, with the major milk production areas being South Auckland and Taranaki (temperate climate, dry summers, perennial ryegrass/ white clover pastures) and Northland (warm humid climate, wet summers, perennial ryegrass/white clover pastures with subtropical grasses in summer). The South Auckland and Northland regions are used as examples here. Pasture Growth Of the rain-fed zones, pasture production is highest in Northland (about 17 t DM ha 1 ), followed by South Auckland and the Cool Temperate zone (about 11 t DM ha 1 ), and is lowest in the Mediterranean zone (about 6tDMha 1 )(Figure 1). In the Inland Irrigation zone, irrigated perennial and annual pastures produce about 15 and 10 t DM ha 1, respectively. The variability in pasture growth and its distribution throughout the year (Figure 1) underpin the vast differences in the pasture-based systems that currently exist within and between regions. The seasonal pasture supply on farms is a key determinant

674 DAIRY FARM MANAGEMENT SYSTEMS/Seasonal, Pasture-Based ± Dairy Cow Breeds (A) (B) Daily pasture growth (kg DM ha 1 ) (C) 100 0 Daily pasture growth (kg DM ha 1 ) (D) 100 0 Daily pasture growth (kg DM ha 1 ) 100 0 Daily pasture growth (kg DM ha 1 ) 100 0 Figure 1 Pasture growth rates representative of the range occurring in dairy production systems in: (A) Northland (15±18 t DM ha 1 ), New Zealand, (B) South Auckland (8±12 t DM ha 1 ; solid line), New Zealand and the Cool Temperate zone (8±12 t DM ha 1 ; broken line) of southern Australia, (C) the Mediterranean zone (northeast Victoria (broken line) and Western Australia (solid line)) and (D) the Inland Irrigation zone (12.5±17.5 t DM ha 1 for perennial pastures (solid line); 7±11 t DM ha 1 for annual pastures (broken line)). of decisions in relation to time of calving, supplementary feeding, stocking rate and targets for milk production per cow. The key constraints to pasture-based dairy production systems are the amount of feed grown and the proportion of this that is utilized (consumed by cows or conserved). There is little doubt that removal of soil-based limitations (water, nutrients and soil structure) and maintenance of sown species are essential in achieving the upper ends of the growth rates depicted in Figure 1. Akey issue in both countries is whether plant systems that produce more digestible dry matter can be developed. Hence, there is increasingly more research on integration of pastures, fodder crops or grain crops, and on the use of irrigation. Grazing Management In all feed-base zones, there is an emphasis on managing grazing to optimize pasture utilization without compromising growth or persistence of sown species. Strip grazing or rotational grazing of small paddocks is practised. Rotation lengths vary throughout the year in accordance with pasture growth rates and are also modulated by the use of supplementary feeds. As an example, in northern Victoria, rotation lengths are 14±29 days in spring, 19±23 days in summer and 17±35 days in autumn. The principles of feed planning and understanding the supply of pasture in relation to demand at the cow and herd level are not new. However, they are becoming more important in containing feed costs in order to remain competitive in world markets. Hence, balancing seasonal feed demand with expected pasture supply, and feed budgeting to estimate how available feed may best be used to ensure optimal or target levels of milk production, is essential in making pro table decisions on pasture use. This information assumes greater importance where annual and seasonal variations in pasture growth are greatest and successful grazing plans include critical decisions on fodder conservation. For example, two key aspects to grazing management in the Mediterranean zone are the need to conserve

DAIRY FARM MANAGEMENT SYSTEMS/Seasonal, Pasture-Based ± Dairy Cow Breeds 675 the maximum amount of feed in spring to ll the summer feed gap, and the rapid re-establishment of pastures after the autumn break. Ideally, grazing management would match pasture consumption with pasture growth rate, such that plants were maintained in a productive state with minimum losses through death and decay. This is dif cult to achieve in practice, but good management involves striking a balance between per cow and per hectare production, while minimizing tradeoffs between pasture production, persistence and nutritive value. In the Cool Temperate zone, the three-leaf stage of perennial ryegrass, just prior to senescence of the oldest leaf, is recommended as the time at which to graze. This ensures high growth rates and persistence, improves utilization and should optimize the digestibility of the feed consumed. However, the pregrazing pasture mass at which ryegrass reaches this stage varies throughout the season, and has practical implications in terms of frequency of defoliation if adhering to these guidelines in winter and summer. It is also not possible to apply such guidelines across regions. For example, grazing of irrigated pastures offers particular challenges in summer when paspalum growth rates exceed those of perennial ryegrass and white clover. As a consequence, it is necessary to graze in relation to the stage of growth of paspalum through summer to limit ingress of this species. Pasture Intake Grazing dairy cows are unable to consume suf cient dry matter and metabolizable energy to achieve their potential milk production, because of constraints involved in harvesting grazed pasture and those imposed by managing the allocation of feed. While milk yields of grazing dairy cows are the direct result of the amount of pasture and supplements consumed, and the nutritive characteristics of these feeds, the regulation of intake of pasture by grazing dairy cows is complex and is undoubtedly affected by: animal factors ± cow size, milk yield, stage of lactation environmental factors ± disease, climatic stress pasture factors ± pasture mass, sward composition, digestibility/nutrient concentrations management factors ± pasture allowance, amounts and types of supplementary feeds. We have a sound understanding of relationships between pasture allowance and herbage intake by grazing cows (Figure 2). Although these relationships are in uenced by pasture mass and species composition, the knowledge exists to predict herbage intake Pasture intake (kg DM per 100 kg LW per day) 6 5 4 3 2 1 0 2 4 6 8 10 12 14 16 18 Pasture allowance (kg DM per 100 kg LW per day) Figure 2 Relationships between pasture intake and pasture allowance for lactating dairy cows grazing pasture in the Cool Temperate zone in spring (middle curve; data supplied by D.E. Dalley) and annual (top curve) and perennial (bottom curve) pastures in the Inland Irrigation zone (data supplied by Richard Stockdale). for cows grazing green pastures with a degree of con dence. For example, pregrazing pasture mass affects the intake/pasture allowance relationship where (at a given pasture allowance) pasture intake will be lower at a low, compared with a high, pasture mass. Grazing cows consume more pasture when grazing clover-dominant than grass-dominant swards. For example, cows grazing clover-dominant swards at pasture allowances of 15 and 30 kg DM per cow may consume about 11 and 19 kg DM day 1, respectively. To achieve the same intakes on ryegrassdominant swards, higher allowances, e.g. and kg DM day 1, would be needed. Pasture intake is also positively related to digestibility, so intake and milk production generally increase as digestibility increases. Predicting pasture intake from pasture allowance and digestibility is more complex where dry pastures of low digestibility are grazed. Annual pasture consumption in the Cool Temperate zone varies from 3 to 9 t DM ha 1, in the Mediterranean zone from 3 to 10 t DM ha 1, and in the Inland Irrigation zone from less than 4 to more than 14 t DM ha 1. This variation within regions may be due to differences in the amounts of pasture grown, in stocking rate, and in grazing management and feeding practices. The ranges illustrate that, on many farms, there is substantial room to improve conversion of pasture into milk. Nutritive Characteristics of Pastures Considerable effort has been invested in de ning seasonal variation in digestibility, and crude protein (CP) and neutral detergent bre (NDF) concentrations

676 DAIRY FARM MANAGEMENT SYSTEMS/Seasonal, Pasture-Based ± Dairy Cow Breeds in pastures used for dairying. Digestibility and CP concentration are generally high during autumn to spring, but decline from late spring and are low in summer and into autumn (Figure 3). Regional differences in digestibility exist because of differences in pasture species present, in the growth patterns of these species and in climatic conditions. These variations are more extreme in regions or years with dry summers. Crude protein concentration in pastures follows a similar pattern to digestibility, but there is greater variation as the differences in protein concentration between leaf and stem components of pasture plants are greater than are the corresponding differences in digestibility. The high CP concentrations in green pastures often exceed cow requirements and there are energy costs incurred in excreting excess nitrogen as urea. In contrast, CP concentrations in summer are sometimes below 15% and protein supplements may be needed. NDF concentrations are the inverse of digestibility and are lowest during winter and spring and highest in summer (Figure 3). While the concentrations in pasture on offer usually exceed those recommended for lactating cows, namely 30±%, selection may create a problem in this regard on highly digestible pastures, particularly those with high clover contents. To better understand essential nutrient supply to grazing dairy cows, it is important to be aware of their concentrations in the feed eaten compared with those in the pasture on offer. In the Cool Temperate and Inland Irrigation zones of southern Australia, cows grazing predominantly green pasture in winter and spring consume material that is higher in digestibility (1.05 to 1.15) and CP concentration (1. to 1.) than the pasture on offer. The potentially high level of consumption of CP from pasture can have important implications in designing supplementary feeding practices that optimise the (A) (B) Nutritive characteristics (% DM) 70 50 30 10 Nutritive characteristics (% DM) 70 50 30 10 (C) (D) Nutritive characteristics (% DM) 70 50 30 10 Nutritive characteristics (% DM) 70 50 30 10 Figure 3 Nutritive characteristics (digestibility (*); crude protein concentration (&); neutral detergent bre concentration (~)) of herbage consumed in dairy production systems in (A) South Auckland, New Zealand, (B) the Cool Temperate (western Victoria) zone, (C) the Mediterranean zone and (D) the Inland Irrigation zone. Data for (A) and (C) were supplied by John Penno and Martin van Houtert, respectively, while those for (B) and (D) were provided by Janna Heard from the Kyabram Dairy Centre pasture database. Bars are standard deviations about means.

DAIRY FARM MANAGEMENT SYSTEMS/Seasonal, Pasture-Based ± Dairy Cow Breeds 677 supply of energy and protein to the rumen microorganisms and to the cow. At these same times, the pasture consumed is lower in NDF (0.75 to 0.95) than is the pasture on offer, principally because leaves have less NDF than stems. In cows grazing extremely high digestibility pastures, rumen ph can be below 6.0 for aconsiderable portion of the day (Figure 4), presumably due to insuf cient bre in the diet. This predisposes the animals to an unstable rumen fermentation pattern and acidosis if they are fed cereal grain. Supplement Use In NZ, the feeding systems are predominantly yearround grazing, supplemented with conserved forage. This is also the case on less intensive, lower stocked farms in southern Australia. At the other extreme, in the Mediterranean zone, the system comprises grazing during the period of growth of annual pastures, followed by complete supplementary feeding with conserved fodder and concentrates during the hot dry summer. The variation in feeding systems within a zone is exempli ed in a survey of the Inland Irrigation region in northern Victoria where energy consumption by milking herds varied from 100% from pasture to 75% from feed brought in from off the milking area. Almost all conceivable combinations of grazing and supplementation with various types and mixes of conserved fodder and concentrates can be found. Pasture conserved as silage or hay has traditionally been used to alleviate pasture shortages. More Rumen ph 6.6 6.4 6.2 6.0 5.8 5.6 5.4 6 10 14 18 22 2 6 Time of day (h) Figure 4 Rumen ph in lactating cows consuming about 19 kg DM day 1 while grazing either Persian clover (&) or perennial ryegrass (~) pastures during spring (data provided by Yvette Williams). recently, there has been increasing interest in the use of fodder crops in pasture-based systems. These fodder crops are incorporated as part of pasture renovation programmes and/or to provide feed of high digestibility, and are either grazed or conserved. Since the early 19s, the average amount of cereal grain-based concentrates fed to dairy cows in southern Australia has increased markedly from virtually zero to about 1000 kg per cow in 00. This is a fundamental difference between the pasture-based systems of southern Australia, where over 75% of farmers now feed concentrates, compared with those in NZ, where use of grains and meals is much lower because of cost. In southern Australia, the amount of concentrates fed varies from 0 to 2500 kg DM per cow, while conserved fodder supplementation varies from 0 to 1500 kg DM per cow. This is a key reason for the higher average per cow production in southern Australia compared with NZ. Cereal grains (see Concentrate Feeds: Cereal Grains), byproducts (see Concentrate Feeds: Byproduct Feeds) and formulated concentrates are used not only to alleviate pasture shortages, but also to overcome limitations in nutrients supplied by grazed pastures at key times of the year and to increase milk production per cow. During the last 5 years, there has been an increased emphasis on better understanding and matching of supplements and pasture to further increase productivity. Interactions between Pastures and Supplements The ef ciency of use of supplements is a critical issue in managing farm costs. Associative effects, and in particular substitution of supplement for pasture in the diet, will affect pasture utilization and the milk response to additional supplement. Substitution will be less of an issue when pasture allowances are low, but is invariably an issue at moderate to high pasture allowances. Many factors affect substitution of supplements for pasture, including pasture intake as affected by pasture allowance and mass, the nutritive characteristics of the sward, the amount and type of supplement fed, physiological state (stage of lactation) of the cows, and their body condition and size. An indication of the in uence of pasture intake before supplementation on the level of substitution that occurs when supplements are fed is illustrated in Figure 5. A major goal for research and extension over the past 5 to 10 years has been to understand the interactions between pasture, supplements (concentrates and forage) and cows to enable development of feeding systems that are pro table. This has been a substantial challenge given the diversity of feeding

678 DAIRY FARM MANAGEMENT SYSTEMS/Seasonal, Pasture-Based ± Dairy Cow Breeds Substitution (kg DM per cow) 1.0 0.8 0.6 0.4 0.2 0.0 systems within and between regions and the differentials between costs and the different milk pricing systems that apply, particularly across Australia. Cow Breeds 4 6 8 10 12 14 16 18 22 24 Daily pasture intake (kg DM per cow) Figure 5 A relationship between level of substitution and unsupplemented pasture intake when concentrates are fed to lactating dairy cows in northern Victoria, with the 95% level of con dence about the curve indicated (data supplied by Richard Stockdale). There are 2.12 million dairy cows in Australia, with Holstein±Friesian the predominant dairy breed, comprising % of the national herd. Nearly all of these cows have some North American parentage. Jersey is the next most popular breed comprising 11% of the national herd (see Dairy Animals: Major Bos taurus Breeds); the remainder includes Holstein± Friesian Jersey cross cows (5%) and other breeds (Australian Illawarra Shorthorn, Ayrshire, Australian Red Breed, Guernsey, Brown Swiss; 4%). In NZ, there are 3.29 million dairy cows, with Holstein± Friesian (57% of the national herd) being the predominant breed, and Jersey (16%), Holstein± Friesian Jersey cross (19%) and other breeds (7%) making up the balance. Over the last years, the shift to Holstein± Friesian animals in Australia has led to a dramatic increase in the size and potential production of cows. For example, the liveweight of mature cows in southern Australia has increased from around 0 to 550 kg during this period while average milk production has increased from 3000 to 5000 l per cow. The increased milk production potential has led to more diverse feeding systems. In NZ, these changes have not been so dramatic and cow size (less than 500 kg for Holstein±Friesian cows) and milk production (about 3500 l per cow) have remained relatively constant over the last decade. In both countries, cows in pasture-only systems are underfed due to the constraints on intake associated with grazing and imposed by management to achieve high levels of pasture utilization. The rationale for continued increases in genetic potential in dairy cows needs to be questioned for pasture-based systems. There is some evidence that the potential increases from improved genetic merit can only be achieved when feeding intensity is increased, and this invariably means increased unit costs of feed and other inputs. Where nutrient intake is inadequate, as is commonly the case with pasture feeding, increased genetic merit and the associated `willingness' of the cow to partition nutrients from feed and/or body reserves to milk can lead to metabolic disorders, reduced reproductive performance and reduced longevity in the herd. Future Trends Milk production per farm in southern Australia and NZ has doubled over the past decade. This has been associated with a general increase in intensi cation of farming, with increased farm and herd size, and decreased farm numbers. Dependence of these industries on exports ensures that production systems will remain pasture based and low cost. Further productivity gains will need to be achieved in an environment where on-farm quality assurance systems for food safety and natural resource management are implemented by cooperatives and proprietary companies. Communities and consumers will require responsible management of water, nutrients and ef uent to limit off-farm impacts, and the industries will need to address greenhouse emission issues. It is likely that improvements in feeding systems on individual farms will be incremental, and to remain competitive, farmers will need to continually analyse their systems and to apply the latest knowledge on matching pasture, conserved fodder and concentrate supplement usage. The need for research products/technologies to impact at industry level will require further development of predictive technologies and effective linkages with private, agribusiness and government service providers. Increasing complexity and intensi cation of farming systems will accelerate the shift to farming as a business, with consequent needs to improve management skills and workforce capability. Finally, increased differentiation in the prices received for milk, based on composition and end use, will mean farmers will look for cow genotypes that are best

DAIRY FARM MANAGEMENT SYSTEMS/Non-Seasonal, Pasture-Optimized 679 adapted to particular feeding management systems and end products. See also: Concentrate Feeds: Cereal Grains; Byproduct Feeds. Dairy Animals: Major Bos taurus Breeds. Dairy Farm Design and Layout: Building and Yard Design, Warm Climates. Forages and Pastures: Perennial Forage and Pasture Crops ± Species and Varieties; Annual Forage and Pasture Crops ± Species and Varieties. Further Reading Armstrong DP, Knee JE, Doyle PT, Pritchard KE and Gyles OA (00) Water-use ef ciency on irrigated dairy farms in northern Victoria and southern New South Wales. Australian Journal of Experimental Agriculture : 643±653. Doyle PT, Stockdale CR, Lawson AR and Cohen DC (00) Pastures for Dairy Production in Victoria, 2nd edn. Kyabram, Victoria, Australia: Department of Natural Resources and Environment: Kyabram Dairy Centre. Holmes CW (1987) Pastures for dairy cattle. In: Nicol AM (ed.) Livestock Feeding on Pasture, pp. 133±143. Wellington, New Zealand: New Zealand Society of Animal Production. Holmes CW and Wilson GF (1984) Milk Production from Pastures. Wellington, New Zealand: Butterworths. Stockdale CR (1999) Effects of season and time since defoliation on the nutritive characteristics of three irrigated perennial pasture species in northern Victoria. 1. Energy, protein and bre. Australian Journal of Experimental Agriculture 39: 555±565. Stockdale CR (00) Levels of pasture substitution when concentrates are fed to grazing dairy cows in northern Victoria. Australian Journal of Experimental Agriculture : 913±921. Stockdale CR, Dellow DW, Grainger C, Dalley D and Moate PJ (1997) Supplements for Dairy Production in Victoria. Melbourne, Australia: Dairy Research and Development Corporation. Non-Seasonal, Pasture- Optimized ± Dairy Cow Breeds in the United States M E McCormick, Louisiana State University Agricultural Center, Franklinton, LA, USA Copyright 02, Elsevier Science Ltd. All Rights Reserved Introduction Pasture-based dairies account for a relatively small percentage of the approximately 87 000 dairies in operation in the United States. A recent US Department of Agriculture survey indicated that the average US dairy contained 133 ha of land, but of that amount only ha, or 14.9% of the total acreage, was devoted to pasture production. Pasture production varies considerably throughout the United States. In the traditional dairying regions, such as the upper midwestern states of Wisconsin and Minnesota, pasture use typically accounts for less than 10% of the farm area, but in the southeast and southern plain states, where long growing seasons and low soil fertility are prevalent, more than half of the average dairy farm land mass is in pasture. Although most US dairies are con nement based, use of pasture in US dairy operations has grown steadily since the early 1990s, a time marked by relatively low milk prices and high production costs for housing, waste management and supplemental feed. Recent surveys indicate that summer grazing of forages has been adopted by as many as % northeastern and midwestern dairymanagers. Likewise, pasture use in Georgia, a state in the southeastern United States, grew from 34.5% in 1985 to 53.5% in 1995. Primary forages used for grazing during the spring and summer in the northeastern region include orchardgrass, bluegrass and perennial ryegrass, often grown in combination with variable amounts (10± 50%) of red or white clover. Major grazing crops grown for lactating dairy cows in the southern United States are annual ryegrass, wheat, oats and cereal rye, which are normally grazed from November to April. Summer grazing crops used by many southern dairy managers include perennials, such as bermudagrass and bahiagrass, and annuals, such as millet, sorghum-sudan, crab grass and signalgrass. Increased interest in pasture dairying has prompted several studies comparing milk production and the economics of cows receiving diets based on pasture to those fed maize or lucerne (alfalfa) silage-based total mixed rations (TMRs) in con nement (Table 1). Study or survey sites ranged geographically from the southern states of Mississippi and Georgia to the more northern states of New York and Minnesota. Generally, grazing seasons in northern states range from 1 to 1 days, depending on rst frost day, and in many southern states may extend from 0 to 300 days per year. In southern states, droughts and low forage quality often restrict the number of days that pastures are suitable for grazing more than cold weather. Based on the university studies and farm surveys cited in Table 1, pasture-based herds may be expected