Contents |
Introduction
Several studies suggest that well-managed pasture-based dairy systems could reduce input costs and increase net returns on small- to medium-sized farms in the United States by as much as $150 per cow when compared to conventional confinement dairy systems (Parker et al., 1992; Rust et al., 1995; Tranel and Frank, 1991). The primary advantage of grazing systems over confinement systems appears to be a reduction in costs of forage production. Increased profitability due to reductions in input costs will quickly be lost if milk production per cow is reduced. For grazing systems to perform financially as well as confinement-based systems, milk production must be maintained at high levels.
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Farmers who are successful at maintaining high milk yield with grazing systems generally are successful in three areas of nutrition and pasture management (Figure 1). The first and most important component of their grazing system is a pasture management strategy that maximizes the amount and quality of forage that cows harvest from pasture. Key management factors include selection of forage species that are adapted for the soils and climate of the farm, optimal soil fertility to maintain forage growth through the grazing season, management of forage growth by manipulating stocking density, selective mechanical harvesting, and strategic use of grain and forage supplements.
The second management issue is provision of supplemental energy to optimize milk production. High-quality pastures will not provide adequate energy to cows of high genetic merit (Table 1). If supplemental energy is not provided to high-producing cows, milk yield, body condition, and reproductive performance will be reduced (Kellaway and Porta, 1993). The amount of grain needed to optimize performance will differ as circumstances change among farms and at different times of the year. Successful grain feeding entails a strategy where adequate supplemental energy is fed to complement, not replace, the supply and quality of pasture. Excessive grain feeding is avoided because it will reduce pasture utilization. A common challenge faced by farmers who feed supplemental grain is maintaining pasture intake. It has been clearly demonstrated that even low levels of grain feeding to pastured cattle will reduce forage consumption if forage supply is not limiting. It becomes critical to recognize that stocking density and mechanical harvest of excess pasture forage will likely have to be adjusted when grain supplements are fed to grazing dairy cows.
| Production level | Pasture type | ||||
|---|---|---|---|---|---|
| Nutrient | Early lactation | 70 lb/day | Grass | Grass-legume | Legume |
| NEL, Mcal/lb | 0.78 | 0.74 | 0.65 – 0.70 | 0.66 – 0.72 | 0.68 – 0.74 |
| CP, % of DM | 19 | 16 | 18 – 22 | 21 – 23 | 23 – 25 |
| Bypass CP, % of DM | 7.2 | 5.7 | 4.4 – 6.3 | 4.2 – 5.7 | 4.6 – 5.0 |
| NDF, % of DM (minimum) | 28 | 28 | 50 | 44 | 38 |
| NFC, % of DM1 | 36 – 40 | 36 – 40 | 15 – 20 | 15 – 20 | 20 – 25 |
| 1NFC = Nonfiber carbohydrate. | |||||
The third important area of management for grazing dairy cattle is when and how much supplemental protein, especially ruminally undegradable protein, to feed. Protein supplements tend to be the most expensive component of the pasture feeding program, and therefore, overfeeding of protein will affect net returns. It is also important to recognize that the optimal amount of supplemental protein to feed will vary depending on the amount of energy provided by the diet. Supplemental protein will be of little benefit to cows that are consuming low to moderate levels of energy, but cows with high genetic potential for milk yield that are consuming adequate energy will likely produce more milk if the pasture supplements contain supplemental protein.
Managing Pastures to Optimize Forage Yield and Quality
Pasture stands should persist for several years and consistently yield high-quality forage throughout the grazing season. In confinement systems, pure stands of alfalfa or rye grass are considered to be among the highest of all forage crops in yield of digestible energy per acre. In the Midwest, however, pure stands of neither are adapted well to intensive grazing systems.
Cool-season grasses and legumes tend to be the highest-producing species of pasture forages in the upper Midwest of the United States. Cool-season grasses yield 60% of their total yearly production in May and June. Cool-season grasses also green up earlier in the spring than legumes, allowing for as much as two weeks earlier start to the grazing season than with pure legume pastures.
Alfalfa is more deeply rooted than grasses or other legumes and maintains pasture production through mid- to late summer better than other legumes or cool-season grasses. Annual grasses such as oats, winter wheat, and winter rye can also be used as pasture forages in the Midwest. They will yield approximately half as much as the perennial legumes and grasses, however, and do not yield well during the warmer, dry months of summer.
Regardless of forage species or mixture of forage species selected, forage production will be greater than can be utilized in May and June and insufficient in late summer and early fall. With dairy cattle, it becomes critical to design grazing systems around forage availability. Well-managed, improved pastures can be stocked at about 1 to 1.5 lactating cows per acre. Approximately 30% of the total summer production forage will have to be mechanically harvested to maintain forage quality and yield. In years with normal rainfall, most of the excess forage can be harvested at the late vegetative stage of maturity in late May or early June. It may also be necessary to harvest a second cutting of forage in July. Stocking rates of pastures that consist of native grass species or warm-season grasses may be as low as 0.5 to 0.75 lactating cows per acre. It also may be necessary to supplement these pastures with higher levels of grain to maintain optimal milk yield.
Planting alfalfa in a mixture with grasses can reduce the risk of bloat and help decrease winter kill problems (Howarth, 1988). There is also evidence that when a legume and a grass are planted as a mixture, total yields will be greater than either of the two species grown in monoculture (Sheaffer et al., 1990). Legume-grass mixtures also ensure against failure of the entire stand under adverse weather conditions.
Depies (1994) compared forage yields, quality, and persistence of two pasture types. It was found that pastures consisting of alfalfa grown in monocultures were not as suitable as alfalfa/red clover/brome/orchard grass mixtures for grazing dairy cattle in a three-year experiment (Table 2). Alfalfa did not persist well in either pasture system because of winter kill in this study. The grasses and red clover in the mixed pastures did survive, however, and yield of forage dry matter in the mixed species pastures increased by approximately 15% in both the second and third year of the trial. Several cattle grazing the pure alfalfa pastures were also treated for bloat during the grazing season, while none of the cows grazing the mixture of grasses and legumes bloated.
| Year | Alfalfa pasture | Mixed pasture | |
|---|---|---|---|
| — Tons DM/acre– | |||
| 1991 | Forage consumed by grazing | 2.5 ± 0.21 | 2.5 ± 0.2 |
| Forage mechanically harvested | 0.9 ± 0.04 | 1.2 ± 0.05 | |
| Total yield for season2 | 3.4 ± 0.2 | 3.7 ± 0.2 | |
| 1992 | Forage consumed by grazing | 1.8 ± 0.1 | 3.5 ± 0.2 |
| Forage mechanically harvested | 0.4 ± 0.07 | 0.52 ± 0.01 | |
| Total yield for season | 2.2 ± 0.12 | 4.0 ± 0.18 | |
| 1993 | Forage consumed by grazing3 | 0 | 3.9 ± 0.15 |
| Forage mechanically harvested | 3.1 ± 3 | 0.67 ± 0.02 | |
| Total yield for season | 3.1 ± 0.3 | 4.6 ± 0.2 | |
|
1Standard deviation of the means of the three pastures for each treatment. 2Based on herbage samples harvested at a 5 cm stubble height. 3Alfalfa pastures were not grazed in 1993. |
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Forage quality of pure grass stands or grass-legume mixtures is usually lower than the quality of pure legumes. Depies (1994) found that, although pasture composed of a mixture of grasses/legumes was lower in ruminal digestibility than a pure alfalfa pasture, there was little difference in milk yield due to pasture. In this study, cattle in a confinement feeding system produced similar yields of 3.5% FCM/acre as compared to the legume-grass pasture system in the first year (Table 3). In the second and third years of the study, the legume-grass pastures systems produced more milk/acre than the confinement feeding system. The legume-grass pastures were better suited for grazing than the pure alfalfa pastures because of greater yields, better forage persistence, and higher milk production per acre. A mixture of legumes and grasses in this study yielded more forage DM, was more persistent, and appeared to be more suitable for grazing than alfalfa pastures.
| Year | Forage System | |||
|---|---|---|---|---|
| Alfalfa silage | Alfalfa pasture | Grass-legume pasture | ||
| 1991 | Milk produced per acre forage consumed, tons/acre1 | 7.4 | 6.1 | 6.8 |
| Milk/acre forage less grain NEL, tons/acre2 | 1.0 | 1.9 | 2.4 | |
| 1992 | Milk produced per acre forage consumed, tons/acre | 6.2 | 3.8 | 7.8 |
| Milk/acre forage less grain NEL, tons/acre | 2.5 | 0.55 | 3.9 | |
| 1993 | Milk produced per acre forage consumed, tons/acre | 7.6 | 0 | 9.2 |
| Milk/acre forage less grain NEL, tons/acre | 1.2 | 0 | 2.8 | |
|
1Milk90 is a spreadsheet used to calculate milk/acre using forage yield and quality (Undersander et al., 1993). 2Grain NEL estimated to be 0.80 Mcal/lb, and the NEL value of milk was 0.32 Mcal/lb. |
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Meeting Energy Requirements of Grazing Cattle
High-producing cows receiving excellent pasture but no grain will show typical signs of energy deficiency in early lactation: low peak daily milk yield, excessive loss of body condition, poor persistence after peak, silent heats, and low conception rates (Kellaway and Porta, 1993). With pure legume pastures, a high-producing cow would be expected to consume only enough digestible energy to support about 50 to 60 lb/day of milk. Under field conditions, however, cattle on high-quality pasture fed no supplement have produced as much as 75 to 80 lb/day. Most of the time, these cattle lose weight rapidly and show poor persistency in mid-lactation. Many nutritionists express concern that it is difficult to maintain body condition and lactation persistency with grazing dairy cattle. Poor lactation performance is often attributed to the inability of cattle to consume adequate amounts of fresh forage. One concern is that the high-moisture content of fresh pasture may limit rumen capacity. In order for cows to consume 25 lb of DM from pasture, cows need to consume approximately 200 lb of fresh material. Another problem may be that forage intake is limited by either sward density, sward height, or grazing pressure. Our research (Depies, 1994) indicates that grazing dairy cattle are not likely limited by rumen fill of fresh material, but it is likely that grazing pressure could be a factor in limiting intake of grazing cattle (Table 4). Grazing cattle appear to be able to consume as much forage DM from pasture as alfalfa silage. In this experiment, cows on alfalfa pasture consumed on average as much as 250 lb/day of wet forage. In order to attain forage DM intakes that were comparable to the confinement system, grazing cattle had to have ample supply of pasture and be allowed to leave at least 35% of the available sward as residue. When we tried to reduce residual pasture, forage intake and milk production declined.
| Year/item | Treatment | ||||
|---|---|---|---|---|---|
| Alfalfa silage | Alfalfa pasture | Grass-legume pasture | |||
| ———-lb/day———- | |||||
| SE1 | |||||
| 1991 | Grain DM offered | 24 | 21 | 21 | |
| Grain DM consumeda | 23 | 18 | 17 | 0.7 | |
| Forage DM offeredc | 31 | 36 | 33 | ||
| Forage DM intake | 22 | 22 | 22 | 2.4 | |
| Total DM intakeb | 45 | 43 | 39 | 2.4 | |
| 3.5% FCM yield Multiparous cowsa Primiparous cows |
70 61 |
72 61 |
73 62 |
1.8 1.8 |
|
| 1992 | Grain DM offered | 20 | 18 | 17 | |
| Grain DM consumeda | 18 | 14 | 14 | 0.4 | |
| Forage DM offeredc | 34 | 37 | 34 | ||
| Forage DM intake | 28 | 29 | 22 | 2.4 | |
| Total DM intakea | 46 | 42 | 38 | 2.2 | |
| 3.5% FCM yield Multiparous cows Primiparous cows |
66 52 |
64 54 |
60 50 |
1.8 1.8 |
|
| 1993 | Grain DM offered | 24 | 20 | ||
| Grain DM consumed | 23 | 20 | 0.7 | ||
| Forage DM offeredc | 32 | 39 | |||
| Forage DM intake | 25 | 29 | 2.6 | ||
| Total DM intake | 48 | 49 | 2.4 | ||
| 3.5% FCM yield Multiparous cowsa Primiparous cows |
74 61 |
81 63 |
0.7 0.7 |
||
|
1 SE = standard error of mean. a Alfalfa silage-fed cows are different from pasture-fed cows (P < 0.01). b Alfalfa pasture-fed cows are different from grass-legume pasture-fed cows (P < 0.05). c Forage offered and consumed by alfalfa silage-fed cows was measured directly. Forage offered and consumed by pasture-fed cattle was estimated by measuring herbage DM yield above 5 cm stubble height before and after grazing. |
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Ohio State work (Table 5) suggests that the production response to supplemental grain on legume-based pastures is similar (1.1 lb milk per pound of supplemented grain DM) to the response to grain on orchard grass pastures (0.85 lb milk per pound of supplemented grain). This work suggests that for both pastures, forage consumption decreased and total DM intake increased as more grain was added to the diet. Total DM intake of cows receiving the highest supplement rates on pastures was similar to the total DM intake of cows fed the alfalfa silage-based diet. The substitution effect of grain on pasture consumption appears to be similar to that observed when grain is added to high-quality hay or silage-based diets. Other studies have reported little or no substitution effect of grain for forage (Jones-Endsley et al., 1997). This may be an indication that pasture consumption was limiting.
| Forage source | Concentrate | Forage intake | Milk yield |
|---|---|---|---|
| ———-lb/day———- | |||
| Alfalfa pasture | 0 | 41 | 44 |
| 10 | 35 | 53 | |
| 22 | 22 | 68 | |
| Orchard grass pasture | 0 | 38 | 29 |
| 13 | 33 | 38 | |
| 22 | 23 | 47 | |
| Alfalfa silage | 18 | 22 | 62 |
Several experiments have attempted to quantify the milk response to supplemental grain for grazing cows (Arriaga-Jordan and Holmes, 1986a, 1986b; Hodge and Rogers, 1984; Hodge et al., 1984; Jennings and Holmes, 1984; Kibon and Holmes, 1987; Moate et al., 1984; Muller, 1993; Stakelum, 1986; Taparia and Davey, 1970). In general, the response in milk yield to each additional pound of grain has been between 0.50 and 0.67 lb/day of 4% FCM. Each pound of grain added to the diet of grazing cows will increase total DM intake by about 0.4 to 0.6 lb/day and decrease forage consumption by 0.6 to 0.4 lb/day. These are typical responses when pasture supply is not limiting. When pasture supply or pasture intake is low, forage intake is often unaffected by grain feeding, and milk production may or may not be affected by grain feeding (Kellaway and Porta, 1993).
The substitution effect of grain for forage can be an important management tool for pasture-based systems. Increasing the level of supplemental grain will increase total intake of digestible energy, which in turn will help meet the energy output of milk and reduce loss of body condition. Grain feeding also can be an effective tool for managing pasture inventories. In late summer or early fall, increasing the rate of grain feeding could slow pasture consumption enough to eliminate the need for supplemental forage while at the same time increasing total energy intake to help replenish body condition.
Supplemental grain also improves body condition score in cattle on pasture. Australian researchers (Kellaway and Porta, 1993) suggest that the greatest economic benefit to grain supplementation is the improvement in body condition. Body condition is correlated to reproduction efficiency. Supplemental grain to cows in late lactation also helps to replenish fat reserves that are critical if cows are to produce well in the next lactation.
Protein Supplements
High-quality immature forages are relatively high in CP but low in protein that “bypasses” ruminal degradation (Table 1). As legumes make up a larger portion of the forage species in the pasture, undegraded intake protein content of the pasture decreases. From NRC (1989) guidelines, it can be calculated that cattle grazing high-quality immature forages and supplemented with corn-soybean concentrates may not consume adequate bypass protein. Fox et al. (1991) evaluated the impacts of supplemental energy versus protein on the growth of Holstein heifers. In this study, heifers grazed high-quality pastures that supplied CP well in excess of NRC feeding guidelines. Their work suggests that average daily gain of both lightweight and heavy heifers increased by 0.2 lb/day when 0.9 lb of soybean meal supplement was fed in place of cracked corn. Daily gains of heifers fed the soybean meal supplement were not different from heifers fed a fish meal supplement. This study suggests that growing heifers consuming lush high CP pastures can respond to supplemental protein. The amount of bypass protein needed, however, appears to be met with a limited amount of protein supplement. Milk production responses to bypass protein have not always supported the hypothesis that fresh forage diets are limiting in bypass protein. Hongerholt et al. (1993) evaluated milk yield response to bypass protein in high-producing Holstein cows grazing immature orchard grass pastures. In this trial, cattle were fed grain at a rate of 1 lb per 5 lb of milk yield. Diets fed the control cows were calculated to be deficient in bypass protein, relative to energy intake. Mature cows fed a grain supplement containing more bypass protein than control diets produced more milk. Milk production responses to bypass protein have not been observed in other grazing studies (Jones-Endsley et al., 1997; Penno et al., 1995; Welch et al., 1990). It would appear that in these trials, energy, not bypass protein, may have limited milk yield. Energy can be limited by inadequate intake of pasture or by insufficient grain supplementation. In experiments where the base diet has been limiting in energy relative to bypass protein, milk production responses to protein supplements typically range from 0.5 to 1 lb of milk per pound of supplement fed. These responses would be consistent with what would be expected if animals were catabolizing the supplement for energy. When energy supply is adequate, milk production responses to protein supplements would be expected to be in the range of at least 7 to 8 lb of milk per pound of supplemental protein fed. Under field conditions, it is extremely important to focus supplement strategies first on supplying energy and secondly on protein.
Summary
The use of intensively managed pastures offers many dairy producers an opportunity to increase profitability with a modest capital input. Well-managed pastures will produce forages that are comparable or better than can be produced with mechanical harvesting systems. Inputs to and net returns from intensive rotational grazing dairy systems appear to compare favorably to more traditional confinement-stored forage feeding systems.
High-producing cattle that are grazed on high-quality pastures will respond to supplemental energy and bypass protein. The response to concentrates and bypass proteins, however, will vary depending on the quantity and quality of pasture. More research is needed to define circumstances when marginal returns to supplemental feeding of grazing cows are economically viable.
Author Information
David K. Combs
Department of Dairy Science
University of Wisconsin-Madison
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