ASC-151 COOPERA TIVE EXTENSION SERVICE UNIVERSITY OF KENTUCKY • COLLEGE OF AGRICULTURE Pasture for Dairy Cattle: Challenges and Opportunities Donna M. Amaral-Phillips, Roger W. Hemken, Jimmy C. Henning, and Larry W. Turner astures have always been and will continue tion as forage digestibility and availability decrease to be a source of forages and nutrients for during an eight- or nine-day rotation. The two- to Pdairy cattle, including heifers, dry cows, and three-day lag in milk production after shifting to the milking herd. During the 1950s and early fresh pasture is attributed to a carryover of the less 1960s, pasture was replaced by confinement feeding digestible pasture forage consumed previously. of stored forages as the preferred means of feeding These fluctuations in milk production also have and managing the milking herd. These changes been observed in beef cows rotated to fresh pasture allowed the amount and quality of forages and every seven days (Martz 1995). concentrates fed to dairy cows to be controlled so Pastures which are intensively grazed result in milk production could be maximized. With the greater forage utilization, higher nutrient quality, advances in fencing and watering systems, im- and greater stand persistency as compared to provements in forage species, and increasing cost of continuously grazed pastures. Continuously grazed equipment, reincorporating pasture into the feeding and management Milk per cow fluctuates with rotational grazing. program for the milking herd has gained interest. Properly managed 35 pastures can provide cows with high- quality forage harvested at a very 34 nutritious stage of maturity. 33 Rotational Grazing 32 Intensive rotational or controlled 31 grazing systems involve intensely grazing a portion of a pasture followed 30 Daily Milk Per Cow, lbs Daily Milk Per Cow, Pasture 1 Pasture 2 Pasture 3 Pasture 4 by a rest period to allow the forage to 29 8 Days 8 Days 9 Days 9 Days regrow. Cows remain on a given paddock for as little as 12 hours for up After available pasture declined from heights of 8 to 10 inches to 2.5 inches, to three days and then are rotated to a cows were rotated to a fresh pasture. “rested” paddock. The timing of these rotations is based on the growth of Figure 1. Variation in milk production when pastures are rotated every forage in the paddocks, not a rigid eight to nine days. (Blaser 1986) time schedule. This rotational scheme ideally uses a minimum of eight different paddocks. The greatest reasons for an intensive rotational schedule are to allow for adequate intakes of veg- Definition of Intensive Rotational Grazing etative, highly nutritious plants and to minimize Cows remain on pasture for 12 hours for up to three the wide fluctuations in milk production due to days and then are rotated to a “rested” paddock. A varying nutrient intake and digestibility. minimum of eight different paddocks is used. Figure 1 shows the data from a study by Blaser which illustrates the fluctuations in milk produc- AGRICULTURE • HOME ECONOMICS • 4-H • DEVELOPMENT pastures contain some areas where forage regrowth ing forage quality, decreasing harvesting costs, and/ is being grazed too closely and other areas that are or increasing the utilization of land close to the overgrown with over-mature, low-quality forage barn which is not well-suited for harvesting forages that is not being consumed. Studies in Florida with due to its excessive slope. When pasture is plentiful Callie bermudagrass (Mathews et al. 1994) show during the spring, it can supply a larger proportion that leaves made up 46 percent to 49 percent of the of the forages fed, and when pasture availability stand when rotational grazed compared to 31 decreases in midsummer, the amount of stored percent to 36 percent when the stand was continu- forages can be increased to ensure that cows main- ously grazed by dairy heifers. With more leaves in tain their feed (dry matter) intakes. A supplemental the stand, a more nutritious forage was available grazing system is an excellent way to learn how to for grazing. In addition, the rotational-grazed stand manage the interrelationships between forages and had 84 percent Callie bermudagrass remaining cattle before relying on pasture as the sole forage after two years versus 62 percent under continuous source during the grazing season. grazing by dairy heifers. A leader-follower scheme within a rotational grazing system can be an effective means of meet- ing the greater nutrient needs of early lactation and Grazing Schemes higher-producing cows (Figure 2). In this scheme, cows or heifers with the highest nutrient require- Grazing Systems for Dairy Cows ments are allowed to graze first and allowed to eat (April through November) the tops and the most nutritious part of the plants. A second group of cows or heifers with lower nutri- • All forage provided by pastures ent requirements then is allowed to graze the • Supplemental grazing where 25 percent to 75 paddock and remove the remaining forage to the percent of forage needs are supplied through desired height before being moved. This scheme grazing depending on forage availability. allows the allocation of the forages with the highest nutrients to cows or heifers with the highest de- Grazing can supply 25 percent to 100 percent of mand for nutrients without sacrificing growth or the forage needs of a high-producing dairy cow milk production. between April and November in Kentucky. Tradi- tionally, pasture systems provided all of the forage Grazing Behavior of Cows consumed with or without a limited amount of hay Cows graze by wrapping their tongues around being fed. Grain, then, is supplied either through the forage and snipping it off with their lower teeth the parlor, outside in feed troughs, or on the ground and upper dental pad. (Cattle do not have upper as a large range pellet. teeth.) They are very selective in their grazing Supplemental grazing systems, where grazed habits, first choosing tender young plants which are forages represent only 25 percent to 75 percent of easily eaten and most palatable. In addition, cows the forage dry matter intake, also can be an eco- eat the top of the plant first, consuming leaves nomical and viable option for using pasture. before stems. Figure 3 illustrates the effect of the Supplemental pasture is used in combination with number of grazing days on crude protein content of harvested silages and/or hay as a means of improv- Pasture No. 1 2 34 5 6 7 First Grazers Last Grazers Sequence of Grazing Pastures Figure 2. Diagram of available pasture when feeding first and last grazers in rotational grazing. (Blaser 1986) 2 inches. In addition, the lower stem is lower in crude protein and relative feed value than the stem found in the upper 6 inches of the alfalfa plant. These changes in nutrient content need to be considered when planning a nutrition program around an intensive rotational grazing program. The “new grazing” varieties of alfalfa are being bred to have more leaves on the stem and to grow closer to the ground. In the future these varieties may help decrease this selective grazing. Pasture intake is related to the amount of time spent grazing, the number of bites per minute, and the size of each bite (Phillips et al. 1988). Dairy cattle generally graze for six to nine hours per day. Because of a cow’s need to ruminate and rest, she seldom grazes over nine hours per day. The number Figure 3. Crude protein content of alfalfa/grass of bites taken per minute does not vary appreciably, pastures when placed in a 12-paddock rotation. ranging from 55 to 65 bites per minute. Thus, dry (Morrow 1995) matter intake from pasture is controlled by the size of the bite of forage. This is directly related to the remaining alfalfa/grass plants. The crude protein height and density of the forage stand being grazed. content of alfalfa decreases dramatically within the In Scotland, Phillip and Leaver (1989) mea- first day of the 12-paddock, three-day rotation as sured forage intake of cows grazing ryegrass pas- the leaves at the top of the alfalfa plant are con- ture in the spring when grass was very lush and sumed first. again in the fall when pasture growth was lower. In the spring, when forage growth was at its maximum, Table 1. Distribution of leaf, stem, and total dry matter in a summer alfalfa cows averaged 60 bites per canopy. Nutrient content of leaf and stem areas is listed on a dry matter minute over an eight-hour basis. grazing period and were able NDF to consume 31.7 pounds of % of CP ADF Digestibility dry matter daily (0.50 grams of dry matter per bite). In the Total Yield (%) (%) RFV (%) fall, cows averaged 65 bites Upper 6 inches of plant 37.3 per minute and grazed for Leaf 30.8 24.0 18.5 250 63.2 nine hours a day but were Stem 6.5 13.0 38.6 104 44.0 able to consume only 19.6 Lower 12 inches of plant 62.7 pounds of dry matter daily Leaf 12.9 22.0 16.6 273 65.7 (0.25 grams of dry matter per Stem 49.8 9.6 52.9 65 31.1 bite). These data illustrate the importance of forage CP=crude protein content, ADF=acid detergent fiber, RFV=relative feed value, density and height when NDF=neutral detergent fiber trying to maximize intake of (Adapted from Henning 1996) dairy cows grazing pasture. The distribution of leaf and stem area differs Cows generally prefer to graze during the early between well-managed grass pastures and those and late daylight hours.