| Grassland Evaluation Contest Study Guide | Fifth Edition: October 2005 | |||||||||||||||||||||||||
| Grassland Evaluation Contest Rules - Matching Livestock and Forage | ||||||||||||||||||||||||||
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To calculate the forage DMI requirements for a specific period use the following calculation: (lbs. dry matter needed per day) X ( number of days in season) Example: What is the forage DMI requirement for this same herd during the spring (100 days). This is a spring calving herd. Solution: Since the herd is spring calving, the cows will be in STAGE ONE. They are lactating and preparing to re-breed. Their requirements will be 2.5% of BW per day. The bull will be working during this time so his need is 2.5 % of BW per day. The heifers will be bred this spring so their need is 3 % of BW per day. The total daily forage DMI need is 1,100 lbs. Calculating actual forage availability required for different grazing management systems To determine if forage availability is adequate for the herd, you must also consider the harvest efficiency of the grazing system. No harvest system is 100% efficient, especially grazing animals. In a pasture system animal utilization of the forage is between 30 and 65 percent of what is actually grown. In continuous grazing systems cattle are allowed to continually graze a pasture with no restrictions on rotation. Much of what is produced is wasted. Only 30 to 35 percent of the total forage produced is actually eaten by the livestock. The other 65 to 70 percent is trampled, soiled by mud, manure, and urine, or used as bedding areas. As grazing management restricts the grazing habits of the animals, forage utilization increases. When management-intensive grazing (MIG) is used, forage utilization can be as high as 65 percent of the forage produced. This level of utilization can only be achieved with a multiple paddock system with frequent pasture rotations of 3 days or less. The following example gives a guideline for calculating the actual amount of forage dry matter production needed in a pasture to carry the same herd during the spring season. Example: (Same herd as used previously) Calculate the actual amount of forage DM needed for this herd for the spring grazing period for continuous and management-intensive grazing systems. Solution: The daily dry matter intake was calculated to be 1,100 lbs. and the total spring season DMI was 110,000 lbs. Forage utilization in the continuous grazing pasture management system is only about 35 percent. This means that forage dry matter availability needs to be almost three times the amount the herd will actually eat per day.
In an intensive grazing management system, forage utilization is about 65 percent so actual forage DM needed is only about 1.5 times as much as what is actually eaten.
It becomes quite clear that by using good grazing management a producer can harvest almost twice as much forage with little extra cost except for fencing materials. The added utilization of forage and extra livestock gain per acre can often pay that cost very quickly.
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