The Importance of Forage Testing
by Dr. Joao Vendramini, University of Florida/IFAS
Warm-season grasses are the dominant forage crops used for cow-calf production in Florida. Bahiagrass
(Paspalum notatum), limpograss (Hermathria altissima), stargrass (Cynodon nlemfuensis), and bermudagrass
(Cynodon dactylon) are the most cultivated species. Despite some differences in yield and nutritive value,
decreased production during the fall and winter months associated with low nutritive value at great
maturities are common characteristics of most warm-season grasses. In order to meet the requirements
of the cow herd during these periods, supplementation is often necessary. In general, winter feeding
can account for 20% of the overall annual cost of cow ownership.
Hay is the most popular source of conserved forage for beef cattle producers. While reducing the need
for hay is desirable, some quantity of hay is sometimes required to avert risk in most livestock
production systems. Increased price of fertilizers and fuel are making hay production a less attractive
option for cattle producers.
Stockpiled forage is a feasible alternative for beef cattle producers in South Florida. Mild winter
allows for having forage standing on the field for longer periods of time. Most warm-season grasses
can be used as stockpiled forage; however, limpograss has been the most used specie in South Florida.
Limpograss fits South Florida production systems because it tolerates soils with poor drainage and maintains
digestibility even at long regrowth periods. Floralta is the most planted cultivar of limpograss in South Florida.
Regardless of the management practice used to conserve and feed forage during the winter, some concentrate
supplementation is commonly necessary to meet the cow-calf requirements. A description of the total digestible
nutrient (TDN) and crude protein (CP) requirements of cows at different ages and lactation stages are presented
in Table 1.
| Table 1. Nutrient concentration requirements of cows at different ages |
Animal Category |
TDN |
CP |
|
% |
Dry cow mid pregnancy |
48 |
7 |
Mature lactating cow (10 lb milk) |
56 |
9 |
2 yr old lactating cow |
63 |
11 |
An estimate of the nutrients present in the forage is essential to maximize the efficiency
of concentrate supplementation. The most accurate way to predict forage nutritive value is
through FORAGE TESTING. A lot of producers allege that they own the forage and it will be
fed anyway, so why to test? Two different scenarios can happen when you do not have an estimate
of the forage nutritive value: 1) The forage has high nutritive value and the producer will be
overfeeding concentrate, or 2) The forage has low nutritive value and the concentrate is not
supplementing the cow adequately. In the first scenario, the producer inflates the production
cost without benefits in production, and in the second scenario, the cows may experience decreased
body condition, pregnancy rates, and finally resulting in fewer calves harvested and a consequent
decrease in profitability.
Producing forage with better nutritive value during the fall and winter is one of the
easiest ways to reduce the need for concentrate. A simulation of forages with different
TDN concentrations and the concentrate required for pregnant first calf heifers to achieve
1 lb gain/d is shown on Table 2.
| Table 2. Concentrate required for pregnant
replacement heifers to achieve 1 lb gain/d when fed with hay with different TDN concentrations. |
Hay (% TDN) |
Gain (lbs/d) |
lb corn/heifer/d |
lb corn/100 d |
$/heifer/100d* |
48 |
1.0 |
4.4 |
440 |
33 |
54 |
1.0 |
1.1 |
110 |
8.3 |
56 |
1.0 |
0 |
0 |
0 |
| * Considering $ 150.00 / ton of dry corn, 80% TDN. |
Considering the importance of forage testing in Florida, the Range Cattle Research and Education Center at
Ona will reactivate the Forage Extension Laboratory in the near future with the objective of providing accurate estimates of forage
nutritive value for forage and cattle producers in Florida. The two parameters that will be analyzed by the Forage
Extension Laboratory will be crude protein and digestibility (TDN). All nutrients are very important on the nutrition
stand point; however, these two are required in greater quantities and generate a greater impact on the economics
of winter feeding.
Sampling
Properly collecting and identifying a forage sample is very important. Hay samples should be
taken with a core where the sampler is driven into the end of a rectangular bale or the rounded
side of a round bale. Several cores should be combined in one composite sample. Each cutting
should be sampled and analyzed separately.
Pastures can be collected by "hand-plucked" samples or cut with scissors from different
places around the pasture. Samples should be sent to the laboratory immediately after they
are placed in a plastic bag. Remember, your results will be as good as your sample.
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