As summer heat and continued drought continue in major US pasture lands, it pays to look at the seasonal nutritional characteristics of pastures.
Perennial warm-season grasses can still look green in midsummer even as their nutritional value declines, said Paul Beck, Oklahoma State University Extension beef cattle nutrition Specialist, in a letter called Cow-Calf Corner.
Forage analysis from several Oklahoma forage systems shows the change begins earlier than many producers expect, Beck said.
TALLGRASS PRAIRIE GRASS
Tallgrass prairie dominated by big and little bluestem, Indiangrass and switchgrass at the OSU Range Cow Research Center near Stillwater peaked in nutritive quality in May with 10.55% and 75% digestibility, he said. After May, protein and digestibility declined steadily as forages mature with less than 6% crude protein and 65% digestibility in late summer.
The same pattern has been observed in other warm-season pastures, Beck said. In OSU data from midgrass prairie, crude protein declined from 9.8% in May to 7.1% in July, while Total Digestible Nutrients declined from 64% to 61%.
Old World bluestem declined even more sharply, from 12.9% crude protein and 60% TDN in May to 7.4% crude protein and 55% TDN in July, he said.
EVALUATING THE CHANGE
One useful way to evaluate this change is the ratio of TDN to crude protein, Beck said. Ratios between about 4:1 and 7:1 generally are considered balanced.
When that ratio approaches 7:1 or above the crude protein is too low for optimal forage fiber breakdown in the rumen, limiting forage digestion and intake, he said. In the early summer the TDN:CP ratio is 7:1, 6.5:1, and 4.6:1 for tallgrass prairie, midgrass prairie, and Old-World bluestem. But, by July, the ratio had increased to 10.8: for tallgrass prairie, 8.6:1 for midgrass prairie and 7.4:1 for Old World bluestem, indicating rumen-degradable protein was becoming limited.
That determines the kind of supplement cattle need, Beck said. When adequate standing forage remains but protein has declined, a pound of high-protein supplement increases microbial activity, fiber digestion, passage rate and forage intake, but only if adequate forage is available.
That is the basis of the Oklahoma Gold supplementation program, where one pound of a high protein supplement (38 to 40% crude protein) increases late summer stocker gains by 0.4 to 0.5 pounds per day, he said. This is a very efficient program requiring only two to 2.5 pounds of supplement for each pound of added gain.
The Oklahoma SuperGold supplementation program is based on feeding 2.5 pounds per day of a moderate (25-30%) protein supplement to provide protein and energy to the calf, Beck said. This can improve daily gains by 0.6 to 0.7 pounds with supplement efficiency of around 3.5 pounds of supplement per pound of added gain.
LIMITED FORAGE QUANTITY
But protein alone cannot replace missing forage, he said. Higher levels of moderate protein-energy supplement will be needed to maintain performance and stocking rates. High feeding rates of supplements containing a large amount of grain can reduce forage intake and fiber digestion.
The first question should not be, “What supplement should I buy?” But, rather “What is limiting performance?” Beck said. Forage testing provides the best answer, but pasture maturity, manure consistency, cattle fill and weight gain also provide clues.
Supplementation should start before gains fall sharply, he said. Supplements and forage quality and availability need to be matched, keeping in mind that that the supplement that fits one forage — or one month — may be the wrong tool for another.
CATTLE, BEEF RECAP
The USDA reported formula and contract base prices for live FOB steers and heifers this week ranged from $230.96 per cwt to $235.00, compared with last week’s range of $230.68 to $237.92 per cwt. FOB dressed steers and heifers went for $361.94 per cwt to $368.61, compared with $361.74 to $377.75.
The USDA choice cutout Wednesday was down $1.68 per cwt at $367.97 while select was up $1.56 at $348.06. The choice/select spread narrowed to $19.91, from $22.15 with 84 loads of fabricated product and 25 loads of trimmings and grinds sold into the spot market.
The USDA-listed the daily weighted average wholesale price for fresh 90% lean beef as $454.59 per cwt, and 50% beef was $137.39.
The USDA said basis bids for corn from feeders in the Southern Plains were unchanged at $1.18 to $1.34 a bushel over the Sep corn contract, which settled at $4.37 1/2 a bushel, down $0.04 3/4.
The CME Feeder Cattle Index for the seven days ended Tuesday was $348.65 per cwt, down $0.48. This compares with Wednesday’s Aug contract settlement of $354.00 per cwt, up $2.80.