Turning cows out on immature forages can have consequences. If forages are overgrazed early, permanent damage to grass stands can lower yields and increase weed pressure. Delaying turnout until forages have reached 8 inches in height is recommended. Even more important is rotating cows through pastures to maintain 4 or more inches of stubble height and giving the plants a rest period. In early spring, rotation should occur more frequently to keep up with faster growth and then slow as summer approaches. Increasing residual heights and rest periods should be considered for abused areas and dry periods.
Grass tetany is another concern with spring grass. Immature grass is high in moisture, low in mineral content and low dry matter (DM). Grass tetany is deficiency of magnesium (Mg); this is why a “high Mg” mineral is recommended. Start feeding the mineral two to three weeks before turnout. After you have the right mineral, they must consume it. If cattle are not consuming mineral at 3 to 4 ounces per head per day, the feeder should be moved more in line with daily travel and closer to the water source. If this fails to increase consumption, then direct feeding the mineral with a grain or co-product supplement is needed. Results of grass tetany to the cow can be dramatic: stumbling, staggering, muscle twitching and possible death – all within a very short amount of time.
The next problem is meeting nutrient requirements of cows out on spring grass. Because spring grass is lush, high in protein and high in water content, it becomes hard to supply adequate nutrition. Mature cow size and milk production have increased in the beef cow population. This means that in some cases, cows cannot physically eat enough grass to meet DM and nutrient requirements. Research at the University of Illinois shows that cows will rarely consume more than 100 to 120 pounds of any feed due to fill and capacity of the rumen. However, a 1,400-pound cow will require 120 to 150 pounds of spring grass to meet her requirements. In some cases, when grass is very immature and wet (less than 20% DM), the intake would need to be even higher. This means it is likely best for cow performance to intervene with a mild supplement level.
Producers can supplement cows with a dry feed that supplies ample energy. Some options for supplement would be soyhull pellets, palatable grass hay or corn. A combination of these feedstuffs will provide DM to slow passage rate and energy to balance out the forage. Research conducted at the Orr Beef Research Center has shown a 7% to 15% improvement in artificial insemination conception rates when cows were supplemented on lush, spring forage.
