Effect of supplement strategy on intake and digestion of prairie Effect of supplement strategy on intake and digestion of prairie hay by beef steers hay by beef steers

The effects of supple mental corn (4 lb/day), rumen-protecte d methionine (4.25 grams DL-methionine per day), or a cooked molasses block (1 lb/day) on intake and digestion of prairie hay were measured i n beef steers. Steers that consumed the cooked molasses block ate more forage than control steers, whereas forage intake was decreased by supplemental corn. Total tract organic matter digestion, expressed as a percent of intake, was numerically greatest for steers consuming the cooked molasses block. Digestible organic m atter intake, a rough estimate of energy available to the steers, was unaffected by methionine but was increased by supplementatio n of either corn or the cooked molasses block. Digestible organic matter intake tended to be greater for the block than for corn. Provi ding protein in a more concentrated form (block) tended to be more beneficial, because the negative effects of starch (corn) on forage intake were avoided.


Introduction
Intake of dorma nt forage often is limited by nutrient deficiencies .Degradable intake protein often is th e most limiting nutrient.Deficiencies of degradable intake protein can reduce forage digestion and intake, thereby reducing the energy availabl e for maintenance and growth of cattle grazing dormant forages.To increase availabl e energy, supplements based on grains or on more concentrated sources of protein often are fed.
Differences have been noted in the ability of these supplements to increas e available energy to cattle.
Methionine is thought t o be the first limiting amino acid in micr obial protein.Supplying that amino acid to cattle may improve performance with low levels of total supplement.Another aspect of supplementing cattle grazing dormant forages is the time and cost associated with supplementati o n.Blocks can be used to s upplement cattle with less time expenditure than hand-feeding supplements.With these points in mind, our objective was to investig ate the effects of supplementation strategy on forage intake and digestion.

Experimental Procedures
Twelve British and British cross steers (average BW = 820 lb) were used in three, 4 × 3 incomplete Latin squares to ev a luate the effect of supplement strategy on forage intake and digestion.Steers were penne d individually in an open-front barn and provided ad libitum access to water and prairie hay (5.7% crude protein, 67.6% NDF (dry basis).
Treatment s were: 1) control, no supplement, 2) 4 lb/day (as fed) of supplemental corn (.31 lb crude protein per day), 3 ) 5 grams/day of Smartamine-M® , a rumen-protected methionine product that provided 4.25 grams/day of DL-methionine , and 4) 1 lb/day of a cooked molasse s block (.31 lb crude protein per day).All steers received 20 grams of salt daily.Smartamine-M was mixed with the salt.
The experimental periods were 2 1 days with a 14-day ad aptation period followed by a 7-day intake and total fecal collection period.Orts and fecal samples were collected daily in the morning , after which supplements and forage were offered.

Results and Discussion
One animal assigned to the cooke d molasses block refused to consume his daily supplement; data from this steer were deleted from our analyses .Forage organic matter (OM) intake increase d (P<.05) wit h cooked molasses block supplementation , but decreased with corn supplementation ; rumen-protected methionine did not improve intake or digestion of forage (Table 1).Because animals ass i gned to the corn treatment received mor e supplemental OM than steers assigned to the other t r eatments, total OM intakes were similar between steers receiving corn and those receiving the cooked molasses block.Thi s illustrates the substitution effect on intake of corn for forage.Organic mat-ter digestibility was numerically highest for steers consuming the cooked molasses block.Corn did not affect digestion of the total diet, probably indicating that forage digestion was decreased when the highly digestible corn was included.Digesti ble OM intake, an indicator of energy available for maintenance and(or) growth, was i ncreased by supplementation with either block or corn but tended to be higher for the block than for corn (P=.06).
In conclusion, supplemental corn increased digestibl e OM intake because the highly digestible starch more than offset its negative effect on forage intake.Digestible OM intake increased when animals received the cooked molasse s block, because the additional protein (withou t extra starch) increased forage digestion, which subsequently increased forage and energy intake.Rumen-protected methionine was ineffective in stimulating forage intake or digestion by steers fed prairie hay.

Table 1 . Intake and Digestion of Prairie Hay by Steers Fed Different Supplements
a,b,c