Impact of increasing amounts of supplemental high-protein Impact of increasing amounts of supplemental high-protein soybean meal on performance of range beef cows soybean meal on performance of range beef cows

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Introduction
Protein supplementation to beef cattle graz-tures contained 76% NDF and 2.7% CP, with ing low-quality, tallgrass-prairie forage has been 49% of the CP as DIP.DIP was estimated using a long-standing practice.However, in recent a single-point enzyme assay.The SBM was years, the mechanisms by which that protein is 10.1% NDF and 53.9% CP, with 66% of the CP utilized have become more clear.We now as DIP (1996 Beef NRC).One hundred and classify the protein that is degraded by microbes twenty Hereford × Angus cows (average initial in the rumen as degradable intake protein (DIP) body weight, 1141 lb; average initial body and the protein that escapes ruminal degradation condition score, 5.3) were allotted randomly to and passes through the rumen to the small one of three pastures.Within each pasture, intestine without being altered as undegradable cows were assigned to one of eight levels of intake protein (UIP).

Experimental Procedures
A performance study was conducted during tion, and pregnancy rate of spring-calving beef cows grazing low-quality, tallgrass-prairie forage.Forage samples clipped from the pas-5.0,and 6.0 lb/head/day as-fed.Cattle in each beginning of the calving season (Table 1) were pasture were gathered daily, sorted into their reduced (linear P<.01) by increasing the level of respective treatments, group-fed their supple-supplemental soybean meal (SBM); however, ment, and then returned to pasture.The treat-both BW and BCS showed a clear plateau ment period began December 2, 1996 and was (quadratic P<.01).Maximal BW response to terminated on February 10, 1997, which was the supplemental SBM was achieved at approxifirst day of the calving season.After the calving mately 3.5 lb/head/ day, and BCS response was season began, all cows were fed 3.8 lb/head/day maximized at approximately 3.8 lb/head/day.until they calved.Following parturition, cows Feeding SBM above these levels yielded no were fed 10 lb/head/day of alfalfa until sufficient further reduction in BW or BCS loss.Below new grass growth was available in the spring.
this point of maximal response (3.5 to 3.8 lb Body weight and condition were measured at SBM/head/day), each 1 lb decrease in SBM fed approximately 1-month intervals until the begin-daily resulted in a 48 lb reduction in BW and a .4ning of the calving season.Thus, measurements unit decrease in BCS. were obtained on December 2, January 6, and February 10, with additional measures The level of SBM fed from the beginning of postcalving (within 48 h after calving), shortly the winter grazing season until the beginning of before the beginning of the breeding season the calving season had no affect on calf birth (May 8), and at weaning (October 1 ).Cows date (Table 2; P>.52) or calf average daily gain were bred by natural service to Angus bulls.
(P>.43).However, there was a trend for level of

Results and Discussion
Losses in cow body weight (BW) and body influenced significantly (P=.51).condition score (BCS) through the supplemental SBM to affect calf birth weight (linear P=.14; quadratic P=.16) and weaning weight (quadratic P=.12).Pregnancy rate not Knowledge of the amount of supplemental SBM at which performance is maximized and the rate of decline below that maximum can be used as a rough guideline for determining the amount of supplemental SBM necessary to achieve a specified level of BW or BCS change in spring-calving beef cows grazing winter range.