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Based on applications of the 1996 National Research Council (NRC) Nutrient Requirement of Beef Cattle (2000 update) model at our laboratories and on use of the model to evaluate published literature, it is our assessment that the NRC model (Level 1) represents an advancement in nutrient requirements of grazing cattle. We evaluated 8 published studies (35 treatment observations) to compare observed changes in body condition score (BCS) to those predicted by the NRC model, and to develop criteria to help with application of the model to range cattle nutrition. When in vitro organic matter disappearance (IVOMD) of grazed diets was converted to DE [DE = (1.07 × IVOMD) − 8.13] and used as a proxy for TDN, there were no differences in observed vs. predicted BCS change (P = 0.44). A critical component of the 1996 NRC model is the incorporation of the metabolizable protein system. An accurate estimate of microbial efficiency is key to application of the metabolizable protein system. We propose the use of an equation to adjust microbial efficiency for diets less that 65% TDN. The NRC model should be applied to 30-d time intervals if animal requirements or forage quality are changing rapidly. Accurate inputs for stage of gestation, days into lactation, breed, milk production, dietary TDN, and microbial efficiency are necessary for the model to yield accurate results. Work is needed to define and model microbial efficiency, nitrogen recycling, and the quality of diets selected by grazing livestock in various environments.

Designing a sound cow-calf nutritional program requires knowledge of nutrient requirements, diet quality, and intake. Effectively using the NRC (1996) beef cattle requirements model (1996 NRC) also requires knowledge of dietary degradable intake protein (DIP) and microbial efficiency. Objectives of this paper are to 1) describe a framework in which 1996 NRC-applicable data can be generated, 2) describe seasonal changes in nutrients on native range, 3) use the 1996 NRC to predict nutrient balance for cattle grazing these forages, and 4) make recommendations for using the 1996 NRC for forage-fed cattle. Extrusa samples were collected over 2 yr on native upland range and subirrigated meadow in the Nebraska Sandhills. Samples were analyzed for CP, in vitro OM digestibility (IVOMD), and DIP. Regression equations to predict nutrients were developed from these data. The 1996 NRC was used to predict nutrient balances based on the dietary nutrient analyses. Recommendations for model users were also developed. On subirrigated meadow, CP and IVOMD increased rapidly during March and April. On native range, CP and IVOMD increased from April through June but decreased rapidly from August through September. Degradable intake protein (DM basis) followed trends similar to CP for both native range and subirrigated meadow. Predicted nutrient balances for spring- and summer-calving cows agreed with reported values in the literature, provided that IVOMD values were converted to DE before use in the model (1.07 ×IVOMD− 8.13). When the IVOMD-to-DE conversion was not used, the model gave unrealistically high NEm balances. To effectively use the 1996NRC to estimate protein requirements, users should focus on three key estimates: DIP, microbial efficiency, and TDN intake. Consequently, efforts should be focused on adequately describing seasonal changes in forage nutrient content. In order to increase use of the 1996 NRC, research is needed in the following areas: 1) cost-effective and accura

Metabolizable protein (MP) requirements of spring calving heifers increase over the winter due to advancing gestation. The MP content of grazed winter forage is low, which may result in an MP deficiency. The objective was to compare the response of supplementing pregnant yearling heifers to meet MP requirements versus conventional CP supplementation. In 1997–98 and in 1998–99, pregnant, March-calving heifers (2,120 animals; 358 kg) at two locations of a commercial ranch in the Nebraska Sandhills, were used following breeding through calving as 2-yr-olds (cows). Heifers were randomly allotted to one of two supplementation treatments (about 265 heifers/treatment) each year at each of two locations (Ashby and Whitman, NE). Treatments were 1) supplementation to meet MP requirements (MPR) or 2) supplementation to meet CP requirements (CPR). Heifers grazed upland range and meadow and were offered supplements three times weekly from mid-September to mid- or late-February. Increasing amounts of meadow hay were fed from mid-December through calving. After supplementation ended in February, heifers were managed in one group at each location until the following October. Body weights and body condition scores were taken in September, February, and October. Two-yr-old pregnancy rates were determined via rectal palpation in October. Capital budgeting techniques were used to determine the economic return of supplementation strategies. There were no differences in BW (P = 0.41) or body condition score (P = 0.99) change during the winter among treatment groups across years and locations, but MPR cows were heavier (425 kg) than CPR cows (421 kg) at the time of 2-yr-old pregnancy testing (P = 0.07). Pregnancy rate was higher (P = 0.001) in the MPR (91%) compared to the CPR treatment (86%). Regression analysis showed that the response of the MPR treatment on pregancy rates tended to be negatively correlated with precalving body condition score (P = 0.11), body condition score loss over

Three experiments were conducted to evaluate the response of supplementing primiparous heifers based on the metabolizable protein (MP) system during pregnancy and lactation. In Exp. 1, 12 pregnant, March-calving heifers (432 ± 10 kg) grazing Sandhills range were randomly allotted to one of two treatments: supplementation based on either the MP system (MPR) or the CP system (CPR). Supplements were fed to individual heifers from October to February and no hay was offered. Grazed forage organic matter intake (FOMI) was measured in November, January, and February. In Exp. 2, 18 heifers (424 ± 8 kg) were randomly allotted to one of three treatments: 1) supplementation based on the MP system with hay fed in January and February (average 2.0 kg/d; MPR/hay), 2) supplementation based on the CP system, with hay fed in January and February (CPR/hay), or 3) supplementation based on the MP system, with no hay fed (MPR/no hay). Supplements were fed from October to February, and FOMI was measured in December and February. In Exp. 3, lactating 2-yr-old cows (394 ± 7 kg) maintained on meadow hay were supplemented to meet either 1) MP requirements (LMPR) or 2) degradable intake protein requirements (LDIPR). Body weight (BW) and body condition score change, hay intake, and milk production were measured. In Exp. 1, grazed FOMI decreased (P = 0.0001) from 1.9% of BW in November to 1.2% in February, but no differences among treatments were detected for FOMI or BW change. In Exp. 2, grazed FOMI declined (P = 0.0001) from 1.7% of BW in December to 1.1% in February, with no differences among treatments. Heifers on the MPR/hay and CPR/hay treatments had higher (P = 0.0018) total intake (grazed forage + hay intake) in February (1.7% BW) than the MPR/no hay heifers (1.1% BW). Heifers on the MPR/ no hay treatment had a lower weight (P = 0.02) and tended (P = 0.11) to have a lower BCS than heifers on other treatments. In Exp. 3, the LMPR cows had higher (P = 0.02) ADG than LDIPR cows (0.41 and 0

Forage proteins are degraded rapidly by rumen microorganisms and therefore supply relatively small quantities of undegraded intake protein (UIP). Growing cattle with high metabolizable protein requirements and lactating beef and dairy cows respond to UIP supplementation when fed high-forage diets, even though degradable intake protein (DIP) is adequate. This observation suggests that an accurate estimate of forage UIP is needed to establish optimal supplementation conditions. Microbial protein must be quantitated in duodenal or in situ residue samples to accurately measure forage UIP. Purines commonly are used as a microbial protein marker. Recent reports suggested that the original purine procedure generates interfering compounds that reduce estimates of microbial protein. Reanalysis of samples with a modified purine procedure yielded three to four times more purines in both duodenal samples and NDF residue incubated in situ. An alternative in situ procedure removes the microorganisms by refluxing with neutral detergent after ruminal incubation. This alternative correlates highly to the purine-corrected in situ procedure, and it is less variable and simpler to perform. Differential centrifugation may be inappropriate for obtaining clean samples of rumen microbes for determination of purine-to- Nratio because it does not represent particle-associated microorganisms. We suggest an alternative method of measuring that ratio in which NDF is incubated in situ and the particle-associated microorganisms can be measured. Rate of passage is used along with in situ rate of degradation to calculate UIP. We propose that a lag time associated with passage should be added to that calculation. Degradation with no passage (applying a lag) reduced UIP values of forage with high potentially available UIP pools. Enzyme analysis and near infrared reflectance spectroscopy show promise for measuring UIP when fistulated cattle are unavailable. Both are useful predictors of UIP and need m

Raman spectra have been obtained for thin (ca. 200 nm) poly(N,N'- bis(phenoxyphenyl)pyromellitimide) films produced by co-deposition of 4,4'- oxydianiline and pyrometallic dianhydride onto polycrystalline copper substrates from the vapor phase. It is demonstrated that even severe overdosing with one of the starting materials produces material which, after curing, is spectroscopically identifiable as polyimide. The details of the spectra obtained are, however, variable according to the dosing and curing conditions and, in some cases are substantially different from those characteristic solutions cast films. These differences are attributed to the presence of reaction products formed by the attach on imide carbonyls by unreacted amines in the matrix to form branched polymer chains. Imides.