The Cornell Net Carbohydrate and Protein System (CNCPS) has a submodel that predicts rates of feedstuff degradation in the rumen, the passage of undegraded feed to the lower gut, and the amount of ME and protein that is available to the animal. In the CNCPS, structural carbohydrate (SC) and nonstructural carbohydrate (NSC) are estimated from sequential NDF analyses of the feed. Data from the literature are used to predict fractional rates of SC and NSC degradation. Crude protein is partitioned into five fractions. Fraction A is NPN, which is trichloroacetic (TCA) acid-soluble N. Unavailable or protein bound to cell wall (Fraction C) is derived from acid detergent insoluble nitrogen (ADIP), and slowly degraded true protein (Fraction B3) is neutral detergent insoluble nitrogen (NDIP) minus Fraction C. Rapidly degraded true protein (Fraction B1) is TCA-precipitable protein from the buffer-soluble protein minus NPN. True protein with an intermediate degradation rate (Fraction B2) is the remaining N. Protein degradation rates are estimated by an in vitro procedure that uses Streptomyces griseus protease, and a curve-peeling technique is used to identify rates for each fraction. The amount of carbohydrate or N that is digested in the rumen is determined by the relative rates of degradation and passage. Ruminal passage rates are a function of DMI, particle size, bulk density, and the type of feed that is consumed (e.g., forage vs cereal grain).

The Cornell Net Carbohydrate and Protein System (CNCPS) has a kinetic submodel that predicts ruminal fermentation. The ruminal microbial population is divided into bacteria that ferment structural carbohydrate (SC) and those that ferment nonstructural carbohydrate (NSC). Protozoa are accommodated by a decrease in the theoretical maximum growth yield (.50 vs .40 g of cells per gram of carbohydrate fermented), and the yields are adjusted for maintenance requirements (.05 vs .150 g of cell dry weight per gram of carbohydrate fermented per hour for SC and NSC bacteria, respectively). Bacterial yield is decreased when forage NDF is < 20% (2.5% for every 1% decrease in NDF). The SC bacteria utilize only ammonia as a N source, but the NSC bacteria can utilize either ammonia or peptides. The yield of NSC bacteria is enhanced by as much as 18.7% when proteins or peptides are available. The NSC bacteria produce less ammonia when the carbohydrate fermentation (growth) rate is rapid, but 34% of the ammonia production is insensitive to the rate of carbohydrate fermentation. Ammonia production rates are moderated by the rate of peptide and amino acid uptake (.07 g of peptide per gram of cells per hour), and peptides and amino acids can pass out of the rumen if the rate of proteolysis is faster than the rate of peptide utilization. The protein-sparing effect of ionophores is accommodated by decreasing the rate of peptide uptake by 34%. Validation with published data of microbial flow from the rumen gave a regression with a slope of .94 and an r2 of .88.

The Cornell Net Carbohydrate and Protein System (CNCPS) has equations for predicting nutrient requirements, feed intake, and feed utilization over wide variations in cattle (frame size, body condition, and stage of growth), feed carbohydrate and protein fractions and their digestion and passage rates, and environmental conditions. Independent data were used to validate the ability of the CNCPS to predict responses compared to National Research Council (NRC) systems. With DMI in steers, the CNCPS had a 12% lower standard error of the Y estimate (Sy.x) and three percentage units less bias than the NRC system. For DMI in heifers, both systems had a similar Sy.x but the NRC had four percentage units less bias. With lactating dairy cows' DMI, the CNCPS had a 12% lower Sy.x. Observed NEm requirement averaged 5% under NRC and 6% under CNCPS predicted values at temperatures above 9 degrees C but were 18% over NRC and 9% under CNCPS at temperatures under 9 degrees C. Energy retained was predicted with an R2 of .80 and .95 and a bias of 8 and 4% for the NRC and CNCPS, respectively. Protein retained was predicted with an R2 of .75 and .85 with a bias of 0 and -1% for NRC and CNCPS, respectively. Biases due to frame size, implant, or NEg were small. Body condition scores predicted body fat percentage in dairy cows with an R2 of .93 and a Sy.x of 2.35% body fat. The CNCPS predicted metabolizable protein allowable ADG with a bias of 1.6% with a Sy.x of .07 kg compared to values of -30% and .10 kg, respectively for the NRC system.

The ovaries of the mosquito Aedes aegypti cultured in vitro secrete material that behaves like ecdysone in a radioimmunoassay. The material was identified as aecdysone by high-resolution liquid and gas-liquid chromatography. Secretion reached a maximum 16 hr after a blood meal as shown by bioassay and direct determination. Ovariectomy reduced the concentration of ecdysone in the adult after a blood meal. Qualitative analysis of whole-body extracts indicated fi-ecdysone to be the principal species present. Thus the ovaries appear to secrete a prohormone, a-ecdysone, which is converted to,-ecdysone. ,-ecdysone plays a significant role in stimulating egg development in the adult mosquito and may have reproductive roles in other insects.In mosquitoes the blood meal triggers egg development. This process, which has been found to be quite complex (1), involves the elaboration of yolk for later use by the developing embryo. The major proteins which become yolk are synthesized by the fat body, secreted into the hemolymph, and selectively taken up by the developing oocyte (2, 3). These proteins have been termed vitellogenins (4). Recent investigations into the control of this process showed that, in contrast with most insects, the mosquito ovary was the source of a hormonal factor which activated and maintained vitellogenin synthesis by the fat body (5). Thus synthesis by the fat body was abolished by ovariectomy and restored by reimplantation. Further, when ovaries from blood-fed females were incubated in vitro with the inactive fat body from unfed females, synthesis of vitellogenin was activated. This ovarian hormone was designated the vitellogenin stimulating hormone, VSH (1).The discovery that injected f3-ecdysone stimulates egg development (6) and dopa decarboxylase activity (7) in the absence of a blood meal led us to investigate the possibility that VSH might be f3-ecdysone. Our results indicated that f3-ecdysone mimicked VSH in vivo and in vitro (8) and that material with ecdysone-like activity could be detected in mosquitoes after a blood meal (9). These lines of evidence strongly suggested that VSH was fl-ecdysone or a closely related steroid. We here describe experiments designed to identify the secretory product of the ovary. METHODSMosquitoes (Aedes aegypti) were reared at 27 + 0.50 using standard techniques (8, 9). The assay for vitellogenin synthesis has been described in detail (1, 8). The radioimmunoassay (RIA) was performed as previously described (10, 11).Ovaries were removed from females 15 hr after a rabbit blood meal and incubated at 250 with gentle shaking in groups of 100 in 100,ul of a defined medium (8). After 24 hr the medium was removed and the ovaries were rinsed with saline. An equal volume of methanol was added to the combined medium and rinse. Particulates were removed by filtration. The extract was evaporated to dryness under reduced pressure, redissolved in chloroform:methanol (2:1) and partitioned against water according to Folch et al. (12). The epiphase was dried under vacuum ...

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