Biomedical subjects

D G Fox

Publications and source records attributed to D G Fox.

At least 37 records · Page 2Linked to original sources

PubMed2000

Whole-herd optimization with the Cornell Net Carbohydrate and Protein System. I. Predicting feed biological values for diet optimization with linear programming.

We developed a diet optimizer for least-cost diet formulation with the Cornell Net Carbohydrate and Protein System (CNCPS) using linear programming. The CNCPS model is intrinsically nonlinear, and feed biological values vary with animal and feed characteristics. To allow linear diet optimization, we first used the CNCPS model to generate biological values to characterize the energy and protein content of each feed for the specific group for which the diet was being formulated. The biological values used were metabolizable energy (Mcal/kg), metabolizable protein [(% dry matter (DM)], passage rate (%/h), bacteria yield efficiencies (g/g), and degradation rate of the carbohydrate B2 fraction (%/h). In addition, the ruminal balances for nitrogen and peptides were included in the optimizer to optimize ruminal degradation of fiber. The objective function was to minimize diet cost subject to animal requirement and feed availability constraints. The animal constraints were set by requirements for DM intake (kg/d), metabolizable energy (Mcal/kg), metabolizable protein (%DM), and effective neutral detergent fiber (%DM) for a given level of production. Data from a dairy farm were used to evaluate this linear diet optimizer. Across all classes of dairy cattle, the CNCPS 4.0 model typically obtained a solution in less than six iterations that met the requirements with nearly 100% accuracy. We conclude this linear optimizer can be used to accurately formulate least-cost diets with the CNCPS model.

Animals↗

PubMed2000

Whole-herd optimization with the Cornell Net Carbohydrate and Protein System. II. Allocating homegrown feeds across the herd for optimum nutrient use.

The objective of this paper was to develop a linear optimization procedure for allocating homegrown feeds across the herd to optimize use of their nutrients in whole farm nutrient management planning. The first step involved developing an optimal diet for each group by a linear programming (LP) procedure developed for the Cornell Net Carbohydrate and Protein System (CNCPS). Information (feed biological values, nutrient requirements, animal and environmental factors, nutrient excretion, and the optimal diet) for each group was exported to a whole farm worksheet, where another LP procedure was used to optimize the allocation of homegrown crops by satisfying the set requirements of each animal group while optimizing return over feed costs and nutrient excretion constraints. A sample evaluation shows how this model was used to reduce N, P, and K excretion by changing feeding strategies while maintaining return over feed costs.

Animal Feed↗

PubMed2000

Whole-herd optimization with the Cornell Net Carbohydrate and Protein System. III. Application of an optimization model to evaluate alternatives to reduce nitrogen and phosphorus mass balance.

The objectives of this paper were to use a linear programming model previously described to evaluate different alternatives for reducing excess nutrients that may influence water quality on a case study farm (300 lactating cows on 430 ha of cropland growing alfalfa, grass, and corn). Several alternatives perceived to influence farm nutrient balance were evaluated for their potential to reduce N and P mass balance. Dividing lactating cow diets into three groups according to their level of milk production versus a one-group total mixed ration decreased mass balance (tonne/yr) from 51.7 to 44.7 for N, from 6.7 to 6.1 for P and from 16.2 to 14.8 for K with little influence on return over feed costs. Increasing forage quality (lower neutral detergent fiber and higher crude protein) did not improve N balance because of the increased N fixation from the air to the soil, but it increased returns over feed costs by $31,385. Improving yields to the maximum potential for the farm reduced mass balance by 29, 51, and 100% for N, P, and K, respectively, and increased returns over feed costs by $70,579. Changing the crop hectare proportions to more corn and less alfalfa reduced N and K balances by 19 and 29%, respectively, and increased returns over feed costs $39,383. Increasing annual milk production 10% by increasing milk production per head 10% compared with increasing animal numbers at the current average milk production per cow until total milk increased 10% gave $34,132 more return over feed costs with less N, P, and K retained on the farm.

Agriculture↗

PubMed1999

Conformational studies of the C-terminal domain of bacteriophage Pf1 gene 5 protein.

The gene 5 protein (g5p) of the bacteriophage Pf1 is a 144 residue single-stranded (ss) DNA binding protein involved in replication and packaging of the viral DNA. Compared to the gene 5 proteins of other filamentous bacteriophages, such as fd, the Pf1 g5p has an additional C-terminal sequence ( approximately 40 residues) with an unusual amino acid composition, being particularly rich in proline, glutamine and alanine. This C-terminal sequence is susceptible to limited proteolysis, in contrast to the globular N-terminal domain of the protein. The C-terminal sequence has been shown to play a role in the stabilisation of the protein-ssDNA complex. In the present study, the DNA sequence corresponding to the 38 amino acid residue C-terminal peptide has been cloned and expressed. A variety of biophysical techniques suggest that this peptide has a largely irregular conformation in solution, in contrast to the N-terminal globular domain that is principally beta-sheet. However, circular dichroism (CD) spectroscopy indicates that the peptide can be induced to form a structure that resembles a left-handed polyproline-like (P(II)) helix, suggesting that the C-terminal tail of the protein may adopt a more structured conformation in the appropriate physiological environment.

Amino Acid Sequence↗

PubMed1999

Predicting requirements for growth, maturity, and body reserves in dairy cattle.

The 1996 National Research Council Nutrient Requirements of Beef Cattle equations used to compute growth requirements, target weights, and energy reserves were modified and evaluated for use with dairy cattle. Coefficients used to compute target weights during growth and equations used to predict body weights (BW) for each condition score in computing energy reserves were modified. Equations used to compute net energy and protein requirements for growth were evaluated with data from studies of body composition changes in Holstein heifers; this model accounted for 96% of the variation in energy retained with a 4% bias. Coefficients used to compute target growth rates and BW were evaluated with data from Holstein heifer growth studies. Actual and target shrunk weight gain and BW values were before first pregnancy, 0.82 versus 0.87 kg/d with a 370-kg weight at first pregnancy versus a target of 352 kg; during the first pregnancy, 0.63 versus 0.69 kg/d with a weight at post first calving of 533 versus 545 kg; and first lactation, 0.136 versus 0.104 kg/d with a second post-calving weight of 592 kg versus 590 kg. The equations used to predict body reserves from BW and condition score were evaluated with data from a study of body composition associated with body condition score in Holstein cows; the revised model accounted for 96% of the variation in body fat and predicted 80 kg shrunk BW change per body condition score compared to 85 kg observed.

Animal Nutritional Physiological Phenomena↗

PubMed1999

Evaluation of tropical grasses for milk production by dual-purpose cows in tropical Mexico.

Two experiments using the Cornell Net Carbohydrate and Protein System were conducted to characterize the carbohydrate and protein fractions and corresponding rates of digestion of 15 tropical pasture grasses and to evaluate their ability to support milk production by dual-purpose cows. In the first experiment, ranges in carbohydrate and protein fractions of 15 grasses at 35 to 42 d of regrowth were: neutral detergent fiber (NDF) 63.5 to 74.9% of DM; permanganate lignin 4.7 to 7.8% of NDF; CP 5.5 to 11.9% of DM; and soluble protein 15.1 to 44.1% of crude protein (CP). The ranges of rates of digestion expressed as percent per hour were neutral detergent solubles (7.5 to 27.4); NDF (3.8 to 8.4); and neutral detergent insoluble protein (2.9 to 9.5). Predictions of the amount of milk that could be produced based on the amount of metabolizable energy supplied by the diet decreased 35% when NDF increased from 60 to 80%, and increased 88% when the rate of digestion of NDF increased from 3 to 6%/h. The milk production that could be sustained based on metabolizable protein in the diet doubled as CP increased from 4 to 12%. In the second experiment, nitrogen fertilization reduced NDF 7.3% and increased CP 84% without changing protein solubility, resulting in increased rumen nitrogen and metabolizable protein balances. With all forages, the Cornell Net Carbohydrate and Protein System predicted that availability of metabolizable protein would limit milk production. Predicted microbial growth was limited by ruminally available protein rather than by available carbohydrate.

Animals↗

PubMed1999

Impact of dairy farming on well water nitrate level and soil content of phosphorus and potassium.

The Cornell Teaching and Research Dairy Farm was used to study the historical influence of dairy farming on water quality and soil chemical properties. The farm has milked approximately 360 cows for the past 20 yr and is situated on 526 ha of cropland (390 ha utilized for dairy production) near Harford, New York. Mass nutrient balances (N, P, K) were constructed with historical data from 1979 and 1994 for the 390 ha used for dairy production. The amount of imported N increased more than 40% from 1979 to 1994, although there were year-to-year variations, depending on crop yields. Although nutrient balance (imported minus exported nutrients) as a percentage of imported nutrients on the farm remained relatively unchanged during this period, balance of N increased from 43.1 metric tonnes in 1979 to 66.0 metric tonnes in 1994. However, P and K remained about the same because of the reduced use of fertilizers in the 1990s. During the 15-yr period, total milk production increased more than 40% (2502 to 3604 metric tonnes from 1979 to 1994). Analysis of well water suggested that increasing amount of N balance on the farm resulted in increased well NO3-N concentration. The mean of five wells located in the corn fields increased from 3.3 to 7.0 mg/kg in NO3-N concentration, 70% of the EPA upper limit. Soil P increased from 6.0 to 24.0 (kg/ha) during the same period. Soil K did not change. Mass nutrient balances are important in determining the amount of nutrients remaining on farm. This study suggests N, P, and K balance can be used as an indicator of potential for increased NO3-N concentrations in wells and soil P and K levels, respectively.

Animal Feed↗

PubMed1998

Equilibrium and kinetic binding analysis of the N-terminal domain of the Pf1 gene 5 protein and its interaction with single-stranded DNA.

The Pf1 gene 5 protein is a single-stranded DNA-binding protein that binds cooperatively to the viral strand of Pf1 DNA during replication. A variety of N-terminal fragments of the Pf1 gene 5 protein have been expressed and purified. We have identified an N-terminal single-stranded DNA-binding domain (residues 1 to 105) that is much more globular than the intact protein (1 to 144). Larger fragments (1 to 115) as well as smaller fragments (1 to 91) were unable to bind DNA effectively. Analysis of the truncated proteins by gel retardation and fluorescence anisotropy indicates that the N-terminal domain binds DNA with a reduced affinity, due principally to a reduction in cooperativity, and that binding is highly concentration-dependent. Kinetic analysis shows that the rates of association and dissociation of the N-terminal domain from the complex with DNA are faster than those observed for the intact protein. The results suggest that the flexible C-terminal domain of the Pf1 gene 5 protein plays an important role in protein-protein interactions that stabilise adjacent protein dimers in the DNA-protein complex.

Biosensing Techniques↗

PubMed1998

Predicting forage indigestible NDF from lignin concentration.

We used chemical composition and in vitro digestibility data from temperate and tropical forages to develop relationships between indices of lignification and forage indigestible NDF. Neutral detergent fiber indigestibility increased nonlinearly as the lignin concentration of the NDF increased. Differences in estimated indigestible NDF using equations developed for a specific forage class (C3 and C4 grasses and legumes) were small and are probably not biologically significant when compared to those estimated from a common equation. Selected equations were compared with the Cornell Net Carbohydrate and Protein System (CNCPS) for the prediction of ADG. The linear equation (2.4 times NDF lignin content) used by the CNCPS and the Beef NRC had some of the largest errors due to mean bias. A log-log model [4.37 x (lignin/NDF)(.84)] provided the best combination of low total prediction error, low mean bias, and minimal error due to regression bias when permanganate lignin was used. A similar equation based on sulfuric acid lignin [6.17 x (lignin/NDF)(.77)] also met the above criteria. These equations then were evaluated with the CNCPS model against animal growth data from diets ranging in forage quality. Regardless of the equation used for predicting unavailable fiber, the CNCPS underpredicted daily gain, with mean biases ranging from -.10 to -.22 kg/d. Regression bias ranged from .13 to .14 kg/d and the coefficients differed from unity (P = .0001). The new equations gave numerically lower energy allowable ADG by steers compared to the linear equation currently used by the CNCPS model. The estimates were lower due to a higher predicted indigestible NDF, which resulted in a lower estimated forage energy value.

Animal Feed↗

PubMed1998

Effects of a dietary mixture of meat and bone meal, feather meal, blood meal, and fish meal on nitrogen utilization in finishing Holstein steers.

Our objective was to determine to what extent rate and efficiency of protein gain in finishing cattle can be enhanced by feeding an amino acid-balanced mixture of undegraded intake proteins. The Cornell Net Carbohydrate and Protein System (CNCPS) model was used to formulate a corn-based diet that would meet the rumen requirements for 410-kg large-framed steers with an estrogen implant and fed an ionophore. The CNCPS model was also used to formulate a highly undegradable intake protein (UIP) mixture from meat and bone meal, blood meal, fish meal, and hydrolyzed feather meal to provide the amino acids needed to supplement those derived from microbial protein to better meet amino acid requirements for growth. Four Holstein steers weighing 407 kg were offered a 90:10 concentrate-forage diet at hourly intervals at 95% of ad libitum intake. The steers were injected with 500 microg of estradiol-17beta at 12-h intervals to mimic the effects of an estrogenic implant. Treatments planned consisted of inclusion of the UIP mixture at 0, 2.5, 5, and 7.5% of the diet DM. Dry matter intake was fixed at 6.4 kg/d, and DM digestibility was not significantly affected by varying the amount of UIP addition. Apparent digestibility of N increased (P = .011) from 63.8 to 65.8, 70.7, and 71.5%, the amount of N absorbed increased (P = .001) from 73 to 84, 100, and 106 g/d, and N balance increased (P = .003) from 20 to 30, 33, and 39 g/d when UIP was fed at 0, 2.6, 5.2, and 7.8% of diet DM, respectively. The efficiency of N use increased 39.7%, and biological value increased 31.6% when the UIP mixture was added to the diet. Circulating concentrations of plasma urea N (PUN) were increased (P = .017) from 4.5 for the control diet to 5.7, 6.2, and 6.1 mg/dL when the UIP mixture was added at 2.6, 5.2, and 7.8%, respectively. Corresponding IGF-I concentrations were also increased from 491 to 558 and 624 ng/mL with 2.6 and 5.2% levels of UIP addition. Plasma glucose, NEFA, and insulin concentrations were not affected by feeding the UIP mix. The rate and efficiency of N use for growth improved with addition of an amino acid-balanced UIP mixture to the diet.

Amino Acids↗

PubMed1998

Evaluation of National Research Council and Cornell Net Carbohydrate and Protein Systems for predicting requirements of Holstein heifers.

This experiment evaluated the effects of prepubertal energy intake and dietary protein source on average daily gain of Holstein heifers. Holstein heifers (n = 273) were assigned to one of three dietary energy treatments that were designed to achieve average daily gains of 0.6, 0.8, and 1.0 kg/d from 90 to 320 kg of body weight. Within each energy treatment, heifers were assigned to diets that were supplemented with animal and plant proteins or plant protein and urea. Diets were formulated using the Cornell Net Carbohydrate and Protein System. Actual mean daily gains by heifers on each energy treatment were 0.68, 0.83, and 0.94 kg/d and were not affected by protein source. Undegradable intake protein was predicted by the Cornell Net Carbohydrate and Protein System to be adequate to support the observed daily gain that was allowed by the amount of energy in the diet and was 13 to 25% lower than the recommendations for undegradable intake protein by the National Research Council. These results suggested that requirements for undegradable intake protein may be met at concentrations that are less than 35% of the dietary crude protein. Energy equations from the National Research Council and Cornell Net Carbohydrate and Protein System were evaluated and accounted for 87 and 86% of the variation in body weight gain that was allowed by the amount of energy in the diet with biases of -7.7 and -5.7%, respectively. The Cornell Net Carbohydrate and Protein System has the primary advantage of improved accuracy in the prediction of nutrient requirements in each unique production situation.

Animal Feed↗

PubMed1998

Effects of three prepubertal body growth rates on performance of Holstein heifers during first lactation.

The effects of body weight (BW) gain, different sources of protein during the prepubertal period (90 to 320 kg of BW), and the performance of Holstein heifers during their first lactation were studied. Heifers (n = 273) were assigned to one of three dietary energy treatments that were designed to achieve average daily gains of 0.6, 0.8, and 1.0 kg/d. Within each energy treatment, different protein sources (plant protein and urea or both plant and animal proteins) were imposed. Actual average daily gains by heifers on each energy treatment were 0.68, 0.83, and 0.94 kg/d for heifers that were fed diets formulated for average daily gains of 0.6, 0.8, and 1.0 kg/d, respectively, which allowed the following ages at first calving: 24.5, 22.0, and 21.3 mo. Breeding was initiated when heifers weighed approximately 340 kg. Protein sources did not affect average daily gain or milk yield. Analysis of the preplanned comparisons of actual 305-d and 4% fat-corrected milk yields indicated that yield was significantly reduced for heifers grown at 0.94 kg/d (9387 and 8558 kg, respectively) compared with that of heifers grown at 0.68 kg/d (9873 and 9008 kg, respectively). However, further regression analysis of fat-corrected milk and residual milk from a test day model on prepubertal BW gain only explained 8 and 2% of the variation in milk yield, respectively. Postcalving BW and body condition score were different among treatments. Posttreatment factors, such as postcalving BW, accounted for more of the variation in milk yield than did prepubertal BW gain. Prepubertal BW gains, when evaluated on a continuum from 0.5 to 1.1 kg/d, explained little of the variation in milk yield; therefore, BW gain during the prepubertal period did not significantly affect milk yield during first lactation.

Adipose Tissue↗

PubMed1998

Accounting for the effects of environment on the nutrient requirements of dairy cattle.

The maintenance requirements of the Cornell Net Carbohydrate and Protein System were revised to evaluate the effects of activity, temperature, and humidity. Four dairy heifer situations were simulated (1 = clean and dry, 2 = moderately matted hair coat, 3 = condition 2 plus 10-cm lot mud from November to March, and 4 = condition 1 plus 16-kph wind) to represent typical conditions of the northern and southwestern US. In the northern condition, predicted daily gain was 0.88, 0.60, 0.53, and 0.68 kg/d for the four environmental situations; corresponding values for the Southwest were 0.88, 0.88, 0.78, and 0.88. Environmentally neutral daily gain was 0.94 kg/d to a BW of 603 kg at first calving at 20.3 mo of age. Calving age was increased when environmental stress extended the age at which puberty weight was reached. Calving weight was decreased when environmental stress occurred after conception. Twelve environmental conditions (variable temperature, humidity, and housing) for lactating dairy cows were simulated. At 30 degrees C and no night cooling, predicted milk production decreased 2.6 and 11.9 kg/d at 20 and 80% humidity, respectively. Increased activity reduced predicted milk production to 0.4 to 1.3 kg/d in confinement scenarios and to 0.9 to 7.5 kg in grazing scenarios.

Animal Nutritional Physiological Phenomena↗

PubMed1997

Length polymorphism within the second variable region of the human immunodeficiency virus type 1 envelope glycoprotein affects accessibility of the receptor binding site.

Sequential mutations were introduced into the V2 region of human immunodeficiency virus (HIV) type 1 HXB2, affecting the length, charge, and number of potential glycosylation sites. The insertions had no effect on cytopathicity or on the ability of virus to replicate in peripheral blood mononuclear cells and established T-cell lines. However, deletion of amino acids 186 to 188, encoding a conserved glycosylation site, resulted in a nonviable virus, suggesting a minimal length requirement of 40 amino acids for a functional V2 loop. However, all amino acid insertions affected the sensitivity of the variants to neutralization by soluble CD4 and monoclonal antibodies specific for epitopes in the V3 and CD4 binding site regions. Furthermore, these mutant viruses showed resistance to neutralization by HIV-positive human sera. Soluble gp120 mutant glycoproteins showed increased affinities for soluble CD4 and monoclonal antibodies specific for a number of epitopes overlapping the CD4 binding site, confirming that length increases in V2 affect exposure of the CD4 binding site. In summary, these data demonstrate that differences in V2 length modulate immunoreactivity of the envelope glycoprotein and support an association between the V2 and CD4 binding site regions.

Binding Sites↗

PubMed1997

Influence of monensin on Holstein steers fed high-concentrate diets containing soybean meal or urea.

We conducted two growth trials to evaluate the effects of monensin on amino acid sparing. When Holstein steers were fed a 90% concentrate diet supplemented with soybean meal (13.5% CP), the DMI, ADG, and efficiencies of feed and nitrogen utilization were greater than with urea (P < .10). Monensin improved ADG with both nitrogen supplements (P < .01), but the positive effects of monensin on efficiencies of feed (P = .12) and nitrogen (P = .26) utilization were greater for soybean meal than for urea. Increasing amounts of monensin (0, 11, or 22 mg/kg of DM) caused a linear increase in DMI with urea. Diets with soybean had greater intakes than diets with urea (P < .01); the greatest intake was of a soybean diet with monensin at 11 mg/kg of DM. Holstein steers fed soybean meal at 13.5% CP had lower DMI and greater efficiencies of feed and nitrogen utilization than steers fed 16.7% CP (P < .10). Crude protein level had no effect on ADG (P > .10). Monensin always increased the efficiencies of feed and nitrogen utilization (P < .05), but these trends were greater for diets with 16.7 than for those with 13.5% CP. Overall, monensin decreased DMI (P < .01), but this effect was greater for 16.7% than for 13.5% CP. Because the positive effects of monensin on diet NEg (P = .16) and efficiency of nitrogen utilization (P = .26) were greater for soybean meal than for urea, it seemed that monensin was sparing amino acids.

Animals↗

PubMed1997

Predicting carcass composition and individual feed requirement in live cattle widely varying in body size.

A total of 192 feeder steers of five breed types and body sizes commonly found in the United States cattle population were fed high-energy diets to three endpoints (275-, 300-, and 360-kg carcass weights) to determine their carcass composition. Before slaughter, ultrasound was used to predict fat thickness, longissimus muscle area, and marbling. Individual steer data were used for developing prediction equations, which were validated with three independent data sets. These data were used to develop and validate equations to predict carcass composition and DM requirements for individuals fed in pens and varying in breed type, body weight and size, and ADG. Equations to predict carcass weight during growth accounted for 84, 83, and 88% of the variation in the three data sets with 0, 1, and 3% bias. An equation to predict percentage of carcass fat from fat thickness and equivalent shrunk weight accounted for 96% of the variation in the percentage of carcass fat. An equation to predict yield grade from longissimus muscle area per 100 kg, fat thickness, and equivalent shrunk weight accounted for 93% of the variation. Dry matter requirement predicted by the system for individuals accounted for 48% of the variation in actual DMI with a 3% overprediction bias. The equations allow the user to allocate feed to individual animals in group-feeding environments along with marketing cattle on an individual basis at optimum endpoints given cattle types, feeding costs, and market prices.

Animals↗

PubMed1997

Evaluation of alternative equations for prediction of intake for Holstein dairy cows.

Six prediction equations for dry matter intake (DMI) were evaluated for accuracy with independent data. The equations were selected based on ease of parameter measurement and practical on-farm use. The equations were assessed for accuracy of predicting individual weekly DMI for primiparous (n = 105) and multiparous (n = 136) cows; three-fourths of these cows were supplemented with a sustained-release form of bovine somatotropin (bST). Large variations in accuracy were identified across the six prediction equations for effects of parity and bST. Prediction accuracy of all equations for cows in wk 1 to 24 of lactation was better for primiparous cows than for multiparous cows. Precision of prediction equations was poor for cows in wk 8 through 12 of lactation and for cows in > 40 wk of lactation. The equation for DMI with the best accuracy measured by a low total lactation mean square prediction error was the modified equation of the National Research Council: DMI (kilograms per day) = -0.293 + 0.372 x fat-corrected milk (kilograms per day) + 0.0968 x body weight 0.75 (kilograms). However, the overall mean bias (predicted minus observed) of the prediction of weekly DMI of a single cow was high for all equations, including the modified equation of the National Research Council. For wk 2, 4, 8, 10, and 20 of lactation, the mean bias for the modified equation was +6, +3.4, -1.3, -2.1, and -2.8 kg/d. The accuracy of prediction was lower for cows treated biweekly with bST. High yielding cows and cows treated biweekly with bST had higher milk yields in relation to body weight, and standardized prediction equations for DMI were less accurate.

Animal Nutritional Physiological Phenomena↗

PubMed1997

Development and evaluation of equations for prediction of feed intake for lactating Holstein dairy cows.

Improved prediction equations for dry matter intake (DMI) of Holstein cows that consume high energy diets were developed using regression techniques applied to a comprehensive database. The equations for predicting DMI, which were dependent on parity, accounted for the effects of milk yield, milk protein, body weight (BW), BW change, days pregnant, ambient temperature, relative humidity, and night cooling. A simplified prediction equation of DMI for farm application was developed and based on milk protein yield and BW at calving. An ambient temperature and a lag adjustment factor for early lactation were developed to improve accuracy of prediction of DMI of dairy cows in early lactation. The developed equations for DMI were evaluated against six independent data files. These equations accounted for 55 to 98% of the variation of the weekly group DMI of the independent validation data. The remainder of the variation in intake was attributed to diet, management, and undescribed animal factors. The equations developed in this study had a mean proportional bias of 5.6% and a mean square prediction error of 5.45 kg2/d. Predicted intake using the new equations was within 3 to 8% of actual intake. The new equations must be applied to situations in which Holstein dairy cows are fed highly digestible diets because dietary fill effects are not considered in these equations. The relationship of milk protein yield and DMI warrants further investigation.

Animal Nutritional Physiological Phenomena↗