Estimating Unit Costs of Nutrients from Market Prices of Feedstuffs

St-Pierre, N.R.; Glamočić, D.

doi:10.3168/jds.s0022-0302(00)75009-0

Cited by 21 publications

(15 citation statements)

References 8 publications

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“…Collinearity of significant variables was measured by the variance inflation factor. Variables were considered highly correlated when the variance inflation factor was >10 and removed from the model as explained by St-Pierre and Glamocic (2000). Inclusion of the random effect of study improves the accuracy of the final model, but using those solutions for predictions for future studies underestimates error for those predictions unless one accounts for the uncertainty surrounding the realized future study effect.…”

Section: Methodsmentioning

confidence: 99%

Intestinal digestibility of long-chain fatty acids in lactating dairy cows: A meta-analysis and meta-regression

Boerman

Firkins

St-Pierre

et al. 2015

Journal of Dairy Science

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The objective of this analysis was to examine the intestinal digestibility of individual long-chain fatty acids (FA) in lactating dairy cows. Available data were collated from 15 publications containing 61 treatments, which reported total and individual FA duodenal flows and calculations of intestinal digestibility. All studies involved lactating dairy cows, and estimates of digestibility were based on measurements either between the duodenum and ileum (18 treatments) or between the duodenum and feces (43 treatments). Fatty acid digestibility was calculated for C16:0, C18:0, C18:1 (cis and trans isomers), C18:2, and C18:3. Digestibility of C18:0 was lower than for C18:1 and C18:3, with no difference in digestibility between saturated FA (C16:0 and C18:0). We weighted the studies by the reciprocal of the variance to generate best-fit equations to predict individual FA digestibility based on duodenal flow of FA and dietary independent variables. The flow of C18:0 negatively affected the digestibility of C18:0 and was also included in the best-fit equations for all other 18-carbon FA using duodenal flow characteristics. The type of fat supplemented had an effect on digestibility of individual FA, with whole seeds having reduced digestibility. Our meta-analysis results showed minimal differences in the digestibility of individual FA. However, C18:0 flow through the duodenum had a negative effect on the digestibility of several individual FA, with the largest negative effect on C18:0 digestibility. The mechanisms that reduce C18:0 absorption at high concentrations are unknown and warrant further investigation.

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Section: Methodsmentioning

confidence: 99%

Intestinal digestibility of long-chain fatty acids in lactating dairy cows: A meta-analysis and meta-regression

Boerman

Firkins

St-Pierre

et al. 2015

Journal of Dairy Science

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“…Co-linearity between independent variables was assessed using their mutual correlations and the variance inflation factor (VIF) generated with PROC REG of SAS (SAS Institute Inc.). In general, estimability is assumed acceptable when all VIF are below 10 (St- Pierre and Glamocic, 2000). Observations from model (1) were considered as outliers when their studentized residuals were higher than three (Sauvant et al, 2008).…”

Section: Daniel Friggens Chapoutot Van Laar and Sauvantmentioning

confidence: 99%

Milk yield and milk composition responses to change in predicted net energy and metabolizable protein: a meta-analysis

Daniel

Friggens

Chapoutot

et al. 2016

animal

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Using a meta-analysis of literature data, this study aimed to quantify the dry matter (DM) intake response to changes in diet composition, and milk responses (yield, milk component yields and milk composition) to changes in dietary net energy for lactation (NE L ) and metabolizable protein (MP) in dairy cows. From all studies included in the database, 282 experiments (825 treatments) with experimentally induced changes in either NE L or MP content were kept for this analysis. These treatments covered a wide range of diet characteristics and therefore a large part of the plausible NE L and MP contents and supplies that can be expected in practical situations. The average MP and NE L contents were, respectively (mean ± SD), 97 ± 12 g/kg DM and 6.71 ± 0.42 MJ/kg DM. On a daily supply basis, there were high between-experiment correlations for MP and NE L above maintenance. Therefore, supplies of MP and NE L above maintenance were, respectively, centred on MP supply for which MP efficiency into milk protein is 0.67, and NE L above maintenance supply for which the ratio of NE L milk/NE L above maintenance is 1.00 (centred variables were called MP 67 and NE L100 ). The majority of the selected studies used groups of multiparous Holstein-Friesian cows in mid lactation, milked twice a day. Using a mixed model, between-and within-experiment variation was split to estimate DM intake and milk responses. The use of NE L100 and MP 67 supplies substantially improved the accuracy of the prediction of milk yield and milk component yields responses with, on average, a 27% lower root mean square error (RMSE) relative to using dietary NE L and MP contents as predictors. For milk composition (g/kg), the average RMSE was only 3% lower on a supply basis compared with a concentration basis. Effects of NE L and MP supplies on milk yield and milk component yields responses were additive. Increasing NE L supply increases energy partitioning towards body reserve, whereas increasing MP supply increases the partition of energy towards milk. On a nitrogen basis, the marginal efficiency decreases with increasing MP supply from 0.34 at MP 67 = −400 g/day to 0.07 at MP 67 = 300 g/day. This difference in MP 67 supply, assuming reference energy level of NE L100 = 0, equates to a global nitrogen efficiency decrease from 0.82 to 0.58. The equations accurately describe DM intake response to change in dietary contents and milk responses to change in dietary supply and content of NE L and MP across a wide range of dietary compositions.Keywords: dairy cow, milk composition, energy, protein, meta-analysis Implications Current feed evaluation systems are not suitable to predict animal responses to dietary changes. This paper quantifies average dry matter intake, milk yield and milk composition responses to change in net energy and metabolizable protein. The equations were derived from a meta-analysis of literature studies, which assembles a large number of dairy cow rations with a large range in dietary net energy and metabolizable protein contents.

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“…its weight in the determination of the slope, grows with its distance from the mean of the predictor variable. The extension of the leverage point calculations to more than one predictor variables is straightforward (St-Pierre and Glamocic, 2000).…”

Section: One Predictor Variablementioning

confidence: 99%

“…Leverage values should be examined. With fixed models (all effects in the models are fixed with the exception of the error term), variance inflation factors (VIFs) should be calculated for each predictor variable (St-Pierre and Glamocic, 2000). An equivalent statistic has not been proposed for mixed models (e.g.…”

Section: One Predictor Variablementioning

confidence: 99%

Meta-analyses of experimental data in animal nutrition

Sauvant

Schmidely

Daudin

et al. 2008

Animal

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367

315

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Research in animal sciences, especially nutrition, increasingly requires processing and modeling of databases. In certain areas of research, the number of publications and results per publications is increasing, thus periodically requiring quantitative summarizations of literature data. In such instances, statistical methods dealing with the analysis of summary (literature) data, known as meta-analyses, must be used. The implementation of a meta-analysis is done in several phases. The first phase concerns the definition of the study objectives and the identification of the criteria to be used in the selection of prior publications to be used in the construction of the database. Publications must be scrupulously evaluated before being entered into the database. During this phase, it is important to carefully encode each record with pertinent descriptive attributes (experiments, treatments, etc.) to serve as important reference points for the rest of the analysis. Databases from literature data are inherently unbalanced statistically, leading to considerable analytical and interpretation difficulties; missing data are frequent, and data structures are not the outcomes of a classical experimental system. An initial graphical examination of the data is recommended to enhance a global view as well as to identify specific relationships to be investigated. This phase is followed by a study of the meta-system made up of the database to be interpreted. These steps condition the definition of the applied statistical model. Variance decomposition must account for inter-and intrastudy sources; dependent and independent variables must be identified either as discrete (qualitative) or continuous (quantitative). Effects must be defined as either fixed or random. Often, observations must be weighed to account for differences in the precision of the reported means. Once model parameters are estimated, extensive analyses of residual variations must be performed. The roles of the different treatments and studies in the results obtained must be identified. Often, this requires returning to an earlier step in the process. Thus, meta-analyses have inherent heuristic qualities.

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Estimating Unit Costs of Nutrients from Market Prices of Feedstuffs

Cited by 21 publications

References 8 publications

Intestinal digestibility of long-chain fatty acids in lactating dairy cows: A meta-analysis and meta-regression

Intestinal digestibility of long-chain fatty acids in lactating dairy cows: A meta-analysis and meta-regression

Milk yield and milk composition responses to change in predicted net energy and metabolizable protein: a meta-analysis

Meta-analyses of experimental data in animal nutrition

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