Maintenance requirement and energetic efficiency of egg production calculated according to different models

Maintenance requirement and efficiency of ME utilization for production can be estimated by means of regression analyses between ME and a number of variables of energy metabolism. The data from series G has been applied to dif-ferent models as the measurements of energy metabolism in this series were carried out in individual balances and respiration experiments with the hens kept singly showing a low activity considered to be at minimum during the lay-ing period. Because of negative energy balances (EBAL) in 29 observations, mostly at the begining of laying period, these measurements were omitted and the calculations were performed with 52 observations with positive EBAL.

Model with one-dimensional regression. In order to calculate the main-tenance requirement (ME^m) and the overall efficiency of ME utilization for EBAL and for deposition of energy in eggs produced (kgo) the total energy re-tention per metabolic body weight (EBAL + OE)/W,kg075 was regressed on ME/W,kg°75 and the following one-dimensional model was applied:

Model 1

(EBAL + OE)/W,kg075 = a + kg0 x ME/W,kg0-75

The model provides an estimate of the overall efficiency (kgo) of ME utiliza-tion for EBAL and energy deposiutiliza-tion in eggs produced (OE) and by extrapo-lating ME to zero level of total energy retention the maintenance requirement can be found as ME^m/W,kg⁰-⁷⁵ = a/k^g0. There were no significant (P > 0.05) dif-ferences between groupwise regressions within periods (cf. Chapter 2.7) and there was no significant difference between regressions calculated for the first four periods versus the last four indicating no influence of the age of hens on MEm and kg0. Subsequently the total regression for all observations (n=52) dur-ing the laydur-ing period from 26 to 47 weeks of age was performed givdur-ing the fol-lowing equation:

(EBAL + OE),kJ/W,kg⁰-⁷⁵ = -287 + 0.71 x ME,kJ/W°⁷⁵ se: 54.9 0.065

n = 52, RSD = 35.1, CV = 11.3%, R² = 0.704

The regression gave a maintenance requirement of 404 kJ/W,kg075 and the overall efficiency of ME utilization for EBAL + OE was kgo = 0.71.

Models with multiple regressions. Metabolizable energy is partly used for maintenance, partly for EBAL and partly for energy deposition in eggs produc-ed (OE) and therefore the following model can be written:

Model 2

ME = a + t>! x W,kg°75 + b2 x EBAL + b3 x OE

If the intercept (a) is not significant then the regression coefficient b^: can be considered as an estimate of maintenance requirement per metabolic body weight (ME^m/W,kg°⁷⁵). Regression coefficient b² is the cost of the energy bal-ance and its reciprocal is the efficiency of ME utilization for EBAL (k^g). The re-gression coefficient b3 is the cost of energy deposition in eggs produced (OE) while the value l/b3 is equal to an efficiency of ME for OE (ko). As the intercept was not significantly (P > 0.05) different from zero the regression was calcu-lated through the origin and the following function for the measurements in series G with positive EBAL was obtained:

ME,kJ= 414 x W,kg075 + 0.86 x EBAL,kJ+ 1.56 x OE,kJ se: 44.4 0.090 0.189 n = 52, RSD = 52.6, CV = 5.10%

The regression was calculated with satisfactory precision, as the coefficient of variation (CV) was 5% and R² from the regression with intercept was 0.787.

The equation gave a maintenance requirement of 414 kJ/W,kg⁰⁷⁵, the effi-ciency of ME utilization for EBAL kg = 1.16 (1/0.86) and the efficiency of ME utilization for energy deposition in the eggs produced ko = 0.64 (1/1.56).

In order to estimate the efficiencies of ME utilization for energy deposition in protein (OPE) and fat (OFE) in eggs produced, the following model has been applied:

Model 3

ME = a + bj x W,kg⁰⁷⁵ + b² x EBAL + b³ x OPE + b⁴ x OFE

The calculations showed that the intercept was not significant (P > 0.05) and the regression through the origin gave the following result for the observations in series G with positive EBAL:

ME,kJ= 419 x W,kg se: 46.0

0-75 0.84 x EBAL,kJ 0.095

1.99xOPE,kJ+ 1.27xOFE,kJ 0.079 0.056

n = 52, RSD = 54.3, CV = 4.54%

The precision of the regression was satisfactory, CV was 4.5% and R2 from the model with intercept was 0.759. The regression gave a maintenance require-ment of 419 kJ/W,kg°⁷⁵ and nearly the same coefficient for EBAL as in model (2). The cost of protein deposition was 2.0 kJ per 1 kJ OPE and the cost of fat deposition was 1.3 kJ per 1 kJ OFE. The values of the partical efficiencies were therefore k^op = 0.50 and k^of = 0.79.

The partition of ME. In order to summarise the calculations performed, the individual data of energy metabolism together with the estimated maintenance requirement and energetic efficiency of egg production was used in the parti-tion of ME for the hens with positive EBAL in series G. All data were calcu-lated per W,kg°75 and the mean values are demonstrated in Fig. 8.2.

MEg = 79

OPE = 99 OE = 229

= 0.80

OFE=124

Figure 8.2. Partition of metabolizable energy based on the results from series G with posi-tive EBAL. Mean values expressed per W,kg075.

Fordeling af omsættelig energi baseret på resultaterne fra serie G med positiv EBAL. Mid-delværdier udtrykt pr. W,kg°-75.

The three regression models gave ME^m about 410 kJ/W,kg⁰⁷⁵ and this value was inserted in the calculations of ME available for production (MEgo) as MEgo

= ME - MEm, giving MEg0 of 432 kJ/W,kg075 and indicating that 51% of the total ME was used for production. The MEg0 is partly used for EBAL and partly for OE. The ME available for OE (ME⁰) was calculated by dividing the value of OE with the coefficient k⁰ estimated to 0.65 by means of model 2 if ME^m is 410 kJ/W,kg°⁷⁵. In relation to the total ME, the ME^O was 42%. The difference between MEgo-MEO is MEgbeing 79 kJ/W,kg075 which in relation to the total ME was 9%. The ME0 consists of ME available for protein energy deposition (MEop) and for fat energy deposition (MEof) in eggs produced. These values were calculated by dividing the OPE and OFE by the coefficients k^op and k^of which for simplicity in calculation were rounded to 0.50 and 0.80 respectively.

The small disagreement between the value of OE and the sum of OPE + OFE was caused by OE being measured directly in a calorimetric bomb while OPE and OFE were calculated from nitrogen and fat content in eggs (cf. Chapter 2.6). The ME^op and ME^of in relation to ME⁰ were 56% and 44% respectively.

8.3 The effect of temperature, origin and housing on energetic efficiency of egg