Date of Award:

1978

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Animal, Dairy, and Veterinary Sciences

Committee Chair(s)

Jay O. Anderson

Committee

Jay O. Anderson

Committee

John E. Butcher

Committee

Ronald V. Canfield

Committee

Joseph C. Street

Committee

Thomas F. Emery

Committee

Paul V. Fonnesbeck

Committee

D. G. Hendricks

Abstract

Previous work at Utah State University determined minimum levels of different nutrients that would produce the maximum rate of gain or gain/feed ratio by feeding graded levels of the nutrients. Fitting broken lines to the data from work with one nutrient tended to underestimate the minimum requirement for that nutrient. It appeared that the response was not linear up to the level required to give maximum performance as the "broken line" approach to estimating the requirement assumes. It seemed worthwhile to try to describe the relation between ration level of a nutrient and chick performance by means of a mathematical equation. Even more valuable equations would be those that expressed accurately the relation between the dietary levels of two ration variables and different performance measures.

Protein and energy are the two most costly items in broiler diets. The first objective of these studies was to compare the performance of chicks fed diets with graded levels of both protein and energy and describe by means of mathematical equations the relationships found. Several measures of performance or performance parameters would be considered. A second objective was to estimate the energy required for maintenance and for deposition of fat and protein by regression analysis.

Semi-practical type diets with ten levels of protein from 15 to 28.5% at 1.5% increments and with six added fat levels (1, 3, 4.5, 8, 11.5 and 15%) were fed to 82 groups of Hubbard chicks from one to 20 days of age. At least one group of five males and one group of five females were fed each energy-protein combination.

Weight gain, feed consumption and gain/feed ratio were recorded. Weight gain ranged from 300 to 443 g, feed consumption ranged from 500.4 to 663.3 g, ME intake ranged from 1574 to 2058 kcal and gain/feed ratios ranged from .551 to .758. Carcass moisture was determined by freeze-drying and the values found ranged from 63.51 to 71.52%. The percentage of fat in the dry matter was determined by chloroform-methanol extraction; the values noted were from 28.33 to 46.75%. The percentage of protein in the dry matter was determined by macro-Kjeldahl method; the values were from 40.20 to 59.30%. Protein gain was calculated by substracting grams protein of the one-day-old chick (7.4) from grams protein of the experimental chicks. Ranges of protein gained were from 43.7 to 70.5 g/chick. Gross energy in the dry matter of the carcasses from 24 chicks selected to cover the ranges of protein and energy levels fed was determined by the bomb calorimeter. Regression analysis of this data gave the following equation relating gross energy in the dry matter to percentage of protein and fat in the dry matter:

GE(kcal/g) of DM = 6.95 + .0276(percent fat in DM) - .0308(percent protein in DM)

From this equation, GE per gram of dry matter and per gram of live weight were calculated. The GE ranged from 5.92 to 7.01 kcal/g for the former and from 1.69 to 2.56 kcal/g for the latter. Energy gains were calculated by subtracting the carcass GE of the dry matter of the one-day-old chick (59.67 kcal) from the final carcass GE of the experimental chicks. The values ranged from 656 to 1017 kcal/chick.

Gross energy in the chloroform-methanol extract from 12 chicks was determined and averaged 8.45 kcal/g with a range of 8.10 to 8.86 kcal/g.

Using these data, equations were found by regression analysis that expressed weight gain, gain/feed ratio, percent carcass moisture, percent protein and fat in the dry matter, gross energy in the dry matter and in the live chick, energy gain and protein gain as functions of dietary levels of protein and energy, their square terms and their product. Equations developed accounted for 60 to 90% of the total variation in the different parameters.

About 21 to 24% protein was required for maximum weight gain. Addition of fat to the diets tended to increase gain. This level of dietary protein also produced maximum protein gain. Additional fat did not increase this parameter.

Gain/feed ratio increased as both protein and energy levels of the diet increased.

Moisture level of the carcass and protein in the dry matter increased with an increase of protein in the diet and decreased with dietary fat addition. Fat in the dry matter decreased with an increase of diet protein and increased with addition of fat.

Gross energy per gram of dry matter and per gram live chick increased with fat addition to the diet and decreased as diet protein increased. Energy gain increased as fat level or protein level was increased. Efficiency of energy gain tended to be greater with diets that produced a high fat level in the carcass.

It was concluded that a diet with 21 to 24% protein and 1 to 3% added fat would be most appropriate for broiler chicks during the first three weeks of the growing period. Higher fat levels resulted in higher gain/feed ratios and more efficient energy gain, but they also produced chicks with excess body fat.

Regression equations developed indicated that the chick performance changed as diet nutrient density increased while holding energy/protein ratio constant. Weight gain, gain/feed ratio, energy consumption, energy gain and fat or energy in the carcass increased as nutrient density increased. Carcass moisture and protein in the dry matter decreased. Energy and protein consumption per unit of gain were minimum and protein gain and the energy gain/energy intake ratio were maximum with an intermediate nutrient density. However, the rations producing these maxima or minima contain rather high levels of fat and produced a carcass with more fat than might be desirable.

Regression analysis, relating metabolizable energy intake to fat and protein gain, was done on all data and subsets of data. In four separate analyses, data were grouped according to diet protein level, added fat level, energy/protein ratio, and sex. Equations gave estimates of energy required for maintenance and deposition of body fat and protein. Most estimates of the energy cost of fat or protein deposition were lower than their gross energy. When subsets of the data were analyzed there appeared to be greater variation in these estimates than random variation would explain. The energy cost of fat and protein deposition appeared to differ as the ration fat and protein levels were changed over the wide ranges fed to these chicks.

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