Egg shell quality was assessed in terms of breaking strength, elasticity, and energy absorbed by the shell up to failure. Two devices were used to determine these characteristics. Simple correlation and simple linear regression analyses showed that elasticity as determined by either device gave equally reliable estimates of breaking strength of the egg shell (r = -.68). A study of the three calcium levels supplemented to a basal ration on shell quality of eggs from two reciprocal crosses of birds showed that each measurement (breaking strength, elasticity, and energy to failure) used to assess shell quality produced different conclusions. In the early part of the experiment, elasticity was significantly lower for the 2% than for the 4% or 6% calcium diets in both crosses of birds. However, there was no significant difference in the effect of 4% and 6% calcium diets on elasticity. On the basis of the energy absorbed to failure, there was no significant effect of dietary calcium in Cross I birds. In Cross 2 birds, 6% calcium produced significantly superior results on energy absorbed as compared to the 2% and 4% calcium diets. For Cross I birds, breaking strength of eggs from the 6% and 4% dietary calcium treatments were significantly higher than those from the 7% calcium treatment. For Cross 2 birds, 4% dietary calcium produced stronger shells than 2%; shell strength from the 6% calcium treatment was inter, mediate to and net significantly different than that of the 2% or 4% calcium diets. No significant difference in the effect of the three calcium diets on shell quality as assessed by any one of the three measurements was observed in the latter part of the experiment. No consistent effect of the age of birds on egg shell strength was apparent. Significant variation in shell strength was found among groups of birds within the same cross on the same ration. Eggs stored under selected environmental conditions for different durations showed that moisture affected egg shell elasticity and the effect Increased In magnitude with time of storage when the egg was not only Immersed in water but also filled with water after removal of the albumen and yolk. Neither oiling nor storage temperature affected egg shell elasticity. There was no consistent effect of storage duration on egg shell elasticity except for the two treatments in which eggs with or without the contents removed were stored under water. It was found that the difference between the two duplicate elasticity readings measured at the equator of the same egg did not change significantly with either storage condition or storage duration. / Land and Food Systems, Faculty of / Graduate

A study was conducted to make a genetic evaluation of egg mass (weight of the total eggs laid in a given period) in order to determine its genetic potential as a new criterion for selection as compared to the conventional selection program based on egg number (early and full production records). In addition, biometrical evaluations of some egg component traits: yolk weight, albumen weight, shell weight, percent yolk, percent albumen, percent shell, albumen percent solid, yolk percent solid, yolk percent protein, albumen percent protein, yolk solid and albumen solid were made. The aforementioned traits were measured on 3 random bred lines of chickens in quarterly periods through the laying year. Within each line, the heritability estimates of egg number and egg mass for any given period (275, 325, 450 and 540 days of age) were found to be in close agreement. In general, for egg number and egg mass, selection from early production records showed higher gains per unit of time than full year production records, A negative genetic correlation between egg number traits and egg weight traits and a positive genetic correlation between egg mass and egg weight traits was found, therefore, selection for egg mass was recommended. Relative merit of early and full year egg records as selection criterion was discussed in the light of the results obtained for the three lines. It was concluded that the decision as to which criterion should be used would have to depend upon the genetic properties of the population in question. Line effects were found to be significant for all the egg component traits studied, except percent shell, A season-age effect was also found to be significant in all the traits studied. Season-age by sire interactions were found to be non-significant for all the traits in all the three lines. The importance of yolk size from a human nutrition standpoint was discussed. A selection program based on total yolk weight produced by a hen in a given period (yolk mass) was suggested. Because of the water in the egg being an essential nutrient for the developing chick embryo, it was suggested that selection be made on the egg solid or egg solid mass (total amount of solid laid by a hen in a given period). The heritability estimates of albumen percent solid and albumen percent protein were high and of the same magnitude. It was, therefore, suggested that an increase in percent protein in albumen should be achieved by selection of albumen percent solid. / Land and Food Systems, Faculty of / Graduate

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