The manipulation of egg size and egg quality

T.R. Morris Department of Agriculture and Horticulture, University of Reading, England Striking improvements in the efficiency of egg production have been achieved in many countries, with the result that eggs are cheap and the market is saturated. In these circumstances, the emphasis shifts from quantity to quality, though what is meant by quality differs considerably from place to place. Some markets pay more for brown eggs and others want only white eggs. In many countries, eggs are graded by mass, larger eggs being worth more per egg than smaller ones; but the premium on size varies considerably and the size of egg which commands the highest price per gram may be as low as 55 g or as high as 65 g. There are also markets where eggs are sold by number, regardless of their individual masses. Freshness is the first attribute to which attention is paid as markets get organized, but in some places 'fresh' means 'not rotten' whilst in other cases considerable care is taken to ensure that eggs are not more than a few days old when sold to the customer. The physical properties of the albumen and the yolk membrane deteriorate at a rate determined chiefly by temperature: An egg held for three days at 30°C loses more of its initial albumen quality than an egg held for 10 days at 5°C. The proper handling and storage of eggs after they have left the farm is therefore one of the most important determinants of egg quality, but this article will be confined to considering quality in the newly laid egg. First the geneticist's contribution to egg quality will be examined and then the attention will be turned to factors which the poultryman can manipulate on the farm.