Pellets of chromic oxide (Cr2O3) and dental plaster for administration of Cr2O3 to ruminants were developed by Pigden and Brisson (1957). When Cr2O3 was administered to sheep in this manner, Troelsen (1961) observed that digestibility coefficients determined by the Cr2O3-ratio method were very variable, and deviated from those obtained by total collection of faeces. It was also observed that the rate at which the pellets disappeared from the rumen or reticulum was correlated with the percentage of alfalfa hay (r = 0 83) and oat grain (r = –0 80) in the diet and that the abomasal ingesta contained pellets or pieces of same in the process of disintegration.

Muscle colour has been recorded on pigs tested at the national pig progeny testing stations in Great Britain since 1958. From September 1960 a muscle colour score on a scale of 1 to 7 points has been given by comparing the muscle colour with a series of seven coloured discs of increasing colour intensity. These discs were prepared specifically (by Tintometer Ltd. Of Great Britain) to score muscle colour in pigs. The higher the colour score the more desirable the colour was adjudged to be by the testing station personnel. However, scores of 6 and 7 were very infrequent and no assessment of their desirability was made. Carcasses were cut at the last rib on the day after slaughter at about 200 lb. live-weight and muscle colour was scored on the cut surface of the longissimus dorsi muscle (eye muscle).

Blood groups and haemoglobin (Hb) variants are well defined genetical characters in man and animals. In 1940 Irwin and his associates initiated the study of cattle blood groups in Wisconsin by following the immunization method and haemolytic technique. Now several laboratories all over the world are engaged in this type of study in cattle and other species of animals. There are about 80–90 antigenic factors known comprising eleven blood group systems in cattle (Stormont, 1962).