Milk yield Shape of the lactation curve Sex linkage Butterfat Protein Other constituents Colour and flavour Vitamin content Curd tension Conformation Efficiency of production and growth The progeny test Reproduction and wastage Breed and herd construction-inbreeding Tropical Artificial insemination MILK YIELD So long as any studies are made upon the inheritance of milking capacity, so long will there be debate as to the relative influence of heredity and environment. In past reviews on this subject, emphasis has been laid upon the work of Von Patow, who produced the "byre average" as a means for assessing the true genetic worth of dairy cattle. In the last review a paper by Lush was quoted, treating the "byre average" from a purely statistical angle, in which he showed that the method was unlikely to lead to a Mendelian analysis which corresponded to reality. The outstanding paper which now falls for review is by Lortscher(l), a Swiss investigator, who has worked in Edinburgh at the Institute of Animal Genetics, under von Patow at Berlin, and with Dr Schmidt at Zurich. Some 4000 lactation records of 1200 cows from a group of British Friesian herds (Terling-Lavenham) in England provide the data. The yields of the individual cows, reduced to the "byre average" by the von Patow formula, were shown to normalize the frequency of distribution, as predicted by Lush. The figures obtained were found to fit von Patow's genetic hypothesis of milk inheritance. Out of 833 daughter-dam comparisons, in only 0-6% was the genotype of the one not in agreement with that of the other. The genotype of the bulls was ascertained by comparing the genotypes of the daughters to their dams. Of forty-three bulls with at least five tested daughters, all were heterozygous for the three factors belonging to those genetic classes which allow the largest possible combinations of genes when mated to cows of all classes. With the bulls arranged according to the periods they were in service in the herds, the distribution of their daughters, with respect to the seven genetic classes, does not show any increasing asymmetry, and for only two of the forty-three bulls was there a small, but significant, difference between the mean of the daughters and of their dams. Accordingly, the author is forced to the deduction that, according to von Patow's hypothesis and method of investigation, there has been in these herds no success as a result of selective breeding for high milk production during the past 20 years. Employing Krtiger's adaptation of the "byre average" (where the yields are corrected for certain environmental factors before being reduced to the average) no significant difference was