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A Comparison of Guernsey Sires

II. Based on the Average Mature Equivalent Fat Production of Daughters During the Month of Maximum Production

Department of Dairy Husbandry, University of Missouri, Columbia, Missouri

ABSTRACT

1. Rather than to attempt a factorial analysis of the milk secreting function of the dairy cow, it is proposed that the characteristics of the lactation curve be studied in order to group together all factors which may affect certain parts and to study these characteristics from a genetic standpoint.
   
2. The two most important characteristics of the lactation curve of milk secretion are believed to be the height of production of milk and fat during the maximum month or other convenient unit of time, and the persistency of secretion or the rate of decline of production.
   
3. A study was made of Guernsey Advanced Registry records to determine the relative effect of the sire and dam on the daughters maximum fat production.
   
4. The results were expressed by the two following equations:(1) Daughter's maximum fat production = 0.20 x dam's maximum fat production + siren's potential transmitting ability(2) Siren's potential transmitting ability = daughter's maximum fat production – 0.20 x dam's maximum fat production
   
5. The cytological studies indicate that the sire and dam contribute the same number of chromosomes to the female. The male is the result of the usual number of chromosomes from the dam and one less from the sire. This is taken to indicate that the above results can not be explained by sex-linked inheritance.
   
6. The results are believed to be explained by assuming that the majority of the genes concerned in the inheritance of large fat secretion are dominant over small secretion. Such being the case, the only true test of an animal's transmitting ability is a test of the progeny as compared to a performance record.