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Subject: search.filters.subject.Dairy cattle physiology

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    A study of diurnal rhythms in milk and fat production in the cow : a thesis submitted in partial fulfilment of the requirements for the degree of Master of Agricultural Science in the University of New Zealand
    (Massey University, 1954) Linklater, Peter Munro
    When cows are milked under commercial conditions milk yields are normally greater in the morning than in the evening, mainly because a longer time interval precedes the morning milking. In addition the percentage of fat in the milk is generally lower in the morning and higher in the evening. The alternation of high milk yields of low fat percentage, with lower milk yields of higher fat percentage, form a diurnal rhythm. This will depend partially on the length of time between morning and evening milkings, for the difference in yield and fat percentage is reduced as the time intervals approach equal length. There is left in the udder after a normal milking an appreciable quantity of milk of high fat percentage which has been termed "residual milk". In a hypothetical case if the volume and fat percentage of this milk remained constant after each milking, then the yield obtained from the udder would represent synthesis, and any diurnal rhythm would be caused solely by synthesis. However, neither the amount, nor the fat percentage of the residual milk remains constant at morning and evening milkings. Thus the diurnal rhythm may be attributed to two general causes, firstly synthesis, and superimposed on to this a diurnal variation in residual milk.
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    Genome-wide association study for stature in New Zealand dairy cattle : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Animal Science at Massey University, Palmerston North, New Zealand
    (Massey University, 2013) Tan, Mun Ee
    The objective of this thesis was to perform a genome-wide association study (GWAS) to identify single nucleotide polymorphism (SNP) associated with stature in New Zealand dairy cattle. The phenotype data set used for this study contained the animal key, sire code of the bull, birth date, breed code, proportion of Holstein-Friesian genes, proportion of Jersey genes, percentage of North American Holstein genes, estimated breeding values (EBV) for live weight and stature and their reliabilities of 3140 bulls. The genotype data set contained the genotype of 692,598 SNPs for every bull and another file contained the name and position of the SNPs. The GWAS was performed on Holstein-Friesian, Jersey and Holstein-Friesian × Jersey crossbred bulls using PLINK software version 1.07. Stature EBV was used as the phenotype. The phenotypes were adjusted for percentage of Holstein-Friesian, Jersey, North American Holstein genes and year of birth using multiple regression. Manhattan plots and multi Manhattan plots of P-values adjusted to genomic control against the chromosomes were plotted to identify top SNPs with the most significant P-values above the significant threshold line. Based on the top 50 SNPs according to the P-value, this study identified nine chromosomes or BTA in the HF population with SNPs significantly associated with stature, BTA2, 3, 4, 5, 6, 11, 12, 14 and 24. SNPs with significant effect on stature were detected in six chromosomes, BTA9, 10, 12, 18, 19 and 25 in the JE population while the SNPs determined to be significantly associated with stature were located on eleven chromosomes, BTA1, 3, 4, 5, 7, 9, 10, 14, 18, 22 and 24 in the XB population. Several SNPs located above the suggestive threshold in the Manhattan plots were also inspected and kept in view for future studies. The results from this study suggest that the highlighted SNPs with significant associations to stature can serve as candidate SNPs for further investigation to determine the regions of QTLs and ultimately the exact genes that affect stature with other correlated traits in dairy cattle.