The objective of the first part of this study was to observe and describe the profile of test-day somatic cell counts throughout a lactation in individual cows, and to examine the correspondence between such profiles and various lactation measures of cell count presently available. The objective of the second part of the study was to obtain estimates of the genetic and phenotypic parameters of lactation measures of cell count in different lactations, possibly for use in a breeding program. / In the first part of the study, the lactation cell count profiles of eighteen Holstein heifers of the Macdonald College Herd were individually examined. Weekly cell counts were expressed as deviations from the herd test-day average and plotted against week of test. A labile cell activity was found for most of the plotted lactations. The cellular responsiveness of cows facing external challenges seemed a trait peculiar to each individual. Lactation measures of cell count were unable to give good descriptions of cell count profiles of individual cows. However, they were better expressions of the lactation cell count performance than single test-day observations. / In the second part of the study, monthly cell count observations were obtained between February, 1977, and February, 1982, for the Holstein cows in herds enrolled on the official option of the Quebec Dairy Herd Analysis Service. Maximum likelihood, I-MINQUE (iterative Minimum Norm Quadratic Unbiased Estimation), and multivariate REML (Restricted Maximum Likelihood) procedures were used for the estimation of genetic and phenotypic parameters. / Repeatabilities of log test-day cell counts and log of test-day cell counts corrected for milk yield varied between 0.36 and 0.42 in first, second, third, fourth, and fifth and later lactations. Repeatabilities of test-day cell counts (cells/ml) in the five lactation groups varied between 0.17 and 0.25. Repeatabilities of lactation expressions for cell count between lactations ranged from 0.13 to 0.44. / Heritabilities of lactation expressions of cell count were low and varied from 0.06 to 0.14 in the five lactation groups examined; however, the genetic correlations between lactations were very close to unity, 0.90 to 0.97.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.71905 |
| Date | January 1984 |
| Creators | Monardes, Humberto Gonzalo. |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Animal Science.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 000182331, proquestno: AAINK66646, Theses scanned by UMI/ProQuest. |
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