Genetic and genomic studies of animal welfare and environmental traits in dairy cattle : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science, School of Agriculture and Environment, Massey University, Palmerston North, New Zealand

Simple item page
dc.confidentialEmbargo : Noen_US
dc.contributor.advisorLopez-Villalobos, Nicolas
dc.contributor.authorAriyarathne, Hewa Bahithige Pavithra Chathurangi
dc.date.accessioned2021-04-16T01:41:04Z
dc.date.accessioned2021-07-27T03:43:30Z
dc.date.available2021-04-16T01:41:04Z
dc.date.available2021-07-27T03:43:30Z
dc.date.issued2020
dc.description.abstractNew Zealand dairy cows graze outdoors throughout the year and are exposed to a wide range of weather conditions also their excreta are dispersed in the paddock. There is an emerging interest in whether between-cow genetic variation could contribute to environmental sustainability and improved animal welfare. The initial objectives of the study were 1) to estimate genetic parameters of rectal temperature (RT) as an indicator of heat stress (HS), 2) to identify gene regions associated with HS through genome-wide association studies (GWAS), and 3) to estimate response of genetic selection for low HS on milk production using conventional selection in grazing dairy cows of New Zealand. The genetic variance of RT estimated in 776 mixed-breed cows at two Massey University experimental dairy farms was very low due to insufficient environmental stress on sampling days. This outcome diverted the topic of study to the genetic basis of milk urea concentration (MU) and efficiency crude protein utilisation (ECPU) and their potential role in improved environmental sustainability. The new study was conducted considering MU as the trait of interest. Additionally, the possible reduction of urinary nitrogen (N) excretion by genetic selection for low milk urea N concentration (MUN) was determined. The heritability estimated for MU (from 0.27 to 0.49) and ECPU (from 0.02 to 0.41) using a random regression model in 634 mixed-breed cows indicated that these traits can be genetically manipulated by direct selection. Estimates of genetic correlations between MU and yield of milk, fat, crude protein, lactose, and liveweight (LWT) in each day of ii lactation were mostly positive and imply that selection for reduced MU would result in reduced production and LWT of cows. The GWAS identified six novel genes (GMDS, E2F7, SIAH1, SLC24A4, LGMN, ASS1) associated with MU that function in protein catabolism, urea cycle, ion transportation and N excretion. This suggests that genomic selection for MU is possible, however, the results should be validated with a larger sample size. Selection index theory was used to estimate correlated responses for different selection indices including MUN with different relative emphasis (RE). The predicted genetic responses per cow per year of the current index were 16.4 kg milk yield (MY), 2.0 kg fat yield (FY), 1.4 kg crude protein yield (CPY), -0.4 kg LWT and -0.05 mg/dl MUN. Including MUN in the selection index with 20% negative RE resulted in annual responses of 5.4 kg MY, 1.6 kg FY, 1.0 kg CPY, -1.1 kg LWT and -0.17 mg/dl MUN. The total N predicted to be excreted in the base year was 336.5 kg/ha. When stocking rate was adjusted by changes in milk production and cow feed requirements, 10 years of selection with a selection index not including MUN increased total N excretion to 338.9 kg/ha. A selection index with 20% negative RE for MUN increased total N excretion to 341.6 kg/ha, and genetic gain in production of milk protein per hectare was reduced, thereby reducing farm profits. The results of this thesis indicate that inclusion of MUN in a selection index with negative RE is not an effective pathway to reduce farm-level N leaching and carbon footprint.en_US
dc.identifier.urihttp://hdl.handle.net/10179/16531
dc.publisherMassey Universityen_US
dc.rightsThe Authoren_US
dc.subjectDairy cattleen
dc.subjectNew Zealanden
dc.subjectGeneticsen
dc.subjectSelectionen
dc.subjectFeed utilization efficiencyen
dc.subjectEnvironmental aspectsen
dc.subjectAnimal welfareen
dc.subject.anzsrc300302 Animal managementen
dc.titleGenetic and genomic studies of animal welfare and environmental traits in dairy cattle : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science, School of Agriculture and Environment, Massey University, Palmerston North, New Zealanden_US
dc.typeThesisen_US
massey.contributor.authorAriyarathne, Hewa Bahithige Pavithra Chathurangien_US
thesis.degree.disciplineAnimal Scienceen_US
thesis.degree.grantorMassey Universityen_US
thesis.degree.levelDoctoralen_US
thesis.degree.nameDoctor of Philosophyen_US
Files
Original bundle
Now showing 1 - 1 of 1
Thumbnail Image
Name:
AriyarathnePhDThesis.pdf
Size:
1.89 MB
Format:
Adobe Portable Document Format
Description:
Download
Collections
Theses and Dissertations