Genetic Parameter Estimates of Milkability Traits in South African Holstein Cattle

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dc.contributor.advisor Bhebhe, E.
dc.contributor.advisor Banga, C. B.
dc.contributor.author Tshilate, Thendo Stanley
dc.date.accessioned 2017-10-30T06:27:21Z
dc.date.available 2017-10-30T06:27:21Z
dc.date.issued 2017-09-18
dc.identifier.uri http://hdl.handle.net/11602/924
dc.description MSCAGR (Animal Science)
dc.description Department of Animal Science
dc.description.abstract Milkability, or ease of milking, is the rate at which milk can be completely drawn from a cow’s udder. It is an important functional trait with regard to milking costs as well as udder health. Milkability traits have not been included in the breeding objectives of South African dairy cattle and their genetic parameters in the population have not been estimated. The primary objective of the study was to estimate genetic parameters for milkability traits in South African Holstein cattle. Data consisted of production and milkability records of 1 532 Holstein cows, from 6 herds, participating in the South African National Dairy Animal Recording and Improvement Scheme during the period 2015 to 2016 . Measures of milkability were average milk flow (AMF), maximum milk flow (MMF) and milking time (MT). Genetic parameters were estimated by a multi-trait sire model using the Restricted Maximum Likelihood (REML) procedure. Means for AMF, MMF and MT were 1.99 kg/min, 3.02 kg/min and 5.50 min, respectively. Non-genetic factors affecting variation in milkability traits were herd-year-season of calving, parity and milk yield. Heritability estimates for AMF, MMF, and MT were 0.23±0.09, h2 = 0.41±0.12 and h2 = 0.36±0.11, respectively. Genetic correlations between the three milkability traits were medium to high, ranging from -0.35±0.23 between AMF and MT to 0.79±0.09 between AMF and MMF. Correlations were positive between AMF and MMF and negative between MT and the other two traits. There was an increase in the mean EBV for AMF of 0.002 kg/min (0.0001 kg/min per year) during the period 2002 to 2014. Maximum milk flow also showed an increasing genetic trend of 0.04 kg/min (0.0003 kg/min per year) over the same period. The genetic trend for MT was undesirable, as it increased by 0.0003 kg/min. There is scope for improving milkability through selection, in South African Holstein cattle, as indicated by the moderate to high heritability estimates. The favourable genetic correlations among milkability traits imply that selection on one trait will result in a correlated improvement in the others. Results of the current study provide a basis for including milkability traits in the breeding objective for South African Holstein cattle. en_US
dc.format.extent 1 online resource (xi, 46 leaves : illustrations)
dc.language.iso en en_US
dc.rights University of Venda
dc.subject Genetic parameters en_US
dc.subject Average milk flow en_US
dc.subject Maximum milk flow en_US
dc.subject Milking time en_US
dc.subject Genetic trends en_US
dc.subject.ddc 636.2340968
dc.subject.lcsh Dairy farming -- South Africa
dc.subject.lcsh Holstein-Friesian cattle -- South Africa
dc.subject.lcsh Dairy cattle breeds -- South Africa
dc.subject.lcsh Milking -- South Africa
dc.subject.lcsh Cattle -- South Africa
dc.title Genetic Parameter Estimates of Milkability Traits in South African Holstein Cattle en_US
dc.type Dissertation en_US

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