Genetic Parameters for Udder and Teat. Type Traits in Icelandic Cattle Breed

Udder balance, fore udder attachment, udder support, udder depth, teat structure, teat length, teat thickness, teat position and teat tip of Icelandic Cattle have been described on a linear scale since 1995. Udder and teats now weigh 20% in Icelandic Cattle’s total merit index, but udder balance, teat structure and teat tip are not included in breeding value estimations. The main objective of this study was to estimate genetic parameters for udder and teat type traits of Icelandic Cattle, but also to describe the traits’ phenotypic structure, to estimate their genetic trends, and to review the current breeding value estimations of udder and teats for Icelandic Cattle. Udder and teat type scores of 76,628 Icelandic Cattle were used for the study’s analyses. Variance components were estimated by linear bivariate animal models. Icelandic Cattle’s current genetic model was compared to four alternative models, differing in fixed and random effects. Correlations among the udder and teat type traits, genetic correlations of udder and teat type traits between first and second lactating cows, and correlations of udder and teat type traits and first lactating somatic cell score were estimated. Breeding values were estimated, and genetic trends were reviewed. Phenotypic variances of udder and teat type traits were small, as more than half of the viewed cows received the same scores for udder balance, teat structure, teat thickness, teat position and teat tip. Heritability of udder and teat type traits ranged from 0.11 to 0.36, lowest for udder balance and udder support, but highest for teat length. Correlations between udder and teat type traits were favorable. Correlations between udder and teat type traits and somatic cell score were favorable, where cows with back-heavy, poorly attached, weakly supported, and deep udders, long, thick, and outwardly positioned teats had higher somatic cell scores during their first lactation. Genetic correlations of udder and teat type traits between first and second lactation ranged from 0.63 to 0.86, but second lactating cows received overall poorer udder and teat type scores than first lactating cows. Genetic trends were positive and favorable for fore udder attachment, udder support, udder depth and teat length, but genetic trends were mostly stable for udder balance, teat structure, teat thickness, teat position and teat tip. For Icelandic Cattle, the current form of linear conformation classifications provides minimal distinction between breeding animals when it comes to udder balance, teat structure, teat thickness, teat position and teat tip. Therefore, these traits’ heritabilities are estimated low, and their stable genetic trends show that artificial selection has not led to their improvement among Icelandic Cattle. It is therefore important to seek ways to expand phenotypic distributions of udder and teat type traits, but for teat position it is proposed that their optimal score is shifted, to provide more scores to describe outwardly positioned front teats. For breeding value estimations, it is proposed that the random yearly herd and classifier effect is corrected for, as well as the fixed herd effect over a five-year period, the fixed effect of classifier, stage of lactation at conformation classification, and the cows’ age at first calving. By correcting for these effects, ranking of breeding animals will change. It is recommended that Icelandic Cattle are classified during their first and second lactation and that breeding values are estimated for both lactations, therefore supporting selection of udder and teats that last between lactations.

Author dc:creator

• Anna Guðrún Þórðardóttir 1997-

Contributors dc:contributor

• Landbúnaðarháskóli Íslands

• Icelandic Cattle
• Linear Type Traits
• Udder
• Teats
• Somatic Cell Score
• Breeding Values
• Genetic Correlations
• Heritability
• Genetic Trends
• Agricultural Sciences
• Kýr
• Íslenskar kýr
• Línulegir byggingareiginleikar
• Júgur
• Spenar
• Frumutala
• Kybótamat
• Erfðafylgni
• Arfgengi
• Erfðaframför
• Ræktun og fæða

Language dc:language.iso

en

Handle dc:identifier.uri

http://hdl.handle.net/1946/44453

OAI identifier oai:identifier

oai:skemman.is:1946/44453