selection of dairy cattle

Question 1

selection objectives

Answer 1

-typically based partly on tradition (e.g. 1-2% milk sells best now yet selected for 3.5%)
-veal and/or meat production under no selection in north america
-in britain the lower half of dairy herd is bred to a beef bull, so selection is pre-breeding
-in israel, twinning is under selection to increase meat availability
-production traits, fertility, longevity, and health
-breeding stock sales are limited

Question 2

selection criteria for reproduction

Answer 2

-fertility (low heritability)
-non additive gene action
-cross breeding for heterosis should (does) improve

-calving interval (.1)
-services/conception (.09)
-days open (.09)

Question 3

why has fertility selection not been a big thing now

Answer 3

-because in the US bST (bovine somatotropin) is allowed and wildly used
-recombinant bST deemed safe by FDA
-fertility therefore under less selection since when cows calve, they just keep her milking
-could have a neg impact on canada and other countries who use semen form US bulls, but dont use bST

Question 4

heritability for milk and butter fat

Answer 4

-milk yield .36
-butterfat yield .40
-lactation persistance .31
-average flow .40

Question 5

genetic correlations for milk and butterfat

Answer 5

-milk yield & fat % -.43
-milk yield & fat yield .81

Question 6

what is the productive life span

Answer 6

-mean milking years
-purchased: 3.9
-home bred: 4.7
(peak 6-8 years)
-most early culls are for: udder problems, low production, reproductive disorders

Question 7

productive lifespan heritability and correlations

Answer 7

-longevity .04
-mastitis resistance .05-.38 (somatic cell count and resistance to mastitis)
-longevity:first lactation yield (r=.60)

Question 8

type and conformation of dairy cattle

Answer 8

-heritability = .25
-functional type includes:
-large udders
-proper placement of teats
-sound feet & legs
-udder conformation is positively correlated with milking ability

Question 9

mule foot

Answer 9

-autosomal recessive
-should have M.F as apart of name if “proven” carrier
-canadian Holstein association decided to mark all pedigrees with genetic defects

Question 10

temperament for dairy cattle

Answer 10

-ideally docile cows “contented”
-although bulls are difficult to handle

Question 11

adjusted measures

Answer 11

-305-day lactation period
-age (6-8 yrs prime)
-twice daily milking
-3.5% butter fat

Question 12

selection of cows

Answer 12

-pedigree selection using female relatives
-repeatability of production is high, therefore using (first lactation milk yield)

Question 13

selection of bulls

Answer 13

-progeny selection using daughters

Question 14

inbreeding in dairy

Answer 14

-for each 1% inc:
-pounds of milk -71.9
-% fat 0
-fertility decreases

Question 15

mating systems of dairy cattle

Answer 15

-linebreeding:
-occasionally to predominant sire
-crossbreding:
-rarely done
-but could be advantageous

Question 16

GEBV

Answer 16

-EBV and DNA chip data combined
-not that chips with different numbers of SNPs have been used
-canadian dairy network is responsible for GEBV and traditional EPDs
-GEBVs begain in 2009 and they say that accuracy of young bull selection doubled to 66% for lifetime profit index and age decrease to 3 years instead of 5
-GEBVs improved accuracy for progeny proven sires for traits of low heritability: longevity or herd life, daughter fert, daughter calving ability
-use of young sires has increased