Young Bull Semen Theory v Practice          
At £3-8 per straw itís potentially a great deal - but should we use them?    
Across the board unproven young bull semen is not for every one, but the industry benefits by testing more
young bulls - particularly those less related to the breed. The herd owner benefits by rapid genetic progress
at substantial cost savings
Take Home Messages
1Young unproven bulls of high genetic merit have a real place in the UK & not just for the short term
2Used intelligently by the commercial producer they can boost financial performance - consistently
3By the time a well proven sire hits the lists, there is or will soon be semen of his sons available - use it
4Beware of Slippage - sons of sires on average show lower PIN2000 ratings than the sire 10-30% less
†††† so use only sons showing high Animal Model PTA's,do pay attention to commercial type
5Maximise the law of averages by selecting only 10 straws per young bull and 30 straws / 100 cows
†††† of a same mating
6Use mating software that minimises inbreeding where possible to 3% (Grandson x Granddaughter)
†††† If the herd is already inbred by cousin, aunt nephew relationships be very selective of matings
†††† Seek young bulls less related to the breed -Vik KAI at 2% full relationship was one such - and in
†††† retrospect superior to Blackstar (16% related) for Productive Life but with similar production.
7Calving ease cannot be predicted with accuracy on maiden heifers,sons of sires with
††† a good history of easy to average calving should be chosen.Reduce straws to 5 per young bull
Slippage
Taking the UK proof of Celsius and Mascot,both of whom are sires of many sons, we would expect
their sons to show on average similar PTA's for type and production.In practice this is not the case
For 244 sons of Mascot PIN 2000 is 82% that of the father - for 29 Celsius sons its 72% of the father
WHY?Matings may be to bull mothers that demonstrate more type than production, ie non Random
Action: On average Young bulls will deliver less than the fathers PTA.
Select young bulls which have the highest Animal Model PTA
Mendelian Inheritance
The "gene lottery" at conception determines whether a stud's a dud or a winner.
The Animal Model gives a prediction from all recorded relatives of the likely Average PTA's of a mating -
We donít know what happens to the share out of genes at conception from an individual mating, only
a wide spread proof will do this.Lets look at 10 proven sons from Celsius x Mascot matings.Their
average PIN 2000 of 56 exceeds a simple parent average of 52 but Festival at 86 won whilst Elmo "also ran"
The Model is more reliaBULL than a simple parent average but is never as accurate as a wide spread
daughter proof ie 100 daughters in 100 herds.A wide spread proof is not 150 daughters in 40 herds with
70% daughters in 1st herd.In such cases the proof has the potential to be well and truly fixed, thus for
UK proven sires such as Rosepary Thor, there will be a question mark whilst the first herd dominates
Action: Young bulls are by no means proven in practice, cast a wide net.
To Maximise the law of Averages, Maximise 10 straws per young bull
and 30 straws per 100 cows of a same mating ie Celsius x Blackstar
Table: Celsius x Blackstar Matings              
CelsiusUK Proof Celsius Sons(29) Mascot Sons(244) Mascot UK Proof Simple Parent Average (Celsius + Mascot)/2 ActualProof Celsius (S) X Mascot (DS) 10 Sons Highest Celsius x Mascot =Festival Lowest Celsius x Mascot =Elmo
PIN 65 47 43 52 52 56 86 38
PLI 59 44 44 49 49 57 83 38
SCC 16 9
SCC Rlb 98 99
Type Merit 1.8 0.4 0.6 0.8 0.9 0.5 0.2 0.9
Dairy 2.2 0.6 0.9 1.1 1.2 0.4 0.7 0.5
Body -0.5 -0.5 0.4 0.4 -0.1 -0.5 -0.1 -0.8
Legs & Feet 3.8 1.2 0.0 -2.1 0.7 0.8 1.2 1.1
Mammary 1.7 0.3 0.6 1.2 0.9 0.7 -0.1 1.4
Dtrs 1773 1962 44 42
ST -0.8 -0.6 -0.0 -0.1 -0.4 -0.5 -0.3 -0.7
CW -2.9 -2.0 0.2 1.4 -0.8 -1.4 -0.8 -1.6
BD -1.2 -0.6 0.6 0.9 -0.1 -0.6 -0.1 -1.2
ANG 2.0 0.5 0.9 0.6 1.0 0.3 0.7 0.4
RA -0.2 -0.0 -0.2 -1.0 -0.3 -0.1 0.4 -0.4
RW -2.6 -1.2 0.2 0.8 -0.7 -0.9 -0.3 -1.3
RLS -2.2 -0.8 0.3 1.9 -0.2 -0.5 -0.7 -0.7
FA 1.8 1.1 -0.4 -1.5 0.2 1.4 0.6 1.6
FUA 0.4 -0.4 0.0 0.6 0.2 -0.0 -0.5 0.0
RUH 1.4 0.8 0.8 1.5 1.1 1.2 1.0 1.4
US 0.8 0.2 0.2 0.1 0.3 0.2 -0.9 1.4
UD -0.7 -0.6 -0.6 -1.0 -0.7 -0.4 -2.1 0.3
TPL 1.0 -0.1 0.6 1.5 0.8 0.5 -0.6 1.5
TL 2.3 1.2 -0.6 -0.7 0.5 0.2 0.4 0.9