1. Domestic vs. imported AI semen for Holstein graziers in the US

2. Background
Increasing interest in grazing to reduce costs (machinery, feed, labor)
Increased importance of fertility to synchronize calvings and pasture availability
New Zealand (NZ) has used grazing as the standard practice for many years

3. Assumptions US producers have used semen from some NZ bulls
Usage may be intended to capitalize on selection for grazing conditions
Value of NZ bulls might be for yield on pasture or better fertility

4. Objective
To compare US performance of daughters of NZ Holstein-Friesian AI bulls with that of contemporaries with US Holstein AI sires
Traits
Milk, fat, and protein yields
Somatic cell score
Days open
Conformation

5. Data
159 US herds with daughters of 26 NZ bulls and US-sired contemporaries
552 daughters of NZ bulls and 6,266 daughters of US bulls
Phenotypes for yield, SCS, and days open for parities 1, 2, and 3 and first conformation scores (79 NZ-sired vs US-sired cows)

6. Method
In addition to studying all herds using NZ bulls, a “grazing” subset was defined by seasonal calvings
More than 3 times as many calvings for March—May as for September—November for 3 consecutive years during 2002—2005
11 herds had 25 reported calvings/year

7. Performance of NZ vs. US daughters (NZ minus US)
Results
Performance of NZ vs. US daughters (NZ minus US)
SCS
.22***
.10
.06
Days open —7
.5*
.6* —1 .7
Parity 1
Parity 2
Parity 3
Milk (kg)
—481
***
—572
—479
Fat (kg) 1 3
Protein (kg) —5 ** —7

8. Results Conformation of NZ vs. US daughters (NZ minus US)
Significant differences
Final score —1
.6*
Stature —2
.3*
Rear udder height
Udder depth —3
.2*

9. Results But are these grazing herds?
Only 11 met seasonal calving requirement
Only 7% of herds, but 25% of NZ daughters
Although yield was lower for those 11 herds (8,647 vs. 9,418 kg milk), likely there was a grain-supplemented diet

10. Performance of NZ vs. US daughters (NZ minus US)
Grazing Results
Performance of NZ vs. US daughters (NZ minus US)
Parity 1
Parity 2
Parity 3
Milk (kg)
—351
***
—538
—745
Fat (kg) 3 2 6
Protein (kg) —4 —8 *
—13 **
SCS
.24*
.16
.11
Days open —6 .5 —1 .0 —0 .7

11. Conclusions
Some (much?) NZ semen likely used for reasons other than grazing characteristics
For all NZ daughters, milk and protein yields were lower, SCS higher, but days open less
For seasonal herds, NZ daughters again lower for milk yield, higher for SCS, higher for 3rd- lactation protein yield, and no longer significantly lower for days open

12. Conclusions
To the degree that NZ semen was used to improve performance on pasture, only fertility was improved in first and second lactations
Daughters of NZ bulls were lower for final score and stature and had lower udders, perhaps because sire selection in NZ was at a much lower level of nutrition and production