Submitted to: Journal of Dairy Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/8/2014
Publication Date: 5/1/2014
Publication URL: aipl.arsusda.gov/publish/jds/2014/97_3213.pdf
Citation: Hutchison, J.L., Cole, J.B., Bickhart, D.M. 2014. Short communication: Use of young bulls in the United States. Journal of Dairy Science. 97(5):3213-3220. Interpretive Summary: Availability of genomic evaluations of dairy cattle in the US since 2008 has resulted in many changes in breeding programs. The increased use of young bulls in breeding programs is one of the more notable changes resulting from genomic selection, and is associated with a reduced generation interval and an increased rate of genetic gain. In 2012, 51% of Holstein and 52% of Jersey matings were to bulls younger than 4 years of age. Holstein and Jersey herds using >75% of young bulls had a +114 and +312 increase for PTA milk, respectively, compared to herds using no young bulls. This corresponds to greater lifetime income from the sale of milk for Holsteins ($3,084) and for Jerseys ($8,436).
Technical Abstract: The availability of genomic evaluations since 2008 has resulted in many changes to dairy cattle breeding programs. One such change has been the increased contribution of young bulls (0.8 to 3.9 yr old) to those programs. The increased use of young bulls was investigated using pedigree data and breeding records obtained from the US national dairy database (Beltsville, MD). The adoption of genotyping was so rapid that by 2009, >90% of all Holstein AI service sires and 86% of Jersey AI service sires were genotyped, regardless of age. The percent of sons sired by young bulls increased 49 percentage points (10% in 2008 compared with 59% in 2012) due to the onset of genomic evaluations for Holsteins and 46 percentage points for Jerseys (11 and 57%, respectively). From US breeding records from 2007 through 2012, 24,580,793 Holstein and 1,494,095 Jersey breedings were examined. Young bulls accounted for 28% and 25% of Holstein and Jersey breedings in 2007, respectively. These percentages increased to 51% of Holstein and 52% of Jersey breedings in 2012, representing a 23 and 27 percentage unit increase, respectively. Matings to genotyped young bulls have rapidly increased while the use of non-genotyped bulls has diminished since the onset of genomics. Mean sire age for Holstein progeny born in 2012 was 2.7 yr younger than males born in 2006, and 1.3 yr younger for females; corresponding values for Jerseys were 2.3 and 0.9 yr. Holstein and Jersey male offspring had an increase of 620 lbs between 2006 and 2012, compared to 434 lbs between 2000 and 2006 for parent averages for milk, an increase of 186 lbs between the two time periods. To demonstrate the economic impact of the differential use of young bulls, herds were grouped by the frequency of their use of young bulls, and average PTA for milk and net merit for cows that were bred in 2003 through 2012 were calculated. In 2012, herds using >75% young bulls had an increase of +114 PTA for milk and +$58 net merit compared to herds using no young bulls. Jersey herds using >75% young bulls had an increase of +312 PTA for milk and +$63 for net merit compared to herds using no young bulls. This change in parent averages corresponds to greater lifetime income from the sale of milk of $3,082 for Holsteins and $8,436 for Jerseys. Use of young bulls has greatly reduced the generation interval and improved the rate of genetic gain since the implementation of genomic evaluations.