Regular reproduction continues to be a challenge in dairy herds. Researchers at the Animal Improvement Programs Laboratory of USDA have reported regional and national statistics on reproduction in the July 2009 issue of the Journal of Dairy Science.

These statistics were obtained from DHI records from 1996 to 2007 for nearly 20 million A.I. breedings.

These breedings occurred during over 8 million lactations of over 5 million Holstein and Jersey cows in over 23,000 herds.

Data reported were days to first breeding (DFB) after calving, nonreturn rate at 70 days after breeding (NRR70), conception rate (CR), number of breedings per lactation (NB), breeding interval between first and last breeding (BI), days between calving and last breeding (DLB) and calving interval (CI).

Statistics were summarized separately for Holsteins and Jerseys by year and for Holsteins by six regions of the U.S. Several changes in reproduction are apparent in reviewing the statistics and are highlighted in Table 1*.

First breedings after calving appear to be taking place sooner in recent years. DFB increased slightly from 1996 to 1999 for both breeds and then decreased until 2007.

For Holsteins, DFB went from 92 up to 94 days and down to 85 days, and for Jerseys, from 85 up to 88 days and down to 83 days. Nonreturn rates at 70 days for first breedings after calving have decreased.

NRR70 decreased in Holsteins by 9 percent ( 54 to 45 percent) while in Jerseys it decreased 5 percent (from 57 to 52 percent). For all breedings, the decrease in NRR70 was 8 percent (from 52 to 44 percent) in Holsteins and 6 percent (from 54 to 48 percent) for Jerseys.

Conception rates for both first and all services declined in Holsteins and Jerseys by 2 percent for first and 3 percent for all services in Holsteins, and by 3 percent for first and 4 percent for all services for Jerseys.

The number of breedings per lactation (NB) increased in both breeds by 0.4 breedings in Holsteins and 0.3 breedings in Jerseys. This was accompanied by a lengthening of the breeding interval from first to last breeding (BI) in Holsteins of 18 days and in Jerseys by 11 days.

Days from calving to last breeding (DLB) reflected the combined changes of decrease in days to first breeding and an increase in the number of breedings. The DLB increased 10 to 11 days from 1996 to 2006 for Holsteins and Jerseys.

Overall calving interval (CI) increased 12 days in both breeds. For Holsteins, CI in 2006 was 12 days longer than for Jerseys.

The effect of number of calvings (parity) on these reproductive measures in the 2006 breeding year revealed Holsteins with more calvings having greater increases in DLB, longer CI and more breedings (NB) than Jerseys with more calvings.

DLB went from 142 days for first-lactation Holsteins to 156 for sixth or greater calvings while the comparable figures for Jerseys were from 131 to 138.

Calving interval was 12 days longer in second versus sixth or greater lactation Holsteins while it was only three days longer in Jerseys of comparable parities.

Number of calvings and number of breedings effects were also apparent in comparisons of nonreturn rates at 70 days (NRR70). NRR70 declined over breedings as well as with more calvings. Holsteins NRR70 declined from 48 percent in first breeding of first-calvers to 45 percent for sixth or greater calvings while Jerseys went from 53 to 51 percent.

Jerseys showed a much greater decline in NRR70 percentage for second to fifth breedings with more calvings than did Holsteins. For Holsteins at third breeding, NRR70 was 43 for both first and sixth or greater calvings while in Jerseys the NRR70 for the third breeding of first-calvers was 49 percent, which declined to 41 percent for sixth and greater calvings.

Fifth breeding of Holsteins for first-calvers had an NRR70 of 39 percent which increased to 40 percent by sixth and greater calvings, while NDD70 of fifth breedings of Jerseys declined from 42 percent for first-calvers to 35 percent for sixth or greater calving.

Conception rates (CR) declined for both Holsteins and Jerseys as more breedings took place in a lactation or as number of calvings increased. CR for first-calf Jerseys was 40 percent which declined to 28 percent by fifth breeding. For sixth or greater calvings, Jersey CR’s were 33 and 25 percent, respectively.

Holstein first-calvers had CR of 34 percent in first breeding which declined to 26 percent in fifth breeding. For sixth or greater calvings, CR at first breeding was 24 percent compared to 25 percent at fifth breeding.

Intervals between breedings, from 2006 breedings, averaged 38.2 days for Holsteins and 35.5 days for Jerseys.

Six geographical regions were defined for the U.S. Holsteins for breedings in 2006 (see Table 2*): Mideast, Midwest, Mountain, Northeast, Northwest, Southeast and Southwest. Kentucky along with Delaware, Maryland, North Carolina, Tennessee, Virginia and West Virginia, were included in the Mideast region.

Regional differences were observed for all reproductive traits. The highest and lowest regions and the overall U.S. average are given in Table 2. Overall, the Southwest region had the most desirable reproductive performance and the Southeast the least. PD

—Excerpts from Kentucky Dairy Notes, July 2009

*References and tables omitted but are available upon request to editor@progressivedairy.com

Jack McAllister
Dairy Cattle Genetics
University of Kentucky
amcallis@uky.edu