|Hutchison, Jana - Edwards|
Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 2/24/2011
Publication Date: 6/30/2011
Citation: Norman, H.D., Hutchison, J.L. 2011. Effects of dam’s dry period length on heifer development. Journal of Animal Science 89(E-Suppl. 1)/Journal of Dairy Science 94(E-Suppl. 1):27(abstr. M66).
Technical Abstract: Effect of the dam’s dry period length on calving ease (CE), stillbirth (SB), and heifer development was investigated using US Holstein field data from January 1997. Dry periods were grouped into 12 days dry (DD) categories. Calving ease scores and SB rates were compared across dam’s DD categories, as well as heifer age at first breeding (AFB) and heifers with a first lactation. Heifers with a first lactation was a binary trait (0=no, 1=yes) and excluded heifer calves stillborn or dead within 24 hours. The linear, fixed effects model for analysis of CE (score of 1 to 5) and SB included herd-year of calving, year-state-month of calving, parity, sex of calf, and DD category. The AFB model included herd-year of breeding, year-state-month of breeding, and DD category. Herd-year of calving, year-state-month of calving, dam’s parity, and heifer’s parent average for daughter pregnancy rate were included in the heifers with a first lactation model. There were 774,821 CE, 347,462 SB, 27,932 AFB, and 274,728 first lactation heifer records. The number of records for AFB was smaller because storage of heifer breeding records began in 2003 and reporting is minimal. Dam’s calving date was required to be within 10 d of expected calving date (previous calving date + previous days open + 280) to ensure producers had knowledge of calving date and dry period length. Heifer birth dates were required to be prior to January 2008 to allow time for the heifer to complete a first lactation. Calving difficulty showed a linear trend, increasing as dam’s DD increased up to about 70 d then leveled. Differences were small but significant ranging from 1.29, 1.36 and 1.42 for 0 to 30 DD, 56 to 60 DD, and 90 to 120 DD. Stillbirth rates were 4.15, 2.36, 3.33% for 0 to 30 DD, 56 to 60 DD, and 90 to 120 DD. Heifer AFB was 463, 458, and 458 d for 0 to 30 DD, 56 to 60 DD, and 90 to 120 DD, a difference of 5 d between short dry periods and DD after 56 d. Heifers with dam’s dry period of 0 to 30 DD, 56 to 60 DD, and 90 to 120 DD had first lactation survival of 67, 72, and 71%, respectively.