Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 3/7/2007
Publication Date: 7/8/2007
Citation: Kuhn, M.T., Hutchison, J.L., Norman, H.D. 2007. Effects of dam's dry period length on calf. Journal of Dairy Science. 90(Suppl. 1):329––330(abstr. T277).
Technical Abstract: Recommendations for shortened dry periods have become increasingly common in recent years. While considerable research has been done to determine effects on cow performance, research to determine what, if any, effect shortened dry periods have on the calf being carried is quite limited, in spite of the fact that in utero weight gain of the calf increases at an increasing rate during gestation, with more than half of fetal weight gain occurring during the last 2 months of gestation. Field data were utilized in this research to compare calving ease (CE) scores and stillbirth (SB) rates across 16 days dry (DD) categories. Heifer ages at first breeding (AFB) were also compared across dam DD categories and the raw percentage of heifers with a first calving was also calculated for each category. The linear, fixed effects model for analysis of CE and SB included herd-year of calving, year-state-month of calving, parity, sex of calf, and DD category. Parity and sex of calf were dropped from this model for analysis of calves' AFB. A total of 454,091 CE, 163,175 SB, and 24,125 AFB records were included for analysis. The number of records for AFB was much smaller because only about 29% of US herds have heifer breedings recorded in the national database and storage of heifer breedings only began in 2003. Although differences were small, CE scores did tend to be lower for dry periods of 0 to 45 d than for 46 to 65 DD, suggesting that calves may be smaller with shorter dry periods. Stillbirths were 1.3% higher for dry periods of 30 d or less, compared to DD between 61 and 65 d (mean SB = 4%). There was no evidence to support an effect on AFB for heifers surviving to breeding age; subclass sample sizes, however, were small and further investigation of this trait may be warranted when more data is available. Simple averages indicated that heifers born after dry periods of 45 d or less survived to first calving 12% less often than heifers born after dry periods of 56 to 70 d. Further research, adjusting for extraneous effects, will be conducted on survival to first calving. Results to date indicate a small, but real, negative impact on the calf for dry periods less than 45 d.