|KEOWN JEFFERY F|
|VAN VLECK L DALE|
Submitted to: Professional Animal Scientist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/1995
Publication Date: N/A
Interpretive Summary: Milk yield and income over feed costs (IOFC) for dairy cows are affected by days open and days dry. Milk yields and IOFC for 50,496 Holstein cows were analyzed to determine optimum days open and days dry. Production level of the cow was not important in determining optimum days open and dry for a specified season of calving. A dry period of 51-60 days was optimum for all production levels and calving seasons. Optimum days open were different for different calving seasons; the period of 76-90 days was best for summer, the period of 61-75 days was best for fall freshenings, and the period of 136-150 days was best for spring calving.
Technical Abstract: Days open, days dry, and season of calving were examined to find the combination to maximize Income Over Feed Cost (IOFC) and 305-day mature equivalent milk production per lactation for three different production levels. Models with all fixed effects were analyzed using SAS PROC GLM for 50,496 Holstein cows calving in the years 1990 and 1991. Days open and days dry for a particular season of calving to maximize IOFC and 305-day milk yield were the same for the three production levels. Cows calving during February through April (Season 2) yielded maximum IOFC when bred back 136-150 days after calving. For cows freshening during May through July (Season 3), days open of 75-90 d yielded maximum IOFC and for cows freshening in August through October (Season 4), 61-75 days open maximized the IOFC. In all calving seasons a range of 76-105 days open was optimum for maximizing 305-day production. Cows calving in Season 3 yielded the highest IOFC, which was $685, $338 and $410 more than cows calving in Season 1, Season 2 and Season 4, respectively. The interaction effects of days open, days dry and season of freshening with parity were not significant (P < .05).