July 6 2012 07:07 AM

Heifers added after the night milking experienced fewer aggressive interactions.

by Amanda Smith, Hoard's Dairyman Associate Editor

We've all heard the benefits of separating our first-calf heifers from their older herdmates. It provides our new cows with a chance to adapt to their surroundings, learn a new routine and, literally, go from zero to 60 overnight. Despite the benefits, not all of our facilities are set up to allow this grouping luxury. When we have to comingle, is there a time of day that works better to add our heifers to their new groups?

Researchers with the Agri-Food and Biosciences Institute, along with colleagues from the Queen's University Belfast in the United Kingdom, studied the differences in welfare and first-lactation performance when first-calf heifers were added to a group after the morning or evening milking. Results were shared in the June Journal of Dairy Science.

Through the duration of the experiment, 28 heifers were split in two groups and added to a pen 30 minutes after the morning or evening milking. The groups heifers were added to were on the smaller side; 18 cows, 12 in the second lactation or greater along with 6 first-lactation cows. As heifers calved, they replaced a first-lactation cow in the established pens. A TMR was fed once daily, with concentrate fed in the parlor.

Researchers observed the first-lactation cows' behavior immediately after introduction to the group and after feed delivery for the first month. Lying times were also evaluated for the first month.

Heifers added in the morning were often on the receiving end of aggressive interactions from older cows immediately after feed delivery compared to animals added at night. The a.m.-added heifers spent more time at the bunk eating, were displaced more often and spent less time exploring their new surroundings.

The time of day at which heifers were added had no significant impact on milk production, overall feed intake levels, body weight or body condition loss. For a.m.-added heifers, however, feed intakes after mixing were higher during the second week. These heifers also spent longer periods at the bunk and consumed more meals, suggesting an elevated willingness to compete for feed.

In both groups, heifers spent less than 4 hours lying in the 24 hours after being added to the pen. Observations of the entire group showed that heifers added in the morning spent less time lying than both animals added at night and their herdmates that were initially in the pen.

With fewer aggressive interactions and a lack of performance parameter differences, researchers suggest it is beneficial to add heifers to an established group after the evening milking.