Length of Dry Period - Don't just jump on a band wagon without knowing if you really want to go that way

Dr. Maurice Eastridge, Dairy Nutrition Specialist, Ohio State University

The traditional length of the dry period for dairy cattle has been 60 days. It is well established from research conducted many years ago and just recently that continuous milking (no dry period) reduces milk yield in the subsequent lactation. However, with the increase in milk yield per cow whereby challenges occur in drying the cow off, new management strategies such as use of bovine somatotropin and greater than two-times-a-day milking, and with the focus more on managing cows by groups rather than as individuals, the traditional length of the dry period is being questioned.

Presently, about 16% of the cows in the Midwest calve with less than 40 days dry, but about 25% of the cows calve with greater than 70 days dry (Dairy Records Management Systems, Raleigh, NC). So on the one hand, producers should be reviewing why so many cows have extended dry periods. Long dry periods reduce milk yield and increase costs. As for reducing length of the dry period to less than 60 days, several factors need to be considered.

Most of the recent attention has been on the dry period being 30 to 60 days in length. Retrospective analysis of production data revealed that cows with about 30 versus 60 days dry had lower milk yield. However with these types of data, we must keep in mind that the 30-day dry period may have occurred as a result of disease implications or twins. Few studies have been done whereby the 30 versus 60 day dry period was planned, but of those conducted, milk yield was generally similar. Milk composition and quality were not affected by length of the dry period. However, if cows are managed as groups for a target days dry of 30, several will calve with less than 30 days dry. Therefore, a 30-day dry period is likely too short in the field given our inability to know exactly when a cow will calve.

It has been known for many years, including the use of DHI records in an OSU study reported in 1982, that optimum dry period is affected by numerous factors, including lactation number and calving interval:

Between Lactations
Calving Interval
< 341 days
341 to 410 days
> 410 days
1 and 2
65
63
60
2 and 3
65
50
35
3 and 4
60
35
30
4 and 5
60
30
30

Although these results are from a retrospective analysis, they seem to match well with recommendations from recent studies where the length of the dry period was managed (planned). Yet, differential days dry requires individual cow management. Therefore, with group management strategies, several things must be considered with dry periods as short as 30 days:

1) There may be increased risks for antibiotic residues in milk.
2) Reducing the dry period length may eliminate the need for a far-off dry cow group, but feeding anionic salts is not warranted for the increased length of the "close-up" group.
3) Although continuous milking greatly reduces colostrum quality, a shortened dry period should result in similar quality as compared to a 60-day dry period. However, the colostrum should be checked with a colostrometer.

Dairy producers should review the factors that are causing cows to have dry periods beyond 60 days and try to correct these with changes in management. Producers who desire to implement a shortened dry period should set their target on about 40 days. This will minimize the number of cows that will calve with less than 30 days dry and will accommodate the longer dry period needed by younger animals in the herd. (Additional information on dry period length will be presented by a guest speaker at the 2004 Ohio Dairy Management Conference to be held in December).