Most farms have clearly defined targets for dry period length. But how many of your cows actually hit that target and does it matter?
Research in the US has found that dry period length has a significant effect on lifetime milk production (see graph) with dry periods of less than 30 days or more than 70 days reducing lifetime yield considerably. The target therefore should be to have as many cows as possible with dry periods of 30 to 70 days.
In recent years we have been monitoring clients’ herd performance through detailed analysis of their milk records. We have looked at records for 60 herds over the past five years and this has given us data on 41,000 dry periods.
Results show almost one-third of cows (29%) do not have an ideal dry period (see table, bottom). The effect of this is to reduce average lifetime yield by about 900 litres for every cow in the herd.
Impact of incorrect dry period length
Shorter dry periods will limit the udder’s ability to regenerate, reducing subsequent milk production. It will also lessen the ability of any dry cow tubes to overcome lingering bacterial infection. For products with a long dry period there is a real risk that the cow will calve while in the milk-withdrawal period.
And if cows do not get three weeks in the close-to-calving group they will not be exposed to the down-calvers diet for long enough to adjust. If they are only in the group for a few days they will not have overcome the social pressures of the group change and feed intakes and energy balance will be reduced at the critical time.
Long dry periods are a bigger problem on many units. Sub-optimal fertility management can result in delays to conception. It is then tempting to milk the cow for longer as the next calving date is delayed. However, as the yield declines it becomes uneconomical to feed the cow the milking diet and the reduced nutrient requirements for milking means she can start getting fat.
Our data suggests a realistic target is to have less than 4% of cows in the herd with a dry period of fewer than 30 days and less than 16% with dry periods of more than 70 days. If you exceed either of these targets then you should be able to make improvements and boost overall lifetime milk yield. Our data also suggests that if you have more than 6.5% of cows with dry periods of less than 30 days or 31% or more with dry periods of more than 70 days, then active intervention should be worthwhile.
Avoiding short dry periods
• Early pregnancy diagnosis – The sooner cows are examined for pregnancy the more precisely the pregnancy can be aged. If cows are examined within 50 days of serving, it should be possible to say to which service a cow conceived. Holding to an earlier service than expected is quite common and will mean the next calving is at least three weeks earlier than expected.
• Where natural service or “sweeper bulls” are used, cows should be examined for pregnancy on a regular basis so that accurate calving dates can be determined.
• Good animal identification and accurate record keeping ensures cows are correctly recorded and can be dried off at the correct time.
Avoiding long dry periods
• Avoid long voluntary waiting periods (VWP). In most herds the probability of a bulling cow conceiving does not change much from 40 days post-calving onwards.
• Avoid stragglers. Once a cow enters the “service window” she needs close monitoring for bulling activity. Heat detection aids help, but making time to watch for bulling activity several times a day remains the best method and is a vital adjunct to any aid.
• Cows that do not come bulling should be examined and any problems treated.
• Cows that have been served should be pregnancy tested as soon as possible so empty cows can be brought back into oestrus.
• A common cause of long dry periods is cows aborting. Any problems with abortions or late returns to bulling should be thoroughly investigated.
Dr Tom Chamberlain, Evidence Based Veterinary Consultancy, Penrith