DHI Notes...

January 07| Suggestions for using DHI somatic cell records | Bennet Cassell

State DHI averages for important management areas in December 2006

Management area	December 2006	Change from last year
Rolling herd average milk	21616	+188 lbs.
Peak yield in heifers	74	0 lbs.
Days to first breeding	95	0 days
Days open	164	+2 days
Net Merit of proven service sires	$292	*
Herd turnover less dairy sales (%)	29%	+1%
Monthly average SCS	3.1	-0.1
Feed cost per cwt. (milking cows)	$5.32	$0.01
Milk blend price	$14.32	-$1.76

*Net Merit changed in August 2006 and averages are not comparable.

One of the strengths of the DHI system over other methods of monitoring cow performance is the analysis of monthly milk samples for fat, protein, and somatic cells. The information these tests provide for herd management is unique to the DHI system, as the tests are available on individual cows. Bulk tank samples can’t be used in the same way. I value the somatic cell information particularly as a monitor of udder health because of the impact it has on profitability of the milking herd. Here are some suggestions for using month somatic cell information for herd management using the DHI 202 Herd Summary Sheet.

• Check the percentage of cows in the herd with somatic cell scores below 3 (140,000 cells) in the “yearly production and mastitis summary”. A good general goal is for 70% or more of the herd to have scores in this category. Of course, if your herd typically has an higher percentage of cows in this category, raise your standard! Look at trends over time by examining results for previous months.
• Look at the percent of early lactation cows (first 40 days in milk) in the herd with somatic cell scores of 4.0 and higher. This number is at the bottom of the “stage of lactation profile”. Less is better and a good general goal would be for less than 20% of fresh cows to have SCS at 4.0 or above. This number is one evaluation of transition cow management, dry cow therapy, conditions in birthing stalls and early lactation conditions for fresh cows. It is worth extra effort to start cows off with low SCS and keep them low.
• Keep an eye on average SCS for the entire milking herd in the same section with the percent of cows with scores below 3.0. Watch the trends over time and take action when the scores start going up. Herds with average SCS of 2.5 or less are doing a very good job overall. Low herd average SCS requires constant vigilance, good milking equipment and procedures, and clean, dry, comfortable housing for lactating cows.

I recommend that herds use the “score” option for somatic cells rather than actual counts because individual cows with really high counts distort the averages, even for large groups. The score option eliminates those distortions, and makes it easier to spot problem cows or detect unfavorable trends for groups of animals.

Bennet Cassell
Genetics and Management