LACTATIONCURVES

DHI Lactation Curves 2

Your Herd

Purpose of option

Lactation curves offer a quick visual check on herd production. Areasfor possible improvement can be quickly identified, leading tomanagement changes aimed at increasing profitability.

Explanation of output

The lactation curve report consists of four separate graphs :• all animals;• 1st lactation animals;• 2nd lactation animals, and;• 3rd+ lactation animals.

Lactation curves for Your Herd are computed from actual test daymilk weights - projections are not used. Each point on the curverepresents the average sample day milk weights for all milking anddry cows currently in that lactation group. A cow that has been testedfor the tenth time in her current lactation will be represented in thesample day averages for tests 1-10, while a cow who has justcompleted one test will be represented in the average for sample day 1only.

When there are fewer than five milk weights available for any sampleday, the average may be unreliable. These sample day averages aremarked with a golf flag near the top or bottom of the graph. A flagmay appear without a corresponding milk weight if the milk weight islower than the lowest value on the graph's vertical axis. For example,if the herd average 305-day production is 7500 kg, the lowest valueon the vertical axis for the 3rd+ Lactation Animals will be 15 kg. Ifa sample day average were 13 kg and only 3 cows contributed to thataverage, a flag would appear but no point would be plotted on thecurve.

Example curves forcows currently intheir third or greaterlactation. Each pointon the curve for yourherd represents theaverage of milkweights on thatsample day for cowsin this lactationgroup.

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Your Herd 9500 Kg. Reference Curve

3rd+ Lactation Animals

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Curves will be incomplete for new DHI herds until they havecompleted at least 10 test days.

Test day averages do not include:• milk weights that may be invalid;• cows that have been tested but were subsequently sold;• cows with no calving date recorded.

The 305-Day Production levels printed in the upper right handcorner of the lactation curve report are the current averages for eachlactation group in your herd on the most recent DHI test day. Theseare used to select the reference curves plotted on each graph.

Thirteen sets of reference curves are used, for 305-dayproduction ranging from below 5000 kg to over 10500kg, with each set representing a 500 kg production rangeas shown in the table on the left. Each set includescurves for each of the three (1st, 2nd and 3rd+) lactationgroups within the herd. These reflect the expectedincrease in peak yield and decrease in persistency forsucceeding lactations shown in the graph below.

The reference curves used on your output are for thenext highest production level within each lactationgroup. For example, if the current average for your 2ndLactation Animals is 7122 kg, the 7500 kg referencecurve for that lactation group is used. For lactationgroup averages less than 5000 kg, the 5000 kg curve isused. For averages greater than 10500 kg, the 11000 kgcurve is used.

ReferenceCurves

REFERENCE CURVES

if 305-day referenceproduction is: curve used is:

less than 5000 50005000 - 5499 55005500 - 5999 60006000 - 6499 65006500 - 6999 70007000 - 7499 75007500 - 7999 80008000 - 8499 85008500 - 8999 90009000 - 9499 95009500 - 9999 10000

10000 - 10500 10500more than 10500 11000

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7500 kg referencecurves for each of thethree lactationgroups. Notice thatpeaks are higher andpersistencies lower aslactation numberincreases.

DHI Lactation Curves 4

Interpretation

Lactation curves should be interpreted inconjunction with the TEST DAY SUMMARYsection of the Monthly Herd Summary Report.That section reports information which is similarto the information contained in graphic form onthe lactation curve report. Briefly :• PEAK MILK AVE KG is the average of thehighest sample day yield recorded for each cow;• PEAK MILK AVE DIM is the average days in milkon which peak yield was recorded;• PERSISTENCY % reflects the rates of change inproduction for each of three stages of thelactation curves for your herd.• PERSISTENCY GUIDELINES are standards forcomparison with your actual results.

The interpretation of peak milk yields and persistency are discussed atlength in the ADHIS publication Persistency of Milk Production.

Peak production normally occurs between six to eight weeks aftercalving. This means that the highest sample day yield for Your Herdon the Lactation Curve ReportLactation Curve ReportLactation Curve ReportLactation Curve ReportLactation Curve Report will normally occur on sample day 2,when most cows will have been 30 to 60 days in milk. The yield atthis test represents the average yields of all cows currently in thelactation group except for those who have only been tested once.Therefore, if the yield on sample day 1 is higher than that at sampleday 2, this would indicate that most of the cows in this lactationgroup are peaking early and failing to reach a potentially higher peakat the normal time. Early peaks most often occur in the secondlactation group and are usually a symptom of energy deficiency due to:

• poor body condition at calving;• inadequate feed intake, or;• low ration energy density.

When the highest yield occurs after sample day 2, most of the cows inthis lactation group have failed to reach their potential early peak.This can happen to individual cows of any age, usually due to ametabolic problem at calving. But, as a lactation group, poorlygrown-out first- and second-lactation animals are most often affected,when the demand for continued growth competes with milkproduction for the available nutrients.

Peak sample day

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Peak height If persistencies can be maintained post-peak, each additional kg ofyield at peak can result in an additional 200-250 kg of milk over a305-day lactation. This is demonstrated in the graph below.

Mature cows should be expected to peak higher than first- or second-lactation heifers. Relationships between peak heights are normally asfollows:

• 1st lactation peak : 70-73% of peak for mature cows;• 2nd lactation peak : 92-93% of peak for mature cows;

• 1st lactation peak : 75-80% of peak for second lactation.

When the peak heights for Your Herd are consistent with theserelationships, each lactation group is 'pulling its weight'. If peakheight for one of your lactation groups is lower than expected, thismay indicate that production in that group is being limited bynutrition or some other management deficiency.

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In this example, a 3kgincrease in peak yieldresults in a 600-750kg increase in 305-day yield. At a milkprice of $50/hL, theincreased productionwould result in anadditional $300-375of gross return.

These referencecurves demonstrate'normal' relationshipsbetween peak heightsfor the three lactationgroups within a herd.

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DHI Lactation Curves 6

Persistency

MILK KG earlier test1 - x 100

(MILK KG earlier test - MILK KG later test) x 30 daysdays between tests

(39.5 - 23.5) x

39.5

30 days150 days

1 - x 100 = 92%

39.5 kg

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150 days between tests

23.5 kg

In this example, thepersistency betweenthe 3rd and 8thsample days was92%. This means thatevery 30 days duringthis period, milk yielddropped to anaverage of 92% ofwhat it was 30 daysbefore.

Persistency is calculated as follows :

Using this formula, it is possible to calculate persistencies betweenany two points on the lactation curve. For example, in the graphbelow, the persistency between the 3rd and 8th tests is :

Between first and second sample days, persistency should be between105 and 107%, indicating a rapid rise to peak. Lower values suggesta failure to reach potential peak production. This is most commonlydue to energy deficiency as discussed above under Peak sample day.

Lower than normal persistencies post-peak may also be due to energydeficiency, but almost any type of ration imbalance can be the cause.A period of low persistency post-peak is often followed by a period ofhigher than normal persistency. In general, high post-peakpersistencies point to an opportunity to improve production in aprevious interval when persistency and/or peak yield was low.

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Evaluation ofCurves

The key points to look at when evaluating lactation curves are asfollows :

• on the All Animals graph, check the relationships between peakheights for 1st vs 3rd+, 2nd vs 3rd+ and 1st vs 2nd lactationgroups - this will help to focus on which group, if any, is limitingherd productivity;

• on the graphs for each lactation group, compare the shape of thecurve for Your Herd against the shape of the reference curve :- do peaks for Your Herd occur at sample day 2?- are persistencies lower or higher than reference curves?- is there a smooth decline in production after peak or are there

distinct breaks which might indicate a change in cow status?

The following examples will help to clarify the interpretation oflactation curve reports :

Herd curves for AllAnimals. Relationshipof peak heights for 1stvs 3rd+ lactation isnormal, but secondlactation peak is low.Post-peak persistencyof 3rd+ cows resultsin their productionafter sample day 8being lower than 1stand 2nd lactationcows.

Lactation curves for1st lactation animals.Early peak and lowpersistency to sampleday 5, followed byhigh persistency toend of lactationsuggests that rationwas indequate inearly lactation.

DHI Lactation Curves 8

Lactation curves for2nd lactation animals.Peak of herd curve islower and post-peakpersistency higherthan for reference.This is a picturetypical of 'sophomoreslump' where heifersfailed to put onadequate conditionafter 1st lactationpeak due to demandsfor continued growthand production.

Curves for 3rd+lactation animalsdemonstrating a herdcurve with a higherpeak but lower post-peak persistenciesthan reference.Dashed linesrepresent averagechanges in productionover three stages ofcurve.

For more information

Lowry, Dennis. : Persistency of Milk Production. Alberta Agriculture(November 1990)

Jones, Lawrence R. : Lactation Curves for Herd Management andGoal Setting. Northeast DHI Records Specialist Conference (1992)

these articles are available at no charge from the WCDHIS library