Selection & Culling Strategies Mario S. Mongeon; OMAFRA

Selection & Culling StrategiesMario S. Mongeon; OMAFRA

Terminology

To clarify the terms used in this module, here are a few definitions:

Culling: Departure of cows (or heifers) from the dairy (replacement) herd for any reason, such as: dairy sale, slaughter, salvage or death on the farm.

Dairy sale: Sale in the context of culling means that the animal was sold alive to another farm for production purposes.

Terminology

Herd Culling Rate, Herd Replacement Rate and Herd Turnover Rate are synonyms, Herd Turnover Rate is the preferred term:

Herd Turnover Rate = Number culled over a specific time period Average herd size* for that period

Example:

Over the last 12 months for a dairy herd:

*Average monthly inventory; Total Cows, including the dry ones : 100

Annual number of cows that left the herd: 33

33 ÷ 100 = 33 % Herd Turnover Rate.

Herd Turnover Rate

In the previous example, the Herd Turnover Rate of 33% implies that 1/3 of the production herd is replace every year.

Within the dairy literature, the consensus is that lower annual herd turnover rates are more profitable, with optimal turnover rates around 25-30%.

According to CanWest-DHI reports, 2011 average provincial herd turnover rate is 39% in Ontario.

Herd Turnover Rate

Have a look at your DHI Herd Management Report.

What is your Herd Turnover Rate ?

Do you know why it is what it is ?

How do you compare to benchmarks ?

25th 50th 75th 90th

47% 39% 32% 26%

Ontario DHI Provincial Percentile; Herd Turnover Rate (2011)

Herd Turnover Rate

Sustained high Turnover Rates should be investigated to identify herd risk factors that devalue cows prematurely within the herd; for example, mastitis, infertility, lameness.

Sustained High Turnover Rates may also indicate that good cows are pushed out the door prematurely by heifers if too many replacements are kept and calved on the farm.

Herds with lower turnover rates tend to be more successful in terms of cow comfort, health, and productivity.

Herd Turnover Rate

A word of caution: Herd Turnover Rates can be misleading, and more detailed information about the reasons for culling and the timing of culling might be needed to assess a case.

The Herd Turnover Rate will dictate, along with other factors, the size of the replacement herd, unless animals are sourced outside the farm.

Replacement Herd Size

Several factors will affect the number of replacements required:

• Age at first calving;• Calf and heifer mortality rates;• Calf and heifer culling rates;• Herd size and potential expansion;• Herd Turnover Rate.

An easy way to avoid sending good cows on a truck ride too early is to limit the number of

heifers raised on your farm.

Replacement Herd SizeAge at first calving

Age at first calving needs to be accounted for because the later the calving occurs, the more heifers you will need to raise.

Decreasing the age at first calving to 24 from 27 months will reduce the number of heifers kept annually by 12.5 % since they start milking earlier in life.

Age at first calving (months)

24 25 26 27 28

% Increase in numbers required

0 4.2% 8.3% 12.5% 16.6%

Multiplication factor

1 1.042 1.083 1.125 1.166


Age at first calving (months)

24 25 26 27 28

Multiplication factor

1 1.042 1.083 1.125 1.166

Example:

For a herd where heifers calve at 24 months, 25 heifers are kept annually

For the same herd, if first calving takes place at 27 months instead of 24, then the number of heifers kept annually needs to be:

25 X 1.125 = 28.13 (29) heifers

Replacement Herd SizeCalf and heifer mortality rates

The greater the mortality and culling rates, the more animals you will need to keep in order to compensate for the losses.

Calf mortality % Heifer culling rates %(before weaning) (after weaning)

5

10

4 6 8 10 12

1.10 1.12 1.15 1.17 1.20

1.16 1.19 1.21 1.24 1.27

Multiplication factors for various mortality and culling rates


Calf mortality % Heifer culling rates %(before weaning) (after weaning)

5

10

4 6 8 10 12

1.10 1.12 1.15 1.17 1.20

1.16 1.19 1.21 1.24 1.27

Multiplication factors for various mortality and culling rates

Example: For a herd where 25 heifers are needed to calve annually, calf mortality is 5% and mortality/culling rate for heifers is 8%

The number of heifers kept annually needs to be:

25 X 1.15= 28.75 (29) heifers


Herd Turnover Rate defines the number of heifers needed to keep the herd size constant, along with all the other factors mentioned previously.

The calculation to define the number of heifers to raise is:

X Herd sizeX Herd Turnover Rate X factor for mortality and culling X factor for age at first calving

Replacement Herd SizeHerd size X Herd Turnover Rate X factor for mortality and culling X factor for age at first calving

Example 1:

Herd size: 100 cows; Herd Turnover Rate is 28%; calf mortality is 5%; mortality/culling rate for heifers is 8% (multiplication factor is 1.15) age at first calving is 26 months (multiplication factor is 1.083)

The number of heifers kept annually should be:

100 X 28% X 1.15 X 1.083 = 34.87 (35 heifers annually)

So the replacement herd size will be 70 head.

(35 heifers from birth to 13 months and 35 from 13 months to calving)

Replacement Herd SizeHerd size X Herd turnover rate X factor for mortality and culling X factor for age at first calving

Example 2:

Effect of reducing Herd Turnover Rate, age at first calving and mortality rate

Herd size: 100 cows; Herd Turnover Rate is 25%; calf mortality is 5%; mortality/culling rate for heifers is 4% (multiplication factor is 1.1) age at first calving is 24 months (multiplication factor is 1.0)

The number of heifers kept annually should be:

100 X 25% X 1.1 X 1.0 = 27.5 (28 heifers annually)

So the replacement herd size will be 56 head.


Let say that for this herd,

the cost of raising a heifer from birth to calving is $2000

Example 2 : 28 heifers kept annually (replacement herd of 56 )

Annual replacement cost: $ 56 000

Example 1 : 35 heifers kept annually ( replacement herd of 70 )


+ $14 000

Let say all the females born (50) are raised and calved on the farm:


+ $ 44 000

Comparing examples:


Age at first calvingCalf and heifer mortality ratesCalf and heifer culling ratesHerd turnover rateNumber of heifers raised

All of these factors have an economic impact.

Replacement Herd SizeHere is the inventory of cows and heifers in Ontario on January 1st 2011

Ontario Canada

Heifers (more than 12 months of age)

156 000 443 100

Cows 322 000 987 000

Heifer/cow ratio 48% 44.8%

Statistic Canada; Table 003-0032

If the expected birth ratio is 50-50, this means that in Ontario, pretty much every female born is raised…not good.


These statistics tells us that there is a lot of room for improvement:

We need to raise less replacements

We need to raise only the best ones

In order to do so, we need to:

Define our objectivesand

Develop a selection strategy

Selection and culling is a balancing act between economics, milk production,

and genetic progress.

Defining objectives

Defining objectives

A key factor will influence which heifers are raised:

Genetic Progress Goals which determine

Selection Intensityand vice-versa

In order to achieve a fast genetic gain, the selection needs to be more intense.

As the selection intensity increases:

Only the best cows and heifers will be selected to raise replacement animals and

Only the best bulls will be used as sires for replacement heifers

Defining Objectives

Genetic Progress Goals which determine

Selection IntensityAnd vice-versa

• How fast do you want to improve your herd?• Do you want all of your heifers to bear your prefix?• Are you willing to outsource animals?• Are you concerned about biosecurity?

Answering these questions will help you define objectives:

Defining Objectives

• How fast do you want to improve your herd?• Do you want all of your heifers to bear your prefix?• Are you willing to outsource animals?• Are you concerned about biosecurity?

Now that you have a better idea about your goals, let’s look at some selection strategies.

Selection

If we take the Lifetime Profit Index (LPI) for each cow in the province and create a graph based on this data, it would look like this:

Lifetime Profit Index

Num

ber

of a

nim

als

Selection

Cows in this range are average:

LPI

50 75 90 99 percentile

Num

ber

of a

nim

als

▪ ▪ ▪ ▪

Selection

Cows in this range are above average:

LPI

50 75 90 99 percentile

Num

ber

of a

nim

al

▪ ▪ ▪ ▪

Cows in this range are bellow average:

LPI

25 50 75 90 99 percentile

Num

ber

of a

nim

al

▪ ▪ ▪ ▪ ▪

Selection

As you select the cows and heifers with the highest LPI or Percentile ranking, the Selection Intensity increases.

LPI


Num

ber

of a

nim

als

▪ ▪ ▪ ▪ ▪

Selection

If all the animals in the herd are used to raise replacements, there is very little selection if any and little or no genetic progress.

LPI


Num

ber

of a

nim

als

▪ ▪ ▪ ▪ ▪

Selection

If the poorest LPI animals in the herd are not used to raise replacements, there is a moderate level of selection and moderate genetic progress.

LPI


Num

ber

of a

nim

als

▪ ▪ ▪ ▪ ▪

Selection

If only the animals with LPI above average in the herd are used to raise replacements, there is a higher level of selection and greater genetic progress.

LPI


Num

ber

of a

nim

als

▪ ▪ ▪ ▪ ▪

Selection

Let’s apply these principles to a small example herd composed of 35 cows and it’s

replacement herd

Selection Strategy

In this example herd, only the cows with a LPI above the herd average will be selected to give birth to replacement animals. Out of 35 cows, only 18 will be selected as potential parents.

The same selection intensity will be applied to the first calf heifers. In this case, only 7 out of 16 heifers will be selected as potential parents.

A list of cows and heifers is prepared and the animals are ranked according to their respective Lifetime Profit Index (LPI).

When the selected animals are bred, the decision as to whether to keep the calf is already made.

Selection Strategy

The cow’s LPI are the following, from worst to best:

The average Lifetime Profit Index (LPI) for this herd is: + 98.5

+ 98,5

-817,-579,-520,-490,-365,-306,-241,-207,121,-23,-2,11,81,85,87,91,92,118,182,210,226,258,261,297,298,306,319,368,391,430,506,551,560,607,687

-817,-579,-520,-490,-365,-306,-241,-207,121,-23,-2,11,81,85,87,91,92,118,182,210,226,258,261,297,298,306,319,368,391,430,506,551,560,607,687

In order to optimize genetic progress, female calves kept for replacement should come from these cows:

Selection Strategy

If we only raise heifer calves from these 18 cows, we

should get an average of 9 females a year.

-12, 22, 407, 453, 493, 501, 529, 541, 601, 629, 762, 882, 1022, 1033,1086,1106

The heifer’s LPI are the following, from worst to best:

The average Life Profit Index (LPI) for this replacement herd is: + 628

-12, 22, 407, 453, 493, 501, 529, 541, 601, 629, 762, 882, 1022, 1033,1086,1106

+ 628

In order to optimize genetic progress, female calves kept for replacement should come from these heifers:

Selection Strategy

If we only raise heifer calves from these 4 animals, we

should get an average of 2 females a year.

LPI in RED are heifers that will calve in the next 12 months

Heifer calves from above average cows: 9 females a year.Heifer calves from above average heifers: 2 females a year.Total : 11 replacement females raised

This Herd Turnover Rate is: 25%Age at first calving is: 24 monthsMortality-Culling rate is: 11%

Herd size X Herd Turnover Rate X factor for mortality and culling X factor for age at first calving 35 25% 1.12 1

35 X 0.25 X 1.12 X 1 = 9.8 (10) replacement animals required

For this example herd, this strategy should provide enough replacements to fulfill needs

The formula to define the number of heifers to raise is:

Selection Strategy

Developing Your Selection Strategy

• Look at your cows. • Rank them according to their genetic potential.

• The Lifetime Profit Index (LPI) is one tool you can use• Divide the herd in 3 groups

• The top group, with LPI above herd average• The average group, with LPI in the average• The tail group with LPI below average


• The top group, with LPI above herd average• The average group, with LPI in the average• The tail group with LPI below average

• Other factors might be used to move cows from one group to another such as temperament, longevity, or other characteristics not accounted for by the LPI index

• Define how many heifers you need to raise this year• Select cows from the above average group to parent the heifers you need

to raise• Avoid using cows in the tail group as parents of replacements

• Pay attention to calving dates in order to distribute replacements over the whole year

• Stick to your plan


If you want to get the best out of the top group of animals, you may want to use sexed semen on the very best individuals in your herd.

Using sexed semen can shift the sex ratio of live calves from the standard 50:50 to an average of 90% females and 10% males or 90:10 ratio.

Using sexed semen

For example, a herd of 100 cows, 2 different strategies: A and B

A- NOT using sexed semen on the best 25 % cows: 25 calves born; 12.5 females

B- Using sexed semen on the best 25 % cows: 25 calves born; 22.5 females

Having 10 more females of higher genetic value means

that you do not need to raise 10 poorer females

So, Genetic Progress will be greater in herd B


Using sexed semen

The downside of sexed semen: • It is more expensive per dose of semen • Usually lower fertility

The key is to use high value bulls. Breeding heifers with sexed semen makes sense as their fertility is higher so better chance of success.

In a situation of expansion, a good strategy could be to breed all replacement heifers to sexed semen increasing the number of high value female offspring to increase herd size.


Using genomics: increased precision

Using genomic testing will increase the precision of the information at hand.

Genomic testing is 2 to 3 times more accurate than the information based on parent average.

Increased precision will help in picking the best animals to give rise to replacement stock.


Using genomics: a selection tool

For heifers, genomics can be a welcome tool to improve the precision of selection as information available can be somewhat limited.

Genomic testing shortly after birth allows:

• more accurate selection of best replacements• better mating decisions for heifers• early culling of poorer heifers

In Summary…

What is your Herd Turnover Rate ? What should it be ?

Limit the number of heifers raised on your farm

Raise only the best ones, it makes economical sense

Define your objectives and develop a selection strategy

Use wisely new tools such as sexed semen and genomics to improve your strategy

In a nutshell:

Documents

Selection & Culling Strategies Mario S. Mongeon; OMAFRA