17.4.2: Infertility in the herd

Question 1

How could we monitor fertility in a flock of sheep?

Answer 1

Measure against last season’s performance:
* Lambing percentage
* Weaning percentage
* Length of lambing period
* Barren ewes

This season’s performance
* Use of a raddle
* Use of scanning
NB: majority of ewes should get pregnant in first cycle - by the time you can see it going wrong, it’s pretty much already too late.

Question 2

How is lambing percentage calculated and what might a sensible target be (dependent on the system)?

Answer 2

Lambing percentage = (lambs born alive / ewes put to ram) x100

Target: 120-200% (lowland systems highest, upland, hill lowest)
200% means each ewe is having 2 live lambs.

Question 3

How is weaning percentage calculated?

Answer 3

(Lambs weaned / ewes put to ram) x 100

Question 4

How long should a lambing period be?

Answer 4

95% of ewes should get in lamb within 2 cycles i.e. 35 day period

Question 5

How is barren ewe percentage calculated and what is a sensible target?

Answer 5

(1- (ewes lambing / ewes put to ram)) x100

Target <2-3%

Question 6

How can a raddle be used to monitor the current season’s fertility?

Answer 6

Use of a raddle:
* Identifies ewes not served
* Identifies ewes returning to serve

Question 7

How can scanning be used to monitor the current season’s fertility?

Answer 7

• Identifies the empty ewes of the end of a breeding season
• Estimates lambing percentage

Question 8

What are the key fertility targets for a beef herd?

Answer 8

• One calf per cow per year
• 90% of the herd should calve within 9 week period with 65% in the first 3 weeks
• <5% barren/empty cows

Question 8

What are the key fertility targets for a beef herd?

Answer 8

• One calf per cow per year
• 90% of the herd should calve within 9 week period with 65% in the first 3 weeks
• <5% barren/empty cows

Question 9

This is data from a beef herd. What % of the herd do we want to calve within the circled block?

Answer 9

65%

Question 10

This is data from a beef herd. What % of the herd do we want to calve within the circled area?

Answer 10

90%

Question 11

This is data from a beef herd. What is a sensible target for the circled column?

Answer 11

<5%

Question 12

Most dairy farms don’t serve cows close after calving (e.g. 20 days after). Why is this?

Answer 12

• Chances of getting her in calf are low due to NEB
• Getting her in calf very quickly can also shorten lactation unprofitably

Question 13

Calving index

Answer 13

Mean calving interval across all cows in the herd

Question 14

What policy on farm can affect calving index and how is this the case?

Answer 14

• Farm culling policy can manipulate the calving index
• Seen esp in seasonal calving herds
• Cows not pregnant at the end of a set breeding season each year are culled
• Diagram below shows the effect of this

Question 15

1

Answer 15

Voluntary wait period (~45 days in this case)

Voluntary wait period is usually 60 days.

This may range from 30-60 days depending on the farm.

Question 16

2

Answer 16

Calving to 1st service interval

Question 17

3

Answer 17

Calving to conception interval

Question 18

4

Answer 18

Gestation period (280 days)

Question 19

5

Answer 19

Calving interval (if single cow)
Calving index (if average of herd)

Question 20

6

Answer 20

Lactation

Question 21

7

Answer 21

Dry period (~50 days)

Many farms aim for 60 day dry period.