Bovine Repro7

Front 1

How does calving interval affect conception rate

Back 1

•The interval between calving and breeding has a significant effect on pregnancy rates
•To maintain a 365 day calving interval cows can only have a maximum of 80 days following calving to conceive.
Fertility improves with increasing interval post calving but is usually optimal by 60 to 80 days 60 post calving

Front 2

How can yuo optimise calving to breed interval

Back 2

• Aim is to increase the proportion of the herd that calves early and is preferably 60 to 80 days post calving at the time breeding commences to optimise conception rates
• Strategic calving induction of late calving cows in dairy herds can be used to increase their calving to mating interval and improve the proportion of the herd that becomes pregnant in the first 6 weeks after the start of breeding
• Synchronisation of oestrus can also be used to increase the number of cows that conceive at the start of the breeding season and in turn increase the calving to breeding interval
• Selective culling of late calving cows and replacement with earlier calving heifers can also be used to help ensure that the majority of cows will have high fertility when mating is scheduled to start
• Alternatively, late calving cows can be left out of a breeding program and bred later in the year when they have had more time to regain optimal fertility. This principle is used in split-calving dairy herds to improve reproductive performance in late calving cows or cows that fail to conceive within a restricted mating period
• If you are buying pregnant cows, make sure that you buy early calving pregnant cows. Late calving cows are a liability

Front 3

How does heat detection affect reproductive performance?

Back 3

As heat detection rate improves the % cows that are submitted for AIincreases and the percentage of cows that become pregnant within 6 weeks of the start of mating increases

Front 4

How does significant loss of BC affect reproductive performance?

Back 4

• Increase intervals from calving to first ovulation
• Decrease conception rates
• Increase embryonic loss rates

Undernourished herds can have more anoestrous ( non-cycling) cows which will have a negative effect on herd reproductive performance.

Front 5

What are uideline to BCS targets for dairy cows?

Back 5

BCS at calving:
<15% of cows below BCS 4.5 (1 – 8), 3.0 (1 –5)
< 15% of cows above BCS 5.5 (1 – 8), 3.75 (1 – 5)
< 15% of herd lose > 1 BCS after calving

Average decrease after calving < 0.6 (1 – 8 scale), < 0.5 (1 -5 scale)

BCS during mating Maintain or gain BCS from the start of mating

BCS late lactation < 15% of cows below BCS 4.5 (1 – 8), or < 3.0 (1 –5) 8 to 10 weeks before drying off

Front 6

Heifer liveweight

Back 6

Heifer liveweight affects:
Reproductive performance of maiden heifers.
Reproductive performance of first-calf heifers.
Lifetime milk production.

Heifers that are in poor body condition at mating may not be cycling and
have reduced fertility
Heifers in poor body condition at calving may produce less milk and take
longer to cycle after calving which will delay conception
First calf heifers which are late to conceive will be at greater risk of culling,
calving induction and are more likely to have a shorter lactation.
The penalties for poorly grown heifers are severe and have implications for
many years

Front 7

What are rules of thumb target breeding weights in heifers?

Back 7

• British breeds: 65% of adult mature weight
• Bos indicus and Continental breeds: 70% of adult mature weight
-> critical weight for Brahman: 320 - 340kg
• For most breeds this will be >300 kg (less in Jerseys)
• Regular weighing heifers enables you to determine if they are on track or whether supplementary feeding will be needed to reach the desired mating weight in time for the start of breeding
• Draft heifers as you weigh them to allow preferential feeding of heifers unlikely to meet their target weights

Front 8

What is the growth Target Rule of Thumb?

Back 8

Assume all your calves are the same age as the oldest
in the group, as they will all be mated at the same time.
Holstein-Friesian target weight (kg) = age (months) x 20 + 40
Jersey target weight (kg) = age (months) x 15 + 35

Front 9

What is the relationship of herd age sttructure and the presence of persistently subfertile cows?

Back 9

• In dairy herds insufficient replacement heifers and inadequate culling of aged cows can increase the number of subfertile cows in a herd. So called “carry over” cows can have reduced reproductive performance and have a negative impact on herd reproductive performance. Such cows are often in the 2nd year
of their lactation having failed to conceive in a previous year, they are often heavier in condition and may have lower milk yields.

• In beef herds older cows (>10 years) may have reduced fertility and if not pregnant at the end of the mating period should be culled or ± speyed, fattened and sold.

Front 10

What are rrecommadations for bull management?

Back 10

• Bulls should be BSE tested, vaccinated for vibriosis, negative for BVDV (ie not persistently infected), not used on other farms (prevent introduction of veneral diseases), not overfed, & they should be looked after.
• Use young bulls over heifers: less likely to carry venereal diseases, lighter & less likely to injure heifers
• Consider bull rotation: every 2 weeks in a dairy herd

Front 11

How much bull power is needed for optimal reproductive performance

Back 11

• 1 bull/30 heifers
• Beef herds: For semen-tested bulls, 2.5% is sufficient, but up to 4% where they have not been tested.
• Where synchronising oestrus without AI - increase bull power ( 1 bull/10 to 15 females)
• Dairy herds: Bull power can be adjusted according to expected number of cows that are pregnant when a bull enters the herd.

Front 12

How would you check insemination practices for optimal reproductive performance?

Back 12

• Review insemination practices on farm
• Review hygiene
• Review thawing protocol
• Check semen if this may be a problem
• Check equipment – is the thermometer accurate, are correct doses of hormones being administered, check volume of delivery of vaccinator guns that are used to administer treatments
• Compare pregnancy rates between inseminators to detect differences which may indicate a problem with a particular inseminator. Require uniformity of cows and >50 cows to have a valid comparison.