Dairy cow reproduction

There are many factors that affect fertility and reproductive outcomes (such as submission rates, conception rates, 6 week in-calf rates and empty rates) in our dairy cattle and these include the following:

• Body condition at calving and at mating and the loss of condition after calving.
• Cow age.
• Transition management.
• Metabolic disease around calving such as ketosis and milk fever.
• Animal health problems such as BVD, mastitis, lameness, uterine infections and retained membranes.
• Rumen health such as acidosis.
• Feed inputs, energy balance, grass quality prior to and during mating.
• Milk production and peak production.
• Trace element levels.
• Heat detection.
• Days since calved.
• Insemination technique, semen handling, semen quality and concentration.
• Environmental conditions – poor weather, low sunlight hours, heat stress.
• Social stress
• Bull fertility, age, numbers etc.

There is a misconception that using reproductive hormones to try and get cows in-calf breeds infertility but, as can be seen from the list above there are many factors that are out their control which also affect fertility. Reproductive hormones are only a management tool to improve reproductive outcomes and they are used to:

• Get anoestrus/non-visible heat cows cycling.
• Maximise the number of cows inseminated within the first few days of mating.
• Maximise the number of potential mating events within a set mating period.
• Condense mating periods and hence calving spread.
• Maximise the number of cows inseminated during the AI/AB period.
• Synchronise animals for a fixed time insemination event (valuable semen, replacement heifers, bypassing heat detection) etc.

Often reproductive hormones are used (like the CIDr synchrony programs) in the here and now when faced with a problem (usually non-cycling, light condition cows at mating) just to get her cycling and to give her a chance of getting a mating event within a specific mating period. We have also been using GNRH hormones in repeat breeder high producing cows (to mixed results) to try to improve their conception rates.

When we follow cows that have been treated with hormones, there are no differences between these cows and other cows that were not treated in the following season. The exception to this is when we have used the hormones to drive mating performance and get an animal in calf that is of genetically lower fertility (i.e. she was always destined to be trouble!). Importantly, whenever we use hormones, they are only in the body for a short period (often metabolised within hours) and are identical to those she already produces herself.

Another tool we have been using is fresh high-density semen sourced from Tararua Breeding Centre (TBC). Dairy farms where we have trialled this have returned up to 1.2 times the conception rates compared to using semen from other sources. There is one main caveat to using fresh semen from TBC though and that is having to use semen from bulls that are part of TBC’s bull team which might not have the same genetics that suit your farm or production outcomes. It’s all about what you want to use the semen for – improving conception rates and hence days in milk or for improving genetics.

If you would like to discuss the options available to you around hormone intervention and the potential for using fresh high-density semen, please chat to us or to the Tararua Breeding Centre to see what approaches may be best for you and your farm. Cows in calf give you options at the end of the day!