Samantha Tennent

Herd fertility is like baking a cake: all the ingredients must be included, exactly measured, then baked for the correct length of time. Cow health, body condition, nutrition, heat detection and bull management are some of the key herd fertility ingredients; and the reproduction ‘cooking’ time is a year-round focus.

Herd fertility ingredients heading into mating

Sift out endometritis

Cows with uterine infections have lower conception rates, lower 6-week in-calf rates, and higher not-in-calf rates.

Cows that have experienced various calving issues, (eg: assisted calving, stillborn calf, retained foetal membranes) can have an increased risk of endometritis. However, not all cows with endometritis have had calving issues so it pays to Metricheck.

My advice is talk to your vet about when to check your herd, as many cows can self-cure. Treatment takes time and cows must be treated at least four weeks before start of mating because this gives the cow the best chance to get in-calf early.

Remove bovine viral diarrhoea (BVD)

Infected animals can have lower fertility, conception rates, embryonic loss, and abortion rates.

When testing for BVD, take bulk milk samples when all the herd is milking into the vat, otherwise individual samples can be taken from cows not milking. It’s important to detect and eliminate BVD well before mating has started.

Mix in body condition

We recommend cows calve at BCS of 5.0, two and three-year olds at BCS 5.5 and they shouldn’t lose more than 1 BCS before Planned Start of Mating (PSM). Cows that don’t achieve these targets take longer to get back in calf and are more likely to be empty resulting in lower herd reproductive performance.

It’s important cows have stopped losing condition and are in positive energy balance before the PSM. There’s very little that can be done in the first four to five weeks after calving to prevent BCS loss, and the biggest driver of BCS loss after calving is BCS and feed management pre-calving.

Sprinkle good nutrition

Inadequate intakes of essential trace elements can result in decreased reproductive performance.

Deficiencies can be primary or secondary. Primary deficiencies arise because of insufficient particular trace element levels in the diet. Secondary deficiencies arise when the pasture contains something that reduces the uptake of the trace element.

Discuss with your vet whether some blood tests or liver biopsies would be worthwhile and what your trace element supplementation strategy should be for your herd.

Add heat detection

Monitoring heats before mating has many benefits. It’s an opportunity to practice heat detection, allows you to check for non-cycling cows and, if they have been recorded, it allows you to anticipate when a cow may be next on heat or help clarify questionable cows.

Apply one tail paint colour to every milking cow 35 days before mating start date. As they cycle and the paint is rubbed off, reapply with a new colour. Apply a different colour to the late-calving cows as they enter the milking herd. Maintain the tail paint throughout the pre-mating period, touching up and changing the paint colour as required.

If you record when cows cycle you will have more information to make decisions during the mating period. For example, when you are unsure if a cow is on heat or not, you can use her recorded pre-mating heat to determine if the timing is correct. It also allows you to gauge approximate numbers expected and if enough cows are being selected.

Check tail paint colours with all staff, make sure there aren’t any issues with colour blindness.

Knead non-cyclers

Pre-mating heat detection also allows you to identify cows that haven’t cycled and are at risk of being late calvers or empty. Work with your vet to formulate a plan with any non-cyclers, if you’re going to do something: do it early.

Mix in bull management

Move your bulls onto the farm two to three months before they will be put to work. Test them when they arrive and quarantine them for at least 10 days while you wait for the results. Use your results from last year to estimate how many bulls you require and continually assess; it may be worth extending AB for a few days to prevent any shortfalls.

The risk of service bulls carrying Mycoplasma bovis is low, particularly on farms that have had no signs of disease and have minimal stock incoming from other farms. Discuss whether getting bulls tested prior to purchase or use should be considered with your vet.

A recipe for success

Each ingredient contributes to the herd fertility mix, you need to add them at the right time to get your herd back in calf quickly and maximise profitability and efficiency.

For more information on reproduction and mating visit

  • Samantha Tennent is DairyNZ InCalf developer