Late-calving cows

Most spring-calving farms are now more than halfway through the breeding season. Some farmers have let bulls out with the cows, while others are continuing to carry out AI. While the first six weeks are critical from a compact calving point of view, failure to get cows in calf over the last few weeks of breeding can have a massive impact on overall empty rates and profitability.

The big issue is with cows that haven’t been seen bulling. Most of these should be the late-calving cows (April calvers). Is it OK to leave them alone and take a chance that they will come into heat, be served and go in-calf? Or should farmers intervene now?

There is a cost to both. Intervention requires the cow to be scanned by a vet and treatment will involve hormones: prostaglandin (PG) to bring forward a heat in the case of a cow who is cycling and progesterone in the case of a cow not cycling. A shot of PG will cost about €15/cow, while a progesterone programme (CIDR/PRID) with fixed-time AI will cost closer to €35/cow. Both of these hormones are available by prescription only, so the vet call-out fee might need to be factored into the costs too.

Not intervening at this stage also carries a cost, as there is a greater likelihood of the cow leaving the farm at the end of the season empty. Intervening at this stage is the only real hope of keeping these cows in the herd, but they will still be late calvers.

I know some farmers will give all cows not seen bulling a shot of PG and wait four or five days to see what comes into heat. At this stage it is too late to do this as too much time is lost waiting for cows to be seen bulling. Stephen Butler in Moorepark recommends that cows calved over 30 days and not yet served should be put on a CIDR and fixed-time AI protocol as in the timeline below. He says that the conception rate to CIDR and fixed time AI ranges from 40% to 60%, depending on time from calving and the fertility status of the cow (breed and body condition score). Similar conception rates are achieved with PG, but he says that the submission rate will be lower as not all cows will show signs of heat after PG.

Heifer calves

At this stage all replacement heifer calves should be off milk and on the best grass available. Aftergrass from baled silage taken in May should be available on many farms and, where this is not going to be eaten by the milking cows, it should be grazed by the calves. If most of this grass is needed for the cows, then fence off a smaller section and give it to the lightest of the calves.

Separating the calves based on liveweight should be a priority. Weighing and monitoring liveweight gains is the gold standard, but even separating the lightest calves on a visual assessment is worthwhile. The key is to know what is on target and what is not. There is no point in separating the lightest calves if even the strong calves are under target weight.

If no scales is available, then try get your hands on a weighband (accurate and easy to use on calves but not very accurate and dangerous on in-calf heifers). Alternatively, put three or four even heifers into a cattle trailer and weigh over the weighbridge in the local co-op to calibrate your own eye.

Target weights for February-born calves with an expected mature liveweight of 580kg are shown in the table. At the moment, they should weigh around 145kg. Over the course of their lifetime, these animals’ daily gain should average around 0.67kg. This seems low, but we must remember that growth rates decrease dramatically during the winter months when animals are housed, so higher than average growth rates are required during the summer months to achieve target weights.

March- and April-born calves need higher daily liveweight gains to get them up to target weight. So these animals should be on the better-quality grass and given preferential treatment. If there isn’t enough good-quality grass for these calves then meal should be fed too.

On meal feeding, 1kg of meal will provide about one-third of the calf’s diet, with the rest coming from grass. So even if meal is being fed, it will not make up for feeding poor-quality grass. The best calf performance seems to be when they are moved onto fresh pasture every four to five days and are not being asked to fully clean out the pastures.

Dosing

Most calves have probably received their first worm dose by now. There are two types of worms that we are trying to prevent; gut worms (Ostertagia) and lung worms (hoose) but lung worms generally aren’t a problem until late summer and autumn.

Before turnout, calves have no immunity to gut worms, maiden heifers should have some immunity and adult cows should have reasonably good immunity. Issues with a lack of immunity in the second year or in adult animals come about as a result of failure to build up enough immunity in the first year. This could be due to using too many doses and/or dosing too soon after turnout. Calves should be left at least three weeks after turnout to build up natural immunity against gut worms, but ideally calves should only be treated for the first time when sysmptoms show. Symptoms are very loose dung and poor thrive as observed by liveweight gains and faecal samples.

There are three options for dosing calves; using a drench dose every three weeks, using an ivermectin based dose at weeks three, eight and 13 or using a long lasting dose such as bolus or an injection behind the ear. Cost wise, there isn’t a whole lot of difference between the three products when you take into account the extra labour and product needed for the drench doses.

Riona Sayers in Moorepark is doing a trial to see if exposure to Ostertagia in dairy cows is affecting milk yield. Her initial findings suggest there is a slight advantage to dosing cows during lactation if a bulk milk sample for Ostertagia is positive and the score on the Svanova test is greater than 0.8. Based on her preliminary analysis, results greater than 1.0 on the same test would indicate a greater benefit of dosing. Farmers who get their bulk tank milk sample screened for disease with their processor will have results on their herd’s exposure to Ostertagia. Dosing during lactation costs between €5/cow and €8/cow so you want to be sure of a benefit before undertaking it. Faecal samples are the best indicator of exposure, but other factors such as thrive and body condition score should be considered before dosing too, she says.

Second-cut silage

Generally speaking, yields of first-cut silage are back on previous years. This stands to reason. While growth rates in the last three weeks of May were high, growth in April was very poor and many silage fields were grazed twice.

Does this mean more second-cut silage is required? Now is the time to decide. Measure what silage you have in the yard. Measure a silage pit in metres (length x width x average settled height) and divide by 1.3 to convert to tonnes. Multiply this by the dry matter of the grass to get tonnes dry matter. Most of the silage was harvested dry so, depending on the wilt, it should be around 25% dry matter. Add this to the silage in round bales, deducting the quantity you expect to feed out before winter. There should be around 220kg of silage dry matter in a bale.

As a rule of thumb, a dry cow will need about 1.2t of silage dry matter over the winter. An in-calf heifer will require a bit less at 0.9t and a weanling will need about 0.5t of silage dry matter. These figures are based on a 3.5-month winter. Extra silage will be required depending on your own farm soil type and how early you can get cows out to grass. A decent crop of second-cut silage will yield about 3t dry matter per hectare in the pit. On Index 3 soils, eight units of phosphorus and 28 units of potash along with 80 units of nitrogen per acre is recommended. Every 1,000 gallons of slurry per acre is equivalent to one bag/acre of 6.5:5:35, but on very sunny days the nitrogen value in slurry will be halved at best.

If buying silage as a standing crop, remember that between 20 and 30% of the silage in the field won’t make it to the cow’s mouth due to losses at harvesting, ensiling and feeding out.