By Dr Clive Dalton
When will a cow come on heat?
- Cattle reach puberty about 6-9 months of age but some calves can come on heat as early as 4 months of age – especially rapidly-growing Friesian calves. Puberty depends more on weight than age.
- If you ever have calves that get pregnant, it’s best to have them aborted as soon as you notice excess udder development as there may be no other signs. Check with your veterinarian for the appropriate action.
- Dairy heifers are mated as yearlings at 12-14 months old to calve around 24 months.
- Gestation in the cow is 283 days but in the dairy industry 14 days either side of this time is accepted as normal variation in terms of deciding the sire of the calf.
- Beef heifers have not traditionally been mated as yearlings, but this is changing if they are well grown to get more profit from the enterprise.
- A cow will cycle (show oestrus or come on heat) about three weeks after calving, but it is more likely to be six weeks. Don’t mate her at that first 3-week cycle: leave her to her second cycle.
- She should then cycle every 21 days after that if not pregnant, with a range from 18-24 days.
- An unmated cow will cycle all year round with slightly less activity in winter.
- There are nymphomaniac cows that cycle every 3 weeks all year round and never get pregnant after mating. They are a great nuisance. If a cow doesn’t get pregnant after 3 cycles, then get rid of her.
How long does a cow stay on heat?
- She normally stays on heat for about 8 hours but this can vary from 4-12 hours. In the short days of winter heat periods can be at the lower end of the range.
- Oestrus will start off with low intensity, rising to a state of “standing heat” when the cow will stand quite still when mounted by other cows.
- If a bull then tries to mount her she’ll often not accept him straight away. This is nature’s way of teasing the bull to concentrate his sperm before ejaculation.
- After this, heat intensity decline as she goes off heat and she’ll let nothing mount her.
What are the signs of heat in cattle?
Cows coming on heat
- They will attempt to ride other cows but will not stand to be ridden themselves.
- They smell other cows around the genital area.
- Have a moist, red swollen vulva.
- Are restless, walk a lot and bellow for company of other cows.
- Stand to be ridden and may also ride other cows.
- Hair will be rubbed off her tail head and muddy feet marks will appear on her flanks from being mounted.
- May stand with back arched and tail raised.
- Are nervous and excitable and graze less.
- Are restless, walk a lot and bellow for company of other cows.
- Have a moist red vulva with clear mucus coming from it.
- Dairy cows will hold their milk and often come into the parlour out of their normal order.
- Also watch any friendly heifers as they may try to mount their owners. It’s a bit scary to turn round and find a beast up on its hind legs about to land on you!
- Will not stand to be ridden any more but may attempt to rid others.
- The still smell other cows around the genital areas.
A SAG. The cow at right front is on heat, and the one waiting to mount her could be coming on. What about the other two watching the action? Are they coming on or going off?
This shows the value of observation skills and good records.
- Cows (especially in dairy herds) at various stages of their oestrus form groups of 2-6 sexually active cows referred to as a SAG.
- They are made up of cows coming on heat, those on heat and cows going off heat.
- They often rotate through the herd, forming, breaking up and reforming with new animals.
- With AI programmes it pays to keep good records of which animals have been inseminated to avoid confusion by this group behaviour.
- These are when a cow has been mated and comes on heat again after a shorter interval than the normal 18-24 days.
- Returning to oestrus in 10 days is a common abnormal interval. If this happens - mate the cow again and if possible use the same bull or semen to avoid confusion over parentage. If parentage is important then you can always have the calf DNA profiling to be certain of the sire.
What is a “silent heat”?
- This is when a cow fails to show outward heat signs but has ovulated (shed an egg). This can be confirmed through palpation of the ovaries by a veterinarian who can feel a Corpus Luteum or yellow body. This is where the follicle on the ovary has burst when the egg was shed.
- Silent heats are very frustrating as you have lost three weeks in time with no gain.
- The cow may have a silent heat for the first one after calving, and then start normal cycling after that.
- This problem has been reported to be more common in Friesian heifers than in Jerseys but the cause has not been fully investigated.
- If you have a cow that never cycles and vet inspection shows that she has had many ovulations – then get rid of her. Check her dam’s records and any other relatives in the herd as it could be a genetic problem.
Why do you use tail paint?
- Paint a short strip (100mm wide and 150mm long) along the tail head of the cow.
- Tail painting is a very cheap and easy way to identify cows coming into heat or on heat.
- When the cow is mounted by another cow, the paint will be scuffed and some rubbed off. It can be a good indicator along with other signs. She may also have skin rubbed off her back bone and muddy feet marks on her flanks.
- Buy the proper approved tail paint and follow the instructions.
- Use one colour and after the cow is mated change the colour. Use the traffic light colour sequence.
Can suckling calves delay return to oestrus?
- Yes it can.
- Suckling one calf will not delay heat much, but if you put more calves on a cow, then return to oestrus can be delayed by quite a few weeks due to the lactation drain on the cow.
- Yes - sometimes.
- Some dairy farmer experience shows that if the herd is slow to start cycling after calving, the sight, smell and sound of a nearby bull when walking past for milking will sometimes help stimulate their breeding cycle.
- Running a teaser bull with beef cows may also be worth trying but this means having access to one.
What is a teaser bull?
- A teaser bull is vasectomised so he is sexually active but does not ejaculate fertile semen.
- If fitted with a mating harness with coloured ink, teasers can identify cows on heat which can then be put up for AI.
- Teasers have all the dangers and disadvantages of keeping entire bulls so beware.
- Don’t keep them for more than one season as they often lose libido.
- If you get a bull vasectomised, get the vet to remove one testicle as a clear indicator of his status. It’s a lot easier than looking for a scar on the neck of his scrotum!
What is AI and AB?
Artificial Insemination (AI) also called Artificial Breeding (AB) in Australia and New Zealand, and is where semen is collected from a bull and after dilution is used either fresh or frozen to inseminate a cow on heat. For a successful programme you have to understand some facts about cow reproduction.
When is the best time to inseminate a cow?
- The best time is when she is going off heat, or has just gone off heat because this is when ovulation occurs.
- So in practice - if you see a cow on heat in the morning, have her inseminated in the afternoon of that day.
- If you see her on heat in the afternoon or evening, them inseminate her the next morning or early afternoon.
Where can you get an AI service?
- Look in the Yellow Pages of the telephone directory under Breeding Services. There is a wide choice of providers.
- Some organisations offer training so you can become a DIY operator, and some offer training with the proviso that you work for them for a period.
How to treat a cow after insemination?
- Quiet handling is important after insemination.
- Let her out of the bail into a small area on her own if she will stay there.
- If she’s getting upset at being on her own, give her a mate for company.
- Try to avoid putting her back with the rest of the cows till all her riding activity has stopped.
- Stray electricity. Check any troughs near your yards for stray voltage. There are cases of low conception rates when cows have drunk from troughs soon after insemination that were found to carry stray voltage from poorly-earthed fences.
- File the insemination certificates in a safe place.
- Mark on the calendar or wall chart the date 21 days after insemination, to watch to see if the cow returns to heat and needs a repeat insemination.
- But always watch out for short returns and file these records with the first insemination record as you’ll have to work out the calf’s correct sire when it is born in relation to the insemination date.
- Remember gestation in the cow is 283 days with a spread and 14 days either side of that is accepted as normal variation.
- This is a rapidly evolving area and it’s hard to keep up with developments.
- But there’s always a gap between what is possible in the lab and what you can achieve on the farm and at what cost.
- MOET – which is “multiple ovulation and ovum transfer” and is where you stimulate a cow to produce a lot of eggs. They can be fertilised naturally inside the cow after insemination or mating, or they can be flushed from the cow and fertilised with semen in the lab called IVF (in vitro fertilization).
- You can also collect the ovaries from old proven cows at slaughter and use the thousands of eggs still left that have not developed as future genetic resources.
- Eggs can now even be taken from young calves before puberty.
- Then there is cloning from body cells like Dolly the sheep that started from her mother’s udder cell. Cloning is now well established in cattle.
- Sexed semen has been on and off the market over the past decade but costs have so far restricted its widespread use.
- Just be aware that if you are going to submit a valuable cow to any of these modern technologies, you’ll have to accept variable results and with all the hormone treatment she will have, her natural reproductive life may be shortened. No doubt these risks will get less as time goes on.
How long will a cow keep on milking?
A dairy cow with good genetics will keep on producing milk for a couple of years without a pregnancy. Her yield will drop off to low levels after about a year but she’ll manage to produce about 3-4 litres/day for a very long time. The milk at these low levels of production may not be top quality as the cow’s udder is trying to shut down.
Drying off a lactating cow.
- This is best done by stopping milking completely or abruptly removing her calf.
- Never milk a cow every other day or increase the milking intervals before stopping and don’t let the calf back with the cow for any reason.
- Keep an eye on her for any sign of mastitis - red, swollen quarters that are painful to touch or her off colour and not eating.
- The teat canal must be allowed to seal naturally with a keratin plug, and milking or suckling again will reopen this and risk infection getting in.
- For cows that have had a lot of mastitis during lactation, talk to your vet about giving her “dry cow treatment” or DCT. You put a tube of long-lasting antibiotic up the teat into the udder where it remains active during the dry period to kill any infections that may arise. Don’t use DCT unless your vet recommends it and never use DCT antibiotics for lactation mastitis.
- You can also buy material to insert into the teat to seal it that has no antibiotic action.
- Before you put any product up a teat, be scrupulous about cleaning the end with meths and cotton wool until no more dirt comes off.
- The teat is the most sensitive part of a cow and they don’t like tubes pushed up them. So make sure she is well restrained and you are as gentle as possible.
- This was a great idea when it was developed over 20 years ago to abort the calf so the cow could return to oestrus and get back on to a yearly calving cycle which is so important to farming cattle profitably in New Zealand.
- But this now has a terrible animal welfare image among the general public, and the veterinary profession is keen to restrict its use and operate under very strict guidelines. Discuss these with your veterinarian who is the only person licensed to administer the drugs.
- Don’t induce very old cows, heifers, skinny cows or any that had problems at calving.
- Induction can be used to abort a heifer that got inadvertently pregnant as a calf, so will calve as a yearling. This pregnancy will generally be too much for the young heifer and will affect her future production.
- The other reason for inducing a cow is when you expect her to have a massive calf and consequently calving trouble. So if you can get her to calve a week or so early, it may make the birth process easier for her and be less risk to both cow and calf. Again seek veterinary advice.
- Intra-vaginal devices (IVDs) were also thought to be a great idea and the solution to getting cows to cycle that were slow to return to oestrus after calving. They were even promoted to improve herd fertility by ending up with less empty cows.
- IVDs are plastic devices that carry the hormone progesterone and are inserted in the cow’s vagina and left there for around 10-12 days.
- Progesterone tells the cow’s hormone system that it is pregnant so it stops cycling.
- When pulled out, the cows start cycling again and if a group has been treated, they will have their heat cycles and hence their calving dates synchronised.
- A cow that has not cycled after calving, treatment with an IVD may kick-start her system when it’s removed.
- As part of the programme, other hormones are used as well as progesterone to stimulate the egg follicle to ripen and then to burst and shed an egg.
- Like inductions, these now have a negative animal welfare image especially on women shoppers. And many farmers are now questioning the cost-benefit of their use.
Farmers don't like twins, as they bring extra work and mortality is high. Added to that is the 'freemartin' problem in cattle where the female in a female-male pair is usually infertile.
But in recent years, because the theory makes sense - i.e. cows which produce and rear two calves are a lot more efficient as measured by 'weight of calf weaned/kg of cow live weight', interest has be renewed.
At Clay Centre Nebraska researchers have a herd of cows selected for twinning which has been increasing at 3%/year since 1984. Calf litter weight for twinning cows is 0.8-0.9kg of calf/kg of cow weight, compared to the singles at 0.5-0.55kg of calf/kg of cow weight.
But the twinning cows have 20% death rates among the calves, dystocia, and triplets which nobody wants. The twinning cows also have lower pregnancy rates than cows suckling singles. At present there is no enthusiam for the idea.
Disclaimer This material is provided in good faith for information purposes only, and the author does not accept any liability to any person for actions taken as a result of the information or advice (or the use of such information or advice) provided in these pages.