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Embryonic Loss in Cattle.

Economic success in dairy herds can be severely affected by pregnancy loss, which has effects on calving index, calving pattern, involuntary culling for failure to conceive, and genetic progress.  In the beef herd, pregnancy losses represent an even more important economic factor because most of the income is determined by the number of calves sold. Overall in the UK cattle industry, reproductive wastage has been estimated to cost £250 million per year (Sheldon, 1997).  In this forthcoming series of articles focussing on fertility, we will investigate in detail, why embryo loss occurs and what we can do to try and prevent it

.What do we mean by embryo loss?

Target pregnancy rates for cows are 55% - 60%, however early and recent experiments indicate that fertilization of the bovine ovum occurs  in up to 95% of cattle post-insemination, yet pregnancy rates in dairy cattle at 35 days after insemination are  around 35-45% - why and how does this occur? -It is this question which we shall investigate over this forthcoming series of articles.  Normally cows return to heat approximately every 18-21 days - and yes the majority of bovine ova are fertilized.  However when considering reproductive wastage and pregnancy loss, 75% of this occurs before day 21, either due to failure of fertilization or early embryonic loss (see Figure 1). As this occurs prior to the first return to heat, there is no noticed extension in the period between heats and the cow will return to oestrus normally by day 21 after insemination.  Late embryonic loss occurs between days 21 and 42 post-insemination, in this case, an extension in the normal period between heats will occur.  The current methods of pregnancy diagnosis, including milk progesterone sampling, ultrasound scanning and rectal palpation of the reproductive tract can only be used to monitor late embryonic death or foetal loss as they cannot be performed reliably before day 21 post-insemination and so early embryonic mortality can only be studied experimentally at present. 

So what goes wrong?

There are many factors associated with embryonic loss. Over the next few months we will approach each of the factors below – starting with the first 2 this month: ·        

Oocyte (or egg) quality and the effect of persistent follicles·        

Pregnancy recognition·

Progesterone and the uterine environment

Insemination protocols

Body condition score

Milk yield

Stress factors and disease

Nutrition

1.    Oocyte quality and persistent follicles

In cattle, low concentrations of progesterone prior to insemination, induces an increased pulse frequency of a hormone known as luteinising hormone (LH).  This can result in delayed ovulation or persistent follicles (also known as cystic ovaries). In both instances the oocyte prematurely ages before ovulating, resulting in chemical and physical changes with consequential embryo loss thereafter.  Fortunately the presence of a persistent follicle does not affect the developmental potential of oocytes from smaller follicles and normal fertility resumes if the persistent follicle or cyst regresses or is treated. 

That said ovulatory follicles develop under maternal influences for approximately 3-4 months before ovulation; and environmental influences, such as nutrition during this period may influence subsequent embryo survival. If we think about this for a second this suggests that in a dairy herd, when we wish to first serve cows by approximately 50-60 days after calving, the ovulatory follicle carrying the egg we wish to fertilise, started its development during the dry period.  Therefore dry period nutrition can have significant impacts on subsequent embryo viability.

To minimise the effects of delayed ovulation there are a number of areas you could revise with your vet.

Ensure prompt identification and treatment of cows with cystic ovarian disease, of cows not seen bulling by 40- 60 days after calving.

Optimise nutritional management 3 weeks pre-and post-calving – remember feed space and intake, not just ration. 

Change hormonal synchronisation protocols to facilitate timed ovulation rather than synchronised oestrus.

Consider use of a gonadotrophin (such as Receptal) at time of service to promote ovulation.

2.    Pregnancy recognition

When an embryo matures, from day 15 until day 28 post-insemination, it signals its presence to its dam by means of a hormonal dialogue, Failure of the embryo to signal its presence effectively during this period will result in the cow not recognising she is pregnant and therefore returning to oestrus.  Embryos vary in their ability to communicate their presence and so may not signal that they are there in a timely fashion.  Also smaller or damaged embryos are less likely to produce an adequate hormonal signal to communicate their presence, resulting in embryo loss.  During its development the embryo is protected from the normal immune response of the dam to foreign tissues, and if there is a failure in this protective mechanism, rejection of the embryo might occur.   

There are a number of “stressors” that may disrupt this tightly controlled recognition of pregnancy and we shall consider these in the next article.  In the meantime have a chat with your vet to discuss how embryo loss might be affecting your enterprise and read up next time on some of the most common causes of embryo loss in cattle and how you can optimise your management decisions to minimise those costly losses.

Tuesday 19^th October 2010 – Winter is on its way!

The temperature at 7am this morning was 3°C, as I started out on the road to my first routine herd health and fertility visit -  this coupled with the fact I am supping a Lemsip is a good indicator that  winter is well and truly on its way!  As I cope with what my wife affectionately terms “man-flu” I can empathise with the calves we have been treating for pneumonia this month.  I am pleased to say that in many of our youngstock units effective vaccination protocols have largely reduced the incidence and severity of calf pneumonia present.

On a number of our dairy units we have implemented a fortnightly calf health management & monitoring service, where calves are weighed and assessed for pneumonia and scours using a calf scoring system,  then where appropriate vaccinated, disbudded and castrated.  This has proved very successful in identifying calves with early onset of clinical signs of pneumonia and proved that early and aggressive treatment with antibiotic, and most importantly, anti-inflammatory drugs can prevent pneumonia outbreaks and limit loss in daily live-weight gain.  A word of caution though, antibiotics will not treat viral pneumonia, but will keep bacterial infections at bay, and furthermore vaccination will not be 100% effective if calves are kept in less than adequate environmental conditions. So when addressing calf health issues look at the bigger picture - investing and getting basic husbandry and environment right in the first instance, will improve calf health and welfare, ultimately saving you money in the long run.That’s it for now, back to my Lemsip and the less than satisfactory sympathy from my wife.

Jon Mouncey BVetMed DBR MRCVS

This article appeared in the November edition of South east farmer

Jon graduated from The Royal Veterinary College in 2003.  After graduation he worked in Carmarthenshire before moving to Cornwall to concentrate and develop his interests in bovine herd health and production medicine.  Jon joined Westpoint in August 2007, was instrumental in setting up the Westpoint Sevenoaks practice and became a Westpoint Veterinary Group director in 2009.  Earlier this year Jon obtained his DBR (Diploma in Bovine Reproduction).Jon is passionate about training and education within the industry and has significant teaching responsibilities, towards students from the Royal Veterinary College and has assisted in the development of the Dairymans Certificate for continued professional training of Westpoint dairy clients.