What are NVO's?

Non cycling cows also known as No Visible Oestrus (NVO) cows are a common and frustrating problem on most farms.

A period of noncycling called "anoestrus", following calving is normal and cows start coming on heat as the uterus recovers from pregnancy and reduces in size. Most cows will start cycling within 40 days of calving, assuming adequate nutrition and body condition. The cow will then come on heat every 21 (18-24) days until pregnancy occurs.

Conditions that prevent cows coming into heat post calving include:

  • Inadequate nutrition pre and post calving.
  • Any chronic debilitating disease process, such as uterine infection "metritis", left displaced abomasum and lameness
  • Any other cause of excessive weight loss.
First calving heifers usually take longer to start cycling activity due to the nutritional stresses resulting from continued growth and lactation, and often make up a major proportion of NVO's.

The veterinary examination and treatment of cows that have not been mated after one round of AI is a common and accepted procedure. Cows that have shown no sign of heat in the first 20 to 30 days of the mating period should be examined by a veterinarian, provided they have been calved for at least one month. In most cases this allows time for the treatment to work and the cow to be submitted for AI.

At this examination these cows will fall into one of the following groups:

  • Pregnancy
  • Uterine or ovarian pathology
  • Corpus luteum (CL) present
  • Active Ovaries
  • Small inactive ovaries
Uterine or ovarian pathology
Disease associated with the reproductive tract. Examples of some of these conditions include; pyometra, endometritis, or cystic ovaries. We are usually able to treat these conditions to get the cow cycling.

 

CL present
These cows may have been cycling and have not been detected, or may have had a silent heat. An injection of prostaglandin (PG) will bring these cows on heat in 2-7 days. Remember that normal heat lengths can be as short as 3 hours. Heat detection aids such as tail paint and KAMAR heat detectors are very useful, especially for cows that have quick heats.

 

Active ovaries
These cows may have already cycled (without showing heat) or they are about to cycle. Most only need more time and should cycle in 2-3 weeks. Again the heat detaction aids are very helpful for detecting these cows.

 

Small Inactive Ovaries
These are true anoestrus cows. Nutrition, lameness or illness are important common causes of anoestrus. After investigation of the causes for anoestrus and necessary treatment, these cows can be inserted with a CIDR and an injection of oestrogen.
This results in a very high percentage of anoestrous cows showing heat after CIDR removal.

Trial results have shown that some cows that fail to conceive do not come back on heat. This problem can be overcome using reinsertion of the used CIDRs (used but cleaned before reuse) and re-treatment with oestrogen. Re-treatment of anoestrous cows, is a low cost option that is worth considering.