Silent Heat

What is a Silent Heat? A suboestrus or silent heat in cattle, is defined as the lack of behavioural oestrus symptoms, although the genital organs undergo normal cyclical changes. The incidence of silent heat varies from 10% to 40% between different herds

Silent heat is the term used when a cow which has already shown heat signs shows them again after 6 weeks or later. The regular heat period at 3 weeks is often referred to as the silent heat. The heat signs might have been weak and therefore not observed. If the cow has been inseminated before, she might have had an early abortion so that she shows heat signs again 6-9 weeks after the last insemination. 

During a normal heat, cows show symptoms such as vocalizing, jumping on colleagues, sniffing, trickling in place, vaginal mucus, swollen and reddened vulva, bending of the back, daily decrease in milk production and decrease in appetite.
 

Normally the oestrus takes about 18 hours, in heifers for about 16 hours. In about 20% of individuals, the oestrus can be observed only for 6 hours, moreover, the symptoms are often shown only at night, which makes it very difficult to detect the heat properly and thus insemination in good time. In herds observed correctly, the detection rate of heat should be at least 80%.

Pyometra or silent heat

Prostaglandin f2 alpha causes regression of the corpus luteum.

Prostaglandin F2-alpha (PGF2-alpha) causes luteolysis or regression of the corpus luteum (CL) from day 5 to 18 of the estrous cycle in animals that are cycling making it useful for estrus synchronization. PGF2-alpha also causes regression of the CL in other conditions with a persistent CL such as pyometra, mummified fetus, mucometra, and macerated fetus.

Etiology

The presence of a CL on the ovary is a factor in creating a condition called pyometra or pus in the uterus. This may also result in a chronic inflammation of the uterus called endometritis. Regression of the CL is also a key event in controlling the bovine estrous cycle.

Causes of silent heat

• Hormonal imbalance
• Abnomal feeding of cows at the beginning of lactation
• Energy shortage (incorrect balance) in the ration
• Deficiency of vitamins,minerals or too many isoflavones(post-extraction soya meal) is also important
• Worse maintenance condition and changes in nutirition related to seasons

Clinical Signs

• Small vulva.
• Long tuft of hair at the ventral end of the vulva.
• Clitoris is prominent when you open the vulva.
• Complete anoestrus.

Diagnosis

• Rectal palpation and use of breeding records.

Prevention

• Proper feeding and mineral supplementation of dairy cows including:
  • Adequate quantity and good quality roughage.
  • Adlibitum mineral supplementation.
• Timely and regular heat detection.

Treatment 

• Use of hormones according to veterinary advice.