Anestrus

What is Anestrus?

Anestrus is the absence of estrus cycles — the cow fails to show heat and cannot be bred. It is one of the most common reproductive disorders in dairy and beef cattle, affecting 10–25% of cows at any given time. Anestrus is a symptom, not a disease — it results from underlying physiological, nutritional, or health problems.

Types of anestrus include: postpartum anestrus (delayed return to cycling after calving, normal up to 60–80 DIM), nutritional anestrus (caused by negative energy balance and low BCS), cystic ovarian disease (follicular or luteal cysts that disrupt the cycle), and lactational anestrus (prolactin from milking suppresses GnRH release).

The most common cause is negative energy balance in early lactation. When BCS drops below 5, the hypothalamus reduces GnRH pulse frequency, which suppresses LH release and prevents ovulation. Cows below BCS 4 at breeding have 30–50% lower conception rates.

Detection methods include: visual observation for heat signs, activity monitors (increased activity), progesterone testing (milk or blood), and rectal palpation/ultrasound (assessing ovarian structures). Treatment depends on the cause: improving nutrition, correcting BCS, treating cystic ovaries, or synchronizing with prostaglandin/progesterone protocols.

Diagnosing Anestrus

Visual observation requires 2x daily checks, 20–30 minutes each, ideally in the early morning and late evening when cows are most active. Look for: standing heat (cow stands when mounted), mounting other cows, mucous discharge from the vulva, restlessness, and reduced feed intake. Activity monitors (pedometers, neck accelerometers, or leg bands) detect increased movement during estrus — accuracy ranges from 85–95% depending on device and placement. Progesterone testing (milk or blood) is the gold standard for confirming cycling status: low progesterone (<1 ng/mL) indicates the cow is in follicular phase or anestrus, while elevated progesterone (>1 ng/mL) indicates a functional CL and active cycling. Rectal palpation or ultrasound assesses ovarian structures: presence of a CL indicates recent ovulation, large follicles (>10 mm) indicate follicular activity, and small inactive ovaries indicate anestrus. Test cows that haven't shown heat by 80 DIM — progesterone test at 50, 70, and 90 DIM to track return to cycling.

Anestrus Treatment Protocols

Nutritional anestrus: increase dietary energy (add concentrate or fat supplement), correct BCS to ≥5, reduce milking frequency to 2x/day if feasible, and minimize heat stress. Hormonal treatments depend on ovarian status: if a CL is present, prostaglandin (PGF2α, 25 mg IM) induces luteolysis and brings the cow into heat within 2–5 days. If no CL is present, GnRH (100 mcg IM) stimulates ovulation — follow with prostaglandin 7 days later (GnRH-PG protocol). CIDR (Controlled Internal Drug Release) protocols: insert CIDR device (1.38g progesterone) for 7 days, remove and administer PGF2α, then breed at observed heat or timed AI 48–60 hours after removal. This protocol achieves 40–50% conception rates in anestrus cows. Cystic ovarian disease: GnRH (100 mcg) followed by PGF2α (25 mg) 7 days later, or two doses of GnRH 10 days apart. Consult your veterinarian for hormonal protocols — proper timing and diagnosis are critical for success.

Prevention Through Nutrition

Calve cows at BCS 5–6 — cows that calve above BCS 7 lose more condition postpartum and are more likely to experience anestrus. Minimize BCS loss to <1 unit from calving to breeding — cows that lose >1 BCS unit have 30–50% lower conception rates. Ensure adequate energy density in early lactation rations: the ration should support peak milk production while maintaining BCS. A common mistake is feeding the same ration throughout lactation — transition to lower-energy rations as milk production declines. Reduce heat stress effects on intake: provide shade (reduces THI by 5–10 points), fans and sprinklers (reduce body temperature 1–2°F), and feed during cooler hours (early morning, evening). Heat-stressed cows eat 10–15% less, which directly impacts energy balance and cycling activity. Monitor BCS monthly — cows below BCS 4.5 at 60 DIM should be flagged for nutritional intervention. A BCS monitoring program costs $2–$5/cow but prevents thousands in reproductive losses.