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Is nutritional anestrus precipitated by subfunctional corpora lutea in beef cows?
F N Schrick1, J C Spitzer, T Gimenez
1Department of Animal, Dairy and Veterinary Sciences, Clemson University, SC 29634.
Domestic Animal Endocrinology
|July 1, 1992
Summary
Restricted nutrition in beef cows can lead to a corpus luteum (CL) with reduced progesterone production in vivo, potentially preceding nutritional anestrus. However, the luteal tissue itself may not be inherently subfunctional when evaluated in vitro.
Area of Science:
- Reproductive endocrinology
- Animal science
- Nutritional physiology
Background:
- Nutritional status significantly impacts reproductive function in livestock.
- Understanding the effects of restricted nutrition on corpus luteum (CL) function is crucial for managing fertility in beef cows.
- Previous studies suggest a link between negative energy balance and impaired reproductive cycles.
Purpose of the Study:
- To investigate the effects of restricted nutrition on corpus luteum (CL) development and endocrine status in postpartum beef cows.
- To determine if nutritional restriction impacts progesterone (P4) secretion, luteinizing hormone (LH) responsiveness, and CL characteristics in vivo and in vitro.
- To explore the relationship between nutritional anestrus and CL function.
Main Methods:
- Thirty-four multiparous, lactating beef cows were assigned to either a control (CON) or restricted (RES) diet for 40 days postpartum.
- Hormone levels (P4, LH, insulin) were monitored daily via blood sampling, and CL development was assessed using ultrasonography.
- Ovariectomy was performed on selected cows to collect CL for in vitro analysis of P4 synthesis, LH responsiveness, and LH receptor number.
Main Results:
- Restricted diet (RES) cows lost bodyweight and body condition score (BCS) compared to controls (CON).
- RES cows exhibited lower serum insulin and progesterone levels during the estrous cycle prior to ovariectomy.
- Despite lower in vivo progesterone, CL and ovarian weights, P4 content, LH responsiveness, and LH receptor number were not significantly different between CON and RES cows.
- Some RES cows developed subfunctional CL (P4 < 1.5 ng/ml), and others showed prolonged periods without estrus or ovulation.
Conclusions:
- Nutritional anestrus in beef cows may be associated with a CL that has reduced steroidogenic output in vivo.
- Luteal tissue from nutritionally restricted cows did not demonstrate subfunctionality in vitro under controlled conditions, suggesting substrate or systemic factors are limiting.
- These findings highlight the complex interplay between nutrition, systemic hormones, and CL function in regulating reproductive cycles.