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Chronic Food Restriction Amplifies the Effect of Lactation on the Duration of Postpartum Anestrus in Rats^1,2,

Division of Nutritional Sciences ^* Department of Animal Sciences, Cornell University, Ithaca, NY 14853

We studied the effects of food intake and lactation on the duration of postpartum infecundability in rats. Sprague-Dawley rats were given free access to a purified diet (AIN-76A^TM) or a similar diet (modified to contain twice the concentrations of vitamins and minerals) in amounts equal to 50% of that consumed by controls. At -65 d of age, animals were bred. At parturition, dams were allowed to nurse 4–5 pups, or all pups were removed. Thus, four groups were created: lactating control (n = 11), nonlactating control (n = 11), lactating food restricted (n = 8), and nonlactating food restricted (n = 10). Vaginal cytology was observed twice daily for the detection of proestrus, which occurred at 4.5 ± 0.5 and 6.7 ± 0.5 d (mean ± SD) postpartum in nonlactating control and food restricted groups, respectively (P < 0.005), and at 16.5 ± 0.5 and 28.8 ± 0.5 d postpartum in lactating control and food restricted groups, respectively (P < 0.0001). The interaction between food intake and lactation was significant (P < 0.0001). These results indicate that maternal food restriction exacerbates the effects of lactation in prolonging postpartum anestrus.

KEY WORDS: • rats • reproduction • ovulation • lactation

¹ Presented in part at the International Society for Research on Human Milk and Lactation, November 1990, Asilomar, CA [McGuire, M. K., Butler, W. R. & Rasmussen, K. M. (1992) Evaluation of the rat as a model for studying the mechanisms by which malnutrition and lactation prolong the duration of postpartum anovulation. In: Mechanisms Regulating Lactation and Infant Nutrient Utilization (Picciano, M. F. & Lonnerdal, B., eds.). Wiley-Liss, New York, NY.

² Supported in part by grants from the National Institutes of Health (R01 HD14953 to K.M.R.; M.K.M. was supported by T32 HD07331).

³ To whom correspondence and reprint requests should be addressed.

Manuscript received 9 December 1991. Revision accepted 20 March 1992.

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