Since results in the literature suggested that ovaries from cows receiving a restricted amount of feed might be less sensitive to LH than normal, an experiment was designed to test whether the sensitivity of the corpus luteum to LH in vitro was reduced by restricted feed intake. Ten Holstein heifers were assigned at estrus to either an adequate (100% TDN) or restricted feed intake (60% TDN). Plasma progesterone and LH were measured throughout the next three and one-half cycles. Progesterone concentration was only slightly affected, and LH concentration was significantly decreased in the cows on the restricted intake. The corpus luteum was removed on day 10 of the fourth cycle and incubated with three levels of LH. LH stimulated the production of progesterone by the corpora lutea from both groups; the increase was less, however, in the restricted group, particularly at the highest level of LH. The reduced response to LH by the corpora lutea from the cows receiving a restricted feed intake could have resulted from a lack of substrate reserves with which to respond to LH rather than to a reduced sensitivity to LH.
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Apgar et al. (1975) studied this question.