A solid-phase radioimmunoassay was used to measure lh in the serum of a Zebu cow and heifer during the oestrous cycle. Shortly after the onset of oestrus, serum levels of lh rose sharply to 20 to 120 ng/ml before dropping to baseline levels of about 2 ng/ml after 8 to 10 hr. Elevated lh values were also detected in mid-cycle, although considerable variation in activity over several days occurred with the heifer. Peak values of lh were considerably higher in the serum of the cow than the heifer.

Progesterone and LH concentrations were measured in the plasma of blood samples taken from forty-eight pregnant ewes on Days 100, 120 and 134 of gestation. The ewes, in two groups of twenty-four were maintained from Day 100 until parturition on two planes of nutrition which supplied daily energy and protein intakes of about 4-1 or 2-3 Mcal metabolizable energy and either 192 or 111 g digestible crude protein per ewe. Within the groups, the ewes carried one, two or three fetuses and the feed intake was adjusted according to litter size to produce a uniform nutritional state within the group. On Day 100, litter size affected the concentration of plasma progesterone (P less than 0-001), but had no effect on Days 120 or 134 when the ewes were fed according to litter size. The low feed intake however caused a significant increase in plasma progesterone concentrations. The LH concentrations showed no major changes during late pregnancy and no effect of nutrition or little size on the plasma hormone concentration was observed. It was concluded that the effect of litter size on plasma progesterone concentration recorded on Day 100 or gestation was partly mediated by level of nutrition.

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