Summary. Uterine fluid and blood serum samples were collected from 100 adult dairy cows during various stages of the oestrous cycle and analysed for their free amino acid content. A total of twenty-five free amino acids and amino compounds were identified in uterine fluids while only twenty-three were identified in blood serum. The concentration of the total and of most of the individual free amino acids was greater in uterine fluid than in blood serum at all stages of the oestrous cycle.The total content of free amino acids and the concentration of several individual free amino acids in uterine fluids showed cyclical variations. The significance of free amino acids in uterine fluids is discussed.

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The histological and histochemical features of the rete ovarii both of the superovulated and the control heifers were similar on each day on which they were studied. The cells of the rete ovarii were located in the ovarian medulla and were composed of oval-shaped nuclei with prominent chromatin and small amounts of light-staining cytoplasm. These cells were arranged both as a single layer and a pseudostratified layer (PI. 1, Fig.

Chemical analyses were conducted on uterine fluid and blood serum collected from eighty-eight normal adult dairy cows during various days of the oestrous cycle. Uterine fluid contained higher concentrations of reducing substances, potassium, inorganic phosphate and alkaline and acid phosphatase activity than blood serum while levels of calcium and sodium were higher in blood serum than in uterine fluid, supporting the concept that bovine uterine fluid is a product of active secretion and not of simple diffusion from the blood. Concentrations of reducing substances, total protein, potassium, chloride, inorganic phosphate and alkaline and acid phosphatase activity in bovine uterine fluid were all found to vary with the stage of the oestrous cycle, indicating that, in the case of these substances at least, secretion into the uterine lumen is under hormonal control. The level of alkaline phosphatase in the blood serum was also found to vary with the stage of the oestrous cycle.

Eighteen pregnant cows were individually housed and allowed to calve normally. None of the cows retained fetal membranes. Tissues were obtained for study on Days 1, 3, 5, 7, 11, 15, 19, 23, 27, 31, 45 and 60 post partum. Because the exact time of calving of each animal was not known, the term`D ay 1' represented an approximated period of 24 hr beginning from the time of observation of the calf with its dam in the maternity stall. Following exposure of the internal genitalia as described by Schultz, Fahning & Graham (1966), caruncular and intercaruncular uterine samples were obtained from an area at the base of the uterine horn by an in-vivo serial surgical technique (Archbald, 1969). Uterine samples were also obtained by percervical biopsy (Skjerven, 1956) and at necropsy. All samples were fixed in 10 % phosphate-buffered formalin for approximately 5 days. After trimming, they were embedded in paraffin wax, and sections cut at 6 µ were stained with haematoxylin and eosin as described by Humason (1967). Table 1 shows the chronological sampling sequence for each cow, and Table 2 shows the total number of samples obtained on each day postpartum and the method of sampling. The histological features of tissue sections from all the animals studied were similar. Sections of caruncular tissue revealed the presence of numerous