The aims of this study were to assess the accuracy of different common methods of differentiating between follicular and luteal
ovarian cysts, and to monitor the response of the
cysts to 12 days treatment with a
progesterone-releasing intravaginal device (
PRID). On the basis of agreement between the different methods, 25 of the 46 cases examined were diagnosed as follicular and 14 as luteal
cysts; for the other seven cases the methods disagreed. The use of ultrasound was more accurate in diagnosing
follicular cysts than luteal
cysts, and combined with plasma
progesterone concentrations gave the most accurate assessment of
cyst type (92 per cent for
follicular cysts and 82 per cent for luteal
cysts). The mean (se) plasma
progesterone concentration was lower in the cows with
follicular cysts than in those with luteal
cysts (0.29 [0.05] v 3.90 [0.63] ng/ml; P<0.05). Luteal
cysts had thicker walls (5.3 [0.04] v 2.5 [0.2] mm; P<0.0001), and the wall thickness of all the
cysts was positively correlated with plasma
progesterone concentration (r=0.52, P<0.0004). Cows with luteal
cysts had more additional follicles greater than 5 mm in diameter (P<0.01). In cows with
follicular cysts and other follicles greater than 5 mm in diameter, the mean
oestradiol concentration was 7.9 (1.8) pg/ml compared with 24.2 (3.1) pg/ml (P=0.002) in cows without other follicles greater than 5 mm in diameter on either ovary. At the time of
PRID removal, plasma
progesterone concentration had increased in the cows with
follicular cysts to 1.59 (0.06) ng/ml (P<0.05) and decreased in the cows with luteal
cysts to 0.87 (0.01) ng/ml (P<0.05), although there was no change in original
cyst structure in 45 per cent of the cases. However, new ovarian structures were frequently observed during the treatment. The overall pregnancy rate for cows with both types of
cyst after treatment was 50 per cent after three inseminations, but the first service pregnancy rate was only 18 per cent for cows with
follicular cysts and 28 per cent for cows with luteal
cysts.
After treatment, the fertility of cows with
follicular cysts was similar to that of paired herdmates, whereas cows with luteal
cysts took 40 days longer to calve again than healthy herdmates. However, the culling rate was higher for cows with
follicular cysts (41 v 11 per cent).