The concentration of lactose in the mammary secretion from individual glands of two sows increased significantly (P < 0·01) between 0 and 24 h after parturition. In six sows studied during the perinatal period there was a negative correlation (r = -0 .80; P < 0·02) at parturition between the concentration of progesterone in the blood and the concentration of lactose in the mammary secretion. Furthermore, the increase in concentration of lactose in the mammary secretion after parturition was related to the timing of the decline of plasma progesterone to low levels. The results indicate that the initiation of lactation occurs within 24 h of parturition in most sows, and the results are consistent with the hypothesis that progesterone withdrawal acts as the 'trigger'. Neither the changes in corticosteroid binding globulin nor the changes in total corticosteroids were temporally related to the initiation of lactation. However, a circadian rhythm was observed for total corticosteroids in the blood of three out of nine lactating and pregnant sows, whereas no circadian rhythm was observed in progesterone of the four pregnant sows. The results are discussed in relation to the disease complex mastitis-metritis-agalactia.

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The effect of progesterone and prostaglandin administration on the timing of farrowing was studied in three groups of 25 sows each .. Progesterone treatment (100 mg/day) on days 112, 113 and 114 of gestation (group I) significantly prolonged the gestation length to 116 A±0·4 (mean±s.e.) days compared to the control sows (group III; 115·5 ±O· 2; P < 0 ·05). Administration of prostaglandin (200 I1g Cloprostanol intramuscularly) on day 115 of gestation following progesterone treatment (group II) resulted in a gestation length of 116 ·0 ±0·1 days, with the sows farrowing 25 ·4± 1 ·0 h after the prostaglandin injection. 80 % of the sows farrowed between 0800 and 1700 h of day 116 of gestation.Plasma progesterone levels were maintained by the exogenous progesterone during treatment. At farrowing, higher levels of progesterone were observed in groups I and II compared to controls. Prostaglandin treatment did not significantly alter withdrawal of progesterone· in progesterone treated sows, suggesting that the actions of exogenous prostaglandin is primarily on the myometrium and the cervix.Hormonal treatment in late pregnancy did not have any adverse effects on piglet viability and growth rate, or subsequent reproductive performances of sows. Lactation was initiated normally, and the concentrations of lactose, protein, fat, IgG, Na +, Ca2+ and K + in colostrum and milk were similar in all groups during the first 5 days of lactation.

Twenty-four cows, diagnosed via rectal palpation as having ovarian cysts were randomly assigned to one of four groups to receive a single IM injection of either 0, 50, 100 or 250 /lg of synthetic gonadotropin-releasing hormone (GnRH). Sixteen lactating dairy cows exhibiting clinically normal estrous cycles were used as controls. Of the 18 cows receiving 50, 100 or 250/ag GnRH, 13 (72%) responded to treatment and returned to estrus 20.1 + 1.5 (range 9 to 27) days after treatment as compared to one of six receiving 0 /~g GnRH. Clinical changes in most cases were evidenced by increasing firmness of the cystic structure(s) which subsequently had palpable characteristics similar to corpora lutea. Plasma LH increased significantly (P<.005) on day 0 in cows following injection of GnRH.

No abstract