PubMed Health⌕ Search

Biomedical subjects

I F Davis

Publications and source records attributed to I F Davis.

6 recordsLinked to original sources
PubMed1993

Feed intake affects metabolic clearance rate of progesterone in sheep.

To study the inverse relationship between feed level and concentrations of peripheral plasma progesterone, 36 ovariectomised ewes were fed rations at levels calculated to maintain liveweight (M). On the seventh day, the ewes were given an intravenous infusion of progesterone and the metabolic clearance rate (MCR) was calculated. The ewes were then randomly allotted to receive either 1/2M, M or 2M rations for seven days at which time the infusion and blood sampling schedules were repeated. The mean (SE) MCR of infused progesterone in ovariectomised ewes fed either 1/2M, M or 2M rations for seven days was 7.1 (0.59), 9.9 (1.64 and 13.0 (1.19) litre h-1 kg-1 of liveweight, respectively. Differences in MCR of progesterone between ewes fed 1/2M and 2M rations were significant (P < 0.05). The inverse relationship between level of feed intake and plasma progesterone concentration was attributed to differences in clearance rate of progesterone rather than to changes in the entry rate of the hormone into the blood.

Animals↗
PubMed1993

Liver blood flow and metabolic clearance rate of progesterone in sheep.

To study the effects of feeding on concentrations of peripheral plasma progesterone, ovariectomised ewes, given exogenous progesterone, were fed 750 g of chopped lucerne hay at either 09.00 (group A, n = 5) or at 15.00 (group B, n = 5) or were fed ad libitum regularly through the experimental period (group C, n = 5). Peripheral blood samples were taken from each ewe at 09.00, 11.00, 15.00, 17.00 and 23.00. In ewes of groups A and B, mean plasma progesterone concentrations declined significantly (P < 0.05) after feeding. Mean progesterone concentrations of group C ewes remained low and were significantly different (P < 0.05) from the pre-feeding values of group A and B ewes. These results showed that the metabolic clearance rate of progesterone changed with the act of feeding. In a second experiment, portal, hepatic and mesenteric vein cannulae were placed in ovariectomised ewes (n = 17). They were then fed a ration calculated to maintain liveweight for seven days (M ration). The ewes were then infused with progesterone into a jugular vein and with p-amino hippuric acid into a mesenteric vein. Ewes were then allotted to receive either half M or twice M rations for seven days after which the infusions and blood sampling procedures were repeated. The mean rate of blood flow in the portal vein was directly related to the level of feed offered when ewes received either 1/2M, M or 2M rations. The liver and gut region removed a mean of 96 per cent of the progesterone entering these tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Overfeeding during early pregnancy reduces peripheral progesterone concentration and pregnancy rate in sheep.

The 330 Merino ewes used in the study were placed with rams at a synchronized oestrus and, on Days 2-14 after mating, the ewes were placed in a feed lot and fed daily a low, medium or high ration (25%, 100% or 200% of maintenance respectively). Progesterone supplement was given to some ewes on Days 8-14 after mating by using a device containing 340 mg progesterone. Blood samples were taken from all ewes on Day 12 for measurement of plasma progesterone concentrations. On Day 14 after mating all ewes were returned to pasture. Pregnancy rate was determined by returns to oestrus and was later confirmed using ultrasound. There was a decline in the peripheral progesterone concentrations with increasing ration. The pregnancy rate in ewes fed a high ration was significantly reduced when compared with those of ewes fed a medium or low ration (48% vs 68 and 67% respectively; P less than 0.05). In ewes fed the high ration exogenous progesterone increased the pregnancy rate from 48 to 76% (P less than 0.01). Progesterone treatment did not influence pregnancy rates in ewes fed medium or low rations. The number of fetuses per ewe pregnant was not influenced by level of nutrition or progesterone treatment.

Animal Nutritional Physiological Phenomena↗
PubMed1982

The time of oestrus and ovulation following various synchronisation techniques using progesterone impregnated intravaginal devices.

Progesterone releasing intravaginal devices (PRIDs) were used in 4 experiments involving 67 cattle to study the effect of the stage of the oestrous cycle and of oestradiol benzoate (ODB) administration on the time interval from PRID removal to oestrus and/or ovulation. Cows in which PRIDs were inserted on days 2 to 4 of the oestrous cycle for 14 days were subsequently observed by endoscopy to ovulate significantly later than cows given identical treatments on days 13 and 14 of the cycle. The concentration of progesterone was higher in the former group at the time PRIDs were removed and remained at a higher level for 3 days thereafter. The length of the oestrous cycle of untreated heifers was significantly longer than in heifers treated for 12 days with PRIDs only inserted on day 3 of cycle (19.7 v 18.2; p less than 0.01). Treatment with PRIDs inserted for 12 days together with ODB further shortened the cycle length from 18.2 days to 16.9 days (p less than 0.01). The intervals from PRID removal to onset of standing oestrus in heifers treated with PRID only and those treated with PRID and ODB were 80h and 45h, respectively (p less than 0.01); the respective variances were 280 and 4; p less than 0.01). Plasma progesterone concentration, at PRID removal, was 3 times higher in heifers treated with PRID only than in heifers treated with PRID and ODB (p less than 0.01) and the interval from PRID removal to the lowest progesterone value following it was 3.8 ad 1.2 days for the 2 groups, respectively (p less than 0.05). The study indicated that the stage of oestrous cycle at PRID insertion is an important factor which influences the interval from withdrawal of PRIDs to ovulation. The results suggest closer synchronisation would follow insertion in the mid-luteal phase (Day 13 to 14) or use of ODB treatment at the time of insertion of PRIDs.

Animals↗