Ultrastructure of Bovine Ovarian Follicles Induced to Extended Growth by Perioestrous Suprabasal Progesterone Levels

The present study was undertaken to determine if a short-term prolonged growth of the ovulatory follicle (12 to 18 h after expected time of ovulation), induced by progesterone implants, would cause ultrastructural changes in the follicular wall. Oestrous behaviour, follicular growth, follicular and blood plasma levels of oestradiol-17ß, progesterone and plasma luteinizing hormone (LH) were monitored in heifers oophorectomized at 9 to 12 h (controls) or 36 h after the onset of oestrus, in order to sample the pre-ovulatory follicle present. The suprabasal plasma progesterone concentrations (approximately 1.2 nmol L−1) allowed expression of oestrus at the expected time, but ovulation was delayed owing to the absence of a LH-surge. The resulting prolongation of follicle growth was associated with mild degenerative changes in the follicle wall, i.e. both granulosa and thecal cells presented increased electron density, higher amounts of secondary lysosomes and lipid droplets, increased intercellular spaces with presence of debris. No signs of luteinization were seen.     

Characterization of estrus detection, conception and pregnancy risk of Holstein cattle from the central area of Chile

The objectives were to characterize the estrus detection risk (HDR), conception risk (CR), and pregnancy rate (PR) of postpartum (pp) Holstein cattle from the central area of Chile. The study used records of 2269 lactations from six dairy farms in central Chile (Mediterranean-type climate) during 2004. Three 21-d periods for estrus detection were considered (50-70, 71-91, and 92-112d pp). Estrus detection risk, CR, and PR at the first, second, and third periods were analyzed by logistic regression, whereas overall PR at the end of the 63-d study (112d pp) was assessed with survival analysis. The overall HDR was 51.1%. The HDR, CR, and PR were 48.4, 42.2, and 17.3%, respectively, during the first period; 52.8, 41.8, and 20.5% during the second period; and 52.9, 39.2, and 19.7% during the third period. The HDR was lower during Period 1 than during Periods 2 and 3 (P< or =0.05). Conception risks were not different among periods (P>0.05); however, PR was lower during Period 1 than during Periods 2 and 3 (P< or =0.05). Overall PR over time differed among parities, but was not significantly different among seasons. There were no significant interactions among parity, season and herd for HDR, CR and PR for the three 21-d periods. Parity 1 had higher CR and PR than Parity 2 and 3+ during Period 3. Overall, survival curves for the risk of non-pregnancy among parities (1, 2, 3 or greater) were different over time (P< or =0.05). Cows of Parity 1 became pregnant earlier than cows of Parity 2, and Parity 3 or greater. Survival curves for the risk of non-pregnancy among seasons (summer, fall, winter, and spring) were not different over time (P>0.05).     

Influence of low plasma progesterone concentrations on the release of prostaglandin F2α during luteolysis and oestrus in heifers

A study was conducted to determine the effect of suprabasal plasma concentrations of progesterone on the release of prostaglandin F_2α (PGF_2α) at luteolysis and oestrus. Heifers received silicone implants containing 2.5 (n = 4), 5 (n = 4), 6 (n = 3), 7.5 (n = 3), 10 (n = 4), or 15 (n = 3) g of progesterone, or an empty implant (controls, n = 4) between Days 8 and 25 post ovulation. Blood was collected frequently between Days 14 and 28 and assayed for progesterone and 15-ketodihydroprostaglandin F_2α. Basal progesterone concentrations in control heifers did not differ from those in heifers with 2.5- or 5-g implants and remained around 0.4−0.5 nmol l⁻¹ until ovulation in all three groups. In the heifers treated with 6–15 g of progesterone, basal concentrations were maintained at higher (P < 0.05) levels compared with those in the controls, ranging from 0.8 to 1.6 nmol 1⁻¹. The effect of these elevated progesterone levels was to delay ovulation by prolonging the growth of the ovulatory follicle, which continued growing until the implant was removed. In all experimental groups, the first significant increase of the PGF_2α metabolite occurred between Days 15.3 and 16.3 (P > 0.05) and was associated with the onset of a decrease in progesterone concentrations, which had reached levels below 3 nmol 1⁻¹ by Days 17.4−19.1. PGF_2α metabolite peaks associated with luteolysis were frequent until Day 20. In the period from Day 20 until implant removal, sporadic peaks were observed, ranging in number from 1.0 ± 1.2 (mean ± SEM) in the control group to 3.0 ± 1.4 peaks in the heifers treated with 7.5 g of progesterone (P > 0.05). The number of PGF_2α metabolite peaks during that period was higher (P < 0.05) in heifers treated with 10 and 15 g than in controls. A positive correlation was found between the basal concentration of progesterone and the number of PGF_2α peaks after luteolysis (r = 0.54; P < 0.01). Plasma progesterone concentrations above approximately 1.4 nmol l⁻¹ were able to maintain the release of PGF_2α until the progesterone implants were removed and plasma levels decreased to basal values. These heifers had a preovulatory PGF_2α release pattern resembling that found in repeat breeder heifers.     

Relationship between serum nonesterified fatty acids at calving and the incidence of periparturient diseases in Holstein dairy cows

The objective was to describe the relationship between concentration of serum nonesterified fatty acids (NEFAs) at calving and the incidence of periparturient disorders in Chilean Holstein dairy cows (Bos taurus). The study was conducted at two dairies (central Chile) with 700 milking cows each and similar management. Between July 2006 and March 2007, 350 cows were selected, and concentrations of serum NEFAs were determined at calving. The incidence of milk fever (MF), retained fetal membranes (RFMs), metritis, and clinical mastitis from calving to 100 d in lactation were consistently recorded. The relationship between concentration of serum NEFAs at calving and the incidence of periparturient diseases was determined using logistic regression. The main explanatory variable was concentration of serum NEFAs at calving. The incidence of MF, RFM, metritis, and mastitis was 5.4%, 15.6%, 10.8%, and 14.4%, respectively. There was no association between concentration of NEFAs at calving and the incidence of these conditions when the median value of NEFAs (0.9 mEq/L) was used as a cutoff. However, when the 75th percentile (1.2 mEq/L) was used as the cutoff, cows with values <1.2 mEq/L were 0.45 and 0.32 times as likely to develop clinical mastitis and MF, respectively, compared with cows with values ≥1.2 mEq/L. When the 90th percentile (1.6 mEq/L) was used as a cutoff, cows with values <1.6 mEq/L were 0.25 times as likely to develop clinical mastitis compared with cows with values ≥1.6 mEq/L. As a continuous variable, for every 0.1 mEq/L increment in NEFAs at calving, cows were 1.11 times more likely to experience clinical mastitis. In conclusion, cows with NEFA concentrations ≥1.2 mEq/L had a higher incidence of clinical mastitis and MF than that of cows with values <1.2 mEq/L.     

Effect of induced suprabasal progesterone levels around estrus on plasma concentrations of progesterone, estradiol-17beta and LH in heifers

A controlled study was carried out to investigate the effects of suprabasal plasma progesterone concentrations on blood plasma patterns of progesterone, LH and estradiol-17beta around estrus. Heifers were assigned to receive subcutaneous silicone implants containing 2.5 g (n=4), 5 g (n=4), 6 g (n=3), 7.5 g (n=3) or 10 g (n=4) of progesterone, or implants without hormone (controls, n=5). The implants were inserted on Day 8 of the cycle (Day 0=ovulation) and left in place for 17 d. The time of ovulation was determined by ultrasound scanning. Blood was collected daily from Days 0 to 14 and at 2 to 4-h intervals from Days 15 to 27. Control heifers had the lowest progesterone concentrations on Days 20.5 to 21 (0.5 +/- 0.1 nmol L(-1)); a similar pattern was observed in heifers treated with 2.5 and 5 g of progesterone. In the same period, mean progesterone concentrations in the heifers treated with 6, 7.5 and 10 g were larger (P < 0.05) than in the controls, remaining between 1 and 2.4 nmol L(-1) until implant removal. A preovulatory estradiol increase started on Days 16.4 to 18.4 in all the animals. In the controls and in heifers treated with 2.5 and 5 g of progesterone, estradiol peaked and was followed by the onset of an LH surge. In the remaining treatments, estradiol release was prolonged and increased (P < 0.05), while the LH peak was delayed (P < 0.05) until the end of the increase in estradiol concentration. The estrous cycle was consequently extended (P < 0.05). In all heifers, onset of the LH surge occurred when progesterone reached 0.4 to 1.2 nmol L(-1). The induction of suprabasal levels of progesterone after spontaneous luteolysis caused endocrine asynchronies similar to those observed in cases of repeat breeding. It is suggested that suprabasal concentrations of progesterone around estrus may be a cause of disturbances oestrus/ovulation.