No abstract

The objective was to test the efficacy of an intravaginal progesterone insert and injection of PGF2alpha for synchronizing estrus and shortening the interval to pregnancy in cattle. Cattle were assigned to one of three treatments before a 31-d breeding period that employed artificial insemination. Control cattle were not treated, and treated cattle were administered PGF2alpha or an intravaginal progesterone-releasing insert (CIDR) for 7 d and treated with PGF2alpha on d 6. The treatments were applied in one of three experiments that involved postpartum beef cows (Exp. 1; n = 851; 56+/-0.6 d postpartum), beef heifers (Exp. 2; n = 724; 442.5+/-2.8 d of age), and dairy heifers (Exp. 3; n = 260; 443.2+/-4.5 d of age). Luteal activity before treatment was determined for individual cattle based on blood progesterone concentrations. In Exp. 1, there was a greater incidence of estrus during the first 3 d of the breeding period in CIDR+PGF2alpha-treated cows compared with PGF2alpha-treated or control cows (15, 33, and 59% for control, PGF2alpha, and CIDR+PGF2alpha, respectively; P < 0.001). The improved estrous response led to an increase in pregnancy rate during the 3-d period (7, 22, and 36% for control, PGF2alpha, and CIDR+PGF2alpha, respectively; P < 0.001) and tended to improve pregnancy rate for the 31-d breeding period for cows treated with CIDR+PGF2alpha, (50, 55, and 58% for control, PGF2alpha, and CIDR+PGF2alpha, respectively, P = 0.10). Improvements in rates of estrus and pregnancy after CIDR+PGF2alpha, were also observed in beef heifers. Presence of luteal activity before the treatment period affected synchronization and pregnancy rates because anestrous cows (Exp. 1) or prepubertal heifers (Exp. 2) had lesser synchronization rates and pregnancy rates during the first 3 d of the breeding period as well as during the entire 31-d breeding period. The PGF2alpha, and CIDR+PGF2alpha but not the control treatments were evaluated in dairy heifers (Exp. 3). The CIDR+PGF2alpha-treated heifers had a greater incidence of estrus (84%) during the first 3 d of the breeding period compared with the PGF2alpha-treated heifers (57%), but pregnancy rates during the first 3 d or during the 31-d breeding period were not improved for CIDR+PGF2alpha compared with PGF2alpha-treated heifers. In summary, the concurrent treatment of CIDR and PGF2alpha improved synchronization rates relative to PGF2alpha alone or control. Improved estrus synchrony led to greater pregnancy rates for beef cows and beef heifers but failed to improve pregnancy rates for dairy heifers.

No abstract

A survey with horses was conducted to determine whether plasma concentrations of triiodothyronine (T3), thyroxine (T4), insulin-like growth factor (IGF)-I and IGF binding proteins (IGFBP) change as horses grow, mature sexually, and age. Jugular blood was sampled from Standardbred fillies and mares at ages 0, 1, 7, and 14 d, at 1, 2, 4, 5, 6, and 9 mo, and at 5 to 8 and 16 to 22 yr (n = 5 to 18). In a second survey, we measured the same variables in eight breeds of horses with markedly different adult body sizes, from Miniatures to Friesians. Plasma T3, T4, and IGF-I were determined by radioimmunoassays validated for horses, and IGFBP were estimated from radioligand assay following separation of the IGFBP by SDS-PAGE electrophoresis. Plasma T3 decreased (P < .01) nearly continuously from 7.9 ng/mL on the day of birth to .9 ng/mL at 6 mo, and then changed little from .7 ng/mL at 9 mo to .5 ng/mL in mares 16 to 22 yr old. Similarly, T4 declined (P < .01) from 233 ng/mL on the day of birth to 49 ng/mL at 14 d and varied from 35 to 9 ng/mL among all of the older age groups. Plasma concentrations of IGF-I increased (P < .01) from 285 ng/mL on the day of birth to 572 ng/mL at 14 d, remained relatively constant until 9 mo of age (530 ng/mL), and then declined (P < .01) to low levels (295 ng/mL) in the oldest mares. We detected six IGFBP. The two smallest IGFBP (26 and 39 kDa) were highest during the first 14 d after birth and lowest (P < .01) in aged mares. The four larger IGFBP were lowest at birth and increased to the highest values during the most rapid growth period, but these changes were not significant (P > .20). In agreement with data for other species, our data suggest that IGF-I and IGFBP modulate growth in horses. Although there were impressive interbreed differences in circulating concentrations of T3, T4, IGF-I, and IGFBP, these were not related to differences in adult body size.

Summary. Doses