Effects of human chorionic gonadotrophin administration on Day 5 after oestrus on corpus luteum characteristics, circulating progesterone and conceptus elongation in cattle

Abstract

The aim of the present study was to test the hypothesis that elevated concentrations of progesterone (P4) resulting from the induction of an accessory corpus luteum (CL) by human chorionic gonadotrophin (hCG) administration on day 5 after oestrus would lead to advanced conceptus elongation on day 14 following embryo transfer on day 7. The oestrous cycles of cross-bred beef heifers were synchronised and animals were randomly assigned to receive either of two treatments: (1) intramuscular injection of 3000 IU hCG on day 5 after oestrus (n=14); or (2) intramuscular injection of saline on day 5 after oestrus (n=13). Ovaries were scanned daily by transrectal ultrasonography to assess CL development. Serum concentrations of P4 were determined from daily blood samples collected from the jugular vein. In vitro-produced bovine blastocysts were transferred to synchronised recipients on day 7 after oestrus (n=15 blastocysts per recipient). Heifers were killed on day 14 after oestrus and the uterus was flushed to recover the embryos. Injection of hCG on day 5 induced ovulation of the dominant follicle in all treated heifers and increased the total area of luteal tissue on the ovary, which was associated with a significant increase (P<0.001) in serum concentrations of P4 from day 7 to day 14. Positive associations were detected between circulating P4 with CL area (within-day correlations ranging from r=0.45 to r=0.67) and total area of luteal tissue (within-day correlations ranging from r=0.65 to r=0.86) Administration of hCG did not affect the proportion of day 14 conceptuses recovered. However, compared with the control group, hCG-treated heifers had increased conceptus length (3.91±1.23 vs. 5.57±1.02 mm, respectively; P=0.06), width (1.00±0.06 vs. 1.45±0.05 mm, respectively; P=0.002) and area (5.71±0.97 vs. 8.31±0.83, respectively; P=0.02). Although numerically greater, mean interferon-τ (IFNT) production in vitro did not differ significantly (P=0.54) between embryos recovered from hCG-treated and control heifers. In contrast, there was a strong positive correlation between individual embryo length (r=0.76; P<0.001) and individual embryo area (r=0.72; P<0.001) and IFNT production. In conclusion, administration of hCG on day 5 after oestrus resulted in the formation of an accessory CL and hypertrophy of the original CL, the result of which was an increase in P4 concentrations from day 7 onwards. These elevated P4 concentrations were associated with an increased conceptus area. Furthermore, conceptus size was highly correlated with IFNT secretion in vitro.

Corpus luteum development and its morphology after aspiration of a preovulatory follicle is related to size and steroid content of the follicle in dairy cows

“…In the current study it became apparent that the diameter of a pre-ovulatory follicle, which can be measured easily by ultrasound, is a suitable parameter for predicting the morphology of a subsequently developing CL and the plasma progesterone concentration for the following dioestrus, as long as ovulation occurs. These results are in accordance with Jinks et al (2013) Rizos et al (2012) and Luttgenau et al (2011b), but run counter to those of Luttgenau et al (2011a). Relationships between an increased size of preovulatory follicles, increased CL and increased pregnancy rates after artificial insemination have been clearly shown (Mussard et al 2007;Perry et al 2010;Sa Filho et al 2010).…”

“…Just before follicle aspiration, the diameters of the follicles were estimated by the distance measurement function (Caliper key) at two frozen images of the apparent maximal areas of each follicle and the calipers were positioned at the inner follicle wall. Measurements of the corpa lutea (diameter, perimeter, cross-section area of the luteal tissue) 14 days after aspiration were performed using the ellipse-function at two frozen images of the apparent maximal areas of each CL, according to Luttgenau et al (2011a) and Rizos et al (2012). The cross-section areas of solid CLs were considered as the cross-section area of the luteal tissue (31 cases).…”

Effect of follicular aspiration just before ovulation on corpus luteum characteristics, circulating progesterone concentrations and uterine receptivity in single-ovulating and superstimulated heifers

“…single-ovulating) heifers. This is important given the linear association between conceptus size and interferon-t production (Rizos et al 2012). Interestingly, while aspiration of multiple dominant follicles before the expected time of ovulation in superstimulated heifers was also associated with a compromised CL in terms of size and P 4 output compared with those that ovulated, there was no deleterious effect on conceptus size on day 14.…”

Paradoxical effect of supplementary progesterone between Day 3 and Day 7 on corpus luteum function and conceptus development in cattle

“…Most studies have used administration on Day 5 after oestrus with the aim of inducing the ovulation of a dominant follicle and the formation of an accessory CL. In a recent study from our group (Rizos et al 2012), as well as in the study of Kerbler et al (1997), P4 concentrations diverged significantly from the control 2-3 days after hCG administration, indicating a trophic effect on the endogenous CL in addition to the formation of an accessory structure.…”

“…This highlights the caution that is required when supplementing P4; it may be that strategies aimed at stimulating the development of the endogenous CL (e.g. manipulation of preovulatory follicle development (Wiltbank et al 2011) or administration of luteotrophic agents such as hCG (De Rensis et al 2010;Lonergan 2011;Rizos et al 2012)) rather than supplementation with exogenous P4 will be most effective. Alternatively, a combination of exogenous P4 and luteal support may prove beneficial in achieving a balancing between the apparent negative effects of P4 supplementation on development of the CL and the positive effects on conceptus development.…”