Comparison between lactating and non-lactating dairy cows on follicular growth and corpus luteum development, and endocrine patterns of ovarian steroids and luteinizing hormone in the estrous cycles

Effect of progesterone supplementation on fertility responses of lactating dairy cows with corpus luteum at the initiation of the Ovsynch protocol

“…One of the initial hypotheses was that supplementing progesterone would decrease the growth rate and the diameter of the ovulatory follicle, supposedly by reducing the frequency of LH pulses during the synchronization protocol [14,15]. However, the effect of supplemental progesterone on follicular diameter on the day of the second GnRH injection was only marginal, and insufficient to achieve statistical significance.…”

“…The underlying mechanism by which progesterone modulates fertility likely involves a change in the pattern of LH release. Endo et al [14] depicted a linear trend for the number of LH pulses to decrease concurrently with the increase in progesterone concentrations as the estrous cycle progressed. Data from beef cows also revealed a reduction in LH pulsatility as the concentration of progesterone increased with supplementation using intravaginal inserts [15].…”

Progesterone Profiles in the Caudal Vena Cava and Jugular Vein in Response to Pulsatile Luteinizing Hormone Stimulation Induced by GnRH Treatment During the Mid-luteal Phase in Lactating Dairy Cows

“…The day of luteolysis, as determined by the decrease in CL diameter and P 4 concentration [4], did not differ significantly between the GnRH and saline groups (day 17.3 ± 0.9 and day 17.5 ± 1.2).…”

“…It is widely accepted that pulsatile LH secretion is necessary for both structural and functional development of the corpus luteum (CL) [1,2,3]. We recently reported that lactating dairy cows had a greater frequency of LH pulses, higher progesterone (P 4 ) concentrations in the circulating blood and greater CL size during the mid-luteal phase than non-lactating cows [4]. A plausible interpretation of our findings is that the increased frequency of LH pulses in lactating dairy cows could enhance P 4 secretion by the CL.…”

Strategies to Manipulate Progesterone for Improved Ovarian and Fertility Responses in Bovines - A Review

“…The underlying mechanism by which P 4 modulates fertility likely involves a change in the pattern of LH release. There is a linear trend for the number of LH pulses to decrease concurrently with the increase in P 4 concentrations as the estrous cycle progresses (Endo et al, 2012). It is reasonable to speculate that these changes in LH pulse frequency are associated with alterations in the process of follicular maturation and subsequent embryo survival (Cerri et al, 2011).…”