Aspects and mechanisms of low fertility in anovulatory dairy cows

Abstract

Postpartum anovulation is a natural process that is observed in most mammals, including women. In lactating dairy cows, the interval from calving to first ovulation typically averages 4 to 5 weeks, but a substantial proportion of cows have not resumed estrous cyclicity by 60 days postpartum. Extended delay in resumption of first postpartum ovulation is known to exert long-lasting detrimental effects on fertility in dairy cows including the lack of spontaneous estrus and subsequent timely insemination postpartum, but when anovular cows have the estrous cycle synchronized for artificial insemination (AI), still pregnancy per AI is reduced and the risk of pregnancy loss increased. Many risk factors exist for extended postpartum anovulatory periods such as negative nutrient balance and diseases, and these risk factors are also known to depress fertility by themselves. A key feature in anovular cows when inseminated is that they develop the ovulatory follicle under subluteal or low concentrations of progesterone. Progesterone from the corpus luteum is pivotal for follicle development, oocyte competence, embryo growth, and endometrial function; however, many of these effects exerted by progesterone are mediated either by secretion of gonadotropins influencing follicular function and oocyte competence or by endometrial histotroph secretion influencing embryo/conceptus growth and developmental biology. Sub-optimal concentrations of progesterone during follicle growth in anovular cows affect morula and early blastocyst quality, alter conceptus gene expression and affect endometrial function increasing the synthesis of prostaglandin F2α . When anovular cows receive sufficient supplemental progesterone during the antral stages of development of the ovulatory follicle, then pregnancy per AI is reestablished and resembled that of estrous cyclic cows that developed the follicle during diestrus. Preliminary data suggest that a minimum concentration of progesterone during follicle growth is needed to optimize fertility in anovular cows, at least 2.0 ng/ml.

Evaluation of efficacy of selected estrous synchronization programs depending on the functional state of the ovaries, heifers and cows of meat breed

“…The effect on P/AI of Model 4 was detected in the 1 st synchronization where the diameter of CL was the same in all group both at day −7 and day 0. The benefit of treating cows with P4 during the TAI programs was greater in cows without CL than those in dioestrus (Santos et al, 2016). The mean size of CL at day 10 after ovulation was similar after synchronized (13.2 ± 1.5 mm) and spontaneous oestrous (13.5 ± 1.7 mm) (Quezada-Casasola et al, 2015).…”

“…Progesterone (P4) for over 30 years has been used to monitor ovarian activity and it is well accepted that blood serum P4 ≥1 ng/ml indicates a functional corpus luteum (CL), whereas concen-trations <1 ng/ml the lack of a functional CL or non-cyclicity (Colazo et al, 2008;Stevenson et al, 2015). In terms of the oestrus cycle phase, cows in dioestrus had higher mean P4 concentrations (6.0 ± 0.05 ng/ml) than those in oestrus or anoestrus (0.8 ± 0.01 and 0.6 ± 0.01 ng/ml), in prooestrus, oestrus and metoestrus usually will have either a small or no visible CL, and concentration will be below 1.0 ng/ml (Colazo et al, 2008;Santos et al, 2016). It is clear that cows that develop the ovulatory follicle ABSTRACT.…”

“…(>10 mm) with low P4 concentrations have marked reductions in pregnancies per artificial insemination (P/AI) (Santos et al, 2016).…”

“…In addition, treatment with PGF 2α in the early stages of the oestrous cycle (first 5 days) was found to be ineffective in causing a luteolytic response in cattle (Dirandeh et al, 2015). The use of exogenous progesterone inserts (for 7-9 days) during a synchronization program increases blood P4 in suckled beef cows, increases the proportion of cows detected in oestrus and increases P/AI of cows subjected to timed AI (Garcia-Ispierto and Lopez-Gatius, 2014;Santos et al, 2016;Stevenson and Lamb, 2016). The observation that the presence of CL and not oestrus cyclic status has the greatest impact on P/AI is critical considering that approximately 25% of the cows receiving the first AI postpartum and 22 to 46% of those receiving resynchronized AI lack a CL when the synchronization protocol is initiated (Santos et al, 2016).…”

Secretory activity of cattle mammary gland tissues during lactation and duration of the interlactation period

“…The sources of these proteins in milk are different: gamma-casein, immune globulins and albumins enter the milk after almost unmodified (or only partially altered) extraction from the blood, casein and lactoalbumins are translation products on the ribosomes of EPR cells of a mammary gland (Kambur et al 2009). According to some data, albumins get into milk not only due to their extraction from the blood, but also partial (within 10%) synthesis by mammary gland cells, which changes the traditional idea of the liver as a single organ -the place of albumin synthesis (Santos et al, 2016). Therefore, the prerequisite for changes in the level of proteins that get into milk are surely the energy value of the feed and the physiological state of their body, because both ways of protein penetration into milkdirectly or indirectly -are determined by circulation of either proteins in the blood or precursors for their synthesis.…”