In this study, the researchers observed egg cells from mice and from monkeys. To conduct the study, they devised a microscope that would allow them to view the concentration and distribution of zinc atoms in individual cells. With the aid of the chemical that gives off light when exposed to zinc, the researchers documented the first zinc sparks 20 minutes after fertilization. Most fertilized eggs released two or three rounds of sparks, but the researchers saw as few as one and as many as five within the first two hours after fertilization. The sparks flared every 10 minutes, on average.
Previous research had shown that fertilization triggers cyclical changes in the level of calcium in the egg cell. The researchers noted that the zinc sparks always occurred after a peak in calcium levels inside the cell.
“The number, timing and intensity of these sparks could tell us something important about the quality of the egg and will be an important area for future research,” said Dr. O’Halloran, the article’s other senior author. “It’s may also be worth investigating whether the amount of zinc in a woman’s diet plays a role in fertility.”
Additional experiments helped confirm a role for zinc in the fertilization process. Typically, once the egg is released from the ovary, it must get rid of excess chromosomes in two stages as it prepares to fuse with the sperm. The team’s earlier research showed that the early accumulation of zinc is essential for properly completing the first stage, Dr. O’Halloran explained. The latest results suggest that zinc may act as a brake in between these stages, as the egg awaits fertilization. If the cell is fertilized, the zinc release appears to lift the brake. The cell discards its excess genetic material and begins to divide.
The researchers also showed that even unfertilized eggs would start to divide if zinc levels were artificially reduced, mimicking release. In addition, when fertilized cells were forced to take on additional zinc, the process was reversed.
“We have shown that zinc appears to regulate this precisely calibrated, intricate process,” Dr. Woodruff said. “The findings give us new insights into what these cells need to grow and mature properly.”
In last few hours of maturation, the mouse oocyte takes up over twenty billion zinc atoms and arrests after the first meiotic division, until fertilization or pharmacological intervention stimulates cell cycle progression toward a new embryo. Using chemical and physical probes, we show that fertilization of the mature, zinc-enriched egg triggers the ejection of zinc into the extracellular milieu in a series of coordinated events termed zinc sparks. These events immediately follow the well-established series of calcium oscillations within the activated egg and are evolutionarily conserved in several mammalian species, including rodents and nonhuman primates. Functionally, the zinc sparks mediate a decrease in intracellular zinc content that is necessary for continued cell cycle progression, as increasing zinc levels within the activated egg results in the reestablishment of cell cycle arrest at metaphase. The mammalian egg thus uses a zinc-dependent switch mechanism to toggle between metaphase arrest and resumption of the meiotic cell cycle at the initiation of embryonic development.
Manganese modulates the synthesis of steroid hormones as a cofactor for several enzymes involved in cholesterol synthesis including mevalonate kinase, geranyl pyrophosphate synthetase, and farnesyl pyrophosphate synthase (Curran, 1954; Benedict et al., 1965; Goering, 2003). Production of squalene is inhibited by a lack of farnesyl pyrophosphate synthase, limiting the precursors available for synthesis of cholesterol (Hurley and Keen, 1987). Cholesterol is a precursor for synthesis of steroid hormones including progestogens, androgens, and estrogens, all essential for optimal reproductive functions.
Mn preferentially accumulates in the CL compared to other tissues
Mn also plays a role in Ca metabolism
Assumptions:
Holstein Cow
BW 1499 lb/680 kg
Peak milk
2 months post calving
69 lb (31.4 kg); 117 lb (53 kg); 165 lb (75 kg) 8% MY decline
Conception at 4 months post calving
ADG 0.4 lb/0.2 kg w/conceptus
NRC predicted DMI
Default Environmental Conditions
Milk fat avg 3.9%
335 d MY
Beef cows were synchronized, bred to timed AI and then underwent the ovum pickup procedure.
Cumuls Oocyte complexes
In brief, category A COCs had an oocyte with homogenous, evenly granulated cytoplasm and numerous layers of compact, nonexpanded cumulus cells. Category B COCs were similar to A, but with fewer layers of cumulus cells. Category C COCs had ooplasmic irregularities, very few cumulus cells, and/or expanding cumulus cells. Category D COCs were atretic with expanded and dark cumulus vestment, denuded, lysed, and/or otherwise morphologically abnormal. All COCs graded A through C were pooled within pen and underwent in vitro maturation, fertilization, and embryo culture
Assumptions:
Holstein Cow
BW 1499 lb/680 kg
Peak milk
2 months post calving
69 lb (31.4 kg); 117 lb (53 kg); 165 lb (75 kg) 8% MY decline
Conception at 4 months post calving
ADG 0.4 lb/0.2 kg w/conceptus
NRC predicted DMI
Default Environmental Conditions
Milk fat avg 3.9%
335 d MY
Control 15mg/kg DM
High 30mg/Kg DM
High grew faster and had higher BCS
1st observed estrus was sooner
Liveweight at first observed estrus was lower
They were served at the same age and weight
Up to 8 months the H heifers had high levels of the liver enzyme GLDH which is an indicator of liver damage
In lactation all heifers had toxic levels of GLDH – 15mg/kg DMI is plenty
The high copper group were fatter at calving, Both groups eat the same, but the high copper lost more BC, by 14 weeks both had the same BCS
Control animals produced more milk in first 6 weeks
BHB was higher in high copper cows