1- Energy intake:

- The optimal age for Holstein heifers at first calving for total life time production was between 23 and 24 months of age.

-To achieve an average age at first calving of 24 months, heifers must reach puberty by 8 to 9 months of age.

- An excellent plane of nutrition is critical for heifers to reach puberty and first calving at 9 and 24 months and age, respectively.

- The nutritional balance of a dairy cow during the periparturient period has a tremendous influence on fertility and reproductive efficiency.

- Negative energy balance (NEB) is the result of increasing milk energy secreted (MES)‏‏‏‏ and maintenance energy (ME) oven the energy intake (EI) as expressed by the equation: NEB = EI – (MES + ME). 

- Negative energy balance can increase the period of postpartum anestrus and decrease fertility at first and subsequent inseminations depending on the severity of the imbalance.

- In cattle, under severe negative energy balance, the secretion of LH is inhibited.  Disrupted or decreased LH secretion slows the growth and development of the follicle which delay ovulation.

- Cows in negative energy balance have reduced levels of insulin–like growth factor –1 (1GF–1) which amplifies the effect of LH on the ovary through potentiating the signaling mechanism for LH.

- Cows that had first ovulation before 40 days postpartum had the highest concentrations of plasma IGF-1. Therefore, the interval to first ovulation is controlled primarily by energy balance.

-  In addition to decreased interval to first ovulation, improved energy balance during early lactation can decrease the incidence of other ovarian diseases.  For example, cystic ovaries are most prevalent in high producing cows that are in negative energy balance.

- Energy status at the time of breeding can also affect reproduction. Cows that loss weight at the time of breeding have lower fertility in association with decreased progesterone secretion by the corpus luteum. Inadequate uterine function may be related to lower progesterone concentration in cows in poor body condition. Furthermore, progesterone release in response to LH is severely diminished in the absence of IGF-1.

- Insulin can be used for induction of estrus in animals. The recommended dose is 0.25 IU/kg body weight subcutaneously for 3–5 days. The treatment of true anestrus buffaloes is satisfactory when single intramuscular injection of PMSG (500 IU) was combined with subcutaneous injections of insulin @ 0.25IU/Kg body weight for five consecutive days.

2- Proteins:

- A severe urea nitrogen level greater than 20 mg/dl, resulted in a lower conception rate.

- Cows fed 19 to 21 percent crude protein diets had higher blood urea nitrogen (21.3 vs 13.8mg /dl) and lower conception rate (62 vs 48 %) compared with cows fed diets containing 15 to 16 percent crude protein.

- Elevated blood levels of ammonia or urea or both could alter secretions produced in the reproductive tract itself and alter viability of the ovum, sperm or embryo. In addition, the hormonal balance required for normal function might also be involved.

-. Excess ammonia absorbed from the rumen of cows fed high– rumen degradable protein or soluble crude protein diets could down – regulate a hormonal or metabolic signal to the ovary.

3- Minerals and vitamins:

- Cows fed high calcium and vitamin- D diets prepartum had more rapid uterine involution, fewer days to first service, and fewer days open.

- Parturient hypocalcemia significantly increases the rate of dystocia and retained placenta. Hypocalcemia could reduce normal uterine function.

- Dairy heifers suffering from phosphorus deficiency have high rates of infertility as measured by services per conception. Increasing phosphorus in the diet returns blood levels to normal and fertility is improved.  A minimum Ca : P ratio of 1.5 : 1.0 and minimum daily intake phosphorus of 30g was suggested.

- Selenium and vitamin-E are the two most often considered for a herd suffering from reproductive problems. Supplemental selenium and vitamin-E 30 days prepartum reduced the incidence of retained placenta.

- Copper supplementation increases fertility when combined with increased phosphorus.

- Manganese has also been shown to influence reproduction. The conception rate was improved by feeding supplemental manganese.

-  Zinc is recognized as an essential nutrient required for normal growth. Zinc deficiency increases the length of labor and bleeding time in the rat and ewe. Zinc is important for testosterone biosynthesis and spermatogenesis.

- Beta–carotene has also been investigated as a nutrient having special requirements for reproduction. High levels of carotene were estimated in the blood, corpus luteum and follicular fluid, but effects on ovarian functions were not described.

- The most common trace mineral deficiencies in beef cow systems are copper and zinc. Supplementation of these minerals is needed. Increased amounts of both will be needed when feeding low quality forages. Copper needs will vary based on molybdenum and sulfur intake.

- Supplemental manganese may be needed if silage is fed; especially if the silage is contaminated with soil.

-  Phosphorus is the most expensive mineral to supplement. Producers should consider the contribution of the forage, and any concentrates (grains/co-products) fed to determine how much, if any, supplemental phosphorus is needed.

-  The less time cows spend grazing green forage, the greater their supplemental vitamin A needs.