√ Mineral and vitamins
An adequate supply of many minerals and vitamins is needed before calving and throughout the breeding period for good reproduction efficiency. Blood calcium is not only important for milk synthesis but also for function of smooth muscle. Thus, hypocalcemia can increase the risk for metritis and displaced abomasum. Adequate (but not excessive) dietary concentrations of calcium, phosphorus, potassium, magnesium, and even sodium, chloride, and sulfur as they relate to dietary cation-anion difference (DCAD) are important for minimizing the risk for hypocalcemia and hypomagnesia.
In addition to its relationship with calcium, phosphorus has been a focus for many years relative to reproduction. A severe deficiency of phosphorus (usually reduced milk yields will occur before any negative effects on reproduction are observed with low phosphorus diets; that is, less than 0.25 percent of diet) will reduce reproductive efficiency; however, overfeeding phosphorus does not boost reproductive performance. As an industry, we went through several years of overfeeding phosphorus (e.g., 0.5 to 0.6 percent of diet); however, with the increased excretion of P and the associated risks to the environment and increased ration costs, phosphorus concentrations in diets were reduced. Dietary concentrations of 0.38 to 0.42 percentare adequate for cows in the breeding herd.
Adequate dietary concentrations of selenium, copper, and zinc are important for reproduction, especially in reducing the incidence of retained placenta and metritis. Dietary concentrations should be 0.3 ppm of supplemental selenium, 20 ppm of copper, and 70 ppm of zinc. Adequate concentrations of vitamins A, D, and E can be important for optimal reproductive efficiency. Adequate concentrations of vitamins E and selenium are important to immune function. The generally recommended dietary concentrations for close-up dry cows is 60,000, 15,000, and 1000 IU/day and for breeding cows 100,000, 25,000, and 500 IU/day for vitamins A, D, and E, respectively. Supplemental B-carotene, independent of its role as a vitamin A precursor, has improved fertility in some studies, but it is expensive.
In evaluating the potential that the feeding problem may be affecting the pregnancy rate in a dairy herd, the first and primary focus should be on energy status of the cows pre- and post-calving. The next step is to assess the calcium status; dietary concentrations of selenium, copper, and zinc; and dietary concentrations of vitamins A, D, and E. Although likely adequate, review the dietary phosphorus concentration. If embryo mortality is an issue in the herd and the herd has high MUN, the amount of RDP likely needs to be reduced. After reviewing the dietary components, discuss with your nutritionist the possibility of fine-tuning the feeding program for optimizing reproductive performance and for adding certain fat sources to provide specific fatty acids during the pre-breeding or post-breeding periods.