This varies considerably and is largely affected by the weather conditions experienced. Excessive spring growth can impact the quality of feed available at this critical time.
Fluctuations in the nutrient quality, lack of energy in the feed particularly when related to the crude protein levels, can be one of the biggest factors impacting the reproductive outcomes of dairy cattle.
Adequate and consistent feed is crucial to achieving good rates of conception, and more importantly, maintaining viable pregnancies. If the rumen is receiving the right balance of energy, fiber, and protein, reasonable reproductive outcomes should be achievable. A well-functioning rumen, when receiving the correct balance of feed will provide the animal a basic level of essential nutrients. The rumen bacteria will be digesting, synthesizing, and then providing a combination of reasonably well-formed essential amino acids (in the form of bypass protein), minerals, and vitamins, to be absorbed further down the digestive tract.
The body requires a good balance of minerals, many of the essential amino acids, vitamins, enzymes, and hormones cannot be correctly synthesized without these essential minerals. A mineral blend designed for mating should be formulated based on robust science.
The focus is to supply the essential minerals in the correct form and adequate levels to fill the likely gaps in the diet, without risking toxicity or negatively impacting rumen performance.
There are some basic minerals that are recognised as essential to dairy cattle. Essential macro elements are phosphorous, potassium, magnesium, calcium, sodium, chloride and sulphur.
Micro elements, copper, zinc, manganese, iodine. Selenium, cobalt, chromium and boron.
Minerals that affect the empty rate include:
Calcium
Deficiency is well recognised as an issue for dairy cattle. What has changed more recently is our approach to managing this deficiency. In the past it has all been about stopping clinical milk fever, yet for every clinical case there is estimated to be up to four sub-clinical cases. Sub-clinical deficiency of calcium is now recognised as a cause in the development of many of the problems experienced during lactation, including poor reproductive outcomes.
Phosphorous
Clinical phosphorous deficiency is now common across many of the country’s dairy herds. In the past, New Zealand pastures delivered good levels of phosphorous. However, in many areas even pasture grasses are now becoming marginal for phosphorous.
Almost every metabolic function in the body relies on phosphorous particularly in energy metabolism. Higher levels of energy, particularly soluble sugars in the diet, increase the phosphorous requirement. Phosphorous is also closely tied to calcium; a deficiency in either element can impact the other.
Magnesium
This is a key catalyst to so many reactions in the body. Without magnesium both calcium and phosphorous utilisation will be limited. Whilst important, there is a tendency for farmers to over focus on magnesium at the expense of some of the other key elements. Balance is the key; it is important to maintain adequate magnesium levels, but not excessive levels which risks upsetting other key essential minerals. At times when cows are critically low in calcium, blood levels can often test excessively high in magnesium; excessive levels of magnesium can cause real mineral balance issues.
Sodium
This element is key to good rumen efficiency and needs more attention. Saliva production alone creates significant demand; large amounts are constantly being digested and excreted. Increasing salt to cows in most cases will have a direct effect on production. Sodium is also beneficial to the absorption and utilisation of most minerals in the diet. Many of the mineral absorption processes within the intestine require sodium.
