Source: University of Massachusetts Amherst
Introduction
Nutritional management requires that dairy cows and their replacements be considered in three distinct groups of animals; a.) mature, non-lactating or dry cows, b.) lactating or milking cows, and c.) growing replacement animals. Each of these groups can in turn be subdivided into two or more groups to more closely match nutritional requirements with the appropriate ration. Meeting, but not exceeding dietary requirements maximizes production and hence profit potential and minimizes soil, water, and atmospheric impacts. It is more desirable to have fewer high producing cows than it is to have many low producing cows. This is due to the dilution effect of maintenance requirements and to lowered environmental impacts. Nutrient requirements for dairy cattle in all stages of growth and production are listed in the Nutrient Requirement of Dairy Cattle (NRC 2001), a book published by the National Research Council. Some nutrients that could have adverse environmental and production impacts are listed in the table below. For specific information regarding other breeds, bodyweights, and levels of production refer to NRC (2001).
| Holstein, 1500 lb., average body condition, 65 mo. age |
90 Days in Milk | Early Lactation | Dry, Pregnant 270 Days in Gestation BW 1656 lb. |
||||
|---|---|---|---|---|---|---|---|
| Milk yield, lb/d | 55 | 77 | 99 | 120 | 55 | 77 | |
| Dry matter intake, lb/d | 44.7 | 51.9 | 59.2 | 66 | 29.7 | 34.3 | 30.1 |
| Net energy, Mcal/lb | 0.62 | 0.67 | 0.7 | 0.73 | 0.94 | 1.01 | .48 |
| Diet % RDP | 9.5 | 9.7 | 9.8 | 9.8 | 10.5 | 10.5 | 8.7 |
| Diet % RUP | 4.6 | 5.5 | 6.2 | 6.9 | 7 | 9 | 2.1 |
| Crude Proteina, % | 14.1 | 15.2 | 16.0 | 16.7 | 17.5 | 19.5 | 10.8 |
| Calcium, % | 0.62 | 0.61 | 0.67 | 0.6 | 0.74 | 0.79 | 0.45 |
| Phosphorus, % | 0.32 | 0.35 | 0.36 | 0.38 | 0.38 | 0.42 | 0.23 |
| Potassiumb, % | 1.00 | 1.04 | 1.06 | 1.07 | 1.19 | 1.24 | 0.52 |
| Sodium, % | 0.22 | 0.23 | 0.22 | 0.22 | 0.34 | 0.34 | 0.10 |
| Copperc, ppm | 11 | 11 | 11 | 11 | 16 | 16 | 13 |
| Zinc, ppm | 43 | 48 | 52 | 55 | 65 | 73 | 22 |
Nutrients
Water The importance of access to clean fresh water for animals of all ages cannot be overemphasized. Vital metabolic reactions occur within the “universal solvent”, water. Failure to provide readily accessible clean water will result in depressed growth and production.
Energy
Energy is often limiting particularly in animals in the first half of lactation. The requirement for energy is satisfied by a combination of forages, concentrates, and a limited amount of supplemental fat. Dairy cattle have a specific requirement for forages, which are fermented by rumen bacteria to volatile fatty acids (VFAs). These VFAs supply a majority of the required energy to support maintenance, growth, and lactation.
Poor quality forages are poorly digested and result in lower production levels and higher volumes of manure. Feeding high quality forages decreases the need to supplement with concentrates. Rations with inadequate amounts of forages, forages that are chopped too finely, or excessive “sorting” of the ration by cows will have adverse effects on the beneficial rumen microbial populations and will result in decreases in quantity and quality (% fat and protein) of the milk. Concentrates and supplemental fats (not to exceed 8% of the ration) are fed to provide additional energy. Over or under supplementation can have profound effects on the production and health of dairy cattle.
Protein
The protein requirement for dairy cows is divided into two groups, the rumen degradable protein (RDP) and rumen undegradable protein (RUP). The RDP is utilized by the rumen microbial population for the production of microbial crude protein (MCP) which includes the microbes themselves as well as all of the proteins that they secrete. Eventually all MCP will flow down to the lower gastrointestinal tract where it will be digested and absorbed at the level of the small intestine. The RUP escapes rumen degradation and flows to the small intestine where it too is digested and absorbed. Excesses of protein, either RDP or RUP, will be excreted in the urine as urea. Milk urea nitrogen (MUN) levels can provide producers information regarding over or underfeeding of protein. The desirable range for MUN is between 9 to 14 mg/dl. Because protein is usually the most expensive component in the ration dietary excesses are not desirable in either an economic and environmental sense.
Phosphorous
Phosphorous (P) in feedstuffs is not utilized efficiently in ruminants. This, coupled with higher than needed requirements (due to misplaced concerns over reproductive and production performance) has led to overfeeding of P in dairy rations. A significant amount of dietary P is excreted in the manure, which has led to accumulating levels of soil P. The current dietary P recommendation for dairy cattle has been reduced (below the 2001 NRC recommendations) to 0.32-0.38%. It is recommended that mineral analysis on feeds be done using wet chemistry instead of NIR.
Note Meeting, but not exceeding dietary requirements maximizes production and hence profit potential and minimizes soil, water, and atmospheric impacts.
Resources
Federation of Animal Science Society. 2001. Feed and Animal Management for Dairy Cattle. https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_022992.pdf(link is external)
Nutrient Requirement of Dairy Cattle; 2001 Seventh revised edition; National Research Council; National Academy Press; Washington, D.C.
Van Soest, Peter, 1994; Nutritional Ecology of the Ruminant; Second Edition; Cornell University Press, Ithaca, NY.
