Over the years, I have had the opportunity to discuss winter feeding programs with numerous cow-calf producers across the country. One positive trend that I have noticed from these discussions is the widespread acceptance of mineral feeding.
However, when it comes to vitamins, there seems to be confusion or in some cases skepticism about the need for supplementation. To clarify this confusion/skepticism, I want to use this column to look at what vitamins cattle require, in what amounts and finally to explore how you meet these needs.
From a nutritionist’s perspective, there are two classes of vitamins — the water- and fat-soluble vitamins. The water-soluble vitamins include the B vitamins (i.e. biotin, vitamin B12 and thiamin) and vitamin C. In the vast majority of feeding situations, there is no need for supplementation, as rumen bacteria synthesize these vitamins and thus provide a supply to the host.
In contrast, the fat-soluble vitamins (vitamins A, D, E and K), with the exception of vitamin K, require supplementation, as rumen bacteria do not synthesize them. Another important difference is that cattle can store the fat-soluble vitamins for later use but do not store the water-soluble vitamins to any appreciable degree.
Newborn calves are an exception to the above, as they do not have a functioning rumen and thus do not have a bacterial source of the water-soluble vitamins or vitamin K. At this point in their life, colostrum and subsequently their dam’s milk are critical sources of both classes of vitamins and underscore the importance of appropriate nutrition of the dam.
Vitamin A is important for vision, reproduction and immune function, while vitamin D plays a critical role in calcium and phosphorus metabolism and bone growth. Vitamin E is an important antioxidant that interacts with selenium to provide protection to cells and tissues and is involved in immune function. In short, the fat-soluble vitamins are critical nutrients for reproduction, disease resistance and growth.
Vitamin requirements are expressed in terms of international units (IU) per kilogram of dry matter (DM). For example, the vitamin A requirement for pregnant and lactating beef cows as listed in the 2016 Nutrient Requirements of Beef Cattle (NRBC) publication is 2,800 and 3,900 IU per kilogram DM, respectively. A 1,400-pound beef cow eating 28 pounds (12.7 kilograms) of DM would require a minimum of 35,500 IU of vitamin A per day in late pregnancy and approximately 50,000 IU per day during early lactation.
While vitamin D is required by all cattle, those housed outdoors and exposed to sunlight — particularly in the spring, summer and fall — have little need for supplementation as the body produces its own vitamin D with the aid of ultraviolet rays from the sun. However, this production is minimal in the winter and thus it is important to supplement during the winter feeding period. The vitamin D requirement is 275 IU per kg of DM for all classes of cattle (NRBC, 2016) or 3,500 IU per day for the 1,400-pound cow discussed above.
Vitamin E requirements are even harder to characterize due to its interaction with selenium. According to the NRBC (2016), vitamin E requirements of mature, non-stressed beef cattle are low and likely met through “normal” dietary ingredients. Many nutritionists and veterinarians, however, recommend supplementation of vitamin E during the last trimester due to low dietary concentrations of this vitamin in conserved forages. Vitamin E requirements for growing calves range from 15 to 60 IU per kilogram DM intake, with higher levels recommended (i.e. 400 to 450 IU per day) for high-risk calves.
Finally, how can you ensure your cows get an adequate supply of the fat-soluble vitamins, particularly during late pregnancy and early lactation? Relying on conserved forages, as indicated above, is not an ideal practice as the level of vitamin A and E varies widely with feed type (i.e. hay vs. silage), maturity at harvest and storage conditions.
As such, supplementation is necessary and accomplished in one of three ways. These include through a mineral/supplement feeding program, as part of a total mixed ration, or as an intra-muscular injection. In the latter case, a two- to three-month supply of A, D and/or E can be injected as per label/veterinary instructions. While this is a proven method of supplementation, it can result in muscle damage and should be avoided if possible. The preferred method is via the feed, typically as part of a mineral program or through a specific supplement.
To determine if a given mineral or supplement has appropriate levels of these vitamins, one can calculate needs based on requirements and expected intake. If we go back to our pregnant 1,400-pound cow, if she is expected to consume three ounces (0.09 kilogram) of mineral daily, the mineral would need to contain (35,500 IU/0.09 kg) at least 400,000 IU per kilogram to meet her requirements. Post-calving, using a similar calculation, the mineral would need to contain a minimum of 550,000 IU per kilogram to meet lactation requirements. Similar calculations can be used to assess vitamin D and E levels in different mineral/supplement sources.