By Rainey Rosemond
This reference serves as a tool for the dairy industry, students, and educators to improve the efficiency of milk production with consideration for animal health. The following information was recently published in the 2021 Eighth Revised Edition of the Nutrient Requirements of Dairy Cattle.
Feed additives are ingredients not required in dairy cattle rations but may aid digestion, metabolism, and production; however, they are not nutrients. Ionophores, yeast and direct-fed microbials, enzymes, and essential oils are the considered feed additives and are highlighted in this article.
Ionophores
Ionophores are chemical compounds produced by bacteria that act as an antibiotic by altering the flow of ions across cell biological membranes. Rumen bacteria can be classified broadly as either gram-positive or gram-negative. Alterations to these populations could change how feedstuffs are broken down and the concentrations and types of volatile fatty acids produced for utilization by dairy cattle. Ionophores typically act on gram-positive bacteria, while gram-negative bacteria remain largely unaffected. Ionophores appear more effective at eliminating gram-positive bacteria because of their simplistic cell wall structure (Figure 1). Ionophores disrupt chemical gradients used by bacteria to balance internal environments, which can lead to cellular death if left unchecked.
Figure 1. Demonstrates the effect of Ionophores on bacteria.
Two main ionophores approved for use in dairy calf and heifer diets are monensin and lasalocid. These ionophores are used as a coccidiostat for young calves and are used to potentially increase feed efficiency in growing heifers. Only monensin is approved for use in the diets of lactating or dry dairy cattle. When monensin is fed to lactating dairy cows, methane production can be reduced along with molar concentrations of acetate. Molar concentrations of propionate are typically increased and assumed to be associated with higher blood glucose levels Ionophores have been shown to have modest impacts on digestibility, protein utilization and availability, and mineral absorption. One meta-analysis, containing 36 papers and 9,600 cows, found that monensin increased milk production but decreased milk protein and fat percentages; however, milk protein yield increased (Duffield et al., 2008b). Within this meta-analysis, monensin’s impact on milk fat percentage varies, and studies where milk fat is impacted are typically similar, with many studies not reporting effects.
Yeast and Direct-Fed Microbials
Direct-fed microbials (DFM) are a feed additive that contain live and viable microorganisms at the time of feeding. Yeast products can be considered a DFM if viable cells are available. Some yeast products do not meet this criterion and are not considered a DFM. When consulting with a nutritionist about adding yeast, discussing how products should be stored and incorporated in rations to be used effectively is best. Yeast products have demonstrated increases in milk yield and fat yield with varying impacts on milk protein and dry matter intake.
Unfortunately, data on direct-fed microbials is limited, and the data available is typically fed in concert with yeast. Direct-fed microbials are typically categorized as either lactic acid-using or lactic acid-producing bacteria. The theory behind supplying lactic acid-producing bacteria is that this group will provide a steady supply of lactic acid, thus, providing the substrates needed to increase the population of lactic acid-using bacteria. In theory, increasing populations of lactic acid-using bacteria would bolster the rumen against the negative impacts of large influxes of fermentable carbohydrates and rapid fluctuations in ruminal pH. Another theory posed in 2011 suggests that lactic acid-producing bacteria altered the intestinal microbiome, improving immune response (McAllister et al., 2011).
While yeast and DFM have typically demonstrated positive impacts on milk yield, their effectiveness in the field can vary. The DFM and some yeast products have to be carefully stored and incorporated into rations to be effective in practice. Make sure to follow all storage, usage, and feeding rate guidelines.
Enzymes
Enzymatic feed additives are produced by bacteria or fungi and target the digestion of fiber, amylose, or proteins. Though many different enzymatic feed additives exist, those used in practice frequently target improved fiber digestion. There are multiple proposed modes for how enzymatic feed additives aid in improved dairy performance which are listed below.
- Pre-ingestion breaking of chemical bonds
- Enzymatic activity within the rumen
- Working in concert with native microbial enzymes
- Enhancing attachment to feed particles
- Improved microbial growth
Many enzymatic feed additives have shown improvements in animal performance and digestibility of the ration; however, interactions between study design, stage of lactation, dietary interactions, and selected enzymes have produced varied animal response.
Though improvement in animal performance can likely be expected with the addition of enzymatic feed additives, the cost to purchase these feed additives should be considered in conjunction with expectations of production response.
Essential Oils and Other Phytonutrients
Phytonutrients are compounds extracted from plants that can directly impact microbial populations in the rumen. A well-known category of phytonutrients includes essential oils extracted by steam distillation and thought to modify microbial populations within the rumen. In theory, essential oils could be added to dairy cow rations to reduce environmental impacts directly by reducing the microbial populations responsible for endogenous methane production and potentially increasing feed efficiency.
While in the early stages of implementation, studies evaluating the use of essential oils in dairy heifer and dairy cow diets have been inconsistent and largely report no changes in milk production or composition or impacts on dry matter intake. Some potential reasons for variable responses include differences in dose, essential oil source, and the currently fed diet. With current knowledge, the future of essential oils in dairy cow diets is largely unknown, but there is potential use for environmental impact mitigation.
Feed additives can be included in dairy cattle diets for a variety of reasons and are advertised as a solution to many feed quality issues. However, feed additives should not be considered a cornerstone of any farm feeding program. The cost of any feed additive and associated animal performance should be carefully monitored and evaluated. If feed additives are frequently needed on a particular farm, or for a particular reason, dairy producers should reevaluate feed management and harvesting practices.
Source : .psu.edu