Rethinking energy for lactating cows
When formulating rations for lactating dairy cows, many nutritionists currently focus solely on the total non-fiber carbohydrate (NFC) fraction. However, it is increasingly important to measure the individual components that make up the NFC, including starch, sugars, soluble fiber and β-glucans — and it is similarly important to formulate rations that optimize the concentration of each component.
Starch, which typically constitutes 50–100% of the nonstructural carbohydrates in most feedstuffs, must be given careful consideration when formulating rations for dairy cows. Generally, the recommendations for dietary starch commonly fall between 23–30% of the ration’s dry matter (DM), depending on the forage content of the diet. It is also crucial to consider the ruminal degradability of the starch and other dietary carbohydrate fractions. This means optimizing the entire carbohydrate profile, including the pool sizes and digestion rates, to formulate the best possible ration.
Dietary starch enhances the diet’s energy content
Starch constitutes a significant portion of dairy cattle diets, varying from less than 20% in dry-cow diets to over 35% in the diets of lactating cows. Cereal grains are the primary source of dietary starch, with their starch content ranging from 60% in corn grain to 79% in broken rice (on a DM basis). Corn silage can vary in its starch content, from less than 1% to as much as 40% of the DM.
The quality of a grain is closely related to its starch content, with broken grains (such as rice and corn) typically having a lower starch value. To boost energy intakes in lactating dairy cattle, feeds that are high in starch are often used to replace fibrous forages and other feeds. Moreover, when diets that are high in starchy grains and, consequently, lower in NDF are provided to lactating cows, their dry matter intake (DMI) usually increases (Allen, 2000).
Starch digestion
Starch digestibility is also affected by other factors, such as the genetics of the grain particle size, grain processing and the moisture content . Furthermore, the harvest maturity, the duration of silo fermentation and the corn endosperm type can also influence starch digestibility.
Lab analysis for Starch
- NIR spectroscopy: This test relies on near-infrared light absorption by molecular vibrations of the sample. Accurate results can be achieved with the proper calibration of each feed ingredient, but results may vary based on the sample matrix, mix feed, TMR, silages, etc.
- Microplate reader/spectrophotometer: This process involves the physical and chemical manipulation of a sample to extract or identify specific components. When performed correctly, this assessment is highly accurate and precise and is suitable for every type of feed, including both individual ingredients and mixed feed.
The starch content of feed stuffs in India
Agronomic practices across India vary according to geography, and as a result, the quality and nutritional parameters of various ag commodities can vary as well.
*Source- Alltech’s IFM Lab
Feed millers across India choose the region from which they will purchase corn grains based mainly on price parity. As a result, the quality of the corn is generally uniform across all regions, resulting in a similar starch quality. The starch content, however, is generally around 60%, which falls short of the ideal book value of 65%.
The starch content of corn silage affects its energy content, with the lowest starch levels reported in samples from East India and the highest in samples from Punjab in North India. Consequently, the net energy for lactation (NeL) of corn silage from North India is higher than that from other regions of India. To address this deficiency, farmers and feed millers must supplement with additional corn grain.
Fecal/dung starch content
Fecal starch analysis can be a valuable indicator of starch digestion efficiency in cows, offering insights into dietary management and digestive health.
The fecal starch concentration (FS) has been proven to be an accurate indicator of total-tract starch digestion (TTSD) by dairy cattle. FS has also been used to assess how effectively grain is processed. Monitoring fecal starch levels is a practical way to assess how effectively dietary starch is utilized within the rumen. High fecal starch concentrations suggest incomplete ruminal fermentation and poor starch digestibility, which can lead to suboptimal nutrient utilization and metabolic disturbances. Conversely, low fecal starch levels indicate efficient starch breakdown and absorption in the rumen, contributing to improved feed efficiency and overall animal performance.
Fecal starch concentrations below 1% may suggest highly efficient starch utilization, but they can also indicate potential issues with underfeeding starch or excessive rumen fermentation of other substrates. Conversely, fecal starch concentrations exceeding 3% may indicate suboptimal starch digestion, which could potentially lead to nutrient wastage, metabolic disturbances or digestive disorders.
Summary
- When balancing rations for starch, 20–30% is an acceptable range in lactating cow diets on a DM basis (Grant, 2019).
- High starch in feed can lead to acidosis and hamper milk production.
- Low starch in feed can result in a low availability of energy, and microbial growth in the rumen may also be affected.
- Samples of grain, silage and/or TMR should be analyzed periodically. Alltech’s IFM lab offers accurate starch analyses via a microplate reader/spectrophotometer.
- Amaize® is an enzymatic supplement from Alltech that is designed to increase the use of grain starch and provide slow glucose release from starch, promoting butyrate, which is an important energy source for cows.
Redefining dairy nutrition through Alltech IFM®
Alltech IFM® is an in-vitro fermentation model for dairy cows made possible in India through a strategic alliance with Bangalore Veterinary College at Karnataka Veterinary Animal & Fisheries Sciences University (KVAFSU). This diagnostic tool simulates rumen fermentation and evaluates the nutritive value of a total mixed ration (TMR), compound feed and/or fodder in terms of its digestibility and end-product formation. IFM helps nutritionists evaluate and troubleshoot their dairy rations to maximize their feed efficiency and combat ever-rising feed costs. Evaluating complete feeds gives producers an advantage, as it allows them to closely simulate animal feedings to evaluate the associative effects of various ingredients within a ration.