In China, straw and natural forage are the primary sources of roughage for cattle. However, these feedstuffs often lack sufficient nutritional value for high-producing dairy cows, making supplementation necessary. When managed properly, the dry matter intake and overall feed consumption can be improved. One key factor in evaluating this is the substitution rate, which indicates how much pasture or straw is replaced by supplementary feeds.
The amount of grass consumed during grazing plays a crucial role in ruminant performance. Although pasture has relatively high nutritional value, high-yielding cows still require additional nutrients to maintain productivity. Supplementary feeding aims to fill nutritional gaps, especially energy deficiencies, which helps improve diet digestibility, milk yield, and overall feed intake. Grazing cows typically consume less than those fed in confinement. Various methods are used to estimate grazing intake, including esophageal sampling, weight difference before and after foraging, canvas bag collection, live weight change, and behavioral observations such as daily licking time, eating rate per unit time, and average bite size.
Several formulas have been developed to estimate dry matter intake for grazing dairy cattle:
1. **IDM/d = 0.13FCM + 0.0053W + 0.96G** (Cox et al., 1956)
Where IDM/d is daily dry matter intake (kg), FCM is 4% fat-corrected milk yield (kg), W is body weight (kg), and G is daily weight gain (kg).
2. **IDM/d = 0.16M + 0.0113W + 2.45G + 4.25** (Bines et al., 1977)
Here, M represents daily milk yield (kg).
3. **IDM/d = 0.20M + 0.22W** (NEAL et al., 1984)
4. **IDM/d = 3.47G + 0.404C + 0.013W - 0.129T + 4.12logT - 0.140M** (Card and Holmes, 1986)
In this formula, C is the amount of supplemental feed (kg), T is the number of weeks post-calving, and M is daily milk yield (kg).
The substitution rate, also known as the replacement coefficient, refers to the proportion of dry matter from pasture or straw that is reduced when supplementary feeds are introduced. The goal of supplementation is to enhance nutrient content—such as crude protein, energy, or minerals—in low-quality forages. Ideally, the reduction in pasture or straw intake should be minimal, indicating a good associative effect between the supplement and the forage.
When forage is abundant, animals may not reach their maximum intake, and adding energy supplements like grains generally has little impact on pasture consumption. For example, if a cow’s organic matter intake drops from 24 kg to 16 kg per day due to supplementation, the substitution rate decreases from 0.5 to 0.1, showing a significant increase in total feed intake.
Forage supplementation can boost total intake when forage is plentiful, but the increase is usually smaller than that from energy supplements because the latter reduces pasture consumption. If the reduction in pasture equals the amount of feed added, the substitution rate is 1, suggesting that the feed has limited impact on production. Conversely, if the feed does not reduce pasture intake, the substitution rate is zero, meaning the supplement plays a major role in improving performance.
Energy supplementation can also affect grazing behavior. As energy levels increase, the intake of forage organic matter declines from 9.25 kg to 6.42 kg per day. Daily foraging time shortens, foraging rate decreases, and both the number of bites and the amount of food per bite drop. This highlights the complex interaction between supplementation and natural grazing patterns.
Feed Additives
Feed additives are small amounts of substances added to ordinary feed to improve animal nutrition, enhance physical fitness, and reduce
Feed dosage and effectiveness in disease prevention and control.Feed additives are divided into microbial feed additives and Chinese herbal feed additives.
The use of feed additives is one of the effective means to prevent intestinal diseases and improve the production performance of broilers and laying hens
The feed additive has achieved good application effect in the breeding of piglets, sows and finishing pigs
Feed additives can improve the weight gain rate of meat sheep, beef cattle and other meat ruminants, increase the net meat percentage of the carcass and improve meat quality
The application of feed additives in aquatic products is reflected in the two aspects of food and water purification. Feed additives can improve the microecological balance of aquatic animals, promote growth and development, and play a role in preventing and controlling diseases and improving production performance
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