CARBOHYDRATE UTILIZATION BY LACTATING DAIRY COWS

Abstract

Carbohydrates are the primary energy source for the animal and microbes in the rumen. They stimulate microbial fermentation that can produce volatile fatty acids, which can be used for maintenance, growth, and milk synthesis. The type and availability of carbohydrates influence the rate and extent of fermentation, affecting utilization and production. It is up to nutritionists to craft a balance between neutral detergent soluble and neutral detergent fiber carbohydrates to maintain rumen health and allow for peak energy availability. A well-designed diet formulation can maximize milk yield, health, and overall profitability. To explore practical strategies for optimizing carbohydrate use and enhancing efficiency in dairy cows, two experiments were conducted to evaluate alternative feed ingredients. The objective of the first experiment was to determine the effects of dietary starch concentration by replacing high-moisture corn with soy hulls and a direct-fed microbial (DFM) containing Bacillus subtilis and Bacillus licheniformis on lactation performance, feeding behavior, total tract nutrient digestibility, and enteric methane emissions by dairy cows. The experiment was conducted as a completely randomized design with a 2 x 2 factorial arrangement of treatments. Diets were formulated with 21% starch without DFM (RS-CON), 21% starch with DFM (RS-DFM), 27% starch without DFM (NS-CON), and 27% starch with DFM (NS-DFM). Cows fed greater starch had increased feed efficiency and decreased methane emissions but also decreased dry matter intake and milk fat concentration. Direct-fed microbials improved dry matter, organic matter, crude protein, ether extract, and neutral detergent fiber digestibility and tended to improve lactose concentration. The results of this experiment demonstrated that soy hulls could be considered as an alternative to starch sources and DFM supplementation may benefit digestibility depending on diet formulation. The objective of the second experiment was to evaluate the effects of forage fiber and starch sources replacement with delactosed whey permeate (DLP) on lactation performance and total tract nutrient digestibility of high-producing dairy cows. This experiment was conducted as a completely randomized design with cows randomly assigned to 12 pens of 8 cows. Diets were fed without DLP (CON), with a 5% replacement of corn silage with DLP (LCS), or a 5% replacement of high-moisture corn with DLP (LHMC). Cows fed CON had greater milk yield and milk lactose compared to LCS and LHMC and tended to have greater intake than LCS. However, LCS and LHMC had greater milk protein concentration than CON. Additionally, LCS had greater dry matter, organic matter, and crude protein digestibility than LHMC and tended to have greater ether extract digestibility than LHMC. Neutral detergent fiber digestibility was greater for LCS than LHMC and CON diets. These results suggest that production may not be able to be maintained with delactosed whey permeate, under certain conditions, when replacing high-moisture corn or corn silage. Overall, our results demonstrate that formulating dairy diets with different carbohydrate sources can affect overall dairy cow performance. For example, cows fed diets with a replacement of high-moisture corn with soy hulls had greater intake and milk yield but also decreased feed efficiency. Additionally, adding delactosed whey permeate to dairy diets through the replacement of high-moisture corn or corn silage may decrease milk yield and milk lactose yield and concentration but increase milk protein concentration. Thus, recognizing that different carbohydrate sources can alter performance is vital in maximizing dairy cow efficiency and farm profitability.