Abstract
Corn is a feedstuff commonly fed to dairy cows as a source of energy. The objective of this study was to evaluate whether partially replacing dietary corn with molasses or condensed whey permeate, in lactating dairy cow diets in a dual-flow continuous culture system, can maintain nutrient digestibility by ruminal microorganisms. Furthermore, this study evaluated whether treating condensed whey permeate before feeding could aid the fermentation of the condensed whey permeate in the rumen. Eight fermentors were used in a 4 × 4 replicated Latin square with 4 periods of 10 d each. The control diet (CON) was formulated with corn grain, and the other diets were formulated by replacing corn grain with either sugarcane molasses (MOL), condensed whey permeate (CWP), or treated condensed whey permeate (TCWP). Diets were formulated by replacing 4% of the diet dry matter (DM) in the form of starch from corn with sugars from the byproducts. Sugars were defined as water-soluble carbohydrates (WSC) in the rations. The fermentors were fed 52 g of DM twice daily of diets containing 17% crude protein, 28% neutral detergent fiber, and 45% nonfiber carbohydrates. Liquid treatments were pipetted into each fermentor. After 7 d of adaptation, samples were collected for analyses of volatile fatty acids (VFA), lactate, and ammonia, and fermentors' pH were measured at time points after the morning feeding for 3 d. Pooled samples from effluent containers were collected for similar analyses, nutrient flow, and N metabolism. Data were statistically analyzed using Proc MIXED of SAS version 9.4 (SAS Institute Inc.); fixed effects included treatment and time, and random effects included fermentor, period, and square. The interaction of treatment and time was included for the kinetics samples. The TCWP and MOL treatments maintained greater fermentor pH compared with CWP. Total VFA concentration was increased in CWP compared with MOL. The acetate:propionate ratio was increased in TCWP compared with CON, due to tendencies of increased acetate molar proportion and decreased propionate molar proportion in TCWP. Lactate concentration was increased in MOL. Digestibility of WSC was increased in the diets that replaced corn with byproducts. The partial replacement of 4% of DM from corn starch with the sugars in byproducts had minimal effects on ruminal microbial fermentation and increased pH. Treated CWP had similar effects to molasses.
Highlights
Dairy nutritionists traditionally classify carbohydrates into structural and nonstructural carbohydrates (NRC, 2001)
We aimed to evaluate whether treating condensed whey permeate with sodium hydroxide before feeding could increase nutrient digestibility and use by mixed ruminal microorganisms
The control diet (CON) was formulated with corn grain, whereas the other diets were formulated by replacing a percentage of corn grain with either sugarcane molasses (MOL; 6.58%), condensed whey permeate (CWP; 4.37%), or treated condensed whey permeate (TCWP; 4.61%)
Summary
Dairy nutritionists traditionally classify carbohydrates into structural and nonstructural carbohydrates (NRC, 2001). Nonstructural carbohydrates include starches and sugars found inside the plant cell. Starch can compose up to 70% of the DM found in corn grain (Ferraretto et al, 2013), a common feedstuff fed in cattle diets. Starch recommendations range from 20% in a dry cow diet to greater than 35% in a lactating cow diet (Grant, 2019). A possible downfall of feeding highstarch diets is that it may reduce NDF digestibility (Firkins et al, 2001; Ferraretto et al, 2013) because it can reduce ruminal pH, favoring against cellulolytic bacteria (Russell and Wilson, 1996), and may lead to ruminal acidosis (Stone, 2004). A potential strategy to prevent reductions in NDF digestibility is to partially
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