Milk production and composition responds to dietary neutral detergent fiber and starch ratio in dairy cows

Abstract

This study was designed to investigate whether dietary neutral detergent fiber (NDF) : starch ratio could be considered as a nutritional indicator to evaluate carbohydrate composition and manipulate milk production and composition synthesis. Eight primiparous dairy cows were assigned to four total mixed rations with NDF : starch ratios of 0.86, 1.18, 1.63 and 2.34 from T1 to T4 in a replicated 4 × 4 Latin square design. Dry matter intake and milk production were decreased from T1 to T4. Digestibility of dry matter, organic matter, NDF and crude protein were linearly decreased from T1 to T4. As NDF : starch ratio increased, milk protein content and production, and milk lactose content and production were linearly reduced. However, milk fat content was linearly increased from T1 to T4. Quadratic effect was observed on milk fat production with the highest level in T3. Averaged rumen pH was linearly increased from T1 to T4, and subacute rumen acidosis occurred in T1. Ruminal propionate and butyrate concentration were linearly decreased, and microbial crude protein and metabolizable protein decreased from T1 to T4. It is concluded that NDF : starch ratio can be considered as a potential indicator to evaluate dietary carbohydrate composition and manipulate milk production and composition synthesis.

Estimation of between-Cow Variability in Nutrient Digestion of Lactating Dairy Cows Fed Corn-Based Diets

“…Thus, the increase of milk fat content with increasing NDF:starch ratio could partially be described by enhanced NDF contents at the expense of starch. This is in agreement with Zhao et al [ 29 ] that milk fat concentration was increased linearly when increasing NDF:starch ratio of diets from 0.86 to 2.34 due to the surge of the molar proportion of acetate in the rumen. In another study, Jenkins and McGuire [ 33 ] also reported that the acetate and butyrate which are contributing from NDF serve as the major precursors to support milk fat synthesis.…”

“…However, DMI as a percentage BW decreased with increasing starch content of diets. In another study, similar DMI was reported within NDF:starch range of 0.86–1.18, and intake was reduced with the further increase of NDF:starch ratio up to 2.34 [ 29 ].…”

“…This was in agreement with Beckman and Weiss that the replacement of byproducts for corn grain increased the dietary proportion of the dietary starch contribution of corn silage led to increasing STRD with increasing NDF:starch [ 28 ]. In contrast, Firkins et al [ 30 ] found a negative relationship between STRD and NDF:starch ratio though no effect was reported by Zhao et al [ 29 ].…”

“…Comparable to our results, one study reported that decreasing NDF:starch ratios from 1.24 to 0.74 did not affect the NDF digestibility of corn silage-based diets when confounding factors are reduced [ 28 ]. In another study, DMD and NDFD decreased linearly when increasing NDF:starch ratios from 0.86 to 2.34 [ 29 ]. Starch digestibility increment with increasing NDF:starch was mostly caused by the change of starch source.…”

Short communication: Effects of different selenium supplements on rumen fermentation and apparent nutrient and selenium digestibility of mid-lactation dairy cows

“…Ammonia was measured using an adapted version of the phenol/hypochlorite method (Broderick and Kang, 1980). Feces samples (100 g) were collected every 6 h in the last 3 d of the experiment, and then each set of samples was mixed (Zhao et al, 2016). The pooled fecal sample was divided into 2 portions; then, 10% (vol/vol) 6 M HCl was added to one subsample for subsequent nitrogen analysis to one subsample, and the other was stored at −20°C for subsequent analysis of Se concentration, DM, OM, NDF, ADF, and ether extract (EE).…”