Effects of ruminally degradable starch levels on performance, nitrogen balance, and nutrient digestibility in dairy cows fed low corn-based starch diets

Guobin Luo,Jinshan Yang,Yizhen Wang,Yonggen Zhang,Liyang Zhang,Cong Lin,Yang Li,Wenbin Xu

doi:10.5713/ajas.16.0371

Abstract

ObjectiveThis trial was performed to examine the effects of ruminally degradable starch (RDS) levels in total mixed ration (TMR) with low corn-based starch on the milk production, whole-tract nutrient digestibility and nitrogen balance in dairy cows.MethodsEight multiparous Holstein cows (body weight [BW]: 717±63 kg; days in milk [DIM]: 169±29) were assigned to a crossover design with two dietary treatments: a diet containing 62.3% ruminally degradable starch (% of total starch, low RDS) or 72.1% ruminally degradable starch (% of total starch, high RDS). Changes to the ruminally degradable levels were conducted by using either finely ground corn or steam-flaked corn as the starch component.ResultsThe results showed that dry matter intake, milk yield and composition in dairy cows were not affected by dietary treatments. The concentration of milk urea nitrogen was lower for cows fed high RDS TMR than low RDS TMR. The whole-tract apparent digestibility of neutral detergent fiber, acid detergent fiber and crude protein decreased, and that of starch increased for cows fed high RDS TMR over those fed low RDS TMR, with no dietary effect on the whole-tract apparent digestibility of dry matter and organic matter. The proportion of urinary N excretion in N intake was lower and that of fecal N excretion in N intake was higher for cows fed high RDS TMR than those fed low RDS TMR. The N secretion in milk and the retention of N were not influenced by the dietary treatments. Total purine derivative was similar in cows fed high RDS TMR and low RDS TMR. Consequently, estimated microbial N flow to the duodenum was similar in cows fed high RDS TMR and low RDS TMR.ConclusionResults of this study show that ruminally degradable starch levels can influence whole-tract nutrient digestibility and nitrogen balance in dairy cows fed low corn-based starch diets, with no influence on performance.

Highlights

Starch is an important source of energy in the diets of dairy cows
The contents of DM, crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF) and starch were similar between the dietary treatments
In situ ruminal incubation of total mixed ration (TMR) showed that dietary ruminally degradable starch (RDS) levels were 62.3 and 72.1 of total starch for the low and high RDS treatments, respectively (Table 2)

Summary

Introduction

Starch is an important source of energy in the diets of dairy cows. It serves as a precursor of propionate from starch fermentation, and as a source of glucose absorbed directly in small intestine. There is no doubt that the profitability of dairy farms will be affected immediately by the increases of cereal price. For these reasons, low starch diet rises the interests of milk producers. Some reports have indicated that more degradable starch improved ruminal microbial protein synthesis [2,3]. Increase of ruminally degradable starch improves the proportion of urea recy-

Methods

Results

Discussion

Conclusion