| Corn silage accounts for a significant proportion of the dry matter(DM)fed to lactating dairy cows;however,the quality is highly variable among and within farms.Thus,it should be sampled and analyzed routinely to formulate diets to avoid the uncertainty associated with the composition of delivered diets and intake to prevent reduced milk yields.Main objectives of the current study were to determine the total variations and variance components associated with corn silage quality within and among dairy farms,to determine variations in DM intake and nutrient digestibility of different corn silage-based diets when fed to lactating dairy cows,further to develop a new index by combining corn silage nutritional,fermentation parameters and measured milk yield of dairy cows fed corn-silage based diets.To determine total variations in silage quality,corn silage samples(n = 250)were collected from 250 dairy farms in China to represent small scale(≤ 150 cows),medium scale(151 to 1,000 cows),large scale(1,001 to 5,000 cows)and very large scale(> 5,000 cows)dairy farms.Nutritional composition,fermentation profiles,and nutrient digestibility were analyzed by wet chemistry.The NEL value was calculated according to NRC(2001).Results revealed that mean nutritional composition values of corn silage produced under all four scales of operations were in agreement with(NRC,2001)nutrient composition data except for lower average DM and higher average ash contents.Fermentation profiles of corn silage produced under four production scales were comparable to that of typical corn silage.Results revealed that mean NEL values of corn silage produced in medium,large and very large scale of operations(> 150 cows)complied with NRC(2001)while a 0.12 percentage decrease was observed in corn silage produced in small scale operation.For the partitioning of total variations in the nutritional composition of corn silage,samples(n = 196)were collected from 14 dairy farms located in seven provinces in China over seven consecutive days having duplicate samples in each day.Samples were analyzed in the laboratory for DM,aNDFom,starch and ash content in duplicate.This design;multiple farms(n = 14),multiple days(n = 7),duplicate samples(n = 2),and duplicate assays(n = 2)allowed us to partition the overall variation into the farm,sampling and analytical.Any variation remaining was assumed to be true day-to-day variation.According to the results,farm-to-farm variation for all measured nutrients was the greatest contributor to overall variation and it was about 37 to 92% of the total variation.Within-farm,analytical variation comprised less than 20% for all parameters.However,sampling variation ranged from about 30 to 70% of the total within farm variation,and it was the major source of within farm variation for ash,aNDFom and DM.True daily variation ranged from 18 to 52% of the total within farm variation and was substantial for all nutrients.An experiment was done to determine sources of variation(diet,cow and farm)on intake,nutrient digestibility and lactation performance of dairy cows fed corn silage-based diets in agreement with randomized complete block design with a factorial treatment structure with diet and sample size(no of cows per treatment)as main factors.Three intensive dairy farms in northern China were used as the blocks and three diets were formulated to result in three NDF:starch ratios(0.7,1.0,and 1.3).In each farm,54 lactating dairy cows were used and a group of 18 cows was assigned for each dietary treatment.Five different sample sizes were simulated for each diet in each farm to have 18,15,12,9 and 6 cow data to determine the optimum sample size under current experimental conditions.The results showed that dry matter intake was not affected by diet or sample size.Dry matter digestibility decreased linearly with increasing NDF: starch ratio,although starch digestibility increased.Digestible NDF was not affected by the diet.Between-cow variation was different across farms and diets with an average standard deviation for digestibility of DM,NDF and starch were 3.8,5.1,and 3.3,respectively.A major implication of the current study is that cow variability is greatest for NDF digestibility and the use of a minimum of 12 cows per dietary treatment is adequate to reliably detect treatment effects on the digestibility of NDF,starch and DM.A study was done to determine the minimum data set(MDS)for corn silage quality evaluation among commonly used parameters for nutritional and fermentation quality and to develop an integrated corn silage quality index(CSQI)based on standard scoring functions and weight assignment approach.Principal component analysis(PCA)and multiple regression analysis(MRA)were used to determine MDS and to assign parameter weights,whereas standard scoring functions were used to normalize silage quality parameters.In order to develop CSQI,corn silage samples(n = 390)representing spatial and seasonal heterogeneity,were collected from 195 intensive dairy farms in China and analyzed for 16 chemical and fermentation parameters.Concurrent with silage sampling,average daily milk yield respective to each silage was collected using 50 mid-lactating dairy cows fed corn silage based diets(i.e.,39-48% DM corn silage in TMR)and used as the dependent variable in MRA.The silage quality parameters retained in the MDS included 30-h in vitro NDF digestibility,and concentrations(DM basis)of starch,crude protein,ether extract,ammonia and lactic acid.The CSQI was developed by summing normalized and weighted quality parameters retained in the MDS and the new index was evaluated against observed daily milk yield measurements and Milk2006 index.Accuracy and precision of predicting corn silage quality using MRA based CSQI were higher than those of the PCA based CSQI.The new MRA based index explained approximately 72% of the total variations in actual milk yield with high accuracy and precision of prediction.Finally,a meta-analysis was done to analyze the linear relationships between new CSQI,intake and milk yield of dairy cows when fed corn-silage based diets from literature data.Ninety-four different cornsilage based dietary treatment means reported in 36 feeding trials in 34 published research articles were used for the meta-analysis.The results revealed that CSQI explained approximately 50% of the total variation in actual milk yield measurements and it was 42% of the variation in when 4% FCM was used as the dependent variable.However,the predictability improved with an increasing inclusion rate of corn silage to the lactating dairy cow diets.Overall,this study revealed that corn silage quality is highly variable;thus,routine evaluation using multiple samples is essential to adjust compositional data for feed formulation.The cow variability is substantial for the nutrient digestibility of lactating dairy cows and the resulting milk production.Thus,the optimum sample size should be used(i.e.,a minimum of 12 cows per treatment)to determine the nutrient digestibility of cows when fed in groups.Multiple regression analysis based new index(CSQI)could be used as a new tool to determine corn silage quality for lactating dairy cows;however,validation against field trials to predict milk production is highly recommended. |
