Effects Of Dietary Nonfiber Carbohydrate On Lactation Performance,Nutrient Digestibility,and Nitrogen Utilization In Lactation Dairy Cows Receiving Corn Stover

A large amount of alfalfa hay?AH?has been imported for Chinese dairy industry,while abundant source of feed resources including cereal straw and stovers are not well utilized yet.The cereal straw and stovers contain low nonfiber carbohydrate?NFC?and are not well digested with low efficiency of utilization by the animals.Therefore,the current study were conducted to investigate the lactation performance,digestition and feed efficiency in lactation dairy cows receiving corn stove?CS?influenced by supplementation and balance of the dietary NFC,in comparision with the AH-fed diet.Two experiments were carried out.In Expt 1,two diets were designed to investigate the effects of supplemental molasses in CS-contating diet?CSM?on lactation performance,rumen fermentation and nutrient digeastibility ofdairy cows compared with alfalfa-containing die?AH?.Expt 2 was conducted to investigate the lactation performance and rumen fermentation characteristics in lactating cows consuming CS with two contents of NFC compared to an alfalfa hay-containing diet.The objectives of the current study aimed at providing reference for the further research and reasonable utilization of CS resource in China.1 Lactation peformance and nutrient utilization in dairy cows fed a diet with alfalfa replaced by CS and supplemented with molasses?Expt 1?.Molasses is rich in easily fermentable sugar,and is one of the few unconventional feed resources which can offer plenty of NFC to dairy cows.The objective of current study was to investigate whether supplementation of the CS-containing diet with molasses to adjust diet NFC content to the level of alfalfa contained diet could improve feed intake and lactation performance of dairy cows approaching to those fed alfalfa contained diet.Sixteen mid-lactation Holstein cows?161 ± 10.3 d in milk,712± 77 kg of body weight?were used in a 2 x 2 crossover design with two dietary treatments:?1?alfalfa hay based diet?AH?,?2?corn stover-containing diet supplemented with molasses?CSM?,Both CS and alfalfa has were included at approximately 15%of total dietary DM in CSM and AH diet.Samples of feeds,milk,blood and rumen fluids were taken for later analysis.Feces were also sampled to determin nutrients digestibility.Main results obtained are summarized as below.1.1 Difference of lactation performance of dairy cows between two diets.The DMI,milk yield and energy corrected milk?ECM?yield were higher for cows fed AH than CSM?P<0.01?.Milk protein content and nitrogen conversion?milk protein yield/CP intake?was higher?P<0.05?and milk urea nitrogen?MUN?was lower?P<0.01?for cows fed AH compared with CSM.No differences were found in feed efficiency?ECM/DMI?,contents of milk total solids,milk fat and lactose,SCC and B W gain between two groups?P>0.10?.The feed costs per kilogram of milk was lower for cows fed CSM than for AH?P<0.01?.1.2 Nutrients digestibility and blood metabolites in cows fed different diets.No differences were found in apparent digestibility of DM,organic matter,CP,NDF,ADF,ether extracts and NFC between the two diets?P>0.10?.Rumen pH tended to be higher?P = 0.06?,while total VFA concentration tended to be lower?P =0.06?for cows fed CSM than AH.Molar proportion of acetate was higher?P<0.05?,but valerate was lower for cows fed CSM than for AH?P<0.05?.The difference tended to be significant in rumen concentration of propionate?P = 0.09?,isobutyrate?P = 0.09?,and ratio of acetate to propionate?P = 0.07?between two diets,with no differences for NH3-N,butyrate and isovalerate?P>0.10?.No differences were found in concentration of plasma TP,albumin,BUN,glucose and NEFA between two diets?P>0.10?.From the above results,it is indicated that supplementing molasses to CS-containing diet could not improve feed intake and lactation performance approaching to AH fed cows.However,there were no differences in feed efficiency,nutrients digestibility and blood biochemical variables between two diets.Furthermore,feed cost per kg of milk production was lower in CSM than in AH diet.2 Effect of dietary NFC content on the utilization of CS-containing diet by lactation dairy cows?Expt 2?.Different NFC content of CS-containing diet were designed to investigate the differences of lactation performance,rumen fermentation,nutrient utilization in comparison with AH-containing diet.Twelve Holstein cows in mid-lactation?159 ±15 d in milk,704 ± 72 kg of body weight?were used as a replicated 3 × 3 Latin square design with three dietary treatments:?1?low NFC content with CS contained diet?NFC = 35.6%,L-NFC?,?2?high NFC content with CS contained diet?NFC = 40.1%,H-NFC?,and?3?alfalfa hay contained diet?NFC = 38.9%,AH?.In both L-NFC and H-NFC diets,CS was included at approximately 15%of total dietary dry matter?DM?instead of alfalfa hay in diet AH.Each period lasted for 21-d each,with the first 14 d for an adaptation,followed by 7 d for collection of rumen,blood and milk samples.Feces were also sampled to determine nutrients digestibility.2.1 Effect on lactation performance of dairy cows receiving CS based diet.The DMI was lower for cows fed H-NFC compared with L-NFC and AH,while milk yield was higher in AH than in H-NFC and L-NFC?P<0.01?with no differences between H-NFC and L-NFC?P>0.10?.The feed efficiency?milk yield/DMI?were higher for cows fed H-NFC and AH than the L-NFC fed cows?P<0.01?;and ECM feed efficiency?ECM/DMI,1.32 vs 1.27,P = 0.06?were higher for cows fed H-NFC than L-NFC even though the overall p-value for three groups was not significant?P=0.16?.Contents of milk protein,lactose and milk somatic cell count were not different among groups?P>0.05?,but milk fat content was higher for cows fed H-NFC and L-NFC than for AH-fed cows?P<0.01?,and the amount of total solids was higher?P<0.01?in cows fed L-NFC compared to cows fed AH with no difference between cows fed H-NFC and AH or L-NFC,and the MUN was lower?P<0.01?for cows fed H-NFC and AH compared to cows fed L-NFC.The feed cost per kg of milk production was different among groups?P<0.01?,with lowest value for cows fed H-NFC.2.2 Effect of on rumen fermentation and microbial community of dairy cows receiving CS based diet.The rumen pH tended to be different?P=0.09?among groups with a lower value for cows fed AH compared to cows fed H-NFC and L-NFC.Rumen NH3-N concentration tended to be different among 3 groups?P = 0.06?,with higher concentration for cows fed L-NFC compared to cows fed H-NFC and AH.The concentration of total VFA and the molar proportion of propionate were different among groups?P<0.05?,with highest values for AH group.The molar proportion of acetate tended to be different among 3 groups?P = 0.06?with lower proportion for cows fed AH compared to cows fed H-NFC and L-NFC,and the ratio of acetate to propionate were significant different among groups?P<0.05?with lowest and highest values for AH and H-NFC group respectively.There was no difference?P>0.05?in the molar proportion of butyrate and valerate among the three groups,but the molar proportion of isobutyrate were different?P = 0.01?and isovalerate tended to be different?P = 0.08?among 3 groups with lowest value in AH group.For the rumen microbe community,total DNA was extracted from the rumen content samples of dairy cows from three groups.Illumina Hiseq was used to obtain 250 bp paired-end sequences data.The abundance of Firmicutes and Spirochaetes bacteria phyla was significantly different among groups?P<0.05?,withhighest and lowest values in H-NFC group,respectively.On genus level,the cows fed L-NFC diet had the highest Acetitomaculum and lowest Treponema₂ among the 3 groups?P<0.01?;while feeding of diet H-NFC resulted in the lowest abundance of Ruminococcaceae_NK4A214_group,Lachnospiraceae_NK3A20_group,and Ruminococcaceae_UCG-005?P<0.01?.No differences were found for other genus among 3 groups.2.3 Effect on nutrient digestibility and nitrogen balance of cows receiving CS based diet.No differences were found in total-tract apparent digestibilities of DM,OM,NDF and ADF among groups?P>0.10?,but the apparent digestibility of NFC was lower?P<0.05?in cows fed fed L-NFC than other two diets;and digestibility of ether extracts were higher?P<0.01?for cows fed H-NFC than cows fed AH or L-NFC,with higher value in AH-fed cows than the cows fed L-NFC.The CP digestibility tended to be different?P = 0.08?among groups,with higher digestibility for cows fed L-NFC compared to the other two groups.The estimated MCP yield were not different?P>0.10?among 3 groups,but the urinary urea nitrogen concentration tended to be higher?P = 0.09?in cows fed L-NFC than other two groups.Nitrogen intake was lower?P<0.01?for cows fed H-NFC compared to L-NFC and AH with no difference between L-NFC and AH.The ratio of N excreted in feces to nitrogen ingested tended to be different among three groups?P=0.08?with lowest value in L-NFC group.The nitrogen excreted in the urine?g/d?was lower?P = 0.03?in the H-NFC-fed cows than that in cows fed L-NFC and AH;and the ratio of urinary N to N intake was 5.4%?42.6%vs 48.0%?lower in cows fed H-NFC than that in cows fed L-NFC,even though the overall p-value were not significant among three groups?P = 0.11?.There was no difference in the ratio of milk N?P = 0.20?among the three groups.Plasma concentration of total protein tended to be different?P = 0.07?among groups with a lower value for cows fed L-NFC compared to cows fed H-NFC and AH;and the BUN concentration was highest?P<0.01?for cows fed L-NFC,followed by the AH-fed cows,and the lowest BUN occurred in cows fed H-NFC.Plasma concentrations of albumin,glucose,cholesterol,NEFA,and BHBA were not different among the three groups?P>0.10?.The results obtained in this part indicated that the increased NFC content in a diet containing CS improved feed efficiency that reached a value similar to the AH diet,resultant from the lowered rumen ammonia nitrogen,reduced urinary nitrogen excretion and improved efficiency of N utilization.Feed cost per kg of milk production was lower in H-NFC group than an alfalfa-containing diet.In summary,the increased NFC content in a diet containing CS can improve nitrogen conversion ratio.The lactation performance of the dairy cows receiving a corn stover supplementing with molassed or with high NFC did not reach to the level of alfalfa based diet,but the feed cost for unit of milk production was lower in cows fed corn stover.In is concluded that increasing of NFC may improve the feed efficiency and benefit the N conversion.Inclusion of corn stove into the dairy diet with increased NFC content may be an alternative feed strategy for dairy farms instead of alfalfa based diet to feed mid-lactation dairy cows.