Effects of infusing milk precursors into the artery on rumen fermentation in lactating cows

This experiment was conducted to investigate the effects of infusing milk precursors into the external pudic artery on rumen fermentation in lactating dairy cows. Eight multiparous Holstein cows were randomly assigned to Group A(experimental group) and Group B(control group) with 4 cows each. A2×4 complex factor crossover design was used. Cows in Group A were fed corn straw as the only roughage, and cows in Group B were fed mixed roughage. The experiment was divided into two periods.In the first period, cows in Group A, received treatments: 1) a basal infusate as a control(CSC); 2) a milk fat precursor infusion including C16:0, C18:0, C18:1 c9, C18:2 c6, C18:3 n3, acetic acid(CSF); 3) a milk protein precursor infusion including 16 amino acids(CSA); 4) the mixed infusion of milk fat and protein precursors(CSFA). And meanwhile, cows in Group B were infused the basal infusate as a control group. In the second period, the cows in both Groups A and B were crossed over, which cows in Group A were named as Group B and the cows originally in Group B were in Group A. The experimental results showed that cows in experimental group had higher ruminal pH compared with the control, and ruminal pH in CSC, CSF, CSA were significantly higher than those in their respective control group(P < 0.05). The concentration of ammonia nitrogen(NH_3-N) was significantly higher in CSA and CSFA compared with Group B(P < 0.05). We also observed that the infusion of mixed amino acids significantly increased the bacterial protein(BCP) content in rumen(P < 0.05) and influenced the rumen acetic acid concentration as well as the acetic to propionic ratio(P < 0.05). Milk fat precursors infusion significantly affected butyric acid concentration(P < 0.05). In addition, the content of lipopolysaccharide(LPS) in CSA was significantly higher than that in the control group(P < 0.05). It is concluded that the milk precursors infused into external pudic artery caused feedback effects on ruminal fermentation under the corn straw roughage conditions. The milk protein precursor increased the ruminal pH, the contents of BCP and acetic acid, which adjust rumen fermentation and improve milk performance.

Quantification and prediction of enteric methane emissions from Chinese lactating Holstein dairy cows fed diets with different dietary neutral detergent fiber/non-fibrous carbohydrate(NDF/NFC)ratios

Methane(CH_(4))emissions from ruminant production are a significant source of anthropogenic greenhouse gas production,but few studies have examined the enteric CH_(4)emissions of lactating dairy cows under different feeding regimes in China.This study aimed to investigate the influence of different dietary neutral detergent fiber/non-fibrous carbohydrate(NDF/NFC)ratios on production performance,nutrient digestibility,and CH_(4)emissions for Holstein dairy cows at various stages of lactation.It evaluated the performance of CH_(4)prediction equations developed using local dietary and milk production variables compared to previously published prediction equations developed in other production regimes.For this purpose,36 lactating cows were assigned to one of three treatments with differing dietary NDF/NFC ratios:low(NDF/NFC=1.19),medium(NDF/NFC=1.54),and high(NDF/NFC=1.68).A modified acid-insoluble ash method was used to determine nutrient digestibility,while the sulfur hexafluoride technique was used to measure enteric CH4 emissions.The results showed that the dry matter(DM)intake of cows at the early,middle,and late stages of lactation decreased significantly(P<0.01)from 20.9 to 15.4 kg d^(–1),15.3 to 11.6 kg d^(–1),and 16.4 to 15.0 kg d^(–1),respectively,as dietary NDF/NFC ratios increased.Across all three treatments,DM and gross energy(GE)digestibility values were the highest(P<0.05)for cows at the middle and late lactation stages.Daily CH_(4)emissions increased linearly(P<0.05),from 325.2 to 391.9 kg d^(–1),261.0 to 399.8 kg d^(–1),and 241.8 to 390.6 kg d^(–1),respectively,as dietary NDF/NFC ratios increased during the early,middle,and late stages of lactation.CH_(4)emissions expressed per unit of metabolic body weight,DM intake,NDF intake,or fat-corrected milk yield increased with increasing dietary NDF/NFC ratios.In addition,CH_(4)emissions expressed per unit of GE intake increased significantly(P<0.05),from 4.87 to 8.12%,5.16 to 9.25%,and 5.06 to 8.17%respectively,as dietary NDF/NFC ratios increased during the early,middle,and late lactation stages.The modelling results showed that the equation using DM intake as the single variable yielded a greater R^(2)than equations using other dietary or milk production variables.When data obtained from each lactation stage were combined,DM intake remained a better predictor of CH_(4)emissions(R^(2)=0.786,P=0.026)than any other variables tested.Compared to the prediction equations developed herein,previously published equations had a greater root mean square prediction error,reflecting their inability to predict CH_(4)emissions for Chinese Holstein dairy cows accurately.The quantification of CH_(4)production by lactating dairy cows under Chinese production systems and the development of associated prediction equations will help establish regional or national CH_(4)inventories and improve mitigation approaches to dairy production.

Effect of High Concentrate Corn Stalk Particle Size on Physical State and Production Performance of Lactating Dairy Cows

In order to realize the application of corn stalk in cow feed, we designed experiments to explore the effect of a certain proportion of corn stalk on the performance of lactating dairy cows. 9 multiparous mid-lactating cows were allocated at random to three groups, each containing 3 intact cows. The trial consisted of three periods and three dietary treatments with a 3 × 3 Latin square design. The diets were normal concentrats plus dried corn stalk chopped to 5 - 8 cm long (N), high concentrates plus dried corn stalks chopped to a length of approximately 5 - 8 cm by a mower (H) while the milled corn stalks were passed through a pulviser with a 2 cm pore size (MH). Each cow was measured for dry matter intake (DMI), ruminal pH, rumen fermentation, selective feeding behavior and production performance. The results showed that MH led to a significantly higher intake of DM, neutral detergent fiber (NDF), forage NDF (FNDF), acid detergent fiber (ADF), crude protein (CP) and organic matter (OM) than N and H (P < 0.05). Cows fed H and MH showed similar selective feeding behavior, while those fed H showed various selectivity for the dietary component. MH resulted in a significantly higher milk production (P < 0.05), and tended to have a higher milk fat production than N (P = 0.055). There were no significant differences in the milk components (P = 0.424) and lactose (P = 0.113) between cows fed N and MH. The high-concentrates plus milled corn stalk diet can increase the milk yield under the premise of normal rumen pH in dairy cows, thereby generating higher economic benefits. And milled corn stalk can effectively inhibit the cow’s selective eating of low-quality roughage.

Assessment of the Effects of Supplemental Rumen Protected B Vitamins and Choline for Periparturient Cows: A Meta-Analysis of 28 Feeding Studies

There are currently no prescribed requirements for B vitamins or choline for dairy cows during the transition period, but many recent studies have shown a variety of benefits from supplying these nutrients to periparturient cows. The purpose of this research effort was to determine the potential benefit of including a rumen protected blend composed of B vitamins (riboflavin, folic acid, vitamin B12) and choline (RPBlend, Jefo Nutrition Inc., St. Hyacinthe, QC, Canada) for dairy cows during the transition period, based on results from 28 on-farm feeding studies (USA-12, Mexico-7, Canada-4, Chile-3, Australia-1, Brazil-1) conducted between 2011 and 2018. All farms participated in monthly herd management record keeping systems and were selected to participate in studies due to their excellent management. Meta-analyses in which risk differences were determined were used to assess the effects of the supplemental RPBlend on health parameters and reproduction. The effect size was used as the determinant of the possible contribution of RPblend on the yields of milk, energy corrected milk (ECM), fat and protein yields during the first four weeks of lactation. Results showed that the inclusion of RPblend reduced (P < 0.05) involuntary culling and mastitis by cows during the first 30 days after calving. There was a tendency (P < 0.10) for reduced retained placenta and metritis. The meta-analyses revealed that the risk of the displaced abomasum and milk fever did not diminish (P > 0.10) with the inclusion of the BPBlend. The incidence rate of subclinical ketosis, determined as blood beta hydroxy butyric acid greater than 1.2 mM was lower (P (than those not supplemented. The proportion of cows confirmed pregnant by 100 days in milk was greater for cows given the BPBlend (P < 0.05). Milk yield and ECM were greater for cows receiving the RPBlend (1.13 and 0.93 kg/cow respectively, P < 0.05). There was no change in fat yield (P > 0.10) while the yield of milk protein was greater (P < 0.05) when the cows received the blend. These results suggest that the inclusion of rumen protected B vitamins and choline can assist cow health, reproduction and production at the start of lactation.

Effects of Saccharomyces cerevisiae fermentation products on performance and rumen fermentation and microbiota in dairy cows fed a diet containing low quality forage

Background： A possible option to meet the increased demand of forage for dairy industry is to use the agricultural byproducts, such as corn stover. However, nutritional value of crop residues is low and we have been seeking technologies to improve the value. A feeding trial was performed to evaluate the effects of four levels of Saccharomyces cerevisiae fermentation product（SCFP; Original XP; Diamond V） on lactation performance and rumen fermentation in mid-lactation Holstein dairy cows fed a diet containing low-quality forage. Eighty dairy cows were randomly assigned into one of four treatments： basal diet supplemented with 0, 60, 120, or 180 g/d of SCFP per head mixed with 180, 120, 60, or 0 g of corn meal, respectively. The experiment lasted for 10 wks, with the first 2 weeks for adaptation.Results： Dry matter intake was found to be similar（P 〉 0.05） among the treatments. There was an increasing trend in milk production（linear, P ≤ 0.10） with the increasing level of SCFP supplementation, with no effects on contents of milk components（P 〉 0.05）. Supplementation of SCFP linearly increased（P 〈 0.05） the N conversion, without affecting rumen pH and ammonia-N（P 〉 0.05）. Increasing level of SCFP linearly increased（P 〈 0.05） concentrations of ruminal total volatile fatty acids, acetate, propionate, and butyrate, with no difference in molar proportion of individual acids（P 〉 0.05）. The population of fungi and certain cel ulolytic bacteria（Ruminococcus albus, R. flavefaciens and Fibrobacter succinogenes）increased linearly（P 〈 0.05） but those of lactate-utilizing（Selenomonas ruminantium and Megasphaera elsdeni） and lactate-producing bacteria（Streptococcus bovis） decreased linearly（P ≤ 0.01） with increasing level of SCFP. The urinary purine derivatives increased linearly（P 〈 0.05） in response to SCFP supplementation, indicating that SCFP supplementation may benefit for microbial protein synthesis in the rumen.Conclusions： The SCFP supplementation was effective in maintaining milk persistency of mid-lactation cows receiving diets containing low-quality forage. The beneficial effect of SCFP could be attributed to improved rumen function; 1）microbial population shift toward greater rumen fermentation efficiency indicated by higher rumen fungi and cel ulolytic bacteria and lower lactate producing bacteria, and 2） rumen microbial fermentation toward greater supply of energy and protein indicated by greater ruminal VFA concentration and increased N conversion. Effects of SCFP were dose-depended and greater effects being observed with higher levels of supplementation and the effect was more noticeable during the high THI environment.

Evaluation of Agolin^®, an Essential Oil Blend, as a Feed Additive for High Producing Cows

There is a growing demand for feed additives that can not only reduce dairy enteric methane emissions but also increase milk production and feed efficiency. Just one product is currently commercially available which accomplishes both of these goals. The purpose of this study was to confirm the performance benefits of the product (Agolin?, Agolin SA, Biere, Switzerland) in high producing mid-lactation dairy cows under United States feeding conditions. Four matched pens of approximately 150 mid-lactation cows/pen and averaging over 50 kg of milk/cow/day were enrolled in a side-by-side study. All pens received a common total mixed diet ad libitum, and the essential oil blend was administered via a concentrated farm pack to provide 1 g/cow/day to cows in the 2 test pens. Milk weights were determined, and samples were collected for compositional analysis over the last 2 days of the pretrial (May 11 and 12, 2020) and end of the trial (July 18 and 19, 2020) periods. Dry matter intake was measured by pen daily for the last 10 days of each feeding period. Milk fat and milk protein yields were greater (P < 0.05) for cows receiving added Agolin. There was a tendency (P = 0.06) for energy corrected milk/dry matter intake to be greater for cows receiving the Agolin (1.88) relative to the control diet (1.76). The trial showed that Agolin assisted in improving production parameters of economic importance to dairy producers.

Evaluation of alfalfa inter-seeding effect on bahiagrass baleage fermentation and lactating Holstein performance

Background：Previous research indicates that bahiagrass may be successfully conserved as baleage,but nutritive value is typically low for lactating dairy cows.The purpose of this study was to determine the effect of adding modest amounts of alfalfa forage（22%）,achieved by inter-seeding alfalfa into an existing bahiagrass pasture,on baleage nutritive value and lactation performance of Holstein cows.Forage treatments employed were monoculture bahiagrass baleage（MBB;negative control）,bahiagrass-alfalfa mixture baleage（BAB） and conventional corn silage（CCS;positive control）.Thirty six mid lactation Holstein cows[34.8 ±5.8 kg 3.5%fat-corrected milk and 112 ± 19 d in milk（DIM）]were stratified according to milk yield and DIM and assigned randomly to 1 of 3 forage treatments.Cows were trained to Calan feeding gates and were offered a common CCS-based TMR in a 10-d covariance period followed by a 42-d treatment feeding period.Results：The BAB contained more protein and less NDF than MBB（12.6 vs 10.3%CP and 71.8 vs 76.6%NDF）.Diet DMI was similar for MBB and BAB（19.5 vs 21.6 kg/hd/d）,but cows consumed more of the CCS diet（25.5 kg/hd/d）than either baleage-based diet.Cows offered BAB tended to produce more milk than cows offered MBB based TMR（28.4 vs 26.1 kg/hd/d）,but both baleage diets generated less milk than CCS-based diets（33.1 kg/hd/d）.Milk cumpusition was similar across diets except for milk protein concentrations which were higher tor CCS than either MBB or BAB diets;however,milk urea nitrogen（MUN） was lowest for cows fed CCS diets.Cow BW gain was higher for BAB than MBB implying that a portion of the higher energy contributed by the alfalfa was being used to replenish weight on these mid lactation cows.Conclusions：Data from this study indicate that alfalfa inter-seeded in bahiagrass sod that produces BAB with as little as 22%alfalfa may improve nutritive value compared to monoculture bahiagrass baleage and marginally improve lactation performance of Holstein cows.However,the CCS diet was vastly superior to either MBB or BAB-based diets for milk production.

The effects of step-wise improvement of forage combination in total mixed rations on fatty acid profile in the rumen and milk of Holstein cows

Five lactating Holstein cows in a 5×5 Latin square experiment were fed five high-concentrate total mixed rations(TMRs) to investigate the effects of step-wise improvement of forage combination on ruminal and milk fatty acid profiles. The ratio of concentrate to forage was fixed as 61:39, and the step-wise improvement of forage combination was applied as: TMR1, a ration containing corn stover; TMR2, a ration containing corn stover and ensiled corn stover; TMR3, a ration containing ensiled corn stover and Chinese wild ryegrass hay(Leymus chinensis); TMR4, a ration containing the ryegrass hay and whole corn silage; TMR5, a ration containing the ryegrass hay, whole corn silage and alfalfa hay. The TMRs were offered to the cows twice daily at 0700 and 1900 h. The entire experiment was completed in five periods, and each period lasted for 18 days. Diurnal samples of rumen fluids were collected at 0100, 0700, 1300 and 1900 h(day 16); 0300, 0900, 1500 and 2100 h(day 17); and 0500, 1100, 1700 and 2300 h(day 18). The step-wise improvement of forage combination increased energy and crude protein contents and decreased fibre content. As a result, the step-wise improvement of forage combination increased dry matter intake and milk yield(P<0.05). The step-wise improvement increased dietary content of linolenic acid(C18:3 n-3), but did not alter dietary proportions of palmitic acid(C16:0), stearic acid(C18:0), oleic acid(C18:1 cis-9), linoleic acid(C18:2 n-6) and arachidic acid(C20:0). In response to the forage combination, ruminal concentration of C16:0, C18:2 n-6 and C18:3 n-3 linearly increased against their dietary intakes(P<0.10). The step-wise improvement increased milk contents of C10:0, C12:0, C14:0, C16:0, C18:2 n-6 and C18:3 n-3(P<0.10) and decreased milk contents of C18:0 and C18:1 cis-9(P<0.05). Milk yields of C16:0, C18:1 cis-9, C18:2 n-6 and C18:3 n-3 were linearly increased by the increase of these fatty acids in the rumen(R2≥0.79, P<0.05), and milk yields of C18:2 n-6 and C18:3 n-3 were also positively correlated with dietary intake of these fatty acids(R2≥0.85, P<0.05). The step-wise improvement increased the transfer efficiencies from feed to milk for C18:2 n-6 from 11.8 to 14.2% and for C18:3 n-3 from 19.1 to 22.3%. In a brief, along with the step-wise improvement of forage combination, more dietary linoleic and linolenic acids might escape microbial hydrogenation in the rumen and consequently accumulated in milk fat though these fatty acids were present in low concentrations in ruminal fluids. The step-wise improvement of forage combinations could be recommended as a dietary strategy to increase the transfer efficiency of linoleic and linolenic acids from feed to milk.

Evaluation of Agolin® Ruminant, an Essential Oil Blend, as a Feed Additive for Cows at Two Levels of Production

Agolin® Ruminant (Agolin) is a commercially available blend of essential oils which has been demonstrated to reduce greenhouse gas emissions in dairy cows and improve energy corrected milk and feed efficiency. Further trials are needed with large numbers of cows to confirm the magnitude of effect of this feed additive on milk production under differing feeding conditions and stages of lactation. Information that can be quantified from newer on-farm systems of measurement is likewise needed. This study was conducted to determine the effects of this additive on high producing (48 kg of milk/day average) just past peak lactation and medium producing dairy cows (43 kg of milk/day average) further along in lactation under commercial conditions that would typically occur in the Pacific Northwest USA. Four pens of approximately 400 Holstein cows/pen (two high producing pens and two medium producing pens) were available for this side-by side study. Performance results were determined using data derived from a subscription standardized monitoring system (High Desert Dairy Laboratory, Inc, Nampa, ID, USA) that provided results for milk yield, fat percentage and protein percentage. As well daily in-stall electronic monitoring of milk only was available. All pens received a common total mixed ration typical of rations fed in the Pacific Northwest, USA. The Agolin feed additive was dispensed through the bulk mineral supply with control cows receiving the normal minerals and the treatment cows receiving the normal minerals plus Agolin. The trial began on August 24, 2021, with treatment cows provided with 1 g/head/day for the duration of the 8-week long study. Dry matter intakes were determined daily for the week before the trial was conducted and the last week of the trial. Treatment results were compared using a general linear model that considered pretrial milk, fat yield and protein yield, days in milk and lactation number. There were 678 high producing cows available for the duration of the study. Based on the standardized testing results, milk yield was greater (1.12 kg/cow/day;P < 0.05) for the cows in the treatment group. There was a tendency for fat corrected milk (FCM) and energy corrected milk (ECM) to be greater for the cows receiving the Agolin feed additive (0.96 and 0.86 kg/cow/day for FCM and ECM respectively, P < 0.10). There were 646 medium producing cows that participated in the trial. There was no treatment effect upon milk production (P = 0.27). There was a significant (P < 0.05) increase in milk fat yield and no change (P = 0.33) in protein yield for the treatment cows in this test group, resulting in greater FCM and ECM (1.12 and 0.95 kg/cow/day;P < 0.05). Daily milk monitoring resulted in a reduced decline in milk yield from the week before to the final week of the trial revealing greater persistency of milk for Agolin-fed cows in both high and medium production pens (1.58 and 2.13 kg/cow/day;P < 0.01). Likewise, overall feed efficiency was improved by 5.3% (P < 0.05) with the test product.

Effects of Supplemental Carbohydrate Sources on Lactation Performance, Nitrogen Balance,and Ruminal Fermentation in Dairy Cows Fed Energy-Deficient Total Mixed Rations

The effects of supplemental carbohydrate （CHO） sources on milk yield and composition, nitrogen （N） balance,and ruminal fermentation were evaluated in lactating dairy cows fed energy-deficient total mixed rations （TMR） . Fifty-six lactating Holstein cows （36. 8 ± 3. 4 kg / d of milk yield; 152 ± 26 days in milk [DIM]） were randomly assigned to one of four diets： （1） basal TMR （control） ; （2） basal TMR ＋ 1. 25 kg / d sucrose （SUC） ; （3） basal TMR ＋ 2. 12 kg /d steam-flaked corn （SFC） ; （4） basal TMR ＋ 2. 23 kg / d wheat （WHE） . The trial lasted 70 days,including the first 10 days of adaptation. Simultaneously, a 4 × 4 Latin square trial was conducted with four ruminally cannulated cows of similar DMI （Dry Matter Intake） fed on the above four diets. Each testing period lasted 18 days： 15 days for adaptation and 3 days for sampling. Cows fed SUC-,SFC-,and WHE-supplemented diets produced 1. 6,2. 9,and 0. 8 kg / d,respectively,more milk than those on the basal TMR control diet,but the difference was not significant （P = 0. 160） . However,the production of energy-corrected milk of cows fed CHO-supplemented diets improved significantly （P = 0. 020） ,and the yield of 4% fatcorrected milk tended to be higher （P = 0. 063） than in control animals. Percentages of milk protein,lactoseand solids-not-fat （SNF） increased significantly in cows fed CHO-supplemented diets （P 〈 0. 05） ,and yields of milk protein and SNF were significantly higher （P 〈0. 05） ; yields of milk fat and lactose were somewhat higher （P 〈 0. 10） . Cows receiving supplementary CHO diets consumed more DM （Dry Matter） （P = 0. 023） ; however,there was no significant difference in N retention,digestibility,or utilization efficiency among the treatments （P 〉 0. 10） . The average ruminal pH was lowest in cows supplemented with SUC,while that in cows supplemented with SFC and WHE was only slightly reduced （P = 0. 025） . Ruminal NH 3 -N concentration was highest with no supplementary CHO （P = 0. 017） ,and changes in postfeeding time were similar across the diets. Total volatile fatty acid concentration was significantly lower in control animals than in those on SUCand WHE-supplemented diets （P = 0. 001） ; significant dietary responses were observed in the concentrations of acetate,butyrate,and branchedchain fatty acids and in the acetate-to-propionate ratio （P 〈0. 001） . These results indicate that supplementation with different CHO sources in energy-deficient diets substantially improved the balance of energy and N in the rumen,altered ruminal fermentation,and improved lactation performance in dairy cows.

Agolin Ruminant®, an Essential Oil Blend, Increases Energy-Corrected Milk and Feed Efficiency in a High Component Dairy Herd

Agolin® Ruminant (Agolin) is a blend of essential oils developed to improve feed efficiency while at the same time reducing rumen enteric methane production. Studies have shown that the product improves lactational performance, but the range of results has been varied. This experiment evaluated the effects of the feed additive Agolinon milk production in a high-component (fat and protein) dairy herd when provided for an extended time. The experiment was conducted at a large commercial dairy in the Pacific Northwest, USA. Eight pens of cows (350 to 500 cows/pen) were blocked by production, and pens within blocks were randomly assigned to treatment. All pens received a common total mixed ration. Treatment consisted of providing 1 g/cow/day of Agolin to the test group. A 4-week adaptation period was followed by an 11-week study period. Milk production and milk composition were determined by cow by averaging daily performance for the one-week period before the start of the trial (covariate period) and the last week of each of the two test periods. Feed intakes were determined by pen at the same time. Milk yield was 1.11 kg/cow/day greater (P < 0.001) at the midpoint and 1.48 kg/cow/day greater (P < 0.001) at the end of the test period for cows receiving the feed additive. Similarly, protein yields were 0.03 (P < 0.001) and 0.07 kg/cow/day greater (P < 0.001) at the midpoint and end of the feeding period. Milk fat yield was not different (P = 0.854) between treatment groups at the midpoint of the trial but increased with treatment (P = 0.002) by the end of the trial. Energy-corrected milk/feed ratio, based on pen parameters, was significantly altered by treatment at the final test period (1.48 vs. 1.64 kg/kg for control and test treatments, respectively).

Effects of moisture content or particle size on the in situ degradability of maize silage and alfalfa haylage in lactating dairy cows

A study using four Holstein cows with ruminal cannulas was conducted to evaluate the degradability of different moisture content or particle size of maize silage and alfalfa haylage. The maize silage(MS; 20-mm length) and alfalfa haylage(AH; 40-mm length) samples were wet(wet maize silage, MSW;wet alfalfa haylage, AHW), dried(dried maize silage, MSD; dried alfalfa haylage, AHD), or ground to pass through a 2.5-mm screen(dried ground maize silage, MSG; dried ground alfalfa haylage, AHG). Samples were incubated in the rumen for 2, 6.12, 24.36.48, and 72 h. Cows were fed ad libitum and allowed free access to water. High moisture content treatment of MSW expressed a lower rinsing NDF and ADF degradability at 2 h(P < 0.05) compared with dried samples(MSD and MSG). Different moisture content and particle size had a significant impact(P < 0.05) on the NDF degradability at 72 h, ADF degradability at36.48, and 72 h, and ruminally degradable ADF. All of the highest values were observed in small particle size and low moisture content AHG treatment. Based on this study, sample processing, such as drying and grinding, should be considered when evaluating nutritive values of forages.

Effect of seasonal thermal stress on oxidative status,immune response and stress hormones of lactating dairy cows

This study aimed to assess the impact of seasonal thermal stress on oxidative stress,immune response,and stress hormones of lactating dairy cows in subtropical regions with different levels of temperature-humidity index(THI).A total of 32 healthy lactating Holstein dairy cows experienced 4 seasons(8 cows/season).The physiological parameters were categorized into low THI(LTHI,THI=42.97±0.95)in winter,moderate THI(MTHI,THI=61.84±0.42)in spring and autumn,and high THI period(HTHI,THI=86.09±0.23)in summer.The blood samples were collected twice in each season to measure oxidative stress,inflammatory and hormonal parameters.Our results showed THI had a positive cor-relation with the rectal temperature(R2=0.821,P<0.001)and respiratory rate(R2=0.816,P<0.001).Dry matter intake,milk yield and fat percentage also significantly differed among groups(P<0.05).Compared with the MTHI group,the LTHI group exhibited a significant increase in malondialdehyde(MDA)level(P<0.001),and the HTHI group displayed a significant increase in levels of cortisol,interleukin(IL)-10,IL-1βand tumor necrosis factor-α(P<0.001).Opposite changes in serum endotoxin and immunoglobulin G levels were observed with the increasing THI(P<0.001).LTHI notably increased the triiodothyronine level,although the thyroxine level was reduced by LTHI and HTHI compared with the MTHI group.In conclusion,LTHI and HTHI conditions may induce different degrees of oxidative stress,inflammation response,and stress hormone imbalances on lactating dairy cows,therefore envi-ronmental management is necessary for the health of dairy cows in extreme weather conditions.