Effects of supplemental potassium and sodium chloride salts on ruminal turnover rates, acid-base and mineral status of lactating dairy cows during heat stress

Effects of added dietary sodium and potassium chloride salts on ruminal turnover rates, acid-base balance and mineral status of lactating dairy cows experiencing a nycterohemeral cycle of heat stress were examined. Black globe-humidity index in the chambers averaged 94 during the daytime and 68 during the nighttime. Four ruminally cannulated multiparous Holstein cows in mid-lactation were confined in climatic chambers for a single-reversal experiment consisting of two 17-d periods. To the basal diet (50% corn silage: 50% concentrate, which contained .97% potassium, .19% sodium and .20% chloride), 1.25% sodium chloride plus 1.85% potassium chloride were added, making the high mineral treatment (1.93% potassium, 68% sodium and 1.85% chloride). Liquid dilution rates from the rumen were measured by chromium-ethylenediaminetetraacetate disappearance. Turnover rates of solids were determined by appearance of ytterbium in feces. Ruminal contents, arterial blood and urine were collected hourly for 26 h. Grab samples of feces were sampled over 6 d. Dry matter intakes and milk yields were not affected by the diets (averaging 17.8 and 21.1 kg/d, respectively). Cows fed the high mineral diet drank 17% more water (P less than .01). Tests for homogeneity of regression were utilized to compare chromium disappearance and ytterbium appearance data, which were best described by second-order polynomial functions. Increased ruminal chromium disappearance (P less than .01) and decreased total volatile fatty acid concentrations (P less than .01) suggested faster liquid dilution rates with high mineral diet, but turnover rates of solids were not affected. Urinary potassium secretion compensated for the high potassium content of the high mineral diet without an alkalogenic effect on acid-base status. Lower urine pH and higher urine ammonium concentrations during cool hours suggested that the high chloride content of the high mineral diet had an acidogenic effect. The results are interpreted to indicate that high level inclusion of sodium and potassium chloride salts altered digestive, acid-base and mineral status of heat-stressed lactating cows.     

The effect of feed regimen on chewing time, digesta passage rate and particle size distribution in Holstein non-lactating cows fed pasture ad libitum

The objective of this study was to evaluate the effect of feeding regimen on chewing activity and ruminal passage of digesta in non-lactating cows fed pasture ad libitum. Six ruminally fistulated Holstein dry cows (mean ± SD; parity = 3.7 ± 0.5, length of pregnancy = 28 ± 2 W, BW = 692 ± 75 kg) were assigned randomly to two dietary treatments using a crossover design; three cows were rotationally grazed pasture (treatment G) and the other was fed harvested pasture ad libitum in confinement (treatment C). Passage of digesta was measured by fecal marker excretion using Co-EDTA and Dysprosium (Dy) labeled grass as fluid phase maker or solid phase marker, respectively. Particle size distribution of ruminal digesta and feces was measured by wet sieving method. No significant difference in dry matter intake (DMI) between treatments was observed. Eating time in treatment G (517 min/day or 38.6 min/kg DMI) was longer treatment C (384 min/day or 31.0 min/kg DM). Chewing time per DMI was similar in both treatments (70.0 vs. 66.1 min/kg DMI). Ruminal liquid outflow rate and rumen volume of cows in treatment G were significant higher and lower than treatment C (9.9 vs. 12.2%/h and 111.0 vs. 79.9 L, respectively). The mean retention time in small particle pool to be able to pass through the reticulo-omasum orifice (CMRT₂) in cows of treatment C was longer (P < 0.05) than that for treatment G.. Logarithmic particle distribution and mean particle size of ruminal digesta at 24 h after feeding and feces particles had no significance between treatments. These results indicated that ingestive behavior of dry cow affected on eating time and ruminal volume, and it might have caused the higher ruminal liquid and particulate passage rate in treatment G compare to treatment C, with minimal effect on the particle size of digesta to pass from the rumen.     

Effects of tallow supplementation and protein withdrawal on ruminal fermentation, microbial synthesis and site of digestion

The effects of tallow supplementation [0% (NT) vs 7.5% (T)] and crude protein level [8.5% (LP) vs 12.0% (HP)] on ruminal fermentation, microbial protein (MCP) synthesis, digesta passage and site of digestion were estimated using yearling Angus X Simmental steers (390 kg) fitted with ruminal and T-type duodenal cannulae. Chromium-EDTA and ytterbium (Yb) chloride were used as markers of the liquid and solid phases. Passage and site of digestion data were estimated from the concentrations of Yb in the duodenal digesta and feces. Dry matter (DM) intakes were 6.8, 6.5, 6.3 and 6.6 kg/d for the NT-LP, NT-HP and T-HP diets, respectively. Ruminal ammonia concentrations (mg/100 ml) for the NT-LP, NT-HP, T-LP and T-HP diets were 1.22, 4.75, 1.05 and 3.41, respectively. Tallow decreased (P less than .05) acetate (mol/100 mol), increased (P less than .01) propionate (mol/100 mol) and decreased the total volatile fatty acid concentration. Tallow depressed apparent ruminal DM and organic matter (OM) digestibilities only on the HP diet. High protein increased ruminal DM, OM and fiber digestibilities. Tallow and LP tended to shift the site of OM digestion to the lower tract. The liquid and solid dilution rates for the NT-LP, NT-HP, T-LP and T-HP diets were 9.53, 3.37; 5.63, 3.28; 6.66, 5.10 and 6.79, 5.34%/h, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Disappearance and passage of propionic acid from the rumen of the beef steer

Studies were conducted to define steady state pH, propionic acid concentrations and fluid turnover in the rumen of steers fed every 3 h and to determine whether rates of ruminal propionic acid disappearance were linearly related to their in situ production rates. Ruminally fistulated beef steers (326 +/- 11 kg; n = 3) were fed eight times daily a 54% mixed hay: 46% corn-based concentrate diet to meet maintenance energy requirements. Maximal acceptable variations from the mean at steady state conditions of pH, propionic acid concentrations and specific activity, and liquid flow (Cr marker concentrations) were defined as 4%, 20%, 30% and 10%, respectively, across 4 h of observation. In situ production of propionic acid, determined by pulse-continuous infusion of 1-14C-propionic acid, was 142 mmol/h (CV = 8.4%). The ruminal half-life of propionic acid was estimated to be 1.5 h and the liquid flow rate was 3.8 liters/h. Propionic acid production rates subsequently were elevated by continuous intraruminal infusion of buffered propionic acid. Irrespective of production (basal and infusion) rate, approximately 66% disappeared (i.e., presumed absorption) and 34% passed from the rumen to the lower tract in the liquid phase. Ruminal disappearance of propionate was linearly related with its production rate, and propionate concentrations and production rates also were linearly related. Liquid passage was linearly related to production rate, but there was insufficient evidence to conclude that fractional dilution rate or ruminal volume were similarly related. When ruminal production of propionic acid is elevated, the rumen has additional absolute capacity to remove propionate, but the fractional removal appears to be constant. The digestive tract distal to the rumen is likely an important site of propionate absorption in cattle when propionate production is high.     

Comparison of rumen bacteria distribution in original rumen digesta,rumen liquid and solid fractions in lactating Holstein cows

Background: Original rumen digesta, rumen liquid and solid fractions have been frequently used to assess the rumen bacterial community. However, bacterial profiles in rumen original digesta, liquid and solid fractions vary from each other and need to be better established.Methods: To compare bacterial profiles in each fraction, samples of rumen digesta from six cows fed either a high fiber diet(HFD) or a high energy diet(HED) were collected via rumen fistulas. Rumen digesta was then squeezed through four layers of cheesecloth to separate liquid and solid fractions. The bacterial profiles of rumen original digesta, liquid and solid fractions were analyzed with High-throughput sequencing technique.Results: Rumen bacterial diversity was mainly affected by diet and individual cow(P 0.05) rather than rumen fraction. Bias distributed bacteria were observed in solid and liquid fractions of rumen content using Venn diagram and LEf Se analysis. Fifteen out of 16 detected biomarkers(using LEf Se analysis) were found in liquid fraction, and these 15 biomarkers contributed the most to the bacterial differences among rumen content fractions.Conclusions: Similar results were found when using samples of original rumen digesta, rumen liquid or solid fractions to assess diversity of rumen bacteria; however, more attention should be draw onto bias distributed bacteria in different ruminal fractions, especially when liquid fraction has been used as a representative sample for rumen bacterial study.     

The ruminal bacterial community in lactating dairy cows has limited variation on a day-to-day basis

Dairy cows rely on a complex ruminal microbiota to digest their host-indigestible feed. Our ability to characterize this microbiota has advanced significantly due to developments in next-generation sequencing. However, efforts to sample the rumen, which typical y involves removing digesta directly from the rumen via a cannula, intubation, or rumenocentesis, is costly and labor intensive. As a result, the majority of studies characterizing the rumen microbiota are conducted on samples col ected at a single time point. Currently, it is unknown whether there is significant day-to-day variation in the rumen microbiota, a factor that could strongly influence conclusion drawn from studies that sample at a single time point. To address this, we examined day-to-day changes in the ruminal microbiota of lactating dairy cows using next-generation sequencing to determine if single-day sampling is representative of sampling across 3 consecutive days. We sequenced single-day solid and liquid fractions of ruminal digesta col ected over 3 consecutive days from 12 cannulated dairy cows during the early, middle, and late stages of a single lactation cycle using the V4 region of the bacterial 16 S r RNA gene. We then generated 97% similarity operational taxonomic units(OTUs) from these sequences and showed that any of the individual samples from a given 3-day sampling period is equivalent to the mean OTUs determined from the combined 3-d data set. This finding was consistent for both solid and liquid fractions of the rumen,and we thus conclude that there is limited day-to-day variability in the rumen microbiota.     

Effect of cereal straw and alfalfa hay diet on amino acid profile of gastrointestinal digesta in lactating dairy cows

This study was conducted to evaluate the effects of replacing alfalfa hay with rice straw (RS) or corn stover (CS) on amino acid (AA) profiles of gastrointestinal digesta in lactating cows. Eighteen lactating dairy cows were randomly assigned to one of three groups (n = 6) and fed identical concentrate and corn silage with different forages on dry matter basis: (i) 23% alfalfa hay and 7% Chinese wild rye hay (AH); (ii) 30% CS; and (iii) 30% RS. After the 14‐week feeding, a total of 18 cows were slaughtered to collect digesta from four representative organs, including rumen, omasum, duodenum and jejunum. The AA profiles of ruminal microbial fraction were similar among the treatments, except for greater Arg in cows fed RS than in cows fed AH or CS. Most of the analysed AA changed under different diets. Significant differences were found among the microbial fraction, rumen fluid and rumen digesta, with greater essential AA in digesta than in microbial fraction or rumen fluid and greater essential AA in microbial fraction than rumen fluid. Significant differences in individual AA profiles of digesta and relevant fluid were found across the four representative digestive tract parts, including rumen, omasum, duodenum and jejunum, showing much lower Leu proportion in CS and RS than in AH in duodenal fluid. In summary, ruminal microbes may prefer using essential AA, rather than non‐essential AA. The AA profile of ruminal microbes was constant except for Arg. The AA composition of digesta across the four digestive tracts changed dramatically, which indicated differences in the ability and efficiency of AA absorption. The lower duodenum absorbable Leu proportion in cows fed CS or RS indicated the shortage of Leu in CS or RS diets, which might also restrict the balanced AA absorption.     

Influence of forage diets on ruminal particle size, passage of digesta, feed intake and digestibility by steers

To assess the influence of forage diets on particle size of digesta in the rumen, three ruminally fistulated steers were fed alfalfa, orchardgrass or switchgrass hays in a 3 x 3 Latin square design. Mean sieve size of ruminal digesta for alfalfa, orchardgrass and switchgrass diets was 671, 652 and 466 microns, respectively. A second experiment examined the influence of ruminal particle size on digesta passage, digestibility and intake. Four ruminally fistulated Angus-Hereford steers were given ad libitum access to different proportions of alfalfa and switchgrass in a 4 x 4 Latin square design. Either a 100% alfalfa, 50% alfalfa:50% switchgrass, 25% alfalfa:75% switchgrass or 100% switchgrass diet was offered once daily. Mean sieve sizes of the ruminal digesta of these diets responded cubically (P less than .01; 1,066, 946, 1,003 and 925 microns, respectively). Mean ruminal turnover times were 24.3, 24.8, 24.7 and 29.8 h, respectively. Dry matter intake increased linearly (P less than .10) as the proportion of legume in the diet increased; no influence of diet on DM digestibility was observed. Passage rate of dosed nylon particles 1, 3 and 5 mm in length was influenced (P less than .01) by size; however, no difference in the passage rates of the nylon particles due to diet was evident. Particle size of ruminal digesta did not respond in a linear manner to the proportion of legume in the diet. A smaller ruminal particle size was not associated with a faster turnover of digesta.     

The effect of modified roofing on the milk yield and reproductive performance of heat‐stressed dairy cows under hot‐humid conditions

The objective was to measure the effects of cooling techniques (shade cloth vs. normal roof) on performance and physiology of 16 Friesian crossbred cows (87.5% Holstein Friesian × 12.5% Brahman) located at Sakol Nakhon Livestock Research and Testing Station, Department of Livestock Development, Ministry of Agriculture and Cooperatives (Sakol Nakhon, Thailand). They were divided randomly into two groups of eight. The two groups were used to evaluate the effects of modified roofing (normal roof fitted with woven polypropylene shade cloth) on the subjects' milk yield and reproductive performance under hot humid conditions. Results indicated that the modified roofing offered a more efficient way to minimize heat stress than the normal roof. The difference was sufficient to enable the cows to have a significantly lower mean rectal temperature and respiration rate (38.56°C, 61.97 breaths/min) than that of the cows housed under normal roofing (39.86°C; 85.16 breaths/min). The cows housed under modified roofing produced more milk (P < 0.05) but did not differ significantly in reproductive performance from the cows housed under normal roofing.     

Milk Production of Dairy Cows Fed Total Mixed Rations After a Grazing Period

Twenty multiparous Holstein cows were used in a completely randomized design with repeated measures to study milk production of cows supplemented or not supplemented with concentrate when they were switched to a total mixed ration (TMR) after grazing. In one group, cows grazed an or-chardgrass/bromegrass pasture and were assigned to one of two treatments: 1) unsupplemented (U; 1 kg/d mineral mix) or 2) concentrate supplemented (CS; 1 kg corn-based concentrate/4 kg milk). Total DMI was greater (26.5 vs 22.0 kg/d), but pasture DMI was less (16.8 vs 21.2 kg/ d), for CS cows because of the substitution rate of 0.49 kg pasture/kg concentrate. Overall, CS cows had greater 3.5% fat-corrected milk (FCM) (32.9 vs 26.5 kg/d), but less milk urea N (MUN; 9.6 vs 14.7 mg/dL) and milk fat (3.13% vs 3.88%), than U cows. Milk response to supplementation averaged 1.08 kg milk/kg concentrate. Cows assigned to both treatments lost BW (-17 kg/d) and body condition score (BCS) (-0.33). At the end of the 6-wk grazing period, all cows were switched to a TMR fed in confinement for 11 wk. Overall, DMI (24.3 kg/d), 3.5% FCM (30.6 kg/d), milk fat (3.26%), milk true protein (2.87%), and MUN (12.7 mg/dL) did not differ between treatments. Cows gained BW (53 kg) and BCS (0.33). A significant treatment × time interaction was found for milk yield. During the first day of TMR feeding, milk yield was greater (30.9 vs 19.3 kg/d) for CS cows. After 10 d on a TMR, milk yields between cows that had previously been on the U or CS treatments did not differ (35.5 kg/d). When cows were switched from only pasture to a TMR, milk yield was comparable with that of cows fed CS after 10 d. Lack of carry-over effects of previous treatments and increased production suggest improvement in nutrition and the potential for greater animal well-being for cows housed in a tiestall barn and fed a nutritionally complete TMR.     

Effects of time of day and monensin on the size distribution of particles in digestive tract sites of heifers fed corn silage

Effects of time of day and dietary monensin in the distribution of size of digesta particles in different digestive tract sites and their intersite relationships were examined in six heifers (290 kg BW) with ruminal, duodenal and ileal cannulas given ad libitum access to corn silage, with or without 100 mg monensin.head-1.d-1, in a two-period crossover design. Ingestive masticate and digesta of corn silage were collected via esophageal, ruminal or intestinal cannulas. The distribution of particulate matter retained on sieves with apertures larger than 20 microm was determined by wet-sieving. The cumulative distribution of particulate matter on a series of sieves was regressed on retaining sieve aperture to estimate the sieve aperture that would retain 50% weight of the particulate matter (median retaining aperture, MRA). The MRA of masticate was 6,494 microm. The MRA of digesta particles decreased (P less than .05) from ventral rumen (1,847 microm) to dorsal rumen (1,797 microm) to duodenum (346 microm), but increased to the rectum (359 microm). The MRA was lower (P = .044) for the monensin treatment only in feces. The MRA of particulate matter in the dorsal and ventral rumen, duodenum and rectum all changed (P less than .05) over 24 h. An inverse pattern between the MRA of ruminal and duodenal digesta occurred, presumably the result of a nycterohemeral pattern of eating and ruminating activity. Across sampling times, an inverse relationship existed between MRA of ventral rumen and duodenal digesta. This relationship suggests that a ruminal digesta raft composed of larger particles (immediately following major meals) is more effective than a raft of smaller particles (prior to such meals) in preventing flux of large particles to the duodenum.     

Effect of ruminal dosing of mechanical stimulating brush on rumination time, ruminal passage rate and rumen fermentation status in Holstein steers fed a concentrate diet

This experiment was conducted to determine the effect of ruminal dosing of a mechanical stimulating brush on rumination time, ruminal passage rate and rumen fermentation status in steers fed a concentrate diet at maintenance level. Animals were dosed three Rumen Faibu (RF) per head through the rumen fistulae (RF treatment) and not dosed (control) in a change‐over design. The organic cell wall content of the concentrate diet was 12.7% of dry matter. Daily time spent on rumination was very short in both treatments with 24 min in RF treatment and 15 min in control. The turnover rate of ruminal fluid in RF treatment was higher than that in control. There were no differences in ruminal pH and total volatile fatty acid concentration between RF treatment and control. Acetic and butyric acid concentrations were not different between the treatments. Propionic acid concentration tended to be higher in the animals on RF treatment than in control animals. The RF dosing in Holstein steers fed a low fiber diet did not affect the rumination time, but increased rumen digesta passage rate and ruminal propionic acid production.     

热应激对荷斯坦奶牛体温和呼吸的影响

本试验旨在研究热应激对不同泌乳阶段奶牛直肠温度、皮肤温度和呼吸频率的影响。选用不同泌乳阶段、胎次相近的荷斯坦奶牛18头,按泌乳天数分为泌乳前期、泌乳中期和泌乳后期3组,每组6个重复,根据牛舍温湿指数(THI)变化情况,进行热应激与非热应激的自身对照试验。结果表明:热应激极显著增加各泌乳阶段奶牛的直肠温度、皮肤温度和呼吸频率(P<0.01);THI与各泌乳阶段奶牛的直肠温度、皮肤温度、呼吸频率呈显著正相关(P<0.05);在同一环境下,不同泌乳阶段奶牛的直肠温度、皮肤温度及呼吸频率无显著差异(P>0.05)。热应激严重影响奶牛的直肠温度、皮肤温度和呼吸频率,与泌乳中、后期奶牛相比,热应激对泌乳前期奶牛的影响趋于较大。     

Shade and water misting effects on behavior, physiology, performance, and carcass traits of heat-stressed feedlot cattle

One hundred twelve crossbred feedlot heifers were used in two experiments to assess the impact of heat stress and its relief by shade and(or) water misting on behavior, physiology, performance, and carcass traits. Treatments were 1) no shading or misting (CONT); 2) only misting (MIST); 3) only shading (SHADE); and 4) shading plus misting (SHMI). Head in the feed bunk, head in or above the waterer, walking, standing, and lying behaviors were observed. Rectal temperature, respiration rate, and carcass traits were measured, as well as DMI, ADG, and feed:gain. Dietary NEm and NEg concentrations were calculated from performance data. In Exp. 1, (32 heifers; average BW 288 kg) the CONT heifers spent more time lying down than all others (P < 0.01). In addition, CONT heifers spent less time (P < 0.01) standing than SHADE and MIST heifers. Misting decreased (P < 0.01) rectal temperature and MIST as well as SHADE lowered (P < 0.05) respiration rates. In Exp. 2 (80 heifers; average BW = 336 kg), lying and walking behaviors did not differ among treatments, but shade increased (P < 0.01) standing behavior in heifers. The MIST cattle performed less (P < 0.05) head-above-water behavior than unmisted cattle. Rectal temperatures did not differ among treatments, but respiration rate was lower in shaded than in unshaded heifers (P < 0.05). Shaded compared with unshaded heifers had greater DMI (9.46 vs 8.80 +/- 0.14 kg/d, P < 0.01) and ADG (1.6 vs 1.41 +/- 0.1 kg/d, P < 0.01). Heifers provided with shade reached their target BW 20 d earlier than the unshaded heifers and differed in final BW (547 vs 520 +/- 6 kg, P < 0.01). Feed:gain and calculated NEg and NEm concentrations did not differ among treatments, and carcass traits were generally similar among treatments. In conclusion, cattle without shade had a physiological and behavioral stress response to heat that negatively affected productivity. Providing shade for beef cattle was a suitable solution to decrease heat stress and to lower the negative effects of heat on performance, whereas misting was largely ineffective.     

应用CNCPS-S模型预测全混合日粮碳水化合物绵羊瘤胃降解率的研究

本研究旨在应用康奈尔绵羊净碳水化合物和蛋白质体系（Cornell sheep net carbohydrate and protein system，CNCPS-S）的瘤胃降解预测模型预测日粮碳水化合物（CHO）瘤胃有效降解率，并实测验证CNCPS-S模型预测值的准确性。选取3只安装瘤胃瘘管、体重分别为（38.03±1.56）kg的哈萨克公羊作为试验动物，配制3种精粗比分别为30：70、35：65、40：60的全混合日粮（TMR），利用瘤胃灌注试验和尼龙袋试验实测3种日粮CHO的瘤胃外流速度（Kp）和降解率，同时利用CNCPS-S模型预测3种日粮CHO的Kp与降解率，对CHO的降解率预测值和实测值进行线性回归分析，评价模型预测的准确性。结果表明：3种TMR的瘤胃食糜Kp随精料比例增加而依次升高（P<0.01），分别为3.58%/h、3.83%/h、4.05%/h，据此计算而得的CHO的降解率分别为42.7%、43.1%、42.3%（P>0.05）；随精料比例的增加，3种TMR的瘤胃食糜Kp的模型预测值依次升高（P>0.05），分别为1.62%/h、1.63%/h、1.64%/h，CHO瘤胃降解率的预测值分别为39.5%、39.1%、39.6%（P>0.05）；3种日粮CHO瘤胃降解率的预测值与实测值之间的平均偏差比较小（≤ 4 g/100 g CHO），相关性较高（R² ≥ 0.86），均方根误差也较低（RMSE ≤ 1.93 g/100 g CHO）。以上结果说明，CNCPS-S瘤胃降解预测模型对日粮CHO的降解率具有较好的预测能力。     

Pancreatic insulin secretory response and insulin action in heat-exposed sheep given a concentrate or roughage diet

The effects of heat exposure and type of diet on the insulin secretory response to glucose and glucose disposal in response to insulin action in female sheep were investigated employing hyperglycemic and euglycemic clamp techniques. Animals were divided into concentrate and roughage diet groups, and were maintained at the same intake levels of metabolizable energy and crude protein in both diets. Each diet group was subjected to either thermoneutral (20°C, 70% RH) or hot (30°C, 70% RH) environment, followed by glucose clamp experiments.

Heat-exposed sheep showed significant increases in respiration rates (P<.001) and rectal temperature (P<.05). Plasma glucose concentrations in the basal conditions were lower (P<.01) in the hot environment than in the thermoneutral environment, but there was no significant difference in basal levels of plasma insulin between the environmental treatments. In the hyperglycemic clamp experiment, mean plasma insulin increments increased (P<.05) during the heat exposure period across diet treatments. The ratio of mean plasma insulin increment to glucose infusion rate tended to be higher (P<.07) in the hot environment than in the thermoneutral environment, but diet treatment did not affect the ratio of mean plasma insulin increment to glucose infusion rate. The euglycemic clamp technique showed that glucose infusion rates remained unchanged among treatments. Insulin secretion response to glucose could be stimulated in the hot environment.     

Effects of whole cottonseed and live yeast culture on ruminal fermentation and fluid passage rate in steers

The effects of adding whole cottonseed (WCS) and live yeast culture (YC) to a diet of 60% alfalfa and 40% concentrate on ruminal fermentation and liquid dilution rate in steers were examined in two trials. Twelve ruminally cannulated Hereford steers (approximately 420 kg) were used. Concentrates were 1) a basal grain mix composed of ground corn, ground barley and rice bran, 2) basal mix with 10% WCS, 3) basal mix with 1.6% YC and 4) basal mix with 10% WCS and 1.6% YC. No differences were detected (P greater than .10) in ruminal pH of steers fed WCS or YC in either trial. Ruminal ammonia levels tended to be higher (P greater than .10) in steers fed WCS. Acetate was higher and butyrate was lower in steers receiving 10% WCS (P less than .10) compared with controls. Molar proportions of acetate and butyrate increased while propionate decreased (P less than .05) over time after feeding. Intake and apparent digestibility of dry matter was not influenced by treatments. Whole cottonseed and(or) YC appear to have minimal effects on ruminal fermentation, but they might alter ruminal liquid passage rate with diets containing 60% ground alfalfa and 40% concentrate.     

Effect of heat stress on early embryonic development in the beef cow

Hereford and Hereford X Angus cows (n = 31) were utilized to determine the effects of heat stress on early embryonic development and survival. After acclimation to handling, cows were cannulated via the jugular vein on d 7 and assigned to either a control (C) chamber environment of 22 C, 35% relative humidity (RH) or one of two heat stress treatments. Ambient temperature was maintained at 37 C for 12 h followed by a decrease to 33 C for the remainder of the day in both treatment groups. Relative humidity was maintained at 27% in treatment 1 (TRT 1) and 38% in treatment 2 (TRT 2). On d 8 to 16, daily measurements of respiration rate (RES), rectal temperature (REC) and water intake were taken along with samples of blood, which were analyzed for hematocrit (HEM) and plasma concentration of protein (PP), progesterone (P4), estradiol-17 beta (E2), thyroxine (T4) and glucose (GLU). The uterus was recovered and flushed with saline on d 17 to recover the conceptus and uterine contents. Conceptus (if present) and corpus luteum (CL) wet weight were determined. Cows subjected to TRT 2 had increased RES and REC (P less than .01), while HEM was decreased (P less than .05) compared with C cows. Plasma T4 concentration was decreased (P less than .10) in TRT 2 compared with TRT 1 and cows, while P4 concentration were not significantly different. Corpora lutea wet weights were reduced (P less than .10) in heat-stressed cows vs C cows.(ABSTRACT TRUNCATED AT 250 WORDS)     

Heat influences on plasma insulin and glucagon in response to secretogogues in non-lactating dairy cows

Four non-lactating cows were offered a maintenance diet of hay wafer and a commercial concentrate. They were housed in a thermoneutral (TN; 20°C) and then a hot (30°C) environment in an artificial climate chamber. Glucose, arginine, butyrate, and insulin were administered through one jugular catheter, and from a catheter on the other side venous blood was collected. The peak increments in plasma insulin after the glucose and butyrate administrations were lower during heat exposure. The response of insulin after arginine injection was smaller in the hot compared with the thermoneutral environment; however, arginine injection resulted in a significantly higher secretion of glucagon in the hot environment. The response area of insulin after the insulin injection was smaller in the hot environment; however, insulin clearance rate was not changed. It is concluded that in non-lactating cows, insulin release is probably lower during heat exposure. With respect to plasma glucose during heat exposure, the lower basal values, lower concentrations after the end of the glucose infusion, and delayed recovery to basal values after the butyrate and insulin administrations observed, may indicate lower gluconeogenesis and glycogenolysis in the hot environment.     

Disappearance of acetic acid from the bovine reticulorumen at basal and elevated concentrations of acetic acid.

Disappearance of acetic acid was quantified to determine whether removal of this acid from the reticulorumen is altered when ruminal acetic acid concentrations are elevated. Ruminally fistulated beef steers (n = 3 per experiment; BW = 320 +/- 9 kg) were fed eight times daily a 46% corn-based concentrate:54% mixed hay diet to meet maintenance energy requirements (3.5 kg of DM/d). In situ production of acetic acid, determined by pulsed-continuous infusion of [1-14C]acetic acid, was 530 mmol/h (CV = 12%). Disappearance from the reticulorumen (i.e., presumed absorption) was 460 mmol/h (CV = 2%) or 87% (CV = 2%) of ruminal production. Variation is described within an operational steady state. Acetic acid concentrations were increased by continuous infusion of unlabeled acetic acid into the reticulorumen. Ruminal disappearance (mmol/h) increased when this simulated production was elevated up to and exceeding in situ rates reported previously (530 to 2,700 mmol/h). These data suggest that two-thirds to three-fourths of ruminal acetate production disappeared across the reticuloruminal wall when concentration was elevated; the complement exited from the rumen with the liquid phase. The reticulorumen has an additional capacity to remove acetic acid; however, it does so with an apparent reduced efficiency at higher production rates. Liquid out-flow may affect the efficiency of reticuloruminal disappearance. Sites distal to the rumen become quantitatively important when ruminal acetic acid concentrations are increased.