Altering palmitic acid and stearic acid ratios in the diet of early-lactation Holsteins under heat stress: Feed intake, digestibility, feeding behavior, milk yield and composition, and plasma metabolites.

The objective of this study was to evaluate the effects of varying the ratio of dietary palmitic (C16:0; PA) and stearic (C18:0; SA) acids on nutrient digestibility, production, and blood metabolites of early-lactation Holsteins under mild-to-moderate heat stress. Eight multiparous Holsteins (body weight = 589 ± 45 kg; days in milk = 51 ± 8 d; milk production = 38.5 ± 2.4 kg/d; mean ± standard deviation) were used in a duplicated 4 × 4 Latin square design (21-d periods inclusive of 7-d data collection). The PA (88.9%)- and SA (88.5%)-enriched fat supplements, either individually or in combination, were added to diets at 2% of dry matter (DM) to formulate the following treatments: (1) 100PA:0SA (100% PA + 0% SA), (2) 66PA:34SA (66% PA + 34% SA), (3) 34PA:66SA (34% PA + 66% SA), and (4) 0PA:100SA (0% PA + 100% SA). Diets offered, in the form of total mixed rations, were formulated to be isonitrogenous (crude protein = 17.2% of DM) and isocaloric (net energy for lactation = 1.69 Mcal/kg DM), with a forage-to-concentrate ratio of 40:60. Ambient temperature-humidity index averaged 72.9 throughout the experiment, suggesting that cows were under mild-to-moderate heat stress. No differences in DM intake across treatments were detected (mean 23.5 ± 0.64 kg/d). Increasing the dietary proportion of SA resulted in a linear decrease in total-tract digestibility of total fatty acids, but organic matter, DM, neutral detergent fiber, and crude protein digestibilities were not different across treatments. Decreasing dietary PA-to-SA had no effect on the time spent eating (340 min/d), rumination (460 min/d), and chewing (808 min/d). As dietary PA-to-SA decreased, milk fat concentration and yield decreased linearly, resulting in a linear decrease of 3.5% fat-corrected milk production and milk fat-to-protein ratio. Feed efficiency expressed as kg 3.5% fat-corrected milk/kg DM intake decreased linearly with decreasing the proportion of PA-to-SA in the diet. Treatments had no effect on milk protein and lactose content. A linear increase in de novo and preformed fatty acids was identified as the ratio of PA to SA decreased, while PA and SA concentrations of milk fat decreased and increased linearly, respectively. A linear reduction in blood nonesterified fatty acids and glucose was detected as the ratio of PA to SA decreased. Insulin concentration increased linearly from 10.3 in 100PA:0SA to 13.1 µIU/mL in 0PA:100SA, whereas blood ß-hydroxybutyric acid was not different across treatments. In conclusion, the heat-stressed Holsteins in early-lactation phase fed diets richer in PA versus SA produced greater fat-corrected milk and were more efficient in converting feed to fat-corrected milk.

Effects of two new formulas of dietary buffers with a high buffering capacity containing Na or K on performance and metabolism of mid-lactation dairy cows.

The present study was conducted to evaluate the effect of two new formulas of dietary buffers on intake, total tract digestibility, rumen pH, blood metabolites, and milk production of mid-lactation dairy cows. Nine multiparous cows (594 ± 46 kg BW; mean ± SD) averaging 120 ± 28 days in milk and producing 46.6 ± 3.4 kg/d were randomly assigned to a triplicate 3 × 3 Latin square. During each 21-d period, cows were offered one of three total mixed rations that varied in dietary buffer. The three types of dietary buffer were 1) 11.2 g/kg of dietary dry matter (DM) sodium bicarbonate (SB; control), 2) 8.7 g/kg of dietary DM high buffering capacity formula contained Na (HBNa), and 3) 7.4 g/kg of dietary DM high buffering capacity formula contained K (HBK). Each period was comprised of 14 d of dietary adaptation followed by 7 d of sampling. Measured buffering capacity was 102, 150 and 137 percent of NaHCO3 for SB, HBNa and HBK, respectively. The amount of Na and K were 270 and 0, 310 and 0, and 250 and 60 g/kg for SB, HBNa, and HBK, respectively. Dry matter intake (DMI) tended (P = 0.06) to be lower with HBK (20.6 kg/d) than SB (21.0 kg/d) and HBNa (21.2 kg/d). No treatment effects were observed on rumen pH (averaged 5.88) and DM digestibility in the total digestive tract (averaged 79.4%). Yields of actual milk (38.1 kg/d) and 3.5% fat corrected milk (31.6 kg/d) were not affected by treatments, whereas yields of solid corrected milk (P = 0.07) and milk fat (P = 0.10) tended to be greater with HBK than SB and HBNa. Milk fat concentration in cows fed HBK was greater than in cows fed other treatments (32.5 vs. 29.5 and 29.6 g/kg; P = 0.04). Concentration of milk protein (32.2 vs. 30.6 g/kg) and lactose (46.8 vs. 44.4 g/kg) also were greater in cows fed HBK than those fed SB (P = 0.02). Efficiency of milk production was greater in cows fed HBK than SB (1.86 vs. 1.80; P = 0.01), whereas efficiency of solid corrected milk production was greater in HBK than SB and HBNa (1.64 vs. 1.51 and 151; P = 0.02). Blood concentration of Ca was higher with HBK compared with SB and HBNa (10.4 vs. 9.7 and 9.9 mg/dL, respectively; P = 0.01). These results indicated that under the current experimental condition, supplementation of dairy cow diet with a high buffering capacity buffer containing 60 g/kg K decreased DMI and improved milk composition and milk efficiency of mid-lactation dairy cows.

Effects of vanadium supplementation on performance, some plasma metabolites and glucose metabolism in Mahabadi goat kids.

This experiment was conducted to investigate the effects of vanadium (V) supplementation on performance, some plasma metabolites (cholesterol and triglycerides) and glucose metabolism in Mahabadi goat kids. Twenty-eight male kids (15 ± 2 kg body weight) were fed for 14 weeks in a completely randomized design with four treatments. Treatments were supplemented with 0 (control), 1, 2, and 3 mg V as vanadyl sulfate/animal/daily. On day 70, an intravenous glucose tolerance test (IVGTT) was conducted. Dry matter intake did not change by V supplementation, but adding V quadraticaly improved feed efficiency (p = .03) and tended to increase average daily gain (Quadratic, p = .09). Blood metabolites were unaffected by V supplementation, except for concentration of glucose in plasma, which decreased linearly as supplemental V level increased (p = .02). Plasma glucose concentrations at 15, 30, 45 and 60 min after glucose infusion were decreased in a quadratic fashion in response to increasing supplemental V level (p < .01). The IVGTT indicated that the kids supplemented with 2 mg V had higher glucose clearance rate (K) and lower glucose half-life (T½ ; p < .05). Glucose area under the response curve from 0 to 60 min and 0 to 180 min after glucose infusion were decreased linearly (p = .04) by supplemental V. The results suggested that moderate supplementation of V may improve glucose utilization and feed efficiency in fattening kids.

Effects of Cr methionine on glucose metabolism, plasma metabolites, meat lipid peroxidation, and tissue chromium in Mahabadi goat kids.

This study was designed to investigate the effects of chromium methionine (Cr-Met) on glucose metabolism, blood metabolites, meat lipid peroxidation, and tissue chromium (Cr) in Mahabadi goat kids. Thirty-two male kids (16.5 ± 2.8 kg BW, 4-5 months of age) were fed for 90 days in a completely randomized design with four treatments. Treatments were supplemented with 0 (control), 0.5, 1, and 1.5 mg Cr as Cr-Met/animal/daily. Blood samples were collected via heparin tubes from the jugular vein on 0, 21, 42, 63, and 90 days of experiment. On day 70, an intravenous glucose tolerance test (IVGTT) was conducted. At the end of the feeding trial, the kids were slaughtered, and the liver, kidney, and longissimus dorsi (LD) muscle samples were collected. Plasma glucose, insulin, and triglyceride concentrations were decreased by Cr supplementation (P < 0.05). LD muscle malondialdehyde (MDA) decreased, and plasma and tissue Cr contents increased with increasing supplemental Cr levels (P < 0.05). Plasma glucose concentrations at 30 and 60 min after glucose infusion were lower in the kids fed 1.5 mg Cr diet than the kids fed control diet (P < 0.05). The IVGTT indicated that the kids supplemented with 1.5 mg Cr had higher glucose clearance rate (K) and lower glucose half-life (T½; P < 0.05). Glucose area under the response curve (AUC) from 0 to 180 min after glucose infusion was decreased linearly (P < 0.01) by supplemental Cr. The results suggested that supplemental Cr may improve glucose utilization and lipid oxidation of meat in fattening kid.

Grain source and marginal changes in forage particle size modulate digestive processes and nutrient intake of dairy cows.

This study investigated the effects of, and interactions between, dietary grain source and marginal changes in alfalfa hay (AH) particle size (PS) on digestive processes of dairy cows. A total of eight Holstein dairy cows (175 days in milk) were allocated in a replicated 4 × 4 Latin square design with four 21-day periods. The experiment was a 2 × 2 factorial arrangement with two levels of theoretical PS of AH (fine = 15 mm or long = 30 mm) each combined with two different sources of cereal grains (barley grain alone or barley plus corn grain in a 50 : 50 ratio). Results showed that cows consuming diets supplemented with corn had greater dry matter and nutrient intakes (P < 0.01), independent of forage PS. In addition, the apparent digestibility of fiber fractions was greater for diets supplemented with corn (P = 0.01). The feeding of barley grain-based diets was associated with greater apparent digestibility of non-fiber carbohydrates, and this variable was even greater when long AH was fed (P = 0.04). Moreover, the feeding of long AH resulted in longer time spent eating (P = 0.03) and higher pH (P < 0.01), as well as a tendency for higher acetate-to-propionate ratio in the rumen fluid (P = 0.06) at 3 h post feeding. In conclusion, the results indicated that the marginal increase of PS of AH may prolong eating time and improve rumen fermentation, particularly in diets based on barley grain. Partial substitution of barley grain by corn can improve feed intake and fiber digestibility in mid-lactation dairy cows.

Effects of supplemental dietary biotin on performance of Holstein dairy cows.

An experiment was conducted to evaluate the effect of different levels of biotin on productive performance of Holstein dairy cow. In this experiment a change-over design with twelve multiparous cows, three rations and three periods was employed. Ingredients of the basal diet were alfalfa hay (24%) corn silage (16%) and concentrate (60%) on dry matter basis. The experimental diets 1 to 3 contained 0, 10 and 20 mg of biotin per day, respectively. The rations were fed to cows as Total Mixed Rations (TMR), but biotin was top-dressed on the a.m. allotment of ration. The cows were individually ad libitum and milked three times per day. Daily milk yielded was recorded and samples of the milk were taken once per week for determination of milk composition. Blood were taken in end of each period. Dry Matter Intake (DMI) and milk yield of cows were not affected by biotin. Also milk compositions were not affected by biotin. The average of Fat Corrected Milk (FCM) yield for 4% fat for rations contain 0, 10 and 20 mg day(-1) biotin, respectively 25.45, 26.2 and 25.9 kg day(-1) were calculated. Blood concentration of were unaffected by different levels of biotin. The differences between averages of the milk cows were not significant.