Characterization of controlled trials on probiotic supplementation to dairy calves: A scoping review.

The objective of this scoping review was to identify, describe, and characterize the literature on probiotic supplementation in dairy calves. Eligible studies were nonrandomized, quasi-randomized and randomized controlled trials in English, Spanish, or Portuguese that evaluated the effect of probiotic supplementation on growth and health of dairy calves. The search strategies were based on a modification of the PICO (Population, Intervention, Comparator, Outcome) framework and used synonyms and words related to "dairy calves" (population), "probiotics" (intervention), and "growth and health measurements" (outcomes). No restrictions for publication year or language were applied. Searches were conducted in Biosis, CAB Abstracts, Medline, Scopus, and the Dissertations and Theses Database. In total, the search identified 4,467 records, of which 103 studies (110 controlled trials) met the inclusion criteria. The studies were published between 1980 and 2021 and originated from 28 countries. Trials were randomized (80.0%), nonrandomized (16.4%), and quasi-randomized (3.6%), ranging in sample size from 5 to 1,801 dairy calves (mode = 24; average = 64). Enrolled calves were frequently Holstein (74.5%), males (43.6%), and younger than 15 d at the beginning of probiotic supplementation (71.8%). Often, trials were conducted in research facilities (47.3%). Trials evaluated probiotics with single or multiple species of the same genus: Lactobacillus (26.4%), Saccharomyces (15.4%), Bacillus (10.0%), Enterococcus (3.6%), or multiple species of various genera (31.8%). Eight trials did not report the probiotic species used. Lactobacillus acidophilus and Enterococcus faecium were the species most supplemented to calves. The duration of probiotic supplementation ranged from 1 to 462 d (mode = 56; average = 50). In trials with a constant dose, it ranged from 4.0 × 106 to 3.7 × 1011 cfu/calf per day. Most probiotics were administered mixed solely into feed (88.5%; whole milk, milk replacer, starter, or total mixed ration) and less frequently orally as a drench or oral paste (7.9%). Most trials evaluated weight gain (88.2%) as a growth indicator and fecal consistency score (64.5%) as a health indicator. Our scoping review summarizes the breadth of controlled trials evaluating probiotic supplementation in dairy calves. Differences in intervention design (mode of probiotic administration, dose, and duration of probiotic supplementation) and outcomes evaluation (type and methods) justify future efforts toward standardized guidelines in clinical trials.

Implications of supplementing mid-lactation multiparous Holstein cows fed high by-product low-forage diets with rumen-protected methionine and lysine in a commercial dairy.

Supplementation of rumen-protected amino acids may improve dairy cow performance but few studies have evaluated the implications of supplementing low-forage diets. Our objective was to evaluate the effects of supplementing rumen-protected methionine (Met) and lysine (Lys) on milk production and composition as well as on mammary gland health of mid-lactating Holstein cows from a commercial dairy farm feeding a high by-product low-forage diet. A total of 314 multiparous cows were randomly assigned to control (CON; 107 g of dry distillers' grains) or rumen-protected Met and Lys (RPML; 107 g dry distillers' grains + 107 g of RPML). All study cows were grouped in a single dry-lot pen and fed the same total mixed ration diet twice a day for a total of 7 weeks. Treatments were top-dressed on the total mix ration immediately after morning delivery with 107 g of dry distillers' grains for 1 week (adaptation period) and then with CON and RPML treatments for 6 weeks. Blood samples were taken from a subset of 22 cows per treatment to determine plasma AA (d 0 and 14) and plasma urea nitrogen and minerals (d 0, 14, and 42). Milk yield and clinical mastitis cases were recorded daily, and milk components were determined bi-weekly. Body condition score change was evaluated from d 0 to 42 of the study. Milk yield and components were analyzed by multiple linear regression. Treatment effects were evaluated at the cow level considering parity and milk yield and composition taken at baseline as a covariate in the models. Clinical mastitis risk was assessed by Poisson regression. Plasma Met increased (26.9 vs 36.0 µmol/L), Lys tended to increase (102.5 vs 121.1 µmol/L), and Ca increased (2.39 vs 2.46 mmol/L) with RPML supplementation. Cows supplemented with RPML had higher milk yield (45.4 vs 46.0 kg/d) and a lower risk of clinical mastitis (risk ratio = 0.39; 95% CI = 0.17-0.90) compared to CON cows. Milk components yield and concentrations, somatic cell count, body condition score change, plasma urea nitrogen, and plasma minerals other than Ca were not affected by RPML supplementation. Results suggest that RPML supplementation increases milk yield and decreases the risk of clinical mastitis in mid-lactation cows fed a high by-product low-forage diet. Further studies are needed to clarify the biological mechanisms for mammary gland responses to RPML supplementation.

First-milking colostrum mineral concentrations and yields: Comparison to second milking and associations with serum mineral concentrations, parity, and yield in multiparous Jersey cows.

This observational study described first-milking colostrum mineral concentrations and total yields, and evaluated its associations with cow serum mineral concentrations, parity, and first postpartum milking yield in 100 multiparous Jersey cows from a single herd fed a negative dietary cation-anion difference diet prepartum. Additionally, first- and second-milking colostrum mineral concentrations and total yields were compared in a subset of 65 cows. Serum minerals (Ca, P, Mg, Na, K, Zn, Fe, Cu) were assessed before first milking. Cows were milked at 9 h and 4 min ± 3 h and 32 min and at 21 h and 11 min ± 3 h and 43 min postpartum (± standard deviation); yields were recorded and samples collected for mineral concentrations assessment (Ca, P, Mg, Na, K, Zn, Fe, Cu). Linear regression was used to evaluate the associations between first-milking colostrum mineral concentrations and total yields and cows' serum mineral concentrations, parity, first-milking colostrum yield, and calving-to-milking interval. The most abundant minerals in first-milking colostrum were (least squares mean ± standard error of the mean) Ca (55.71 ± 13.52 mmol/L; 8.75 ± 5.74 g) and P (41.91 ± 13.01 mmol/L; 5.26 ± 3.72 g), followed by Na (39.65 ± 13.23 mmol/L; 3.08 ± 1.77 g), K (36.47 ± 7.57 mmol/L; 5.79 ± 4.20 g), Mg (13.43 ± 3.09 mmol/L; 1.25 ± 0.78 g), Zn (272.12 ± 113.34 µmol/L; 71.98 ± 55.34 mg), Fe (12.51 ± 3.79 µmol/L; 2.56 ± 1.55 mg), and Cu (3.34 ± 1.22 µmol/L; 0.77 ± 0.56 mg). Higher concentrations of Ca, Mg, Na, Zn, Fe, and Cu, and total yields of Mg, Zn, Fe, and Cu were observed at first- compared with second-milking colostrum. Serum and first-milking colostrum Cu concentrations were positively associated, but no significant associations were observed between other minerals' serum and first-milking colostrum concentrations or total yields. Parity was associated with first-milking colostrum Ca, P, K, and Fe concentrations and yields; younger multiparous cows had higher concentrations and total yields of these minerals. Linear (Fe), quadratic (P, Na, and K), and cubic (Mg, Zn, and Cu) associations were observed between first-milking colostrum mineral concentrations and yield. In all cases, mineral total yields were linearly associated with first-milking colostrum yield. In conclusion, variation in first-milking colostrum mineral concentrations and total yields across cows could be partially explained by cow parity and colostrum yield. Further research including primiparous and cows under different management settings is needed to expand the knowledge and understanding of colostrum mineral concentrations and total yields in dairy cows.

Effects of postpartum milking strategy on plasma mineral concentrations and colostrum, transition milk, and milk yield and composition in multiparous dairy cows.

The effects of postpartum milking strategy on plasma mineral concentrations, blood ß-hydroxybutyrate (BHB) concentration, and colostrum, transition milk, and first monthly test milk yield and composition were evaluated in 90 multiparous Jersey and Jersey × Holstein crossbreed cows from a commercial farm. Before first postpartum milking, cows were randomly assigned to the following milking strategies, implemented during the first 2 d postpartum: twice-a-day milking (M2, standard industry practice, milking every 12 h; n = 22), once-a-day milking (M1, milking every 24 h; n = 24), restricted milking (MR, 3-L milking every 12 h; n = 21), and delayed milking (MD, no milking for the first 24 h, and milking every 12 h afterward; n = 23). Blood samples for total plasma Ca, P, and Mg determination were collected from enrollment every 4 h up to 48 h, and at 3 d in milk. Blood BHB concentration was determined at 3 and 11 d in milk. Colostrum and transition milk yields were recorded, and samples were collected at each study milking for IgG and somatic cell count (SCC) determinations. Information for first monthly test milk yield and composition was obtained from the Dairy Herd Improvement Association. Statistical analyses were conducted using generalized multiple linear and Poisson regressions with Dunnett adjustment and M2 as reference group for mean comparisons. Overall, plasma Ca concentration within 48 h after enrollment was higher for MD (2.17 mmol/L), tended to be higher for MR (2.15 mmol/L), and was similar for M1 (2.09 mmol/L) compared with M2 cows (2.06 mmol/L). No statistically significant differences compared with M2 cows were observed for plasma P and Mg concentrations. Colostrum and transition milk and total Ca harvested within 48 h after enrollment were lower for M1, MR, and MD compared with M2 cows. The MD strategy prevented harvesting colostrum with >50 g of IgG/L. No statistically significant effects were detected on plasma mineral concentrations at 3 DIM, blood BHB concentration, colostrum and transition milk SCC within 48 h after enrollment, or milk yield, energy-corrected milk yield, and SCC at first monthly test. Our results suggest that postpartum plasma Ca concentration may be influenced by postpartum milking strategy, without interfering with future milk yield and udder health. Further studies should evaluate whether the proposed milking strategies in early postpartum affect production, reproduction, or health.

Effect of prophylactic oral calcium supplementation on postpartum mineral status and markers of energy balance of multiparous Jersey cows.

The effects of prophylactic oral Ca supplementation on blood mineral status and markers of energy balance were evaluated on 205 multiparous Jersey cows at a commercial dairy. Postpartum, cows were systematically assigned to control (n = 105) or oral Ca supplementation (CaOS; 50 to 60 g of Ca as boluses; n = 100) at 0 and 1 d in milk (DIM). Blood samples for analysis of serum minerals (Ca, P, Mg, K, Na, Fe, Zn, and Cu) were collected before and 1 h after treatment at 0 and 1 DIM, and at 2 DIM. Urine pH was measured immediately before and 1 h after treatment administration (n = 96). A subset of 74 cows was evaluated for plasma glucose and fatty acid concentrations at 0, 1, and 2 DIM. Cows were classified according to their initial calcemic status (Ca status) as normocalcemic (NC; serum Ca >2.12 mmol/L) or subclinically hypocalcemic (SCH; serum Ca ≤2.12 mmol/L). Average serum Ca concentration was higher in CaOS than control cows (2.12 vs. 2.06 mmol/L); this treatment effect was higher for SCH [CaOS (2.03 mmol/L); control (1.89 mmol/L)] than NC cows [CaOS (2.22 mmol/L); control (2.22 mmol/L)]. The incidence of subclinical hypocalcemia was lower for CaOS than control cows (53 vs. 65%); however, at 2 DIM the prevalence of subclinical hypocalcemia tended to be higher for CaOS cows, mostly because it was higher for CaOS-NC than control-NC cows (70 vs. 25%). Urine pH was lower for CaOS than control cows (6.10 vs. 7.04). Lower serum Mg concentration was detected for CaOS-SCH (1.06 mmol/L) than for control-SCH (1.10 mmol/L) cows. Cows in the CaOS group had higher serum K (4.68 vs. 4.53 mmol/L), lower plasma glucose (2.97 vs. 3.10 mmol/L), and at 2 DIM higher plasma fatty acid concentrations (0.43 vs. 0.35 mmol/L) than control cows. Our results showed that postpartum serum Ca concentration increases with oral Ca supplementation, but calcemic status influenced treatment response. Future studies should evaluate the long-term implications on production and reproduction of oral Ca supplementation in Jersey cows.

Efficacy of colostrum replacer versus maternal colostrum on immunological status, health, and growth of preweaned dairy calves.

Commercially available colostrum replacers (CR) are commonly used when maternal colostrum (MC) is unavailable, for managerial convenience, to ensure quality consistency at first feeding, or in disease control and eradication programs. The objective of this study was to determine the efficacy of feeding First Day Formula (Accelerated Genetics, Baraboo, WI) CR versus pooled MC on immunological status, growth, and health of preweaned dairy calves. A total of 1,220 Jersey and Jersey × Holstein calves born on a California Central Valley dairy farm were assigned after birth to receive either CR or MC following a systematic allocation procedure. Calves assigned to MC were tube fed 2.8 L of MC, and calves assigned to CR were tube fed a total of 500 g of CR (150 g of immunoglobulin G; IgG) mixed into 1.9 L of water at 1 h ± 5 min after the calf was born. A subset of calves was selected for passive transfer (n = 592) and growth (n = 268) analyses. Although both coliform count and total bacteria count were low for MC and CR fed to calves during the study, the predicted probability of calves receiving contaminated liquid feed (coliform count >10,000 cfu/mL) at first feeding was reduced for calves fed CR (1.5%) compared with calves fed MC (6.1%). The mean blood concentration of IgG was lower for calves fed CR than for calves fed MC (19.6 vs. 23.4 mg/mL). However, the apparent efficiency of absorption of IgG did not differ between treatments (34.4 and 35.9% for CR and MC, respectively). Total proteins were lower in calves fed CR compared with MC at 24 h (5.16 vs. 5.84 g/dL, respectively). Calves fed CR were 1.5 kg lighter at weaning and gained 0.03 kg less per day (0.30 vs. 0.33 kg/d, respectively) than calves fed MC before weaning. Height at weaning did not differ between the 2 treatment groups. Calves fed CR tended to have a higher predicted probability of not being treated for diarrhea than calves fed MC (0.142 vs. 0.110, respectively). However, when the disease was present, CR had a higher number of treatment days compared with MC (11.6 vs. 10.8 d, respectively). The hazard ratio of dying did not differ between MC and CR; however, CR calves had a numerically higher risk (hazard ratio = 1.347) of dying compared with calves that received MC. In conclusion, IgG absorption and serum concentration of calves were adequate when calves were fed either CR or MC. The CR-fed calves had a lower probability of receiving contaminated liquid feed and performed similar in terms of health compared with calves receiving high-quality MC, although they were slightly lighter at weaning. Therefore, the CR evaluated in this study is a valid alternative to high-quality (>50 mg of IgG/mL) MC.

Responses of fresh cows to three feeding strategies that reduce starch levels by feeding beet pulp.

The study objective was to evaluate the effects of reducing dietary starch content in fresh cow diets while maintaining NDF levels by substituting barley grain (BG), corn silage (CS), or both with beet pulp (BP) on nutrient digestion, ruminal fermentation, DMI, lactation performance, meal patterns, chewing activity, and sorting behavior. Thirty-six multiparous cows were randomly assigned to 1 of 4 experimental diets from calving to 21 d in lactation. Experimental diets were a high-starch diet with ground BG (CO; 24.9% starch; 0% BP) and 3 low-starch diets: the CO with BP substituted for ground BG (BB; 19.6% starch; 7% BP), the CO with BP substituted for CS (BC; 20.6% starch; 12% BP), or the CO with BP substituted for CS and ground BG (BCB; 20.3% starch; 12% BP). The CO, BB, BC, and BCB contained 33.4, 34.4, 32.9, and 33.7% NDF, respectively, and 23.1, 22.0, 18.2, and 19.2% forage NDF, respectively. There was no effect of diet on total tract nutrient digestibility ( > 0.20), ruminal pH ( = 0.49), or total VFA ( = 0.39). However, diets affected molar proportions of propionate and acetate ( ≤ 0.01). Relative to CO cows, the molar propionate percentage was less in BB cows ( < 0.01) and tended to be greater in BC cows ( = 0.10), whereas the molar percentage of acetate was less in BC cows than in BB ( < 0.01) and CO cows ( = 0.02). Relative to CO cows (16.50 kg/d), DMI was greater for BC (17.70 kg/d; < 0.01) and BCB cows (17.50 kg/d; = 0.01), but it was less in BB cows (15.60 kg/d; = 0.02). Similar to DMI results, milk yields tended to be greater for BC (37.89 kg/d; = 0.08) and BCB cows (37.81 kg/d; = 0.09) compared with CO cows (35.41 kg/d), but BB cows (33.05 kg/d) tended to produce less milk than CO cows ( = 0.1). Milk fat content tended to be less in BC ( = 0.08) and BCB cows ( = 0.10) than in CO cows. There was no effect of diet on eating and rumination patterns ( ≥ 0.18), except shortened meal intervals for BC and BCB cows compared with CO cows ( = 0.02). Dietary treatments did not affect chewing activities per day or bout ( = 0.50), but BC and BCB cows spent less time on chewing activities per kilogram DM ( < 0.01) and NDF intake ( < 0.01) compared with CO cows. Cows fed the BC and BCB sorted for long particles (>19 mm; < 0.01) but against particles < 1.18 mm ( < 0.01). In the present study, propionate did not seem to play a central role in feed intake regulation of fresh cows, because BB cows had depressed DMI and the lowest molar proportion of propionate. However, reducing starch levels in fresh cow diets by replacing CS and both CS and BG with BP positively affected DMI and milk yield.

Colostrum immunoglobulin G concentration of multiparous Jersey cows at first and second milking is associated with parity, colostrum yield, and time of first milking, and can be estimated with Brix refractometry.

The objective of this study was to evaluate colostrum IgG concentration harvested at first and second milking from multiparous Jersey cows, the dam's lactation number, colostrum yield, and time of first milking. In addition, we validated the use of a Brix refractometer to estimate IgG concentration in colostrum from multiparous Jersey cows using radial immunodiffusion as the reference method. Colostrum samples and total weight of colostrum harvested at first (n = 134) and second (n = 68) milking were collected from 134 multiparous Jersey cows housed in a California herd. Fresh colostrum samples were analyzed for IgG concentration with Brix refractometry and frozen samples by radial immunodiffusion. A total of 90.4 and 42.7% of the samples from first and second milking met industry standards of quality for IgG concentration (>50 g/L). Second and third lactation cows had similar colostrum IgG concentration but lower than cows on their fourth and greater lactation. At second milking, 56.4% of cows on their fourth or greater lactation had colostrum IgG concentrations >50 g/L. When colostrum yield increased from low (<3 kg), medium (3 to 6 kg), to high (>6 kg), IgG concentration decreased. Higher IgG concentration was observed on colostrum harvested at <6 h (short) versus 6 to 11 h (medium) after calving. However, IgG concentration in colostrum harvested after 11 h (long) was similar to that harvested at short and medium time. Readings of %Brix were highly correlated with IgG at first (r = 0.81) and second (r = 0.77) milking. The best Brix threshold to identify colostrum from first milking with >50 IgG g/L was 20.9% based on logit equations with Youden's index criterion and 18.0% based on accuracy criterion. For colostrum harvested at second milking, similar Brix thresholds were obtained, 19.2 and 19.0%, regardless of whether Youden's index or accuracy was used as the selection criterion. Our results indicate that the dam's lactation number, colostrum yield, and time of first milking relative to calving are associated with IgG concentration in colostrum from multiparous Jersey cows. Second milking colostrum from mature Jersey cows should be evaluated to extend colostrum supply on dairies especially during times of shortage. Readings of %Brix can be used to rapidly estimate IgG concentration in Jersey colostrum harvested at first and second milking.

Effects of subcutaneous calcium administration at calving on mineral status, health, and production of Holstein cows.

The objective of this study was to determine effects of subcutaneous (s.c.) infusions of Ca at calving day on serum concentrations of Ca, P, Mg, ß-hydroxybutyrate (BHB), glucose, body condition score (BCS), milk yield, and health in fresh cows receiving a dietary cation-anion difference diet during the dry period. Three hundred seventy-five fresh Holstein cows were blocked based on parity (143 cows in first parity, 108 cows in second parity, and 124 cows in third or greater parity) and randomly assigned to 1 of 4 experimental treatments immediately after calving. Treatments were control group without infusion (control; n=190); 1 s.c. infusion of 250mL of 40% Ca borogluconate (1SC250; n=72) at calving; 1 s.c. infusion of 500mL of 40% Ca borogluconate (1SC500; n=63) at calving; 2 s.c. infusions of 250mL of 40% Ca borogluconate, one immediately after calving and the second 12 to 18h after first infusion (2SC250; n=50). Blood samples were collected immediately after parturition and at 1, 2, 4, and 7d in milk (DIM) for Ca, P, and Mg determination. Milk production, milk composition, and somatic cell count were recorded monthly up to 90 DIM. The evaluation of BCS was performed at calving and at 38 DIM. A subset of 9 cows per treatment group was randomly chosen to measure serum concentration of glucose and BHB at 2, 4, and 7 DIM. Total serum Ca in 1SC250 (8.95mg/dL), 1SC500 (9.27mg/dL), and 2SC250 (9.07mg/dL) was greater during the first week postpartum compared with control (8.45mg/dL). Serum concentrations of P, Mg, BHB, glucose, and milk yield were not affected by treatments. The dry matter intake during the first 24h after calving was higher for treatments 1SC250 (13.5kg), 1SC500 (15.0kg), and 2SC250 (15.6kg) relative to control (12.5kg). Milk somatic cell counts were lower for 1SC500 (90.5 cells/mL) and 2SC250 (82.2 cells/mL) than control (132.8 cells/mL). Risk ratio was >1 for development of metritis, and clinical and subclinical endometritis in control cows relative to 2SC250 cows, which indicates a higher risk of developing disease for control cows (2.03, 1.7, and 1.8 times, respectively). These results suggest that prophylactic s.c. infusions of Ca at calving can improve postpartum Ca status in Holstein cows and intake at 1 DIM. Given the reduction of metritis, clinical and subclinical endometritis, and subclinical hypocalcemia with treatment, the effect of s.c. Ca supplementation on immune status warrants further investigation.

Blood calcium dynamics after prophylactic treatment of subclinical hypocalcemia with oral or intravenous calcium.

Total serum Ca dynamics and urine pH levels were evaluated after prophylactic treatment of subclinical hypocalcemia after parturition in 33 multiparous Jersey × Holstein crossbreed cows. Cows were blocked according to their calcemic status at the time of treatment [normocalcemic (8.0-9.9 mg/dL; n = 15) or hypocalcemic (5.0-7.9 mg/dL; n = 18)] and randomly assigned to 1 of 3 treatments: control [no Ca supplementation (n = 11)]; intravenous Ca [Ca-IV (n = 11), 500 mL of 23% calcium gluconate (10.7 g of Ca and 17.5 g of boric acid as a solubilizing agent; Durvet, Blue Springs, MO)]; or oral Ca [Ca-Oral (n = 11), 1 oral bolus (Bovikalc bolus, Boehringer Ingelheim, St. Joseph, MO) containing CaCl2 and CaSO4 (43 g of Ca) 2 times 12h apart]. Total serum Ca levels were evaluated at 0, 1, 2, 4, 8, 12, 16, 20, 24, 36, and 48 h, and urine pH was evaluated at 0, 1, 12, 24, 36, and 4 8h after treatment initiation. Total serum Ca levels were higher for Ca-IV than for control and Ca-Oral cows at 1, 2, and 4h after treatment initiation, but lower than Ca-Oral cows at 20, 24, and 36 h and lower than control cows at 36 and 48 h. At 1h after treatment initiation, when serum Ca levels for Ca-IV cows peaked (11.4 mg/dL), a greater proportion of Ca-IV (n = 8) cows had total serum Ca levels >10mg/dL than control (n = 0) and Ca-Oral (n = 1) cows. At 24h after treatment initiation, when Ca-IV cows reached the total serum Ca nadir (6.4 mg/dL), a greater proportion of Ca-IV (n = 10) cows had serum Ca levels <8 mg/dL than control (n = 5) and Ca-Oral (n = 2) cows. Treatment, time, and treatment × time interaction were significant for urine pH. Mean urine pH was lower for Ca-Oral cows (6.69) than for control (7.52) and Ca-IV (7.19) cows. Urine pH levels at 1h after treatment were lower for Ca-IV cows compared with both control and Ca-Oral cows, a finding likely associated with the iatrogenic administration of boric acid added as a solubilizing agent of the intravenous Ca solution used. At 12, 24, and 36 h, urine pH levels were lower for Ca-Oral cows compared with both control and Ca-IV cows. This was expected because the oral Ca supplementation used (Bovikalc) is designed as an acidifying agent. Wide fluctuations in blood Ca were observed after prophylactic intravenous Ca supplementation. The implications for milk production and animal health, if any, of these transient changes in total serum Ca have yet to be evaluated.

Effects of abomasal infusion of linseed oil on responses to glucose and insulin in holstein cows.

The objective was to study the effects of abomasal infusion of linseed oil, a source rich in n-3 C18:3, on whole-body response to insulin (experiment 1) and on insulin antilipolytic effects during feed restriction (experiment 2). In experiment 1, eight nonlactating, non-gestating cows were assigned to a crossover design, fed to meet maintenance requirements, and infused abomasally with either linseed oil (LIN) or tallow (TAL) at a rate of 0.54 g/kg of body weight per d for 5.5 d. Infusions were performed every 8 h during the first 3 d of each period and every 4 h thereafter. Intravenous glucose tolerance tests (IVGTT) were performed on d 5 of each period, followed by i.v. insulin challenges (IC) 12 h later. In experiment 2, six nonlactating, nongestating cows were assigned to a replicated 3 x 3 Latin square design. The experimental protocol included a water (WTR) treatment and feeding was suspended on d 3, leading to 50 and 62 h of feed restriction before IVGTT and IC, respectively. Clearance of glucose during IVGTT and IC was not affected by treatments in either experiment. However, LIN had an insulin sensitizing effect in experiment 1, because a lower insulin concentration led to the same clearance of glucose as TAL. In experiment 1, plasma nonesterified fatty acid (NEFA) concentration was low, reflecting a postprandial state, but NEFA was greater for LIN than TAL during IVGTT (108 vs. 88 +/- 4 microEq/L) and IC (133 vs. 83 +/- 9 microEq/L). In experiment 2, insulin concentrations during IVGTT did not differ across treatments. Basal plasma NEFA concentration before IVGTT tended to be greater for LIN than for TAL (612 vs. 508 microEq/L). Plasma NEFA clearance rate during IVGTT was greater for LIN than for TAL (2.8 vs. 2.5%/min), leading to a shorter time to reach half NEFA concentration (25 vs. 29 min) and greater absolute value of NEFA response area under the curve [AUC; -64,150 vs. -46,402 (microEq/L) x 180 min]. Data suggest that LIN enhanced the antilipolytic effects of insulin. Yet, other factors could have been involved because plasma NEFA concentration before IVGTT was 104 muEq/L greater for LIN than TAL for unknown reasons.

Supplemental choline for prevention and alleviation of fatty liver in dairy cattle.

Two experiments were conducted to evaluate if supplementing rumen-protected choline (RPC; Reashure, Balchem Encapsulates, Slate Hill, NY) could prevent or alleviate fatty liver in dairy cattle. The first experiment evaluated the effect of supplementing RPC on hepatic triacylglycerol (TAG) accumulation during fatty liver induction. Twenty-four dry cows between 45 to 60 d prepartum were paired by body weight (BW) and body condition score (BCS) and randomly assigned to control or supplementation with 15 g of choline as RPC/d. From d 0 to 6, before treatment application, all cows were fed 1.4 kg/d of concentrate and forage ad libitum. Samples of blood and liver, obtained during the pretreatment period, were used for covariate adjustment of blood metabolites and liver composition data. During fatty liver induction (d 7 to 17), cows were fed 1.4 kg/d of concentrate with or without supplementation with RPC, and forage intake was restricted, so cows consumed 30% of the total energy requirements for pregnancy and maintenance. Supplementation with RPC during fatty liver induction did not affect plasma glucose and plasma beta-hydroxybutyrate (BHBA) concentration but did decrease plasma nonesterified fatty acid (NEFA; 703 vs. 562 microEq/L, SE = 40) and liver TAG accumulation (16.7 vs. 9.3 microg/microg of DNA, SE = 2.0). In the second experiment, we evaluated the effect of supplementing RPC on the clearance of liver TAG when cows were fed ad libitum after the induction of fatty liver by feed restriction. Twenty-eight cows between 45 and 60 d prepartum were paired according to BCS and BW and assigned to treatments. Fatty liver was induced by feeding 1.4 kg/d of concentrate (without RPC) and restricting forage intake, so cows consumed 30% of maintenance and pregnancy energy requirements for 10 d. From d 11 to 16, after feed restriction, cows were fed forage ad libitum and 1.4 kg/d of concentrate with or without RPC. Treatments were not applied during fatty liver induction; however, following feed restriction, liver for cows assigned to control and RPC treatments contained 6.8 and 12.7 microg of TAG/microg of DNA, respectively. Measurements obtained before treatment served as covariates for statistical analysis. During the depletion phase, plasma glucose, BHBA, and NEFA were not affected by treatment. Liver TAG, expressed as covariate adjusted means, was 6.0 and 4.9 microg/microg of DNA (SE = 0.4) on d 13, and 5.0 and 1.5 microg/microg of DNA (SE = 0.9) on d 16 for control and RPC, respectively. Rumen-protected choline can prevent and possibly alleviate fatty liver induced by feed restriction.