Plasma and milk metabolomics revealed changes in amino acid metabolism in Holstein dairy cows under heat stress.

Our understanding of metabolic alterations triggered by heat stress is incomplete, which limits the designing of nutritional strategies to mitigate negative productive and health effects. Thus, this study aimed to explore the metabolic responses of heat-stressed dairy cows to dietary supplementation with vitamin D3/Ca and vitamin E/Se. Twelve multiparous Holstein cows were enrolled in a split-plot Latin square design with two distinct vitamin E/Se supplementation levels, either at a low (ESe-, n = 6, 11.1 IU/kg vitamin E and 0.55 mg/kg Se) or a high dose (ESe+, n = 6 223 IU/kg vitamin E and 1.8 mg/kg Se) as the main plot. Treatment subplots, arranged in a replicated 3 × 3 Latin square design, comprised heat challenge (Temperature Humidity Index, THI: 72.0-82.0) supplemented with different levels of vitamin D3/Ca: either low (HS/DCa-, 1 012 IU/kg and 0.73%, respectively) or high (HS/DCa+, 3 764 IU/kg and 0.97%, respectively), and a pair-fed control group in thermoneutrality (THI = 61.0-64.0) receiving the low dose of vitamin D3/Ca (TN). The liquid chromatography-mass spectrometry-based metabolome profile was determined in blood plasma and milk sampled at the beginning (day 0) and end (day 14) of each experimental period. The results were analyzed for the effect of (1) TN vs. HS/ESe-/DCa-, and (2) the vitamin E/Se and vitamin D3/Ca supplementation. No group or group × day effects were detected in the plasma metabolome (false discovery rate, FDR > 0.05), except for triglyceride 52:2 being higher (FDR = 0.03) on day 0 than 14. Taurine, creatinine and butyryl-carnitine showed group × day interactions in the milk metabolome (FDR ≤ 0.05) as creatinine (+22%) and butyryl-carnitine (+190%) were increased (P < 0.01) on day 14, and taurine was decreased (-65%, P < 0.01) on day 14 in the heat stress (HS) cows, compared with day 0. Most compounds were unaffected by vitamin E/Se or vitamin D3/Ca supplementation level or their interaction (FDR > 0.05) in plasma and milk, except for milk alanine which was lower (-69%, FDR = 0.03) in the E/Se+ groups, compared with E/Se-. Our results indicated that HS triggered more prominent changes in the milk than in the plasma metabolome, with consistent results in milk suggesting increased muscle catabolism, as reflected by increased creatinine, alanine and citrulline levels. Supplementing with high levels of vitamin E/Se or vitamin D3/Ca or their combination did not appear to affect the metabolic remodeling triggered by HS.

Dietary supplementation of vitamin D3 and calcium partially recover the compromised time budget and circadian rhythm of lying behavior in lactating cows under heat stress.

Heat stress (HS) impedes cattle behavior and performance and is an animal comfort and welfare issue. The objective of this study was to characterize the time budget and circadian rhythm of lying behavior in dairy cows during HS and to assess the effect of dietary supplementation of vitamin D3 and Ca. Twelve multiparous Holstein cows (42.2 ± 5.6 kg milk/d; 83 ± 27 d in milk) housed in tiestalls were used in a split-plot design with the concentration of dietary vitamin E and Se as main plots (LESe: 11.1 IU/kg and 0.55 mg/kg, and HESe: 223 IU/kg and 1.8 mg/kg, respectively). Within each plot cows were randomly assigned to (1) HS with low concentrations of vitamin D3 and Ca (HS, 1,012 IU/kg and 0.73%, respectively), (2) HS with high concentrations of vitamin D3 and Ca (HS+D3/Ca; 3,764 IU/kg and 0.97%, respectively), or (3) thermoneutral pair-fed (TNPF) with low concentrations of vitamin D3 and Ca (1,012 IU/kg and 0.73%, respectively) in a Latin square design with 14-d periods and 7-d washouts. Lying behavior was measured with HOBO Loggers in 15-min intervals. Overall, cows in HS spent less time lying per day relative to TNPF from d 7 to 14. Daily lying time was positively correlated with milk yield, energy-corrected milk yield, and feed efficiency, and was negatively correlated with rectal temperature, respiratory rate, fecal calprotectin, tumor necrosis factor-α, and C-reactive protein. A treatment by time interaction was observed for lying behavior: the time spent lying was lesser for cows in HS than in TNPF in the early morning (0000-0600 h) and in the night (1800-2400 h). The circadian rhythm of lying behavior was characterized by fitting a cosine function of time into linear mixed model. Daily rhythmicity of lying was detected for cows in TNPF and HS+D3/Ca, whereas only a tendency in HS cows was observed. Cows in TNPF had the highest mesor (the average level of diurnal fluctuations; 34.2 min/h) and amplitude (the distance between the peak and mesor; 17.9 min/h). Both the mesor and amplitude were higher in HS+D3/Ca relative to HS (26.6 vs. 25.2 min/h and 3.91 min/h vs. 2.18 min/h, respectively). The acrophase (time of the peak) of lying time in TNPF, HS, and HS+D3/Ca were 0028, 0152, and 0054 h, respectively. Lastly, a continuous increase in daily lying time in TNPF was observed during the first 4 d of the experimental period in which DMI was gradually restricted, suggesting that intake restrictions may shift feeding behavior and introduce biases in the behavior of animals. In conclusion, lying behavior was compromised in dairy cows under HS, characterizing reduced daily lying time and disrupted circadian rhythms, and the compromised lying behavior can be partially restored by supplementation of vitamin D3 and Ca. Further research may be required for a more suitable model to study behavior of cows under HS.

Increased dietary vitamin D3 and calcium partially alleviate heat stress symptoms and inflammation in lactating Holstein cows independent of dietary concentrations of vitamin E and selenium.

Twelve multiparous Holstein cows (42.2 ± 5.6 kg of milk/d; 83 ± 27 d in milk) were used in a split-plot design testing the effects of mineral and vitamin supplementation on the time course of animal performance, metabolism, and inflammation markers during heat stress. The main plot was the average concentrations of dietary vitamin E and Se (adequate: 11.1 IU/kg of vitamin E and 0.55 mg/kg of Se, and high: 223 IU/kg of vitamin E and 1.8 mg/kg of Se, respectively). Within each plot, cows were randomly assigned to (1) heat stress (HS) with adequate concentrations of vitamin D3 and Ca (1,012 IU/kg and 0.73%, respectively), (2) HS with high concentrations of vitamin D3 and Ca (HS+D3/Ca; 3,764 IU/kg and 0.97%, respectively), or (3) pair-feeding (PF) in thermoneutrality with adequate concentrations of vitamin D3 and Ca (1,012 IU/kg and 0.73% Ca) in a Latin square design with 14-d periods and 7-d washouts. The highest rectal temperature was recorded at 1700 h for HS (39.4°C; mean of d 1 to 14), being 1.2 and 0.8°C greater than for PF and HS+D3/Ca, respectively. Respiratory rate and water intake were higher in HS (73 breaths/min and 115 L/d, respectively) relative to PF (28 breaths/min and 76 L/d). Heat stress decreased dry matter intake progressively, reaching a nadir on d 5 to 7 (33% reduction) and was not different between treatments. Milk yield decreased progressively in all treatments, but remained greater in PF relative to HS from d 3 to 14 (10%), whereas HS and HS+D3/Ca were not different. Milk fat, protein, and lactose concentrations and yields were lower in HS relative to PF from d 3 to 14, but not different between HS and HS+D3/Ca. Relative to PF, preprandial insulin concentrations were increased in HS, whereas plasma nonesterified fatty acids were decreased on d 7 and 14. Plasma lipopolysaccharide-binding protein concentrations increased in HS cows on d 7 and 14, respectively, relative to PF, whereas they were reduced in HS + D3/Ca on d 14. Plasma C-reactive protein, tumor necrosis factor-α, and fecal calprotectin were increased in HS relative to both PF and HS+D3/Ca on d 7 and 14. Rectal temperature was positively associated with plasma lipopolysaccharide-binding protein (r = 0.72), tumor necrosis factor-α (r = 0.74), C-reactive protein (r = 0.87), and with milk somatic cells (r = 0.75). Plasma 8-hydroxy-2-deoxyguanosine concentrations presented a 3-way interaction, where 8-hydroxy-2-deoxyguanosine was lower in HS than in PF on d 7 and 14, and lower in HS+D3/Ca relative to HS on d 14 in the adequate vitamin E and Se treatment, but no effects were observed in the high vitamin E and Se group. Plasma superoxide dismutase concentrations increased over time, and were higher in HS relative to PF on d 14, whereas HS+D3/Ca was similar to HS. Heat stress markedly reduced milk production and milk components while increasing markers of leaky gut and inflammation. In contrast, vitamin D3 and Ca supplementation reduced hyperthermia (d 7-14), markers of leaky gut, and inflammation independent of dietary concentrations of vitamin E and Se.

Effect of dietary supplementation or cessation of magnesium-based alkalizers on milk fat output in dairy cows under milk fat depression conditions.

We aimed to evaluate the effects of dietary supplementation with magnesium oxide and calcium-magnesium dolomite on milk fat synthesis and milk fatty acid profile or persistency in milk fat synthesis after their cessation in dairy cows under milk fat depression conditions. Twenty-four multiparous dairy cows in early lactation (mean ± standard deviation; 112 ± 14 d in milk) were used in a randomized complete block design. Milk fat depression was induced in all cows for 10 d by feeding a diet containing 35.2% starch, 28.7% neutral detergent fiber, and 4.8% total fatty acid (dry matter). The experiment was conducted in 2 periods. During the Mg-supplementation period (d 1-20), cows were randomly assigned to (1) the milk fat depression diet used during the induction phase (control; n = 8), (2) the control diet plus 0.4% magnesium oxide (MG; n = 8), or (3) the control diet plus 0.8% calcium-magnesium dolomite (CMC; n = 8). Compared with the control group, feeding the magnesium-supplemented diets increased milk fat concentration and yield by 12% within 4 d. During the 20-d Mg-supplementation period, both the MG and CMC diets increased milk fat concentration and yield, as well as 3.5% fat-corrected milk and energy-corrected milk yield, without affecting dry matter intake, milk yield, and milk protein and lactose concentrations. In the Mg-cessation period (d 21-30), all cows received the control diet, which resulted in a greater milk fat concentration and yield in the cows that had already received the MG and CMC diets in the Mg-supplementation period. Whereas, milk fat concentration and yield remained high after discontinuation of the magnesium-containing alkalizer until d 27. The difference in milk fat synthesis was associated with lower trans-10 C18:1 (-22%) and higher trans-11 C18:1 (+12.5%) concentrations in milk during the Mg-supplementation period. Furthermore, it was evident that within 2 d of supplementation, the trans-10:trans-11 ratio was lower in MG and CMC cows compared with cows receiving the control. This suggested that the effect of magnesium-based alkalizers on milk fat synthesis was mediated via a shift in ruminal biohydrogenation of cis-9,cis-12 C18:2 in the rumen. In conclusion, abrupt addition of magnesium oxide and calcium-magnesium dolomite increased milk fat synthesis, which persisted for 7 d after cessation of magnesium-based alkalizers. A similar ability to recover milk fat synthesis and normal fatty acid biohydrogenation pathways was observed for magnesium oxide and calcium-magnesium dolomite.

Potassium carbonate as a supplement to improve milk fat concentration and yield in early-lactating dairy goats fed a high-starch, low-fiber diet.

This study investigated the use of K2CO3 as dietary buffer to prevent or to recover from low milk fat production when early-lactating dairy goats are fed a high-starch, low-fiber (HSLF) diet. At kidding, 30 Alpine goats housed in pens with Calan gate feeders received a total mixed ration with a forage-to-concentrate ratio of 55:45 on a dry matter (DM) basis for a baseline period of 27 ± 4 d. Goats (milk yield, 4.14 ± 0.88 kg/d; milk fat, 4.28 ± 0.52%; mean ± SD) were then assigned to 1 of 10 blocks according to parity (first vs. second or more) and milk fat concentration, and fed a HSLF diet containing 45% forages and 55% concentrates for 2 experimental periods of 28 d. Treatments were identified as (1) control, in which the HSLF diet was fed throughout both periods; (2) preventive, in which the HSLF diet supplemented with K2CO3 (1.6% of DM) was fed during both periods; and (3) recovery, in which the HSLF diet was fed during the first period (P1) and the HSLF diet supplemented with K2CO3 was fed during the second period (P2). Data from P1 and P2 were analyzed separately. In P1, preplanned contrasts were used to evaluate the preventive effect of K2CO3 (control and recovery, both groups receiving the same diet during this period, vs. preventive), and in P2, to assess the potential of K2CO3 to alleviate an already existing state of low milk fat (control vs. recovery and preventive vs. recovery). Feeding the HSLF diet in P1 moderately decreased milk fat concentration (-16%) and yield (-13%) as compared with baseline. Dietary addition of K2CO3 decreased DM intake by 12 and 14% in P1 and P2, respectively. Ruminal pH was not different among treatments. There was also no significant difference in milk yield (4.13 and 3.71 kg/d on average in P1 and P2, respectively) for any tested contrasts. In P1, milk fat concentration and yield did not differ among goats fed control (3.58% and 151 g/d, respectively) and preventive (3.67% and 148 g/d, respectively) diets. In P2, milk fat concentration and yield did not differ among goats fed the control diet (3.38% and 137 g/d, respectively), and diets where K2CO3 was used as preventive (3.44% and 126 g/d, respectively) or recovery treatment (3.25% and 113 g/d, respectively). Supplementing a high-concentrate diet with 1.6% K2CO3 was therefore not effective in either preventing or suppressing already existing conditions of low milk fat production in dairy goats.

Abomasally infused SFA with varying chain length differently affect milk production and composition and alter hepatic and mammary gene expression in lactating cows.

The aim of the present study was to compare the effects of post-ruminally infused fat supplements, varying in fatty acid (FA) chain length, on animal performance, metabolism and milk FA. Eleven multiparous Holstein dairy cows were used in a replicated incomplete 3 × 3 Latin square design with 7-d periods, separated by 7-d washouts. Treatments were administered as abomasal infusions of enrichments providing 280 g/d of FA: (1) palmitic acid (98·4 % 16 : 0; PA), (2) caprylic and capric acids (56·2 % 8 : 0, 43·8 % 10 : 0; medium-chain TAG (MCT)) and (3) stearic acid (99·0 % 18 : 0; SA). Relative to PA, SA decreased the efficiency of fat-corrected milk production, which was associated with a tendency for higher DM intake and lower FA absorption with SA, whereas MCT was not different from PA for these variables. Milk fat concentration and yield were increased by PA relative to SA, but only fat yield tended to be greater relative to MCT. Relative to PA, MCT increased milk fat concentration of FA < 16 C, whereas SA increased FA > 16 C. Expression of mammary stearoyl-coA desaturase 1 was lower with SA than with PA. Relative to PA, liver expression of adenosine monophosphate-activated protein kinase-1 and pyruvate kinase was increased with MCT, whereas expression of these genes tended to be increased by SA. The mechanism of increased fat secretion with PA does not seem to be related to a modulation of the expression of lipogenesis-related genes, but rather to increased substrate availability as reflected by milk FA profile.

Technical note: An in vivo method to determine kinetics of unsaturated fatty acid biohydrogenation in the rumen.

Rumen microbial biohydrogenation (BH) of unsaturated fatty acids (UFA) has been extensively studied in vitro; however, in vitro BH pathways, rates, and extents may not parallel those in vivo. The objective was to develop an assay to assess in vivo rates, pathways, and extent of BH of oleic (OA), linoleic (LA), and α-linolenic (ALA) acids. Each UFA was characterized in a separate experiment, each using 4 ruminally cannulated lactating Holstein cows. A single bolus consisting of 200 g of a UFA-oil [experiment 1 (EXP1): 87% OA sunflower, experiment 2 (EXP2): 70% LA safflower, and experiment 3 (EXP3): 54% ALA flaxseed] and 12 g of heptadecanoic acid (C17:0) was mixed into the rumen through the fistula. Rumen digesta was collected at -1, -0.25, 0.1, 0.25, 0.5, 0.75, 1, 1.5, 2, 3, 4, and 6 h relative to the bolus. Overall, the triglyceride boluses increased total fatty acids (FA) in the rumen from 3.9 (standard deviation = ±1.4) to 7.3% (±1.4) of rumen dry matter and enriched C17:0 from 0.4 (±0.1) to 2.5% (±0.5) of FA. The bolus enriched OA from 8.9 (±1.0) to 30.1% (±4.6) of FA in EXP1, LA from 11.1 (±1.8) to 35.9% (±5.0) of FA in EXP2, and ALA from 2.1 (±0.1) to 19.8% (±4.3) of FA in EXP3. The disappearances of C17:0, OA, LA, and ALA were fit to a single exponential decay model. The first-order rate of C17:0 rumen disappearance (turnover) was 9.1, 6.9, and 5.2%/h in EXP1, EXP2, and EXP3, respectively, and was used as a marker of FA passage. The rate of total rumen turnover of OA was 54.1%/h, LA was 60.5%/h, and ALA was 93.0%/h in EXP1, EXP2, and EXP3, respectively. Rumen concentration of all 3 UFA reached prebolus concentrations within 4 h. The calculated extent of lipolysis and initial isomerization was 85.6% for OA, 89.8% for LA, and 94.7% for ALA in EXP1, EXP2, and EXP3, respectively. Assuming that BH equals total disappearance minus passage, the rates of lipolysis and initial isomerization were 45.0, 53.6, and 87.8%/h for OA, LA, and ALA in EXP1, EXP2, and EXP3, respectively. Analysis of the data using compartmental modeling showed that the normal BH pathways proposed in the literature explained 46.0, 37.3, and 49.8% of the BH of OA, LA, and ALA in EXP1, EXP2, and EXP3, respectively. Based on the model, BH of trans C18:1 FA was the rate-limiting step to complete BH. Importantly, oils were provided as triglycerides and the reported rates represent the rate of lipolysis and BH. In conclusion, the rate of ruminal BH of OA, LA, and ALA was higher than that commonly observed in vitro, but the extent of BH was near expected values. The method developed provides a potential in vivo assay of ruminal BH for use in future experiments and modeling efforts.

Short communication: Effects of lysolecithin on milk fat synthesis and milk fatty acid profile of cows fed diets differing in fiber and unsaturated fatty acid concentration.

Thirteen multiparous Holstein cows were used in a crossover design that tested the effect of lysolecithin in diets differing in neutral detergent fiber (NDF) and unsaturated fatty acid (FA) concentrations. Experimental periods were 20 d in length and included two 10-d phases. A standard fiber and lower fat diet was fed the first 10 d (30.5% NDF, no added oil, lower-risk phase) and a lower NDF and higher oil diet was fed during the second 10 d (29.0% NDF and 2% oil from whole soybeans and soybean oil, high-risk phase). Treatments were control and 10 g/d of lysolecithin (LYSO) extended in a ground corn carrier. Milk was sampled on d 0, 5, and 10 of each phase for determination of fat and protein concentration and FA profile. We found no effect of treatment or treatment by time interaction for dry matter intake, milk yield, or milk protein concentration. A treatment by time interaction was observed for milk fat concentration and yield. Milk fat concentration was higher in LYSO on d 5 of the lower-risk phase, but decreased progressively in both treatments during the high-risk phase. Milk fat yield was not different among treatments during the lower-risk phase, but was lower in LYSO on d 15 and tended to be lower on d 20 during the high-risk phase. Concentrations of milk de novo FA decreased and preformed FA increased during the high-risk phase, but we found no effect of treatment or treatment by time interactions. We noted an effect of time, but no treatment or treatment by time interactions for milk trans FA isomers. Briefly, trans-11 C18:1 and cis-9,trans-11 conjugated linoleic acid progressively decreased as trans-10 C18:1 and trans-10,cis-12 conjugated linoleic acid progressively increased during the high-risk phase. The LYSO increased milk fat concentration when feeding a higher fiber and lower unsaturated FA diet, but decreased milk fat yield when feeding a lower fiber and higher unsaturated FA diet, although biohydrogenation pathways and capacity did not appear to be modified. The effect of lysolecithin on rumen fermentation warrants further investigation, but is not recommended when feeding lower fiber and higher unsaturated fat diets.

Effect of lipid supplementation on milk odd- and branched-chain fatty acids in dairy cows.

Eight ruminally fistulated, multiparous Holstein cows were arranged in a double 4×4 Latin square with 14-d periods to investigate the effects of lipid supplementation on performance, rumen parameters, the milk odd- and branched-chain fatty acid (OBCFA) profile, and the relationships between milk OBCFA and rumen parameters. Lipid supplementation is known to inhibit microbial growth in the rumen, decrease de novo microbial fatty acid synthesis, and increase the uptake of circulating fatty acids by the mammary gland; treatments were selected to isolate these effects on the milk OBCFA profile. The 4 treatments were (1) a lipid-free emulsion medium infused in the rumen (CTL), (2) soybean oil as a source of polyunsaturated fatty acids infused in the rumen (RSO), (3) saturated fatty acids (38% 16:0, 40% 18:0) infused in the rumen (RSF), and (4) saturated fatty acids infused in the abomasum (ASF). Fat supplements were provided continuously as emulsions at a rate of 450g/d. Preplanned contrasts compared CTL to RSO, RSO to RSF, and RSF to ASF. Infusing RSO slightly decreased ruminal pH, but did not affect volatile fatty acids profile and milk fat concentration as compared with CTL. The yields of energy-corrected milk, fat, and protein were greater with RSF compared with RSO. The concentration of odd-chain fatty acids was decreased by RSO, whereas even-chain iso fatty acids were not affected. Milk fat concentration of 17:0 + cis-9 17:1 was higher for RSF than for RSO, due to the saturated fatty acids supplement containing 2% 17:0 + cis-9 17:1. Limited differences were observed in the milk OBCFA profile between RSF and ASF. A multiple regression analysis yielded the following equation for predicting rumen pH based on milk fatty acids: pH=6.24 - (0.56×4:0) + (1.67 × iso 14:0) + (4.22 × iso 15:0) + (9.41×22:0). Rumen propionate concentration was negatively correlated with milk fat concentration of iso 14:0 and positively correlated with milk 15:0, whereas the acetate-to-propionate ratio gave the opposite correlations with milk iso 14:0 and 15:0. Milk fat concentration of 17:0 + cis-9 17:1 was not related to rumen propionate or to acetate-to-propionate ratio, due to the presence of 17:0 and cis-9 17:1 in the saturated fatty acids supplement. The results suggest that although lipid supplementation can affect the profile of milk OBCFA, the promise remains of using these milk fatty acids to evaluate rumen function.

Production, composition, and oxidative stability of milk highly enriched in polyunsaturated fatty acids from dairy cows fed alfalfa protein concentrate or supplemental vitamin E.

Given its elevated content of carotenoids, alfalfa protein concentrates (APC) have the potential to prevent oxidation of milk enriched in polyunsaturated fatty acids. The effects of feeding APC or supplemental vitamin E on production, composition, and oxidative stability of milk enriched in polyunsaturated fatty acids were evaluated using 6 lactating Holstein cows (224±18d in milk) in a replicated 3×3 Latin square (21-d periods, 14d for adaptation). Treatment diets contained (dry matter basis) (1) 9% soybean meal (control, CTL); (2) 9% soybean meal + 300 IU of vitamin E/kg (VitE treatment); or (3) 9% APC (APC treatment). Cows received a continuous abomasal infusion of 450g/d of linseed oil. As a result, milk fat content of cis-9,cis-12 18:2 increased from 1.08±0.13 to 3.9±0.40% (mean ± SD), whereas cis-9,cis-12,cis-15 18:3 increased from 0.40±0.04 to 14.27±1.81% during the experimental period compared with the pretrial period. Milk yield tended to be higher for APC (14.7kg/d) compared with CTL (13.4kg/d), and was greater than that for VitE (13.0kg/d). Protein yield was higher in cows fed APC (518g/d) compared with VitE (445g/d) but was not different from that in cows fed CTL (483g/d). These effects resulted in improved milk N efficiency in cows fed APC (26.1% of N intake secreted in milk) compared with CTL (23.0%) and VitE (22.9%). Feeding APC increased milk fat content of lutein (252µg/g) compared with CTL (204µg/g) and VitE (190µg/g). Milk fat content of vitamin E was higher for APC (34.5µg/g) compared with CTL (19.0µg/g) and tended to be lower than that with VitE (44.9µg/g). Redox potential of fresh milk from cows fed APC (152mV) was similar to that of VitE (144mV), but lower than that of CTL (189mV). Treatments had no effect on fresh milk contents of dissolved oxygen (8.1±1.5mg/L), and conjugated diene hydroperoxides (2.7±0.5mmol/L). The concentrations of volatile lipid oxidation products (propanal, hexanal, hept-cis-4-enal, 1-octen-3-one) tended to be decreased by APC relative to CTL, whereas similar values were observed for VitE, except for hexanal, which was reduced by 40% in VitE. In conclusion, feeding APC to lactating dairy cows could serve as a source of dietary protein that improves dietary N utilization efficiency, and also as a preharvest technology to increase natural antioxidant levels in milk to limit oxidation.

Prediction of enteric methane emissions from Holstein dairy cows fed various forage sources.

Milk fatty acid (FA) profile has been previously used as a predictor of enteric CH4 output in dairy cows fed diets supplemented with plant oils, which can potentially impact ruminal fermentation. The objective of this study was to investigate the relationships between milk FA and enteric CH4 emissions in lactating dairy cows fed different types of forages in the context of commonly fed diets. A total of 81 observations from three separate 3×3 Latin square design (32-day periods) experiments including a total of 27 lactating cows (96±27 days in milk; mean±SD) were used. Dietary forages were included at 60% of ration dry matter and were as follows: (1) 100% corn silage, (2) 100% alfalfa silage, (3) 100% barley silage, (4) 100% timothy silage, (5) 50:50 mix of corn and alfalfa silages, (6) 50:50 mix of barley and corn silages and (7) 50:50 mix of timothy and alfalfa silages. Enteric CH4 output was measured using respiration chambers during 3 consecutive days. Milk was sampled during the last 7 days of each period and analyzed for components and FA profile. Test variables included dry matter intake (DMI; kg/day), NDF (%), ether extract (%), milk yield (kg/day), milk components (%) and individual milk FA (% of total FA). Candidate multivariate models were obtained using the Least Absolute Shrinkage and Selection Operator and Least-Angle Regression methods based on the Schwarz Bayesian Criterion. Data were then fitted into a random regression using the MIXED procedure including the random effects of cow, period and study. A positive correlation was observed between CH4 and DMI (r=0.59, P0.19). Milk FA profile and DMI can be used to predict CH4 emissions in dairy cows across a wide range of dietary forage sources.

Effect of diet fermentability and unsaturated fatty acid concentration on recovery from diet-induced milk fat depression.

Diet-induced milk fat depression is caused by highly fermentable and high-unsaturated fatty acid (FA) diets, and results in reduced milk fat concentration and yield, reduced de novo FA, and increased trans isomers of the alternate biohydrogenation pathways. The hypothesis of the current experiment was that a diet higher in fermentability and lower in unsaturated FA (UFA) would accelerate recovery compared with a high-UFA and lower-fermentability diet. Eight ruminally cannulated and 9 noncannulated multiparous Holstein cows were randomly assigned to treatment sequences in a replicated Latin square design. During each period milk fat depression was induced for 10 d by feeding a low-fiber, high-UFA diet [25.9% neutral detergent fiber (NDF) and 3.3% C18:2]. Following the induction phase, cows were switched to recovery treatments for 18 d designed to correct dietary fermentability, UFA, or both fermentability and UFA concentration. Treatments during recovery were (1) correction of fiber and UFA diet [control; 31.8% NDF and 1.65% C18:2], (2) a diet predominantly correcting fiber, but not UFA [high oil (HO); 31.3% NDF and 2.99% C18:2], and (3) a diet predominantly correcting UFA, but not fiber concentration [low fiber (LF); 28.4% NDF and 1.71% C18:2]. Milk and milk component yield, milk FA profile, ruminal pH, and 11 rumen microbial taxa were measured every third day during recovery. Milk yield decreased progressively in HO and control, whereas it was maintained in the LF diet. Milk fat concentration increased progressively during recovery in all treatments, but was on average 9% lower in LF than control from d 12 to 18. Milk fat yield increased progressively in all treatments and was not different between control and LF at any time point, but was lower in HO than control on d 15. Milk trans-10 C18:1 and trans-10,cis-12 conjugated linoleic acid decreased progressively in all treatments, but was higher in HO than control from d 3 to 18 [136 ± 50 and 188 ± 57% (mean ± SD)], whereas LF caused a smaller increase in these FA compared with control (67 ± 25 and 90 ± 22%). Additionally, milk trans-11 C18:1 and cis-9,trans-11 conjugated linoleic acid was decreased in control and LF and increased in HO during recovery. Selected microbial species observed changed during recovery, but major treatment differences were only observed for Streptococcus bovis. The LF diet that was similar in UFA but 3.4% units lower in NDF compared with to the control had a similar decrease in alternate trans biohydrogenation intermediates in milk. The HO diet that was similar in NDF but 2.0% units higher in UFA compared with the control had higher alternate trans biohydrogenation intermediates in milk compared with control. However, recovery of milk fat yield was similar between treatments at most time points.

Comparison of enriched palmitic acid and calcium salts of palm fatty acids distillate fat supplements on milk production and metabolic profiles of high-producing dairy cows.

A variable response to fat supplementation has been reported in dairy cows, which may be due to cow production level, environmental conditions, or diet characteristics. In the present experiment, the effect of a high palmitic acid supplement was investigated relative to a conventional Ca salts of palm fatty acids (Ca-FA) supplement in 16 high-producing Holstein cows (46.6±12.4kg of milk/d) arranged in a crossover design with 14-d periods. The experiment was conducted in a non-heat-stress season with 29.5% neutral detergent fiber diets. Treatments were (1) high palmitic acid (PA) supplement fed as free FA [1.9% of dry matter (DM); 84.8% C16:0] and (2) Ca-FA supplement (2.3% of DM; 47.7% C16:0, 35.9% C18:1, and 8.4% C18:2). The PA supplement tended to increase DM intake, and increased the yields of milk and energy-corrected milk. Additionally, PA increased the yields of milk fat, protein, and lactose, whereas milk concentrations of these components were not affected. The yields of milk de novo and 16-C FA were increased by PA compared with Ca-FA (7 and 20%, respectively), whereas the yield of preformed FA was higher in Ca-FA. A reduction in milk fat concentration of de novo and 16-C FA and a marginal elevation in trans-10 C18:1 in Ca-FA is indicative of altered ruminal biohydrogenation and increased risk of milk fat depression. No effect of treatment on plasma insulin was observed. A treatment by time interaction was detected for plasma nonesterified fatty acids (NEFA), which tended to be higher in Ca-FA than in PA before feeding. Overall, the palmitic acid supplement improved production performance in high-producing cows while posing a lower risk for milk fat depression compared with a supplement higher in unsaturated FA.

Effect of a high-palmitic acid fat supplement on milk production and apparent total-tract digestibility in high- and low-milk yield dairy cows.

The effect of a high-palmitic acid fat supplement was tested in 12 high-producing (mean = 42.1 kg/d) and 12 low-producing (mean = 28.9 kg/d) cows arranged in a replicated 3 × 3 Latin square design. Experimental periods were 21 d, with 18d of diet adaptation and 3 d of sample collection. Treatments were (1) control (no supplemental fat), (2) high-palmitic acid (PA) supplement (84% C16:0), and (3) Ca salts of palm fatty acid (FA) supplement (Ca-FA). The PA supplement had no effect on milk production, but decreased dry matter intake by 7 and 9% relative to the control in high- and low-producing cows, respectively, and increased feed efficiency by 8.5% in high-producing cows compared with the control. Milk fat concentration and yield were not affected by PA relative to the control in high- or low-producing cows, although PA increased the yield of milk 16-C FA by more than 85 g/d relative to the control. The Ca-FA decreased milk fat concentration compared with PA in high-, but not in low-producing cows. In agreement, Ca-FA dramatically increased milk fat concentration of trans-10 C18:1 and trans-10, cis-12 conjugated linoleic acid (>300%) compared with PA in high-producing cows, but not in low-producing cows. No effect of treatment on milk protein concentration or yield was detected. The PA supplement also increased 16-C FA apparent digestibility by over 10% and increased total FA digestibility compared with the control in high- and low-producing cows. During short-term feeding, palmitic acid supplementation did not increase milk or milk fat yield; however, it was efficiently absorbed, increased feed efficiency, and increased milk 16-C FA yield, while minimizing alterations in ruminal biohydrogenation commonly observed for other unsaturated fat supplements. Longer-term experiments will be necessary to determine the effects on energy balance and changes in body reserves.

Effect of monensin on recovery from diet-induced milk fat depression.

The objective of the present experiment was to investigate the effect of monensin (MN) on the time course of recovery from diet-induced milk fat depression. Milk fat depression was induced in all cows (n = 16) during the first phase of each period by feeding a low-fiber, high-unsaturated fat diet [25.3% neutral detergent fiber (NDF), 6.9% fatty acids (FA), and 3.24% C18:2] with MN (450mg/cow per day) for 10 to 14d. A recovery phase of 18d followed, where cows were switched to a higher-fiber and lower unsaturated fat diet (31.2% NDF, 4.3% FA, and 1.7% C18:2). According to a crossover design, treatments during recovery were (1) control (no MN supplementation) or (2) continued MN supplementation. Milk yield, milk composition, and milk FA profile were measured every 3d during recovery. No effect was observed of MN on dry matter intake or yield of milk, milk protein, and lactose. Milk fat concentration and yield increased progressively during recovery in both treatments. Monensin decreased milk fat yield from d 6 to 15, but it was the same as the control on d 18. A treatment by time interaction on milk fat concentration was detected, which was decreased by MN only on d 3 and 6. The yield of milk de novo synthesized FA increased progressively in both treatments and was not affected by treatment. Similarly, yield of 16-C FA increased progressively, but was decreased by MN on d 6 and 9. Preformed FA yield was lower in the MN group from d 6 to 15, but was not different from the control on d 18. Importantly, milk FA concentration of trans-10 C18:1 and trans-10,cis-12 conjugated linoleic acid rapidly decreased in both groups; however, MN slightly increased trans-10 C18:1 concentration above baseline on d 15 and 18. In conclusion, MN supplementation had minimal effect on recovery of normal rumen biohydrogenation and de novo FA synthesis during recovery from milk fat depression by correction of dietary starch, NDF, and polyunsaturated FA concentration, but moderately decreased recovery of preformed FA in milk.

Effects of partially replacing dietary starch with dry glycerol in a lactating cow diet on ruminal fermentation during continuous culture.

The effects of dry glycerol as a partial replacement for dietary starch in a lactating cow diet on ruminal fermentation and bacterial protein synthesis were evaluated using 4 single-flow, continuous-culture fermentors (ranging from 1,015 to 1,040 mL in volume). The basal lactating cow diet was formulated to have partial contents of dietary starch provided from a corn starch supplement [at 12.37% diet dry matter (DM)], which was partially or completely replaced by a dry glycerol product. Both the corn starch supplement and dry glycerol product contained 65% of pure corn starch or glycerol, respectively. The final inclusion rate for pure glycerol was at 0, 3, 5, or 8% of DM in the basal diet. The experiment was conducted using a 4 × 4 Latin square design with four 9-d periods, with the first 6 d for adaptation and last 3 d for sampling. Fermentors were inoculated with 1L of ruminal fluid and 25 g of ruminal digesta from a ruminally cannulated cow receiving a lactation total mixed ration (16% crude protein, 32% neutral detergent fiber, and 25% starch; DM basis). Each fermentor was fed 75 g of DM of its respective experimental diet daily in 3 equal portions (at 0800, 1400, and 2000 h). Liquid dilution rate of the fermentors was maintained at 10%/h and solids retention time was set at 24 h. Fermentation fluid and the effluent from each fermentor were sampled once daily (at 1330 h) from d 7 to 9 of each period and pooled by period. Postprandial ruminal fermentation was studied by sampling the fermentors hourly for 5 h after the 0800 h feeding on d 9 of each period. The total fermentation contents were harvested at the end of the period for estimations of bacterial protein synthesis. Replacing corn starch with dry glycerol linearly increased the proportions of propionate and valerate at the expense of acetate in the fermentation fluid measured daily or for the first 5h after feeding. Replacing corn starch with dry glycerol also linearly increased the digestibility of dietary neutral detergent fiber without a change on the flow or efficiency of bacterial protein synthesis during continuous culture. Results indicate that glycerol as a dry product can replace dietary starch as corn starch at a level of up to 8% of DM in the diet without negatively affecting ruminal fermentation and digestibility during continuous culture.