Effects of plane of nutrition and 2,4-thiazolidinedione on insulin responses and adipose tissue gene expression in dairy cattle during late gestation

Specific mechanisms by which dry period dietary energy affects transition cow metabolism have been intensively investigated but those of thiazolidinedione (TZD) administration have not. We hypothesized that effects of both are mediated via changes in insulin, glucose, or fatty acid metabolism. The objective of this experiment was to determine the effects of the insulin-sensitizing agent TZD and dietary energy level on glucose and fatty acid metabolism during late gestation in dairy cows. Multiparous Holstein cows (n = 32) approximately 50 d before expected calving date were dried-off and assigned to 1 of 2 dietary energy levels for 3 wk (high: 1.52 Mcal/kg of NE_L, or low: 1.34 Mcal/kg of NE_L) and treated daily during the final 14 d with 4.0 mg of TZD/kg of body weight (BW) or saline in a completely randomized design. Cows fed the low energy diet had lower dry matter intake (12.8 vs. 16.1 kg/d) and higher plasma nonesterified fatty acid (NEFA) concentrations (103.3 vs. 82.4 μEq/L) compared with cows fed the high energy diet. Cows administered TZD had higher plasma glucose concentrations (62.5 vs. 59.6 mg/dL) than saline controls and cows fed the high energy diet had higher plasma insulin concentrations (35.1 vs. 25.3 μU/mL) compared with those fed the low energy diet. After 2 wk of TZD treatment, all cows were subjected to an intravenous glucose tolerance test (GTT; 0.25 g of dextrose/kg of BW) followed 110 min later by an insulin challenge (IC; 1.0 μg of insulin/kg of BW). Differences in plasma glucose response to GTT were minimal based on diet; however, cows fed the low energy diet had more negative NEFA areas under the curve (AUC; −4,838 vs. −2,137 μEq/L × min over 90 min) and greater rates of NEFA decrease (1.35 vs. 0.63%/min) during GTT, suggesting differential responses of tissue glucose and fatty acid metabolism in response to dietary energy level. During IC, the TZD-treated cows tended to have more negative glucose AUC (−45.0 vs. −12.1 mg/dL × min over 15 min) than controls, suggesting that TZD-treated cows had greater responses to insulin. Limited interactions were observed between dietary and TZD treatments in all response variables measured. Adipose tissue biopsies performed on the final day of treatment suggested higher expression of peroxisome proliferator-activated receptor-γ (0.71 vs. 0.50 relative expression) and lipoprotein lipase (0.71 vs. 0.40 relative expression) in cows fed the high energy diet as measured by quantitative real-time PCR. These results indicate that energy level and insulin-sensitizing agents affect glucose and lipid metabolism during the dry period.     

Etiology of fatty liver in dairy cattle: effects of nutritional and hormonal status on hepatic microsomal triglyceride transfer protein

We conducted three experiments to determine the effects of nutritional and hormonal status on microsomal triglyceride transfer protein (MTP) activity and mass. In experiment 1, 18 nonlactating Holstein cows, 75 d before expected calving date, in their second gestation or greater were monitored from d 75 to 55 prepartum. Cows were fed a control diet from d 75 to 62 prepartum for covariable measurements. From d 61 to 55 prepartum, six cows continued to receive the control diet, six cows were restricted to 2.3 kg of grass hay/d, and six cows were fed the control diet plus 1.8 kg of concentrate/d and 500 ml of propylene glycol given 2 times/d as an oral drench. Plasma glucose and serum insulin concentrations were highest in cows that received propylene glycol and lowest in feed restricted cows. Plasma nonesterified fatty acids (NEFA) and liver triglyceride (TG) concentrations were highest in feed restricted cows and not different between cows that received the control diet and cows that received propylene glycol. Hepatic MTP activity and mass were not affected by treatment in experiment 1. In experiment 2, bovine hepatocytes isolated from the caudate process of five preruminating Holstein bull calves were incubated with either 0, 0.5, 1.0, or 2.0 mM NEFA for 48 h. Intracellular TG increased linearly as NEFA concentration in the media increased. Concentration of NEFA in the incubation media had no effect on MTP activity or mass. There was a quadratic effect of concentration of NEFA in the incubation media on MTP mRNA. In experiment 3, bovine hepatocytes isolated from the caudate process of five preruminating Holstein bull calves were incubated with 2 mM [1-14C]oleate for 24 h to accumulate TG, followed by a 36-h period of TG depletion, during which hepatocytes were incubated with no hormone, 10 nM insulin, or 10 nM glucagon. There was no effect of insulin or glucagon on intracellular TG, MTP activity or mass. Cells incubated with no hormone had higher levels of MTP mRNA compared to cells incubated with insulin or glucagon during the depletion period. Results suggest that hepatic MTP mRNA may be affected by TG accumulation, insulin, and glucagon in vitro. However, hepatic MTP activity and mass are not affected by nutritional status of nonlactating dairy cows, TG accumulation in vitro, or insulin and glucagon in vitro.     

Effects of day relative to parturition and dietary crude protein on rumen fermentation in prepartum transition cows

Twelve Holstein cows and eight heifers were used in a randomized block design to examine changes in rumen fermentation and blood metabolites as animals fed diets containing 9.1 (low protein, LP) or 11.2% crude protein (moderate protein, MP) approached parturition. Animals were blocked by expected calving date and parity. Diets were isocaloric (1.58 Mcal/kg of dry matter), and the difference in dietary crude protein was achieved by the addition of urea. Diets were fed as total mixed rations for ad libitum intake. Dry matter intake decreased from 12.2 kg/d on d -21 to 9.1 kg/d on d -1 relative to parturition and was unaffected by dietary crude protein or parity. Rumen ammonia concentrations were higher for animals fed the MP diet compared with those fed the LP diet (1.8 vs. 3.7 mM). In situ neutral detergent fiber disappearance was not affected by dietary crude protein after 8 h of incubation, but it did decrease from 25.8% on d -21 to 23.3% on d -1. After 16, 24, and 48 h of incubation, neutral detergent fiber disappearance was greater for animals consuming MP than for animals consuming LP (30.6 vs. 34.4%, 37.0 vs. 44.1%, and 57.9 vs. 65.1%, respectively). There was a parity x treatment interaction after 48 h of incubation. Fiber disappearance was 55.7 or 65.9% for heifers and 60.0 or 64.7% for cows fed LP or MP, respectively. The solids rate of passage was not affected by treatment, parity, or day relative to parturition. Concentrations of plasma nonesterified fatty acid (NEFA) increased from 218 microEq/L on d -21 to 619 microEq/L on d -1. There was an interaction between day relative to parturition and parity on NEFA concentrations. Heifers had plasma NEFA concentrations of 272 and 772 microEq/L on d -21 and -1, respectively. Cows had NEFA concentrations of 164 and 467 microEq/L on d -21 and -1, respectively. Plasma glucose concentrations were affected by parity (65.8 and 58.8 mg/dl for heifers and cows). Plasma urea, NEFA, beta-hydroxybutyrate, and glucose concentrations were not affected by dietary treatment. In conclusion, heifers tended to have higher plasma concentrations of NEFA and glucose, but did not have elevated concentrations of beta-hydroxybutyrate. Rumen fermentation was relatively unaffected by day relative to parturition, but feeding less than 11% crude protein to prefresh transition cows may limit ruminal fiber degradation.     

Effects of heat stress on energetic metabolism in lactating Holstein cows

Heat stress has an enormous economic impact on the global dairy industry, but the mechanisms by which hyperthermia negatively affect systemic physiology and milk synthesis are not clear. Study objectives were to evaluate production parameters and metabolic variables in lactating dairy cows during short-term heat stress or pair-fed conditions coupled with bST administration. Twenty-two multiparous Holstein cows were subjected to 3 experimental periods: 1) thermoneutral conditions with ad libitum intake for 7 d (P1); 2) heat stress (HS) with ad libitum intake (n = 10) or pair-fed (PF) in thermoneutral conditions (n = 12) for 7 d (P2), and 3) 7 d of HS or PF in conditions as described in P2 with recombinant bovine somatotropin administered on d 1 (P3). All cows received an intravenous glucose tolerance test (GTT) on d 5 of each period. Heat stress conditions were cyclical and temperatures ranged from 29.4 to 38.9°C. Rectal temperatures and respiration rates increased during heat stress (38.6-40.4°C and 44-89 breaths/min, respectively). Heat stress reduced dry matter intake by 30% and by design PF cows had similar intake reductions (28%). During heat stress and pair-feeding, milk yield decreased by 27.6% (9.6 kg) and 13.9% (4.8 kg), respectively, indicating that reduced feed intake accounted for only 50% of the decreased milk production. Milk yield increased with recombinant bovine somatotropin in both HS (9.7%) and PF (16.1%) cows. Cows in both groups were in positive energy balance (3.95 Mcal/d) during P1 but entered negative energy balance during P2 and P3 (−5.65 Mcal/d). Heat stress and pair-feeding treatments decreased (9.3%) basal glucose concentrations. Heat stress conditions had no effect on basal NEFA levels during P2; however, PF cows (despite a similar calculated energy balance) had a 2-fold increase in basal NEFA concentrations. Both groups had increased plasma urea nitrogen levels during P2 and P3 compared with P1. Basal insulin levels increased (37%) during P2 and P3 in HS cows but did not differ between periods in PF cows. During P2 and compared with P1, PF cows had a decreased rate of glucose disposal, whereas HS cows had a similar disposal rate following the GTT. During P2 and compared with P1, PF cows had a reduced insulin response whereas HS cows had a similar insulin response to the GTT. In summary, reduced nutrient intake accounted for only 50% of heat stress-induced decreases in milk yield, and feed intake-independent shifts in postabsorptive glucose and lipid homeostasis may contribute to the additional reduction in milk yield.     

The effects of overstocking Holstein dairy cattle during the dry period on cortisol secretion and energy metabolism

The objective was to determine whether overstocking during the dry period could alter physiological parameters in dairy cattle associated with cortisol secretion and energy metabolism. Four groups of 10 late-gestation, nonlactating Holstein cows (6 multiparous cows and 4 heifers per group) were exposed to both a control [1 lying stall/cow and 0.67 m of linear feed bunk (FB) space/cow] and an overstocked (1 stall/2 cows and 0.34 m of FB space/cow) stocking density treatment in a replicated crossover design with 14-d treatment periods. On d 1, 3, 5, 7, 9, and 11 of each 14-d treatment period, blood and fecal samples were collected from each cow for the determination of plasma nonesterified fatty acids (NEFA), glucose, insulin, and fecal cortisol metabolite (11,17-dioxoandrostane; 11,17-DOA) concentrations. Glucose and ACTH challenges were conducted on d 13 and 14, respectively, of each treatment period. Dry matter intake per cow was greater during the overstocked period than during the control period (15.9 vs. 14.9 ± 0.5 kg/d). Plasma NEFA and glucose concentrations were greater (0.11 vs. 0.09 ± 0.006 mEq/L and 65.3 vs. 64.2 ± 1.1mg/dL, respectively) and 11,17-DOA concentration tended to be greater (891 vs. 792 ± 86 ng/g of fecal dry matter) during the overstocked period than during the control period. Insulin concentration was the same during the overstocked (29.0 ± 2.1 μIU/mL) and control (31.2 ± 2.1 μIU/mL) periods. Overstocking was associated with slightly slower glucose clearance from circulation as evidenced by a greater area under the curve estimate for the glucose response curves (2,882 vs. 2,657 ± 165 mg/dL × 180 min) but a more attenuated insulin response (insulin area under the curve = 5,258 vs. 6,692 ± 1,104 μIU/mL × 180 min for the overstocked and control periods, respectively). Changes in tissue glucose uptake may be mediated by changes in pancreatic insulin secretion or peripheral tissue responses to insulin. The role of glucocorticoids in mediating these changes in energy metabolism is still unclear because stocking density treatment was not associated with changes in adrenal secretion of cortisol following ACTH stimulation.     

Effect of protein level and methionine supplementation on dairy cows during the transition period

Cows experience a significant negative protein balance during the first 30 d of lactation. Given the functional effects of AA on health, especially in challenging periods such as calving, higher levels of protein and specific AA in the diet may act to improve health and feed intake. The response of dairy cows to 3 protein supplementation strategies during the transition period and through the first 45 d in milk was evaluated. The final data set had 39 Holstein cows blocked based on parity (primiparous vs. multiparous) and expected calving and randomly assigned within each block to one of 3 dietary treatments: low protein (LP), high protein (HP), or high protein plus rumen-protected methionine (HPM). Treatments were offered from d ?18 ± 5 to 45 d relative to parturition. Pre- and postpartum diets were formulated for high metabolizable protein (MP) supply from soybean meal, and HP and HPM provided higher MP balance than LP. Preplanned contrasts were LP versus HP+HPM and HP versus HPM. Significance was declared at P ≤ 0.05 and trends at 0.05 < P ≤ 0.10. Cows fed HP and HPM had greater fry matter intake (DMI) prepartum than LP (+2 kg/d), and there was a trend for greater DMI with HPM than with HP (+1.6 kg/d). Body weight and condition score before and after calving did not differ among treatments. High protein (HP and HPM) tended to increase milk yield during the first 45 d of lactation (+1.75 kg/d), increased milk lactose content and urea-N in milk and plasma, tended to increase blood BHB 14 d postpartum, and tended to reduce milk/DMI compared with LP. Blood concentrations of calcium at calving and of glucose, and nonesterified fatty acids pre- and postpartum did not differ. High protein induced lower concentration of plasma IL-1 at calving and lowered blood lymphocytes 21 d postpartum, suggestive of a reduced inflammatory status compared with LP. The concentrations of IL-10, tumor necrosis factor alpha, and other hemogram variables did not differ among treatments. Addition of rumen-protected methionine to the HP diet did not alter milk yield but increased fat and total solids concentrations. The rumen-protected methionine had no effect on blood metabolites and immunity markers, with the exception of increased pre-partum insulin concentrations. The data indicate that dairy cows around calving respond positively to an increase in the supply of MP and to rumen-protected methionine supplementation of the HP diet by increasing intake and improving immune status.     

Effects of feeding propionate and calcium salts of long-chain fatty acids on transition dairy cow performance

Multiparous Holstein cows (n = 40) were used in a randomized complete block design to determine the effects of feeding Ca and Na salts (1:1, wt/wt) of propionate and Ca salts of long-chain fatty acids (LCFA) on transition cow performance. All cows were fed the same basal diet once daily for ad libitum intake. Treatments (g/d) were 320 cornstarch (CS) as a control, 120 propionate (PRO), 120 propionate and 93 LCFA (PF1), and 178 propionate and 154 LCFA (PF2). Treatments were hand-mixed into the upper one-third of the TMR from 2 wk pre- through 3 wk postpartum. Intakes were recorded from 21 d pre- through 21 d postpartum. Energy density and crude protein were 1.54 and 1.65 Mcal/kg and 14.4 and 18.8% for pre- and postpartum diets, respectively. All cows received a common diet from 22 to 70 days in milk (DIM). Milk composition was analyzed on d 7, 14, and 21. Blood was sampled at 14, 7, and 2 d prepartum and 2, 7, 14, and 21 DIM. Pre- and postpartal dry matter intake (DMI) averaged 11.9 and 16.4 kg/d, respectively, and did not differ among treatments. A diet x week interaction for postpartal DMI was observed as cows fed PF2 consumed 2 kg/d less DM during wk 2 relative to other treatments. Milk yields from 22 to 70 DIM were 48.8, 48.5, 47.8, and 51.3 kg/d for CS, PRO, PF1, and PF2, respectively, and were not significantly affected by treatments. Milk true protein (3.32 vs. 3.16%) was increased and MUN (12.5 vs. 14.4 mg/dL) was decreased for CS relative to other treatments. Milk fat yield from cows fed PRO tended to be greater than those fed PF1 (1.58 vs. 1.29 kg/d). Plasma glucose, insulin, and beta-hydroxybutyrate were not affected by treatments. The PF2 treatment tended to decrease NEFA in plasma relative to PF1 over all times measured (492 and 670 muEq/L) and significantly decreased plasma NEFA relative to those fed PF1 postpartum (623 and 875 muEq/L). Relative to PF1, feeding propionate and LCFA at the higher level in this experiment improved energy balance postpartum as evidenced by decreased concentrations of plasma NEFA.     

Effects of dietary energy allowance and decline in dry matter intake during the dry period on responses to glucose and insulin in transition dairy cows

We assessed whether high energy intake during the early dry period [144% of metabolizable energy (ME) requirements/d] followed by a gradual restriction of energy intake in the close-up dry period (119% of ME/d; HEI) impaired whole-body insulin sensitivity compared with a controlled energy intake (100% of ME/d; CEI) throughout the 6-wk dry period. Multiparous Ayrshire dairy cows (n = 16) were blocked by body weight, body condition score, and expected date of parturition and were used in a randomized complete block design until 10 d after parturition. Cows were fed either HEI or CEI diets based on grass silage during the first 3 wk of the dry period and grass silage supplemented with a commercial concentrate (30% of ME intake) during the final 3 wk of gestation. After calving, all cows were fed grass silage ad libitum and an increasing amount of commercial concentrate (maximum 9 kg at d 10 postpartum). Intravenous glucose tolerance tests (IVGTT) and intravenous insulin challenges were performed ?10 ± 5 d (n = 15) and +10 ± 1 d (n = 14) relative to parturition. Following glucose injection, we did not find any treatment effects on glucose and insulin responses. The prepartal nonesterified fatty acid (NEFA) response of the HEI group was blunted, basal NEFA and the decrement of NEFA were smaller, and the area under the response curve (AUC) of NEFA was less negative in HEI cows than in CEI cows. The NEFA response reversed after parturition; the NEFA AUC of the HEI group was more negative than that of the CEI group. We did not find similar responses after insulin injection. Across the treatments, NEFA AUC correlated strongly with the basal NEFA concentration during the IVGTT pre- and postpartum. Calculated and model-based indices characterizing the overall glucose tolerance and β-cell function and the insulin sensitivity were higher after parturition than during the dry period. Consistent with the lower basal insulin, the acute insulin release after the glucose infusion was smaller in postpartal IVGTT than in prepartal IVGTT. The results suggest that whole-body insulin sensitivity of the cows increased after parturition. However, the role of peripheral insulin sensitivity in the regulation of glucose partitioning seems to be minor relative to the major change in insulin secretion and clearance during the periparturient period.     

Effect of rumen-protected niacin on lipid metabolism, oxidative stress, and performance of transition dairy cows

The objective of this study was to evaluate the effect of a rumen-protected niacin product (RPN; 65% nicotinic acid; NiaShure, Balchem Corp., New Hampton, NY) on lipid metabolism, oxidative stress, and performance of transition dairy cows. Thirty nonlactating multiparous Holstein cows in late gestation were paired according to expected calving date and randomly assigned to 12 g/cow per day of RPN product or to an unsupplemented control (CON) diet. Treatment diets were fed from 21 d before expected calving through 21 d after parturition. Blood samples were taken on d -21, -14, -7, 1, 7, 14, and 21 relative to calving for plasma nonesterified fatty acid (NEFA), β-hydroxybutyrate (BHBA), glucose, and superoxide dismutase (SOD) analyses. Liver samples were taken by biopsy on d 1 and 21 relative to calving for triglyceride (TG) analysis. Data were analyzed for a randomized complete block design with repeated measures. Pre- and postpartum dry matter intake, milk yield, and protein were unaffected by treatment. Milk fat percentage (5.08 vs. 4.44%) and somatic cell score (3.93 vs. 2.48) were reduced for RPN. Treatment × time interactions were observed for energy-corrected milk (ECM) and fat-corrected milk (FCM) yields; RPN reduced ECM and FCM yields by 8.5 and 8.9 kg/cow per day, respectively, in the first week of lactation. Although body weight and condition score decreased during the experimental period, no differences due to treatment were observed. However, calculated postpartum energy balance tended to be improved for RPN because of the reduction in ECM yield. Time and treatment × time effects were observed for plasma NEFA. On d 1 postpartum, NEFA reached 1,138±80 μEq/L for CON compared with 698±80 μEq/L for RPN. Cows supplemented with RPN tended to have lower plasma NEFA concentrations than CON cows on d 7 and 14 postpartum. Plasma BHBA, glucose, and SOD and liver TG concentrations were unaffected by treatment. In conclusion, supplementation with 12 g/cow per day of the RPN product provided a bioavailable source of niacin that modified lipid metabolism but did not affect milk yield over the first 3 wk of lactation or oxidative stress of transition dairy cows.     

Decreased insulin response in dairy cows following a four-day fast to induce hepatic lipidosis

Negative energy balance has been implicated in the development of fatty liver, insulin resistance, and impaired health in dairy cows. A 4-d fasting model previously was reported to increase liver triglycerides more than 2.5-fold. The purpose of the present study was to evaluate insulin response in this fasting model. Nonlactating, nonpregnant Holstein cows were fasted for 4 d (6 cows) or fed continuously as control cows (4 cows). Samples were collected 5 d before fasting, during fasting, and immediately after the 4-d fast, 8 d after the fast, and 16 d after the fast. Fasted cows had greater liver triglyceride content (49.4 vs. 16.2 mg/g, wet-weight basis) at the end of the fasting period compared with control cows. Fasted cows also had increased plasma nonesterified fatty acid (NEFA) concentrations (1.24 vs. 0.21 mmol/L) and increased plasma β-hydroxybutyrate (BHBA) concentrations at the end of the fasting period. Liver triglyceride, plasma NEFA, and plasma BHBA in fasted cows returned to prefasting concentrations by the end of the experiment. Plasma glucose concentrations were not affected by fasting. Plasma insulin concentrations were decreased (6.3 vs. 14.1 μU/mL) and insulin-stimulated blood glucose reduction was decreased (24.9 vs. 48.6%) in the fasted cows compared with control cows at the end of the fast, indicating reduced insulin response. Insulin response was negatively correlated with plasma NEFA and liver triglycerides. Decreased insulin response may be an important complication of negative energy balance and hepatic lipidosis.     

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 × 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 μEq/L) and IC (133 vs. 83 ± 9 μEq/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 μEq/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 (μEq/L) × 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 μEq/L greater for LIN than TAL for unknown reasons.     

Effects of peripartal yeast culture supplementation on lactation performance,blood biomarkers,rumen fermentation,and rumen bacteria species in dairy cows

Feeding yeast culture fermentation products has been associated with improved feed intake and milk yield in transition dairy cows. These improvements in performance have been further described in terms of rumen characteristics, metabolic profile, and immune response. The objective of this study was to evaluate the effects of a commercial yeast culture product (YC; Culture Classic HD, Phibro Animal Health) on performance, blood biomarkers, rumen fermentation, and rumen bacterial population in dairy cows from −30 to 50 d in milk (DIM). Forty Holstein dairy cows were enrolled in a randomized complete block design from −30 to 50 DIM and blocked according to expected calving day, parity, previous milk yield, and genetic merit. At −30 DIM, cows were assigned to either a basal diet plus 114 g/d of ground corn (control; n = 20) or a basal diet plus 100 g/d of ground corn and 14 g/d of YC (n = 20), fed as a top-dress. Cows received the same close-up diet from 30 d prepartum until calving [1.39 Mcal/kg of dry matter (DM) and 12.3% crude protein (CP)] and lactation diet from calving to 50 DIM (1.60 Mcal/kg of DM and 15.6% CP). Blood samples and rumen fluid were collected at various time points from −30 to 50 d relative to calving. Cows fed YC compared with control showed a trend for increased energy-corrected milk (+3.2 kg/d). Lower somatic cell counts were observed in YC cows than in control. We detected a treatment × time interaction in nonesterified fatty acids (NEFA) that could be attributed to a trend for greater NEFA in YC cows than control at 7 DIM, followed by lower NEFA in YC cows than control at 14 and 30 DIM. In the rumen, YC contributed to mild changes in rumen fermentation, mainly increasing postpartal valerate while decreasing prepartal isovalerate. This was accompanied by alterations in rumen microbiota, including a greater abundance of cellulolytic (Fibrobacter succinogenes) and lactate-utilizing bacteria (Megasphaera elsdenii). These results describe the potential benefits of supplementing yeast culture during the late pregnancy through early lactation, at least in terms of rumen environment and performance.     

Effects of pre- and postfresh transition diets varying in dietary energy density on metabolic status of periparturient dairy cows

Effects of dietary energy density during late gestation and early lactation on metabolic status of periparturient cows were studied. Four weeks before expected calving, animals were fed a low (DL; 1.58 Mcal of NE_L/kg) or high energy density diet (DH; 1.70 Mcal of NE_L/kg). After calving, half of the cows from each prepartum treatment were assigned to a low (L; 1.57 Mcal of NE_L/kg) or high energy density diet (H; 1.63 Mcal of NE_L/kg) until d 20 postpartum. After d 20, all animals were fed H until d 70. Animals fed DH had a more positive energy balance during the prepartum period. Animals fed DH had higher plasma concentrations of glucose and insulin and lower concentrations of plasma nonesterified fatty acid (NEFA) on d −7 relative to calving compared with animals fed DL. No differences in blood concentrations of metabolites, insulin and liver triglycerides (TG) content were observed on d 1. Liver TG content at d 1 and 21 were more related to magnitude of change in energy intake prepartum than to energy intake in the last week of gestation. Cows fed H had higher concentrations of plasma glucose and insulin, but similar plasma NEFA during the postpartum period compared with cows fed L. Plasma concentrations of β-hydroxybutyrate (BHBA) and liver TG content on d 21 were 46 and 30% lower, respectively, for cows fed H compared with cows fed L. Interactions between prepartum and postpartum treatments indicated that negative effects of delaying higher concentrate feeding until d 21 postpartum can be partially offset by increasing concentrate in the diet before calving. Cows fed L had a higher increase in white line hemorrhage scores between prepartum and 10 wk postpartum compared with cows fed H. Energy density of prepartum diets had a minor influence on metabolic status of cows postpartum. A more favorable metabolic profile occurs when increasing the concentrate content of the diet immediately postpartum compared with delaying the increase until d 21 postpartum.     

Effect of cooling heat-stressed dairy cows during the dry period on insulin response

Heat stress (HT) during the dry period affects hepatic gene expression and adipose tissue mobilization during the transition period. In addition, it is postulated that HT may alter insulin action on peripheral tissues. Our objective was to evaluate the effect of cooling heat-stressed cows during the dry period on insulin effects on peripheral tissues during the transition period. Cows were dried off 46d before expected calving and assigned to 1 of 2 treatments: HT (n = 16) or cooling (CL, n = 16). During the dry period, the average temperature-humidity index was 78, but CL cows were cooled with sprinklers and fans, whereas HT cows were not. After calving, all cows were housed and managed under the same conditions. Rectal temperatures were measured twice daily (0730 and 1430h) and respiration rate recorded 3 times weekly during the dry period. Dry matter intake was recorded daily from dry-off to 42d relative to calving (DRC). Body weight and body condition score were measured weekly from dry-off to 42 DRC. Milk yield and composition were recorded daily to 42wk postpartum. Glucose tolerance tests (GTT) and insulin challenges (IC) were performed at dry-off, -14, 7, and 28 DRC in a subset of cows (HT, n = 8; CL, n = 8). Relative to HT, CL cows had lower rectal temperatures (39.3 vs. 39.0°C) in the afternoon and respiration rate (69 vs. 48 breath/min). Cows from the cooling treatment tended to consume more feed than HT cows prepartum and postpartum. Compared with HT, CL cows gained more weight before calving but lost more weight and body condition in early lactation. Cows from the cooling treatment produced more milk than HT cows (34.0 vs. 27.7kg/d), but treatments did not affect milk composition. Treatments did not affect circulating insulin and metabolites prepartum, but CL cows had decreased glucose, increased nonesterified fatty acid, and tended to have lower insulin concentrations in plasma postpartum compared with HT cows. Cooling prepartum HT cows did not affect the insulin responses to GTT and IC during the transition period and glucose responses to GTT and IC at -14 and 28 DRC were not affected by treatments. At 7 DRC, CL cows tended to have slower glucose clearance to GTT and weaker glucose response to IC relative to HT cows. Cows from the cooling treatment had stronger nonesterified fatty acid responses to IC postpartum but not prepartum compared with HT. In conclusion, cooling heat-stressed dairy cows in the dry period reduced insulin effects on peripheral tissues in early lactation but not in the dry period.     

Dietary trans octadecenoic acids upregulate the liver gene encoding peroxisome proliferator-activated receptor-alpha in transition dairy cows

Effects of feeding calcium salts of conjugated linoleic acid (CLA) or trans octadecenoic acids (trans 18:1) on lipid metabolism and hepatic contents of mRNA encoding carnitine palmitoyltransferase 1 (CPT1), microsomal triglyceride transfer protein (MTP) and peroxisome proliferator-activated receptor alpha (PPARalpha) were examined in 15 early post-partum Holstein cows. Dietary treatments were initiated at approximately 4 weeks prior to expected calving dates and continued for 7 weeks post partum. Treatments prepartum consisted of 1) a basal diet (Control), 2) basal diet+150 g/d of CLA mix (CLA), or 3) basal diet+150 g/d of trans 18:1 mix (TRANS). Intakes of calcium salts of CLA and trans 18:1 mixes were adjusted to 225 g/d during the 7-week postpartum treatment period. Blood samples were collected at weeks 1, 2 and 4 post partum and plasma was harvested immediately for subsequent hormone and metabolite assays. Concentrations of insulin, insulin-like growth factor-I (IGF-I), and leptin in blood did not vary among cows fed the three diets. Plasma nonesterified fatty acid (NEFA) concentrations decreased between weeks 1 and 4 of lactation and were lower in cows fed the diet supplemented with trans 18:1 than in those fed a control diet at week 2 post partum. Periparturient fat supplementation had no detectable effects on CPT1 mRNA content in the liver. Steady-state concentration of MTP mRNA in the liver was greater in the TRANS treatment group than in the control group at week 1 postpartum. Feeding trans 18:1 supplements to transition dairy cows upregulated hepatic PPARalpha mRNA content during the first month of lactation. Under the present experimental conditions, dietary CLA had minimal effects on plasma and hepatic lipid metabolite concentrations in early lactation Holstein cows. Results indicate that dietary trans fatty acids may affect liver lipid metabolism in post-partum dairy cows through alterations in PPARalpha gene expression.     

Effects of feeding level and milking frequency on behavior of dairy cows before dry-off

Drying-off may challenge the welfare of especially high-yielding dairy cows. In this study, 119 loose-housed Holstein cows yielding ≥20 kg milk/d were enrolled in a 2 × 2 factorial design aiming to investigate effects of changes in diet energy density and daily milking frequency on behavior. The last 7 d before the dry-off day, cows were milked either twice or once daily, and were fed either a lactation diet or the same diet diluted with 30% barley straw, both offered in individual bins for ad libitum intake. All cows were fitted with sensors to record lying time and activity, and data from 109 of these cows were used together with behavioral observations obtained from video recordings of 52 of the cows. Data from activity sensors and video recordings were obtained during 24 h on d −6, −3, and −1 relative to the dry-off day (i.e., the day of the last milking). Across all days of observation, cows milked once daily spent more time feeding (149 vs. 130 min/d) than cows milked twice daily. Cows on the reduced diet and milked twice daily had a shorter lying time compared with cows on the normal diet and milked twice (759 vs. 837 min/d), whereas lying times of cows on the remaining 2 treatments were intermediate. Among cows on the lactation diet, reduced milking frequency increased time spent perching (from 11.1 to 28.7 min/d). Cows fed the energy-reduced diet spent more time feeding (154 vs. 124 min/d), showed more attempts to feed from unassigned feed bins (31.7 vs. 15.4 attempts daily), and spent less time using a mechanical brush (6.5 vs. 9.2 min/d) than cows fed the lactation diet. These results show that several aspects of cows' behavior, including main activities such as lying and feeding, but also behaviors of low resilience such as brush use, and to some extent more subtle and complex behaviors such as perching and attempts to feed from unassigned feed bins, are sensitive to management changes typically applied during the days before dry-off. The behavioral effects of the reduced feed energy level support earlier findings suggesting that qualitative feed restriction renders cows hungry. The effects of the reduced milking frequency on behavior were generally less pronounced, but 2 noteworthy interactions between milking frequency and diet were seen. First, cows milked twice daily and fed the energy-reduced diet spent less time lying, which is possibly related to increased energy demand and hunger. Second, cows milked once daily and fed the lactation diet spent more time perching, which may be related to udder discomfort. However, these more complex findings warrant further study. Taken together, the results of this study show that a dry-off procedure involving reduced energy supply induces behavioral changes indicating a higher degree of compromised welfare compared with reduced milking frequency.     

Effects of abomasal infusion of tallow or camelina oil on responses to glucose and insulin in dairy cows during late pregnancy

Late pregnancy is associated with moderate insulin resistance in ruminants. Reduced suppression of lipolysis by insulin facilitates mobilization of nonesterified fatty acids (NEFA) from adipose tissue, resulting in elevated plasma NEFA concentrations. Decrease in dry matter intake (DMI) before parturition leads to accelerated lipomobilization and increases plasma NEFA, which may further impair insulin sensitivity. The aim of the study was to evaluate the effects of elevation of plasma NEFA concentration by abomasal infusions tallow (TAL) or camelina oil (CAM) on whole-body responses to exogenous glucose and insulin. We further assessed whether CAM, rich in C18:3n-3, enhances whole-body insulin sensitivity compared with TAL. Six late-pregnant, second-parity, rumen-cannulated dry Ayrshire dairy cows fed grass silage to meet 95% of metabolizable energy requirements were used in a replicated 3 × 3 Latin square with 5-d periods and 5 recovery days between each period. Treatments consisted of abomasal infusion of 500 mL/d (430 g of lipids/d) of water (control), TAL, or CAM administered in 10 equal doses daily. Intravenous glucose tolerance test (IVGTT) and i.v. insulin challenge (IC) were performed on d 5 after 98 and 108 h of treatment infusions, respectively. Infusion of lipids increased basal plasma NEFA concentrations on d 5 (CAM: 0.25; TAL: 0.28; control: 0.17 mmol/L). Following glucose injection, the rate of glucose clearance (CR) was lower in lipid-treated cows (CAM: 1.34; TAL: 1.48; control: 1.74%/min) and time to reach half-maximal glucose concentration (T(1/2)) was longer (CAM: 54; TAL: 47; control: 42 min). Similar responses were observed after insulin injection. Increased plasma NEFA concentration tended to decrease insulin secretion in IVGTT. Infusion of CAM increased plasma C18:3n-3 content (CAM: 26.4; TAL: 16.1; control: 20.9 g/100g of fatty acids). Data suggest that CAM had an insulin-sensitizing effect, because the disposition index and insulin sensitivity index, derived from minimal model analysis, were higher in CAM than in TAL during IVGTT, and lower insulin concentrations during IC led to similar glucose clearance in CAM as in TAL. These results indicate that elevated plasma NEFA concentration per se induces whole-body insulin resistance in late-pregnant dry cows.     

Effect of supplementary concentrate type on nitrogen partitioning in early lactation dairy cows offered perennial ryegrass-based pasture

Forty-four early lactation (64 ± 20 d in milk) dairy cows of mixed parity were used to assess the effect of 4 supplementary concentrate types (n=11) on N partitioning. Animals were blocked on parity and calving date, and blocks were balanced for previous milk yield and milk protein yield. Cows received grazed pasture plus 5.17 kg of dry matter (DM)/d of one of the following isoenergetic concentrates: high crude protein (CP) with rolled barley (HP, 19% CP); low CP with rolled barley (LP, 15% CP); low CP with barley and supplementary 2-hydroxy-4-methylthio butanoic acid (HMBi; LP+HMBi, 15% CP); and low CP with ground corn (LP Corn, 15% CP). Nitrogen partitioning studies were conducted at wk 6 and 10 postpartum by using the n-alkane technique to determine pasture dry matter intake (DMI). Pasture DMI (13.3kg of DM/d) and dietary digestibility of DM were not affected by concentrate type. Milk yield was lower for LP compared with other concentrate types (25.4 vs. 28.3 kg/d). Yields of milk protein and milk casein were not affected by concentrate type. However, milk solid yield and milk fat yield were higher for LP+HMBi (1.97 and 0.92 kg/d) compared with LP (1.72 and 0.87 kg/d). Concentrations of fat, protein, lactose, and casein were not affected by concentrate type. Dietary N intake was higher for HP compared with other treatments (0.545 vs. 0.482 kg/d, HP vs. average of the 3 LP treatments). Dietary N intakes were not different among low CP concentrates. Fecal N excretion was not affected by concentrate type. However, urinary N excretion was related to N intake and was higher for HP compared with other treatments (0.261 vs. 0.195 kg/d, HP vs. average of the 3 LP treatments). Urinary N excretion was not different among low CP concentrates. Milk N output was higher for HP (0.139 kg/d) compared with LP (0.12 kg/d) but not LP+HMBi (0.137 kg/d) or LP Corn (0.138 kg/d). The portion of feed N excreted as feces N was lower for HP compared with other treatments (0.272 vs. 0.327, HP vs. average of the 3 LP treatmentsHowever, the portion of feed N excreted as urine N was higher for HP (0.466) compared with LP+HMBi (0.408) and LP Corn (0.366) but not compared with LP. The portion of feed N excreted as milk N was higher for LP Corn (0.282) compared with HP (0.257) but not LP+HMBi or LP. Dietary reformulation to reduce N excretion in pasture-based dairy production systems is possible. However, maintenance of milk yield and milk N when concentrate CP was reduced (19 vs. 15%) required the use of either protected AA (HMBi) or ground corn.     

Metabolism of dairy cows as affected by prepartum dietary carbohydrate source and supplementation with chromium throughout the periparturient period

Holstein cows (n = 72) entering second or later lactation were used to determine whether metabolic indices and hepatic capacities for oxidation and gluconeogenesis from propionate are affected by source of carbohydrate in the prepartum diet and chromium-l-methionine (Cr-Met) supplementation throughout the periparturient period. Cows were fed prepartum diets as total mixed rations with the concentrate portion based either on starch-based cereals [high nonfiber carbohydrate (NFC); 1.59 Mcal/kg of net energy for lactation (NE_L), 14.4% crude protein (CP), 40.3% NFC] or nonforage fiber sources (low NFC; 1.54 Mcal/kg of NE_L, 14.5% CP, 33.6% NFC) from 21 d before expected parturition until parturition. After parturition all cows were fed a common lactation total mixed ration (1.74 Mcal/kg of NE_L, 16.5% CP, 40.0% NFC). The Cr-Met was supplemented once daily via gelatin capsule at dosages of 0, 0.03, or 0.06 mg of Cr/kg of BW^0.75. Thus, treatments were in a 2 (carbohydrate source) × 3 (Cr-Met) factorial arrangement. There was no effect of prepartum carbohydrate source on pre- and postpartum plasma concentrations of glucose, nonesterified fatty acids (NEFA), β-hydroxybutyrate (BHBA), insulin, glucagon, or insulin to glucagon ratio. However, cows fed the low NFC diet during the prepartum period tended to have greater plasma NEFA and lower BHBA concentrations postpartum. Liver glycogen concentrations tended to be greater on d 1 postpartum for cows fed low NFC prepartum. Supplementing 0.03 mg/kg of BW^0.75 of Cr as Cr-Met increased prepartum plasma glucose and glucagon concentrations and tended to decrease prepartum plasma NEFA concentrations compared with either 0 or 0.06 mg of Cr/kg of BW^0.75. Postpartum plasma glucose concentrations decreased linearly and glucagon concentrations were increased quadratically by administering increasing amounts of Cr-Met. Supplementing Cr-Met did not affect prepartum plasma concentrations of insulin or BHBA, postpartum NEFA or BHBA, or liver composition. There was an interaction of prepartum carbohydrate source and Cr-Met supplementation such that in vitro hepatic conversion of [1-¹⁴C]propionate to both CO₂ and glucose was similar or increased when Cr-Met was supplemented to cows fed the low NFC diet but decreased when Cr-Met was supplemented to cows fed the high NFC diet. Insulin addition in vitro did not affect hepatic metabolism of propionate on d 1 postpartum. Overall, both the NFC content of the prepartum diet and Cr-Met had only modest effects on metabolic indices in this experiment.     

Effects of supplementing a Saccharomyces cerevisiae fermentation product during the periparturient period on performance of dairy cows fed fresh diets differing in starch content

The objective of this study was to evaluate the effects of supplementing a Saccharomyces cerevisiae fermentation product (SCFP; NutriTek, Diamond V, Cedar Rapids, IA) during the periparturient period (d ?28 ± 3 to 44 ± 3 relative to calving) on dry matter intake (DMI), milk production, apparent total-tract nutrient digestibility, and postpartum ovarian activity of dairy cows fed fresh diets varying in starch content. From d 28 ± 3 before the expected calving date until d 44 ± 3 after calving, 117 Holstein cows were fed diets with SCFP (SCFP; n = 59) or without (control, CON; n = 58). A common, basal, controlled-energy close-up diet (net energy for lactation: 1.43 Mcal/kg; 13.8% starch) was fed before calving. Cows within each treatment (CON or SCFP) were fed either a low- (LS; 22.1% starch) or high-starch (HS; 28.3% starch) diet from d 1 to 23 ± 3 after calving (fresh period), resulting in 4 treatment groups: LS-CON (n = 30), LS-SCFP (n = 29), HS-CON (n = 28), and HS-SCFP (n = 30). All cows were fed the HS diets from d 24 ± 3 to 44 ± 3 after calving (post-fresh period). Cows were assigned to treatment balanced for parity, body condition score, body weight, and expected calving date. Milk yield was higher for cows fed the LS diets compared with those fed the HS diets during the fresh period (34.1 vs. 32.1 kg/d), whereas DMI and 3.5% fat-corrected milk yield (FCM) were not affected by dietary starch content, and LS cows tended to lose more body condition than HS cows (?0.42 vs. ?0.35 per 21 d) during the fresh period. Overall DMI during the close-up and fresh periods did not differ between SCFP and CON cows. However, SCFP supplementation transiently increased DMI on d 1 (13.0 vs. 11.9 kg/d) and 5 (15.5 vs. 14.1 kg/d) after calving compared with CON. During the post-fresh period, SCFP cows tended to eat less than CON cows (19.8 vs. 20.6 kg/d) but had similar 3.5% FCM (44.9 vs. 43.6 kg/d), resulting in greater feed efficiency for SCFP cows (FCM/DMI; 2.27 vs. 2.13). Neither starch content of fresh diets nor SCFP supplementation affected the interval from calving to first ovulation or the incidence of double ovulation. These findings suggest that feeding low-starch diets during the fresh period can increase milk production of dairy cows during the fresh period, and that supplementation of SCFP may increase feed intake around calving and feed efficiency in the post-fresh period.