Effects of prepartum roughage neutral detergent fiber levels on periparturient dry matter intake, metabolism, and lactation in heat-stressed dairy cows

Heat stress of lactating cattle results in dramatic reductions in dry matter intake (DMI). As a result, energy input cannot satisfy energy needs and thus accelerates body fat mobilization. Decreasing the level of roughage neutral detergent fiber (NDF) in prepartum diets, and thereby increasing the amount of nonfiber carbohydrates, may provide an adequate supply of energy and glucose precursors to maintain and minimize the decrease in DMI while reducing mobilization of adipose tissue. The effects of 3-wk prepartum diets containing different amounts of roughage NDF on DMI, blood metabolites, and lactation performance of dairy cows were investigated under summer conditions in Thailand. Thirty cross-bred cows (87.5% Holstein × 12.5% Sahiwal) were dried off 60 d before their expected calving date and were assigned immediately to a nonlactating cow diet containing the net energy for lactation recommended by the National Research Council (2001) model. The treatment diets contained 17.4, 19.2, and 21.0% DM as roughage NDF from bana grass (Pennisetum purpureum × Pennisetum glaucum) silage. Levels of concentrate NDF were 39.8, 40.2, and 38.6% of dietary NDF, so the levels of dietary NDF were 28.9, 32.1, and 34.2% of DM. After parturition, all cows received a lactating cow diet containing 12.7% roughage NDF and 23% dietary NDF. During the entire experiment, the minimum and maximum temperature-humidity index averaged 77.7 and 86.8, respectively, indicating conditions appropriate for the induction of extreme heat stress. As parturition approached, DMI decreased steadily, resulting in a 12.9, 25, and 32.8% decrease in DMI from d −21 until calving for nonlactating cows fed prepartum diets containing 17.4, 19.2, and 21% roughage NDF, respectively. During the 3-wk prepartum period, intakes of DM and net energy for lactation and concentrations of plasma glucose and serum insulin were higher for cows fed diets containing less roughage NDF. In cows fed the 3-wk prepartum diets containing less roughage NDF, calf birth weights, milk yield, and 4% fat-corrected milk were higher, whereas periparturient concentrations of serum nonesterified fatty acids and plasma β-hydroxybutyrate were lower. There was a carryover effect of the prepartum diet on serum nonesterified fatty acids and plasma β-hydroxybutyrate during the first 7 d in milk, and therefore on milk production. These results suggest that feeding diets containing decreased amounts of roughage NDF during the 3-wk prepartum period may minimize the decrease in DMI and lipid mobilization as parturition approaches. This strategy may thus minimize the effect of hormonal factors and heat stress on periparturient cows.     

Demonstration of a role for insulin in the regulation of leptin in lactating dairy cows

In lactating dairy cows, the onset of negative net energy balance (EB) at parturition causes a reduction in plasma leptin and is also associated with increased concentration of growth hormone (GH) and decreased concentration of insulin. These observations raise the possibility that opposite changes in plasma insulin and GH are partly responsible for reduced plasma leptin. To test this hypothesis, we first examined the effects of undernutrition without the confounding influence of parturition by using late lactating dairy cows fed 120% of their nutrient requirements or restricted to 33% of maintenance requirements. Plasma leptin was reduced within 24 h of feed restriction, and was associated with increased plasma GH and decreased plasma insulin. Complete food deprivation for 48 h caused similar changes in the plasma concentration of leptin. To determine if an elevation in GH is responsible for the fall in plasma leptin, dairy cows were treated with excipient or bovine somatotropin in early lactation or in late lactation. Growth hormone treatment had no significant effect on plasma leptin irrespective of stage of lactation. Finally, the effects of insulin were studied by performing euglycemic hyperinsulinemic clamps in mid-lactating dairy cows. After 96 h of hyperinsulinemia, plasma leptin was increased significantly. These data indicate that insulin regulates plasma leptin in lactating dairy cows. They also suggest that, in undernourished lactating dairy cows, reduced plasma insulin could account for a portion of the decline in plasma leptin but that elevated plasma GH is unlikely to have a major effect.     

Metabolism and lactation performance in dairy cows fed a diet containing rumen-protected fat during the last twelve weeks of gestation

Effects of dietary fat supplementation prepartum on liver lipids and metabolism in dairy cows are contradictory. Thus, we examined in 18 German Holstein cows (half-sib; first lactation 305-d milk yield >9,000 kg) whether dietary fat:carbohydrate ratio during the last trimester of gestation affects lipid metabolism and milk yield. The diets were formulated to be isoenergetic and isonitrogenous but differed in rumen-protected fat (FD; 28 and 46.5 g/kg of dry matter during far-off and close-up dry period; mainly C16:0 and C18:1) and starch concentration [carbohydrate diet (CD); 2.3 times as much starch as FD]. Diets were given ad libitum starting 12 wk before expected parturition. After parturition all cows were fed a single lactation diet ad libitum for 14 wk. With the FD treatment, dry matter intake was depressed prepartum, milk yield during first 4 wk of lactation was lower (36.9 vs. 41.0 kg/d), and postpartum energy balance during this period was more negative. During the first 4 wk, cows in the FD group had lower lactose percentage and yield but higher milk fat, whereas milk protein and fat yield as well as energy-corrected milk did not differ. Between wk 5 and 14, milk fat and milk protein percentage was lower in CD than in FD. Milk fat C14:0 was lower and C16:1 was higher in the FD group. For FD cows, plasma triacylglycerol, nonesterified fatty acids, and cholesterol concentrations were higher prepartum, whereas plasma β-hydroxybutyrate and glucose concentrations were lower. During the first 10 d after parturition, plasma triacylglycerol concentration was higher in FD, and prepartum plasma glucose and cholesterol differences persisted during the first 14 wk of lactation. Irrespective of prepartum nutrient composition, concentrations of plasma leptin and subcutaneous fat leptin mRNA decreased between −10 d to +10 d relative to parturition, and liver lipids and glycogen reached maximum and minimal values, respectively, 10 d after parturition. Acetyl-coenzyme A carboxylase α mRNA abundance in subcutaneous fat decreased between −10 d to +1 d relative to parturition by 97%, whereas it was generally much lower in the liver and remained at a low level until wk 14 of lactation. In conclusion, feeding a diet containing rumen-protected fat during late lactation and dry period until calving negatively affected dry matter intake, energy balance, and milk yield during subsequent lactation, did not change acetyl-coenzyme A carboxylase α mRNA abundance in subcutaneous fat, and was not beneficial for liver lipid accumulation.     

Effects of feeding intensity during the dry period. 2. Metabolic and hormonal responses

The metabolic response to different feeding levels during the dry period was studied in 24 multiparous dairy cows of the Swedish Red and White breed. The cows represented two lines, selected for high or low milk fat percentage, at the same amount of energy produced in milk. The cows were fed one of three different amounts of the same total mixed diet during the dry period, starting 8 wk prior to the expected parturition. The rations provided 71, 106, or 177 MJ metabolizable energy per day. After parturition the cows were offered another total mixed diet ad libitum for the first 12 wk of lactation. Glucose challenges were performed 3 wk prior to and 3 wk after parturition. Prepartum the glucose clearance rate was related to feeding level. Insulin response to the glucose challenge was reduced during the postpartum period, compared to the prepartum period. During about 6 wk prepartum, the insulin level in plasma was related to feeding level. At the sampling 3 wk prior to parturition the plasma level of leptin also was related to the feeding level. After parturition both leptin and insulin were reduced. In early lactation plasma leptin concentration was not related to adiposity as reflected by body condition scoring. It was suggested that lactation as such affected the leptin concentration in plasma.     

Effect of body fatness and glucogenic supplement on lipid and protein mobilization and plasma leptin in dairy cows

Twenty-four multiparous Ayrshire cows were used in an experiment to test the effect of body fatness and glucogenic supplement, fed during the transition period, on lipid and protein mobilization and plasma hormone concentrations. Eight weeks before their expected calving date, the cows were divided into blocks of 4. Two cows with the highest body condition score within each block were then allocated to a test (T) group and the other 2 cows to a control (C) group. To scale up the differences between fatter and thinner cows, the estimated energy allowance was 40% higher in group T than in group C between d 56 and 21 prepartum. For the final 3 wk before calving, all the cows were fed according to energy recommendations for pregnant cows. Within C and T groups and blocks, cows were randomly assigned into groups with (G1) or without (G0) glucogenic supplement. Division to G0 and G1 groups was made 2 wk before the expected calving and continued for 56 d postpartum. After calving, all the cows received grass silage ad libitum and a common daily concentrate allowance. No significant differences were detected in feed intake and milk yield between C and T. The T groups showed an earlier rise of nonesterified fatty acids as calving approached and had higher plasma nonesterified fatty acids during the final week of pregnancy and lactation wk 1 to 3. At the same time, adipose tissue samples from fatter cows tended to show higher in vitro lipolytic responses to added norepinephrine, as monitored by glycerol release. Protein mobilization was elevated during the final week of pregnancy and tended to be more increased in fatter cows. Glucogenic supplement did not decrease lipid or protein mobilization. Fatter cows had higher plasma leptin concentration prepartum, showed a more pronounced decrease in leptin concentration near calving, and had higher plasma leptin concentration after calving. In conclusion, fatter cows initiated more extensive mobilization of body fat before calving and this continued during the first lactation weeks. Plasma leptin concentration in early-lactation cows was associated with body fatness and not with estimated energy balance.     

Alpha-lactalbumin in bovine serum: relationships with udder development and function

Concentrations of alpha-lactalbumin in blood from cattle in various physiological states were measured as an index of udder development and function. Included were primiparous heifers during gestation and the peripartum period, nonlactating, nonpregnant cows hormonally induced into lactation, and cows milked two or three times daily in early, middle, or late lactation. Concentrations of alpha-lactalbumin in serum increased in two phases during gestation. Initial values (7.3 ng/ml, up to 120 d prepartum) rose, then leveled at 29.9 ng/ml on d 120 to 30 prepartum. Concentrations subsequently increased, averaging 133.2 ng/ml over the 30 d prior to parturition. During the peripartum period, alpha-lactalbumin rose from 221.2 ng/ml on d 4 prepartum, peaked at calving (918.8 ng/ml), then declined, stabilizing at approximately 500 ng/ml (1.5 to 3 d postpartum). Concentrations of alpha-lactalbumin in cows induced to lactate were low on d 1 to 9 of hormone treatment (15.7 ng/ml), rose to a maximum on d 17 (803.4 ng/ml), then fell to a plateau (185.8 ng/ml) on d 21 to 25. alpha-Lactalbumin concentrations were higher in early (101.9 ng/ml) than in middle or late lactation (81.4 and 79.2 ng/ml, respectively). Concentrations were also greater in twice versus thrice milked cows (101.9 vs. 73.0 ng/ml). Changes in alpha-lactalbumin concentrations in serum are associated with developmental and functional status of the udder. The measurement provides a noninvasive method to assess mammary gland activity.     

Effects of prepartum dietary carbohydrate source and monensin on periparturient metabolism and lactation in multiparous cows

Eighty-five multiparous Holstein cows were used in a completely randomized design with restrictions to evaluate the effects of prepartum carbohydrate (CHO) source and monensin on periparturient dry matter intake (DMI), blood parameters, and lactation performance of dairy cows. Dietary treatments were arranged in a 2 × 2 factorial arrangement with a conventional (CONV) dry cow diet and a nonforage fiber source (NFFS) dry cow diet not supplemented (−) or supplemented (+) with 330 mg/cow per d of monensin as a top dressing. The CONV diet contained 70% forage and the NFFS diet contained nonforage fiber sources such that 28% of the forage was replaced with cottonseed hulls and soyhulls. The experimental diets (CONV and NFFS) were fed throughout the entire dry period (for 60 d before parturition). Monensin was top dressed once daily starting 28 d (27 ± 1.8 SD) before the expected calving date and continued until parturition. After parturition, all cows received the same lactating cow diet. During the last 28 d of gestation, cows receiving the NFFS diets prepartum had greater DMI (15.8 vs. 11.9 kg/d), DMI as a percentage of body weight (2.1 vs. 1.6% of body weight), plasma glucose (67.4 vs. 64.6 mg/dL), and serum insulin concentrations (0.59 vs. 0.45 ng/mL), and lower plasma nonesterified fatty acid concentrations (185 vs. 245 μEq/L) compared with cows receiving the CONV diets prepartum. Average milk production or composition during the first 56 d of lactation was not significantly affected by prepartum source of CHO, monensin, or their combination; however, there was a trend for the prepartum CHO source to affect milk production over time. Supplementation of monensin as a top dressing for 28 d prepartum had no effect on periparturient measurements. The prepartum diet did not affect postpartum DMI, blood glucose, nonesterified fatty acids, insulin concentrations, or liver triglyceride content. Results from this research demonstrated that partly replacing conventional dietary carbohydrate sources with NFFS, cottonseed hulls and soyhulls, in the dry cow diet improved or maintained the prepartum DMI and therefore enhanced the prepartum metabolic status, as indicated by key blood metabolite concentrations. This greater prepartum DMI may potentially increase milk production during early lactation.     

Changes in the lipid composition of the secretions of the bovine mammary gland during the dry period.

To study initiation of milk fat synthesis, lipid composition of mammary secretions at -60, -40, and -10 d prepartum was studied in lactating and nonlactating Holstein cows. Eleven cows were dried off, and 13 cows were milked twice per day throughout the normal dry period. Total neutral lipid was similar in late lactation milk (-60 d) from lactating cows, 2.1 g/dl, and in milk from the dry group, 2.2 g/dl. Neutral lipids decreased to 1.3 and .9 g/dl in quarters from dry cows at -40 and -10 d prepartum. In secretions from dry quarters, triglycerides were 97% of total lipids at -60 d and decreased to 85 and 91% at -40 and -10 d, respectively. Conversely, FFA and monoglycerides increased during the dry period. Lipids associated with fat globule membrane components increased during the dry period. These increases were 10 times for cholesterol, 20 times for cholesteryl esters, and twice for phospholipids. In general, the content of fat globule core lipids (triglycerides) exhibited a pattern opposite that of membrane lipids (cholesterol, cholesteryl esters, phospholipids) during the prepartum period. Proportions of core lipids tended to decrease, whereas proportions of membrane lipids increased in prepartum mammary secretions. Lipid composition of prepartum secretions may be influenced by blood lipids, somatic cells, and alterations in mammary lipid synthesis.     

Priming the cow for mobilization in the periparturient period: effects of supplementing the dry cow with saturated fat or linseed

High-producing dairy cows experience negative energy balance in early lactation. Dry-cow feeding management will affect the performance and metabolic status of dairy cows in the following early lactation. The present study evaluates dry-cow feeding strategies for priming lipid metabolism in the dairy cow to overcome the metabolic challenges in the following early lactation. Five weeks before expected calving, 27 cows were assigned to 1 of 3 isonitrogenous and isoenergetic dietary treatments: a low-fat control diet (dry-control); a high saturated fat diet (dry-HSF); and a high linseed diet (dry-HUF). The cows were fed the same TMR lactation diet after calving. The treatments were evaluated by performance and metabolic parameters in blood and liver. The cows fed dry-HSF and dry-HUF had significantly greater plasma nonesterified fatty acid concentrations compared with dry-control, and the dry-HUF cows had the greatest C18:3 concentrations in plasma in the prepartum period. Further, the cows fed dry-HSF and dry-HUF diets had a tendency for the greatest capacity for incomplete β-oxidation of fatty acids in the liver in wk 3 prepartum. The plasma cholesterol concentration was greatest for cows fed dry-HSF in the prepartum period compared with those fed dry-control and dry-HUF. The cows fed dry-HSF had the lowest plasma nonesterified fatty acid and liver fat concentrations in early lactation compared with the cows fed dry-control and dry-HUF. Data in the literature and the present experiment indicate that supplementing dry cows with a saturated fatty acid source is a positive strategy for priming dairy cows for body fat mobilization in the following early lactation.     

Continuous lactation in dairy cows: effect on milk production and mammary nutrient supply and extraction

Reports over the past decade have indicated that normal lactational performance can be achieved in genetically superior and high-producing dairy cows, even when the dry period between 2 lactations is omitted. The hypothesis tested in this experiment was that normal lactogenesis I and metabolic function may be achievable in continuously milked high-yielding dairy cows as a result of the genetic selection for lactation performance and hence longevity of mammary epithelial cells. The milk production and mammary nutrient uptake in response to omission of the dry period for cows with an expected peak milk yield higher than 45 kg/d were studied in 28 Holstein dairy cows managed without bovine somatotropin. Performance and metabolic parameters were followed in late gestation and in the following early lactation. Fourteen cows were milked continuously throughout late gestation, and another 14 dairy cows experienced a 7-wk prepartum dry period. Continuous milking during the prepartum period reduced milk production in the following early lactation period by >20%. The reduced milk production could not be readily ascribed to inefficiency of the mechanisms responsible for nutrient uptake by the lactating mammary epithelial cells, nor to systemic endocrine changes. This suggests that lowered mammary nutrient uptake must have been associated with reduced mammary blood flow, metabolic activity, or both, most likely as a result of disturbed lactogenesis I prepartum or lactogenesis II postpartum triggered by as yet unknown local mechanisms. Milk protein content was elevated by 0.4 percentage units in the continuously milked cows. The underlying reason is unknown, but given the current pricing system for milk, it deserves to be further investigated.     

Plasma concentrations of metabolic hormones in high and low producing dairy cows

Concentrations of insulin, glucagon, growth hormone, adrenocorticotropin, and cortisol were determined in plasma samples obtained at 20-min intervals for 6 h from low and high producing dairy cows at d 30 and 90 postpartum. Four nonpregnant, nonlactating cows also were sampled. Insulin concentrations were reduced at d 30 in both groups of lactating cows compared with concentrations in nonlactating cows; glucagon concentrations were unchanged. The molar insulin: glucagon was reduced at d 30 in both groups and at d 90 for low, but not high producers. Growth hormone concentrations were higher at d 30 in high producers than at d 90, in low producers at d 30, and higher than in nonlactating cows. Cortisol concentrations were lower in high producing cows at d 30 than at d 90 or in nonlactating cows due to a reduced pulse amplitude. No differences were observed for adrenocorticotropin. Reduced molar insulin: glucagon may be an integral response of the cow to lactation, while the difference in the insulin: glucagon for high and low producers at d 90 postpartum may indicate a continued need for a gluconeogenic stimulus in low producers. The elevated growth hormone and low cortisol concentrations likely participate in the enhanced production observed in high producing dairy cows.     

Influence of lactation on metabolic characteristics and embryo development in postpartum Holstein dairy cows

The aim of this study was to examine the direct effect of lactation on the ability of the reproductive tract of postpartum dairy cows to support early embryo development. Twenty-one primiparous Holstein heifers were used. Immediately after calving, half of the cows were dried off (i.e., never milked), and the other half entered the milking herd and were milked twice daily. Jugular blood samples were taken twice per week from 15 d before calving to approximately 100 d postpartum to measure nonesterified fatty acids, β-hydroxybutyrate, glucose, insulin, and insulin-like growth factor-I. At the same time, body weight and body condition score were recorded for each cow. At approximately 60 d postpartum (experiment 1), approximately 65 two- to four-cell embryos, produced by in vitro maturation and fertilization, were endoscopically transferred to the oviduct ipsilateral to the corpus luteum of all cows on d 2 of the estrous cycle. Five days later (d 7), the oviduct and uterus were flushed nonsurgically and the number of embryos developing to the blastocyst stage was recorded. At approximately 90 d postpartum (experiment 2), the estrous cycles of the same cows were resynchronized and 15 to 20 in vitro-produced blastocysts were transferred to the uterus of each recipient on d 7. All cows were slaughtered on d 14 to assess embryo survival and dimensions. Body weight and body condition score were significantly different between groups for the entire postpartum period of the study. Concentrations of nonesterified fatty acids and β-hydroxybutyrate were higher and concentrations of glucose, insulin, and insulin-like growth factor-I were lower in lactating compared with nonlactating cows. Embryo recovery rates from lactating and dry cows were similar. In experiment 1, fewer embryos developed to the blastocyst stage in the lactating cows compared with the nonlactating cows. In experiment 2, embryo survival and conceptus dimensions were not different between lactating and nonlactating cows. In conclusion, the data indicate that the reproductive tract of the lactating dairy cow is compromised in its ability to support early embryo development compared with that of matched dry cows and this may contribute to early embryo mortality observed in such animals.     

Effects of prepartum milking on milk production and health performance

A field study using seven Holstein herds was conducted to determine effects of prepartum milking on milk production, health disorders, and reproductive performance. In each herd, 80 cows (30% first lactation cows) were assigned 1 mo prior to expected calving date to one of two treatments: postpartum or prepartum milking. The group milked prepartum was machine-milked twice daily at regular milking intervals beginning 14 d prior to date of expected calving. The group milked postpartum was milked for the first time after calving. The day prior to calving, 36, 33, and 31% of the cows milked prepartum produced less than 4.5 kg, 4.5 to 9 kg, and greater than 9 kg of milk, respectively. No relationship existed between days milked prepartum and prepartum milk yield. Lactation milk yield and persistency were not affected by prepartum milking. Prepartum milking reduced incidence of milk fever and mastitis during the 1st mo after parturition. Treatment was not a significant source of variation for reproductive performance or body condition; however, culling was higher for cows milked postpartum. Results indicate no adverse effects on cow performance due to prepartum milking nor increase in lactation milk yield.     

Physiological adaptations in early-lactation cows result in differential responses to calcium perturbation relative to nonlactating,nonpregnant cows

The peripartal cow experiences a rapid change in calcium metabolism at the onset of lactation. Research has focused on understanding how mammary-derived factors, such as serotonin (5HT) and parathyroid hormone like hormone (PTHLH), aid in coordinating these calcemic adaptations to lactation. Therefore, the aim of our study was to determine how induced subclinical hypocalcemia influences physiological responses, specifically the 5HT-PTHLH-Ca axis, in lactating and nonlactating dairy cows to elucidate the potential contribution of the mammary gland. Twelve nonlactating, nonpregnant (NL) multiparous Holstein cows and 12 early-lactation (EL) multiparous Holstein cows received either (1) a continuous 24-h intravenous solution of 0.9% NaCl or (2) 5% ethylene glycol tetraacetic acid (EGTA) solution in 0.9% NaCl (n = 6 EL, n = 6 NL per treatment) with the aim of maintaining blood ionized calcium (iCa) less than 1.0 mM. Mammary gland biopsies were taken immediately after and 48 h after termination of infusion. Blood was sampled hourly during infusion and 4, 8, 12, 24, 48, and 72 h after termination of infusion. Infusion of EGTA successfully decreased blood iCa concentrations. However, EL EGTA-infused cows required increased rates of EGTA infusion to maintain iCa below 1.0 mM. Circulating and mammary serotonin concentrations were increased in EL relative to NL cows, with no difference as a result of EGTA infusion. Mammary PTHLH expression was increased in EL cows, with highest expression observed in EL EGTA-infused cows. Collectively, these data demonstrate the robust adaptations EL cows have to maintain Ca homeostasis and the supporting roles 5HT and PTHLH may play.     

Short communication: The association of adiponectin and leptin concentrations with prepartum dietary energy supply,parity, body condition,and postpartum hyperketonemia in transition dairy cows

Adipokines—hormones produced by adipose tissue—have important regulatory functions, and their concentrations can change around the time of calving when energy balance rapidly decreases. Hence, energy balance may be an important factor in determining the circulating concentrations of adipokines, particularly adiponectin and leptin. The objective of our study was to investigate the association between the level of energy fed to prepartum Holstein cows and circulating concentrations of adiponectin and leptin before and after calving. Holstein dairy cows entering second or greater lactation were fed either a controlled-energy diet formulated to supply approximately 100% of energy requirements (n = 28) or a high-energy diet formulated to supply approximately 150% of energy requirements throughout the entire dry period (n = 28). Serum samples were analyzed for adiponectin and leptin concentrations at 56, 28, 10, and 1 d prepartum as well as on d 1, 10, 21, and 42 postpartum using ELISA. Parity was dichotomized into cows entering second versus higher parity. Average peripartum body condition score (BCS) was computed from weekly measurements and dichotomized into animals with an average BCS of ≤3.25 and >3.25. In addition, cows were classified according to the occurrence of hyperketonemia (β-hydroxybutyrate concentrations ≥1.2 mmol/L at any time between 3 and 21 d in milk). Data were analyzed using repeated-measures ANOVA. Serum leptin but not adiponectin concentrations were associated with prepartum feeding level such that leptin concentrations increased transiently during the dry period in cows overfed energy, but concentrations were not different postpartum. Cows entering second parity had higher adiponectin and lower leptin concentrations compared with cows in higher parities. Cows that developed hyperketonemia postpartum had consistently lower adiponectin concentrations during the study period. Cows with average BCS >3.25 had higher leptin concentrations during the dry period only, but adiponectin concentrations were not associated with BCS. In conclusion, prepartum energy level had only transient effects on leptin concentrations and did not lead to changes in adiponectin concentrations.     

Short communication: Glucose and fructose concentrations and expression of glucose transporters in 4- to 6-week pregnancies collected from Holstein cows that were either lactating or not lactating

Glucose is an essential nutrient for the conceptus. The objective was to determine if lactation affected the amount of glucose crossing the placenta by measuring glucose and fructose in placental fluids in lactating and nonlactating cows. Holstein cows were assigned to one of 2 treatments immediately after parturition [lactating (n=23) or nonlactating (dried off immediately after calving; n=20)]. Pregnant cows were slaughtered at one of 3d of pregnancy (d 28, 35, or 42) and tissues were collected. Plasma glucose and insulin were less in lactating cows. Pregnancies collected from lactating cows had less glucose and fructose in placental fluids compared with those from nonlactating cows. Relative to endometrium, the placenta expressed greater amounts of the glucose transporters SLC2A1 (Glut1), SLC2A3 (Glut3) and SLC2A4 (Glut4) mRNA. The mRNA for SLC2A1 decreased whereas the mRNA for SLC2A4 increased from d 28 to d 42 of pregnancy. Stepwise regression analyses for fetal and placental weight (dependent variable) retained day of pregnancy and maternal plasma insulin concentrations in the final model. The conclusion is that lower blood glucose and insulin in lactating cows may lead to less glucose crossing the placenta and slower fetal development during lactation. The slower fetal development may predispose lactating cows to fetal loss if developmental milestones are not reached.     

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.     

Fibroblast growth factor-21 (FGF21) administration to early-lactating dairy cows. II. Pharmacokinetics,whole-animal performance,and lipid metabolism

Dairy cows cope with severe energy insufficiency in early lactation by engaging in intense and sustained mobilization of fatty acids from adipose tissue. An unwanted side effect of this adaptation is excessive lipid accumulation in the liver, which in turn impairs hepatic functions. Mice experiencing increased hepatic fatty acid flux are protected from this condition through coordinated actions of the newly described hormone fibroblast growth factor-21 (FGF21) on liver and adipose tissue. The possibility of an analogous role for FGF21 in dairy cows is suggested by its rapid increase in plasma levels around parturition followed by chronically elevated levels in the first few weeks of lactation. To test this hypothesis, dairy cows were randomly assigned on d 12.6 ± 2.2 (± standard error) of lactation to receive either an excipient (control; n = 6) or recombinant human FGF21 (n = 7), first as an FGF21 bolus of 3 mg/kg of body weight (BW) followed 2 d later by a constant i.v. infusion of FGF21 at a rate of 6.3 mg/kg of metabolic BW for 9 consecutive days. After bolus administration, human FGF21 circulated with a half-life of 194 min, and its constant infusion increased total plasma concentration 117-fold over levels in excipient-infused cows. The FGF21 treatment had no effect on voluntary feed intake, milk yield, milk energy output, or net energy balance measured over the 9-d infusion or on final BW. Plasma fatty acids circulated at lower concentrations in the FGF21 group than in the control group for the 8-h period following bolus administration, but this reduction was not significant during the period of constant i.v. infusion. Treatment with FGF21 caused a 50% reduction in triglyceride content in liver biopsies taken at the end of the constant i.v. infusion without altering the mRNA abundance of key genes involved in the transport, acyl coenzyme A activation, or oxidation of fatty acids. In contrast, FGF21 treatment ablated the recovery of plasma insulin-like growth factor-1 seen in control cows during the 9-d i.v. infusion period despite a tendency for higher plasma growth hormone. This effect was associated with increased hepatic mRNA abundance of the intracellular inhibitor of growth hormone receptor trafficking, LEPROT. Overall, these data confirm the ability of FGF21 to reduce lipid accumulation in bovine liver and suggest the possibility that FGF21 does so by attenuating the hepatic influx of adipose tissue-derived fatty acids.     

Plasma growth hormone and insulin during early lactation in cows fed silage based diets.

Peripheral plasma insulin, growth hormone, and blood glucose were determined in 24 dairy cows during early lactation. Blood samples were obtained at 4-day intervals during the first 56 days of experimental lactations 1 and 3 of a 3-lactation experiment. The cows were divided equally among three groups and fed one of the following forage rations for three consecutive lactations: corn silage (18.2 kg/day) plus alfalfa-timothy hay ad libitum; corn silage (18.2 kg/day) plus alfalfa-timothy silage ad libitum; or corn silage ad libitum. These diets were continued throughout the intervening dry periods except in the latter group where corn silage intake was limited if individual animals exhibited excessive body weight gain. Four animals in each group received prepartum supplemental concentrates. The remaining four animals received no prepartum concentrate supplementation. Following parturition, concentrates were fed in increasing amounts to a maximum of 14.6 kg/day during the first 56 days of lactation. Plasma insulin, growth hormone, and blood glucose were not affected by forage diet or prepartum supplemental concentrate feeding. Plasma insulin and blood glucose increased and plasma growth hormone decreased with time after parturition. These changes were correlated with nutrient intake which increased during the experiment. Changes in plasma insulin and growth hormone are related to metabolic adjustments during early lactation.     

Expression of growth hormone receptor 1A messenger ribonucleic acid in liver of dairy cows during lactation and after administration of recombinant bovine somatotropin.

The mRNA for growth hormone receptor is transcribed from at least three different promoters in cattle. The first promoter (P1) is liver-specific and transcribes growth hormone receptor mRNA containing exon 1A (growth hormone receptor 1A). The second and third promoters (P2 and P3) are active in a variety of tissues and transcribe growth hormone receptor mRNA containing exon 1B and 1C. The objective was to characterize P1 activity by measuring the amount of growth hormone receptor 1A mRNA in liver of dairy cows at different stages of lactation as well as after administration of recombinant bovine somatotropin (rbST). In study 1, liver RNA was isolated from Holstein cows during the dry period (nonlactating, n = 6) and during early (n = 6), mid (n = 6), and late (n = 11) stages of lactation. Six of the late-lactation cows received injections of rbST (25 mg/d) for 7 d prior to collection of liver tissue. In study 2, lactating Holstein cows received either no infusion (control, n = 10) or continuous infusion of rbST (29 mg/d, n = 10) for 63 d. The amount of growth hormone receptor 1A mRNA was decreased in early- and mid-lactation cows compared with late-lactation cows or nonlactating cows (study 1). Administration of rbST increased growth hormone receptor 1A mRNA (studies 1 and 2). The total amount of growth hormone receptor transcribed from alternative promoters (growth hormone receptor P2 and P3) remained unchanged during different stages of lactation or in response to rbST. We conclude that changes in liver growth hormone receptor mRNA in lactating dairy cattle primarily depend on growth hormone receptor P1 activity.