A dynamic model to simulate potassium balance in dairy cows

High-performing dairy cows require a particular composition of nutritional ingredients, adapted to their individual requirements and depending on their production status. The optimal dimensioning of minerals in the diet, one being potassium, is indispensable for the prevention of imbalances. Potassium balance in cows is the result of potassium intake, distribution in the organism, and excretion, and it is closely related to glucose and electrolyte metabolism. In this paper, we present a dynamical model for potassium balance in lactating and nonlactating dairy cows based on ordinary differential equations. Parameter values were obtained from clinical trial data and from the literature. To verify the consistency of the model, we present simulation outcomes for 3 different scenarios: potassium balance in (1) nonlactating cows with varying feed intake, (2) nonlactating cows with varying potassium fraction in the diet, and (3) lactating cows with varying milk production levels. The results give insights into the short- and long-term potassium metabolism, providing an important step toward the understanding of the potassium network, the design of prophylactic feed additives, and possible treatment strategies.     

Ovarian structures and circulating steroids in heifers and lactating cows in summer and lactating and dry cows in winter

Two experiments compared follicular and luteal development and circulating steroid concentrations from induced luteolysis to ovulation in lactating Holstein cows (n = 27; 40.0 +/- 1.5 kg milk/day) vs. nulliparous heifers (n = 28; 11 to 17 mo-old) during summer (Experiment 1), and in lactating (n = 27; 45.9 +/- 1.4 kg milk/d) vs. dry cows (n = 26) during winter (experiment 2). All females received PGF2,, 6 d after ovulation and were monitored until next ovulation by daily ultrasound and assay of serum progesterone (P4) and estradiol (E2). Every female was used two or three times. In Experiment 1, lactating cows had high incidence of multiple ovulation (63.5%) compared with heifers (1.3%). Among single ovulators, there was no difference in maximal size of ovulatory follicles between lactating cows and heifers (15.8 vs. 16.5 mm, respectively). However, lactating cows had lower peak serum E2 (8.6 vs. 12.1 pg/ml), took longer to ovulate after luteolysis (4.6 vs. 3.8 d), developed more luteal tissue volume (7,293.6 vs. 5,515.2 mm3), and had lower serum P4 on d 6 after ovulation (2.0 vs. 3.0 ng/ml) than heifers (data included multiple ovulators). In experiment 2, multiple ovulations were similar between lactating and dry cows (17.9 vs. 17.2%, respectively). Peak serum E2 was also similar between lactating and dry cows (7.6 vs. 8.5 pg/ml) although lactating cows had larger ovulatory follicles (18.6 vs. 16.2 +/- 0.4 mm). Lactating cows took longer to ovulate (4.8 vs. 4.2 d), developed more luteal tissue (7,599 vs. 5,139 +/- 468 mm3), but had similar serum P4 (2.2 vs. 1.9 ng/ ml) compared with dry cows. Therefore, lactating cows had similar or lower circulating steroid concentrations than dry cows or heifers, respectively, despite having larger ovarian structures.     

Effects of feed delivery time on feed intake, milk production, and blood metabolites of dairy cows

The objective of the study was to determine the effects of feed delivery time and its interactions with dietary concentrate inclusion and parity on milk production and on 24-h averages and patterns of feed intake and blood metabolites. Four multiparous and 4 primiparous lactating Holstein cows were used in a 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments. Experimental periods included 14 d of adaptation and 7 d of sampling. A higher concentrate diet with a forage:concentrate ratio (dry matter basis) of 38:62 or a lower-concentrate diet with a forage:concentrate ratio of 51:49 was delivered at either 0900 or 2100 h. During sampling periods, daily feed intakes, as well as feed intakes during 3-h intervals relative to feed delivery, were determined. During 2 nonconsecutive days of the sampling period, jugular blood was sampled every 2 h. Average temperature and relative humidity in the experimental facility were 20.4°C and 68.1%, and the maximum daily air temperature did not exceed 25°C. This data does not suggest that cows were heat-stressed. Changing feed delivery time from 0900 to 2100 h increased the amount of feed consumed within 3 h after feeding from 27 to 37% of total daily intake but did not affect daily dry matter intake. The cows fed at 2100 h had lower blood glucose at 2 h after feeding but greater blood lactate and β-hydroxybutyrate acid at 2 and 4 h after feeding than cows fed at 0900 h. These effects of feed delivery time on the 24-h patterns in blood metabolites may be caused by the greater feed intake during the 3 h after feed delivery of the cows fed at 2100 h. Daily averages of glucose, urea, lactate, and β-hydroxybutyrate acid and nonesterified fatty acids in peripheral blood were not affected by time of feeding. The change in feed delivery time did not affect milk yield and milk protein but increased milk fat percentage from 2.5 to 2.9% and milk fat yield from 0.98 to 1.20 kg/d in multiparous cows, without affecting milk fat in primiparous cows. The interactions between diet and time of feeding on daily feed intake, milk production, and blood metabolites were not significant. The effects of the time of feed delivery on the 24-h patterns in blood metabolites suggest that this time may affect peripheral nutrient availability. Results of this study suggest beneficial effects of feeding at 2100 h instead of at 0900 h on milk fat production of lactating cows, but parity appears to mediate this effect.     

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.     

Flooring in front of the feed bunk affects feeding behavior and use of freestalls by dairy cows

In 2 experiments we assessed how preferences, time budgets, and feeding behavior of dairy cows change in response to flooring surfaces in front of the feed bunk. In Experiment 1, 12 nonlactating dairy cattle were individually housed with access to 2 standing platforms filled with either concrete or sawdust. In Experiment 2, 24 nonlactating dairy cattle were given access to either concrete or Animat rubber flooring in front of the feed bunk. In Experiment 1, cows preferred the sawdust to the concrete flooring. In both experiments, cows provided with a softer floor in front of the feed bunk spent more time standing near the feed bunk without eating (Experiment 1: 67 vs. 40 min/d on sawdust vs. concrete, respectively, SEM = 5.6 min/d; Experiment 2: 176 vs. 115 min/d on Animat vs. concrete, respectively, SEM = 20.5 min/d) compared with when they were kept on concrete. The increased time spent at the feed bunk was due to a combination of more frequent eating and standing bouts, indicating that cows were more willing to move on nonconcrete flooring. Total time spent eating was significantly greater on the softer floor in Experiment 2, but not in Experiment 1 (Exp. 1: 289 vs. 275 min/d on sawdust and concrete, respectively, SEM = 7.3 min/d; Exp. 2: 330 vs. 289 min/d on Animat and concrete, respectively, SEM = 15.4), although feed intake was increased on the sawdust treatment in Experiment 1. Cows spent significantly more time lying in the feed alley when the flooring was rubber (219 vs. 53 min/d on Animat and concrete, SEM = 53.6 min/d), perhaps because the lying area in Experiment 2 was inadequate. In conclusion, cows prefer to stand on softer flooring in front of the feed bunk, and are more willing to move on and spend more time standing in front of the feed bunk when provided with softer flooring. These results indicate that cows find softer flooring surfaces more comfortable to stand on than concrete, and highlight the importance of evaluating the comfort of the entire facility.     

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.     

Variability in behavior and production among dairy cows fed under differing levels of competition

The objective of this study was to investigate the effects of differing levels of competition for feed access on group-housed dairy cows, and on variations in behavior and productivity between individuals within each group. Eighteen lactating Holstein cows, averaging 77 ± 20 d in milk with a production of 46 ± 7 kg/d at the start of the trial, were divided into subgroups of 3 and fed a total mixed ration 3×/d. Groups were exposed to each of 3 competition levels: high (3 cows:1 feed bin), moderate (3 cows:2 feed bins), and low (3 cows:3 feed bins). Treatments were assigned in random order according to a modified Latin-square design, and each was applied for 10 d. Using an automated feed intake system, feeding behavior data (dry matter intake, feeding time, feeding rate, and meal patterns) were recorded for each cow on d 6 to 10 of each treatment period. Additional behavioral [sorting, rumination, competitive interactions (replacements), lying time] and production (milk yield and components) data were collected. Greater competition resulted in a reduction in feeding time (low = 202.6, moderate = 194.9, high = 183.6 min/d; SE = 8.84), and an increased rate of feed intake (low = 0.16, moderate = 0.18, high = 0.20 kg of dry matter/min; SE = 0.01), especially following fresh feed delivery and milking. Dry matter intake was similar across treatments (average of 29.1 kg/d). Meal length increased under high competition (low = 37.0, moderate = 36.6, high = 47.3 min/meal; SE = 5.05) due to greater non-feeding time within meals, which was approximately twice as long under high competition (low = 10.0, moderate = 10.8, high = 20.3 min/meal; SE = 3.24). Daily lying time (low = 10.2, moderate = 10.2, high = 9.5 h/d; SE = 0.51) and milk protein yield (low = 1.41, mod = 1.42, high = 1.36 kg/d; SE = 0.05) were reduced under high competition. Analysis of individual within-group variability, calculated as the daily standard deviation of each group, averaged across 5 recording days, revealed greater variability in feeding time, feeding rate, meal length, non-feeding time within meals, milk yield, milk fat composition (%), and milk fat component yield (kg/d) under high competition. These results suggest that at elevated competition levels, cows modify their feeding behavior to consume feed in a shorter period and devote a large portion of their mealtime toward waiting to gain feed access, resulting in reduced daily lying time. Furthermore, meal patterns and milk production vary greatly within groups of cows at high levels of competition for feed access.     

Responses of dairy cows with divergent residual feed intake as calves to metabolic challenges during midlactation and the nonlactating period

Residual feed intake (RFI) is defined as the difference between the actual and expected feed intake required to support animal maintenance and growth. Thus, a cow with a low RFI can obtain nutrients for maintenance and growth from a reduced amount of feed compared with a cow with a high RFI. Variation in RFI is underpinned by a combination of factors, including genetics, metabolism, thermoregulation and body composition; hypothalamic-pituitary-adrenal (HPA) axis responsiveness is also a possible contributor. Responses to 3 metabolic challenges were measured in lactating and nonlactating dairy cattle. Sixteen Holstein Friesian cows with phenotypic RFI measurements that were obtained during the growth period (188–220 d old) were grouped as either low-calfhood RFI (n = 8) or high-calfhood RFI (n = 8). An ACTH (2 µg/kg of body weight), insulin (0.12 U/kg), and epinephrine (a low dose of 0.1 µg/kg and a high dose of 1.6 µg/kg of epinephrine) challenge were each conducted during both midlactation (122 ± 23.4 d in milk) and the nonlactating period (dry period; approximately 38 d after cessation of milking). Cows were housed in metabolism stalls for the challenges and were fed a diet of alfalfa cubes ad libitum for at least 10 d before the experiment (lactating cows also were offered a total of 6 kg of dry matter/d of crushed wheat grain plus minerals fed as 3 kg of dry matter at each milking) and were fasted for 12 h before the challenges. The efficiency of conversion of feed into milk (the ratio of feed consumed to milk produced over the 7 d before the experiment) during midlactation was better (lower) in low-calfhood RFI cows, although dry matter intake did not differ between RFI groups. Low-calfhood RFI cows exhibited a lower plasma cortisol response to the ACTH challenge than high-calfhood RFI cows, particularly in midlactation (?15%). The low-calfhood RFI cows had a greater plasma insulin-like growth factor-1 response to the insulin challenge and plasma fatty acid response to epinephrine compared with the high-calfhood RFI cows. These data suggest that high-calfhood RFI cows exhibit a more responsive HPA axis. As divergence in RFI measured during growth is retained (although reduced) during lactation, it is possible that energy is used to respond to HPA axis activation at the expense of production in high-calfhood RFI dairy cattle during lactation and contributes to a decrease in overall feed use efficiency.     

Ovarian follicular responses to high doses of pulsatile luteinizing hormone in lactating dairy cattle

Two experiments in lactating dairy cows examined ovarian follicular responses to high, frequent doses of exogenous LH pulses at levels associated with follicular cysts. In Experiment 1, estrus was synchronized in 12 cyclic lactating cows >40 d postpartum. Emergence of the second follicular wave (d 0) was determined by ultrasonography. Starting on d 1, cows received LH (40 microg/h; n = 7) or saline (2 mL/h; n = 5) in hourly pulses for up to 5 (n = 5) or 7 (n = 7) d. On d 2, all cows received two injections of PGF2alpha, 12 h apart. In experiment 2, 14 lactating cows (7 to 12 d postpartum) received LH (40 microg/h; n = 7) or saline (1 mL/h; n = 7) in hourly pulses for 7 d, beginning 24 h after start of the first follicular wave. Daily samples were used to determine serum concentrations of progesterone (P4), estradiol-17beta (E2), LH, and FSH. Profiles of LH were determined from blood samples collected at 12-min intervals for 8 h on d 3. During infusion of LH, serum P4 and FSH were similar across treatments in both experiments. Serum E2 concentrations were similar in experiment 1, but serum E2 was greater on d 2, 3, and 5 in LH-treated cows in experiment 2. Infusion increased LH pulse frequency and amplitude in both experiments. Formation of cysts did not differ between LH- and saline-treated cows in either experiment (1 of 7 vs. 0 of 5 and 1 of 6 vs. 0 of 7, respectively). Cows that ovulated had similar intervals to ovulation in experiment 1 [6.0 +/- 0.1 d (LH) vs. 6.4 +/- 0.2 d (saline)], but in experiment 2, ovulation was 14 d earlier in LH-treated cows (5.6 +/- 1.8 d vs 19.9 +/- 1.5 d). In conclusion, high concentrations of LH are not solely responsible for formation of cysts in lactating dairy cows. Pulsatile infusion of LH stimulated follicular growth and steroidogenesis and decreased time to first ovulation in anestrous postpartum cows.     

Effect of hormonal and energy-related factors on plasma adiponectin in transition dairy cows

In transition dairy cows, plasma levels of the insulin-sensitizing hormone adiponectin fall to a nadir at parturition and recover in early lactation. The transition period is also characterized by rapid changes in metabolic and hormonal factors implicated in other species as positive regulators of adiponectin production (i.e., negative energy balance, lipid mobilization) and others as negative regulators (i.e., reduced leptin and insulin and increased growth hormone and plasma fatty acids). To assess the role of onset of negative energy balance and lipid mobilization after parturition, dairy cows were either milked thrice daily (lactating) or never milked (nonlactating) for up to 4 wk after parturition. Plasma adiponectin was 21% higher across time in nonlactating than lactating cows. Moreover, nonlactating cows recovered plasma adiponectin at similar rates as lactating cows even though they failed to lose body condition. Next, we assessed the ability of individual hormones to alter plasma adiponectin in transition dairy cows. In the first experiment, dairy cows received a constant 96-h intravenous infusion of either saline or recombinant human leptin starting on d 8 of lactation. In the second experiment, dairy cows were studied in late pregnancy (LP, starting on prepartum d ?31) and again in early lactation (EL, starting on d 7 postpartum) during a 66-h period of basal sampling followed by 48 h of hyperinsulinemic-euglycemia. In the third experiment, cows were studied either in LP (starting on d ?40 prepartum) or EL (starting on d 7 postpartum) during a 3-h period of basal sampling followed by 5 d of bovine somatotropin treatment. Plasma adiponectin was reduced by an average of 21% in EL relative to LP in these experiments, but neither leptin, insulin, or growth hormone treatment affected adiponectin in LP or EL. Finally, the possibility that plasma fatty acids repress plasma adiponectin was evaluated by intravenous infusion of a lipid emulsion in nonpregnant, nonlactating cows in the absence or presence of glucagon for 16 consecutive hours. The intralipid infusion increased plasma fatty acid concentration from 102 to over 570 µM within 3 h but had no effect on plasma adiponectin irrespective of presence or absence of glucagon. Overall, these data suggest that energy balance around parturition may regulate plasma adiponectin but do not support roles for lipid mobilization or sustained changes in the plasma concentration of leptin, insulin, growth hormone, or fatty acids.     

Effect of L-carnitine infusion and feed restriction on carnitine status in lactating Holstein cows

Previously we determined that abomasal infusion of l-carnitine increased in vitro hepatic fatty acid oxidation, decreased liver lipid accumulation, and supported higher fat-corrected milk yield in feed-restricted lactating cows. The objectives of this study were to examine the effects of supplemental l-carni-tine and amount of feed intake on free carnitine and carnitine ester concentrations in liver, muscle, milk, and plasma of lactating dairy cows. Eight lactating Holstein cows (132 ± 36 d in milk) were used in a replicated 4 × 4 Latin square design with 14-d periods to test factorial combinations of water or l-carnitine infusion (20 g/d; d 5 to 14) and ad libitum or restricted (50% of previous 5-d intake; d 10 to 14) dry matter intake. Plasma was obtained 3 times daily on d 4, 8, and 12; milk samples were collected on d 8, 9, 13, and 14. Liver and muscle were biopsied on d 14 of each period. Free carnitine, short-chain acylcarnitine, and long-chain acylcarnitine concentrations were determined using a radioenzymatic assay coupled with ion exchange chromatography. Abomasal l-carnitine infusion increased total carnitine in plasma on d 8 and d 12. All liver carnitine fractions were increased by carnitine infusion. Feed restriction elevated concentrations of free carnitine, long-chain acylcarnitine, and total carnitine in liver tissue from carnitine-infused cows but not in those infused with water. In muscle, acid-soluble carnitine, long-chain acylcarnitine, and total carnitine concentrations were increased by carnitine infusion and feed restriction without significant interaction. Feed restriction increased free carnitine concentrations in muscle from water-infused cows but not in carnitine-infused cows. Carnitine infusion increased the concentration of each milk carnitine fraction as well as milk carnitine output on d 8 to 9. On d 13 to 14, all carnitine fractions except short-chain acylcarnitine were increased in milk from water-infused, feed-restricted cows, whereas all fractions were increased in carnitine-infused, feed-restricted cows. Carnitine infusion increased total carnitine in plasma, liver, muscle, and milk during feed restriction, whereas feed restriction alone increased carnitine concentrations in muscle and milk but not in liver. Liver carnitine concentrations might limit hepatic fatty acid oxidation capacity in dairy cows during the periparturient period; therefore, supplemental l-carnitine might decrease liver lipid accumulation in periparturient cows.     

Supplemental nicotinic acid or nicotinamide for lactating dairy cows

In two experiments with multiparous Holstein cows, the effects of feeding supplemental nicotinic acid or nicotinamide on milk production and metabolite changes associated with early lactation were measured. In Experiment 1, 30 cows were assigned to three groups. The treatment groups received 6 g nicotinic acid or 6 g nicotinamide per head per day beginning 2 wk prepartum to 12 wk postpartum. Control group received no treatment. Cows receiving nicotinamide produced more milk (wk 9, 11, and 12) and had higher milk fat test (wk 1 and 4) than did controls. Concentrations of beta-hydroxybutyrate in blood serum (wk 4) were lower for cows receiving nicotinic acid or nicotinamide. Serum glucose concentration (wk 4 to 6) was higher and FFA (wk 4) were lower for cows receiving nicotinamide than for controls. In Experiment 2 with six multiparous Holstein cows, the effects of feeding nicotinamide on metabolic changes associated before, during, and after a 48-h period without feed initiated at 4 wk postpartum were studied. The treatment groups received 12 g nicotinamide per head per day beginning 2 wk prepartum to 4 wk postpartum. The control group received no treatment. Supplementing nicotinamide to lactating cows had no effect on serum glucose, beta-hydroxybutyrate, or free fatty acids before, during, or after 48-h period without feed.     

An assessment of absorbable lysine requirements in lactating cows

Two experiments were conducted to ascertain lysine required for maintenance and milk production in lactating dairy cows. Multiparous Holstein cows fitted with abomasal cannulas were utilized in a replicated 3 x 3 extra-period Latin square design and infused with 0, 45, or 90 g of L-lysine-HCl daily (Experiment 1). In Experiment 2, 12 cows were utilized in a 5 x 5 Latin square design (with 2 replacement cows) and infused with 0, 22.5, 45, 90, and 180 g of L-lysine-HCl daily. Cows were housed in comfort stalls, milked at 0600 and 1700 h, exposed to a 16:8 h light:darkness cycle, and fed for ad libitum intake a 15.7% CP diet formulated to contain approximately 75% of dietary protein from corn-based feed ingredients. Milk yield was not affected in Experiment 1, but milk production increased linearly with lysine infusion level in Experiment 2. A linear response in daily yield of milk protein to lysine infusion was observed in both experiments. As lysine infusion increased, coccygeal plasma lysine concentrations tended to increase in Experiment 1, but in Experiment 2 free lysine increased linearly and quadratically in coccygeal plasma and increased linearly in plasma from the subcutaneous abdominal vein. The quadratic response in plasma free lysine (Experiment 2) suggested that lysine was the limiting AA for milk production from the composite protein flow to the small intestine. Using break-point analysis of plasma free lysine, it was estimated that the additional amount of abomasal lysine required to satisfy requirements was 64 g/d in cows producing about 30 kg of milk daily. Although additional lysine above microbial and undegraded intake protein lysine flow stimulated milk protein production, conversion efficiency to milk protein lysine was low.     

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.     

Dairy Ration Formulation and Evaluation Program for Microcomputers

An interactive ration evaluation and formulation computer program for lactating and nonlactating dairy cows was developed using electronic spreadsheet software (Lotus 123). The program has five subunits: 1) a nutrient requirement section; 2) a feed bank section that stores nutrient composition of available feeds; 3) a computational section where rations are evaluated or formulated; 4) a feeding recipe section, which displays or prints grain mix, mineral mix, total mixed ration, or stanchion barn feeding recommendations; and 5) a comparative economic evaluator, which ranks feeds by a nutritional cost and benefit algorithm. Up to 12 fixed feed ingredients are able to be selected by the operator from a bank of up to 100 feeds on the basis of evaluation, farm availability, and nutrient constraints. Selected variable ingredients are used to balance the ration for dry matter, net energy, crude protein, bypass protein, and acid detergent fiber. Calcium and phosphorus are balanced using a combination of mineral sources. Trace mineral mixes may be either custom formulated or selected from a bank of proprietary supplements on the basis of limiting trace elements in the ration. Individualized farm data storage and retrieval capability facilitates regular nutritional monitoring and reformulation procedures.     

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.     

Effects of intraruminal infusion of sodium,potassium, and ammonium on hypophagia from propionate in lactating dairy cows

The objective of this experiment was to evaluate effects of salt type on hypophagic effects of intraruminal infusion of propionate in lactating dairy cows. Our working hypothesis is that oxidative metabolism of propionate causes satiety by increasing hepatic ATP concentration and decreasing the discharge rate of the hepatic vagus. We hypothesized that hypophagic effects of propionate are reduced by ammonium and potassium. We speculated that ammonium infusion lowers hepatic ATP concentration because ATP is used for urea synthesis and potassium increases the discharge rate of the hepatic vagus. Eight ruminally cannulated Holstein cows in midlactation were used in a duplicated 4 x 4 Latin square design experiment. Treatments were intraruminal infusion of propionic acid, ammonium propionate, sodium propionate, and potassium propionate. Treatment solutions were 0.93 M for propionate and 0.67 M for salts among the treatments except for propionic acid. Treatment solutions were infused over 14 h starting 2 h before feeding at 17.9 ml/min, which is equivalent to 16.7 and 11.9 mmol/min for propionate and salts, respectively. Infusion of ammonium propionate decreased dry matter intake compared with sodium propionate and potassium propionate (P < 0.04; 11.0 vs. 14.0 and 13.9 kg/12 h) by decreasing meal frequency without affecting meal size, indicating that ammonium delayed the sense of hunger. No difference in DMI and feeding behavior was observed between infusion of sodium and potassium propionate. Contrary to the hypothesis, ammonium infusion did not reduce hypophagic effects of propionate, possibly because the urea cycle indirectly stimulated oxidative metabolism in the liver by generating oxidizable carbon from amino acid catabolism.     

Short communication: Effect of feed barrier design on the behavior of loose-housed lactating dairy cows

The objective of this study was to evaluate the effects of 2 feed barrier systems on feeding and social behavior of dairy cows. Forty-eight lactating Holstein cows were subjected to each of 2 treatments in a cross-over design. The treatments were 2 types of feed-line barriers: 1) post-and-rail, and 2) headlock. Time-lapse video was used to quantify the feeding behavior and incidence of aggressive displacements of the cows at the feed bunk. Average daily feeding time did not differ when cows used the headlock barrier compared with the post-and-rail barrier. However, there were certain changes in feeding time during periods of peak feeding activity: cows that had lower feeding times relative to group mates when using the post-and-rail barrier showed more similar feeding times to group mates when using the headlock barrier. There were 21% fewer displacements at the feed bunk when cows accessed feed by the headlock barrier compared with the post-and-rail barrier. These results suggest that using a headlock barrier reduces aggression at the feed bunk and improves access to feed for socially subordinate cows during peak feeding periods.     

In vitro and in vivo analysis of fatty acid effects on metabolism of 17β-estradiol and progesterone in dairy cows

Some studies have reported improved reproductive performance with dietary fat supplementation. This study examined effects of fatty acids with different lengths, or desaturation, or both, on metabolism of estradiol (E2) and progesterone (P4) in bovine liver slice incubations (experiments 1 and 2) and in vivo (experiment 3). In experiment 1, effects of fatty acids C16:0 (palmitic acid), C16:1 (palmitoleic acid), C18:1 (oleic acid), and C18:3 (linolenic acid) were evaluated at 30, 100, and 300 μM on P4 and E2 metabolism in vitro. In experiment 2, stearic acid (C18:0) and C18:3 were evaluated in the same incubation conditions. In experiment 1, all of the fatty acids had some significant inhibitory effect on metabolism of P4, E2, or both (300 μM C16:0 on E2; 100 μM C16:1 on E2; 300 μM C16:1 on both P4 and E2; 300 μM C18:1 on P4; and 100 and 300 μM C18:3 on both P4 and E2). In experiment 2, C18:3 (100 and 300 μM) but not C18:0 decreased P4 and E2 metabolism. Overall, the most profound increase (∼60%) in half-life of P4 and E2 was observed with incubations of 300 μM C18:3 in both in vitro experiments. Based on these in vitro results, in experiment 3 linseed oil (rich in C18:3) was supplemented into the abomasum and acute effects on metabolism of E2 and P4 were evaluated. Cows (n = 4) had endogenous E2 and P4 minimized (corpus luteum regressed, follicles aspirated) before receiving continuous intravenous infusion of E2 and P4 to analyze metabolic clearance rate for these hormones during abomasal infusion of saline (control) or 70 mL of linseed oil every 4 h for 28 h. Linseed oil infusion increased C18:3 in plasma by 46%; however, metabolic clearance rate for E2 and P4 were similar for control cows compared with linseed-treated cows. Thus, in vitro experiments indicated that E2 and P4 metabolism can be inhibited by high concentrations of C18:3. Nevertheless, in vivo, linseed oil did not acutely inhibit E2 and P4 metabolism, perhaps because insufficient C18:3 concentrations (increased to ∼8 μM) were achieved. Further research is needed to determine the mechanism(s) of fatty acid inhibition of P4 and E2 metabolism and to discover practical methods to mimic this effect in vivo.     

Effects of lipid and propionic acid infusions on feed intake of lactating dairy cows

Propionic acid is more hypophagic for cows with elevated hepatic acetyl coenzyme A (CoA) concentration in the postpartum period. The objective of this experiment was to evaluate the interaction of hepatic acetyl CoA concentration, which is elevated by intravenous lipid infusion, and intraruminal propionic acid infusion on feed intake and feeding behavior responses of lactating cows. Eight multiparous, ruminally cannulated, Holstein dairy cows past peak lactation were used in a replicated 4 × 4 Latin square experiment with a 2 × 2 factorial arrangement of treatments. Treatments were propionic acid (PI) infused intraruminally at 0.5 mol/h for 18 h starting 6 h before feeding and behavior monitoring or sham control (CO), and intravenous jugular infusion of lipid (LI, Intralipid 20%; Baxter US, Deerfield, IL) or saline (SI, 0.9% NaCl; Baxter US) infused at 250 mL/h for 12 h before feeding and behavior monitoring, and then 500 mL/h for 12 h after feeding. Changes in plasma concentrations of metabolites and hormones and hepatic acetyl CoA from before infusion until the end of infusion were evaluated. We observed a tendency for an interaction between PI and LI for the change in plasma nonesterified fatty acid (NEFA) concentration from the preliminary day to the end of the infusion period. Infusion of propionic acid decreased dry matter intake (DMI) 15% compared with CO, but lipid infusion did not affect DMI over the 12 h following feeding. Infusion of propionic acid tended to decrease hepatic acetyl CoA concentration from the preliminary day to the end of the infusion compared with CO, consistent with PI decreasing DMI by stimulating oxidation of acetyl CoA. Contrary to our expectations, LI did not increase concentration of NEFA or β-hydroxybutyrate in plasma, concentration of acetyl CoA in the liver, or milk fat yield, suggesting that the infused lipid was stored or oxidized by extra-hepatic tissues. As a result, we detected no interaction between PI and LI for DMI. Although the effect of PI on DMI was consistent with our previous results, this lipid infusion model using cows past peak lactation was not useful to simulate the lipolytic state of cows in the postpartum period in this experiment.