CTL Cows Research Articles

Proteomic analysis of peripheral blood mononuclear cells and inflammatory status in postpartum dairy cows supplemented with different sources of omega-3 fatty acids

We examined the effects of dietary n-3 fatty acids on the proteome of peripheral blood mononuclear cells (PBMC) in transition dairy cows. Forty-two dry cows were divided into three groups supplemented with: saturated fat (CTL); flaxseed oil (FLX); or fish oil (FO). PBMC were collected from five cows per group at week 1 postpartum for proteomic analysis. The n-3 fatty acid content in plasma and PBMC was higher in FLX and FO than in CTL cows. In PBMC, 3807 proteins were quantified and 44, 42 and 65 were differently abundant in FLX vs. CTL, FO vs. CTL and FLX vs. FO, respectively. In FLX vs. CTL, the abundance of the p65-subunit-of-transcription-factor NF-κB was higher, whereas albumin, C4b-binding protein and complement factor H levels were lower. In FLX vs. FO, complement factors B and H and hemopexin were higher. The top canonical pathway enriched in FLX compared to other groups was acute-phase-response signaling. The percentage of CD25+ blood cells was lower in FLX and FO at 1 week postpartum, and gene expression of NF-κB in white blood cells was lower in FLX than in CTL. Dietary sources of n-3 fatty acids differentially affected the proteome of PBMC, possibly altering the inflammatory status. SignificanceThe transition dairy cow experiences a variable degree of systemic subacute inflammation, and proteomics of peripheral blood mononuclear cells (PBMC) may contribute to obtain insight into this process. Omega-3 fatty acids can moderate the immunological effect, and therefore we examined the effects of these fatty acids from flaxseed (FLX) or fish oils (FO) on the proteome of PBMC at week 1 postpartum. More than 3800 proteins were quantified, and in cows supplemented with FLX, enrichment of the acute-phase-signaling and complement systems were apparent in the PBMC compared to CTL and FO PBMC. This information may be useful to further explore the mechanism by which dietary omega-3 fatty acids affect the immune system in postpartum dairy cows.

The effects of omega-3 α-linolenic acid from flaxseed oil supplemented to high-yielding dairy cows on production, health, and fertility

Among the long-chain fatty acids (FA), the omega-3 (n-3) FA have the most potent immunomodulatory activities. In the present large-scale study, we tested the effects of supplementation of α-linolenic acid (ALA) from flaxseed commenced at the dry period on milk yield, health and fertility of dairy cows. Cows in a large commercial dairy farm were randomly divided into two groups 21 days before expected calving. During the dry period, cows in the treatment group were fed a diet that contained, on a DM basis, 40 g/kg of an extruded flaxseed supplement (EFLX; n = 276); their postpartum diet contained 50 g/kg of the same supplement. The cows were group-fed, and based on average cow's intake, the EFLX cows consumed 80 and 220 g ALA/day per cow prepartum and postpartum, respectively. The control cows received a diet with a different composition but a similar content of nutrients (CTL; n = 240). A veterinarian routinely examined the cows 7 to 10 days after calving, treated them according to the farm's routine practice, and determined their body condition score at that visit and at peak lactation. Milk yield was 4.5% greater (1.8 kg/day; P < 0.0001), and fat (P < 0.0001) and protein (P = 0.002) contents were lower in the EFLX vs. CTL group. The proportion of n-3 FA in milk was 3.9 times higher in EFLX than in CTL cows (P < 0.0001), and the omega-6 (n-6):n-3 ratio in the milk fat decreased from 13.0 in the CTL cows to 4.1 in the EFLX cows (P < 0.0001). The unsaturated FA content in milk fat was 20.1% greater in EFLX than in CTL cows (P < 0.0001). Ketosis incidence was lower in the EFLX vs. CTL group, 23.5 and 31.2%, respectively (P = 0.05), and ketosis was less severe in the former (P = 0.03). The mortality rates in EFLX and CTL cows were 0.7 and 4.6%, respectively (P = 0.005). No differences were observed in conception rates at first or second insemination, but days from first service to conception and calving to conception were 17 (P = 0.07) and 18 days (P = 0.09) less in the EFLX cows, respectively. In conclusion, supplementation of EFLX to dairy cows from the dry period increased milk yield, decreased incidence of ketosis and severe metritis, reduced mortality, and tended to enhance fertility performance. Overall, ALA supplementation improved milk quality and was beneficial to the cow's health and fertility.

Effects of milking frequency and domperidone injections on milk production and prolactin signaling in the mammary gland of dairy cows

Eleven mid-lactation Holstein cows were milked twice daily during the first 2 experimental weeks. During wk 3 to 10, the cows were differentially milked: right quarters were milked thrice daily (3×) and left quarters were milked once daily (1×). During wk 11 to 14, all quarters were milked twice daily. After 4 wk of differential milking, the cows received daily i.m. injections of the dopamine antagonist domperidone (DOMP; 300 mg; n = 6) or of dimethyl sulfoxide as the control (CTL; n = 5) for 8 wk (wk 7-14). During the differential milking period (wk 3-6), milk production was greater for quarters milked 3× than for those milked 1× but did not differ between DOMP and CTL cows. During the differential milking + injection period (wk 7-10), milk production continued to differ according to milking frequency. However, DOMP injection did not have an effect or interact with milking frequency on milk production. During the injection period (wk 11-14), milk production remained greater in the quarters previously milked 3× and milk production increased in DOMP injected cows but not in CTL cows. Injections of DOMP increased prolactin concentration, which was greater in the serum of DOMP cows than in that of CTL cows during the differential milking + injection and the injection periods. The expression of genes that are directly related to milk synthesis (CSN2, LALBA, and ACACA) was greater in the 3× quarters than in the 1× quarters. In addition, DOMP increased CSN2 expression during the injection period. The expression of both isoforms of the PRLR gene was greater in the 3× quarters during the differential milking + injection and the injection periods. At the protein level, injections of DOMP tended to increase the number of long PRLR isoform during the differential milking + injection period. The number of short PRLR isoform was greater in the 1× quarters than in the 3× quarters during the differential milking, the differential milking + injection, and the injection periods. The total amount of STAT3 protein was greater in the 1× quarters during the differential milking and the differential milking + injection periods. The amount of phosphorylated STAT3 protein was greater in the 1× quarters during the differential milking period. The total amount of phosphorylated STAT5 protein was greater in the 3× quarters during the differential milking and the differential milking + injection periods. The results of this experiment support the hypothesis that the responsiveness of the mammary gland to PRL is modulated by milking frequency, although the underlying mechanism remains to be determined.

PSI-11 Anti-inflammatory treatment modifies epigenetics changes to muscle tissue caused by altered nutrient demand in early lactation dairy cows

Abstract Short-term treatment with non-steroidal anti-inflammatory drugs (NSAIDs) has been shown to alter whole-lactation milk yield; perhaps because epigenetic modifications are responsible for long-term effects, although mechanisms are unclear. Altered nutrient demand due to fasting or exercise in other species has been shown to affect DNA methylation in muscle tissue. Our objective was to determine if NSAID treatment or alterations to nutrient demand have epigenetic effects on muscle tissue in early lactation. In this study, 33 multiparous Holstein cows were enrolled at parturition and randomly assigned to milking frequency (MF; 1× or 3×/day), and either sodium salicylate (SS; 2.3 g/L administered via drinking water) or control (CTL; molasses carrier alone) treatment in a 2×2 factorial design, beginning ~24 h postpartum. Milking frequency treatments were designed to alter nutrient demand, and 3× milked increased milk yield by 24%. After 5 days of treatment, tissue biopsies were collected from the Longissimus dorsi muscle and snap-frozen. DNA was isolated and global methylation (GM) was assessed with a 5-methylcytosine enzyme-linked immunosorbent assay. An interaction between MF and SS treatment was detected (P = 0.02), with GM of muscle tissue decreased by more frequent milking only in the CTL cows (4.9 and 1.4 ± 1.0% of DNA methylated for 1× and 3×, respectively; P &lt; 0.001). No effect of MF was detected in SS-treated cows (2.9 and 2.4 ± 1.0% of DNA methylated for 1× and 3×, respectively; P &gt; 0.1). Observed changes to DNA methylation in muscle tissue due to altered nutrient supply are consistent with results reported after fasting and exercise. Additionally, increased demand for milk component precursors in 3×-milked cows may alter the availability of methyl donors for DNA methylation. Our data support a link between SS and epigenetic changes, but further research is needed to determine how SS may have altered the muscle DNA methylation response to nutrient demand.

Effect of bovine somatotropin injection in late pregnant Holstein heifers on metabolic parameters and steroidogenic potential of the first postpartum dominant follicle

The aim of this study was to determine the effect of pre-partum injections of bovine somatotropin (bST) in dairy heifers on metabolic markers and the steroidogenic potential of the first postpartum dominant follicle. Heifers were assigned to two groups: bST (ST; n = 29), that received two doses of bST (500 mg/dose) at −28 and −14 days relative to calving; and control (CTL; n = 30), that did not received bST. Follicular development was monitored via ultrasound every 3 days starting at 8 days in milk (DIM) in a subset of 20 heifers until the day the first large follicle reached a diameter of 16 mm. From these cows follicular fluid was aspirated and the follicular cells recovered (ST; n = 8 and CTL; n = 10). Blood samples were collected weekly for all heifers. Follicular fluid IGF-I concentrations of the first postpartum dominant follicle was higher (P = 0.05) in ST (87.1 ± 7.7 mg/mL) than CTL cows (64.3 ± 6.8 mg/mL). Also, E2 concentration in the follicular fluid was higher (P = 0.02) for ST (199.7 ± 55.9 ng/mL) than CTL cows (74.5 ± 37.7 ng/mL). The expression of LHCGR and STAR mRNA in follicular cells was higher (P < 0.05) in ST than CTL cows. Nonetheless, HSD3B, P450scc, P450c17, IGFr and CYP19A1 mRNA expression was not different between groups (P > 0.05). Serum IGF-I concentration was higher in ST treated heifers during the pre-partum period (P = 0.01) and no difference was observed in the postpartum period (P = 0.19). In conclusion, pre-partum bST treatment in dairy heifers increased intrafollicular IGF-I and expression of LHCGR and STAR mRNA in follicular cells of the first postpartum dominant follicle. These changes were associated to increased intrafollicular and serum E2 concentration, which can potentially increase the chance of ovulation of the first follicular wave.

Conjugated linoleic acid supplementation during the transition period increased milk production in primiparous and multiparous dairy cows

Trans-10, cis-12 conjugated linoleic acid (CLA), a bioactive fatty acid, has the potential to alter energy metabolism in lactating dairy cows by marginally reducing milk fat synthesis in the mammary gland. The objective of this study was to determine the effects of pre- and postpartum CLA supplementation on lactation performance in a commercial dairy setting. Multiparous (mp) and primiparous (pp) Holstein cows managed in an automatic milking system were blocked by expected calving month, and randomly assigned to either a CLA supplementation (CLA-ME; mp n=99, pp n=38) or control (CTL; mp n=97, pp n=38) group. Cows were supplemented 100g/d of lipid encapsulated CLA methyl esters containing 10g each of cis-9, trans-11 and trans-10, cis-12 CLA, mixed 50:50 with soybean meal, and delivered via an automated mineral dispenser. Supplementation continued from −21 d pre-calving through 30 d in milk (DIM) for mp or 70 DIM for pp. Daily milk yield, fat and protein content, body weight, and rumination minutes were recorded and averaged by wk for the first 100 DIM. Milk yield was increased (P=0.04) during the supplementation period (44.7 vs. 46.6±0.64kg/d) for mp CLA-ME cows and was increased (P=0.03) during the post-supplementation period (31.3 vs. 34.2±0.91kg/d) for pp CLA-ME cows. Milk fat content was decreased (P=0.03) during the supplementation period for mp CLA-ME cows and post-supplementation period for pp CLA-ME cows (P=0.02); but only tended to be decreased (P=0.09) in the supplementation for pp CLA-ME cows. Fat yield was not altered (P>0.10) in either period for mp and pp CLA-ME. Supplementation with CLA did not change milk protein content or yield during the supplementation period for either mp or pp CLA-ME. During the post-supplementation period protein content was decreased (P=0.02); however, yield remained unchanged for mp CLA-ME cows while protein content was unchanged and yield increased for pp CLA-ME cows. Body weight and rumination minutes were unchanged by CLA supplementation. Intervals to first estrus, first service, and conception were similar for CTL and CLA-ME mp and pp cows. First service conception rate was similar for mp CTL and CLA-ME cows; but, tended to be increased (P=0.10) in pp CLA-ME compared to CTL. These results suggest that transition period CLA supplementation altered energy metabolism to increase milk production during the supplementation period for mp cows and post-supplementation period for pp cows without adversely affecting reproductive performance in mp cows and improving conception in pp cows.

The acute effect of intravenous lipopolysaccharide injection on serum and intrafollicular HDL components and gene expression in granulosa cells of the bovine dominant follicle

The aim of this study was to evaluate the effect of an acute systemic inflammatory response induced by lipopolysaccharide (LPS) in the serum and follicular fluid (FF) high-density lipoprotein (HDL) components, hormone concentrations and granulosa cell gene expression. For this purpose, twenty non-lactating Jersey dairy cows were submitted to a progesterone (P4) – estradiol (E2) based synchronization protocol. Cows received a single i.v. dose of LPS (2.5 μg/kg of body weight) or saline solution (CTL Group) 2 h after P4 insert removal. Blood, granulosa cells and FF samples were collected six hours after LPS injection. Five hours after LPS injection rectal temperature was increased in LPS (P < 0.0001, 40.4 ± 0.1 °C) compared to the CTL cows (38.8 ± 0.1 °C). Serum PON1 activity was reduced by LPS injection (130.2 ± 5.1 vs. 99.6 ± 3.3 U/mL; P < 0.001), as well as HDL-cholesterol concentrations (70.3 ± 5.3 vs. 50.1 ± 6.2 mg/dL; P < 0.05). The FF E2 and P4 concentrations were not different between groups (P > 0.05). The PON1 activity in the FF was also decreased by LPS injection (P = 0.01). In comparison to CTL group, cows injected with LPS had a ten fold reduction in STAR, TLR4 and TNF mRNA expression (P < 0.05). In conclusion, an intravenous LPS challenge in cows induced an acute systemic inflammatory response reducing HDL and its components in serum but not in the FF. Only PON1 activity serum reduction was reflected in the FF in the short term. Additionally, steroidogenic and inflammatory genes had reduced expression in the granulosa cells.

The dopamine antagonist domperidone increases prolactin concentration and enhances milk production in dairy cows

In previous studies, our team showed that the inhibition of prolactin (PRL) secretion by the dopamine agonist quinagolide reduces milk production in dairy cows. The objective of this study was to determine the effects of administration of a dopamine antagonist on basal and milking-induced PRL concentrations in blood and on milk production during positive energy balance and feed restriction in dairy cows. Eighteen mid-lactation Holstein cows received daily s.c. injections of either domperidone (300mg, DOMP, n=9) or the vehicle, canola oil (CTL, n=9), for 5wk. During wk 5, all cows were fed at 65% of their dry matter intake in the previous week. Blood and milk samples were collected before (for blood) and during (for milk) the a.m. milking thrice weekly from d −9 to 41 (8d after the last injection). In addition, blood samples were collected during the a.m. milking on d −1 (before the first injection), and on d 1, 28, and 34. Basal PRL concentration was similar in both groups before the start of the treatments. Domperidone injections caused a gradual increase in basal PRL concentration. Feed restriction reduced basal PRL concentration in both the CTL and DOMP cows, but PRL concentration remained higher in the DOMP cows. Prolactin concentration remained elevated in the DOMP cows 7d after the last injection. The milk concentration of PRL increased during the DOMP treatment, but the increase was smaller than that observed in serum. In the CTL cows, the milking-induced PRL release above the premilking concentration was similar on d −1, 1, and 28 but was reduced during feed restriction. In the DOMP cows, the milking-induced PRL release was similar on d −1 and 1 but was reduced on d 28 and 34. Milk production was similar for both groups before the treatments started but was greater in the DOMP cows during the treatment period, at 2.9±0.6 and 2.4±0.6kg/d greater during wk 3 and 4 of treatment, respectively. Milk production declined in both groups during feed restriction but remained higher in the DOMP cows. Milk production became similar again for both groups after the last injection. In addition, dry matter intake was increased by DOMP. These results support the hypothesis that PRL is galactopoietic in dairy cattle.

Rumination behavior of grazing dairy cows in response to restricted time at pasture

The short-term adaptations of cattle behavior to time restrictions at pasture are poorly understood. This study explored the diurnal rumination pattern of dairy cows in response to restrictions to time at pasture. Six groups of eight Holstein–Friesian cows (470±47kg, 35±9days in milk) were strip-grazed on a perennial ryegrass (Lolium perenne L.) pasture over 21days (2 groups per treatment) for either 4h after each milking (2×4), one period of 8h between milkings (1×8), or 24h excluding milking times (control, CTL). All cows were equipped with HR Tag™ rumination collars which recorded chewing activity and regurgitation of digesta boluses during rumination. Cows in 1×8 reduced daily rumination time by 36% compared with cows in 2×4 and CTL (304, 402 and 423 SED 26.3min, respectively). There were no differences in the average intervals between regurgitation of digesta boluses (48.9±0.96s) and average interval between chewing actions was also similar (0.7±0.02s) between treatments. Treatment affected the diurnal rumination pattern. There was little rumination during the time at pasture for the restricted cows (1×8 and 2×4), whereas the CTL cows ruminated for almost a third of the time between the am and pm milking. In all treatments, cows ruminated the longest during the night. These results suggest grazing dairy cows modulate their time for rumination to compensate for a reduction in available grazing time. This behavioral study contributes to the understanding of changes in rumination behavior and associated effects in grazing dairy cattle in response to hunger.

Improved milk production efficiency in early lactation dairy cattle with dietary addition of a developmental fibrolytic enzyme additive

A 3-part study was conducted to evaluate the effect of a developmental fibrolytic enzyme additive on the digestibility of selected forages and the production performance of early-lactation dairy cows. In part 1, 4 replicate 24-h batch culture in vitro incubations were conducted with alfalfa hay, alfalfa silage, and barley silage as substrates and ruminal fluid as the inoculum. A developmental fibrolytic enzyme additive (AB Vista, Marlborough, UK) was added at 5 doses: 0, 0.5, 1.0, 1.5, and 2.0 μL/g of forage dry matter (DM). After the 24-h incubation, DM, neutral detergent fiber (NDF), and acid detergent fiber (ADF) disappearance were determined. For alfalfa hay, DM, NDF, and ADF disappearance was greater at the highest dosage compared with no enzyme addition. Barley silage NDF and ADF and alfalfa silage NDF disappearance tended to be greater for the highest enzyme dosage compared with no enzyme addition. In part 2, 6 ruminally cannulated, lactating Holstein dairy cows were used to determine in situ degradation of alfalfa and barley silage, with (1.0 mL/kg of silage DM) and without added enzyme. Three cows received a control diet (no enzyme added) and the other 3 received an enzyme-supplemented (1.0 mL/kg of diet DM) diet. Enzyme addition after the 24h in situ incubation did not affect the disappearance of barley silage or alfalfa silage. In part 3, 60 early-lactation Holstein dairy cows were fed 1 of 3 diets for a 10-wk period: (1) control (CTL; no enzyme), (2) low enzyme (CTL treated with 0.5mL of enzyme/kg of diet DM), and (3) high enzyme (CTL treated with 1.0mL of enzyme/kg of diet DM). Adding enzyme to the diet had no effect on milk yield, but dry matter intake was lower for the high enzyme treatment and tended to be lower for the low enzyme treatment compared with CTL. Consequently, milk production efficiency (kg of 3.5% fat-corrected milk/kg of DM intake) linearly increased with increasing enzyme addition. Cows fed the low and high enzyme diets were 5.3 (not statistically significant) and 11.3% more efficient, respectively, compared with CTL cows. This developmental fibrolytic enzyme additive has the potential to increase fiber digestibility of forages, which could lead to greater milk production efficiency for dairy cows in early lactation.

Effect of peripartum dietary energy supplementation of dairy cows on metabolites, liver function and reproductive variables

Multiparous Holstein cows ( n = 58) were used to study the effects of peripartum dietary supplementation on metabolic status, liver function and reproduction variables. Diets for cows were as follows: (a) no supplementation (CTL), (b) prilled fatty acids as 1.9% of DM (PrFA), (c) calcium salts of long chain n-6 fatty acids as 2.24% of DM (CaLFA) or (d) daily topdressing with 769 g of 65% propylene glycol (PGLY). Supplements were fed during the last 21 days before expected calving except for PGLY that continued until 21 days after parturition. Ovarian activity was monitored by transrectal ultrasonography and days to first ovulation were recorded. Liver biopsies were obtained on day 8 and 21 postpartum and analyzed for triglyceride content and mRNA expression of pyruvate carboxylase, cytosolic phosphoenolpyruvate carboxykinase, carnitine palmytoyltransferase 1A, and peroxisome proliferator-activated receptor-α. At 71 days following parturition, stage of ovarian cycles was synchronized and at day15 of the cycle oxytocin was injected i.v., blood samples were obtained at frequent intervals, and analyzed for 13,14 dihydro, 15-keto PGF 2α (PGFM). Milk production and milk components were not different among treatment groups. Cows in PGLY gained body condition score (BCS) prepartum and net energy balance prepartum tended to be greater, but was not different postpartum from other groups. PGLY supplementation increased plasma insulin concentration prepartum, but not during the postpartum period. No significant differences were observed in plasma concentrations of glucose, NEFA, and insulin-like growth factor or hepatic triglyceride content, but all supplements tended to decrease β hydroxybutyrate postpartum compared to CTL cows. Abundance of mRNA of gluconeogenic and lipid oxidation genes was not different among treatment groups. Days to first ovulation and uterine PGF 2α production in response to an oxytocin treatment were not significantly different among treatment groups. Peripartum supplementation did not result in the substantial improvement of metabolic profile in early lactation nor significantly affect days to first ovulation and PGFM response to an oxytocin treatment.

Insulin increases 17 beta-estradiol production by the dominant follicle of the first postpartum follicle wave in dairy cows.

Prolonged anovulation following parturition has a negative impact on fertility in dairy cows. Insulin plays an important role in ovarian function in many species, and is profoundly depressed in dairy cows during early lactation. We hypothesized that hypoinsulinemia during early lactation represents a key indicator of nutritional status, resulting in delayed ovulation. Holstein cows (n = 10) were subjected to either a hyperinsulinemic-euglycemic clamp (INS) or saline infusion (CTL) for 96 h, beginning on day 10 after parturition during the first postpartum follicular wave. Insulin was infused continuously (0.3 microg/kg body weight per h) via a jugular catheter, and euglycemia was maintained by infusion of glucose. Circulating insulin concentrations were elevated 2.6-fold in INS cows compared with CTL cows (0.73 +/- 0.026 vs 0.28 +/- 0.026 ng/ml; P < 0.001). Insulin treatment did not affect (P > 0.05) luteinizing hormone (LH) pulse frequency, pulse amplitude or mean circulating LH. Circulating estradiol was elevated in INS cows (P < 0.01) and circulating testosterone also tended to be higher. The ratio of testosterone to estradiol was not different between treatments for the initial 30 h of infusion, but was significantly reduced thereafter in response to insulin (P < 0.01), suggesting that hyperinsulinemia increased follicular aromatase activity. Insulin treatment also resulted in reduced circulating nonesterified fatty acids, and increased circulating total and free insulin-like growth factor-I concentrations. Insulin infusion increased estradiol secretion by the dominant follicle of the first postpartum follicular wave in dairy cows, and this effect appears not to be mediated through changes in pulsatile LH release.

Insulin restores GH responsiveness during lactation-induced negative energy balance in dairy cattle: effects on expression of IGF-I and GH receptor 1A.

Early lactation in dairy cattle is a period of severe negative energy balance (NEB) characterized by reduced blood glucose and insulin concentrations and elevated blood GH concentrations. The liver is refractory to GH during NEB and this uncoupling of the GH-IGF axis results in diminished plasma concentrations of IGF-I. Our objectives were to examine the effects of insulin administration during the immediate postpartum period on plasma IGF-I and GH concentrations and to examine the hepatic expression of total GH receptors (all GH receptor transcripts), GH receptor 1A (GHR 1A) and IGF-I. In addition, we examined adipose tissue for total GH receptor and IGF-I mRNA levels to establish the effects of chronic hyperinsulinemia on an insulin-responsive peripheral tissue. Holstein cows (n=14) were subjected to either a hyperinsulinemic-euglycemic clamp (insulin; INS) or saline infusion (control; CTL) for 96 h starting on day 10 postpartum. Insulin was infused i.v. (1 micro g/kg body weight per h), blood samples were collected hourly, and euglycemia was maintained by infusion of glucose. Insulin concentrations during the infusions were increased 8-fold in INS compared with CTL cows (2.33+/-0.14 vs 0.27+/-0.14 ng/ml (S.E.M.); P<0.001) while blood glucose concentrations were not different between treatments (45.3+/-2.2 vs 42.5+/-2.2 mg/dl; P>0.1). Plasma IGF-I increased continuously during the insulin infusion, and reached the highest concentrations at the end of the clamp, being almost 4-fold higher in INS compared with CTL cows (117+/-4 vs 30+/-4 ng/ml; P<0.001). Hepatic expression of GHR 1A and IGF-I mRNA was low in CTL cows, but was increased 3.6-fold (P<0.05) and 6.3-fold (P<0.001) respectively in INS cows. By contrast, in adipose tissue the changes in gene expression in response to insulin were reversed with decreases in both total GHR and IGF-I mRNA. The expressions of GHR 1A and IGF-I mRNA in liver tissue were correlated in INS (r=0.86; P<0.05), but not CTL cows (r=0.43; P>0.1). Insulin appears to be a key metabolic signal in coupling the GH-IGF axis, thus orchestrating a marked elevation in circulating IGF-I concentrations.

Effects of supplementation of organic and inorganic combinations of copper, cobalt, manganese, and zinc above nutrient requirement levels on postpartum two-year-old cows.

The objective of this study was to determine whether a combination of Cu, Co, Mn, and Zn in an organic or inorganic form fed at higher than nutrient recommendations for 2-yr-old cows from calving to breeding would affect pregnancy rate, calving date, calf performance, and cow liver and serum mineral concentrations. Crossbred 2-yr-old cows were used after calving in 1994 (n = 127) and 1995 (n = 109). Cows were blocked by calving date to one of three treatments: 1) no supplemental minerals (CTL), 2) organic minerals (ORG), or 3) inorganic minerals (ING). Minerals were fed for the same daily intake for both organic and inorganic treatments: Cu (125 mg), Co (25 mg), Mn (200 mg), and Zn (360 mg). Cows were individually fed a mineral-protein supplement with grass hay from calving (February-March) to before breeding (May 15). Hay intakes were calculated using chromium oxide boluses to determine fecal output. Fecal excretion of minerals was calculated following trace element analysis of feces. Liver biopsies were obtained before calving, after calving (start of supplementation), at the end of supplementation, and in midsummer. Over 2 yr, more cows did not become pregnant (P < .01) in ORG (11/78) and ING (11/78) treatments than in CTL (0/80) treatments. A treatment x year interaction was found for day of conception. Cows in the ORG group conceived later (P < .01) than cows in the ING or CTL groups in 1994. In 1995, there was no difference (P > .10) in day of conception among groups. Liver Zn and Mn concentrations were not different (P > .10) and Cu concentrations increased (P < .01) for the ORG and ING groups. Cows in the ORG and ING groups had higher (P < .01) concentrations of Cu, Mn, and Zn in the feces than the CTL cows. Trace elements in the feces did not differ for ORG and ING groups. Results indicate that combinations of Cu, Co, Mn, and Zn fed at higher levels than are required reduced reproductive performance.