Short communication: Feeding a rumen-degradable amino acid affects plasma thyroxine and triiodothyronine concentrations.

Our previous published work demonstrated that feeding rumen-degradable valine to late-lactation dairy cows increased milk production compared with control-fed cows, with a response that was equivalent to that of recombinant bovine somatotropin. To further elucidate the response mechanism, we hypothesized that thyroxine (T4) and triiodothyronine (T3), which are important regulators of basal metabolism, may be involved. Previous short-term studies have demonstrated increased milk production when feeding iodinated casein. Eight multiparous Holstein dairy cows (255 ± 26.4 d in milk) were blocked by milk yield (34.1 ± 8.25 kg/d) and randomly assigned to 1 of 4 treatments using a replicated 4 × 4 Latin square design with 21-d periods (7 d for dietary adaptation and 14 d for data collection). Treatments were control (CON), a single injection of recombinant bovine somatotropin (rbST), and synthetic valine fed at 40 (V40) or 80 (V80) g/cow per day. Cows were fed a total mixed ration with a distillers dried grains carrier fed at 113.4 g/d containing no valine or added valine. Blood samples were collected twice during wk 2 and 3 of each period for T3 and T4 analysis. Concentrations of T4 (3.28, 3.90, 3.98, and 3.87 µg/dL for CON, rbST, V40, and V80, respectively) were increased for cows receiving rbST, V40, and V80 compared with CON cows. Concentrations of T3 (125.7, 140.7, 148.8, and 139.7 ng/dL) were increased for cows receiving rbST, V40, and V80 compared with CON cows, with cows receiving V40 having the highest T3 concentrations. In conclusion, feeding rumen-degradable valine increases plasma T4 and T3 concentrations, which would explain the mechanism leading to increased milk production.

Effects of treatment of preweaning dairy calves with recombinant bovine somatotropin on immune responses and somatotropic axis.

Weaning may be associated with negative energy balance and body weight loss when calves are still immunologically immature, predisposing them to infectious diseases. The aim of the present experiment was to investigate the effects of treatment of preweaning dairy calves with recombinant bovine somatotropin (rbST) on the somatotropic axis, selected immune parameters, and hematology of calves around weaning. Thirty-six Holstein female calves were randomly assigned to receive 1.5 to 1.8 mg of rbST (Posilac, Elanco Animal Health, Greenfield, IN) per kilogram of body weight or to receive injections of saline (saline solution 0.9%, Valley Vet Supply, Marysville, KS) every 7 d from 21 to 63 d of life. Calves were fed milk replacer ad libitum from birth to 38 d of age (d -11), when progressive weaning started, and calves were weaned at 49 d of age (d 0). Calves were weighed at birth and weekly from 21 to 63 d of age, when wither height also was measured. Calves were vaccinated with 0.5 mg of ovalbumin on study d -28 and -7. Blood samples were collected on d -28, -25, -21, -11, 0, 3, 7, and 14. Polymorphonuclear leukocytes were isolated and challenged ex vivo with Escherichia coli to determine phagocytosis and oxidative burst capacity. Additionally, expression of cluster of differentiation (CD)62L and CD18 by granulocyte, lymphocyte, and CD14+ monocyte were determined. Blood samples were also used to determine hematological parameters and concentrations of growth hormone, insulin-like growth factor-1, insulin, glucose, fatty acids, ß-hydroxybutyrate, haptoglobin, and anti-ovalbumin IgG. Calves treated with rbST had greater concentrations of growth hormone and insulin-like growth factor-1 from d -25 to 14 than control calves, whereas insulin, fatty acid, and ß-hydroxybutyrate concentrations did not differ. On d -11, glucose concentration was greater for rbST-treated calves. Treatment did not affect polymorphonuclear lymphocyte phagocytosis and oxidative burst, but intensity of expression of CD62L and CD18 by granulocytes tended to be increased by rbST treatment. Treatment did not affect the concentration of anti-ovalbumin IgG in serum. Haptoglobin concentration was reduced in rbST treated calves on d 3 and we noted a tendency for hematocrit to be lower in rbST-treated calves. Treatment did not affect body weight, wither height, and average daily gain, despite the fact that rbST-treated calves had lower daily milk replacer intake. The relatively minor improvements in immune responses resulting from rbST treatment of weaning calves may not be sufficient to reduce the incidence of infectious diseases.

Effects of treatment of periparturient dairy cows with recombinant bovine somatotropin on health and productive and reproductive parameters.

The objectives of the current experiment were to evaluate the effects of treating periparturient dairy cows with recombinant bovine somatotropin (rbST) on incidence of postpartum diseases and performance. Holstein (HO) and Jersey (JS) cows from 2 herds were enrolled in the experiment at 253 ± 3 d of gestation and assigned to the control (n = 432) and rbST125 (n = 437) treatments. Cows in the rbST125 treatment received 125 mg of rbST, weekly, from -21 to 21 d relative to calving. Blood sampled weekly, from -21 to 21 d relative to calving, from a subsample of cows was used to determine the concentrations of growth hormone (GH, HO = 106) and insulin-like growth factor 1 (IGF-1, HO = 147 and JS = 49). Cows were scored for body condition (BCS) at enrollment and at 1 ± 3, 30 ± 3, and 60 ± 3 d in milk (DIM). Cows were milked thrice daily and energy-corrected milk (ECM) yield was recorded for the first 30 DIM. Treatment of cows with rbST resulted in greater concentrations of GH during the prepartum (log10 back-transformed concentrations of GH: HO-control = 7.83 and HO-rbST125 = 10.36 ng/mL) and postpartum (log10 back-transformed concentrations of GH: HO-control = 10.45 and HO-rbST125 = 18.47 ng/mL) periods. Similarly, IGF-1 concentrations were higher during the prepartum (HO-control = 115.1 ± 4.9, HO-rbST125 = 137.7 ± 4.7, JS-control = 120.2 ± 8.3, JS-rbST125 = 167.1 ± 8.1 ng/mL) and postpartum (HO-control = 61.3 ± 4.0, HO-rbST125 = 75.2 ± 3.8, JS-control = 35.5 ± 6.9, JS-rbST125 = 54.6 ± 6.9 ng/mL) periods for rbST-treated cows. During the prepartum period, BCS was not affected by treatment, but during the postpartum period, BCS was reduced for rbST-treated cows (HO-control = 3.00 ± 0.03, HO-rbST125 = 2.90 ± 0.03, JS-control = 2.64 ± 0.02, JS-rbST125 = 2.61 ± 0.02). Cows from the rbST125 treatment tended to have lower incidence of retained fetal membranes (HO-control = 14.3, HO-rbST125 = 6.1, JS-control = 1.5, JS-rbST125 = 1.2%) and had reduced incidence of metritis (HO-control = 26.2, HO-rbST125 = 16.6, JS-control = 19.9, JS-rbST125 = 13.3%) compared with control cows. Ketosis incidence tended to be higher for rbST125 cows (HO-control = 9.4, HO-rbST125 = 11.3, JS-control = 8.5, JS-rbST125 = 13.4%) compared with control cows. The interaction between treatment and herd tended to affect yield of ECM during the first 30 DIM because HO cows treated with rbST during the periparturient period had greater yield than control HO cows (HO-control = 35.5 ± 1.0 vs. HO-rbST125 = 39.4 ± 1.0 kg/d), but treatment with rbST did not affect yield of ECM of JS cows (JS-control = 26.7 ± 0.6 vs. JS-rbST125 = 27.8 ± 0.6 kg/d). Treatment of periparturient dairy cows with 125 mg of rbST decreased the incidence of uterine disorders in HO and JS cows and increased yield of ECM during the first 30 DIM among HO cows, despite slightly increasing the incidence of ketosis.

Effects of cinnamaldehyde or monensin on performance of weaned Holstein dairy heifers.

The objective of this 70-d study was to determine the effects of the essential oil cinnamaldehyde compared with the ionophore monensin on performance of weaned Holstein dairy heifers. Eighty-four Holstein dairy heifers (91 ± 3.33 d of age; 109 ± 7.55 kg) were housed in a naturally ventilated curtain sidewall, straw-bedded barn in 12 pens with 7 heifers/pen (3.98 m2/head). Heifers were randomly assigned to 1 of 4 treatments in a completely randomized design: (1) control (CON; carrier, 908 g of ground corn), (2) monensin sodium [MON; 1 mg/kg of body weight (BW) + carrier], (3) cinnamaldehyde (CIN1; 1 mg/kg of BW + carrier), or (4) cinnamaldehyde (CIN2; 2 mg/kg of BW + carrier). The treatments were hand-mixed into a 20% crude protein (CP) whole shelled corn and protein pellet mix fed at 2.21 kg/heifer daily. Heifers had access to free-choice hay and water daily. Initial BW and hip heights were taken at the start of the study and every other week thereafter until calves reached 23 wk of age. Blood samples were also taken on each weigh day to determine plasma urea nitrogen, glucose, and insulin-like growth factor-1 concentrations. Fecal samples were taken from the same 3 heifers/pen initially and then at d 28, 56, and 70 of the study for coccidia counts. Cinnamaldehyde had no performance effects on growth, hay intake, hip height, or blood metabolites compared with MON or CON. Average daily gains were 0.98, 0.99, 1.01, and 1.03 kg/d, and average hay intakes per pen were 17.08, 16.34, 18.11, and 17.60 kg/d for CON, MON, CIN1, and CIN2, respectively. Fecal samples by pens indicated the presence of viable coccidia, but the counts were low and not consistent across heifers within each pen. No benefits were associated with supplementing cinnamaldehyde or monensin into grain mixes for weaned heifers.

Growth performance of calves fed microbially enhanced soy protein in pelleted starters.

Our objective was to determine effects of feeding calves pelleted starters with microbially enhanced (fungi-treated) soy protein (MSP) in replacement of soybean meal (SBM) with different milk replacers (MR). Thirty-six Holstein calves (2 d old; 24 females, 12 males) in individual hutches were used in a 12-wk randomized complete block design study. Treatments were (1) MSP pellets with MR formulated for accelerated growth (28% crude protein, 18% fat; MSPA), (2) SBM pellets with MR formulated for accelerated growth (SBMA), and (3) MSP pellets with conventional MR (20% crude protein, 20% fat; MSPC). Pellets were similar except for 23% MSP or 23% SBM (dry matter basis). Pellets and water were fed ad libitum throughout the study. Feeding rates of MR on a dry matter basis were 0.37kg twice daily during wk 1, 0.45kg twice daily during wk 2 to 5, and 0.45kg once daily during wk 6. Intakes were recorded daily. Body weights, frame size measurements, and jugular blood samples were collected 2 d every 2 wk at 3 h after the morning feeding. Fecal grab samples were collected 5 times per d for 3 d during wk 12 and then composited by calf for analysis of apparent total-tract digestibility of nutrients using acid detergent insoluble ash as an internal marker. Total and starter pellet dry matter intake were greatest for calves fed SBMA and least for MSPC. Calves had similar average daily gain among treatments, but there was a treatment by week interaction and during the last few weeks of the study calves on MSPC had less body weight compared with MSPA or SBMA. Gain-to-feed ratio was similar among treatments; however, there was a treatment by week interaction. Serum glucose was similar among treatments. Plasma urea nitrogen was greatest for calves fed MSPA and least for MSPC. Plasma concentrations of IGF-1 were greatest for calves fed SBMA. Plasma concentrations of triglycerides were greatest for calves fed MSPC. Plasma concentrations of ß-hydroxybutyrate had a treatment by time interaction. Treatments had similar total-tract dry matter digestibility, but calves fed MSPC had greater crude protein digestibility than SBMA, with MSPA similar to both. Results demonstrated calves fed pelleted starters with MSP had maintained growth performance with less starter intake compared with SBM.

Evaluation of camelina meal as a feedstuff for growing dairy heifers.

The objective of this research was to compare the growth performance, metabolic profile, and nutrient utilization of dairy heifers fed camelina meal (CAM), linseed meal (LIN), or distillers dried grains with solubles (DDGS). A 12-wk randomized complete block design study was conducted using 33 Holstein and 9 Brown Swiss heifers (144.8±22d of age) with 3 treatments. Treatments were 10% of the diet as CAM, LIN, or DDGS (dry matter basis). All diets contained 60% grass hay and 40% concentrate mix. Diets were balanced with corn and soybean meal to be isonitrogenous and comparable in energy content. Diets were individually limit-fed to 2.65% of body weight using a Calan gate feeding system. Frame sizes, body weights, and body condition scores were measured on 2 consecutive days during wk 0, 2, 4, 6, 8, 10, and 12. Jugular blood samples were taken at the beginning of the study and then every 4wk throughout at 3.5h postfeeding for analysis of blood metabolites and metabolic hormones. Rumen fluid samples were taken at the same time as blood sampling via an esophageal tube during wk 8 and 12. Over the duration of the study, dry matter intake and average daily gain were similar among treatments. Body weights tended to be less for heifers fed CAM and greatest for LIN. Gain to feed was similar for the CAM and DDGS and greatest for the LIN. Overall, most frame measurements were similar among treatments. Body length had a tendency to be greater for CAM compared with LIN with DDGS similar to both. Body condition scores were greater for CAM and DDGS compared with LIN. Rumen total volatile fatty acids, acetate:propionate, and pH were similar among treatments. Butyrate was less in the CAM treatment, intermediate for LIN, and greatest for DDGS. Rumen ammonia was less in DDGS compared with CAM and LIN, which were similar. Blood concentrations of glucose, triglycerides, plasma urea N, and cholesterol were similar among treatments. Metabolic hormones, including insulin-like growth factor-1 and thyroid hormones triiodothyronine and free thyroxine, were similar among treatments. Heifers fed CAM had lesser insulin concentration than other treatments. Total-tract digestion of nutrients were similar among treatments, but CAM tended to have greater digestion of organic matter compared with LIN, with DDGS similar to both. Feeding CAM maintained growth performance compared with DDGS and LIN. This study demonstrates that CAM can be used as a protein source for growing dairy heifers.

Feeding fat from distillers dried grains with solubles to dairy heifers: II. Effects on metabolic profile.

The objective of this study was to determine if increased dietary fat from dried distillers grains with solubles (DDGS) in diets of growing heifers affected metabolic profile, plasma fatty acid profile, and reproductive maturation. Thirty-three Holstein heifers (133±18 d of age) were used in a 24-wk randomized complete block design with 3 treatment diets. Treatment diets were (1) control (CON) containing ground corn (15.9% of DM) and soybean products (17.9%), (2) low-fat (LFDG) containing low-fat DDGS (21.9%) and ground corn (11.9%), or (3) high-fat (HFDG) with traditional DDGS (33.8%). Diets were isonitrogenous and isocaloric, but the HFDG diet was formulated to contain 4.8% fat compared with 2.8% in the CON and LFDG diets. All 3 diets were limit-fed to 2.45% of body weight on a dry matter basis, and resulted in a mean average daily gain of 0.96kg/d across treatments. Every 4wk, jugular blood was collected for analysis of metabolites and metabolic hormones. During wk20 of the feeding period, blood samples were collected for analysis of plasma fatty acid profiles. When heifers weighed between 200 and 300kg of body weight, coccygeal blood samples were taken twice weekly for analysis of progesterone to determine if puberty had been reached. Plasma concentrations of nonesterified fatty acids were similar among treatments and consistent over the duration of the study. Plasma concentrations of ß-hydroxybutyrate, insulin, insulin-like growth factor-1, and leptin were similar among heifers fed each treatment diet, but increased over the duration of the feeding period. Serum concentrations of glucose tended to be less in heifers fed HFDG compared with heifers fed the CON diet. Glucose concentrations fluctuated throughout the feeding period, but no treatment by time interactions were noted. Plasma urea N concentrations were less in heifers fed LFDG compared with heifers fed HFDG and CON diets. The concentrations of plasma urea N increased over the duration of the feeding period, with no treatment by week interaction. Total plasma cholesterol was greater in heifers fed HFDG compared with the CON and LFDG diets, and a significant week effect and a week by treatment interaction were observed. Fatty acid profiles also differed among treatments based on the supply of fatty acids from the diet. Progesterone analysis indicated that heifers fed HFDG tended to be pubertal at a younger age than heifers on CON. These results demonstrate that dietary fat from DDGS can be used in high-plane of nutrition rations for growing heifers and maintain metabolic energy status compared with starch from corn, but alters the concentrations of different blood lipids.

Plasma ghrelin concentrations of beef cattle consuming a similar amount of dietary energy supplied by different ingredients.

Previous research demonstrated increased plasma ghrelin concentrations in beef cattle when intake of a high-grain diet was restricted. Two experiments were conducted to determine whether differences in DMI influenced plasma ghrelin concentrations when energy intake was similar but cattle were in either an anabolic or a catabolic state. In Exp. 1, five steers (BW = 592.6 +/- 9.3 kg) were offered dietary treatments of 1) 50:50 hay:concentrate (HY) to meet the NE(m) requirement and were supplied an additional 3.4 Mcal of NE(g) daily, 2) or a diet composed of 10:90 hay:concentrate but were limit-fed to achieve an energy intake similar to that of the HY steers (LFC). The LFC treatment met the NE(m) requirement of each steer and supplied 3.6 Mcal of NE(g) daily. The experiment was conducted as a crossover design composed of 2 21-d periods. In the first period, 2 steers were assigned to the HY treatment and 3 steers were assigned to the LFC treatment. On d 21 after initiation of the dietary treatment, serial blood samples were collected via indwelling jugular catheter, using periods of frequent sampling in which samples were collected at 15-min intervals. The periods of frequent sampling were spread throughout the beginning, middle, and end of the 12-h feeding interval. After the first period, steers were weighed, dietary treatments were switched between steer groups, and intake amounts were recalculated on the basis of the first-period ending BW. The second-period adaptation and sampling were repeated as described for the first period. Plasma samples were assayed for ghrelin, insulin, GH, and NEFA concentrations. Experiment 2 was conducted using the same methodology as Exp. 1, except that steers were in a catabolic state. Five steers (BW = 718.3 +/- 12.8 kg) were offered the HY or LFC diet at an amount that would supply 80% of the NE(m) required to maintain BW. For Exp. 1, energy intake was sufficient to result in similar (P = 0.14) BW gains between treatment groups. Experiment 2 energy intake resulted in a loss of BW that was similar (P = 0.66) between treatment groups. In both experiments, the decreased energy density of the HY diet resulted in greater (P < or = 0.001) DMI for HY steers compared with LFC steers. Regardless of catabolic or anabolic state, plasma ghrelin, GH, and insulin were similar (P > or = 0.44) when energy intakes were similar despite differences in DMI between HY and LFC steers. Plasma NEFA concentrations were similar (P > or = 0.45) between treatment groups in an anabolic state but tended to differ (P = 0.09) as a result of treatment for cattle in the catabolic state. These data are consistent with the hypothesis that quantity of DMI does not influence plasma ghrelin concentrations of steers when energy intake is similar.

Prolonged, moderate nutrient restriction in beef cattle results in persistently elevated circulating ghrelin concentrations.

Four ruminally cannulated steers (BW 581 +/- 12.8 kg) were used in a crossover design to determine the effects of prolonged, moderate nutrient restriction on plasma ghrelin concentrations and to establish the relationship of plasma ghrelin concentrations with hormones and metabolites indicative of nutritional status and end products of rumen fermentation. A high-grain diet was offered at 240% of the intake needed for BW maintenance (2.4xM) or 80% of the intake needed for BW maintenance (0.8xM). To standardize, all steers were acclimated to 2.4xM before initiation of the treatment periods. During period 1, 2 steers continued at 2.4xM, whereas intake for the remaining 2 steers was restricted to 0.8xM. On d 7, 14, and 21 after initiation of the restriction, serial blood samples were collected at 15-min intervals via indwelling jugular catheter and were assayed for ghrelin, GH, NEFA, insulin, and glucose concentrations. Rumen fluid was collected at hourly intervals for evaluation of pH and VFA concentrations. After period 1, steers were weighed, the treatments were switched between steer groups, and the intake amounts were recalculated. Intake of 2.4xM was established for previously restricted cattle, and period 2 was then conducted as described for period 1. Data were analyzed statistically as repeated measures in time, and stepwise regression was used to define the relationship of plasma ghrelin with hormones, metabolites, and end products of rumen fermentation. Throughout the 21-d treatment period, plasma ghrelin concentrations were elevated (P

Circulating ghrelin concentrations fluctuate relative to nutritional status and influence feeding behavior in cattle.

The objective of these experiments was to establish the relationship of plasma ghrelin concentrations with feed intake and hormones indicative of nutritional state of cattle. In Exp.1, 4 steers (BW 450 +/- 14.3 kg) were used in a crossover design to compare plasma ghrelin concentrations of feed-deprived steers with those of steers allowed to consume feed and to establish the relationship of plasma ghrelin concentrations with those of GH, insulin (INS), glucose (GLU), and NEFA. After adaptation to a once-daily feed offering (0800), 2 steers continued the once-daily feeding schedule (FED), whereas feed was withheld from the other 2 steers (FAST). Serial blood samples were collected via indwelling jugular catheter from times equivalent to 22 h through 48 h of feed deprivation. Average plasma ghrelin concentrations were greater (P < 0.001) in FAST compared with FED (690 and 123 +/- 6.5 pg/mL) steers. Average plasma ghrelin concentrations for FED steers prefeeding were elevated (P < 0.001) when compared with those postfeeding (174 and 102 +/- 4.2 pg/mL, respectively). Average plasma GH concentration was elevated (P < 0.05) for FAST steers compared with FED steers. Plasma GLU concentrations were not different; however, for FAST steers, NEFA concentrations were elevated (P < 0.001) and INS concentrations were decreased (P < 0.001). In Exp. 2, 4 steers (BW 416 +/- 17.2 kg) were used in a crossover design to determine the effects of i.v. injection of bovine ghrelin (bGR) on plasma GH, INS, GLU, and NEFA concentrations; length of time spent eating; and DMI. Steers were offered feed once daily (0800). Serial blood samples were collected from steers via indwelling jugular catheter. Saline or bGR was injected via jugular catheter at 1200 and 1400. A dosage of 0.08 microg/kg of BW bGR was used to achieve a plasma ghrelin concentration similar to the physiological concentration measured in a FAST steer in Exp. 1 (1,000 pg/mL). Injection of bGR resulted in elevated (P < 0.005) plasma GH concentrations after the 1200 but not the 1400 injection. Plasma INS, GLU, and NEFA concentrations were not affected by bGR injection. For the combined 1-h periods postinjection, length of time spent eating was greater (P = 0.02) and DMI tended to be increased (P = 0.06) for bGR steers. These data are consistent with the hypothesis that ghrelin serves as a metabolic signal for feed intake or energy balance in ruminants.

Effects of decreased estradiol-17beta on the serum and anterior pituitary IGF-I system in pigs.

To further delineate the role of estradiol in the IGF system an experiment was conducted to determine the dosage of the aromatase inhibitor, anastrozole, needed to decreases serum concentrations of estradiol-17beta (E2) in maturing boars. A second experiment was conducted to determine if administration of anastrozole to growing boars decreased serum concentrations of E2 and affected components of the serum and anterior pituitary gland (AP) IGF system vs untreated boars and barrows. In Experiment 1, 12 crossbred boars (292 days, 158 kg) were administered either 0, 1 or 10 mg/day anastrozole (n = 4/group) beginning on day 1. Blood samples were collected every 7-14 days. Mean serum concentrations of E2 were decreased (P < 0.05) in the 10 mg group vs the 0 and 1 mg groups by day 36; however, no difference (P > 0.05) existed between the 0 and 1 mg groups. In Experiment 2, 24 crossbred boars and 12 barrows (101 days, 44 kg) were stratified by litter to one of three treatment groups (n = 12): boars administered 10 mg/day anastrozole, boars administered 0 mg/day, and barrows administered 0 mg/day. Blood samples were collected and pigs were weighed on day 0 and every 14 days thereafter, then killed on day 84 when blood and APs were collected. The 10 mg/day pigs were fed the anastrozole-amended diet beginning on day 1. Mean serum concentrations of E2 did not differ (P > 0.05) between the 10 mg/day pigs and 0 mg/day pigs on day 0; however, on day 15 through to 84 mean serum concentrations of E2 were greater (P < 0.05) in 0 mg/day pigs than in the 10 mg/day pigs. Mean percentage increase in serum concentrations of IGF-I was greater (P < 0.05) in untreated boars than anastrozole-treated boars and barrows from day 58 through to 84. Mean percentage of basal IGF-I increased (P < 0.05) from day 29 through to 84 in untreated boars. Mean relative amounts of AP IGF-binding protein (IGFBP)-2 and -5 were less (P < 0.01) in 10 mg/day pigs than in the 0 mg/day pigs, but each was greater (P < 0.01) than in barrows administered 0 mg/day. These results indicate anastrozole administered at a dosage of 10 mg/day suppresses serum concentrations of E2 in pigs. Administration of anastrozole to boars reduced the percentage increase in serum concentrations of IGF-I and relative amounts of AP IGFBP-2 and -5. These data further support a role for E2 in regulating components of the IGF system in pigs.

Effects of high-protein/low-carbohydrate swine diets during the final finishing phase on pork muscle quality.

The aim of this study was to lower the glycogen stores in pork muscle in order to improve pork muscle quality by feeding an ultra-high-protein/low-carbohydrate (HIPRO) diet. Forty-eight barrows (average live weight = 92 kg) were assigned across five treatments and two replications (four or five pigs per treatment by replication combination). All barrows were fed a control diet (13.1% CP) until their assigned treatment began. A treatment was the number of days the barrows were fed the HIPRO diet prior to slaughter (0, 2, 4, 7, or 14 d). The HIPRO diet (35.9% CP) was 97% extruded soybeans. Daily feed intake and weekly live weights were recorded for all barrows. At-death blood glucose levels were determined. Muscle pH, temperature, and electrical impedance were measured in the longissmus lumborum and semimembranosus muscles at 45 min, 3 h, and 24 h postmortem. Glycolytic potential; Minolta L*a*b* values; visual scores for color, firmness, and marbling; water-holding capacity traits (drip loss, purge loss, and cooking loss); and Warner-Bratzler shear force values were determined in the longissmus thoracis et lumborum. Weight gain per day decreased the longer the pigs were fed the HIPRO diet (P < 0.05). Daily feed intake decreased during the 1st wk on the HIPRO diet but returned to near-control levels during the 2nd wk, which when coupled with the continued decreases in daily gain resulted in substantial decreases in feed efficiency during the 2nd wk on the HIPRO diet (P < 0.05). Blood glucose levels and glycolytic potentials were not lowered by feeding the HIPRO diet (P > 0.05); therefore, no differences in rate of pH decline or ultimate pH among dietary treatments were found (P > 0.05). Likewise, there were no differences among dietary treatments in any of the measured meat quality attributes (P > 0.05). Feeding barrows the HIPRO diet for a time period prior to slaughter decreased feed intake, rate of gain, and feed efficiency and was not effective at lowering glycolytic potential or improving pork muscle quality.

Administration of estradiol-17beta increases anterior pituitary IGF-I and relative amounts of serum and anterior pituitary IGF-binding proteins in barrows.

Two experiments were conducted to determine whether 1) administration of estradiol-173 (E2) implants to barrows elevates serum concentrations of E2 to levels similar to those of adult boars and subsequently affects the anterior pituitary gland IGF system and 2) administration of E2 to barrows increases serum concentrations of E2, serum and anterior pituitary concentrations of IGF-I, and relative amounts of serum and anterior pituitary IGF-binding proteins (IGFBP), vs boars and unimplanted barrows. In Exp. 1, 20 crossbred barrows (150 +/- 6 d, 103 +/- 8 kg) were administered varying number of E2 implants (0, 2, 3, 4; n = 5/group) on d 1. Blood samples were collected weekly by jugular venipuncture, beginning on d 1. Pigs were killed on d 36 when a blood sample and anterior pituitary were collected. Serum concentrations of E2 were increased (P < 0.05) in pigs with 2,3, and 4 implants vs 0 implants, but no difference (P > 0.05) was detected in serum concentrations of E2 among pigs with 2, 3, and 4 implants. Orthogonal contrasts identified that three or four E2 implants were necessary to increase serum concentrations of E2 to that similar to boars. Serum and anterior pituitary concentrations of IGF-I were increased (P < 0.05) in pigs with 2, 3, and 4 implants vs 0 implants. Relative amounts of anterior pituitary IGFBP-2 and - 5 increased (P < 0.05) in response to administration of E2. In Exp. 2, three treatment groups were randomly allotted by litter; boars (n = 11), E2-implanted barrows (n = 9), and unimplanted barrows (n = 12). A blood sample was taken from all pigs on d 1 and every 14 d thereafter. Implanted pigs received four implants on d 1. Pigs were killed on d 91, when a blood sample and anterior pituitary were collected. Mean serum concentrations of E2 were greater (P < 0.05) in implanted pigs vs boars. Mean serum concentrations of IGF-I (ng/mL) were greater (P < 0.05) in boars (238.7 +/- 6.8) than in implanted barrows (170.2 +/- 8.9) and unimplanted (150.4 +/- 6.7) pigs and tended to be greater (P = 0.08) in implanted vs unimplanted pigs. Mean anterior pituitary concentrations of IGF-I (ng/mg tissue) were greater (P < 0.05) in implanted (773.6 +/- 57.0) pigs than boars (251.9 +/- 51.6) and unimplanted (185.6 +/- 49.4) pigs. Relative amounts of serum IGFBP-2 were greater (P < 0.05) in implanted pigs vs boars. Relative amounts of anterior pituitary IGFBP-2 and -5 were greater (P < 0.05) in boars than in implanted and unimplanted pigs. These data suggest that E2 may influence components of the porcine IGF system in the serum and anterior pituitary. Other gonadal factors present in boars may additionally affect the serum and anterior pituitary IGF system.

Antagonism of central vasopressin receptors blocks hypoglycemic stress induced inhibition of luteinizing hormone release in male rhesus macaques.

The first objective of this study was to investigate whether the inhibitory effect of insulin-induced hypoglycemia (IIH) on luteinizing hormone (LH) secretion was the same in unrestrained adult male rhesus macaques as has been previously reported in restrained female macaques. Since IIH did inhibit pulsatile LH secretion in adult male macaques, and some previous studies have implicated arginine vasopressin (AVP) as a central mediator of this inhibition, the second objective was to investigate whether antagonism of AVP action could reverse the IIH-induced inhibition of LH release in males. Ten adult male rhesus macaques (Macaca mulatta) were studied during 15-h periods (07.00-22.00 h), with blood samples collected every 15-min. There were three experimental groups; controls (n = 5), IIH (n = 6) and IIH plus vasopressin antagonist (AVPa; n = 6). During the hypoglycemia studies, the first 5 h served as a control for that occasion and an insulin bolus of 1 U/kg was administered intravenously at 12.00 h. During the IIH plus AVPa, the vasopressin antagonist was infused intravenously from 12.00 h to 17.00 h. LH and testosterone decreased progressively after the insulin bolus in the IIH group reaching a minimum value at 4 h after the infusion. However, compared to the preinfusion levels, secretion of LH and testosterone was not suppressed by hypoglycemia in the group treated with the AVP antagonist. The present study shows that in male macaques not subjected to the psychological stress of restraint, IIH suppresses LH and testosterone secretion. This inhibition of LH release can be blocked in some animals by antagonism of central vasopressin receptors, suggesting that vasopressin is involved in the suppression of gonadotropin releasing hormone/LH release induced by hypoglycemia.

The effect of insulin-like growth factor analogs on turkey satellite cell and embryonic myoblast proliferation.

The effects of several human and chicken insulin-like growth factor (IGF) analogs on turkey satellite cell and embryonic myoblast proliferation were examined in serum-free medium. Similar rates of proliferation were observed when human or chicken IGF-I or IGF-II (13.1 nM) was administered to satellite cells. The biopotency of two analogs, which were modified to prevent interaction with IGF-binding proteins, was also examined. Human Des(1-6)IGF-II was equipotent to native human and chicken IGF-II. However, the chicken LR3 IGF-I analog was significantly less active toward satellite cells and embryonic myoblasts compared with chicken IGF-I. Human [Leu27] IGF-II, an analog designed to have reduced affinity to the IGF Type I receptor but unaltered binding to IGF-binding proteins, had a diminished effect on cell proliferation. Examination of IGF receptor binding characteristics revealed that chicken LR3 IGF-I had reduced ability to compete with [125I]hIGF-I for binding to satellite cells or embryonic myoblasts compared with chicken IGF-I. The observed biological responses to IGF suggest that IGF-binding proteins have little effect on Type I IGF receptor action in these cell types in serum-free medium. The results also suggest that alterations of the IGF molecule to prevent interaction with binding proteins may also alter receptor binding affinity.

Serum concentrations of IGF-I, estradiol-17beta, testosterone, and relative amounts of IGF binding proteins (IGFBP) in growing boars, barrows, and gilts.

The purpose of this research was to determine whether serum concentrations of steroids, IGF-I, and relative amounts of serum IGF-binding proteins (IGFBP) differ in growing boars (n = 11), barrows (n = 11), and gilts (n = 12) from 70 to 140 d of age. Pigs of similar age and weight were housed in pens of three or four and given ad libitum access to a 17% CP corn-soy diet and water. Pigs were weighed and blood samples were collected every 14 d beginning at 70 d of age. Serum concentrations of IGF-I and steroids were determined by RIA and relative amounts of IGFBP were determined by ligand blot analysis. By 84 d of age and continuing through 140 d of age, mean serum concentrations of IGF-I were greater (P < .05) in boars than in barrows or gilts. Relative amounts of 46-kDa IGFBP3 and 28-kDa IGFBP-4 were similar (P > .05) among pigs at 70 d of age; however, boars and barrows had greater (P < .05) relative amounts of 24-kDa IGFBP-4 and 41-kDa IGFBP-3 than gilts. Relative amounts of IGFBP-2 were greater (P < .01) in barrows than in gilts or boars at 70 d of age. From 84 d of age through 140 d of age, relative amounts of both forms of IGFBP-3 and the 28-kDa IGFBP-4 were greater (P < .05) in boars than in gilts or barrows. Relative amounts of IGFBP2 were greater (P < .05) in barrows than in gilts or boars at 98 d of age, but by 140 d of age relative amounts were greater (P < .05) in boars and barrows than in gilts. Mean serum concentrations of estradiol-17beta were similar (P > .05) between gilts and boars at 70 d of age, but by 98 d of age, and continuing through 140 d of age, mean serum concentrations of estradiol-17beta were greater (P < .05) in boars than in gilts. Mean serum concentrations of testosterone in boars increased (P < .05) with increasing age and were greatest at 128 and 140 d of age. Serum concentrations of testosterone were negatively correlated (P < .01) with relative amounts of serum IGFBP-2 but positively correlated (P < .01) with serum concentrations of IGF-I and estradiol-17beta. Serum concentrations of estradiol-17beta were positively correlated (P < .01) with serum concentrations of IGF-I in boars. Changes in serum concentrations of IGF-I and relative amounts of IGFBP resulting from changes in serum concentrations of estradiol-17beta and testosterone may contribute to growth differences observed among sexes.

Serum concentrations of melatonin during scotophase and photophase in 3, 4, 5 and 6 months old gilts and barrows.

One-hundred-twenty prepubertal crossbred gilts (Hampshire x Duroc) x (Yorkshire x Landrace) were removed from the nursery at 68.7+/-0.4 days of age and 23.6+/-0.9 kg body weight and relocated to a conventional grower-finisher unit. In addition, 60 barrows of similar genetics were relocated from the nursery at 71.0+/-0.5 days of age and 27.4+/-0.5 kg body weight to the same building. Twelve mature anestrous ewes that weighed 77.0+/-2.4 kg were assigned randomly to one of four pens of equal dimensions among the pens containing pigs. Ewes were included in this study to serve as positive controls since their secretory profiles of melatonin are well characterized. All pigs were bled by jugular venipuncture at approximately 3, 4, 5 and 6 months of age. At each age in the pigs and the mature ewes, a single sample was obtained during photophase and scotophase. Illumination intensity during the period of incandescent lighting averaged 220 1x. Blood collection was initiated approximately 4 h after sunrise and 3.5-4 h after sunset. The proportion of animals that exhibited a nocturnal rise in melatonin (MEL) was similar (P > 0.05) between gilts and barrows, but was higher (P < 0.002) in ewes than in pigs at each age examined. A greater proportion (P = 0.007) of 3 month old barrows had a nocturnal rise of MEL than any other age of barrow. Similarly, there was a tendency (P = 0.06) for more 3 month old gilts to exhibit a nocturnal increase in serum MEL than 4, 5 or 6 month old gilts.

Insulin-like growth factor-I, insulin-like growth factor-binding proteins, and gonadotropins in the hypothalamic-pituitary axis and serum of nutrient-restricted ewes.

Body condition scores (BCS) of ovariectomized estradiol-treated ewes were controlled to examine effects of suboptimum BCS on insulin-like growth factor (IGF)-I, IGF-binding proteins (IGFBPs), and LH in the anterior pituitary gland, hypophyseal stalk-median eminence (SME), and circulation. Serum LH increased in ewes with BCS (1 = emaciated, 9 = obese) > 3 (HIGH-BCS), but not in ewes with BCS

Regulation of ovine GnRH receptor gene expression by progesterone and oestradiol.

The objective of this study was to determine whether progesterone prevents the stimulatory effects of oestradiol on GnRH receptor gene expression. In Expt 1, ewes were treated during the luteal phase (days 10-12 of the oestrous cycle) with either one or five subcutaneous implants containing oestradiol (n = 6 per group). Control ewes received no treatment (n = 6). Anterior pituitary glands were collected 16 h after treatment with oestradiol. Steady-state amounts of GnRH receptor mRNA were similar among all three treatment groups despite increased circulating concentrations of oestradiol in implanted ewes at the time of pituitary collection (4.3 +/- 0.6 and 24.7 +/- 2.6 pg ml-1 in ewes treated with one or five implants, respectively, compared with 0.5 pg ml-1 in controls). Experiment 2 was designed to determine whether progesterone was the ovarian factor preventing the stimulatory effects of oestradiol on expression of the GnRH receptor gene in Expt 1. Twenty-five ewes were ovariectomized on day 6 or day 7 of the oestrous cycle and assigned to one of five treatment groups (n = 5 per group). Control ewes received no further treatment. Endogenous luteal phase concentrations of progesterone were replaced in three groups of ewes at the time of ovariectomy via intravaginal implants. Three days after ovariectomy, one group of progesterone-treated ewes received one oestradiol implant, while another group of progesterone-treated ewes received five oestradiol implants. An additional group was treated with five oestradiol implants only, and anterior pituitary glands were collected from all ewes 16 h later. Compared with untreated ovariectomized ewes, treatment with progesterone alone did not affect amounts of GnRH receptor mRNA. In ewes treated with progesterone and either one or five oestradiol implants, steady-state amounts of GnRH receptor mRNA were increased twofold (P < 0.01). Treatment with oestradiol in the absence of progesterone increased amounts of GnRH receptor mRNA threefold (P < 0.001). These results provide evidence that the stimulatory effects of oestradiol on the expression of the GnRH receptor gene are prevented during the natural luteal phase in ewes. However, progesterone does not appear to act independently to mediate this effect.

Steady-state concentrations of mRNA encoding two inhibitors of protein kinase C in ovine luteal tissue.

Prostaglandin F2 alpha (PGF2 alpha) decreases secretion of progesterone from the corpus luteum in domestic ruminants. However, it is less effective during the early part of the oestrous cycle (Louis et al., 1973) and at the time of maternal recognition of pregnancy (Silvia and Niswender, 1984; Lacroix and Kann, 1986). Decreased luteal responsiveness may be due to failure of PGF2 alpha to activate fully its normal second messenger system, protein kinase C (PKC). Alternatively, increased resistance of the corpus luteum to PGF2 alpha might be attributable to greater concentrations of recently identified biological inhibitors of PKC. These possibilities were addressed by measuring steady-state concentrations of mRNA encoding PGF2 alpha receptor and two inhibitors of PKC, protein kinase C inhibitor-1 (PKCI-1) and kinase C inhibitor protein-1 (KCIP-1, brain 14-3-3 protein), in corpora lutea collected from ewes on days 4, 10 and 15 of the oestrous cycle (n = 5 per day) and day 15 of pregnancy (n = 7). There were no differences in mean concentrations of mRNA encoding PGF2 alpha receptor among the groups. However, concentrations of mRNA encoding both inhibitors of PKC were higher (P < 0.01) on day 4 of the oestrous cycle compared with the other groups. Treatment of ewes with a luteolytic dose of PGF2 alpha, which activates PKC, did not change concentrations of mRNA encoding either PKCI-1 or KCIP-I up to 24 h later. Luteal expression of mRNA encoding the PKC inhibitors and PGF2 alpha receptor was also examined in ewes treated with oestradiol in vivo for 16 h in the midluteal phase. High concentrations of oestradiol in serum (20 and 70 pg ml-1) did not influence quantities of any of the mRNAs examined. Therefore, an increase in PKC inhibitors may be involved in resistance of the corpus luteum to PGF2 alpha during the early part of the oestrous cycle but does not appear to mediate the increased resistance of the corpus luteum to PGF2 alpha during maternal recognition of pregnancy. Neither PGF2 alpha nor oestradiol affected steady-state concentrations of mRNAs encoding PKCI-1 or KCIP-I.