Effect of long-term administration of human growth hormone-releasing factor and (or) thyrotropin-releasing factor on hormone concentrations in lactating dairy cows

Fifteen cows (87 +/- 8 d in lactation; 641 +/- 33 kg BW) were randomly assigned to treatment and then subjected for 182 d to daily sc injection (1000 hr), in the cervical area, of saline (control), thyrotropin-releasing factor (TRF: 1 micrograms/kg BW), growth hormone-releasing factor (1-29)NH2 (GRF; 10 micrograms/kg BW) or GRF plus TRF (10 and 1 micrograms/kg BW, respectively) according to a 2 x 2 factorial design. On days 1, 31, 88 and 179, jugular blood samples were collected from 2 hr before to 6 hr after injection. Samples were also collected for 5 consecutive days after cessation of treatment. GRF always induced growth hormone (GH) release (600 vs 7925 ng.min/ml) with augmentation of response with time (interaction GRF * day; P less than .001). TRF did not affect (P greater than .25) GH release; there was no interaction (P greater than .25) with time. There was no significant interaction (P greater than .25) between GRF and TRF on GH release. However, the amount of GH release with GRF plus TRF was always greater than with GRF alone (9419 vs 6431 ng.min/ml). TRF induced a significant release of prolactin (23769 vs 42175 ng.min/ml) but GRF reduced the amount of prolactin release on the last day of sampling. TRF induced thyroid stimulating hormone (TSH) release only on the first day of injection while triiodothyronine (T3) and thyroxine (T4) continued to respond to TRF throughout the treatment period. Concentrations of T3 and T4 fell below control levels after cessation of TRF injection. In conclusion, GRF-induced GH release and TRF-induced Prl and thyroid hormone release were maintained over a 6-mo treatment period. TRF induced TSH release only on the first day of injection. Overall, these results raised the possibility of a direct effect of TRF on the thyroid gland.     

Effect of human growth hormone-releasing factor and(or) thyrotropin-releasing factor on hormone concentrations in dairy calves

To determine the effect of chronic treatment with human growth hormone-releasing factor (1-29)NH2 (GRF) and(or) thyrotropin-releasing factor (TRF), 20 calves averaging 70.2 kg BW were divided into four groups (n = 5) according to a 2 X 2 factorial design. For 86 d, calves in each group received twice daily s.c. injections of either .9% NaCl, GRF (5 micrograms/kg BW), TRF (1 microgram/kg BW) or GRF (5 micrograms/kg BW) plus TRF (1 microgram/kg BW). On d 87, all calves received a s.c. injection of GRF (5 micrograms/kg BW) plus TRF (1 microgram/kg BW). Blood samples were collected every 20 min for 18 h on d 1, 29, 57 and 85, and for 8 h on d 87. Hormone responses were measured as area under the hormone concentration curve over time. GRF and TRF acted in synergy (P less than .10) on GH release throughout the treatment period. Growth hormone responsiveness to GRF and(or) TRF decreased (P less than .01) with days of treatment, but this decrease was due to aging rather than to chronic treatment, because GH response to GRF plus TRF was similar (P greater than .10) between control and treated calves on d 87. TRF increased prolactin (Prl) concentration until the end of the treatment period (P less than .01). The response of thyroid-stimulating hormone (TSH) to TRF disappeared (P greater than .10) after 1 mo of treatment, whereas the thyroxine (T4) response decreased (P less than .01) throughout the treatment period. GRF did not induce nor did it interact with TRF on TSH and T4 release.(ABSTRACT TRUNCATED AT 250 WORDS)     

Negative energy balance increases periprandial ghrelin and growth hormone concentrations in lactating dairy cows

The reported effects of feeding on growth hormone (GH) secretion in ruminants have been inconsistent, and are likely influenced by energy status of animals. High-producing dairy cows in early lactation and late lactation were used to assess the effects of energy balance on temporal variation of plasma metabolites and hormones. Cows were fed a single diet once daily, and feed was withdrawn for 90 min prior to feeding. Beginning at the time of feed withdrawal, plasma samples were collected via jugular catheters hourly for 24h. Concentrations of non-esterified fatty acids and GH were measured for all samples, while insulin, glucose, and acylated (active) ghrelin were quantified for four sample times around feeding. As expected, calculated energy balance was significantly lower in early lactation than late lactation cows (-43.5 MJ retained/day versus 7.2 MJ retained/day). Following the primary meal of the day, a GH surge was observed in early lactation but not in late lactation cows. This difference was not explained by temporal patterns in non-esterified fatty acid, insulin, or glucose concentrations. However, a preprandial ghrelin surge was observed in early lactation only, suggesting that ghrelin was responsible for the prandial GH surge in this group. Results of a stepwise regression statistical analysis showed that both preprandial ghrelin concentration and energy balance were significant predictors of prandial GH increase over baseline. Adaptations to negative energy balance in lactating dairy cattle likely include enhanced ghrelin secretion and greater GH response to ghrelin.     

Synergism and diurnal variations of human growth hormone-releasing factor (1-29)NH2 and thyrotropin-releasing factor on growth hormone release in dairy calves

Sixteen male Holstein calves averaging 168 kg body weight (BW) were used to determine the effects of human growth hormone-releasing factor (1–29)NH₂ (hGRF (1–29)NH₂; .22 μg/kg BW), thyrotropin-releasing factor (TRF; .165 μg/kg BW) or hGRF (1–29)NH₂ plus TRF (.22 and .165 μg/kg BW, respectively) on growth hormone (GH) release in animals exposed to 16 hr of light (L): 8 hr of dark (D) (lights on at 0100 hr) and hGRF plus TRF (.22 and .165 μg/kg BW, respectively) in animals exposed to 8L:16D (lights on at 0900 hr). For each treatment, times of iv injection were 0400, 1000, 1600 and 2200 hr. In animals exposed to 16L:8D, average GH peaks reached after hGRF (1–29)NH₂ or TRF injections were 49.7 and 32.0 ng/ml while the area under the GH response curve (AUC) were 1247 and 1019 ng/ml^*min, respectively. There was no significant effect of times of injection on GH release following the separate injection of hGRF (1–29)NH₂ or TRF. In animals exposed to 16L:8D, GH peaks and AUC after hGRF plus TRF injections were 226.4, 189.2 and 116.8 ng/ml, and 4340, 3660 and 2415 ng/ml^*min at 0400, 1000 and 1600 hr (lights on), respectively but only 42.3 ng/ml and 1692 ng/ml^*min at 2200 hr (lights off). In animals exposed to 8L:16D, GH levels and AUC after hGRF plus TRF injections reached 177.5 and 180.5 ng/ml, and 2759 and 3704 ng/ml^*min at 1000 and 1600 hr (lights on) but only 84.0 and 72.7 ng/ml, and 1544 and 1501 ng/ml^*min at 0400 and 2200 hr (lights off), respectively. These results demonstrated that hGRF (1–29)NH₂ and TRF can act in synergy to potentiate GH release in dairy calves. This synergistic action occurred only when both peptides were injected during the lighted phase of short and long day photoperiods.     

Effect of subluteal concentrations of progesterone on luteinizing hormone and ovulation in lactating dairy cows

Two experiments were conducted to determine if administration of progesterone within a low, subluteal range (0.1-1.0 ng/mL) blocks the luteinizing hormone (LH) surge (experiments 1 and 2) and ovulation (experiment 2) in lactating dairy cows. In experiment 1, progesterone was administered to cycling, lactating dairy cows during the luteal phase of the estrous cycle using a controlled internal drug release (CIDR) device. CIDRs were pre-incubated in other cows for either 0 (CIDR-0), 14 (CIDR-14) or 28 days (CIDR-28). One group of cows received no CIDRs and served as controls. One day after CIDR insertion, luteolysis was induced by two injections of prostaglandin (PG) F(2alpha) (25 mg) at 12 h intervals. Two days after the first injection, estradiol cypionate (ECP; 3 mg) was injected to induce a LH surge. Concentrations of progesterone after luteolysis were 0.11, 0.45, 0.78 and 1.20 ng/mL for cows treated with no CIDR, CIDR-28, CIDR-14, and CIDR-0, respectively. LH surges were detected in 4/4 controls, 4/5 CIDR-28, 2/5 CIDR-14 and 0/5 CIDR-0 cows following ECP. In experiment 2, progesterone was administered to cycling, lactating, Holstein cows during the luteal phase of the estrous cycle as in experiment 1. Luteolysis was induced as in experiment 1. The occurrence of an endogenous LH surge and ovulation were monitored for 7 days. Concentrations of progesterone after luteolysis were 0.13, 0.30, 0.70 and 1.20 ng/mL for cows treated with no CIDR, CIDR-28, CIDR-14 and CIDR-0, respectively. LH surges and ovulation were detected in 5/5 controls, 3/7 CIDR-28, 0/5 CIDR-14 and 0/5 CIDR-0 cows. It was concluded that low concentrations of progesterone can reduce the ability of either endogenous or exogenous estradiol to induce a preovulatory surge of LH and ovulation.     

Active immunization of pigs against growth hormone-releasing factor: effect on concentrations of growth hormone and insulin-like growth factor 1

Cyclic gilts (96 +/- 1 kg) were used to determine the effect of active immunization against growth hormone-releasing factor GRF(1-29)-NH2 on concentrations of growth hormone (GH) and insulin-like growth factor 1 (IGF-1). Gilts were immunized against GRF conjugated to human serum albumin (GRF-HSA, n = 5) or HSA alone at 180 d of age (wk 0). Booster doses were administered at wk 9 and 13. Seven days after the second booster (wk 14), blood samples were collected at 15-min intervals for 6 h before feeding and 30, 60, 120, 180 and 240 min after feeding. Eight days after the second booster, all gilts were administered a GRF analog, [desNH2Tyr1,Ala15]-GRF(1-29)-NH2, followed by an opioid agonist, FK33-824. Blood samples were collected at 15-min intervals from -30 to 240 min after injection. Immunization against GRF-HSA resulted in antibody titers, expressed as dilution required to bind 50% of [125I]GRF, ranging from 1:11,000 to 1:60,000 (wk 11 and 14); binding was not detectable or was less than 50% at 1:100 in HSA gilts (P less than .05). Episodic release of GH was abolished by immunization against GRF-HSA (P less than .05). Mean GH was decreased (P less than .07), but basal GH concentrations were not altered (P greater than .15) by immunization against GRF-HSA. Serum concentrations of IGF-1 were similar at wk 0, but concentrations were lower in GRF-HSA than in HSA gilts (P less than .05) at wk 14.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of long-term administration of porcine growth hormone-releasing factor and(or) thyrotropin-releasing factor on growth hormone, prolactin and thyroxine concentrations in growing pigs

Long-term administration of porcine growth hormone-releasing factor (pGRF(1-29)NH2) and(or) thyrotropin-releasing factor (TRF) was evaluated on serum concentrations of growth hormone (GH) thyroxine (T4) and prolactin (PRL). Twenty-four 12-wk-old female Yorkshire-Landrace pigs were injected at 1000 and 1600 for 12 wk with either saline, pGRF (15 micrograms/kg), TRF (6 micrograms/kg) or pGRF + TRF using a 2 x 2 factorial design. Blood samples were collected on d 1, 29, 57 and 85 of treatment from 0400 to 2200. Areas under the GH, T4 and PRL curves (AUC) for the 6 h (0400 to 1000) prior to injection were subtracted from the postinjection periods (1000 to 1600, 1600 to 2200) to calculate the net hormonal response. The AUC of GH for the first 6 h decreased similarly (P less than .05) with age for all treatments. The GH response to GRF remained unchanged (P greater than .10) across age. TRF alone did not stimulate (P less than .05) GH release but acted in synergy with GRF to increase (P less than .05) GH release. TRF stimulated (P less than .001) the net response of T4 on all sampling days. Animals treated with the combination of GRF + TRF showed a decreased T4 AUC during the first 6 h on the last three sampling days. Basal PRL decreased (P less than .05) with age. Over the four sampling days, animals injected with TRF alone showed (P less than .01) a reduction (linear effect; P less than .01) followed by an increase (quadratic effect; P less than .05) in total PRL concentration after injection; however, when GRF was combined with TRF, such effects were not observed (P greater than .10). Results showed that 1) chronic injections of GRF for 12 wk sustained GH concentration, 2) TRF and GRF acted synergistically to elevate GH AUC, 3) TRF increased T4 concentrations throughout the 12-wk treatment period, 4) chronic TRF treatment decreased the basal PRL concentration and 5) chronic GRF + TRF treatment decreased the basal concentration of T4.     

Effect of active immunization against growth hormone releasing factor on concentrations of somatotropin and insulin-like growth factor I in lactating beef cows.

Two experiments were conducted to determine the effects of immunoneutralization of growth hormone-releasing factor [GRF(1-29)-NH2] on concentrations of somatotropin (ST) and insulin-like growth factor I (IGF-I) in lactating beef cows. In Experiment 1, multiparous Hereford cows were immunized against 2 mg GRF(1-29)-(Gly)4-Cys-NH2 conjugated to human serum albumin (GRFi, n = 3) or 2 mg human serum albumin (HSAi, n = 3) at 52 +/- 1 d prior to parturition. Boosters (1 mg) were administered on days 12, 40 and 114 postpartum (pp). Serum samples were collected at 15-min intervals for 5 hr on days 18, 46 and 120 pp, followed by administration (IV) of an opioid agonist (FK33-824; 10 micrograms/kg) and an antagonist (naloxone; .5 mg/kg) at hours 5 and 7, respectively. A GRF-analog ([desamino-Tyr1, D-Ala2, Ala15] GRF (1-29)-NH2; 3.5 micrograms/kg) and arginine (.5 g/kg) were administered at hour 10 on days 47 and 121, respectively. Percentage binding of [125I]GRF (1:100 dilution of serum) 28 d after primary immunization was greater in GRFi (14.3 +/- 4.9) than in HSAi (.7 +/- .3) cows. Binding increased to 29.3 +/- 6.5% after first booster in GRFi cows. Episodic release of ST was abolished by immunization against GRF; concentration and frequency of release of ST were lower (P less than .05) in GRFi than in HSAi cows on all days pp. Concentrations of IGF-I were lower in GRFi than in HSAi cows throughout lactation. Serum ST failed to increase following FK33-824 or arginine in GRFi; however, ST increased after both compounds in HSAi cows. Concentrations of ST following GRF-analog were greater (P less than .05) in HSAi than in GRFi cows. Experiment 2 was conducted to determine if a lower dose of antigen and a single booster would be sufficient to lower ST and IGF-I in lactating cows. Multiparous Hereford and Angus cows were assigned to GRFi (n = 6) or HSAi (n = 6). Primary (1.2 mg) and booster (.5 mg) immunizations were administered -14 and 8 d from calving, respectively. Cows were restricted to 60% of recommended intake of energy during lactation in order to elevate concentrations of ST. Serum samples were collected at 15-min intervals for 6 hr on days 26, 50, 73, 90 and 109 pp. Two of six GRFi cows had binding less than 10% (1:1,000 dilution of serum) and were omitted from further analyses.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effect of daily injections of growth hormone-releasing factor and thyrotropin-releasing hormone on growth and endocrine parameters in chickens

The control of growth is a complex mechanism regulated by several metabolic hormones including growth hormone (GH) and thyroid hormones. In avian species, as well as in mammals, GH secretion is regulated by hypothalamic hypophysiotropic hormones. Since thyrotropin-releasing hormone (TRH) and growth hormone-releasing factor (GRF) are potent GH secretagogues in poultry, we were interested in determining the influence of daily intravenous administration of either peptide or both simultaneously on circulating GH and IGF-I concentrations and whether an improvement in growth rate or efficiency would be obtained.

Male broiler chicks were injected once daily for a period of 21 days with either GRF (10 μg/kg), TRH (1 μg/kg) or both GRF and TRH (10 and 1 μg/kg respectively) between four and seven weeks of age. On the last day of the experiment, following intravenous injection of TRH, GRF or a combination of GRF and TRH, plasma GH levels were significantly (P<.05) increased to a similar extent in control chicks and in those which had received daily peptide injections for the previous 21 days. Circulating GH levels between 10 and 90 min post-injection were significantly (P<.05) greater and more than additive than GH levels in chicks injected with both GRF and TRH when compared to those injected with either peptide alone. Mean plasma T₃ concentrations during that same time period were significantly elevated (P<.05) above saline-injected control chick levels in birds treated with TRH or GRF and TRH respectively, regardless of whether the chicks had received peptide injections for the previous 21 days. There was no evidence of pituitary refractoriness to chronic administration of either TRH or GRF injection in terms of growth or thyroid hormone secretion.

Despite the large elevation in GH concentration each day, growth rate, feed efficiency and circulating IGF-I concentrations were not enhanced. Thus the quantity or secretory pattern of GH secretion induced by TRH or GRF administration was not sufficient to increase plasma IGF-I concentration or growth.     

Dose response of two synthetic human growth hormone-releasing factors on growth hormone release in heifers and pigs

This study was undertaken to evaluate the biological potency of two synthetic human growth hormone-releasing factors, hGRF (1-44)NH2 and hGRF (1-29)NH2, on growth hormone (GH) release in young dairy heifers (n = 10) and pigs (n = 10). In each species, the GH response to an iv injection (0, .067, .2, .6 and 1.8 nmol.kg-1 body weight) of each peptide was evaluated in a double 5 X 5 Latin square design. In each square, there were five animals injected with either hGRF (1-44)NH2 or hGRF (1-29)NH2. Main effects were doses (n = 5) of hGRF and days (n = 5) of injection. In both species, data indicated that hGRF (1-44)NH2 and hGRF (1-29)NH2 equally stimulate GH secretion at all doses. In dairy heifers, average peak concentrations (81.7, 94.7, 84.5 and 93.7 ng.ml-1 vs 91.5, 81.0, 94.3 and 91.6 ng.ml-1) and area under the GH response curve (3,661, 4,541, 7,196 and 6,788 ng.ml-1.min vs 3,000, 3,982, 5,639 and 6,724 ng.ml-1.min) were not different (P greater than .05) between hGRF(1-44)NH2 and hGRF(1-29)NH2 at .067, .2, .6 and 1.8 nmol.kg-1, respectively. Similarly, in pigs, average peak concentrations (35.6, 38.6, 76.5 and 73.8 ng.ml-1 vs 28.7, 30.0, 41.3 and 80.8 ng.ml-1) and area under the GH curve (1,576, 1,567, 3,299 and 3,622 ng.ml-1.min vs 1,115, 1,658, 1,482 and 2,528 ng.ml-1.min) were not different (P greater than .05) between both peptides. A biphasic release of GH after hGRF (1-44)NH2 and hGRH (1-29)NH2 injection was observed at the highest dose in heifers. The GH response to hGRF injection was much more variable in pigs as compared with dairy heifers. In conclusion, hGRF (1-44)NH2 and its (1-29)NH2 fragment are equipotent in stimulating GH release in dairy heifers and pigs.     

Effect of human growth hormone-releasing factor and(or) thyrotropin-releasing factor on growth, carcass composition, diet digestibility, nutrient balance, and plasma constituents in dairy calves

Sixty male dairy grain-fed calves, raised from 70 to 223 kg BW in individual crates, were used in a 2 X 2 factorial arrangement to determine the effect of administration of human growth hormone-releasing factor (1-29)NH2 (GRF) and(or) thyrotropin-releasing factor (TRF). Calves received twice-daily s.c. injections of .9% NaCl (control), GRF (5 micrograms/kg BW), TRF (1 micrograms/kg BW) or GRF (5 micrograms/kg BW) plus TRF (1 micrograms/kg GTRF). Average daily gain and days on feed were not affected by treatments, but TRF treatment increased (P less than .05) total intake of dry matter (DM) and feed conversion ratio: 3.00, 3.02, 3.08, and 3.22 kg DM/kg weight gain for control, GRF, TRF, and GTRF, respectively. During two 7-d periods, after 66 and 75 d of treatment, feces and urine were collected from 40 calves (5 per treatment per period). Treatment with GRF increased (P less than .05) digestibility of DM, nitrogen (N), and energy and tended (P less than .20) to increase N retention. At slaughter, withers height was increased (P = .05) by GRF and carcass length was increased (P less than .05) by TRF. Pituitary and liver weights were increased (P less than .05) by TRF. The combination of GRF and TRF slightly increased (P less than .10) protein content and decreased (P less than .05) fat content of the 9-10-11th rib section. After d 1, GRF treatment chronically increased (P less than .05) insulin concentrations and also increased (P less than .10) IGF-I concentrations on d 29 and 57. In summary, chronic treatment with GRF and(or) TRF did not improve growth or efficiency, although GRF increased digestibility of DM, N, and energy and the GRF plus TRF combination resulted in slightly leaner carcasses.     

Luteinizing hormone and growth hormone secretion in early lactating Spanish beef cows

The episodic release of luteinizing hormone (LH) and growth hormones (GH) was studied in three suckling regimens and two breeds of Spanish suckled cows. Parda de Montaña (PA) cows (n = 21) were assigned to once‐daily, twice‐daily or ad libitum (ADLIB) suckling. Pirenaica (PI) cows (n = 7) were used to evaluate the breed effect in twice‐daily suckling. Coccygeal blood samples were collected twice weekly during lactation to determine the interval from calving to first ovulation through peripheral progesterone. On day 32 ± 3 post‐partum, jugular blood samples were drawn at 15 min intervals during 8 h to analyse circulating LH and GH. The interval to first ovulation was greater in PA cows suckling ADLIB than in restricted suckling treatment (RESTR1), whereas in RESTR2 it did not differ from the other two treatments. There were no differences between PA and PI cows in the interval to first ovulation. RESTR1 cows showed a tendency to have shorter LH peak widths than ADLIB cows. PA cows showed a tendency to have longer LH peak widths than their PI counterparts. There were no differences across treatments or breeds in any of the GH measures of secretion. The LH release was more affected by breed than by suckling frequency, whereas that of GH was not influenced by any of these parameters. The variables that best allowed discrimination between ADLIB and restricted nursing systems were the interval to post‐partum first ovulation, LH peak number and the mean GH concentration.     

Dose confirmation of moxidectin pour-on against natural nematode infections in lactating dairy cows.

The nematocidal effectiveness of moxidectin, administered topically at the rate of 500 mcg/kg BW, was determined for lactating dairy cows. Naturally infected animals were given either topical vehicle or moxidectin (Cydectin Pour-On Fort Dodge Animal Health) at the rate of 1 ml/10 kg BW (10 animals per treatment group), and sacrificed 14-18 days post-treatment for nematode enumeration. 100% efficacies were recorded for Ostertagia lyrata males, Cooperia punctata males and Oesophagostomum radiatum L4, with treatment group differences in geometric means significant (P < 0.05) for all. Populations of Trichostrongylus L4 and adult O. radiatum were also reduced by 100%, but low prevalence rates in the control animals precluded meaningful statistical inference. Nematode populations for which efficacies ranged from 96.7 to 99.6% (based on geometric means) and for which treatment group differences were significant (P < 0.05) included Ostertagia spp. adult females, inhibited L4 and developing L4, O. ostertagi adult males, Trichostrongylus axei adults and Cooperia spp. adult females. For all nematodes combined, moxidectin was 98.9% efficacious. In addition to exhibiting excellent nematocidal effectiveness, topical moxidectin was demonstrated to be safe, with animal health and milk production unaffected during the study.     

Long-term growth hormone-releasing factor administration on growth hormone, insulin-like growth factor-I concentrations, and bone healing in the Beagle.

Twelve 11 month old male Beagles were assigned to two treatment groups: a control group (saline) and a group receiving human growth hormone (GH)-releasing factor (hGRF) [1-29]NH2 (25 micrograms/kg, SC, TID). Treatment was started 6 days prior to surgery (day 1) and continued until necropsy (3 dogs per group/day) on d 29 or 58. Two porous polyethylene rods were surgically implanted on the lateral diaphysis of the femoral shaft and a 3 mm hole was drilled through the cortex between the two implants of each dog on day 1. Blood and urine were collected on d -6, 27 and 56. Human GRF injections produced a significant (P < 0.05) increase in GH release following each injection. An increase in GH response was also observed (P < 0.05) over time. The concentration of insulin-like growth factor-1 (IGF-1) increased for 5 weeks and then reached a plateau. None of the hematologic or urine measured parameters was affected by the treatment (P > 0.05). Albumin, calcium, and protein concentrations were higher (P < 0.05) on d 27 and 56 in GRF-treated animals. Histological sections of the onlay sites showed that bony ingrowth tended to be greater into the porous polyethylene material in GRF-treated animals than the controls at d 28 and 57, while no difference was observed in the degree of periosteal bone formation around the implants at either time period (P > 0.05). Bone formation into the cortical defect was greater in the GRF-treated dogs when compared to controls at day 57 only. In conclusion, chronic hGRF [1-29]NH2 treatment in Beagle dogs produced an increased GH response over time and increased IGF-1 concentrations. It also appeared to promote bony ingrowth into a porous polyethylene onlay and into a bony deficit.     

Pharmacokinetics of sulphadiazine-trimethoprim in lactating dairy cows

Five Finnish Ayrshire cows in mid or end-lactation were treated with 40 mg sulphadiazine/kg and 8 mg trimethoprim/kg using intravenous (i.v.), intramuscular (i.m.) and subcutaneous (s.c.) routes. Elimination of sulphadiazine was not affected by the route of administration (median t1/2 4.4-5.0 h) while elimination of trimethoprim was strongly limited by slow absorption from the injection site after s.c. and i.m. administration (median for apparent t1/2 21-25 h) compared to that after i.v. administration (median t1/2 1.2 h; p < 0.05). The median bioavailability of trimethoprim was also decreased, being 37% and 55% after s.c. and i.m. administration, respectively. When i.v. administration was used, trimethoprim concentration exceeded 0.1 mg/l in milk between 0.15-8 h while sulphadiazine concentrations above 2 mg/l were maintained from 0.5-2 h to 8 h. After s.c. and i.m. administration sulphadiazine in milk behaved similar to that after i.v. administration, while trimethoprim time-concentration curves were flat and trimethoprim concentrations were around 0.1 mg/l for an extended period of time (8-12 h). Median Cmax values in milk were only 0.07 mg/l and 0.10 mg/l for s.c. and i.m. administrations, respectively. After s.c. administration, 4 out of 5 cows showed signs of pain. After i.m. administration, 2 of the cows showed clear signs of pain and one had some local tenderness at the site of injection.     

Luteinizing hormone concentrations in serum of postpartum beef cows injected with microencapsulated luteinizing hormone-releasing hormone analog

Twenty-five cows were divided equally into five groups to determine whether [D-Trp6]-luteinizing hormone releasing hormone (LHRH-A) microencapsulated in poly (DL-lactide co-glycolide) would increase basal serum concentrations of LH during the postpartum period. On d 5 postpartum, cows were injected i.m. with 2 ml of vehicle alone (Group 1) or vehicle containing microcapsules calculated to release .4, 1.6, 6.4 or 25.6 micrograms LHRH-A per day for approximately 30 d (Groups 2, 3, 4 and 5, respectively). Cows were bled every 15 min for 4 h immediately before and after injection and every 15 min for 4 h at weekly intervals for the next 4 wk to evaluate serum profiles of LH. Estrus was determined by twice daily observations and confirmed by serum progesterone. More cows in Groups 2, 3, 4 and 5 exhibited pulsatile patterns of LH after LHRH-A injection than in Group 1 (P less than .06). More pulses of LH were observed after LHRH-A injection in Groups 4 and 5 than in Group 1 (P less than .01). Mean concentrations of LH within treatment groups did not change during the initial injection, except in Group 5. All cows in Group 5 had a surge of LH immediately after injection. The induced surge of LH in two cows in Group 5 cows resulted in progesterone profiles similar to those during a normal luteal phase. Days to first postpartum estrus were not different among the five treatment groups. Microencapsulated LHRH-A given at a dose estimated to release 25 micrograms LHRH-A/d was effective in elevating LH concentrations following injection. However, effectiveness of this hormonal treatment in shortening postpartum anestrus was not substantiated.     

Hemogram changes in lactating dairy cows given human recombinant granulocyte colony stimulating factor (r-MethuG-CSF).

As a prelude to mammary gland challenge experiments, this investigation was implemented to assess the hematologic changes in lactating dairy cattle induced by two dosage regimes of human recombinant colony stimulating factor (Hr-GCSF). This study documents the capability of the human recombinant colony stimulating factor to produce hematologic changes in both a time and dose dependent manner when administered to the adult lactating bovine. A screening dose of 1 microgram/kg of Hr-GCSF administered to three study subjects produced a three- to four-fold increase in peripheral blood mature neutrophil counts (P less than 0.043) by day 12 of the trial. The priming dose treatment group of four lactating cows (3 micrograms/kg of Hr-GCSF) exhibited a three- to five-fold increase in peripheral blood mature neutrophil counts (P less than 0.05) and two- to three-fold increases in white blood cell counts by day 5 of the trial. Hematologic examinations of the control group (n = 4; no Hr-GCSF administration) did not detect significant changes in their neutrophil counts over baseline values. The milk somatic cell counts did not statistically shift over baseline values in any of the control or Hr-GCSF treatment groups. When attempting to alter the course of infectious disease processes, potential applications of colony stimulating factors provide interesting speculations about new therapeutic modalities.     

Antepartal insulin-like growth factor concentrations indicating differences in the metabolic adaptive capacity of dairy cows

Cows with different Insulin-like Growth Factor-I (IGF-I) concentrations showed comparable expression levels of hepatic growth hormone receptor (GHR). Suppressor of cytokine signaling 2 (SOCS2), could be responsible for additional inhibition of the GHR signal cascade. The aims were to monitor cows with high or low antepartal IGF-I concentrations (IGF-I^high or IGF-I^low), evaluate the interrelationships of endocrine endpoints, and measure hepatic SOCS2 expression. Dairy cows (n = 20) were selected (240 to 254 days after artificial insemination (AI)). Blood samples were drawn daily (day -17 until calving) and IGF-I, GH, insulin, thyroid hormones, estradiol, and progesterone concentrations were measured. Liver biopsies were taken (day 264 ± 1 after AI and postpartum) to measure mRNA expression (IGF-I, IGFBP-2, IGFBP-3, IGFBP-4, acid labile subunit (ALS), SOCS2, deiodinase1, GHR1A). IGF-I concentrations in the two groups were different (p < 0.0001). However, GH concentrations and GHR1A mRNA expression were comparable (p > 0.05). Thyroxine levels and ALS expression were higher in the IGF-I^high cows compared to IGF-I^low cows. Estradiol concentration tended to be greater in the IGF-I^low group (p = 0.06). It was hypothesized that low IGF-I levels are associated with enhanced SOCS2 expression although this could not be decisively confirmed by the present study.     

Variation in plasma growth hormone during first parity in lactating cows

This study analyzed genetic and phenotypic variation in plasma GH during lactation in first parity dairy cows. The heritability and repeatability were examined using an algorithm for separation of basal and peak concentrations and different power transformations. Blood samples were obtained 17 times during first parity in 85 Holstein, 67 Red Dane, and 62 Jersey cows and assayed for GH. Each breed comprised 2 genetic groups; thus, a total of 6 genetic groups were defined. Across genetic groups, cows were assigned to 1 of 2 total mixed rations with a low or a normal energy concentration. The separation algorithm identified only 4.0% of the plasma GH concentrations as peaks. After excluding peak concentrations, the repeatability of GH during lactation was improved. A log-transformation was found appropriate for GH. The log-transformed GH concentrations for lactating dairy cows had a heritability ranging between 0.14 in early lactation to 0.08 in mid and late lactation. The repeatability was 0.24 in early lactation and increased to between 0.58 and 0.61 in mid and late lactation. We conclude that for GH concentrations in lactating cows that are sampled infrequently, the exclusion of peak values to obtain a basal GH concentration was not effective in clarifying phenotypic or genetic effects.     

Urinary pseudouridine excretion in lactating dairy cows

Introduction   A number of systems based on metabolizable protein, such as that adopted in the UK (A gricultural and F ood R esearch C ouncil 1992) have been developed to improve the accuracy of protein rationing for ruminants. Quantification of microbial protein synthesis in the rumen is a fundamental requirement of all such systems. In the UK system, microbial protein supply is predicted from an estimate of fermentable metabolizable energy intake, using a correction for the effects of level of feeding on the energetic efficiency of microbial protein synthesis. Use of such an approach is however subject to considerable error due to large variations in the energetic efficiency of microbial protein synthesis (A gricultural R esearch C ouncil 1984). Consequently there is an urgent requirement for an on-farm diagnostic marker of microbial protein supply as a basis for adjusting diets to maximize efficiency of dietary nitrogen utilization by dairy cows (D ewhurst et al. 1996). Urinary purine derivative excretion has been proposed as a noninvasive index of microbial protein supply in ruminant animals (T opps and E lliot 1965). Use of this microbial marker is based on the assumption that purines entering the duodenum are essentially microbial in origin (M c A llan 1982), and that following metabolism, their derivatives are quantitatively recovered in the urine (C hen et al. 1990; V erbic et al. 1990). Purine metabolites excreted in ruminant urine are primarily derived from the metabolism of absorbed purines, but as a consequence of tissue adenosine triphosphate and nucleic acid turnover, a proportion of purine bases are not salvaged and re-utilized, but enter catabolic pathways, constituting an endogenous loss.