Plasma GH, IGF-I, and conception rate in cattle treated with low doses of recombinant bovine GH

Effects of Administering Exogenous Bovine Somatotropin During the First Trimester of Pregnancy Altered Uterine Hemodynamics in Suckled Beef Cows

The objective of this study was to examine the effects of recombinant bovine somatotropin (bST) administration on uterine hemodynamics and subsequent fetal programming in suckled cows during the first trimester of gestation. Crossbred beef cows (n = 152) were stratified by breed, days postpartum, parity, cyclicity status, and body condition score (BCS) before being assigned to either receive injections of bST every other week (BST; 500-mg/14 d) starting at fixed-time artificial insemination (TAI; d 0) until d 97 or to receive no bST (CTL). Blood samples were collected until d 97 for analysis of plasma concentrations of insulin-like growth factor 1 (IGF-1). Pregnancy was assessed via transrectal ultrasonography on d 41 and 173. A subset of pregnant cows (BST, n = 24; CTL, n = 28) were selected for assessment of uterine arterial blood flow (BF), pulsatility index, and resistance index (RI) of the uterine arteries ipsilateral and contralateral to the conceptus via color Doppler ultrasonography on d 97 and 233 of gestation. No differences (P = 0.99) were detected in body weight (BW) or BCS of dams; however, plasma concentrations of IGF-1 were greater (P < 0.001) in BST-treated cows. Color Doppler ultrasonography parameters differed whereby a treatment × day interaction (P = 0.007) was detected for RI on d 97 (P = 0.048); however, on d 233, RI did not differ (P > 0.10) but ipsilateral BF for BST-treated cows was greater (P = 0.0319) than controls. Mean heart girth diameter, crown-to-rump length, and neonate BW at 7 ± 5 d of calf age did not differ (P > 0.10). Liver tissue samples from each calf were collected for analysis of mRNA expression of target insulin-like growth factor system ligands. There was no difference in gene expression of hepatic IGF-1 between treatments (P = 0.99). A treatment × sex interaction was determined, where BST heifers had increased mRNA expression of IGFR1 compared to BST bulls (P = 0.03). Bi-weekly administration of bST until d 97 of pregnancy increased plasma concentrations of IGF-1, altered uterine hemodynamics in dams, induced sex-specific changes in liver gene expression of the offspring but failed to alter calf morphometries or calf performance until weaning.

Productive and physiological responses of lactating dairy cows supplemented with phytogenic feed ingredients

This experiment compared milk production, milk composition, and physiological responses in lactating dairy cows supplemented with or without a mixture of condensed tannins, encapsulated cinnamaldehyde, curcumin, capsaicin, and piperine. Thirty-six lactating, multiparous, pregnant ¾ Holstein × ¼ Gir cows were maintained in a single drylot pen with ad libitum access to water and a total-mixed ration and were milked twice daily (d -7 to 84). On d 0, cows were ranked by days in milk (86 ± 3 d), milk yield (27.8 ± 1.0 kg), body weight (BW; 584 ± 10 kg), and body condition score (BCS; 3.04 ± 0.06) and assigned to receive (SUPP; n = 18) or not (CON; n = 18) 30 g/cow daily (as-fed basis) of Actifor Pro (Delacon Biotechnik GmbH; Steyregg, Austria). From d 0 to 84, SUPP cows individually received (as-fed basis) 15 g of Actifor Pro mixed with 85 g of finely ground corn through self-locking headgates before each milking of the day. Each CON cow concurrently received 85 g (as-fed basis) of finely ground corn through self-locking headgates. Throughout the experimental period (d -7 to 84), cows from both treatments were administered 500 mg of sometribove zinc at 14-d intervals and were monitored daily for morbidity, including clinical mastitis. Individual milk production was recorded daily, whereas milk samples were collected weekly for analysis of milk composition. Cow BW, BCS, and blood samples were also collected weekly. Cows receiving SUPP gained more BCS (P = 0.05) and had greater (P = 0.04) milk yield during the experiment compared with CON cows (0.22 vs. 0.07 of BCS, SEM = 0.05; 29.5 vs. 27.9 kg/d, SEM = 0.5). Milk composition did not differ (P ≥ 0.15) between SUPP and CON cows; hence, SUPP cows also had greater (P ≤ 0.02) production of fat-corrected and energy-corrected milk. Incidence of clinical mastitis did not differ (P ≥ 0.49) between SUPP and CON cows. No treatment differences were also detected (P ≥ 0.21) for serum concentrations of glucose and serum urea N. Mean serum haptoglobin concentration during the experiment was greater (P = 0.05) in CON vs. SUPP cows. Cows receiving SUPP had less (P ≤ 0.04) serum cortisol concentrations on d 21 and 42, and greater (P ≤ 0.05) serum concentrations of insulin-like growth factor-I on d 7, 35, and 63 compared with CON cows (treatment × day interactions; P ≤ 0.02). Collectively, supplementing phytogenic feed ingredients improved nutritional status and milk production of lactating ¾ Holstein × ¼ Gir cows.

Proteomic Analysis of Cyclic Ketamine Compounds Ability to Induce Neural Differentiation in Human Adult Mesenchymal Stem Cells

Neural regeneration is of great interest due to its potential to treat traumatic brain injuries and diseases that impact quality of life. Growth factor mediated differentiation can take up to several weeks to months to produce the cell of interest whereas chemical stimulation may be as minimal as a few hours. The smaller time scale is of great clinical relevance. Adipose derived stem cells (ADSCs) were treated for up to 24 h with a novel differentiation media containing the cyclic ketamine compounds to direct neurogenic induction. The extent of differentiation was investigated by proteome changes occurring during the process. The treatments indicated the ADSCs responded favorably to the neurogenic induction media by presenting a number of morphological cues of neuronal phenotype previously seen and a higher cell population post induction compared to previous studies. Furthermore, approximately 3500 proteins were analyzed and identified by mass spectrometric iTRAQ analyses. The bioinformatics analyses revealed hundreds of proteins whose expression level changes were statistically significant and biologically relevant to neurogenesis and annotated as being involved in neurogenic development. Complementing this, the Bioplex cytokine assay profiles present evidence of decreased panel of stress response cytokines and a relative increase in those involved in neurogenesis.

Pre- and post-weaning injections of bovine somatotropin to optimize puberty achievement of Bos indicus beef heifers

The present study evaluated the growth and puberty attainment of Bos indicus heifers administered recombinant bovine somatotropin (bST) or saline injections during preweaning and/or postweaning. On day 0, 177 suckling Nellore heifers were stratified by initial age and body weight (BW) (80 ± 10 d; 97 ± 16 kg), and randomly assigned, in a 2 × 2 factorial design (n = 44 to 45 heifers/treatment), to receive s.c. injections of saline (5 mL 0.9% NaCl) or sometribove zinc (Posilac; Elanco, Greenfield, IN; 6.14 mg/kg of BW^0.75) on days 0 and 10 (PRE) and/or days 167 and 177 (POS). All heifers were managed as a single group in Brachiaria decumbens pastures from day 0 until 24 d postweaning (day 191), and then provided a corn silage–based TMR from days 191 to 380 to achieve 65% to 70% of mature BW at the end of the study (day 380). Heifer full BW was collected on days 0, 10, 167, 177, and monthly from days 191 to 380. Transrectal ultrasonography of ovaries was performed on days 1 and 10 of each month from days 229 to 380 to assess the percentage of pubertal heifers. Liver biopsies and blood samples from jugular vein were collected on days 0, 10, 167, 177, and 380. Additional blood samples were collected monthly from days 259 to 380 (n = 10 to 15 heifers/treatment). No interactions among day of the study, PRE, and POS injections of saline or bST were detected (P ≥ 0.11). Preweaning bST injections increased heifer average daily gain (ADG) from days 0 to 10 and plasma IGF-1 on day 10 (P ≤ 0.03), did not affect ADG from days 0 to 177, plasma IGF-1 from days 259 to 380, and any liver gene mRNA expression (P ≥ 0.19), but tended to decrease ADG from days 191 to 380 (P = 0.07) and percentage of pubertal heifers on days 349 (P = 0.07), 359 (P = 0.002), and 380 (P = 0.0001) compared with saline injections. Postweaning bST injections increased plasma IGF-1 on day 177 and overall liver mRNA expression of GHR-1A (P ≤ 0.05), decreased plasma IGF-1 from days 259 to 380 (P = 0.03), tended to decrease liver mRNA expression of GHR-1B on day 177 (P = 0.08), but did not affect ADG from days 167 to 177 and 191 to 380, and puberty attainment from days 229 to 380 (P ≥ 0.12) compared with saline injections. Thus, preweaning and postweaning injections of bST successfully increased heifer plasma IGF-1 concentrations 10 d after first injection. Postweaning injections of bST had no impact on puberty attainment, whereas preweaning bST injections of bST impaired puberty attainment of Nellore beef heifers.

Administration of recombinant bovine somatotropin prior to fixed-time artificial insemination and the effects on fertility, embryo, and fetal size in beef heifers

Our objectives were to determine the effects of the administration of recombinant bovine somatotropin (bST) at the initiation of a fixed-time AI (TAI) protocol on concentrations of plasma IGF-1, follicle diameter, embryo/fetal size, and pregnancy rates in replacement beef heifers. Four hundred and fourteen Angus-based beef heifers were enrolled in a completely randomized design at 4 locations from January to July of 2016. All heifers were exposed to the 7-d CO-Synch + controlled internal drug release (CIDR) protocol where they received a 100-µg injection of GnRH and a CIDR insert on day -9, 25 mg of PGF2α at CIDR removal on day -2, followed by a 100-µg injection of GnRH and TAI 54 ± 2 h later on day 0. Within location, all heifers were randomly assigned to 1 of 2 treatments: 1) heifers that received 650 mg of bST on day -9 (BST; n = 191); or 2) heifers that did not receive bST on day -9 (CONTROL; n = 223). Blood samples were collected on day -9, 0, 28, and 60 to determine the plasma concentrations of IGF-1. Follicle diameter was determined on day -2 and 0 by transrectal ultrasonography. Pregnancy was diagnosed via transrectal ultrasonography on day 28 or 35, and again at least 30 d after the end of the breeding season. Embryo morphometry was assessed by measuring crown-to-rump length (CRL) on day 28, and fetal size was assessed by measuring crown-to-nose-length (CNL) on day 60. Concentrations of plasma IGF-1 did not differ between treatments on day -9 (P = 0.924), 28 (P = 0.075), and 60 (P = 0.792); however, concentrations of plasma IGF-1 were greater (P < 0.001) in BST-treated heifers at TAI (372.4 ± 16.6 vs. 193.7 ± 16.6 ng/ml). No differences (P = 0.191) were detected for follicle diameter between CONTROL and BST treatments on day -2 or 0. Pregnancy rates to TAI (PR/AI) were greater (P = 0.028) for CONTROL compared to BST heifers (42.5 ± 4.0 vs. 29.9 ± 4.1%). No differences (P = 0.536) in CRL were observed on day 28 between CONTROL and BST heifers. In addition, no difference (P = 0.890) was observed for CNL between CONTROL and BST treatments. Final pregnancy rates did not differ (P = 0.699) between treatments. The administration of bST to beef heifers at the initiation of a TAI protocol increased plasma concentrations of IGF-1 at TAI; however, failed to enhance follicle diameter, embryo/fetal size, and reduced PR/AI.

Preweaning injections of bovine ST enhanced reproductive performance of Bos indicus-influenced replacement beef heifers

A 3 yr study evaluated the effects of three preweaning injections of bovine ST, administered 14 d apart, on growth and reproductive performance of Bos indicus-influenced beef heifers. On d 0 of each year, suckling Angus × Brangus heifers (n = 15 heifers/treatment/yr) were stratified by BW (147 ± 20 kg) and age (134 ± 11 d) and randomly assigned to receive an s.c. injection of saline (SAL; 5 mL; 0.9% NaCl) or 250 mg of sometribove zinc (BST; Posilac, Elanco, Greenfield, IN) on d 0, 14, and 28. Heifers and respective dams were managed as a single group on bahiagrass (Paspalum notatum) pastures from d 0 until weaning (d 127). From d 127 to 346, heifers were grouped by treatment, allocated to bahiagrass pastures (1 pasture/treatment/yr) and fed a molasses-based supplement (2.9 kg/heifer daily; DM basis) until d 346. Blood samples were collected on d 0, 14, 28, 42, and then every 9-10 d from d 179 to 346. In yr 3, liver biopsy samples were collected on d 0, 42, and 263. Heifers were exposed to mature Angus bulls from d 263 to 346. Growth performance and physiological parameters were analyzed using the MIXED procedure, whereas reproductive variables were analyzed using the GLIMMIX procedure of SAS. Effects of treatment × year and treatment × year × time were not detected for any variable measured in this study (P ≥ 0.14), except for calving percentage (P = 0.03). Heifers assigned to BST injections had greater overall plasma concentrations of IGF-1 and ADG from d 0 to 42 (P ≤ 0.05), less ADG from d 42 to 127 (P = 0.04), but had similar BW at weaning and postweaning ADG (P ≥ 0.25) compared to SAL heifers. Heifers assigned to BST tended to achieve puberty 26 d earlier (P = 0.10), had greater percentage of pubertal heifers on d 244, 263, 284, and 296 (P ≤ 0.04), tended to have greater overall pregnancy percentage (P = 0.10), and had greater (P ≤ 0.05) calving percentages in yr 1 and 2 (but not yr 3; P = 0.68) compared to SAL heifers. Liver mRNA expression of GHR-1B and IGF-1 on d 0 and 42 did not differ between treatments (P ≥ 0.15), but was greater for BST vs. SAL heifers on d 263 (P ≤ 0.02). Hence, administering three injections containing 250 mg of sometribove zinc at 14 d intervals before weaning (between 135 and 163 d of age) induced long-term impacts on liver gene expression and may be a feasible management practice to enhance puberty and pregnancy attainment in B. indicus-influenced replacement beef heifers.

Effects of recombinant bovine somatotropin administration at breeding on cow, conceptus, and subsequent offspring performance of beef cattle

The effects of administration of recombinant bovine ST (bST) on plasma hormone concentrations of cows, conceptus development, and postnatal calf performance were examined. Lactating beef cows ( = 190) were exposed to a fixed-time AI (TAI) protocol from d -10 to 0 (TAI on d 0). Cows were blocked by breed and stratified by days postpartum and then randomly assigned to receive, subcutaneously 1) 2 injections of saline (1 mL of 0.9% saline), 1 on d 0 at TAI and a second injection on d 14 (CTRL; = 53); 2) an injection of 325 mg of bST on d 0 and a saline injection on d 14 (bST0; = 48); 3) a saline injection on d 0 and an injection of 325 mg of bST on d 14 (bST14; = 49); or 4) 2 injections of 325 mg of bST, 1 on d 0 and a second injection on d 14 (bST0+14; = 40). Pregnancy status, crown-to-rump length (CRL) on Day 35, and crown-to-nose length (CNL) on Day 65 were determined via transrectal ultrasonography. Blood samples were collected on d 0, 7, 14, 21, 35, and 65, relative to TAI, to determine plasma concentrations of progesterone (P4), IGF-1, and pregnancy-specific protein B (PSPB) and also on d 18 and 21 for isolation of peripheral blood leukocytes for RNA extraction and measurement of interferon-stimulated genes transcript abundance. Individual calf BW was determined at birth and every 30 d until weaning. A subset of 24 calves was randomly selected for liver biopsies at birth to determine mRNA expression of target genes. Administration of bST to cows increased ( < 0.0001) concentrations of plasma IGF-1 for 14 d after injection compared with CTRL but did not affect fetal CRL and CNL ( = 0.23). Cows receiving bST only on d 0 had a greater ( = 0.05) transcript abundance in myxovirus resistance 2 on d 21 compared with 2bST cows (2.0- and 0.8-fold for bST0 and 2bST, respectively), whereas cows receiving bST14 and CTRL were intermediate (1.2- and 0.9-fold, respectively). Calf BW did not differ ( ≥ 0.100) among treatments on d 0, 30, 60, 90, 120, and 150 relative to birth. Injection of bST only on d 0 tended ( = 0.062) to increase calf liver mRNA expression of at birth compared with the calves born to cows in other treatments. Therefore, during a TAI protocol, the administration of 1 or 2 injections of 325 mg of bST to lactating beef cows enhanced their plasma concentrations of IGF-1 but failed to improve fetal size and plasma concentrations of maternal PSPB and P4 and had no effect on postnatal calf growth performance.

Paradoxical effects of bovine somatotropin treatment on the ovarian follicular population and in vitro embryo production of lactating buffalo donors submitted to ovum pick-up

The aim of the present study was to evaluate the effect of bovine somatotropin (bST; 500mg) administration on lactating buffalo donors submitted to two different ovum pick-up (OPU) and in vitro embryo production schemes with a 7 or 14d intersession OPU interval. A total of 16 lactating buffalo cows were randomly assigned into one of four experimental groups according to the bST treatment (bST or No-bST) and the OPU intersession interval (7 or 14d) in a 2×2 factorial design (16 weeks of OPU sessions). The females submitted to OPU every 14d had a larger (P<0.001) number of ovarian follicles suitable for puncture (15.6±0.7 vs. 12.8±0.4) and an increased (P=0.004) number of cumulus-oocyte complexes (COCs) recovered (10.0±0.5 vs. 8.5±0.3) compared to the 7d interval group. However, a 7 or 14d interval between OPU sessions had no effect (P=0.34) on the number of blastocysts produced per OPU (1.0±0.1 vs. 1.3±0.2, respectively). In addition, bST treatment increased (P<0.001) the number of ovarian follicles suitable for puncture (15.3±0.5 vs. 12.1±0.4) but reduced the percentage (18.9% vs. 10.9%; P=0.009) and the number (1.4±0.2 vs. 0.8±0.1; P=0.003) of blastocysts produced per OPU session compared with the non-bST-treated buffaloes. In conclusion, the 14d interval between OPU sessions and bST treatment efficiently increased the number of ovarian follicles suitable for puncture. However, the OPU session interval had no effect on embryo production, and bST treatment reduced the in vitro blastocyst outcomes in lactating buffalo donors.

Effects of bovine somatotropin administration on growth, physiological, and reproductive responses of replacement beef heifers

This experiment compared growth, body composition, plasma IGF-I and leptin, and reproductive development of beef heifers receiving or not recombinant bovine ST (BST) beginning after weaning until the first breeding season. Fifty Angus × Hereford heifers (initial BW = 219 ± 2 kg; initial age = 208 ± 2 d), weaned at approximately 6 mo of age, were assigned to the experiment (d 0 to 210). On d 0, heifers were ranked by initial BW and age and assigned to 1) treatment with BST or 2) saline control. Heifers assigned to the BST treatment received subcutaneous (s.c.) injections containing 250 mg of sometribove zinc whereas control heifers received a 5-mL s.c. injection of 0.9% saline every 14 d. Treatments were initiated on d 14 and last administered on d 196. Heifers were maintained on separate pastures harvested for hay the previous summer according to treatment and received grass and alfalfa hay at a rate to provide a daily amount of 7.0 and 1.0 kg of DM per heifer, respectively. Heifer shrunk BW was collected on d 1 and 211 for heifer ADG calculation. Blood samples were collected weekly from d 0 to 210 for determination of plasma progesterone to estimate puberty attainment as well as plasma concentrations of IGF-I and leptin in selected samples. On d 0, 63, 133, and 189, heifers were evaluated for intramuscular marbling, LM depth, and backfat thickness via real-time ultrasonography. No treatment effects were detected (P = 0.27) for heifer ADG (0.49 vs. 0.51 kg/d for control and BST heifers, respectively; SEM = 0.02). Mean backfat thickness was lesser (P < 0.01) in BST heifers compared with control cohorts (3.56 vs. 3.92 mm, respectively; SEM = 0.08). Heifers receiving BST had greater plasma IGF-I concentrations compared with control cohorts 7 d after treatment administration (treatment × day interaction; P < 0.01). Mean plasma leptin concentrations were lesser (P = 0.05) in BST heifers compared with control cohorts (1.82 vs. 2.03 ng/mL, respectively; SEM = 0.07). Onset of puberty was hastened in BST heifers compared with control cohorts (treatment × day interaction; P = 0.04). In summary, a greater proportion of BST heifers reached puberty during the experiment compared with control cohorts, despite lesser plasma leptin concentrations, backfat thickness, and similar ADG. Hence, circulating IGF-I was positively associated with hastened puberty attainment independently of growth rate, circulating leptin concentrations, and body fat content of replacement beef heifers.

Plasma progesterone concentration in beef heifers receiving exogenous glucose, insulin, or bovine somatotropin

Three experiments were conducted to evaluate plasma concentrations of glucose, insulin, IGF-I, and progesterone (P4) in pubertal beef heifers receiving exogenous glucose, insulin, or sometribove zinc. All heifers used had no luteal P4 synthesis but received a controlled internal drug-releasing device containing 1.38 g of P4 to estimate treatment effects on hepatic P4 degradation. In Exp. 1, 8 pubertal, nulliparous Angus × Hereford heifers (initial BW = 442 ± 14 kg; initial age = 656 ± 7 d) were randomly assigned to receive, in a crossover design containing 2 periods of 10 h, intravenous (i.v.) infusions (10 mL) of insulin (1 μg/kg of BW; INS) or saline (0.9%; SAL). Treatments were administered via jugular venipuncture in 7 applications (0.15 μg insulin/kg BW per application) 45 min apart (from 0 to 270 min). Blood samples were collected immediately before each infusion as well as at -120, -60, 330, 390, and 450 min relative to the first infusion. Heifers receiving INS had greater (P < 0.01) plasma insulin, reduced (P ≤ 0.04) plasma glucose and IGF-I, and similar (P = 0.62) plasma P4 concentrations compared with SAL heifers. In Exp. 2, the same heifers were assigned to receive, in a similar experimental design as Exp. 1, i.v. infusions (10 mL) of 1) insulin (1 μg/kg BW) and glucose (0.5 g/kg BW; INS+G) or 2) SAL. Heifers receiving INS+G had greater (P ≤ 0.02) plasma insulin, glucose, and P4 but reduced (P = 0.01) plasma IGF-I concentrations compared with SAL heifers. In Exp. 3, the same heifers were assigned to receive, in a crossover design containing 2 periods of 14 d, subcutaneous (s.c.) injections of 1) 250 mg of sometribove zinc (BST) or 2) SAL. Blood samples were collected 3 h apart (0900, 1200, 1500, and 1800 h) from heifers on d 6, 8, and 10 relative to treatment administration (d 1). Heifers receiving BST had greater (P < 0.01) plasma glucose and IGF-I and similar (P ≥ 0.67) plasma insulin and P4 concentrations compared with SAL heifers. Results from this series of experiments suggested that concurrent increases in glucose and insulin are required to reduce hepatic catabolism and increase plasma concentrations of P4 in bovine females.

Hormone variations in serum and milk of buffaloes (Bubalus bubalis) as potential indicators of treatment with recombinant bovine somatotropin

Recombinant bovine somatotropin (rbST) is used to increase milk yield in cows, but it has been forbidden in some countries and in the EU. However, rbST misuse represents a concern in both bovine and buffalo dairy production. A number of studies on rbST treatment have been performed on bovines, but there are few data on buffaloes. In this study, we treated eight lactating buffaloes with biweekly injections of a slow-release formulation of rbST, for five cycles of administration, and analysed total ST and insulin-like growth factor 1 (IGF-1) variations in serum and IGF-1 in milk. The aim was to assess their power as potential indicators of rbST-treatment. Blood was collected on days 2, 5, 9 and 14 of each cycle, and milk on days 2, 9 and 14 of cycles 2 and 5. Results showed an extraordinary increase in ST levels on day 2 in treated animals, followed by a rapid decrease over the following days, while a significant increase in IGF-1 was observed both in serum and in milk throughout most of each cycle. These results suggest that serum ST levels are a good indicator of treatment. However, the rapid decrease after the peak limits the useful period of sample collection.

The influence of tropical adaptation on plasma concentrations of insulin-like growth factor-I in purebred and crossbred beef cattle

In an effort to determine whether tropical adaptation influences circulating concentrations of the growth-related hormone IGF-I, 3-breed diallel matings were conducted using temperate Bos taurus (Angus), tropical Bos indicus (Brahman), and tropical Bos taurus (Romosinuano). Purebred Angus, Braham, and Romosinuano and crossbred Angus-Braham, Angus-Romosinuano, and Braham-Romosinuano heifers and steers were evaluated in 2 separate calf crops from 2003 and 2004. Blood samples were obtained from 10 heifers of each breed group (n = 90) for each year at weaning and on d 0 and 84 of postweaning trials. Samples were also taken from 10 steers of each breed group (n = 90) at weaning and on d 0 and 60 of individual finishing phase feeding trials for each year. Concentrations of IGF-I were determined by RIA. Analyses included effects of sire breed, dam breed, year of record, the age of the dam of the calf in years, and interactions. Age of calf in days was investigated as a linear and quadratic covariate. Separate analyses were conducted for steers and heifers. The direct effect of Angus was to reduce (P < 0.03) heifer concentrations of IGF-I at d 84 and in the repeated measures analysis. In the repeated measures analysis, the direct effect of Romosinuano was to increase concentrations of IGF-I (P = 0.01). Relative to the temperate Bos taurus breed, plasma concentrations of IGF-I were numerically greater in male and female tropically adapted breed groups.

Effects of flunixin meglumine, recombinant bovine somatotropin and/or human chorionic gonadotropin on pregnancy rates in Nelore cows

The objective was to compare pharmacological strategies aiming to inhibit prostaglandin F2 alpha (PGF(2α)) synthesis (flunixin meglumine; FM), stimulate growth of the conceptus (recombinant bovine somatotropin; bST) and progesterone (P(4)) synthesis (human chorionic gonadotropin; hCG), as well as their combinations, regarding their ability to improve pregnancy rates in beef cattle. Lactating Nelore cows (N = 975), 35 to 70 days postpartum, were synchronized and inseminated by timed artificial insemination (TAI) on Day 0. On Day 7, cattle were allocated into eight groups and received one of the following treatments: saline (S) on Days 7 and 16 (Group Control); S on Day 7 and FM on Day 16 (Group FM); bST on Day 7 and S on Day 16 (Group bST); bST on Day 7 and FM on Day 16 (Group bST + FM); hCG on Day 7 and S on Day 16 (Group hCG); hCG on Day 7 and FM on Day 16 (Group hCG + FM); bST and hCG on Day 7 and S on Day 16 (Group bST + hCG), or bST and hCG on Day 7 and FM on Day 16 (Group bST + hCG + FM). The aforementioned treatments were administered at the following doses: 2.2 mg/kg FM (Banamine®; Intervet Schering-Plough, Cotia, SP, Brazil), 500 mg bST (Boostin®; Intervet Schering-Plough), and 2500 IU hCG (Chorulon®; Intervet Schering-Plough). Pregnancy diagnosis was performed 40 days after TAI by transrectal ultrasonography. Pregnancy rates were not significantly different among treatments. However, there was a main effect of hCG treatment to increase pregnancy rates (63.0 vs. 55.4%; P = 0.001). Concentrations of P(4) did not differ significantly among groups on Day 7 or on Day 16. However, consistent with the higher pregnancy rates, hCG increased P(4) concentrations on Day 16 (10.6 vs. 9.6 ng/mL, respectively; P = 0.05). We concluded that hCG treatment 7 days after TAI improved pregnancy rates of lactating Nelore cows, possibly via a mechanism leading to induction of higher P(4) concentrations, or by reducing the luteolytic stimulus during maternal recognition of pregnancy.

Effect of bovine somatotropin (500 mg) administered at ten-day intervals on ovulatory responses, expression of estrus, and fertility in dairy cows

The objectives of this study were to evaluate the effect of administering 500 mg of recombinant bovine somatotropin (bST) every 10 d on ovulatory responses, estrous behavior, and fertility of lactating Holstein cows. Lactating dairy cows were assigned to 1 of 2 treatments: a control with no administration of bST (73 primiparous and 120 multiparous cows) or 6 consecutive administrations of 500 mg of bST (83 primiparous and 123 multiparous cows) given subcutaneously at 10-d intervals starting 61+/-3 d postpartum (study d 0), concurrent with the initiation of the timed artificial insemination (AI). Blood samples were collected thrice weekly from 61+/-3 to 124+/-3 d in milk (DIM), and plasma samples were analyzed for concentrations of estradiol, glucose, insulin, insulin-like growth factor 1, and progesterone. The estrous cycle of cows was presynchronized with 2 injections of PGF(2alpha) at 37+/-3 and 51+/-3 DIM, and the Ovsynch timed AI protocol was initiated at 61+/-3 DIM. Ovaries were scanned to determine ovulatory responses during the Ovsynch protocol. Pregnancy was diagnosed at 33 and 66 d after AI. Body condition was scored on study d 0, 10, 42, and 76. Sixty-four cows were fitted with a pressure mounting sensor with radiotelemetric transmitters to monitor estrous behavior. Treatment of lactating dairy cows with 500 mg of bST at 10-d intervals increased yields of milk and milk components in the first 2 mo after treatment. Body condition of bST-treated cows remained unaltered, whereas control cows gained BCS. Treatment with bST increased concentrations of insulin-like growth factor 1 chronically, but concentrations of insulin and glucose increased only transiently in the first 7 d after the first injection of bST. Concentrations of progesterone during and after the Ovsynch protocol remained unaltered after treatment with bST; likewise, ovulatory responses during the Ovsynch protocol were mostly unaltered by treatment. Concentration of estradiol tended to be greater for bST cows than for control cows immediately before induction of ovulation in the Ovsynch protocol. Similarly, the mean and the peak concentrations of estradiol were greater for bST cows than for control cows when monitored during spontaneous estrus. Nevertheless, duration of estrus and the median number of standing events were less for bST cows than for control cows. Pregnancies per AI after the first and second postpartum inseminations were not affected by bST treatment. Treatment of lactating dairy cows with 500 mg of bST every 10 d improved lactation performance, but it did not affect pregnancies per AI and it reduced expression of estrus.

On the alterations in serum concentration of somatotropin and insuline-like growth factor 1 in lactating cows after the treatment with a little studied recombinant bovine somatotropin

A study was performed to delineate bST and IGF-1 variation, over a whole lactation, in cows treated with a nowadays widely commercialised but little studied sustained release formulation of recombinant bST. Total bST levels were found to be exceptionally high in the first days after administration, but decreased rapidly in the second week after injection. The increase in the IGF-1 serum concentration was significant for almost the entire biweekly cycle. Based on this study, the peaks of ST (often above 100 ng/ml) are considered particularly unlikely to be found in non-treated bovines, even under pathological conditions, especially when detected in a number of animals within a herd. Notwithstanding the great heterogeneity of results on this topic, these data suggest that tests against fraud involving the use of rbST in dairy products may be regarded as a feasible possibility.

Pregnancy success of lactating Holstein cows after a single administration of a sustained-release formulation of recombinant bovine somatotropin

Background

Results regarding the use of bovine somatotropin for enhancing fertility in dairy cattle are variable. Here, the hypothesis was tested that a single injection of a sustained-release preparation of bovine somatotropin (bST) during the preovulatory period would improve pregnancy success of lactating dairy cows at first service.

Results

The first experiment was conducted in a temperate region of Mexico. Cows inseminated following natural estrus or timed artificial insemination were given a single injection of bST or a placebo injection at insemination (n = 100 cows per group). There was no significant difference between bST and control groups in the proportion of inseminated cows diagnosed pregnant (29 vs 31% pregnant). The second experiment was performed during heat stress in Florida. Cows were subjected to an ovulation synchronization regimen for first insemination. Cows treated with bST received a single injection at 3 days before insemination. Controls received no additional treatment. As expected, bST did not increase vaginal temperature. Treatment with bST did not significantly increase the proportion of inseminated cows diagnosed pregnant although it was numerically greater for the bST group (24.2% vs 17.8%, 124–132 cows per group). There was a tendency (p = 0.10) for a smaller percent of control cows to have high plasma progesterone concentrations (≥ 1 ng/ml) at Day 7 after insemination than for bST-treated cows (72.6 vs 81.1%). When only cows that were successfully synchronized were considered, the magnitude of the absolute difference in the percentage of inseminated cows that were diagnosed pregnant between bST and control cows was reduced (24.8 vs 22.4% pregnant for bST and control).

Conclusion

Results failed to indicate a beneficial effect of bST treatment on fertility of lactating dairy cows.

A single dose of bovine somatotropin 5 days before the end of progestin-based estrous synchronization increases prolificacy in sheep

Bovine somatotropin (bST) enhances ovarian follicular and embryonic development in sheep and cattle. In the present study, the objective was to assess whether bST given 5 days before the end of progestin-based estrous synchronization improves prolificacy and lambing rate in sheep. Pelibuey ewes (n=92) exhibiting estrous cycles at regular intervals received an intravaginal sponge containing 45mg of FGA for 12 days. Five days before sponge withdrawal, ewes were treated with either 125mg of bST sc (bST group; n=47) or saline solution (control; n=45). After the sponge was removed, ewes were observed for estrus and subsequently mated twice. Lambing rate and prolificacy was determined at birth. Blood samples were taken from the time of treatment until day 15 after estrus in eight ewes from the bST group and nine from the control group. Concentrations of IGF-I were determined by immunoradiometric assay and progesterone by RIA. Treatment with bST increased (P<0.01) the proportion of ewes with more than one lamb (bST, 56% compared with control, 26%) and prolificacy (bST, 1.6 compared with control, 1.3). Treatment with bST increased (P<0.05) the lambing rate of multiparous (bST, 92% compared with control, 67%) but not in ewes at the first time they were mated (bST, 71% compared with control, 87%; P>0.05). IGF-I concentrations were greater (P<0.01) in ewes treated with bST than in control ewes from 2 days after treatment. Progesterone concentrations did not vary (P>0.05) between groups. It is concluded that a single dose of bST 5 days before progestin withdrawal increases lambing rate and prolificacy in sheep. These effects are associated with an increase in circulating concentrations of IGF-I.

Influence of body condition and bovine somatotropin on estrous behavior, reproductive performance, and concentrations of serum somatotropin and plasma fatty acids in postpartum Brahman-influenced cows1,2

Ninety-nine multiparous Brahman-influenced (1/4 to 3/8 Brahman) cows were managed to achieve low (BCS = 4.3 +/- 0.1; n = 50) or moderate (BCS = 6.1 +/- 0.1; n = 49) body condition (BC) to determine the influence of bovine somatotropin (bST) on estrous characteristics, reproductive performance, and concentrations of serum GH and plasma NEFA. Beginning 32 d postpartum, cows within each BC were assigned randomly to treatment with or without bST. Non-bST-treated cows received no treatment, and treated cows were administered bST (Posilac, 500 mg s.c.) on d -35, -21, and -7 before initiation of the breeding season. On d -7, all cows received an intravaginal, controlled internal drug-releasing (CIDR) device. On d 0 (initiation of the 70-d breeding season), the CIDR were removed and cows received prostaglandin F2alpha (PGF2alpha). Blood samples were collected from the median caudal vein of the cows at each bST treatment and at d -28 and 0. Estrous behavior was monitored by radiotelemetry during the first 30 d of the breeding season. Growth hormone was increased (P < 0.05) in low and moderate BC cows treated with bST. The percentage of cows detected in estrus during the first 30 d of the breeding season was decreased (P = 0.05) for low BC (64%) compared with moderate BC (82%) cows. The interval to first estrus tended (P = 0.07) to be shorter in low BC-bST-treated cows (3.7 +/- 1.9 d) than in moderate BC-bST-treated cows (9.6 +/- 1.8 d). During the first 30 d of the breeding season, cows in low BC had a decreased (P = 0.02) number of mounts received and increased (P = 0.001) quiescence between mounts compared with cows in moderate BC. The number of mounts received was reduced (P = 0.04) in bST-treated cows. More (P = 0.02) cows treated with bST became pregnant during the first 3 d of the breeding season compared with non-bST-treated cows. The cumulative first-service conception rate tended (P = 0.07) to be greater for bST-low BC cows than non-bST-treated cows in low or moderate BC. On d 0, NEFA were greater (P < 0.05) in bST-treated vs. non-bST-treated cows. Low BC and bST reduced the intensity of behavioral estrus in postpartum Brahman-influenced cows. However, bST increased the first-service conception rate during the first 30 d of breeding and pregnancy rates during the first 3 d of breeding in postpartum Brahman-influenced cows.

Fertility of Lactating Dairy Cows Administered Recombinant Bovine Somatotropin During Heat Stress

Administration of recombinant bovine somatotropin (bST) to lactating dairy cows during heat stress increases milk yield, but it also can increase body temperature and may therefore compromise fertility. However, it is possible that bST treatment could increase fertility during heat stress because it has been reported to increase fertility in lactating cows. In addition, bST increases secretion of insulin-like growth factor-I (IGF-I) that promotes embryo survival. The purpose of this study was to determine effects of bST on reproductive function in lactating dairy cows during heat stress. The experiment was conducted in southern Georgia from July to November 2005 using lactating Holstein cows (n = 276 for reproductive traits). For first service timed artificial insemination (TAI), cows were presynchronized with 2 injections of PGF(2alpha) given 14 d apart followed by a modified Ovsynch protocol (GnRH and insemination at 72 h following PGF(2alpha) ). Pregnancy was diagnosed by using ultrasonography on d 29 and reconfirmed by palpation between d 45 and 80 post-TAI. Nonpregnant cows were resynchronized with the modified Ovsynch protocol and received a second TAI. Treatment with bST started 1 wk before the start of Ovsynch and continued at 2-wk intervals. Blood samples were collected from a subset of cows to determine IGF-I profiles immediately before the first bST injection, 1 wk later, and at d 35 of bST treatment. Rectal temperatures were assessed on d 29 of bST treatment. Pregnancy rates (d 45 to 80 post-TAI) did not differ between bST and control cows for first- (16.7 vs. 15.2%) or second-service TAI (14.8 vs. 17.2%). Plasma concentrations of IGF-I and milk yield were greater for bST-treated cows following the initiation of bST treatment and bST increased rectal and vaginal temperatures. Body condition score was less for bST-treated cows. In conclusion, treatment with bST during heat stress increased IGF-I concentrations, milk yield over time, and rectal and vaginal temperatures without affecting first- or second-service pregnancy rates. Thus, at least under certain housing conditions, bST can be used to improve milk yield during heat stress without compromising fertility.

Pregnancy, Bovine Somatotropin, and Dietary n-3 Fatty Acids in Lactating Dairy Cows: I. Ovarian, Conceptus, and Growth Hormone–Insulin-Like Growth Factor System Responses

The objective was to examine effects of bovine somatotropin (bST), pregnancy, and dietary fatty acids on reproductive responses in lactating dairy cows. Beginning at approximately 17 d in milk (DIM), a comparison was made of isoenergetic diets comprising supplementary lipids of whole cottonseed vs. calcium salts of fish oil enriched lipid (FO). Ovulation was synchronized in cows with a presynchronization plus Ovsynch protocol, and cows were inseminated artificially by appointment or not inseminated (d 0 = time of synchronized ovulation; 77 +/- 12 DIM). On d 0 and 11, cows received bST (500 mg) or no bST. All cows were slaughtered on d 17. Number of cows in each group was as follows: control diet had 5 bST-treated cyclic (bST-C), 5 non-bST-treated cyclic (no bST-C), 4 bST-treated pregnant (bST-P), and 5 non-bST-treated pregnant (no bST-P) cows; and cyclic cows fed FO diet had 4 bST-treated (bST-FO) and 5 non-bST-treated cyclic (no bST-FO-C) cows. Feeding FO increased milk production, number of class 1 follicles (2 to 5 mm), and decreased insulin during the period before d 0 compared with control-fed cows. The bST increased milk production, pregnancy rate [83% (5/6) vs. 40% (4/10)], conceptus length (45 vs. 34 cm), and interferon-tau in the uterine luminal flushings (9.4 vs. 5.3 microg) with no effect on interferon-tau mRNA concentration in the conceptus. Treatment with bST increased plasma growth hormone (GH) and insulin-like growth factor (IGF)-I. Among control-fed cows (cyclic and pregnant), bST decreased progesterone concentration in plasma. Cows fed FO had less plasma insulin than control-fed cyclic cows, and FO altered the plasma GH (bST-FO > bST-C) and IGF-I (bST-C > bST-FO-C) responses to bST injections. Endometrial IGF-I mRNA was reduced in pregnant cows and tended to decrease in those fed FO. The IGF-II mRNA was increased in the endometrium of pregnant and bST-treated cows fed the control diet. Cows fed FO had increased concentrations of IGF-II mRNA, when bST was not injected. The insulin-like growth factor binding protein-2 (IGFBP-2) mRNA was increased in bST-P cows, whereas bST decreased the IGFBP-2 mRNA in all cyclic cows. In summary, bST and FO seemed to modulate reproductive responses that may be beneficial to the developing conceptus and pregnancy rate.

Effect of a single growth hormone (rbST) treatment at breeding on conception rates and pregnancy retention in dairy and beef cattle

Initiation of long-term treatment with rbST (Posilac, Monsanto, St. Louis, MO) coincident with first insemination increased pregnancy rates in dairy cattle, but neither the efficacy of using only the initial injection, nor its effects on retention of pregnancy are known. Lactating dairy cows, dairy heifers, and lactating beef cows were assigned at random to treatment (rbST) or control. Dairy cows, dairy heifers, and beef cows received 500 mg rbST (n = 48, 35, 137 inseminations, respectively) at artificial insemination or were left untreated (n = 62, 33, 130 inseminations, respectively). Pregnancy was diagnosed by ultrasonography at 28-36 days. Treatment with rbST at insemination improved conception rates in dairy cows (60.4% versus 40.3%; P < 0.05), but not in dairy heifers or beef cows. Conception rates did not differ in dairy cows at < or =100 days in milk (DIM), but were improved in cows treated with rbST after 100 DIM (64.3% versus 25.8%; P < 0.05). Retention of pregnancy to approximately 60 days and sizes of CL, diameter of follicles > or =5 mm, and crown-rump lengths of embryos were not affected by treatment. The second objective was to examine the effects of rbST at insemination on birth weight and post-natal calf growth in beef cows. However, birth and weaning weights of beef calves were not affected by treatment. In conclusion, a single treatment with rbST at insemination increased conception rates in dairy cows, specifically in those >100 DIM.

Relationships between the plasma concentrations of insulin-like growth factor-I in dairy cows and their fertility and milk yield

The relationships between insulin-like growth factor-I (IGF-I) and the fertility and milk yield of Holstein-Friesian dairy cows were investigated. The concentration of IGF-I in blood was measured weekly from one week before to 12 weeks after calving in 177 multiparous cows and at four times during this period in 142 primiparous cows; the concentration of IGF-I in milk was measured in 50 of the multiparous cows. The plasma concentrations of IGF-I were higher in the primiparous than in the multiparous animals. In the primiparous cows, high concentrations of IGF-I before calving were associated with longer calving to conception intervals. Conversely, in the multiparous cows low concentrations of IGF-I before and after calving were associated with a failure to conceive, despite repeated services. Multiparous cows with IGF-I concentrations of greater than 25 ng/ml in the week after calving were 11 times more likely to conceive to first service than those with lower concentrations. Concentrations of IGF-I greater than 50 ng/ml at first service increased the likelihood of conception five-fold. Cows with higher peak milk yields had lower plasma concentrations of IGF-I and took longer to return to ovarian cyclicity. The negative relationship between milk yield and return to cyclicity was stronger in the multiparous cows (P < 0.002) than in the primiparous cows (P < 0.04). The concentrations of IGF-I in milk followed a different pattern and were not associated with the changes in plasma IGF-I or fertility.

Pregnancy rates and metabolic profiles in cattle treated with propylene glycol prior to embryo transfer

The objective of this study was to determine the effect of a sustained propylene glycol administration to recipients of frozen/thawed in vivo derived bovine embryos. Heifers were treated with oral propylene glycol for the last 20 days before embryo transfer (n = 142), and untreated as controls (n = 133). Progesterone, insulin, insulin-like growth factor-I, glucose, urea and triglyceride were analysed in blood on Day 0 and Day 7 of the estrous cycle corresponding to embryo transfer. The heifers were selected as recipients when showing progesterone levels <2.0 ng/ml (Day 0) and >2.5 ng/ml (Day 7), according to corpus luteum quality on Day 7 by technicians unaware of animals treated. Within treated animals, significantly more recipients were selected, and increased progesterone, corpus luteum quality, pregnancy and calving rates were recorded. Day 7 progesterone concentrations were higher in heifers treated and transferred. Propylene glycol increased insulin and insulin-like-growth factor-I, but glucose, urea and triglyceride did not vary. Furthermore, insulin-like-growth factor-I, glucose and triglyceride increased at estrous time, but urea decreased and insulin remained unaltered. Together with the sustained gain in pregnancy rates throughout the experiment (2 years), other evidences suggested that the observed effects did not rely on nutritional deficiency. Thus, propylene glycol improved pregnancy rates after embryo-transfer, and progesterone, insulin and insulin-like-growth factor-I are probably involved in this effect.

Pregnancy and Bovine Somatotropin in Nonlactating Dairy Cows: I. Ovarian, Conceptus, and Insulin-Like Growth Factor System Responses

Nonlactating dairy cows were used to examine effects of bovine somatotropin (bST) on components of the insulin-like growth factor (IGF) system. Estrus was synchronized in cows with a Presynch + Ovsynch protocol and timed AI (TAI; n = 55) or not TAI (cycling, C; n = 23) on d 0 (time of synchronized ovulation). On d 0 and 11, cows received bST (500 mg) or no bST, and were sacrificed on d 17. Pregnancy rates were less in bST cows (27.2%, 9 of 33) than in controls (63.6%; 14 of 22). In contrast, conceptuses were larger in bST-treated cows (39.2 +/- 4.8 cm) than in controls (20 +/- 4.3 cm). Total interferon-tau in uterine luminal flushings (ULF) was greater in bST-treated cows (7.15 > 2.36 microg). Number of class 2 follicles (6 to 9 mm) was less in bST-C cows on d 7 and 16. On d 17, corpus luteum (CL) weight tended to be greater in bST-treated cows. Concentrations of progesterone were greater after d 10 in C than in pregnant (P) cows. In the ULF, IGF-binding protein-3 was greater in bST-P cows than in pregnant cows. A tendency for an increase in IGF-I hormone concentrations in the ULF was detected on d 17 in bST-treated and cyclic cows. Endometrial mRNA for IGF-I, IGF-II, IGFBP-2, and IGFBP-3 increased in bST-C, but not in bST-P cows. Treatment with bST increased plasma concentrations of insulin, IGF-I, and growth hormone (GH). In conclusion, bST may have hyperstimulated plasma IGF-I and insulin to cause asynchrony between conceptus and uterus that was detrimental to pregnancy.

Transition cow: interaction with fertility

In recent years a progressive worsening of fertility indices in dairy cow herds has been observed. Several factors (genetic, dietary and management) seem to be more related to poor fertility than milk yield level. The degree and the length of the energy deficit during the transition period are inversely related to reproductive indices (e.g. conception rate is <30% for BCS decreases over one unit). A serious energy deficit reduces (or suppresses) pulsatile secretion of gonadotrophins (ovarian dysfunction and/or smaller follicles): IGF-I and insulin plasma levels (slower follicle growth and higher embryonic mortality); and progesterone production from the corpus luteum (higher rate of embryonic abortions). The diet influences fertility in several ways. Excess of rumen degradable proteins, apart from negative energy balance, negatively affects reproductive activity. Conversely, some nutrients (i.e. some polyunsaturated fatty acids or some amino acids) seem to show positive effects on fertility. Finally, the relationship between health status, often compromised during the transition period, and fertility efficiency is discussed. The release of cytokines seems to be related directly and indirectly (mainly by the change in usual hepatic metabolism to the malfunction of reproductive apparatus. Quick recovery of reproductive activity requires the adoption of strategies around calving to cover the higher environmental and nutritive requirements and to prevent disorders of any kind.

Effects of lasalocid on circulating concentrations of leptin and insulin-like growth factor-I and reproductive performance of postpartum Brahman cows

Objectives were to determine effects of lasalocid on reproductive performance and serum concentrations of leptin and IGF-I, and to correlate concentrations of leptin and IGF-I with reproductive performance of beef cows. Forty-one purebred, multiparous Brahman cows were blocked to control (C; n = 20) or lasalocid (L; n = 21) treatments by BW, BCS, and predicted calving date. Treatment began 21 d before expected calving. Cows were each fed 1.4 kg daily of an 11:1 corn:soybean meal supplement, with the L group receiving 200 mg of lasalocid/cow daily. Cows and calves were weighed, and cow BCS was assessed at calving and at 28-d intervals thereafter. Blood samples were collected weekly precalving, at parturition, and twice weekly thereafter. Sterile marker bulls were maintained with cows for estrous detection. Six days after estrus, ovaries were evaluated for corpus luteum formation, and blood samples from d 6, 7, and 8 after estrus were collected. Serum samples were assayed for progesterone (P4), IGF-I, and leptin concentration. Progesterone concentrations > 1 ng/mL were considered indicative of a functional corpus luteum. Treatment ended after completion of a normal estrous cycle, and cows removed from treatment were placed with a fertile bull equipped with a chinball marker. There were no treatment differences in calving date, calf sex, cow BW, BCS, calf BW, calf ADG, or in serum concentrations of P4, IGF-I, or leptin. Prepartum cow ADG was increased (P < 0.01) in L cows and tended (P < 0.011) to be increased from calving to d 56 after calving in L cows. Postpartum interval (PPI) was not affected by treatment; however, a greater percentage (P < 0.05) of L cows conceived by 90 d after calving (43% L vs. 15% C). First-service conception rate tended (P < 0.08) to be greater in L vs. C cows (68 vs. 40%), but pregnancy rate was not different (P < 0.12; 86% for L vs. 65% for C). There were no treatment differences (P > 0.18) for serum IGF-I concentrations. At calving, leptin was positively correlated with IGF-I (P < 0.04; r = 0.32), BCS (P < 0.06; r = 0.29), and cow BW (P < 0.02; r = 0.36), and was negatively correlated with PPI (P < 0.06; r = -0.29). These results provide evidence that feeding an ionophore before calving and during the postpartum period may increase the number of cows that rebreed to maintain a yearly calving interval. Cows with higher concentrations of leptin postpartum may exhibit shorter PPI.

Effect of recombinant bovine somatotropin on superovulatory response and recipient pregnancy rates in a commercial embryo transfer program

Recombinant bovine somatotropin (rbST) has been shown to increase follicular growth in cattle and some studies have demonstrated an increase in superovulatory response for rbST-treated cows. Pregnancy rates have also been shown to increase when rbST was administered around the time of insemination or prior to embryo transfer. The application of rbST for the purpose of increasing superovulatory responses of donor cows and increasing pregnancy rates of recipient heifers was tested in a commercial embryo transfer program. In Experiment 1, embryo donor cows (n = 56) underwent three cycles of control superovulation (two before and one after weaning) and subsequently underwent up to four additional superovulations while being treated with either rbST (500 mg sustained-release rbST; Posilac, Monsanto, St. Louis, MO; n = 28) or excipient (control; n = 28) once every 14 days. In Experiment 2, lactating embryo donor cows (n = 37) underwent a control superovulation and then underwent a superovulation while lactating and being treated with either rbST (n = 16) or excipient (n = 21). In Experiment 3, embryo recipient heifers that were being implanted with either in vitro or in vivo produced embryos were treated with either rbST (n = 146) or excipient (n = 143) at the time of embryo transfer. Treatment of non-lactating (Experiment 1) or lactating (Experiment 2) donor cows with rbST during repeated superovulation did not affect the number of corpora lutea, the sum of transferable embryos, degenerate embryos, and unfertilized oocytes, or the number of transferable embryos. Treatment of recipient heifers with rbST (Experiment 3) did not affect pregnancy rates for either in vitro or in vivo produced embryos. We conclude that superovulatory response and pregnancy rates (respectively) are similar to control for rbST-treated cows undergoing repeated superovulations and rbST-treated recipient heifers treated at the time of embryo transfer.

Effects of whole cottonseed diet and recombinant bovine somatotropin on ovarian follicles in lactating dairy cows

The effects of whole cottonseed (WCS) in the diet and the administration of bovine somatotropin (bST) on ovarian follicular dynamics and plasma progesterone (P4) concentrations were examined in cows during a period of synchronized follicular growth. Lactating Holstein cows (n = 28) were randomly assigned to treatments in a 2 x 2 factorial arrangement. Diets consisted of WCS (15% of dry matter) or no WCS, and bST at a dose of 0 or 208 mg/14 d. Dietary treatments began within 24 h of calving and bST treatments began within 7 d postpartum. Cows received GnRH at 65 +/- 3 d postpartum (d 0), PGF2alpha, (d 7), a second dose of GnRH (d 9), and were inseminated 16 h later (d 10). Ovarian changes were monitored daily by ultrasonography from d 0 to 9. On d 9,93% of cows had a preovulatory follicle and 86% ovulated. For Class 2 (6 to 9 mm) follicles, a diet x bST interaction was detected, with bST stimulating Class 2 follicles in cows fed WCS, but not in cows on the control diet. Neither diet nor bST affected numbers of Class 1 (2 to 5 mm) or Class 3 (> or = 10 mm) follicles or sizes of the subordinate and dominant follicles. During the luteal phase of the cycle, lactating cows fed WCS tended to have elevated concentrations of plasma P4, whereas bST was without effect. Plasma concentrations of high-density lipoprotein cholesterol were increased in cows fed WCS. Number and diameter of corpora lutea did not differ among treatments.

Reduced insulin-like growth factor-I after acute feed restriction in lactating dairy cows is independent of changes in growth hormone receptor 1A mRNA

Growth hormone receptor (GHR) and insulin-like growth factor-I (IGF-I) mRNA decrease in the liver of dairy cows at parturition. Epinephrine is released and feed intake is decreased at the same time. The objective of this study was to determine whether feed restriction and (or) administration of epinephrine could recapitulate the changes in the hepatic GHR 1A and IGF-I mRNA that occur at parturition. Eight lactating cows were randomly assigned to one of two rations (ad libitum or restricted). The cows assigned to the restricted ration were fed 75, 60, 60, and 25% of feed consumed by the ad libitum cows on successive days to mimic the changes in feed intake around parturition. Liver samples were collected by needle biopsy before and after feed restriction. Cows received either 0.02 mg/kg of epinephrine or saline approximately 24 h before the second liver biopsy so that a 2 x 2 factorial arrangement of treatments was created. Feed restriction increased plasma nonesterified fatty acids and liver triglyceride percentages and decreased plasma IGF-I concentrations. The decrease in plasma IGF-I after feed restriction was associated with a decrease in IGF-I mRNA in feed-restricted cows. The amount of GHR 1A mRNA did not change after feed restriction. Epinephrine treatment did not affect the amount of GHR 1A or IGF-I mRNA. We conclude that the decrease in feed intake at parturition may be partially responsible for the decrease in IGF-I but may not cause the decrease in GHR 1A.

Effects of growth hormone on female reproductive organs

During the last decade many experiments have been performed to study the effects of growth hormone (GH, somatotropin) on reproductive functions. Most of the studies found only slight or no effects of GH treatment, both on the oestrous cycle and on gonadotropin, progesterone. or oestrogen serum levels. In GH-treated animals, elevated levels of insulin-like growth factor I and GH in the serum could be correlated with an increased number of small (< 5 mm in diameter) ovarian follicles, possibly as a consequence of a reduction of apoptosis and follicular atresia. There is still controversy over the effects of GH on in vivo and in vitro embryo production and on the gestation period. Recent studies produced some evidence that GH-receptor is expressed in ovarian tissue, implying a direct role for GH in the ovary.

Effect of short-term treatment with bovine somatotropin at estrus on conception rate and luteal function of repeat-breeding dairy cows

We studied the effect of recombinant bovine somatotropin (rbST) at the time of estrus on progesterone concentrations and conception rates of repeat-breeding Holstein cows. We used repeat-breeding cows of varied parity (n = 510). All the animals were clinically healthy and had had at least three unsuccessful services before entering the study. After detection of estrus, the cows were randomly assigned to either a treated (n = 201) or a control (n = 309) group. The animals in the treated group were given rbST (500 mg s.c.) at the time of estrus and again 10 d later. Artificial insemination was performed 12 h after the first detection of estrus. In order to evaluate the effect of rbST on luteal function, blood samples were taken from 10 cows in each group every 3 d for 18 d, starting on the day of insemination (Day 0) to determine progesterone concentrations. Conception rates were significantly higher (P < 0.05) in the cows treated with rbST (29.3%) than in the control cows (16.9%). The effects of rbST were maximal in cows with 8 or more previous unsuccessful services and in cows with 2 to 4 calvings. Progesterone concentrations tended to be higher in nonpregnant cows that were treated with rbST than in those that were not treated. The difference between groups was significant (p < 0.05) on Day 18 after insemination. In pregnant cows there were no significant differences in progesterone concentrations between treated and nontreated animals at any time. Treatment with rbST at estrus improved the conception rate of repeat-breeding Holstein cows. This effect was associated with an increase in circulating progesterone concentrations on Day 18.

Reproductive loss in high-producing dairy cattle: where will it end?

The dairy industry in the United States has changed dramatically in the last decade. Milk production per cow has increased steadily because of a combination of improved management, better nutrition, and intense genetic selection. Dairy farms are larger, and nearly 30% of the dairy cows in the United States are on farms with 500 or more cows. The shift toward more productive cows and larger herds is associated with a decrease in reproductive efficiency. Cows with the greatest milk production have the highest incidence of infertility, but epidemiological studies suggest that, in addition to milk production, other factors are probably decreasing reproductive efficiency in our dairy herds. The reproductive physiology of dairy cows has changed over the past 50 yr, and physiological adaptations to high milk production may explain part of the reproductive decline. Critical areas for new research include control of the estrous cycle, metabolic effects of lactation on reproduction, mechanisms linking disease to reproduction, and early embryonic mortality. Solving reproductive loss in dairy cows will not be easy because only a small number of research groups study reproduction in postpartum dairy cows. Therefore, the present research base will need to be expanded. For this to occur, research funding must be increased above its current level and a renewed emphasis must be placed on solving the emerging crisis of infertility in dairy cows.

Growth and the initiation of steroidogenesis in porcine follicles are associated with unique patterns of gene expression for individual componentsof the ovarian insulin-like growth factor system

Ovarian follicular growth and steroidogenesis are controlled by the interaction of insulin-like growth factors (IGFs) and gonadotropins. The objective was to determine the temporal and spatial relationships for gonadotropin receptor, steroidogenic enzyme, and IGF system gene expression during the development of preovulatory porcine follicles. Sows (n = 18) were weaned and follicles were monitored by transrectal ultrasonography. Ovaries were collected from sows when the mean diameter of the preovulatory follicular cohort was approximately 2, 4, 6, or 8 mm. mRNA were measured by in situ hybridization for individual follicles within the preovulatory cohort (3 to 5 follicles per sow). Patterns of gene expression detected by in situ hybridization were confirmed by RNase protection analyses of pooled RNA samples. The amount of LH receptor mRNA and steroidogenic enzyme mRNA (17alpha-hydroxylase and aromatase) increased as the mean diameter of the follicular cohort increased from 2 to 6 mm, but then decreased abruptly for 8-mm follicles. Estradiol concentrations in follicular fluid closely followed the expression patterns of steroidogenic enzymes and LH receptor mRNA. FSH receptor mRNA was present in cohorts of 2-mm follicles but declined in 4-mm follicles and was undetectable in 6- and 8-mm follicles. The expression of IGF-I and type I IGF receptor mRNA were similar for follicles of 2, 4, 6, and 8 mm. In contrast, IGF-II mRNA progressively increased in follicles collected from 2-, 4-, and 6-mm cohorts, and then decreased slightly at 8 mm. Type II IGF receptor mRNA was greatest in 8-mm follicles. IGF binding protein-2 (BP-2) mRNA decreased as follicles achieved progressively larger sizes during the preovulatory period (2 to 8 mm), whereas the IGFBP-4 mRNA remained relatively low for follicles in 2- to 6-mm cohorts but then increased markedly in 8-mm follicles. In summary, temporal and spatial patterns of gene expression for gonadotropin receptor, steroidogenic enzyme, and IGF system genes were characterized in preovulatory porcine follicles by using in situ hybridization and RNase protection analyses. The unique patterns of gene expression suggest interdependence among specific genes that may be essential for preovulatory follicular development.