Luteinizing hormone releasing hormone, estrogen, and progesterone receptors in canine mammary lesions and tumor cell lines.

Nineteen canine mammary lesions were analyzed for estrogen receptor (ER), progesterone receptor (PR) and luteinizing hormone releasing hormone receptor (LHRHR) content. In addition, nine previously established canine mammary tumor cell lines with known ER and PR were analyzed for LHRHR. The incidence of receptors in the mammary tumor lesions was 21% for LHRHR, 10% for ER and 30% for PR. Statistical correlation was not observed between receptor status and diagnosis of malignant, benign, or hyperplastic lesions. A relationship between LHRHR and ER and PR content of canine mammary lesions or cell lines was not evident. The presence of functional hormone receptors offers opportunity for hormonal treatment of mammary cancer which may not be completely treatable by surgery. The observation of LHRHR in canine mammary tumors may offer therapeutic interventions other than surgery for mammary tumors unresponsive to antiestrogens.

Myosin heavy chain gene expression in bovine fetuses and neonates representing genotypes with contrasting patterns of growth.

Fetal and neonatal myosin heavy chain (MHC) gene expression was examined in bovine genotypes that differed in their postnatal growth pattern and mature size. Pregnancies were established that would be expected to produce early-, intermediate-, or late-maturing postnatal growth. Fetal skeletal and cardiac muscles were collected at 100 and 200 days of gestation and at 30 days of age. Muscle tissue was analyzed for relative levels of MHC RNA and protein. Longissimus muscle MHC RNA/microgram RNA was greater at the 100-day time point for the intermediate maturity type (P < 0.05), which differed from the 200-day time point where the early maturity type had the greater RNA level (P < 0.05). Triceps muscle MHC RNA/microgram RNA weights differed due to genotype at 200 days gestation but did not differ at 100 days gestation or at 30 days postnatal. Ventricular muscle MHC RNA did not differ due to genotype at any of the three developmental stages. Differences due to maturity type in MHC protein/mg DNA were observed at 30 days of age, but no differences due to maturity type were observed at the prenatal time points. These results indicate that bovine fetal skeletal muscle MHC RNA production can be influenced by genotype and that genotype may be an important factor for future studies examining the role of external influences on fetal muscle growth.

Maternal treatment with somatotropin alters embryonic development and early postnatal growth of pigs.

A possible management strategy to alter fetal development and enhance sow productivity and progeny performance was examined by maternal administration of porcine somatotropin during early gestation. Eighteen crossbred gilts were bred naturally to boars of similar genetics, and pregnancy was confirmed between Days 21 and 24 of gestation by ultrasound. All animals were allowed ad libitum consumption of a 16% CP gestation diet through Day 21 of gestation and 3.0 kg/d for the remainder of gestation. Gilts were injected twice daily with 0 (n = 10) or 15 micrograms/kg body weight (BW) (n = 10; total, 30 micrograms/kg BW per d) pituitary-derived porcine somatotropin (pST) during Days 28 to 40 of gestation. Data were collected postmortem during embryonic, neonatal, and market-weight phases. At 41 d of gestation, pST treatment increased embryonic survival (87.9 versus 77.0%; P < 0.05) and embryo crown rump lengths (77.96 versus 65.14 mm; P < 0.01), but embryo weight was not altered (10.15 and 9.03 g; P > 0.10). Pigs from pST-treated gilts had increased (P < 0.01) crown rump lengths at birth (31.5 versus 30.4 cm) and 21 d (50.9 versus 48.4 cm). However, no differences were observed in birth or 21-d weights as a result of pST treatment (P > 0.10). Neonatal carcasses of progeny (20 kg BW) from the pST-treated gilts had heavier semitendinosus muscles (76.1 versus 66.0 g; P < 0.10), larger longissimus muscle cross-sectional area (10.1 versus 8.2 cm2; P < 0.05), longer sides (51.2 versus 47.9 cm; P < 0.001), and decreased 10th rib backfat (6.67 versus 8.64 mm; P < 0.001) compared with those of controls. Carcasses of market-weight progeny (100 kg BW) from pST-treated gilts had larger longissimus muscle cross-sectional area (P < 0.10), heavier trimmed loins (P < 0.10), and longer carcass sides (P < 0.05). Data are supportive of a hypothesis that mechanisms during early embryonic development are sensitive to manipulation through selected management strategies of the sow and that modifications of this strategy may serve as a model for the examination of molecular and cellular events controlling early embryonic growth.

Growth and development of bovine fetuses and neonates representing three genotypes.

Growth was examined in bovine fetuses and neonates that typically differ in mature size and postnatal developmental pattern. Pregnancies were established from matings expected to produce early (E), late (L), and intermediate (I) maturing postnatal growth patterns. Tissues were collected at 100 and 200 d of gestation and 30 d postnatal. Muscle:body weight ratios were lower at 100 and 200 d for the E maturity type than for the L maturity type (P < .05). This differs from observations of muscle:body weight ratios made at 30 d postnatal, at which time ratios for E were either greater than (triceps brachii, P < .05) or similar to those for L. Few differences due to maturity type were observed at 100 d for bone weight:body weight ratios; however, at 200 d of gestation E bone weight:body weight ratios were generally lower (P < .05) than those for L. The genotypic relationship for bone weight:body weight ratio at 30 d postnatal was similar to that observed at 200 d of gestation. Observations of organ weight:body weight ratios revealed no clear patterns due to maturity type. The genotypic relationship for total muscle DNA content was similar to that observed for muscle weight. These results indicate that fetal muscle development differs in cattle that have different postnatal growth patterns by as early as 100 d of gestation and that differences in fetal muscle growth are related to differences in muscle hyperplasia.

Molecular cloning, sequencing, and characterizing the bovine receptor for gonadotropin releasing hormone (GnRH).

Receptors for gonadotropin releasing hormone (GnRH), located in the cell membranes of adeno-hypophysial gonadotropes, mediate the action of GnRH to stimulate the secretion of the gonadotropic hormones (LH and FSH). In the present studies, we have isolated a GnRH receptor cDNA from bovine pituitary, determined its primary structure, and studied the regulation of its gene expression. The cDNA is composed of 1326 nucleotides and encodes a protein containing 328 amino acids. The GnRH receptor of cattle, like that in humans and mice, is a seven transmembrane receptor and has structural characteristics homologous with the family of G protein-coupled receptors. It exhibits 91% identity at the amino acid level with the human and 86% identity with mouse and rat receptors. Northern blot analysis of the RNA from bovine pituitary, probed with 32P-labeled bovine GnRH receptor cDNA, revealed the presence of four different transcripts (5.0, 3.5, 2.5 and 1.5 kb) in the pituitary of which the 5.0 kb form was most abundant. Using the reverse transcriptase/PCR technique, we detected expression of GnRH receptor mRNA in the pituitary but not in any other extrapituitary tissues such as the hypothalamus, hippocampus, testis, corpus luteum, ovary (containing follicles), myoendometrium, adrenal, kidney, liver and spleen. Higher levels of GnRH receptor mRNA were found in the pituitaries of steers than in cohort bulls, suggesting regulation of GnRH receptor gene expression by testicular steroids.

Growth and endocrine responses of cattle to implantation of estradiol-17 beta during continuous or discontinuous grazing of high- and low-endophyte-infected tall fescue.

Forty-eight Angus x Hereford steers (initial BW = 336 +/- 8.3 kg) were used in a 56-d study to evaluate growth and endocrine responses to continuous or discontinuous grazing of high-endophyte-infected Kentucky-31 (K; > 57% infestation rate) or low-endophyte-infected Johnstone tall fescue (J; < 1% infestation rate) and implantation with 0 or 24 mg/steer of estradiol-17 beta (E2; Compudose). Steers were allotted by weight to eight 3-ha paddocks (four paddocks of each fescue variety) with six steers per paddock. Two paddocks of each variety were grazed continuously (KK and JJ), whereas steers on the remaining four paddocks were rotated every 14 d from K to J (KJ) or from J to K (JK). Three steers in each paddock were implanted with E2 on d 0. The study extended from May 25, 1988 to July 20, 1988 with steers exposed to potential heat-stress conditions for 52 d of the 56-d study. Body weights were obtained on d 0, 28, and 56, and blood samples were taken on d 28 and 56. Overall ADG, serum prolactin, and serum alkaline phosphatase activity were greater (P < .05) in JJ than in KK steers. Rotation from K to J did not increase overall ADG, prolactin, insulin-like growth factor I (IGF-I), or alkaline phosphatase activity compared with the continuously grazed KK, whereas JK steers had lower (P < .10) ADG, prolactin, and alkaline phosphatase activity than JJ steers. Estradiol-17 beta increased (P < .10) IGF-I in JJ, KJ, and JK steers but not in KK steers.(ABSTRACT TRUNCATED AT 250 WORDS)

Differences in GH secretion from individual somatotropes in rats genetically selected for fast and slow growth.

A reverse hemolytic plaque assay was used to examine effects of selection for fast (F) and slow (S) growth on growth hormone (GH) secretion by individual somatotropes. Anterior pituitaries (AP) from 32 male Charles River CD strain rats selected for F and S growth for 20 generations were used. Four rats per line were used at 4, 6, 8, or 10 wk of age. Body weight (P < 0.0001) of F rats was greater compared with S rats. AP (P < 0.05) were heavier at 8 and 10 wk of age in F compared with S line rats. Percentages of GH-secreting cells were unaffected by age (range = 32.7-35.5%) and line [F = 33.1 +/- 1.2% (SE) vs. S = 34.5 +/- 1.2%] or by human GH-releasing factor (hGRF). At 8 and 10 wk, mean plaque-forming area was greater (P < 0.0001) in F compared with S rats under both nonstimulated (2,704 +/- 202 vs. 1,648 +/- 202 microns2) and hGRF-stimulated secretion (4,503 +/- 202 vs. 2,682 +/- 202 microns2). Results indicate that differences in growth observed in the two lines may be due to a greater secretory capacity of individual somatotropes rather than to a greater percentage of somatotropes or sensitivity of somatotropes to secretagogue.

Effect of consuming fungus-infected and fungus-free tall fescue and ergotamine tartrate on selected physiological variables of cattle in environmentally controlled conditions.

Two experiments were conducted to determine the physiological responses of consuming a fungus-free (FF) or fungus-infected (INF) tall fescue diet (Exp. 1) or the FF diet plus ergotamine tartrate at 30 ppm (FF/ET, Exp. 2) in a thermoneutral (21 degrees C) or heat-stressed environment (32 degrees C, dry bulb; 10 degrees C dew point). Treatment periods lasted 28 d after a 10-d adaptation period. Experiment 1 was replicated three times, and Exp. 2 was replicated twice, with eight Holstein steers in each replicate (mean BW = 185 kg). Feed intake (FI), rectal temperature (RT), and respiration rate (RR) were recorded daily, and heart rate (HR) and infrared temperatures at the ear canal (ECT), ear tip (ETT), pastern (PT), coronary band (CBT), and tail tip (TTT) were recorded weekly. Consumption of INF and FF/ET compared with FF diets decreased (P less than .10) FI, HR, ECT, PT, CBT, and TTT and elevated (P less than .10) RT and RR by 2.8, 2.77 kg/d; 17, 23 beats/min; .8, 1.1 degrees C; .9, 1.1 degrees C; .8, .9 degrees C; 1.1, 2.6 degrees C; .3, .5 degrees C; and 8, 8 breaths/min; respectively. Ear-tip temperature was reduced (P less than .10) 1.6 degrees C by consumption of INF but not by consumption of FF/ET. Reduction of peripheral temperatures is indicative of reduced blood flow to peripheral areas as a result of vasoconstriction.(ABSTRACT TRUNCATED AT 250 WORDS)

L6 myoblast proliferation in response to muscle-derived extracts and serum from exercise-trained rats.

Serum and skeletal muscle-derived extracts (MDE) were bioassayed for their ability to promote [3H]thymidine incorporation in L6 myoblasts to determine if exercise-training increases mitogenic growth factor activity. Rats were trained by climbing a 60 cm vertical grid with progressively greater weight for 7 and 28 days. Serum from 7 day trained rats and vastus MDE from 7 and 28 day trained rats, but not rectus femoris MDE, had increased mitogenic activity compared to serum and MDE from untrained rats. These data suggest that exercise may increase mitogenic growth factors in some skeletal muscles.

Endocrine changes in sows exposed to elevated ambient temperature during lactation.

Seven sows were placed into one of two environmental chambers at 22 C, 5 d prior to farrowing. On day 9 of lactation, one chamber was changed to 30 C (n = 4) and the other remained at 22 C (n = 3). On days 24 and 25, blood samples were collected every 15 min for 9 hr and 7 hr, respectively. On day 24, thyrotropin releasing hormone (TRH) and gonadotropin releasing hormone (GnRH) were injected iv at hour 8. On day 25 naloxone (NAL) was administered iv at hour 4 followed 2 hr later by iv injection of TRH and GnRH. Milk yield and litter weights were similar but backfat thickness (BF) was greater in 22 C sows (P less than .05) compared to 30 C sows. Luteinizing hormone (LH) pulse frequency was greater (P less than .003) and LH pulse amplitude was less (P less than .03) in 22 C sows. LH concentrations after GnRH were similar on day 24 but on day 25, LH concentrations after GnRH were greater (P less than .05) for 30 C sows. Prolactin (PRL) concentrations were similar on days 24 and 25 for both groups. However, PRL response to TRH was greater (P less than .05) on both days 24 and 25 in 30 C sows. Growth hormone (GH) concentrations, and the GH response to TRH, were greater (P less than .0001) in 30 C sows. Cortisol concentrations, and the response to NAL, were less (P less than .03) in 30 C sows. NAL failed to alter LH secretion but decreased (P less than .05) PRL secretion in both groups of sows. However, GH response to NAL was greater (P less than .05) in 30 C sows. Therefore, sows exposed to elevated ambient temperature during lactation exhibited altered endocrine function.

Physiological responses to resistance-exercise in athletes self-administering anabolic steroids.

Endocrine and metabolic responses to resistance exercise were compared in 5 athletes self-administering (SL) anabolic steroids and 8 athletes (L) not using these compounds. Exercise consisted of 5 sets of 10 repetitions in the squat and quarter squat. Blood samples were collected before (pre) and immediately after (post) exercise, and following 30 minutes of recovery (post-30). Except for significantly lower lactate concentrations in SL (p less than 0.015) at post-30, the responses to exercise and recovery were similar in both groups. Significantly higher hematocrits (p less than 0.0001), total androgen concentrations (p less than 0.0001), and androgen/cortisol ratios (p less than 0.0001) were observed in the SL group across all time periods. Plasma androgen concentrations increased about 22% in SL following exercise, even though plasma LH concentrations were significantly lower (p less than 0.0001) than in L. Plasma ACTH and cortisol concentrations were not significantly affected. Both groups displayed similar endocrine and metabolic responses to an acute bout of resistance exercise. The higher androgen/cortisol ratios and lower plasma lactate concentrations during recovery are two potential factors which may help explain the lower subjective level of fatigue following training sessions often reported by individuals who use anabolic steroids.

Effects of acute insulin deficiency on catecholamine and indoleamine content and catecholamine turnover in microdissected hypothalamic nuclei in streptozotocin-diabetic rats.

The effects of streptozotocin-induced diabetes on catecholamine and indoleamine concentrations and catecholamine turnover rates in individual microdissected hypothalamic nuclei known, or believed, to be involved in the control of neuroendocrine function, were examined in control, insulin-treated diabetic and acutely insulin-withdrawn diabetic female rats. Streptozotocin-induced diabetes and acute insulin deficiency were demonstrated to result in increased concentrations of epinephrine in the suprachiasmatic nucleus, decreased turnover of epinephrine in the arcuate nucleus and decreased turnover of dopamine in the ventromedial nucleus was found to be increased in the insulin-treated diabetic animals. These data indicate that experimental diabetes and acute insulin deficiency result in the rapid onset of detectable alterations in epinephrine and dopamine activity in specific hypothalamic nuclei. These diabetes-induced changes may cause, or contribute to, the development of secondary neuroendocrine abnormalities known to occur in the diabetic condition.

Secretory patterns and metabolic clearance rate of porcine growth hormone in swine selected for growth.

Eleven Landrace pigs (six boars and five gilts, 50 kg) representing lines selected for three generations for maximum weight at 200 d of age were compared to eight pigs (four boars and four gilts, 50 kg) representing contemporary randomly selected Landrace controls to determine the effect of selection for growth on the metabolic clearance rate (MCR) and plasma concentrations of porcine growth hormone (GH). To estimate MCR of GH, the disappearance of a bolus of porcine GH was monitored over 120 min following its i.v. injection. Blood samples also were collected every 15 min over a 6-h period before injecting GH to determine baseline and overall mean GH concentrations, mean peak amplitude and number of GH secretory episodes. Boars exhibited greater overall mean GH concentrations (4.80 vs 3.11 ng/ml; P less than .05) and had greater maximum GH concentrations associated with secretory episodes (16.11 vs 10.80 ng/ml; P less than .05) than did gilts. There were no differences between boars and pigs exhibited greater baseline GH concentrations (2.04 vs 1.25 ng/ml; P less than .01) than did those from the unselected Landrace line. Selected and control pigs exhibited similar (P greater than .15) overall mean concentrations of GH, frequency of secretory episodes, amplitude of GH peaks and MCR. These data demonstrate that pigs selected for heavier weight at 200 d of age had greater basal plasma GH concentrations than did unselected control pigs.

Adenohypophyseal receptors for LHRH, pituitary content of gonadotropins and plasma concentrations of LH in cyclic, pregnant and postpartum beef cows.

Adenohypophyseal concentrations of LHRH receptors, pituitary content of LH and FSH, and plasma concentrations of LH were determined in thirty Hereford, Angus or Hereford-Angus heifers that were randomly assigned by breed and weight to five periods including day 3 of the estrous cycle (CY), pregnant day 120 (P120), 200 (P200), 275 (P275), or day 2 postpartum (PP). Jugular blood samples were collected at 10-min intervals for 8 hr from all cows. Within 2 hr after completion of blood sampling, animals were slaughtered and the pituitary gland frozen at -196 C. LH pulse frequency/8 hr was reduced (P less than .05) during gestation (.5, .2, and 1.5 +/- .5/8 hr, for P120, P200, and P275, respectively) and PP (.5 +/- .5/8 hr) compared to CY (7.8 +/- .5/8 hr). Frequency of LH pulses/8 hr was not different (P greater than .1) among P120, P200 or PP periods but was different (P less than .05) between P200 and P275. There were no differences in LH pulse height (P greater than .1) among periods; however, pulse amplitude was greatest (P less than .05) at P120 (1.3 +/- .2 ng/ml) and lowest between P200 and PP (.6 to .8 +/- .2 ng/ml). Baseline concentrations of plasma LH did not differ (P greater than .1) among P and PP periods (.3 +/- .1 ng/ml), but were lower (P less than .05) than in CY animals (.7 +/- .1 ng/ml). Concentration of adenohypophyseal LHRH receptors was approximately two-fold greater (P less than .05) at P120 (25.85 +/- 2.2 fmol/mg) than at all other periods (9.5 to 14.9 +/- 2.2 fmol/mg).(ABSTRACT TRUNCATED AT 250 WORDS)

Endocrine and reproductive responses of beef cattle to a synthetic gonadotropin-releasing hormone agonist (fertirelin acetate).

A synthetic gonadotropin-releasing hormone (GnRH) agonist (fertirelin acetate, FA) was administered to beef cattle within 12 h after onset of estrus (Day = 0) to study effects on subsequent endocrine responses and fertility. In Study 1, 16 crossbred beef heifers were injected with either 100 mug FA (n = 8) or saline (n = 8) at 6 or 12 h (n = 7; n = 9) after onset of estrus. Concentrations of luteinizing hormone (LH) over time were affected (P<0.01) by the interaction of treatment and interval from onset of estrus to treatment. Heifers treated with FA at 6 h after onset of estrus exhibited the greatest increase in LH after treatment. There was no effect of treatment, interval from onset of estrus to treatment or treatment by interval interaction on duration of the estrous cycle, on concentrations of progesterone from Days 1 through 14 posttreatment, or on concentrations of progesterone prior to subsequent estrus (Day -10 through 0, posttreatment estrus). In summary, FA administered to beef cattle within 12 h after onset of estrus effectively increased peripheral plasma concentration of LH, but this increase had no effect on subsequent luteal function as measured by duration of the estrous cycle or concentrations of plasma progesterone. In Study 2, 86 parous beef cows were bred artificially to one of two bulls following natural or prostaglandin F(2)alpha induced estrus. Cows received either no treatment or 50 or 100 mug FA at the time of AI. There was no effect of treatment, breed, parity, technician, service sire or interactions on conception rate (mean = 76.7%). Although not significant, the numerical pattern of conception rate among experimental groups (control = 71.4%, 50 mug FA = 76.7%, 100 mug FA = 82.1%) supports further investigation of this GnRH agonist with larger numbers of cattle.

Effect of transportation stress on ovarian function in superovulated Hereford heifers.

A study was conducted to determine the effect of transportation stress on ovarian function in superovulated heifers. Thirty cyclic Hereford heifers of similar age and weight and in good body condition were randomly assigned to control and stress-treated groups. All animals received two daily injections of 5 mg follicle stimulating hormone (FSH) for 4 d beginning on Day 10 to 12 of the estrous cycle. A blood sample was collected at each FSH injection. On the fourth day of injections, heifers were given 25 mg prostaglandin F(2)alpha (PGF(2)alpha) in the morning and a second injection of 15 mg PGF(2)alpha in the afternoon. During superovulation, the stressed heifers were transported to a different location every 12 h whereas control animals remained at the pretrial site. Following 4 d of intermittent transporting and FSH treatment, stress-treated heifers were recombined with control animals. Ovaries were examined 8 d following the onset of standing estrus to determine length, width, thickness, and number of corpora lutea (CL). Peripheral plasma levels of cortisol were higher in the stressed group (P< 0.1). Least squares means for numbers of CL were 20.4 +/- 2.1 and 15.4 +/- 1.7 for control and treated heifers, respectively (P< 0.1). There were no treatment differences (P> 0.1) between length, width, or thickness of ovaries when the number of CL was held constant. These data suggest that stress of the type, intensity, and duration imposed in this study increased plasma levels of cortisol and reduced ovulation rate as determined by CL formation in superovulated heifers.

Effect of animal density on endocrine development in gilts.

A study was conducted to determine the effect of social crowding on the development of endocrine organs involved in the reproductive process in growing and finishing gilts. One hundred four littermate gilts weighing approximately 30 kg were randomly assigned to treatment groups of either 8 or 16 pigs/pen. Gilts raised in pens of eight were allotted 1.06 m2 per pig from 30 to 65 kg and 1.25 m2 from 65 to 100 kg; whereas, one-half the area was provided for gilts raised in pens of 16. Littermate gilts raised in pens of 8 and 16 were slaughtered on the same day when the average weight of pigs reached 100 kg. At slaughter, the brain, adrenals, pituitary, uterus and ovaries were removed and weighted. The brain was lyophilyzed and reweighed to yield dry brain weight. Gilts raised in the low-density groups had heavier adrenal (P less than .01), pituitary (P less than .08), brain (P less than .11), dry-brain (P less than .02), uterine (P less than .09) and ovarian (P less than .07) tissues. Furthermore, significantly more gilts in the low-density, compared with the high-density groups, had ovulated at slaughter. In a second study, eight littermate gilts raised in pens of 8 or 16 and weighing approximately 100 kg were moved to individual pens and fitted with a jugular vein catheter. Following blood sample collection at 15-min intervals for 2 h, 200 IU of adrenocorticotropin (ACTH) were infused into the cannula. Blood samples were collected at 15-min intervals for an additional 2 h. There were no differences between basal or ACTH-stimulated concentrations of plasma cortisol between treatment groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of photoperiod and temperature on prolactin secretion in ovariectomized gilts.

Five ovariectomized (OVX) gilts were placed in each of two chambers at 20 C with a photoperiod of 12 h light and 12 h dark for 8 d (12L:12D). On d 1, blood samples were collected via jugular cannula every 30 min from 0830 to 1630. At 1630, 200 micrograms of thyrotropin releasing hormone (TRH) were injected iv and blood samples taken every 10 min for 1 h and every 30 min for the next 2 h. On d 2, samples were taken every 30 min from 0830 to 0930 and from 1530 to 1630. Temperature was changed to 10 C or 30 C on d 3. Samples were taken from 0830 to 1630 on d 3, 4 and 9. At 1630 on d 9, the TRH challenge was repeated. Mean basal serum concentrations of prolactin (PRL) were similar for all gilts and for all periods. However, serum PRL response (ng PRL X ml-1 X 150 min-1) to TRH increased (P less than .0001) after exposure to 30 C, while exposure to 10 C failed to alter PRL response. In Exp. 2, six ovariectomized gilts were assigned to each chamber. The protocol of Exp. 1 was followed through d 3, except temperature and photoperiod were changed to 10 C and 8L:16D or 30 C and 16L:8D. On d 34 the TRH challenge was repeated. Mean basal serum concentration of PRL was similar for all gilts and all periods. However, simultaneous increases in temperature and photoperiod increased (P less than .005) serum PRL response to TRH, whereas simultaneous decreases in temperature and photoperiod failed to alter PRL response to TRH.

The effect of pen density during rearing on subsequent reproductive performance in gilts.

A study involving 109 crossbred gilts of Duroc and Landrace breeding that were reared in equal-sized pens with 8 or 16 pigs/pen was initiated to determine the effects of pen density during rearing on subsequent reproductive and maternal performance. Gilts in pens of eight were allowed 1.06 m2/animal from 30 to 65 kg and 1.25 m2/animal from 65 to 100 kg, whereas those in pens of 16 were allowed only one-half as much floor area per animal. Gilts raised in groups of eight farrowed 1.0 more pigs/litter (P less than .05), and .7 more pigs/litter born alive (P = .15), than gilts reared in groups of 16 pigs/pen. There were no pen-density differences in the number of corpora lutea at 30 d of gestation (P = .33) or in litter birth weight (P = .26). After adjusting by covariance for the number of live pigs at the beginning of the lactation period, gilts from the pen density of 16 had more pigs per litter alive (P less than .01) and heavier litter weights (P less than .05) at 21 d postpartum and higher piglet survival rates to 21 d (P less than .02) than gilts that were reared in the low pen-density of eight pigs/pen. Results of this study indicate that pen density during the growing-finishing period may affect subsequent reproductive and maternal performance of gilts.

Glucagon, insulin, and growth hormone responses to glucose infusion in lactating dairy cows.

Early lactation in the dairy cow is associated with an increased demand for energy that can only be met by hormone-mediated partitioning of nutrients. The purpose of this study was to determine adaptive responses of basal and glucose-stimulated glucagon (IRG), insulin (IRI), and growth hormone (GH) concentrations to early lactation. Blood was collected via jugular cannulas from nonpregnant nonlactating (NPNL) cows and cows 14 days antepartum (AP) and 5 and 30 days postpartum (PP). Basal concentrations of IRI decreased with lactation, IRG was essentially unchanged, and GH was increased with lactation. The molar IRI/IRG (I/G) ratio was decreased from 4.6 at day 14 AP to 1.3 at day 30 PP. The effects of exogenous glucose (0.56 mM/kg body wt) on IRI were greatest during pregnancy and declined with lactation. IRG responses to glucose were similar except in NPNL cows, which had a minimal but prolonged IRG inhibition, GH responses to glucose infusion were absent in NPNL cows and were most significant at 5 days PP. The decreased I/G and elevated GH concentrations suggests that both IRG and GH play a role in nutrient partitioning during early lactation.