Quantification of naloxone binding sites in brains from suckled beef cows during postpartum anestrus and resumption of estrous cycles

Thirty beef cows, approximately 3 yr of age, were randomly assigned to be slaughtered on d 7, 14, 28, 42 or 56 postpartum. Each cow suckled one calf until slaughter. Data from cows slaughtered on d 42 and 56 were pooled and further classified as anestrous or cyclic based on the presence of a corpus luteum and elevated serum concentrations of progesterone at slaughter. Specific binding of [3H]naloxone (3H-NAL) to homogenates of tissue from hypothalamus (HYP), preoptic area (POA) and basal forebrain (BF) was assessed using multiple-point Scatchard analyses. Nonspecific binding was estimated in the presence of 10(-6) M naloxone. Separation of bound from free 3H-NAL was achieved by centrifugation at 20,000 X g. Concentration (fmol/mg original tissue wet wt) of 3H-NAL binding sites in POA tissue was higher (P less than .05) on d 28 postpartum in anestrous cows than in cyclic cows on d 42 + 56 postpartum (2.58 +/- .32 vs 1.58 +/- .10). When all anestrous cows were compared with cyclic cows, concentrations of 3H-NAL binding sites in POA tissues and in BF tissue were higher (P less than .05) in anestrous cows (anestrous POA, 2.12 +/- .17, cyclic POA, 1.58 +/- .10; anestrous BF, 2.94 +/- .41, cyclic BF, 2.19 +/- .16). Compared across brain regions for all cows, the concentration of specific binding sites for 3H-NAL was greater (P less than .01) in BF (2.5 +/- .2) than in POA (1.9 +/- .1) and greater (P less than .01) in POA than in HYP (1.5 +/- .1).(ABSTRACT TRUNCATED AT 250 WORDS)     

Endocrine changes and ultrasonography of ovaries in suckled beef cows during resumption of postpartum estrous cycles

Changes in follicular and luteal structures were assessed and concentrations of estradiol and progesterone were measured in 13 Hereford X Angus suckled beef cows during resumption of estrous cycles. Transrectal ultrasonography was used to monitor follicular size, ovulation, and formation and regression of the corpus luteum (CL). The interval from parturition to first postpartum ovulation (FO) was 82 +/- 4.7 d. Serum progesterone remained low before FO. One cow exhibited standing estrus, two cows showed other signs of estrus, and 10 displayed no signs of behavioral estrus preceding FO. All cows exhibited standing estrus before the second postpartum ovulation (SO). All cows had a short luteal phase after FO, with an average interval of 8.5 +/- .2 d between FO and SO. Concentrations of estradiol in serum during the 8 d preceding ovulation were similar before FO and SO. Maximal diameter of the preovulatory follicle was similar before FO and SO. However, the ovulatory follicle was larger in diameter at 2 d (P = .02) and 3 to 8 d (P less than .005) before FO than before SO. The time from detection until ovulation was less (P = .005) for the ovulatory follicle preceding SO than for the follicle associated with FO (8.5 vs 10.2 d, respectively, SE = .4). The second-largest follicle was larger (P less than .005) in diameter during the 8 d preceding the FO than before the SO. The difference in size between the ovulatory follicle and the second-largest follicle on the day before ovulation was greater (P less than .005) preceding SO than preceding FO (8.7 vs 6.6 mm, respectively, SE = .4).(ABSTRACT TRUNCATED AT 250 WORDS)     

Endocrine changes during restoration of estrous cycles following induction of anestrus by restricted nutrient intake in beef heifers

The working hypotheses in this experiment were: that ovarian estradiol would inhibit luteinizing hormone (LH) secretion in heifers that were anestrus as a result of restricted dietary energy intake and the responsiveness of LH secretion to estradiol negative feedback would decrease during the period when restoration of estrous cycles occurred following feeding of diets adequate in energy. Fifteen heifers weighing 341 +/- 12 (mean +/- SE) kg were fed a diet containing 50% of the energy required for maintenance until 40 to 50 d following cessation of estrous cycles. Heifers were assigned to intact control (C, n = 5), ovariectomized (OVX, n = 5) or ovariectomized-estradiol-17 beta-implanted (OVX + E2, n = 5) treatments. Heifers were subsequently provided a high-energy (HE) diet until termination of the study. Progesterone concentrations indicating cessation of corpus luteum function were detected after heifers had lost 71 +/- 8 kg body weight over 186 +/- 28 d. Control heifers re-initiated estrous cycles as indicated by increased progesterone concentrations in serum at 49 +/- 9 d after initiation of feeding the HE diet (360 +/- 18 kg body weight). Initiation of pulsatile LH secretion was observed in heifers by d 12 following OVX. Estradiol suppressed LH secretion in OVX + E2 heifers during the period of nutritional anestrus in C heifers. Suppressive effects of E2 on LH secretion continued in OVX heifers after C heifers had initiated corpus luteum function. Therefore, the working hypothesis that LH secretion is inhibited by E2 in the nutritionally anestrous heifer is accepted but responsiveness to estradiol does not subside with re-initiation of estrous cycles, thus this working hypothesis is rejected.     

Influence of estradiol on duration of anestrus and incidence of short estrous cycles in postpartum cows

The influence of exposure to exogenous estradiol on the interval from parturition to first ovulation, luteinizing hormone (LH) secretion and luteal function was examined in cows. Cows were assigned at parturition to one of three treatments. Cows received either a 3.0 (1-E; n = 30) or .75 cm (1/4-E; n = 28) implant containing 17 beta-estradiol or served as untreated control animals (C; n = 33). Implants were administered within 2 days following parturition and removed on day 40 postpartum (day 0 = day of parturition). Single blood samples were collected twice weekly and analyzed for progesterone to determine length of postpartum anestrus and duration of the initial increase in progesterone. Sequential blood samples were collected on day 35 +/- .1 postpartum (15 min intervals for 18 hrs) from 5 cows in each treatment and analyzed for LH. Concentrations of estradiol were higher (P less than .01) in the 1-E (5.3 +/- .24) than in C (3.9 +/- .23) or 1/4 E (3.9 +/- .25) cows on day 35 postpartum. The interval from parturition to the first estrous cycle of normal duration was similar for cows in the C and 1-E treatment (53 +/- 2.4 and 56 +/- 2.4 days, respectively). Cows in the 1/4-E treatment had a longer (P less than .05) interval (68 +/- 2.5 days). Secretion of LH was similar among treatments on day 35 postpartum. The first normal luteal phase after parturition was preceded by a transient rise in progesterone in 81, 64 and 85% of the cows in the C, 1-E and 1/4-E treatments, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Potential treatments for anestrus in gilts and sows

Pregnant mares' serum gonadotrophin (400 IU) combined with human chorionic gonadotrophin (200 IU) was administered to anestrous gilts (n=31) and sows (n=20) in commercial herds. Two-thirds of the treated animals were mated successfully within seven days and, although no control animals were included, the response indicated that this hormone combination would be useful in herds with anestrous problems. A second experiment was conducted to evaluate the occurrence of estrus and/or ovulations in prepuberal gilts (n=eight/treatment) following injection with pregnant mares' serum gonadotrophin/human chorionic gonadotrophin or other hormones that might stimulate ovarian activity. The pregnant mares' serum gonadotrophin/human chorionic gonadotrophin combination and follicle-stimulating hormone produced estrus within ten days of injection in at least half of the treated gilts but the response was lower with gonadotrophin-releasing hormone and a prostaglandin analogue. Combinations of human chorionic gonadotrophin with small amounts of estradiol benzoate stimulated estrus and ovulation in most of the treated gilts.     

Influence of exposure to bulls on resumption of estrous cycles following parturition in beef cows

The effect of bull exposure on the resumption of estrous activity following parturition was studied in an experiment using mature Hereford and Hereford X Angus beef cows. In the spring of 1981 and 1982, cows were assigned by breed and calving date to one of two treatment groups. Cows were exposed to bulls either from 3 to 85 d postpartum (BE; n = 45, 1981; n = 35, 1982) or from 53 to 85 d postpartum (NE; n = 39, 1981, n = 36, 1982). Blood samples were collected from all cows once weekly from calving until 85 d postpartum to determine progesterone concentrations. The first increase in progesterone, which indicated onset of estrous cycles occurred at 43 +/- 2 vs 63 +/- 2 d (P less than .01) in 1981 and at 39 +/- 2 vs 61 +/- 3 d (P less than .01) postpartum in 1982 in BE cows and NE cows, respectively. Early postpartum exposure of cows to bulls reduced the postpartum anestrous interval.     

Factors associated with shortened estrous cycles after abortion in beef heifers

Forty-six crossbred Hereford heifers were allotted into five experimental groups. Fenprotalene, a prostaglandin analogue, was administered to induce abortion and (or) to regress the corpus luteum (CL) in four groups of heifers about 75 d after conception. The four groups were 1) pregnant heifers, 2) pregnant heifers with the ovary contralateral to the gravid uterine horn removed 24 h after fenprostalene injection, 3) same as Group 2 but with the ipsilateral, rather than the contralateral, ovary removed and 4) heifers with uterus removed (ovaries intact) about 35 d after conception. A fifth group of nonpregnant heifers received implants containing norgestomet from 10 to 76 d after estrus and were given fenprostalene 24 h before removal of the implant. Average length of the first estrous cycle after the fenprostalene injection was 11.2, 8.3, 9.7 and 19.1 for Groups 1, 2, 3 and 5, respectively. Estrous cycles were longer (P less than .05) in norgestomet-treated heifers. Hysterectomized heifers (Group 4) did not exhibit a second estrus by 50 d after fenprostalene treatment; otherwise, all first estrous cycles after the fenprostalene injection were either "short" (7 to 13 d) or "normal" (17 to 23 d). Twenty-two of 24 heifers that aborted had short estrous cycles and two had normal estrous cycles. Short estrous cycles occurred after abortion regardless of whether the ovary ipsilateral or contralateral to the previously gravid uterine horn ovulated. Early regression of the CL (short luteal phase) did not occur in nonpregnant heifers after long-term progestogen stimulation or after hysterectomy, but it did occur in heifers with a previously gravid uterus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Scheduled breeding of gilts after estrous synchronization with altrenogest

Fertility of 104 gilts artificially inseminated (AI) at a predetermined time (scheduled AI) after estrous synchronization with altrenogest (15 mg X gilt-1 X d-1 for 18 d) was compared with that of 103 gilts checked for estrus (estrus checked) and inseminated after altrenogest. Scheduled-AI gilts were inseminated once on d 5, 6 and 7 after the last altrenogest feeding (d 0). Estrus-checked gilts were exposed to a boar twice daily at 0830 and 1630 h and inseminated after the second and third estrous detection period following first detected estrus. Percentage of gilts assigned to treatment that farrowed (72.8 vs 67.3%), total pigs farrowed (11 +/- .4 vs 11.3 +/- .4) and pigs born alive (10.1 +/- .4 vs 10.5 +/- .4) were similar for estrus-checked and scheduled-AI gilts, respectively. We conclude that scheduled AI can be used with estrous synchronization for gilts and may have advantages in breeding herd management and the use of AI in swine.     

The influence of growth hormone injections on the endocrine and metabolic status of gilts

Twelve Yorkshire x Landrace prepubertal gilts were assigned equally to treatments involving daily injections of either porcine growth hormone (GH, 90 micrograms/kg) or vehicle buffer from 150 to 159 d of age. Blood samples were obtained every hour from 0600 hr at 153 d until 0500 hr at 154 d of age, inclusively. At 0800 hr on 154 d, gilts received an injection of 500 IU PMSG, followed 96 hr later by 250 IU hCG. Gilts were slaughtered at 163 d and the ovaries recovered for an assessment of the ovarian response to the gonadotrophic stimulation. Five control gilts (83%) exhibited a normal ovulatory response but only one GH gilt (17%) was so designated (P less than 0.05). There was no apparent effect of treatment on serum concentrations of LH, FSH or cortisol. Growth hormone treatment reduced serum concentrations of T4 (P less than 0.001) and prolactin (P less than 0.02), but increased serum GH (P less than 0.001), T3 (P less than 0.06), insulin (P less than 0.001) and glucose (P less than 0.001). Serum concentrations of free fatty acids (FFA) were not significantly altered by exogenous GH. The concomitant elevation of serum insulin and glucose suggests that an insulin-resistant state was induced which, if evident at the ovarian level, may be a factor mediating the adverse effects of exogenous GH on ovarian function. The data presented also suggests that circulating concentrations of thyroid originating hormones are altered by exogenous GH.     

Body condition scores in dairy cows: associations with metabolic and endocrine changes in healthy dairy cows

Relationships between body condition scores (BCS), metabolic profiles and endocrine traits were investigated in 53 healthy Red Holstein cows. Cows were categorized into groups based on BCS ante-partum (a.p.: >3.25 or < 3.25) and on BCS losses during the first 8 weeks after calving (ABCS8 > 0.75 or < or = 0.75). Blood samples were collected 1 week before calving and every 2 weeks post-partum (p.p.). Cows with BCS a.p. >3.25 and deltaBCS < or = 0.75 were oldest and cows with BCS a.p. < or = 3.25 and deltaBCS < or = 0.75 were youngest. Cows with BCS > 3.25 a.p. and that lost > 0.75 BCS in the first 2 months of lactation exhibited signs of subclinical ketosis. If statistically adjusted for the effect of lactation number, average milk yield within the first 8 weeks p.p. and milk fat concentrations were similar between BCS groups, whereas milk protein concentrations differed significantly between BCS groups. Significant differences between groups were observed for blood plasma glucose, bilirubin, beta-hydroxybutyrate, non-esterified fatty acids and insulin concentrations. No differences were seen for albumin, urea, insulin-like growth factor-1, and 3.5.3'-triiodothyronine concentrations and for plasma activities of glutamate-oxalacetate transaminase, gamma-glutamyltransferase and glutamate dehydrogenase. There was a good agreement between BCS and profiles of metabolites and hormones related to energy metabolism in clinically healthy cows. Cows in good body condition a.p. had greater risks of metabolic problems because of excessive mobilization of body reserves. However, the metabolic status was best in cows with a BCS > 3.25 a.p.. if they did not lose much body condition p.p.     

Ovarian mass in three mares with regular estrous cycles.

Three mares with regular estrous cycles and a large ovary were examined. In each case, the ovary was composed of a single, fluid-filled cavity with a thick capsule. The ovarian mass was surgically removed from each mare. Histologic diagnosis of each mass was different.     

Endocrine changes associated with a dietary-induced increase in ovulation rate (flushing) in gilts

Effects of an increased level of dietary energy (flushing) on plasma concentrations of FSH, LH, insulin, progesterone and estradiol-17 beta and ovulation rate were studied in 16 gilts. Gilts received 5,400 kcal ME/d for one estrous cycle and the first 7 d of a second. On d 8 of the second estrous cycle, gilts received either 5,400 kcal ME/d (control [C], n = 8) or 11,000 kcal ME/d (flushed [F], n = 8) for the remainder of the estrous cycle. Blood was collected daily at 15-min intervals for 6 h from d 8 through estrus. Gilts were examined by laparotomy 6 d after estrus. Ovulation rate was greater (P less than .05) in F than C gilts (16.0 vs 9.4). Mean daily concentrations of FSH were greater (P less than .05) in F gilts at 5 d, 4 d and 3 d prior to estrus compared with C females. In both C and F gilts, FSH decreased (P less than .05) prior to estrus. Mean daily concentrations of LH and LH pulse amplitude were not different (P greater than .05) between treatments. Mean number of LH pulses/6 h at 4 d, 3 d and 2 d prior to estrus were greater (P less than .05) in F than in C gilts. In both treatments, LH pulse amplitude decreased (P less than .05) and pulse frequency increased (P less than .07) prior to estrus. Mean plasma concentrations of insulin tended to be higher (P less than .07) in F than in C females during the 7-d period before estrus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of increasing levels of undegradable intake protein on metabolic and endocrine factors in estrous cycling beef heifers

To determine the influence of three levels of undegradable intake protein (UIP) supplementation on metabolic and endocrine factors that influence reproduction, 23 yearling crossbred heifers (body condition score = 4.5 +/- 0.5; initial BW = 362 +/- 12 kg) were stratified by BW and assigned randomly to one of three supplements: 1) low UIP (1,135 g x heifer(-1) x d(-1); 30% CP, 115 g UIP, n = 7); 2) mid UIP (1,135 g x heifer(-1) x d(-1); 38% CP, 216 g UIP, n = 8); or 3) high UIP (1,135 g x heifer(-1) x d(-1); 46% CP, 321 g UIP, n = 8). Heifers were estrually synchronized before initiation of supplementation. Supplement was individually fed daily for 30 to 32 d, at which time heifers were slaughtered (d 12 to 14 of the estrous cycle) and tissues collected. Heifers were fed a basal diet of sudan grass hay (6.0% CP) ad libitum. On d 28 of supplementation (d 10 of the estrous cycle), no differences were observed (P > 0.10) in serum insulin or IGF-I among treatments. At slaughter (d 10 to 12 of the estrous cycle), treatments did not influence corpus luteum weight, cerebral spinal fluid leptin, or IGFBP; serum estradiol-17beta, progesterone, leptin, IGF-I, and IGFBP; or anterior pituitary content of IGFBP (P > 0.10). Follicular fluid IGFBP-2 and IGFBP-4 were greater in high-UIP heifers than low- or mid-UIP heifers on d 12 to 14 of the estrous cycle (P < 0.05). Basal serum LH concentrations and LH area under the curve (every 15 min for 240 min) did not differ (P > 0.10) following 28 d of supplementation (d 10 of the estrous cycle); however, basal serum FSH concentrations were greater (P = 0.06) in low- and mid- vs. high-UIP heifers (5.2 and 5.2 vs. 4.6 ng/mL, respectively), and FSH area under the curve was greater (P = 0.03) in low- vs. high-UIP heifers. At slaughter (d 12 to 14 of the estrous cycle), anterior pituitary LH and FSH content and steady-state mRNA encoding alpha, LHbeta, and GnRH receptor did not differ (P > 0.10) among treatments. However, FSHbeta mRNA was increased approximately twofold (P = 0.03) in mid vs. low UIP. In summary, low and mid levels of UIP supplements fed to estrous cycling beef heifers seemed to enhance pituitary expression and/or secretion of FSH relative to high levels of UIP. Moreover, high-UIP supplementation was associated with increased low-molecular-weight IGFBP compared with supplementation of low and mid levels of UIP. These data suggest that differing levels of UIP supplementation may alter pituitary and ovarian function, thereby influencing reproductive performance in beef 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)     

PG600配合营养调控处理乏情母猪的试验

对部分猪场及个体养殖户所提供的278头乏情母猪,采用PG600配合营养调控方法进行处理,处理后8d内,乏情母猪发情率达74.1%(206/278),重复配种后受胎率达77.7%(160/206),平均产仔数为7.9头(1189/151)。试验证明,PG600配合营养调控处理母猪乏情是可行的。     

Midazolam and ketamine induction before halothane anaesthesia in ponies: cardiorespiratory, endocrine and metabolic changes

Six Welsh gelding ponies were premedicated with 0.03 mg/kg of acepromazine intravenously (i.v.) prior to induction of anaesthesia with midazolam at 0.2 mg/kg and ketamine at 2 mg/kg i.v.. Anaesthesia was maintained for 2 h using 1.2 % halothane concentration in oxygen. Heart rate, electrocardiograph (ECG), arterial blood pressure, respiratory rate, blood gases, temperature, haematocrit, plasma arginine vasopressin (AVP), dynorphin, ß-endorphin, adrenocorticotropic hormone (ACTH), cortisol, dopamine, noradrenaline, adrenaline, glucose and lactate concentrations were measured before and after premedication, immediately after induction, every 20 min during anaesthesia, and at 20 and 120 min after disconnection. Induction was rapid, excitement-free and good muscle relaxation was observed. There were no changes in heart and respiratory rates. Decrease in temperature, hyperoxia and respiratory acidosis developed during anaes-thesia and slight hypotension was observed (minimum value 76 ± 10 mm Hg at 40 mins). No changes were observed in dynorphin, ß-endorphin, ACTH, catecholamines and glucose. Plasma cortisol concentration increased from 220 ± 17 basal to 354 ± 22 nmol/L at 120 min during anaesthesia; plasma AVP concentration increased from 3 ± 1 basal to 346 ± 64 pmol/L at 100 min during anaesthesia and plasma lactate concentration increased from 1.22 ± 0.08 basal to 1.76 ± 0.13 mmol/L at 80 min during anaesthesia. Recovery was rapid and uneventful with ponies taking 46 ± 6 min to stand. When midazolam/ketamine was compared with thiopentone or detomidine/ketamine for induction before halothane anaesthesia using an otherwise similar protocol in the same ponies, it caused slightly more respiratory depression, but less hypotension. Additionally, midazolam reduced the hormonal stress response commonly observed during halothane anaesthesia and appears to have a good potential for use in horses.     

Periparturient endocrine and metabolic changes in healthy cows and in cows affected by mastitis

Transition from pregnancy to lactation in dairy cows involves considerable metabolic adaptation. Additional stress is incurred during infections such as periparturient mastitis. Multiparous Holstein-Friesian cows kept under normal production conditions (n = 15) were used to evaluate changes in circulating metabolite and hormone concentrations from 5 days before to 5 days after calving. Insulin-like growth factor binding protein (IGFBP) profiles were also monitored. Marked time-related changes were observed for plasma thyroid hormone, IGF, cortisol, insulin, beta-hydroxybutyrate (BHB) and non-esterified fatty acid (NEFA) concentrations but not for plasma leptin. A decrease in IGF-II concentration and maximal intensity of the putative IGFBP-1 band occurred at parturition. When compared with the five healthy cows,low IGF-II levels were prolonged to day 2 post-partum in five cows with Escherichia coli-associated mastitis. However, marked decreases in IGFBP-2 band intensity were evident only in two of the four cases examined. Individual total ligand (IGF-I + IGF-II) concentration and IGFBP pattern prepartum were largely regained 5 days post-partum in all cows. Hormone and metabolite concentrations in the two cows with Staphylococcus aureus-associated mastitis were very similar to those in the five healthy cows. Plasma thyroxine (T4) was lower 2 days prepartum in the cows, which later developed Gram-negative mastitis. Multiregression analysis showed that variance in T4 concentration was significantly and independently associated with triiodothyronine (T3) and IGF-I positively and with cortisol negatively (R2 = 0.648). This study confirms the close inter-relationship between the thyroid hormone and IGF axes in cattle and indicates possible effects of Gram-negative mastitis infection on IGF-II metabolism.     

Cardiorespiratory, endocrine and metabolic changes in ponies undergoing intravenous or inhalation anaesthesia

Six Welsh gelding ponies (weight 246 ± 6 kg) were premedicated with 0.03 mg/kg of acepromazine intravenously (i.v.) followed by 0.02 mg/kg of detomidine i.v. Anaesthesia was induced with 2 mg/kg of ketamine i.v. Ponies were intubated and lay in left lateral recumbency. On one occasion anaesthesia was maintained for 2 h using 1.2% halothane in oxygen. The same group of ponies were anaesthetized 1 month later using the same induction regime and anaesthesia was maintained with a combination of detomidine, ketamine and guaiphenesin, while the ponies breathed oxygen-enriched air. Electrocardiogram, heart rate, mean arterial blood pressure, cardiac output, respiratory rate, blood gases, temperature, haematocrit, glucose, lactate and cortisol were measured and cardiac index and systemic vascular resistance were calculated in both groups. Beta-endorphin, met-enkephalin, dynorphin, arginine vasopressin (AVP), adrenocorticotrophic hormone (ACTH) and catecholamines were measured in the halothane anaesthesia group only and 11-deoxycortisol during total intravenous anaesthesia (TIVA) only. Cardiorespiratory depression was more marked during halothane anaesthesia. Hyperglycaemia developed in both groups. Lactate and AVP increased during halothane anaesthesia. Cortisol increased during halothane and decreased during TIVA. There were no changes in the other hormones during anaesthesia. Recovery was smooth in both groups. TIVA produced better cardiorespiratory performance and suppressed the endocrine stress response observed during halothane anaesthesia.