A retrospective analysis of factors contributing to calf mortality and dystocia in beef cattle

Records of 2191 calvings from the Clemson University Beef Physiology Unit between 1981 and 1993 were analyzed to determine factors affecting malpresentation, mortality and dystocia. Only 20 (0.91%) parturitions involved malpresentation: posterior presentation (n = 14), leg deviations (n = 3), head deviations (n = 2) and breech birth (n = 1). Dystocia affected calf mortality within 24 h of birth (P < 0.05), with mortality increasing as the severity of dystocia increased. There was an overall 4.5% death loss within 24 h of birth, with 4 and 7% mortality rates for calves from multiparous and primiparous dams, respectively (P < 0.05). Mortality was higher for bull vs heifer calves (P < 0.05). Ninety-four percent of calvings were unassisted, while 6% were assisted births. Dystocia was greater (P < 0.01) in primiparous (17%) than in multiparous dams (4%). In births involving dystocia, 28.1% required mild traction, 69.3% required heavy traction and 2.6% required Cesarean section. Birth weights associated with normal births and mild traction (36 and 36 kg) were lighter than those associated with heavy traction and Cesarean section (40 and 42 kg, respectively; P < 0.05). In conclusion, malpresentations were too few to be of significance, and dystocia influenced mortality within 24 h of birth. Calf birth weight and parity of dam explained most of the observed variations in dystocia.     

A second postcooling afterdrop: more evidence for a convective mechanism.

An attempt was made to demonstrate the importance of increased perfusion of cold tissue in core temperature afterdrop. Five male subjects were cooled twice in water (8 degrees C) for 53-80 min. They were then rewarmed by one of two methods (shivering thermogenesis or treadmill exercise) for another 40-65 min, after which they entered a warm bath (40 degrees C). Esophageal temperature (Tes) as well as thigh and calf muscle temperatures at three depths (1.5, 3.0, and 4.5 cm) were measured. Cold water immersion was terminated at Tes varying between 33.0 and 34.5 degrees C. For each subject this temperature was similar in both trials. The initial core temperature afterdrop was 58% greater during exercise (mean +/- SE, 0.65 +/- 0.10 degrees C) than shivering (0.41 +/- 0.06 degrees C) (P < 0.005). Within the first 5 min after subjects entered the warm bath the initial rate of rewarming (previously established during shivering or exercise, approximately 0.07 degrees C/min) decreased. The attenuation was 0.088 +/- 0.03 degrees C/min (P < 0.025) after shivering and 0.062 +/- 0.022 degrees C/min (P < 0.025) after exercise. In 4 of 10 trials (2 after shivering and 2 after exercise) a second afterdrop occurred during this period. We suggest that increased perfusion of cold tissue is one probable mechanism responsible for attenuation or reversal of the initial rewarming rate. These results have important implications for treatment of hypothermia victims, even when treatment commences long after removal from cold water.     

Occurrence of neonatal and postnatal mortality in range beef cattle. I. Calf loss incidence from birth to weaning, backward and breech presentations and effects of calf loss on subsequent pregnancy rate of dams

Data from 13,296 calvings collected over a 15-yr period indicated 893 calves died from birth to weaning for an average loss of 6.7%. Calves lost from birth through Day 3 postcalving accounted for a 4.6% loss with an additional 2.1% loss from Day 4 through weaning. Calf deaths from primiparous 2- and 3-yr-old dams accounted for 41.0% of total mortality. Losses within groups were primiparous 2-yr-olds, 10.9%; primiparous 3-yr-olds, 8.7%; second-calf 3-yr-olds, 4.1%; second-calf 4-yr-olds, 8.3%; multiparous 4-yr-olds, 4.8%; and dams 5 yr and older, 5.3%. The majority of calf deaths (57.4%) occurred within the first 24 h postpartum with 75% of the total occurring Days 0 through 7. This loss was similar among all dam age and parity groups. Calf death due to dystocia accounted for the single largest loss category through the first 96 h postpartum, resulting in 69.6, 39.6, 30.8 and 33.3% of the loss incidence for Day 0, 1, 2 and 3 postpartum, respectively. More (P < 0.01) male calves (510, 57.6%) died than females (376, 42.4%). Backward presentations occurred more frequently (P < 0.01) than breech (1.6 vs 0.6% of all births, respectively). Incidence of backward presentation was 2.3%, 5.6% and 0.9% for primiparous 2-yr-old, 3-yr-old and multiparous dams, respectively (P < 0.01); 64.2% of the backward calves were males and 35.8% females (P < 0.01). Survival of calves in backward presentation exceeded (P < 0.01) that of breech calves (70.7 vs 32.9%). Fall pregnancy rate of dams that lost calves and reentered the breeding herd that same year was 72.4% compared to 79.4% (P < 0.01) for contemporary females that did not lose calves. The depression in pregnancy rate was not specifically due to dystocia but apparently to some general effect of calf loss.     

Pelvic growth, calf birth weight and dystocia in Holstein x Hereford heifers

The pelvic area was measured in 129 Holstein x Hereford heifers at 10, 16 and 22 months of age. The heifers were fed an all forage diet. Pelvic growth was not linear over time, changing from an increase of 0.27 +/- 0.2 cm(2)/day during the first 6 months of the study to 0.13 +/- 0.13 cm(2)/day during the last 6 months (P<0.01). The relationship of pelvic area to body weight, height at hooks, and distance from hooks to pins did not change with age, and a moderate correlation between the pelvic area and these other measures (R=0.20 to 0.80) was noted. The pelvic area was measured within 24 hours after calving in 76 of the heifers. The rate of increase of pelvic area/day increased significantly (P < 0.01) in the month prior to calving from 0.14+/-0.13 cm(2) to 1.15 +/- 0.88 cm(2). As a result, the pelvic area at calving had a moderate correlation (R=0.29 to 0.52) to the pelvic area prior to calving. Logistic regression and discriminant analysis techniques were used to model the influence of the pelvic area and calf birth weight on the incidence of dystocia. Ratio of the pelvic area at calving to calf birth weight significantly (P < 0.01) influenced the incidence of dystocia. Logistic regression techniques were not superior to discriminant analysis; both correctly predicted 73% of the cases. Pelvic area measurement at any time other than calving was not associated with dystocia (P >0.05). Pelvic area and calf birth weight are important determinants of dystocia in heifers. The high degree of variation noted in pelvic growth, in particular during the month prior to calving, resulted in low correlation between pelvic area at calving and the precalving measurement. Therefore, we were not able to predict dystocia by measuring the pelvic area prior to calving.     

Muscle glycogen utilization during shivering thermogenesis in humans

The purpose of the present study was to clarify the importance of skeletal muscle glycogen as a fuel for shivering thermogenesis in humans during cold-water immersion. Fourteen seminude subjects were immersed to the shoulders in 18 degrees C water for 90 min or until rectal temperature (Tre) decreased to 35.5 degrees C. Biopsies from the vastus lateralis muscle and venous blood samples were obtained before and immediately after the immersion. Metabolic rate increased during the immersion to 3.5 +/- 0.3 (SE) times resting values, whereas Tre decreased by 0.9 degrees C to approximately 35.8 degrees C at the end of the immersion. Intramuscular glycogen concentration in the vastus lateralis decreased from 410 +/- 15 to 332 +/- 18 mmol glucose/kg dry muscle, with each subject showing a decrease (P less than 0.001). Plasma volume decreased (P less than 0.001) markedly during the immersion (-24 +/- 1%). After correcting for this decrease, blood lactate and plasma glycerol levels increased by 60 (P less than 0.05) and 38% (P less than 0.01), respectively, whereas plasma glucose levels were reduced by 20% after the immersion (P less than 0.001). The mean expiratory exchange ratio showed a biphasic pattern, increasing initially during the first 30 min of the immersion from 0.80 +/- 0.06 to 0.85 +/- 0.05 (P less than 0.01) and decreasing thereafter toward basal values. The results demonstrate clearly that intramuscular glycogen reserves are used as a metabolic substrate to fuel intensive thermogenic shivering activity of human skeletal muscle.     

Human temperature regulation during narcosis induced by inhalation of 30% nitrous oxide.

The study investigated the effect of inhalation of 30% nitrous oxide (N2O) on temperature regulation in humans. Seven male subjects were immersed to the neck in 28 degrees C water on two separate occasions. They exercised at a rate equivalent to 50% of their maximum work rate on an underwater cycle ergometer for 20 min and remained immersed for an additional 100 min after the exercise. In one trial (AIR) the subjects inspired compressed air, and in the other trial (N2O) they inspired a gas mixture containing N2O (20.93% O2-30% N2O-49.07% N2). Sweating, measured at the forehead, and shivering thermogenesis, as reflected by O2 uptake, were monitored throughout the 100-min recovery period. The threshold core temperatures at which sweating was extinguished and shivering was initiated were established relative to resting preexercise levels. Neither the magnitude of the sweating response nor the core threshold at which it was extinguished was significantly affected by the inhalation of N2O. In contrast, shivering thermogenesis was both significantly reduced during the N2O condition and initiated at significantly lower core temperatures [change in esophageal temperature (delta T(es)) = -0.98 +/- 0.33 degrees C and change in rectal temperature (delta T(re)) = -1.26 degrees C] during the N2O than during the AIR condition (delta T(es) = -0.36 +/- 0.31 degrees C and delta T(re) = -0.44 +/- 0.22 degrees C).(ABSTRACT TRUNCATED AT 250 WORDS)     

Ovarian responses and oocyte recovery in prepubertal swamp buffalo (Bubalus bubalis) calves after FSH or PMSG treatment

Stimulation of follicular growth was examined using two different gonadotropin treatments in 10 prepubertal swamp buffalo calves (8 to 12 mo old). Each calf received an ear implant consisting of 3 mg norgestromet and 5 mg estradiol valerate during hormonal treatment. Five calves were additionally administered FSH (24 mg, im) and, 2 mo later, PMSG (3,000 IU). The remaining 5 calves were first treated with PMSG followed by FSH. Ovarian responses to treatments were examined by laparotomy, 72 h after ear implant removal, and by the number of follicles (diameter > or = 0.8 cm) and corpora hemorrhagica present. Ovaries had more significant response to FSH than PMSG treatment (13.9+/-8.6 vs 5.9+/-3.3 follicles; P<0.01). Although the recovery rate tended to be lower for FSH treated (64%) than PMSG-treated (82%) animals, more oocytes/animal were harvested in the PMSG treatment (8.3+/-5.0 vs 4.6+/-3.2, respectively). The immature oocytes (n = 38) were cultured for 24 to 25 h in maturation medium (TCM-199 NaHCO3+10% fetal calf serum [FCS] in 5%CO2 in air at 39 degrees C). Oocyte maturation was assessed after fixation and staining with aceto orcein. The in vitro maturation rate was 52.6% (20/38). This study shows the possibility of harvesting oocytes from prepubertal swamp buffalo calves and maturing the oocyte in vitro.     

Effect of water temperature on cooling efficiency during hyperthermia in humans.

We evaluated the cooling rate of hyperthermic subjects, as measured by rectal temperature (T(re)), during immersion in a range of water temperatures. On 4 separate days, seven subjects (4 men, 3 women) exercised at 65% maximal oxygen consumption at an ambient temperature of 39 degrees C until T(re) increased to 40 degrees C (45.4 +/- 4.1 min). After exercise, the subjects were immersed in a circulated water bath controlled at 2, 8, 14, or 20 degrees C until T(re) returned to 37.5 degrees C. No difference in cooling rate was observed between the immersions at 8, 14, and 20 degrees C despite the differences in the skin surface-to-water temperature gradient, possibly because of the presence of shivering at 8 and 14 degrees C. Compared with the other conditions, however, the rate of cooling (0.35 +/- 0.14 degrees C/min) was significantly greater during the 2 degrees C water immersion, in which shivering was seldom observed. This rate was almost twice as much as the other conditions (P < 0.05). Our results suggest that 2 degrees C water is the most effective immersion treatment for exercise-induced hyperthermia.     

Analysis of body measurements of newborn purebred Belgian Blue calves

At calving, purebred animals of the Belgian Blue (BB) breed are compromised by the incompatibility in size and shape of the dam and her calf, resulting in a very high incidence of dystocia problems. To clarify which body parts of the calf are of decisive importance to allow natural delivery and to investigate both the mean value as well as the variation among these body sizes within this breed (variation being an important condition for selection), measurements of nine body parts (body weight at birth (BW), body length (BL), length of the head (LH), shoulder width (SW), hip width (HW), heart girth (HG), withers height (WH) and the circumference of the fetlock of both the front (CFF) and the hind leg (CFH)) were assessed in 147 newborn purebred BB calves on 17 farms. Simple and partial correlations were assessed and we examined whether environmental factors (gender of the calf, parity of the cow, type of calving, season of birth and time of measurement after birth) were significantly associated with these specific calf measurements. The mean BW was 49.2 ± 7.1 kg. The average BL was 56.4 ± 4.5 cm and the mean LH was 24.4 ± 2.3 cm. Measurements obtained for SW and HW were 22.4 ± 2.2 and 22.9 ± 2.1 cm, respectively, whereas the mean WH was 71.1 ± 4.7 cm. Measurements of circumferences revealed a CFF of 17.9 ± 1.1 cm, a CFH of 18.0 ± 1.0 cm and a mean HG of 78.0 ± 5.4 cm. Partial correlations of the BW with eight body measurements were significant (P < 0.01) and ranged between 0.17 and 0.85; 0.42 and 0.88; and 0.24 and 0.88 when corrected for gender, parity and type of calving, respectively. BL (P < 0.01) and the CFF and CFH (P < 0.001) are larger in bull calves than in heifer calves. Calves born through caesarean section had broader SW (P < 0.01) and HW (P < 0.01) when compared with calves born after natural calving (defined as born per vaginam without assistance or with slight traction). Sizes of calves born out of multiparous cows were generally larger than of calves born out of heifers (SW: P < 0.001; HW: P < 0.05). As SW and HW are the broadest points of a BB calf, they are both candidates for being the limiting measures for calving ease, but the difference between HW and SW for the total data set was not different from zero (P > 0.05). In contrast to male calves in which no significant difference (between HW and SW) could be found, female calves show the difference between HW and SW that was significantly different from zero (P < 0.001); thus, in female calves, the HW is the most limiting factor of the calf's body. The significant variation in some body measures between the calves and the strong correlation within these sizes raises the possibility of selection towards smaller calves aiming to limit the dystocia problem in the BB breed. Furthermore, on the basis of our results, we were able to build equations for the farmer to use at the moment of calving containing the LH, the CF and the calf's gender to estimate SW and HW, the limiting body parts of the calf to be born naturally. Together with the knowledge of the pelvic size of the dam, this information gives the obstetrician or the farmer a more accurate prediction of the probability of natural calving at parturition.     

Influence of 48 hour calf separation on milk production and calf growth in range cows

Hereford cows and their calves were either left together or separated for a 48-hr period between 50 and 80 days postpartum. Milk production and calf weights were determined 1 and 2 weeks prior to and 1 and 3 weeks after calf separation. Daily milk production of separated cows (5.6+/-.1 kg) was not different from that of control cows (5.3+/-.1 kg) at any sampling period. Similarly, calf growth was not affected (P > .10) by separation; both groups of calves gained .64 kg/day. Average 205-day adjusted weaning weights were also similar, for the control (173.5+/-4.6 kg) and separated calves (181.8+/-4.6 kg). These results indicate that 48-hr calf separation could be used in a treatment regime to decrease the postpartum anestrous interval in range cattle without detrimental effects on milk production, calf growth or 205-day adjusted weaning weight.     

Influence of prepartum exposure of beef heifers to winter weather on concentrations of plasma energy-yielding substrates, serum hormones and birth weight of calves

The influence of exposure to ambient winter weather conditions (WW) during the final 90 d of gestation on serum hormones, plasma substrates, and birth weight of calves was evaluated in spring-calving, primiparous beef heifers. At of 192 +/- 14 d of gestation, heifers were assigned by expected calving date, breed, and sire of fetus to one of two treatments. Thirteen heifers were assigned to thermoneutral environment (TN; 12 degrees C) and housed in temperature-controlled rooms. Heifers in WW (n = 16) were maintained outdoors in drylots without access to shelter and given additional dietary energy when average weekly windchill fell below -6.7 degrees C. Body weights, hip-heights and samples of serum and plasma were obtained biweekly until heifers were relocated, approximately 7 d prior to expected calving. Polynomial response curves for concentrations of glucose and nonesterified fatty acids (NEFA) in plasma and cortisol in serum were not influenced by treatment. However, average concentrations of NEFA in plasma were increased (P < 0.02) and glucose tended to be higher (P = 0.13) in WW heifers compared to TN heifers (172.5 +/- 8.9 vs 136.9 +/- 7.7 mumol/L and 87.8 +/- 2.4 vs 83.3 +/- 2.7 mg/100ml for NEFA and glucose, respectively). Time trends of concentrations of estradiol in serum (P < 0.01) and hip-height to weight ratios were different (P < 0.05) for WW and TN. Birth weights of calves from TN heifers were greater (P < 0.06) than calves from WW heifers (42.3 +/- 2.0 vs 36.9 +/- 1.8 kg), but average calving difficulty scores were similar for both heifer groups (3.2 +/- 0.5 vs 2.7 +/- 0.4). These data suggest that exposing spring-calving cows to reduced effective ambient temperatures during the final 90 d of pregnancy may elevate energy-yielding metabolites in plasma and alter endocrine function. These changes may contribute to reduced birth weight of calves.     

Heat debt as an index for cold adaptation in men

Several types of cold adaptation in men have been described in the literature (metabolic, insulative, hypothermic). The aim of this study is to show that the decrease of heat debt can be considered as a new index for cold adaptation. Ten male subjects were acclimated by water immersions (temperature 10-15 degrees C, 4 immersions/wk over 2 mo). Thermoregulatory responses before and after acclimation were tested by a standard cold test in a climatic chamber for 2 h at rest [dry bulb temperature (Tdb): 10 degrees C; relative humidity (rh): 25%]. After adaptation, four thermoregulatory modifications were observed: an increase in the delay for the onset of shivering (32.7 +/- 7.99 instead of 14.1 +/- 5.25 min); a decrease of body temperature levels for the onset of shivering [rectal temperature (Tre): 37.06 +/- 0.08 instead of 37.31 +/- 0.06 degrees C; mean skin temperature (Tsk): 24.83 +/- 0.56 instead of 26.86 +/- 0.46 degrees C; mean body temperature (Tb): 33.03 +/- 0.20 instead of 34.16 +/- 0.37 degrees C); a lower level of body temperatures in thermoneutrality (Tre = 37.16 +/- 0.08 instead of 37.39 +/- 0.06 degrees C; Tsk = 31.29 +/- 0.21 instead of 32.01 +/- 0.22 degrees C; Tb = 35.92 +/- 0.08 instead of 36.22 +/- 0.05 degrees C); a decrease of heat debt calculated from the difference between heat gains and heat losses (5.66 +/- 0.08 instead of 8.33 +/- 0.38 kJ/kg). The different types of cold adaptation observed are related to the physical characteristics of the subjects (percent body fat content) and the level of physical fitness (VO2max).(ABSTRACT TRUNCATED AT 250 WORDS)     

The influence of ambient temperature on metabolism and body temperature of newborn and growing reindeer calves (Rangifer tarandus tarandus L.)

Thermoregulatory capacities of 51 reindeer calves (Rangifer tarandus tarandus L.) aged 1-35 days were studied at -26.5 to +35.0 degrees C ambient temperatures at Kaamanen reindeer research station, Finland (69 degrees 10' N) during calving periods in May 1981 and May-July 1982. The newborn calves aged 1-4 days maintained a high body temperature (Tre) (mean +40.2 degrees C) even at the lowest experimental temperature of -22.5 degrees C by increasing their metabolic rate five-fold above the level at +11.0 degrees C. Heat production of the new-born calves was largely based on the metabolism of brown adipose tissue, stimulated by cold-induced discharge of the sympathetic nervous transmitter, noradrenaline (NA). Sensitivity of the calves to exogenous NA disappeared during the first 3-4 weeks of life. Thermal conductance of the calves was low at low ambient temperatures, but rose strongly as Ta increased above +10 degrees C. The extensive peripheral cooling, especially in the feet, was demonstrated in the calves aged 1-10 days. The lowest foot temperature (+10.5 degrees C) was measured in a 4-day-old calf at -14.5 degrees C. Slight shivering thermogenesis was recorded in the calves aged 1-4 days and occasionally in the older calves at low values of Ta. Shivering appears to be a reserve mechanism against severe cold. At about +20 degrees C and above the calves increased their Tre (approximately 1 degree C), oxygen consumption and heart rate. In the newborn calves oxygen consumption rose four- to five-fold and in 1-month-old calves about two-fold. Fast growing calves (maximum 400 g/day) appear to be more stressed by heat than by cold exposure.     

Effect of relaxin on facilitation of parturition in dairy heifers

Purified pig relaxin (3000 U/mg) was injected i.m. into pregnant Holstein dairy heifers on Day 276 or 277 to determine its effect on parturition and sequential measurements of the pelvic area, cervical dilatation, and peripheral blood-plasma concentrations of progesterone and relaxin. Treatments included phosphate-buffer saline (2 ml, Group C, N = 7), relaxin once (1 mg, Group 1R, N = 7), and twice (2 mg, 12 h apart; Group 2R, N = 7). Intervals (mean +/- s.e.) between the first injection of relaxin or PBS and calving were 64 +/- 17, 80 +/- 19 and 125 +/- 34 h for Groups 2R, 1R and C, respectively. The calving intervals were reduced in Groups 2R (P less than 0.01) and 1R (P less than 0.05) compared with Group C. The incidence of dystocia was 29% (2 of 7) in Group 2R and 43% (3 of 7) in Group 1R compared with 57% (4 of 7) in Group C (P less than 0.01). Body weights and ratios of males to females of the calves were similar (P greater than 0.05) between groups. Progesterone plasma concentrations decreased (P less than 0.01) earlier in Groups 1R and 2R compared with Group C, and this acute decrease began within 6 h of treatment. At 24 h after relaxin or PBS injection, progesterone concentrations were 2.7 +/- 1.1 ng/ml for Group 2R, 3.5 +/- 0.9 ng/ml for Group 1R, and 6.0 +/- 0.1 ng/ml for Group C. Relaxin reached peak blood-plasma levels of 19 +/- 2.2 ng/ml 1 h after injection of relaxin, but remained unchanged, 0.3 +/- 0.01 ng/ml, in Group C. Pelvic area was increased 26%, 22% and 14% and cervical dilatation was increased 109%, 76% and 53% 48 h after injection in Groups 2R, 1R and C, respectively, but these responses were similar among groups at the time of parturition. We conclude that two i.m. injections of relaxin facilitated earlier calving, acutely decreased progesterone secretion, increased cervical dilatation and pelvic area expansion, and decreased the incidence of dystocia in dairy heifers.     

Transfer of fresh and cryopreserved IVP bovine embryos: normal calving, birth weight and gestation lengths

In vitro and in vivo developmental competence of fresh and cryopreserved in vitro produced (IVP) bovine embryos was evaluated up to birth. Three experiments were done. The objective in the first experiment was to develop an optimal vitrification procedure for IVP bovine embryos by determining effects of exposure time (2, 5, 10, 20 min) and temperature (4, 22, 27 degrees C) in cryoprotective agents prior to vitrification on their post-thaw viability. The best combination was used in Experiments 2 and 3. In the second experiment, the importance of post-thaw morphologic selection on pregnancy rates was determined by transferring either selected or unselected single embryos. In the third experiment, pregnancy initiation, maintenance and calving results of vitrified embryos were compared with fresh and conventionally frozen embryos. Fetal losses, birth weights, gestation lengths and frequency of dystocia in the third experiment were monitored. The interaction of exposure time and temperature on both post-thaw re-expansion and hatching rates was significant (P < 0.01). Five minute exposure at 27 degrees C was optimal. In the second experiment, post-thaw selected vitrified embryos had higher pregnancy rates than unselected embryos (P < 0.05). In the third experiment, the pregnancy rate of vitrified embryos did not differ from that of fresh embryos (P > 0.05). However, pregnancy rate of conventionally frozen embryos was lower than that of fresh or vitrified embryos (P < 0.05). Of 92 calves born, 53 were male and 39 were female. Birth weights and dystocia scores of single-born calves did not differ between sexes (P > 0.05). Twin-born calves were lighter than single-born calves (P < 0.05). Overall, the data demonstrate that the transfer of vitrified IVP bovine embryos can result in healthy, apparently normal calves similar to those derived from transfer of fresh and conventionally frozen IVP bovine embryos.     

Predicting dystocia in heifers

The relationship of heifer size, calf size and sire on dystocia was studied in approximately one thousand Angus, Hereford X Angus and Charolais heifers bred to Angus, Hereford and Charolais bulls. Heifers were weighed and pelvic measurements taken 35 days post breeding, at midgestation, and on a random group of 135 heifers two weeks prior to calving. Dystocia score, calf birth weight, calf body length, calf hip width and calf sex were recorded at calving.Correlation coefficients for calf traits indicate that birth weight and birth weight to body measurement ratios were the most highly correlated variables with dystocia score. For traits of the dam, pelvic area was the most highly correlated variable to dystocia score, while dam weight had a low and nonsignificant correlation.Sires experiencing a higher than average incidence of dystocia had calves that were larger for all measures of body size. Individual sire differences for dystocia indicate a large number of calves and an accurate randomization of heifers bred to each bull is necessary to make precise judgements as to a bull's potential for siring easy-calving offspring.Calf size measurements were positively correlated with heifer weight and pelvic area; however, correlations tended to be low. Breed of calf, sire, heifer weight I and II and pelvic area I, II and III accounted for only 23.6% of the variation in calf birth weight.Charolais calves were larger (P<.05) and had more dystocia (P<.05) than Hereford or Angus sired calves. Hereford sired crossbred calves were larger (P<.05) and had more dystocia than Angus crossbred or straightbred calves. Angus crossbred calves were larger (P<.05) but had no more dystocia than Angus straightbred calves.Heritability estimates for calf body length (0.35) and calf hip width (0.42) indicate calf skeletal measurements were more heritable than calf birth weight (0.28).Pelvic area measurements were correlated (P<.01) with heifer weight; however, heifer weight I and II accounted for only 37% and 30% of the variability in pelvic area I and II, respectively. Average pelvic area was largest in Charolais heifers, followed by Crossbred and Angus heifers. Pelvic area growth was .275 cm²/day in Angus, .254 cm²/day in Crossbred, and .250 cm²/day in Charolais heifers.Dystocia score was most highly related to calf size and pelvic area I. Pooled over all breeds, a regression analysis showed 37% of the variability in dystocia score being accounted for by the ratio of calf birth weight to calf body length and pelvic erea I. Very little increase in the R² value occurred by the addition of the other independent variables.Histogram analyses demonstrates that a constant level of dystocia can be maintained only if pelvic area increases in proportion to calf size. However, regardless of the size of calf, heifers that had very small pelvic openings had a high rate of dystocia, just as heifers having very large calves experienced high rates of dystocia even when they had large pelves.     

The influence of whole-body vs. torso pre-cooling on physiological strain and performance of high-intensity exercise in the heat

Little research has been reported examining the effects of pre-cooling on high-intensity exercise performance, particularly when combined with strategies to keep the working muscle warm. This study used nine active males to determine the effects of pre-cooling the torso and thighs (LC), pre-cooling the torso (ice-vest in 3 degrees C air) while keeping the thighs warm (LW), or no cooling (CON: 31 degrees C air), on physiological strain and high-intensity (45-s) exercise performance (33 degrees C, 60% rh). Furthermore, we sought to determine whether performance after pre-cooling was influenced by a short exercise warm-up. The 45-s test was performed at different (P<0.05) mean core temperature [(rectal+oesophageal)/2] [CON: 37.3+/-0.3 (S.D.), LW: 37.1+/-0.3, LC: 36.8+/-0.4 degrees C] and mean skin temperature (CON: 34.6+/-0.6, LW: 29.0+/-1.0, LC: 27.2+/-1.2 degrees C) between all conditions. Forearm blood flow prior to exercise was also lower in LC (3.1+/-2.0 ml 100 ml tissue(-1) x min(-1)) than CON (8.2+/-2.5, P=0.01) but not LW (4.3+/-2.6, P=0.46). After an exercise warm-up, muscle temperature (Tm) was not significantly different between conditions (CON: 37.3+/-1.5, LW: 37.3+/-1.2, LC: 36.6+/-0.7 degrees C, P=0.16) but when warm-up was excluded, T(m) was lower in LC (34.5+/-1.9 degrees C, P=0.02) than in CON (37.3+/-1.0) and LW (37.1+/-0.9). Even when a warm-up was performed, torso+thigh pre-cooling decreased both peak (-3.4+/-3.8%, P=0.04) and mean power output (-4.1+/-3.8%, P=0.01) relative to the control, but this effect was markedly larger when warm-up was excluded (peak power -7.7+/-2.5%, P=0.01; mean power -7.6+/-1.2%, P=0.01). Torso-only pre-cooling did not reduce peak or mean power, either with or without warm-up. These data indicate that pre-cooling does not improve 45-s high-intensity exercise performance, and can impair performance if the working muscles are cooled. A short exercise warm-up largely removes any detrimental effects of a cold muscle on performance by increasing Tm.     

Effects of modafinil on heat thermoregulatory responses in humans at rest

The effects of modafinil on heat thermoregulatory responses were studied in 10 male subjects submitted to a sweating test after taking 200 mg of modafinil or placebo. Sweating tests were performed in a hot climatic chamber (45 degrees C, relative humidity <15%, wind speed = 0.8 m x s(-1), duration 1.5 h). Body temperatures (rectal (Tre) and 10 skin temperatures (Tsk)), sweat rate, and metabolic heat production (M) were studied as well as heart rate (HR). Results showed that modafinil induced at the end of the sweating test higher body temperatures increases (0.50 +/- 0.04 versus 0.24 +/- 0.05 degrees C (P < 0.01) for deltaTre and 3.64 +/- 0.16 versus 3.32 +/- 0.16 degrees C (P < 0.05) for deltaTsk (mean skin temperature)) and a decrease in sweating rate throughout the heat exposure (P < 0.05) without change in M, leading to a higher body heat storage (P < 0.05). AHR was also increased, especially at the end of the sweating test (17.95 +/- 1.49 versus 12.52 +/- 1.24 beats/min (P < 0.01)). In conclusion, modafinil induced a slight hyperthermic effect during passive dry heat exposure related to a lower sweat rate, probably by its action on the central nervous system, and this could impair heat tolerance.     

Reproductive responses to grazing endophyte-infected tall fescue by postpartum beef cows

The objective was to determine pregnancy rate and stage of embryonic loss in response to grazing endophyte-free (E-; n = 20) or infected (E+; n = 30) tall fescue in postpartum beef cows with calves. Three weeks before estrus synchronization, cow-calf pairs were introduced to pastures (April 1999). Cows were synchronized and bred by AI after detected estrus for a period of 6 d and then by natural service for 62 d. Bulls were rotated weekly to minimize effects of fescue toxicosis on male fertility. Fetal development was monitored weekly between 30 and 60 d of pregnancy and at weaning using transrectal ultrasound. Respiration rate (52.0 +/- 1.4 vs 46.6 breaths/min; P < 0.02) and rectal temperature (39.6 +/- .09 vs 38.8 +/- .12 degrees C; P < 0.001) increased in E+ cows and serum concentrations of prolactin (7.2 vs 57.4 +/- 4.4 ng/mL; P < 0.001), total cholesterol (123.2 vs 149.6 +/- 3.6 mg/dL; P < 0.001), body condition (3.8 vs 5.2 +/- 0.15; P < 0.001; 1 = thin, 9 = fat) and adjusted weaning weight of calves (195.8 vs 210.8 +/- 4.5 kg; P < 0.02) were reduced compared to that of E- cows. Differences were not detected (E- vs E+) for estrus detection rate (84.9 +/- 10.6% vs 80.2 +/- 8.4%), pregnancy rate to synchronized estrus (41.7 +/- 11.8% vs 46.8 +/- 9.5%), overall pregnancy rate 30 d postbreeding (93.8 +/- 6.2% vs 93.5 +/- 5.1%), overall pregnancy rate at 60 d postbreeding (86.7 +/- 10.1% vs 81.2 +/- 8.3%), or serum concentrations of progesterone on day of PGF2alpha treatment (4.5 +/- 0.7 vs 4.5 +/- 0.8 ng/mL). Pregnancy losses that occurred between 30 and 60 d gestation were 6.0 (E-) vs 15.0 (E+) +/- 8.0% (P > 0.10) and occurred after environmental temperatures rose above 37.8 degrees C for three weeks. Total pregnancy losses that occurred by weaning (between 70 and 126 d of gestation) were 5.5 (E-) vs 17.6 (E+) +/- 8.0% (P > 0.10). Pregnancy rate and embryonic losses were not different between cows grazing E- and E+ tall fescue under these management conditions.     

Inhibition of shivering during restraint hypothermia

Restraint hypothermia has often been described, but its cause has never been clarified. We hypothesized that it might be due to a suppression of shivering thermogenesis. Thus, we restrained conscious rats in an ambient temperature of 2 degrees C while measuring rectal (Tre) and tail skin temperatures, metabolic rate (MR), and shivering activity. When rats were cold exposed but not restrained, Tre fell 1.4 +/- 0.2 degrees C (SE) during the 1st h. When these same rats were restrained, Tre fell at a rate of 6.5 +/- 0.2 degrees C/h. MR averaged 15.7 +/- 1.4 W/kg for the unrestrained rats, but it averaged only 9.0 +/- 1.1 W/kg for the restrained rats. The restrained rats showed no signs of shivering. The animals were then subjected to a restraint adaptation regimen and then reexposed to cold. Restraint now produced a fall in Tre of only 2.6 +/- 0.7 degrees C/h. The animals shivered and generated an MR of 15.8 +/- 0.9 W/kg. Naive rats became hypothermic because restraint suppressed shivering activity. However, adapted rats continued to shiver and remained normothermic. We suggest that a stressful or threatening situation, such as restraint for a naive rat, inhibits shivering and leads to hypothermia in a cold environment. This would not occur in adapted rats because restraint is no longer stressful.