The productivity and well-being of animals can be substantially affected by stress. This is particularly true in the case of beef calves that are subjected to a multitude of stressors over a short period during the first year of life. Perhaps the most often studied stress-responsive variable has been blood corticosteroid concentrations. Factors such as age, gender, genetics, and degree of prior experience, can influence how an animal perceives and responds to a given stressor. Few studies have tried to control these variables, and accordingly, many conflicting results have been published regarding the impact of various stressors on cortisol response. We measured baseline plasma cortisol concentration over a 44-day study in Bos indicus and Bos taurus calves. Plasma cortisol values in Bos indicus calves were higher (32.60 +/- 0.66 ng/ml) than values in calves of Bos taurus (25.81 +/- 0.76) breeding. A precipitous decrease in cortisol concentration was observed 7 days after transport stress in all calves. Baseline cortisol concentration did not provide any indication of the intensity of the various stressors. However, significant differences were readily observed after ACTH administration. On the basis of cortisol secretion, stresses of transport and weaning were similar and were the most stressful to calves, regardless of genotype.

The study reported here was part of a long-term investigation of the effects of genotype on growth, reproduction, and metabolism in cattle grazing common Bermuda grass and endophyte-infected fescue pastures. In June 1990, blood samples were collected from the tail vein of yearling heifers and steers (Angus [AA], Brahman [BB], and their reciprocal crosses [AB, BA], n = 97). Serum amylase activity was assayed enzymatically; serum Ca and Mg concentrations were determined by atomic absorption spectrophotometry. The effects of endophyte-infected fescue depended on genotype (P < 0.001). In yearlings having at least 1 Angus parent (AA, AB, BA), grazing endophyteinfected fescue was associated with higher serum amylase activity than was grazing Bermuda grass. But serum amylase activities of BB yearlings consuming either forage were similar. Moreover, for either forage, substantial differences were related to genotype (P < 0.007) and gender (P < 0.05). Angus yearlings had higher serum amylase activity than did Brahman yearlings; AB and RA yearlings had intermediate values. Heifers had higher amylase activity than did steers. The relationship among serum values of amylase, Ca, and Mg depended on forage. Yearlings consuming endophyte-infected fescue and having at least 1 Angus parent had a moderate negative correlation between serum amylase activity and Ca concentration (r = -0.53; P < 0.0005); that is, in calves of genotypes with increased amylase activity while consuming endophyte-infected fescue (AA, AB, BA), the higher the amylase activity, the lower the serum Ca concentration. However, in yearlings consuming Bermuda grass, serum amylase and Ca values were not correlated. Conversely, grazing Bermuda grass was associated with moderate positive correlation between Ca and Mg concentrations (r = 0.46; P < 0.0003), but in yearlings grazing endophyte-infected fescue, Ca and Mg concentrations were independent. The cause, pathophysiologic mechanism, and clinical importance of these effects remain to be determined. In conclusion, serum amylase activity in yearling cattle was influenced by genotype, gender, and consumption of endophyte-infected fescue. We speculate that yearlings having at least 1 Angus parent may develop a persistent subclinical derangement of the exocrine portion of the pancreas when exposed to common environmental toxins associated with endophyte-infected fescue grass, and that purebred Brahman yearlings can resist this aspect of fescue toxicosis.

We investigated the biochemical composition of blood from Holstein cows, native breed (criollas), and cows descended from fighting bulls (Vacas de lidia) raised at an altitude of 3,000 m (moderately high altitude, MHA), and compared the results with those from Holsteins and cows of similar genetic ancestry as the criollas (scrub cows), both raised at sea level (SL), to determine blood biochemical values characteristic of adaptation to high altitude. Only potassium and calcium concentrations were similar among groups. Glucose concentration was lower in MHA cows, with the exception of Vacas de lidia. Serum bicarbonate concentration was lower in MHA cows; this finding can be explained by hyperventilation in the hypoxic environment. Serum magnesium concentration was lower in SL and MHA Holsteins than in other groups. Serum phosphate concentration was lower in scrub cows, MHA Holsteins, and criollas than in other groups. Cholesterol concentrations were lower in SL Holsteins, whereas triglycerides were higher in scrub cows and MHA Vacas de lidia. Concentration of high-density lipoprotein was significantly greater in Vacas de lidia and less in MHA criollas than in the other groups. Uric acid and total protein were higher in MHA groups. Using radioimmunoassay for human proteins, thyroxine-binding globulin was undetectable. Total and free thyroxine and free triiodothyronine were higher in scrub cows, followed by Vacas de lidia; lower values were detected in SL and MHA Holsteins and MHA criollas.

A hospital-based case-control study was conducted to evaluate and compare risk factors for abomasal volvulus (AV) and left displaced abomasum (LDA) in cattle. Medical record abstracts were derived from 17 North American veterinary schools by the Veterinary Medical Data Program for all cattle admitted between Jan 1, 1977 and Dec 31, 1986, and for those with a diagnosis of AV or LDA. From a total of 108,956 individual cattle records, 1,036 cases of AV and 7,695 cases of LDA were identified, with a ratio of LDA to AV cases of 7.4 to 1. In-hospital mortality was 23.5% for AV and 5.6% for LDA. Age, breed, gender, and season each had significant (P < 0.05) effects on risk for AV and LDA. Risk for AV and LDA increased with increasing age, with greater risk in cattle aged 4 to 7 years. Dairy cattle were at higher risk of developing AV (adjusted odds ratio, 36.4) and LDA (adjusted odds ratio, 95.2) than were beef cattle. The odds of AV in Brown Swiss cattle were significantly (P < 0.0001) lower, and the odds of LDA in Guernsey cattle were significantly (P < 0.0001) higher than those in Holstein cattle. Female cattle were also at higher risk of developing AV (adjusted odds ratio, 3.3) and LDA (adjusted odds ratio, 29.1) than were male cattle. The odds of AV and LDA varied considerably throughout the year, with the lowest number of cases observed in autumn. Seasonal development of AV differed significantly (P < 0.0001) from that Of LDA, with the odds of AV and LDA being highest in January and March, respectively. The medical records for all cattle with AV and LDA examined at the teaching hospital over a 10- and 5-year period, respectively, were reviewed, and the time interval since parturition, as well as the existence and nature of concurrent disease, were recorded. Proportionately fewer cases of AV than LDA developed during the first 2 weeks after parturition (28.3% of AV cases vs. 57.0% of LDA cases). Concurrent disease existed in 30.4% of AV cases and 53.6% of LDA cases, with the rates of concurrent disease differing significantly (P < 0.0001) between the 2 groups. The misclassification rate for data generated at the teaching hospital was estimated to be 6.5% for AV and 5.3% for LDA. On the basis of the findings of this study, we hypothesize that: abomasal atony is a prerequisite for AV and LDA; existence of an abdominal void immediately after parturition facilitates development of AV and LDA; normal rumen volume provides a moderately effective barrier against LDA; risk of LDA does not increase appreciably with advancing pregnancy; and the direction of abomasal displacement (AV or LDA) after abomasal atony and dilation is influenced principally by rumen volume.

The mean area and minimal diameter of 3 histochemically determined myofiber types (1, 2A, and 2B; myosin ATPase in acid buffer) were calculated in middle gluteal muscle biopsy specimens from 62 stallions, 47 Andalusians and 15 Arabians, ranging in age from 6 to 12 years. Fourteen Andalusians and 7 Arabians were untrained, and the remainder were actively endurance-trained. The 6-month training schedules involved walking, slow trotting, and cantering. Fourteen Andalusians were moderately endurance-trained, whereas the other 19 Andalusians and 8 Arabians were strongly endurance-trained. Significant differences were not recorded between untrained and endurance-trained Arabians with respect to the area (type 1, 3,194 +/- 869 micrometers(2) and 3,150 +/- 370 micrometers(2); type 2A, 3,819 +/- 890 micrometers(2) and 3,380 +/- 356 micrometers(2); and type 2B, 4,872 +/- 962 micrometers(2) and 4,417 +/- 646 micrometers(2) or minimal diameter (type 1, 52.2 +/- 7.4 micrometers and 52.8 +/- 3.1 micrometers; type 2A, 58.1 +/- 6.7 micrometers and 55.0 +/- 2.8 micrometers; and type 2B, 65.3 +/- 6.4 micrometers and 63.4 +/- 4.3 micrometers) of the 3 fiber types, nor between untrained and endurance-trained Andalusians with respect to the area (untrained, 3,990 +/- 690 micrometers(2) moderately endurance-trained, 3,882 +/- 347 micrometers(2); and strongly endurance-trained, 3,758 +/- 510 micrometers(2)) and minimal diameter (untrained, 58.1 +/- 4.7 micrometers; moderately endurance-trained, 59.7 +/- 2.7 micrometers; and strongly endurance-trained, 58.7 +/- 4.5 micrometers) of 2A fibers. Moderately endurance-trained Andalusians had larger 2B fibers (area 18.6%; minimal diameter 14.3%) than untrained Andalusians, and the minimal diameter of type-1 and type-2B fibers was greater in strongly endurance-trained Andalusians than in untrained Andalusians (9.5% for type 1; 10.0% for type 2B). These results suggest minimal effects of endurance training on the myofiber size of adult Andalusians and Arabians, but a tendency toward increased type-1 and -2B fiber size was found for Andalusians.

The aerobic bacterial flora of the genital tract was characterized in 15 stud dogs in an 18-month study. The dogs represented 4 breeds and were from 3 kennels. Bacterial samples from the prepuce and semen were collected every month, except in connection with matings, when they were collected weekly (464 samples). The dogs that were included all mated at least once during the study. The mean pregnancy rate, litter size, and pup mortality for the bitches with which they had mated were all within normal limits. The most frequent bacteria isolated from the prepuce and semen were Pasteurella multocida, beta-hemolytic streptococci, and Escherichia coli. There was a tendency for breeds to differ in frequency of the most common bacterial species. Bacterial culture yielded no aerobic growth in 14.2% of the preputial samples and 69.8% of the semen samples. Bacteria were transferred between dog and bitch at mating. In this study of healthy breeding dogs, neither the fertility of the dog nor that of the bitch was affected by the bacteria transferred.

The aerobic bacterial flora of the genital tract was characterized in 59 bitches in an 18-month study. The bitches represented 4 breeds and were from 3 kennels. Collection of vaginal swab specimens for bacterial culturing was performed every month, except during estrus when specimens were collected every week (n = 826). The capsule of the swab containing transport media was broken before specimen collection to moisten the tip, which helped to reduce the number of negative cultures. All bitches whelped at least once during the study and, thus, had known reproductive functions. Pregnancy rates, litter sizes, and pup mortality were within normal limits. Pasteurella multocida, beta-hemolytic streptococci group G, and Escherichia coli were the most common bacteria isolated. Although these species generally were isolated from mixed cultures, pure cultures were obtained from 18% of the specimens. There was a tendency for the various breeds to differ in their vaginal bacterial flora. The flora also varied during the reproductive cycle. Pasteurella multocida was isolated significantly more often during proestrus, estrus, metestrus, and pregnancy, than during anestrus and the postpartum period, and beta-hemolytic streptococci were isolated significantly more often during proestrus than during estrus, pregnancy, or the postpartum period. Staphylococcus intermedius was almost exclusively found after parturition. Culture results were negative for only 5.2% of specimens cultured. On the basis of our findings, bacterial culturing of vaginal swab specimens from bitches without signs of genital disease is of little value.

Concentrations of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were measured in serum samples obtained from 100 dogs. Groups (n = 25/group) consisted of sexually intact and ovariohysterectomized bitches and sexually intact and castrated male dogs. Mean (+/- SD) concentrations of LH in the serum of sexually intact and ovariohysterectomized bitches were 1.2 (+/- 0.9) and 28.7 (+/- 25.8) ng/ml, respectively. Mean concentrations of FSH in the serum of sexually intact and ovariohysterectomized bitches were 98 (+/- 49) and 1,219 (+/- 763) ng/ml, respectively. Mean concentrations of LH in the serum of sexually intact and castrated male dogs were 6.0 (+/- 5.2) and 17.1 (+/- 9.9) ng/ml, respectively. Mean concentrations of FSH in the serum of sexually intact and castrated male dogs were 89 (+/- 28) and 858 (+/- 674) ng/ml, respectively. In addition to history, physical examination results, and other laboratory values, the measurement of serum gonadotropin concentrations may aid in determining whether dogs have been neutered.

Gene frequencies of RBC antigens were determined in Holsteins and Colombian (criollas) cattle living at 3,000 m, and in cattle descended from fighting bulls (Vacas de lidia) living at 2,500 m. These frequencies were compared with those of Holsteins, cattle native to Florida (scrub cattle), longhorns, and native cattle from Brazil (caracu cattle) living at sea level. The criollas, Vacas de lidia, scrub cows, longhorns, and caracu are descendants of original Iberian stock introduced to the Americas. We found that despite common ancestry (scrub cattle, longhorns, criollas, and caracu), genetic differences may have been derived through years of demographic isolation. The most remarkable blood-group differences were found in the high prevalence of the B system phenogroup (heritable group of antigenic factors) BQA'G'34 in the Vacas de lidia, and of the S system phenogroup U1H' in these cattle and in caracu. Furthermore, the gene frequencies differed in the Holsteins maintained at moderately high altitude (descended from Holsteins kept at sea level), and may have been reflective of the need to adapt to moderately high altitude and chronic hypoxemic conditions. Blood group polymorphism was found in all groups of cattle, although it was reduced in the Vacas de lidia, possibly because their breeding has been carefully controlled and they appear to be highly inbred.