Genetic diversity among Angus, American Brahman, Senepol and Romosinuano cattle breeds

The objective of this study was to quantify the genetic diversity among breeds under evaluation for tropical adaptability traits that affect the performance of beef cattle at the USDA/ARS SubTropical Agricultural Research Station (STARS) near Brooksville, FL, USA. Twenty-six microsatellite loci were used to estimate parameters of genetic diversity among the breeds American Brahman, Angus, Senepol and Romosinuano; the latter was comprised of two distinct bloodlines (Costa Rican and Venezuelan). Genotypes of 47 animals from each of these STARS herds were analysed for genetic diversity and genetic distance. Using two methods, the greatest genetic distance was detected between the Costa Rican line of Romosinuano and the Senepol. Gene diversity ranged between 0.64 (Costa Rican line of Romosinuano) and 0.75 (American Brahman). The breed relationship inferences, which are based on genetic distance, provide additional tools for consideration in future crossbreeding studies and for testing the relationship between quantified breed diversity and observed heterosis.     

Seasonal influences on conception efficiency in Minnesota dairy herds

This study was undertaken to investigate the influence of climatological factors on the conception efficiency of cows in 23 Minnesota dairy herds between March 1982 and March 1985. It was found that year of insemination (P < 0.005), herd (P < 0.005), linear and quadratic terms of days open (P < 0.05), and linear and quadratic terms of minimum temperature (MNT), maximum temperature (MXT) and temperature humidity index (THI) were similarly related to observed monthly variations in first service conception rates. The year of insemination (P < 0.005), herd (P < 0.005), and linear and quadratic terms of MNT, MXT and THI were also related to the variation in overall conception rate. Conception rate declined from April to August and increased from August to January. There was an 11% difference between the month of lowest fertility (August) and the month of highest fertility (November). It can be concluded that climatological factors appear to depress herd fertility in the northern United States as well as in the warmer southern areas. Thus, consideration should be given to strategies which will minimize the impact of the observed fertility depression due to these climatic factors.     

Prolactin levels in ovariectomized Brahman, Brahman x Hereford and Hereford cows following a 20 mg dose of estradiol-17beta

Six Brahman (B), six Brahman x Hereford (BxH) and six Hereford (H) chronically ovariectomized cows were injected intramuscularly with 20 mg of estradiol-17beta (E2). The cows were bled via coccygeal vessel puncture immediately before E2 injection, every 2 hr from 0 to 8 hr post-injection, every hr from 9 to 24 hr post-injection and every 2 hr from 26 to 36 hr post-injection. Serum prolactin (PRL) concentrations were quantitated by a validated radioimmunoassay. All cows exhibited a PRL surge following the E2 injection. A PRL surge was defined as a sustained elevation in PRL of at least one standard deviation above the level of PRL before the rise. Nadir levels of PRL prior to the surge did not differ significantly between breeds. Time (hr) to the onset of the E2-induced PRL surge was 5.0, 5.0 and 6.2 in B, BxH and H, respectively (P<.10). Elapsed time (hr) from E2 injection to the PRL peak level varied (P<.01) between B (10.8) and H (17.8) and BxH (11.8) and H. Peak PRL levels (ng/ml) varied (P<.10) between breeds (B, 70.6; BxH, 123.9; H, 49.4). Area under the PRL curve (sq cm) varied (P<.05) between BxH (45.2) and H (24.7) but not between BxH and B (34.3; P>.10) or B and H (P>.10). Duration (hr) of the PRL surge did not differ significantly between breeds (B, 19.3; BxH, 20.5; H, 21.2). Overall, bleeding period effects (P<.01), breed effects (P<.10), and breed x period interactions (P<.01) were found.     

Response to GnRH on day 6 of the estrous cycle is diminished as the percentage of Bos indicus breeding increases in Angus, Brangus, and Brahman x Angus heifers

Angus (n=6), Brangus (5/8 Angus x 3/8 Brahman, n=6), and Brahman x Angus (3/8 Angus x 5/8 Brahman, n=6) heifers exhibiting estrous cycles at regular intervals were used to determine if the percentage of Bos indicus breeding influenced the secretory patterns of LH in response to a GnRH treatment on Day 6 of the estrous cycle. Heifers were pre-synchronized with a two-injection PGF(2 alpha) protocol (25 mg i.m. Day -14 and 12.5 mg i.m. Day -3 and -2 of experiment). Heifers received 100 microg GnRH i.m. on Day 6 of the subsequent estrous cycle. Blood samples were collected at -60, -30, and -1 min before GnRH and 15, 30, 60, 90, 120, 150, 180, 240, 300, 360, 420, and 480 min after GnRH to determine concentrations of serum LH. Estradiol concentrations were determined at -60, -30, and -1 min before GnRH. On Day 6 and 8, ovaries were examined by ultrasonography to determine if ovulation occurred. On Day 13, heifers received 25 mg PGF(2 alpha) i.m. and blood samples were collected daily until either the expression of estrus or Day 20 for heifers not exhibiting estrus to determine progesterone concentrations. There was no effect (P>0.10) of breed on ovulation rate to GnRH as well as size of the largest follicle, mean estradiol, and mean corpus luteum volume at GnRH. Mean LH was greater (P<0.05) for Angus (7.0+/-0.8 ng/mL) compared to Brangus (4.6+/-0.8 ng/mL) and Brahman x Angus (2.9+/-0.8 ng/mL), which were similar (P>0.10). Mean LH peak-height was similar (P>0.10) for Brangus (13.9+/-3.4 ng/mL) compared to Angus (21.9+/-3.4 ng/mL) and Brahman x Angus (8.0+/-3.4 ng/mL), but was greater (P<0.05) for Angus compared to Brahman x Angus. Interval from GnRH to LH peak was similar (P>0.10) between breeds. As the percentage of Bos indicus breeding increased the amount of LH released in response to GnRH on Day 6 of the estrous cycle decreased.     

Reproductive studies of Brahman cattle III. Comparison of weight, progesterone content, histological characteristics, and 3β-hydroxysteroid dehydrogenase activity in corpora lutea of Brahman, Hereford, and Brahman × Hereford heifers

Sixty corpora lutea (CL), 30 from day 8 and 30 from day 13 of the estrous cycle were collected from 10 Brahman, 10 Hereford and 10 Brahman × Hereford F-1 (B×H) heifers and compared for weight, progesterone concentration and progesterone content. 3β-hydroxysteroid dehydrogenase (3β-HSD) activity and histological and morphological differences were evaluated in CL from 10 animals from each breed at each day.

The Brahman CL were significantly smaller than either Hereford or B×H Cl, 2.616, 3.836 and 4.211 g, respectively. No statistically significant differences were detected for luteal progesterone concentration or content, however, Brahman and B×H CL tended to have less progesterone per CL than did Hereford CL. The histology and morphology of the luteal tissue appeared similar for the three breeds, since there were no detectable differences in the organization, apparent population of cells per area, or the cell types present in the CL. Brahman CL had significantly higher 3β-HSD activity than Hereford or B×H. Day 13 corpora from all breeds had higher 3β-HSD enzyme than CL from day 8 of the cycle. It is evident from this study that major differences exist in CL from Brahman and B×H as compared to Hereford.     

Reproductive studies of Brahman cattle IV. Luteinizing hormone levels in ovariectomized Brahman, Brahman × Hereford and Hereford cows following a 20 mg dose of Estradiol-17β

Luteinizing Hormone (LH) levels were quantitated by radioimmunoassay (RIA) in six mature, long-term ovariectomized cows each of Brahman (B), Brahman × Hereford (B×H) and Hereford (H) breeding following an in-tramuscular injection of 20 mg of Estradiol-17_β (E) suspended in corn oil. After E administration all cows were bled via coccygeal venipuncture every two hours from 0–8 hours post-injection, every hour from 9–24 hours post-injection, concluding with bleedings every two hours from 26–36 hours post-injection. An LH surge was observed in 5/6 B cows, 6/6 B×H cows and 6/6 H cows. Basal LH levels (mean of first eight data points of each breed type) did not differ (P>.10) between B (3.5 ng/ml), B×H (2.4 ng/ml) and H (2.4 ng/ml). Elapsed time from E injection to peak LH value varied significantly (P<.05) between B, B×H and H, respectively (27.8 hrs, 23.8 hrs, 22.2 hrs). Peak LH values also varied between breed (B, 20.2 ng/ml; B×H, 36.0 ng/ml; H, 113.2 ng/ml: P<.005). The area under the LH curve differed significantly between B, B×H and H (P<.05), however, the duration of the LH surge was not different between breeds; B (13.2 hrs), B×H (16.2 hrs) and H (15.3 hrs). Overall significant period effects (P<.05), breed effects (P<.10) and period × breed interactions (P<.05) were found. In summary, B are less reactive to a 20 mg dose of E than are B×H or H using the following criteria: time to peak LH value, peak LH value and area under the LH curve. These data strongly indicate inherent differences between breeds regarding estrogen feedback mechanisms at the hypophysial-hypothalamic axis.     

Pubertal traits and seasonal variation of the sexual activity in Brahman, Hereford and crossbred heifers

Age and weight at puberty and the pattern of ovulatory activity from puberty to 26 mo of age were studied in a total of 55 Brahman (B), Hereford (H), 5/8B-3/8H (B(5)H(3)) and 5/16B-11/16H (B(5)H(11)) heifers. The trial was conducted over two years. Heifers were kept during the whole experimental period on a paddock of native pasture at a stocking rate of 0.5 animals per hectare. Vasectomized bulls were used for estrus detection and blood was collected from the heifers twice weekly to monitor ovulatory activity through progesterone level as determinated by RIA. In addition to age and weight at puberty, the weights and dates at the time of cessation and resumption of ovulatory activity were also considered. There were significant effects (P<0.05 or P<0.01) of genetic group (purebreds vs crossbreds) for age and weight at puberty; the difference being 60 d and 18 kg, respectively, favoring the crossbred groups. After puberty attainment, an anestrous period was detected in all Brahman (118.6 d) and B(5)H(3) (113.4 d) heifers; anestrus was observed in only 14% of B(5)H(11) heifers and for a shorter (43.5 days) period. Hereford heifers did not exhibit interruption of ovulatory activity. In Brahman and B(5)H(3) heifers, the pattern of interruption and resumption of estrus and ovulatory activity correlated closely (0.89 and 0.95 for Brahman and B(5)H(3) heifers, respectively) with the photoperiod curve, suggesting the probable influence of this environmental factor on the regulation of estrous cycle activity in heifers with a higher proportion of Bos indicus genes. Thus, the genetic factor needs be taken into account when establishing programs in reproductive management.     

Effect of dietary energy on growth and reproductive characteristics of Angus and Senepol bulls during summer in Florida

Pubertal Angus bulls (n=10, 503 days of age and weighing 366 kg) and Senepol bulls (n=10, 457 days of age and weighing 381 kg) were stratified by age and weight into 2 dietary treatments formulated to provide equal amounts of crude protein and 75% (below) or 150% (above) of the maintenance requirements for metabolizable energy. Measurements to assess body growth and libido were collected at 28-day intervals for 112 days (June through September). Twice during each 28-day interval, the bulls were subjected to breeding soundness examinations. At the end of the experiment, gonadotropin releasing hormone (GnRH) - induced secretion of luteinizing hormone (LH) and testosterone (T) in the serum were determined. At the end of the experiment, bulls fed the above maintenance diet (P<0.0001) were 91 kg heavier, had 1.7 mm more backfat thickness and 12.6 cm(2) larger ribeye area than bulls on a below maintenance diet. Diet affected (P<0.003) the average daily change in scrotal circumference, but not the libido score (P>0.1) or semen quality. In general, Angus bulls had superior initial semen quality (P<0.06); however, during summer, semen quality tended to decrease in Angus but not in Senepol bulls. The final rectal temperature was 0.5 degrees C lower (P<0.003) in Senepol than in Angus bulls. Basal T concentrations and area under the GnRH-induced T curve were greater (P<0.07) for bulls fed the above rather than the below maintenance diet. Angus bulls had a higher (P<0.03) maximal LH response to GnRH and larger area under the GnRH-induced LH curve than Senepol bulls.     

Cortisol and prolactin concentrations during three different seasons in relocated Brahman and Hereford bulls

The objective of this study was to evaluate seasonal changes of cortisol and prolactin (PRL) concentrations in Brahman and Hereford bulls moved to locations that differ in geographical and environmental conditions. Postpubertal Hereford bulls from Montana (n = 15) and Nebraska (n = 15) and Brahman bulls from Texas (n = 18) were located in or relocated to Montana, Nebraska or Texas so that each location had 5 Montana Herefords, 5 Nebraska Herefords and 6 Texas Brahman bulls. Blood samples were collected at 20-minute intervals for 8 hours in November (Fall 1), April (Spring) and November (Fall 2) of the next year. These dates corresponded to 6, 12 and 18 months, respectively, after relocation in May of the first year. Cortisol concentrations were higher (P<0.05) in Fall 1 than in Fall 2 and were higher (P<0.05) for bulls in Montana than for bulls in Texas. The decrease in cortisol concentrations from Fall 1 to Fall 2 was negatively related (P<0.05) to age and weight. There was a three-way interaction (P<0.05) of breed-type origin, location and season for PRL concentrations. Seasonal patterns of PRL concentrations differed between relocated Texas Brahman and Hereford bulls, and patterns for relocated bulls differed from those of the nonrelocated bulls. Seasonal patterns of PRL were influenced to a greater extent by relocation in Texas Brahman bulls than in Hereford bulls.     

The effect of feeding and management practices on calving rate in dairy herds

The objective of this study was to examine the effects of nutrition and management practices on reproductive performance in 31 Irish dairy herds participating in the Moorepark Dairy Management Information System (DairyMIS) during the period 1991-1998. Fifty variables relating to herd reproductive indices, calving events, stocking rate, disease, concentrate feeding, fertiliser usage, milk production and economic performance were studied using factor analysis. A factor analysis, followed by varimax rotation, identified 13 factors, which accounted for 83% of the total variance of the original variables. A regression model was used to predict calving rate from the orthogonal factor scores identified by factor analysis. Calving rate was defined as the proportion of services, for which an outcome was known, which resulted in a subsequent calving. Year, farm code and factor 3 (labelled herd size) together accounted for 40% of the observed variation in calving rate. The factor scores for factor 3 (herd size) were plotted against calving rate and because the plot was not linear, it was decided that dividing the factor scores into quartiles would produce a better fitting model. The factor scores for herd size were sorted and assigned to four equal categories (n = 47 per category), from lowest to highest. The ranges in herd size according to category were as follows: category 1 (34-96), category 2 (47-103), category 3 (66-152) and category 4 (108-359). The calving rate (%), (+/-S.E.) was 67.0 +/- 2.5 for category 1, 61.8 +/- 1.8 for category 2, 56.9 +/- 1.5 for category 3 and 53.2 +/- 2.85 for category 4. Using pair-wise comparisons, calving rates differed significantly (P < 0.05) between all categories except between categories 3 and 4 (P > 0.05). Herd-level milk production was not associated with calving rate indicating that good management may overcome any adverse effects of high milk production on reproductive performance. Larger herds, in combination with other associated herd characteristics, are likely to have poorer calving rates than medium or small herds.     

Reproductive studies of Brahman cattle II. Luteinizing hormone patterns in ovariectomized Brahman and Hereford cows before and after injection of gonadotropin releasing hormone

Six Brahman and six Hereford long-term ovariectomized cows were bled via tail vessel at 15 minute intervals for a period of 4 hours. Serum was collected and analyzed via radioimmunoassay (RIA) for luteinizing hormone (LH) to determine if ovariectomized Brahman and Hereford cows have pulsatile LH patterns and if breed of animal influenced LH patterns. Brahman and Hereford ovariectomized cattle did have pulsatile LH patterns. Although the trend was for higher LH levels in Hereford than Brahman cows there were no significant differences in mean serum LH levels, number or magnitude of LH peaks or serum LH pulse height.Six Brahman and five Hereford long-term ovariectomized cows were injected (IM) with a single dose of 500μg of gonadotropin releasing hormone (GnRH). Animals were bled via tail vessel at 15 minute intervals for a period of 6 hours. Serum was assayed for LH via RIA to determine if ovariectomized Brahman and Hereford cows differ in GnRH induced LH response. All animals showed increased serum LH in response to GnRH injection within the first 15 minute collection interval. There were no significant differences in duration of response between ovariectomized Brahman or Hereford cows. Ovariectomized Brahman cows had significantly lower (P<.005) Lh values per period than ovariectomized Hereford cows. It was therefore concluded that ovariectomized Brahman cows were significantly less responsive to GnRH induced LH release than were ovariectomized Hereford cows, although duration and shape of the response curves were not different.     

A Sperm Midpiece Defect in a Hereford Bull with Variable Semen Quality and Freezability

A midpiece sperm defect with a frequency of 25-35% in ejaculates obtained from a Hereford bull with a 60 d non-retum rate of 76.4% after careful pre- and postfreeze semen selection was studied in light microscope and by transmission electron microscopy. The defect consisted in a folding and coiling of the distal midpiece characterized by disorganization and irregularity of mitochondria surrounding the axial fiber bundle, combined with retraction of doublet fibers and dislocation and fracturing of these elements and the corresponding dense fibers. Based on examination of the sper- matogenic epithelium it was concluded that the alterations in the axial fiber bundle were secondary to those in the mitochondrial sheath. The abnormality appeared to be related to the “Dag-like” defect earlier observed in different breeds.     

A 2.5-Mb contig constructed from Angus, Longhorn and horned Hereford DNA spanning the polled interval on bovine chromosome 1

The polled locus has been mapped by genetic linkage analysis to the proximal region of bovine chromosome 1. As an intermediate step in our efforts to identify the polled locus and the underlying causative mutation for the polled phenotype, we have constructed a BAC-based physical map of the interval containing the polled locus. Clones containing genes and markers in the critical interval were isolated from the TAMBT (constructed from Angus and Longhorn genomic DNA) and CHORI-240 (constructed from horned Hereford genomic DNA) BAC libraries and ordered based on fingerprinting and the presence or absence of 80 STS markers. A single contig spanning 2.5 Mb was assembled. Comparison of the physical order of STSs to the corresponding region of human chromosome 21 revealed the same order of genes within the polled critical interval. This contig of overlapping BAC clones from horned and polled breeds is a useful resource for SNP discovery and characterization of positional candidate genes.     

Persistent influences of birth date on dominance, growth and reproductive success in bison

Long-term influences of birth date were examined in bison (Bison bison) over a nine-year period. Variation in birth date was related to differences in individual quality in both juveniles and adults. Earlier-born animals of both sexes were socially dominant to their later-born peers. Earlier-born females showed greater long-term fecundity. Long-term growth patterns also varied with birth date, earlier-born animals being larger. In females the relationship between body weight and birth date was significant as late as the eighth year of life, whereas in males effects on growth were weaker. For mothers, late parturition imposed immediate costs, increasing the likelihood of subsequent reproductive failure. There was no evidence that calving date varied with maternal condition, except that old females bore their last calves unusually late. These findings suggest that, in seasonally breeding ungulates, the benefits of early birth persist well into adulthood and have fitness consequences.     

Serum luteinizing hormone, 13,14-dihydro-15-keto-prostaglandin F2alpha and cortisol profiles during postpartum anestrus in Brahman and Angus cows

Pluriparous suckled Brahman and Angus cows were utilized to evaluate the effect of breed, day after calving and endogenous opioid peptides (EOP) on hormonal profiles during postpartum anestrus. On Days 17 and 34 after calving, blood samples with and without heparin were collected at 15- and 30-min intervals, respectively, for a 7-h period via jugular cannula. Two hours after the start of blood sampling, cows of each breed were administered either 1 mg/kg iv naloxone or saline. Three hours later, all animals received 10 ng/kg iv GnRH. On Day 34 after calving cows received 0.2 IU/kg iv ACTH. Mean LH, basal LH and area under the LH curve increased (P < 0.01) from Day 17 to Day 34 after calving. Height of LH pulses increased (P < 0.05) by Day 34 after calving. Brahman cows had higher (P < 0.05) mean LH, basal LH, LH pulse frequency and area under the LH curve than Angus cows. Naloxone increased postchallenge area under the LH curve in treated cows above that of control cows (P < 0.06). Naloxone also increased the postchallenge area under the LH curve above that of the prechallenge level (P < 0.01). No breed differences in the response to the naloxone challenge were observed. The LH response to naloxone challenge occurred earlier on Day 34 than on Day 17 after calving but the amount of LH released was similar between days. The GnRH-induced LH release was greater in Brahman than in Angus cows (P < 0.04). Mean cortisol concentrations and area under the cortisol curve decreased (P < 0.05) between Day 17 and Day 34 after calving. Mean cortisol concentrations and area under the cortisol curve were lower (P < 0.01) in Brahman than in Angus cows. Cortisol secretion after ACTH treatment was similar between Brahman and Angus cows. The cortisol response after ACTH challenge was positively correlated (r=0.68; P < 0.001) to the prechallenge area under the cortisol curve. Under optimal environmental conditions Brahman cows have a greater LH release and their anterior hypophysis is more sensitive to GnRH challenge than the Angus cows.     

Effect of estrus synchronization with Syncro-Mate-B((R)) on serum luteinizing hormone, progesterone and conception rate in Brahman heifers

Twenty-two estrous cyclic, 2-yr-old Brahman heifers were randomly assigned to receive either estrus synchronization with Syncro-Mate-B((R)) (SMB; 11) or no treatment (Control; 11). Blood samples were collected via tail vessel puncture at onset of estrus and daily thereafter until Day 11 after estrus. Blood samples were also collected from five SMB and five Control heifers at 0, 4, 8 and 12 h after the onset of estrus. All samples were processed to yield serum and stored at -20 degrees C until radioimmunoassay. Heifers were inseminated by one technician using semen from a single ejaculate of a Brahman bull 12 h after the onset of estrus. All SMB heifers exhibited estrus within 72 h of implant removal. All heifers had corpora lutea (CL) detected by rectal examination 8 to 12 d following estrus. Serum luteinizing hormone (LH) was not affected by treatment, time (4 - h intervals) or an interaction of treatment by time (P > 0.10). Independent analysis with h indicated that at h 12, SMB (2.2 +/- 0.06 ng/ml) had lower LH than did control heifers (8.9 +/- 2.1 ng/ml). Serum progesterone increased from Day 1 through Day 12 in all heifers, which is indicative of functional CL. Serum progesterone was affected by treatment (P < 0.0001) and time (d intervals; P < 0.10). Progesterone elevation was lower (P < 0.05) and area under the progesterone curve was lower (P < 0.03) in SMB (5.6 +/- 0.5 ng/ml, 32.0 +/- 4.5 units, respectively) when compared with control heifers (7.0 +/- 4 ng/ml, 43.7 +/- 2.4 units, respectively). Conception rate was lower (P < 0.01) in SMB heifers (2 of 11) than in control heifers (8 of 11). The lowered conception rate in SMB treated Brahman heifers may be due to altered timing of LH release following estrus, resulting in an altered time of ovulation.     

Assessment of progesterone profiles and postpartum onset of luteal activity in spring calving Hereford beef suckler cattle

Background  

Reproduction is the single greatest factor limiting beef cattle production. Previous research on beef suckler luteal activity has largely focused on the mechanisms, and duration, of postpartum anoestrus. However, the temporal pattern of luteal activity after resumption of post-partum ovarian activity, and the impact of pattern type on days open (DO) in purebred beef suckler cows, are unknown.