Temporal associations among ovarian events in cattle during oestrous cycles with two and three follicular waves

For 18 two-wave interovulatory intervals in heifers, the follicular waves were first detected on Days -0.2 +/- 0.1 and 9.6 +/- 0.2, and for 4 three-wave intervals on Days -0.5 +/- 0.3, 9.0 +/- 0.0 and 16.0 +/- 1.1 (ovulation is Day 0). The day-to-day mean diameter profile of the dominant follicle of the 1st wave and the day of emergence of the 2nd wave were not significantly different between 2-wave and 3-wave intervals. There were no indications, therefore, that events occurring during the first half of the interovulatory interval were associated with the later emergence of a 3rd wave. The dominant ovulatory follicle differed significantly (P less than 0.05 at least) between 2-wave and 3-wave intervals in day of emergence (Day 9.6 +/- 0.2 and 16.0 +/- 1.1), length of interval from emergence of follicle to ovulation (10.9 +/- 0.4 and 6.8 +/- 0.6 days), and diameter on day before ovulation (16.5 +/- 0.4 and 13.9 +/- 0.4 mm). The mean length of 2-wave interovulatory intervals (20.4 +/- 0.3 days) was shorter (P less than 0.01) than for 3-wave intervals (22.8 +/- 0.6 days). The mean day of luteal regression for 2-wave and 3-wave intervals was 16.5 +/- 0.4 and 19.2 +/- 0.5 (P less than 0.01). For all intervals, luteal regression occurred after emergence of the ovulatory wave, and the next wave did not emerge until near the day of ovulation at the onset of the subsequent interovulatory interval. In conclusion, the emergence of a 3rd wave was associated with a longer luteal phase, and the viable dominant follicle present at the time of luteolysis became the ovulatory follicle.

Association between surges of follicle-stimulating hormone and the emergence of follicular waves in heifers

The effects of ablation of a dominant follicle and treatment with follicular fluid on circulating concentrations of follicle-stimulating hormone (FSH) were studied and the temporal relationships between surges of FSH and follicular waves were studied in heifers with two or three follicular waves/interovulatory interval. Cauterization of the dominant follicle on Day 3 or Day 5 (ovulation on Day 0) (six control and six treated heifers/day) resulted in a surge (P less than 0.05) in FSH beginning the day after cautery. The FSH surge prior to wave 2 (first post-treatment follicular wave) occurred 4 days (Day 3 cautery) and 2 days (Day 5 cautery) before the surge in control groups, corresponding to a 4-day and a 2-day advance in emergence of wave 2 compared with controls. It was concluded that the dominant follicle on Day 3 and Day 5 was associated with the suppression of circulating FSH concentrations. Heifers (n = 4/group) were untreated or treated intravenously with a proteinaceous fraction of bovine follicular fluid on Days 0-3, 3-6, or 6-11. Concentrations of FSH were suppressed (P less than 0.05) for the duration of treatment, regardless of the days of treatment. Cessation of treatment was followed within 1 day by the start of a surge in FSH. The FSH surge prior to wave 2 occurred 2 days earlier (treatment on Days 0-3), 1 day later (treatment on Days 3-6), and 6 days later (treatment on Days 6-11) than in controls, corresponding to an equivalent advance or delay, respectively, in the emergence of wave 2 compared with controls. The results suggest that the effects of exogenous follicular fluid on follicular development were mediated, in whole or in part, by altering plasma FSH concentrations. Control heifers combined for the two experiments were separated into those with 2-wave (n = 11) or 3-wave (n = 5) interovulatory intervals. Two-wave heifers had two FSH surges and 3-wave heifers had three apparent FSH surges during the interovulatory interval. Results of the cautery and follicular fluid experiments indicated that a surge in FSH necessarily preceded the emergence of a wave. The FSH surges in treated and control heifers began 2-4 days before the detectable (ultrasound) emergence of a follicular wave (follicles of 4 and 5 mm), peaked 1 or 2 days before emergence and began to decrease approximately when the follicles of a wave begin to diverge into a dominant follicle and subordinate follicles (follicles 6-7 mm).

Invited review: Changes in the dairy industry affecting dairy cattle health and welfare

The dairy industry in the developed world has undergone profound changes over recent decades. In this paper, we present an overview of some of the most important recent changes in the dairy industry that affect health and welfare of dairy cows, as well as the science associated with these changes. Additionally, knowledge gaps are identified where research is needed to guide the dairy industry through changes that are occurring now or that we expect will occur in the future. The number of farms has decreased considerably, whereas herd size has increased. As a result, an increasing number of dairy farms depend on hired (nonfamily) labor. Regular professional communication and establishment of farm-specific protocols are essential to minimize human errors and ensure consistency of practices. Average milk production per cow has increased, partly because of improvements in nutrition and management but also because of genetic selection for milk production. Adoption of new technologies (e.g., automated calf feeders, cow activity monitors, and automated milking systems) is accelerating. However, utilization of the data and action lists that these systems generate for health and welfare of livestock is still largely unrealized, and more training of dairy farmers, their employees, and their advisors is necessary. Concurrently, to remain competitive and to preserve their social license to operate, farmers are increasingly required to adopt increased standards for food safety and biosecurity, become less reliant on the use of antimicrobials and hormones, and provide assurances regarding animal welfare. Partly because of increasing herd size but also in response to animal welfare regulations in some countries, the proportion of dairy herds housed in tiestalls has decreased considerably. Although in some countries access to pasture is regulated, in countries that traditionally practiced seasonal grazing, fewer farmers let their dairy cows graze in the summer. The proportion of organic dairy farms has increased globally and, given the pressure to decrease the use of antimicrobials and hormones, conventional farms may be able to learn from well-managed organic farms. The possibilities of using milk for disease diagnostics and monitoring are considerable, and dairy herd improvement associations will continue to expand the number of tests offered to diagnose diseases and pregnancy. Genetic and genomic selection for increased resistance to disease offers substantial potential but requires collection of additional phenotypic data. There is every expectation that changes in the dairy industry will be further accentuated and additional novel technologies and different management practices will be adopted in the future.

Ovarian follicular dynamics in heifers: test of two-wave hypothesis by ultrasonically monitoring individual follicles

The two-wave hypothesis for follicular development during the bovine estrous cycle was tested by ultrasonically monitoring individual follicles in 10 heifers during an interovulatory interval. A dominant follicle was defined as one that reached a diameter of at least 11 mm. Subordinate follicles were defined as those that appeared to originate from the same follicular pool as a dominant follicle. A dominant follicle and its cohorts were defined as a wave. Two waves during an interovulatory interval were identified in 9 of 10 heifers. The first wave was first identified, retrospectively, on a mean of Day 0.2 +/- 0.1 (ovulation = Day 0) and gave origin to a dominant anovulatory follicle and a mean of 1.4 +/- 0.3 identified subordinates. The dominant follicle reached maximum diameter (mean, 15.8 +/- 0.8 mm) on an average of Day 7 and then decreased (P less than .04) by Day 11. The subordinate follicles increased in diameter for a few days and then regressed. The second wave was first identified on a mean of Day 10.0 +/- 0.4 and gave origin to the ovulatory follicle and a mean of 0.9 +/- 0.3 subordinates. One of the 10 heifers had 3 waves of follicular activity characterized by an anovulatory wave emerging on Day 0, another anovulatory wave emerging on Day 10, and an ovulatory wave emerging on Day 16. Results strongly supported the two-wave hypothesis but also indicated that a minority of interovulatory intervals in this heifer population may have 3 waves of follicular activity.

Lower Pregnancy Losses in Lactating Dairy Cows Fed a Diet Enriched in α-Linolenic Acid

The objectives were to determine if a diet enriched in alpha-linolenic acid (ALA) would influence ovarian function, early embryo survival, conception rates, and pregnancy losses in lactating dairy cows. Beginning 28 d before breeding, Holstein cows (55 +/- 22 d postpartum; mean +/- SD) were assigned to diets supplemented with either rolled flaxseed (FLAX; 56.7% ALA, n = 62) or rolled sunflower seed (SUNF; 0.1% ALA, n = 59) to provide approximately 750 g of oil/d. Diets continued for 32 d after timed artificial insemination (TAI, d 0) following a Presynch/Ovsynch protocol. Barley silage- and barley grain-based TMR were formulated to meet or exceed National Research Council requirements. Metabolizable protein and net energy for lactation concentrations were similar in the 2 diets. Based upon a mean dry matter intake of 22 kg/d, cows fed FLAX or SUNF consumed > 410 g or < 1 g of ALA, respectively. Pregnancy was confirmed by ultrasound 32 d after TAI. Nonpregnant cows were placed on a second Ovsynch regimen and reinseminated 42 d after first TAI, and received oilseeds for 32 d after second TAI. Relative to prediet levels, FLAX increased the ALA content of milk by 187%. Ovarian ultrasonography was performed in 8 cows per diet; the mean diameter of ovulatory follicles was larger in cows fed FLAX compared with SUNF (16.9 +/- 0.9 vs. 14.1 +/- 0.9 mm), but follicle number, corpus luteum size, and plasma progesterone concentrations remained unaffected. Presumptive conception (progesterone < 1 ng/mL on d 0 and > 1 ng/mL on d 21) rates to first TAI were greater in FLAX than in SUNF (72.6 vs. 47.5%). Pregnancy losses were lower in cows fed FLAX (9.8%) compared with those fed SUNF (27.3%). Including flaxseed in the ration of dairy cows increased the size of the ovulatory follicle and reduced pregnancy losses.

Ultrasonic morphology of corpora lutea and central luteal cavities during the estrous cycle and early pregnancy in heifers

Ultrasonography was used once daily to quantify corpora lutea, central luteal cavities, and luteinized tissue during interovulatory intervals (n=66) and during Days 0 to 60 of pregnancy (n=14) in nulliparous Holstein heifers (ovulation=Day 0). The corpus luteum of the estrous cycle was detectable by ultrasonography in most heifers from the day of ovulation (mean, Day 0.5) and extending into the regressive phase beyond the next ovulation (mean, Day 1.4+/-0.2 after the next ovulation). During pregnancy, the corpus luteum was detected until Day 60 (end of study). Maximal central luteal cavity area detected on Days 0 to 20 was used retrospectively to group luteal glands into four cavity categories: no, small, medium, and large. These categories corresponded to approximate cavity diameters of <2 mm, 2 to 5 mm, 6 to 10 mm, and >10 mm, respectively. The incidence of each cavity category was similar between interovulatory intervals and pregnancies (combined incidence, 17/80, 8/80, 33/80, and 22/80 for no, small, medium, and large cavities, respectively; total with cavities, 63/80, 79%). Mean day of first detection of a central cavity was earliest for large cavities during interovulatory intervals (means, Days 4.7, 4.4, and 3.0 for small, medium, and large cavities, respectively; P<0.04) and during pregnancies (means, Days 5.5, 4.2, and 3.3, respectively; NS). However, the day that the cavities reached maximum size (range of means, Days 5.5 to 7.0) did not differ among categories. Mean day of last detection of the central cavity was significantly different among cavity categories during interovulatory intervals (means, Days 9.3, 11.1, and 17.4 for small, medium, and large cavities, respectively) and pregnancies (means, Days 7.0, 8.8, and 20.2, respectively). Time of loss of central cavities was similar between nonbred and pregnant heifers, and there was no significant difference among cavity categories in the length of the interovulatory interval (mean, 20.1 d). Luteal tissue area was not significantly different among cavity categories during interovulatory intervals. There were no indications that cavities were functionally important. Luteal tissue area increased linearly in pregnant heifers on Days 21 to 60 (mean slope, 2.6 mm2/day).

Effect of LH or GnRH on the dominant follicle of the first follicular wave in beef heifers

A study was designed to characterise ovarian follicular dynamics in heifers treated with porcine luteinizing hormone (pLH) or gonadotropin releasing hormone (GnRH) on days 3, 6 or 9 (ovulation = day 0), corresponding to the growing, early-static, and late-static phases of the first follicular wave. Following ovulation, 65 beef heifers were assigned, by replicate, to the following seven treatment groups: 25 mg im of pLH on days 3, 6 or 9 (n = 9 per group); 100 microg im of GnRH on days 3, 6 or 9 (n = 9 per group); or controls (no treatment; n = 11). Ovulation occurred within 36 h in 67%, 100% and 67% of heifers treated with pLH and in 89%, 56% and 22% of heifers treated with GnRH on days 3, 6 or 9, respectively (treatment-by-day interaction, P < 0.09). Combined for all treatment days, ovulation rates were 78% and 56% in pLH- and GnRH-treated groups, respectively (P < 0.09). Overall, mean day (+/- SD) of emergence of the second follicular wave in heifers that ovulated was different from that in controls or in heifers that did not ovulate (P < 0.05). Mean (+/- SD) day of emergence of the second wave occurred earlier (day 5.6+/-1.2; P < 0.05) in heifers that ovulated after treatment on day 3 (n = 14) than in controls (day 8.7+/-1.6; n = 11); however, wave emergence in all heifers treated on day 6 (day 8.1+/-0.5; n = 18) did not differ from controls, regardless of whether or not ovulation occurred. In the heifers that ovulated in response to treatment on day 9 (n = 8), the emergence of the second follicular wave was delayed (day 10.9+/-0.4; P < 0.05). The day of emergence of the second wave in the 14 treated heifers that failed to ovulate, irrespective of the day of treatment (day 8.9+/-1.4) did not differ from control heifers. The emergence of the second wave was more synchronous in day 6 heifers (regardless of whether they ovulated) and in day 9 heifers that ovulated compared to control heifers (P < 0.05). Results did not support the hypothesis that the administration of pLH or GnRH at known stages of the follicular wave in cycling heifers would consistently induce ovulation or atresia and, thereby, induce emergence of a new follicular wave at a predictable interval. New wave emergence was induced consistently (1.3 days post-treatment) only in those animals that ovulated in response to treatment. However, 22% of LH-treated heifers and 44% of GnRH-treated heifers failed to ovulate. Treatments did not induce atresia of the dominant follicle or alter the interval to new wave emergence in animals that did not ovulate in response to treatment.

Effects of a dominant follicle on ovarian follicular dynamics during the oestrous cycle in heifers

Two hypotheses were tested: (1) a dominant follicle causes regression of its subordinate follicles, and (2) a dominant follicle during its growing phase suppresses the emergence of the next wave. Cyclic heifers were randomly assigned to one of four groups (6 heifers/group): cauterization of the dominant follicle of Wave 1 or sham surgery (control) on Day 3 or Day 5 (day of ovulation = Day 0). Ultrasonic monitoring of individually identified follicles was done once daily throughout the interovulatory interval. The onset of regression (decreasing diameter) of the largest subordinate follicle of Wave 1 was delayed (P less than 0.01) by cauterization of the dominant follicle of Wave 1 on Day 3 compared to controls (mean onset of regression, Days 10.8 +/- 2.1 vs 4.3 +/- 0.4). Cauterization of the dominant follicle of Wave 1 on Days 3 or 5 caused early emergence (P less than 0.01) of Wave 2 when compared to controls (Day-3 groups: Days 5.5 +/- 0.4 vs 9.6 +/- 0.7; Day-5 groups: Days 7.0 +/- 0.3 vs 9.1 +/- 0.4). The results supported the two hypotheses. In addition, cauterization of the dominant follicle of Wave 1 on Days 3 or 5 increased the incidence of 3-wave interovulatory intervals.

Testicular thermoregulation in Bos indicus, crossbred and Bos taurus bulls: relationship with scrotal, testicular vascular cone and testicular morphology, and effects on semen quality and sperm production

Mechanisms of testicular thermoregulation, the relationship of scrotal, testicular vascular cone (TVC), and testicular morphology with thermoregulatory capability, and their effects on semen quality and sperm production were studied in 20 Bos indicus, 28 crossbred, and 26 Bos taurus bulls. The ratio of testicular artery length and volume to testicular volume were larger (P<0.05) in B. indicus and crossbred bulls than in B. taurus bulls (1.03 and 0.94 cm/cm3 versus 0.48 cm/cm3; 0.034 and 0.047 ml/cm3 versus 0.017 ml/cm3, respectively). Testicular artery wall thickness (average 192.5, 229.0, and 290.0 microm, respectively) and arterial-venous blood distance in the TVC (average 330.5, 373.7, and 609.4 microm, respectively) were smallest in B. indicus, intermediary in crossbred, and greatest in B. taurus bulls (P<0.05); the proximity between arterial and venous blood was consistent with the estimated decrease in arterial blood temperature after passage through the TVC (5.9, 5.0, and 2.9 degrees C, in B. indicus, crossbred, and B. taurus bulls, respectively). In crossbred and B. taurus bulls, there was a positive top-to-bottom scrotal temperature gradient and a negative testicular subtunic temperature gradient. However, in B. indicus bulls, both scrotal and testicular subtunic temperatures gradients were positive. Differences in the vascular arrangement, characteristics of the artery (e.g. wall thickness) or thickness of the tunica albuginea may have affected the testicular arterial blood and subtunic temperatures in B. indicus bulls. Better testicular thermoregulatory capability was associated with increased scrotal shape (pendulosity), testicular artery length and volume, and top-to-bottom gradient of the distance between the artery wall and the veins in the TVC. Increased semen quality was associated with increased testicular volume and scrotal subcutaneous (SQT) temperature gradient, and with decreased scrotal surface and testicular temperatures. Increased sperm production was associated with increased testicular artery volume, testicular volume, and SQT temperature gradient, and with decreased testicular artery wall thickness, scrotal circumference (SC), and scrotal surface, testicular subtunic, and epididymal temperatures. In conclusion, morphology of the TVC may contribute to the greater resistance of B. indicus bulls to high ambient temperatures by conferring a better testicular blood supply and by facilitating heat transfer between the testicular artery and veins. Testicular thermoregulation was associated with opposing scrotal and testicular subtunic temperatures gradients only in crossbred and B. taurus bulls. Scrotal, TVC, and testicular morphology influence testicular thermoregulatory capability and were associated with differences in semen quality and sperm production.

Comparison of methods to evaluate the plasmalemma of bovine sperm and their relationship with in vitro fertilization rate

The objectives of this study were to compare different methods of evaluating sperm plasmalemma and to determine their relationship with in vitro fertilization rate. A single batch of frozen semen from each of eight beef bulls was used for assessment of sperm viability and for in vitro fertilization. Conventional viability tests included sperm morphology, motility, acrosome integrity, and abnormal DNA condensation. Methods for evaluation of the sperm plasmalemma included eosin/nigrosin (EN) and trypan-blue (TB) vital stains, propidium iodide (PI) in combination with carboxyfluorescein diacetate (CFDA) or SYBR-14 (SYBR) fluorescent vital stains, and the hypoosmotic swelling test (HOST). A total of 133-150 oocytes were fertilized in vitro with sperm from each bull and cleavage rates were determined. There were high correlations between the results obtained with vital stains and good to excellent interclass correlation coefficients of agreement, indicating that these stains provide measures of the same sperm attribute, i.e. plasmalemma integrity. However, the proportions of membrane-intact sperm identified by EN or TB stains were greater (P<0.0001) than identified by CFDA/PI or SYBR/PI fluorescent stains. The results obtained with the HOST had moderate correlations but poor agreement with the results of the vital stains. The proportion of viable sperm identified by the HOST was lower (P<0.05) than the proportion identified by vital stains, indicating that response to the HOST did not depend only on the integrity of the plasmalemma. Although there were significant differences in fertilization rates and sperm viability among bulls, there was no sharp distinction for the results of sperm viability tests from bulls producing different in vitro fertilization rates. Proportions of normal, motile, acrosome-intact, and HOST-responsive sperm were identified as significant predictors of in vitro fertilizing potential; each of these endpoints explained 12-18% of the variation when evaluated separately (linear regression) and 48% when evaluated collectively (stepwise regression). In conclusion, EN and TB stains overestimated the proportion of plasmalemma-intact sperm compared to PI-based fluorescent stains. Vital stains evaluated the morphological integrity of the plasmalemma, whereas the HOST assessed plasmalemma function. In that regard, the HOST was the only plasmalemma evaluation method that significantly contributed to conventional sperm quality tests in predicting in vitro fertilization rate, indicating that the test could be incorporated to the routine of semen analysis.

Knowledge gaps that hamper prevention and control of Mycobacterium avium subspecies paratuberculosis infection

In the last decades, many regional and country-wide control programmes for Johne's disease (JD) were developed due to associated economic losses, or because of a possible association with Crohn's disease. These control programmes were often not successful, partly because management protocols were not followed, including the introduction of infected replacement cattle, because tests to identify infected animals were unreliable, and uptake by farmers was not high enough because of a perceived low return on investment. In the absence of a cure or effective commercial vaccines, control of JD is currently primarily based on herd management strategies to avoid infection of cattle and restrict within-farm and farm-to-farm transmission. Although JD control programmes have been implemented in most developed countries, lessons learned from JD prevention and control programmes are underreported. Also, JD control programmes are typically evaluated in a limited number of herds and the duration of the study is less than 5 year, making it difficult to adequately assess the efficacy of control programmes. In this manuscript, we identify the most important gaps in knowledge hampering JD prevention and control programmes, including vaccination and diagnostics. Secondly, we discuss directions that research should take to address those knowledge gaps.

The use of progestins in regimens for fixed-time artificial insemination in beef cattle

Four experiments were conducted to investigate modifications to gonadotropin releasing hormone (GnRH)-based fixed-time Al protocols in beef cattle. In Experiment 1, the effect of reducing the interval from GnRH treatment to prostaglandin (PGF) was examined. Lactating beef cows (n = 111) were given 100 mg gonadorelin (GnRH) on Day 0 (start of treatment) and either 500 microg cloprostenol (PGF) on Day 6 with Al and 100 microg GnRH 60 h later, or PGF on Day 7 with Al and GnRH 48 h later (6- or 7-day Co-Synch regimens). Pregnancy rates were 32/61 (53.3%) versus 26/50 (52.0%), respectively (P = 0.96). In Experiment 2. cattle (n = 196) were synchronized with a 7-day Co-Synch regimen and received either no further treatment or a CIDR-B device (Days 0-7). Pregnancy rates were 32/71 (45.1%) versus 33/77 (42.9%) in cows (P < 0.8), and 9/23 (39.1 %) versus 17/25 (68.0%) in heifers (P < 0.05). In Experiment 3, 49 beef heifers were randomly assigned to receive 12.5 mg pLH on Day 0, PGF on Day 7 and 12.5 mg of pLH on Day 9 with Al 12 h later (pLH Ovsynch), or similar treatment plus a CIDR-B device from Days 0 to 7 (pLH Ovsynch + CIDR-B), or 1 mg estradiol benzoate (EB) and 100 mg progesterone on Day 0, a CIDR-B device from Days 0 to 7 (EB/ P4 + CIDR-B), PGF on Day 7 (at the time of CIDR-B removal) and 1 mg i.m. EB on Day 8 with AI on Day 9 (52 h after PGF). Pregnancy rate in the EB/P4 + CIDR-B group (75.0%) was higher (P < 0.04) than in the pLH Ovsynch group (37.5%): the pLH Ovsynch + CIDR-B group was intermediate (64.7%). In Experiment 4, 266 non-lactating cows were allocated to a 7-day Co-Synch protocol (Co-Synch), a 7-day Co-Synch plus 0.6 mg per head per day melengestrol acetate (MGA) from Days 0 to 6 inclusive (Co-Synch + MGA) or MGA (Days 0-6) plus 2 mg EB and 50 mg progesterone on Day 0. 500 microg PGF on Day 7, 1 mg EB on Day 8 and fixed-time Al 28 h later (EB/ P4 + MGA). Pregnancy rates (P < 0.25) were 44.8% (39/87: Co-Synch), 47.8% (43/90; Co-Synch + MGA), and 60.7% (54/89: EB/P4 + MGA). In conclusion, a 6- or 7-day interval from GnRH to PGF in a Co-Synch regimen resulted in similar pregnancy rates in cows. The addition of a progestin to a Co-Synch or Ovsynch regimen significantly improved pregnancy rates in heifers but not in cows. Progestin-based regimens that included EB consistently resulted in high pregnancy rates to fixed-time Al.

Ovarian follicular dynamics in heifers during early pregnancy

Daily ultrasonic monitoring of individual follicles was used to compare follicular wave characteristics of nonbred (n = 6) and pregnant heifers (n = 6). The dominant follicle of the first wave (Wave 1) did not differ significantly between reproductive statuses for any endpoint. The dominant follicle of Wave 2 was the ovulatory follicle in all nonbred heifers. The maximum diameter of the dominant follicle of Wave 2 was greater (p less than 0.05) for the nonbred heifers (14.8 mm) than for the pregnant heifers (13.0 mm). The dominant follicle of Wave 3 was detected later (p less than 0.003; Day 19.7 vs. Day 17.3) and reached a greater diameter (p less than 0.05; 16.6 mm vs. 12.0 mm) in the nonbred than in the pregnant heifers. On the mean day of onset of luteolysis (Day 15.2) in the nonbred heifers, the dominant follicle was similar in diameter for the two groups. Within a few days, the follicle began to regress in the pregnant heifers but maintained or increased in diameter in the nonbred heifers so that a greater maximum diameter was attained. During Days 0 70 of pregnancy, the interval from emergence of a wave to the emergence of the next wave was constant (not significantly different; mean intervals, 8.5 9.8 days). The mean maximum diameter attained by the dominant follicles differed significantly among the first 6 follicular waves; diameter was greatest for Wave 1 (15.7 mm), smallest for Waves 2 (13.1 mm) and 3 (12.6 mm), and intermediate for Waves 4 (14.0 mm), 5 (13.7 mm), and 6 (14.5 mm).(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of follicular wave emergence for estrus synchronization and artificial insemination in heifers

The objective was to synchronize follicular wave emergence among cattle for synchronization of estrus and ovulation, and to determine pregnancy rate after AI at observed estrus. At random stages of the estrous cycle, a controlled internal drug release device (CIDR-B) was inserted intravaginally (Day 0) in 67 cross-bred beef heifers, and they were randomly allocated to receive either no further treatment (Control; n = 18); 5 mg of estradiol-17beta and 100 mg of progesterone im (E/P; n = 16); 100 microg im of GnRH (GnRH; n = 16); or transvaginal ultrasound-guided follicular ablation of all follicles > or = 5 mm (FA; n = 17). All heifers received a luteolytic dose of PGF (repeated 12 h later), and CIDR-B were removed on Days 9, 8, 6 or 5, in Control, E/P, GnRH or FA groups, respectively, so the dominant follicle of the induced wave was exposed to exogenous progesterone for a similar period of time in each group. Mean (+/- SEM) intervals (and range, in days) from treatment to follicular wave emergence in these groups were 3.5 +/- 0.6 (-2 to 8), 3.4 +/- 0.1 (3 to 4), 1.5 +/- 0.3 (-1 to 4), and 1.0 +/- 0.1 (0 to 2), respectively. Although the interval was longest (P<0.01) in the E/P and Control groups, it was least variable (P<0.01) in the E/P and FA groups. Intervals (and range, in days) from CIDR-B removal (and first PGF treatment) to estrus were 2.3 +/- 0.2 (1.5 to 4.5), 2.2 +/- 0.2 (1.5 to 3.0), 2.1 +/- 0.1,(1.5 to 3.5), and 2.5 +/- 0.1 (2.0 to 3.5), and to ovulation were 3.5 +/- 0.2 (2.5 to 5.5), 3.4 +/- 0.1 (3.0 to 4.5), 3.5 +/- 0.1 (2.5 to 4.5), and 3.8 +/- 0.1 (3.0 to 4.5), for Control, E/P, GnRH and FA groups, respectively (ns). The proportion of heifers displaying estrus was higher in the Control than in the FA group (94% versus 65%, P<0.05) and intermediate in EP and GnRH groups (87% and 75%). Heifers were inseminated approximately 12 h prior to ovulation (based on estrous behavior and ultrasound examinations). Pregnancy rates were 78%, 80%, 69% and 65% for Control, E/P, GnRH and FA groups, respectively (P=0.73). Results support the hypothesis that synchronous follicular wave emergence results in synchronous follicle development and, following progesterone removal, synchronous estrus and ovulation with high pregnancy rates to AI. The synchrony of estrus and ovulation in the E/P, GnRH and FA groups suggest that these treatments, in combination with CIDR-B, could be adapted to fixed-time insemination programs.

Associations among serum pro- and anti-inflammatory cytokines, metabolic mediators, body condition, and uterine disease in postpartum dairy cows

BACKGROUND

Adipose tissue is an active endocrine organ which secretes a wide range of hormones and protein factors, collectively termed adipokines. Adipokines affect appetite and satiety, glucose and lipid metabolism, inflammation and immune functions. The objectives were to evaluate serum concentrations of adipokines (adiponectin, leptin, tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta and IL-6) in lactating dairy cows with postpartum uterine inflammatory conditions (metritis, clinical endometritis or subclinical endometritis) and in cows experiencing loss of body condition, and to assess the relationship of adipokines and body condition loss in the establishment of persistent uterine inflammatory conditions.

METHODS

Lactating multiparous Holstein cows (N = 40), with body condition scores (BCS) from 2 to 4 (eight cows for each 0.5 score increment) were enrolled. Body condition was monitored for all cows weekly for 7 weeks post calving; cows with uterine inflammatory conditions were also re-evaluated 2 weeks later. Blood samples were collected from 1 week prior to calving to 7 weeks after calving for determination of serum concentrations of adipokines, insulin and insulin like growth factor (IGF)-1.

RESULTS

Cows with metritis or clinical endometritis had higher serum concentrations of adiponectin, leptin, TNF-alpha, IL-1beta and IL-6 compared to normal cows (P < 0.05). Furthermore, serum leptin, TNF-alpha, IL-1beta and IL-6 were higher in cows with subclinical endometritis compared to normal cows (P < 0.05), and insulin and IGF-1 concentrations were lower in cows with metritis or clinical endometritis. Cows with low BCS (2 and 2.5) had significantly higher adiponectin, TNF-alpha, IL-1beta and IL-6 than those with high BCS (3 to 4). Cows with persistent uterine inflammatory conditions had higher adiponectin, leptin TNF-alpha, IL-1beta and IL-6 and insulin compared to normal and spontaneously recovered cows, except for IGF-1 (P < 0.05).

CONCLUSIONS

Serum concentrations of adipokines, insulin, and IGF-1 had significant associations with BCS categories (low vs. high) and postpartum uterine inflammatory conditions. Perhaps loss of body condition mediated increases in anti- and pro-inflammatory cytokines, whereas increased pro- and anti-inflammatory cytokines concentrations mediated body condition loss and thereby prolonged persistence of uterine inflammation in dairy cows.

Antimicrobial resistance profiles of 5 common bovine mastitis pathogens in large Chinese dairy herds

The prevalence of antimicrobial resistance (AMR) is increasing in human and animal pathogens, becoming a concern worldwide. However, prevalence and characteristics of AMR of bovine mastitis pathogens in large Chinese dairy herds are still unclear. Therefore, our objective was to determine the AMR profile of bacteria isolated from clinical mastitis in large (>500 cows) Chinese dairy herds. A total of 541 isolates of the 5 most common species, Staphylococcus aureus (n = 103), non-aureus staphylococci (NAS; n = 107), Streptococcus species (n = 101), Klebsiella species (n = 130), and Escherichia coli (n = 100), isolated from bovine clinical mastitis on 45 dairy farms located in 10 provinces of China were included. Presence of AMR was determined by minimum inhibitory concentrations using the microdilution method. Prevalence of multidrug resistance (resistance to >2 antimicrobials) was 27% (148/541). A very wide distribution of minimum inhibitory concentrations was screened in all isolates, including Staph. aureus isolates, which were resistant to penicillin (66%). In addition, NAS (30%) were more resistant than Staph. aureus to oxacillin (84%), penicillin (62%), tetracycline (34%), and clindamycin (33%). Prevalence of resistance to tetracycline was high (59%) in Streptococcus spp. Additionally, prevalence of resistance of both E. coli and Klebsiella spp. was high to amoxicillin/clavulanate potassium (81 and 38%, respectively), followed by tetracycline (only Klebsiella spp. 32%). A high proportion (27%) of isolates were multidrug resistant; the most frequent combinations were clindamycin-cefalexin-tetracycline or enrofloxacin-cefalexin-penicillin patterns for Staph. aureus; enrofloxacin-oxacillin-penicillin-tetracycline patterns for NAS; clindamycin-enrofloxacin-tetracycline patterns for Streptococcus spp.; amoxicillin/clavulanate potassium-ceftiofur-polymyxin B patterns for Klebsiella spp.; and amoxicillin/clavulanate potassium-ceftiofur-polymyxin B patterns for E. coli. Resistance for 4 kinds of antimicrobials highly critical for human medicine, including daptomycin, vancomycin, imipenem, and polymyxin B, ranged from 0 to 24%. In conclusion, prevalence of AMR in mastitis pathogens was high on large Chinese dairy farms, potentially jeopardizing both antimicrobial efficacy and public health. Results of this study highlighted the need for improvements in antimicrobial stewardship and infection control programs in large Chinese dairy farms to reduce emergence of AMR.

Effects of scrotal insulation on sperm production, semen quality, and testicular echotexture in Bos indicus and Bos indicus x Bos taurus bulls

The objectives of the present study were to evaluate the effects of scrotal insulation on sperm production, semen quality, and testicular echotexture in Bos indicus and Bos indicus x Bos taurus crossbred bulls. In one experiment, B. indicus bulls (n=12) were allocated to control and whole-scrotum insulation groups, while in a second experiment, crossbred bulls (n=21) were allocated into control, whole-scrotum, and scrotal-neck insulation groups. Insulation was applied for 4 days (start of insulation = Day 0) and semen collection and testicular ultrasonographic examinations were performed twice weekly until Day 35. Sperm concentration and total sperm output during the post-insulation period were greater in control groups, but significant differences were observed only in B. indicus bulls. Overall, sperm motility in scrotal-insulated B. indicus bulls was lower (P<0.05) than in the control group. After whole-scrotum insulation in crossbred bulls, sperm motility was lower (P<0.05) than pre-insulation levels between Days 21 and 31, and lower than control levels on Day 24. The proportion of normal sperm after whole-scrotum insulation was lower than pre-insulation and control values from Day 11 to the end of the experiment in B. indicus bulls (P<0.05 from Days 14 to 21 and on Day 27), and from Days 14 to 25 in crossbred bulls (P<0.05 on Days 14 and 18). Insulation of the scrotal neck in crossbred bulls did not significantly affect semen quality. Loose sperm heads (Day 11), midpiece defects (Days 11 and 14), and acrosome defects (Days 27 and 31) increased (P<0.05) in insulated B. indicus bulls, while proximal cytoplasmic droplets (Days 14, 18 and 27 in B. indicus; Days 24 and 27 in crossbred bulls) and sperm vacuoles (Days 18 and 21 in B. indicus; Day 18 in crossbred bulls) increased (P<0.05) in whole-scrotum insulation groups in both experiments. There was considerable variation among bulls in the incidence of specific sperm defects. The timing of appearance of sperm defects after insulation provided insights into the pathogenesis of specific abnormalities. Neither whole-scrotum nor scrotal-neck insulation affected testicular echotexture in either experiment. In conclusion, whole-scrotum insulation resulted in decreased sperm production and semen quality in B. indicus and B. indicus x B. taurus bulls, but those changes were not associated with changes in testicular echotexture.

Effects of oestradiol and some of its esters on gonadotrophin release and ovarian follicular dynamics in CIDR-treated beef cattle

Three experiments were conducted to: (1) compare the effect of three oestradiol formulations on gonadotrophin release in ovariectomised cows; (2) compare the effects of either oestradiol-17beta (E-17beta) or oestradiol benzoate (EB), given at two doses, on the synchrony of ovarian follicular wave emergence in CIDR-treated beef cattle; and (3) determine the timing of ovulation of the dominant follicle of a synchronised follicular wave following administration of E-17beta or EB 24h after progesterone withdrawal. In Experiment 1, ovariectomised cows (n = 16) received a once-used CIDR on Day 0 (beginning of the experiment) and were allocated randomly to receive 5mg of E-17beta, EB or oestradiol valerate (EV) plus 100mg progesterone i.m. The CIDR inserts were removed on Day 7. There were effects of time, and a treatment-by-time interaction (P < 0.0001) for plasma concentrations of both oestradiol and FSH. Plasma oestradiol concentrations peaked 12h after treatment, with highest (P < 0.01) peak concentrations in cows given E-17beta; estradiol concentrations subsequently returned to baseline by 36 h in E-17beta-treated cows and by 96 h in EB- and EV-treated cows. Plasma FSH concentrations decreased by 12h after oestradiol treatment in all groups (P < 0.0001), reached a nadir at 24h, and increased by 60 h in all groups; plasma FSH reached higher (P < 0.02) concentrations in E-17beta-treated than in EB- or EV-treated cows. In Experiment 2, non-lactating Hereford cows (n = 29) received a new CIDR on Day 0 (beginning of the experiment), and were assigned randomly to receive 1 or 5mg of E-17beta or EB i.m. on Day 1. On Day 8, CIDR were removed and PGF was given. Transrectal ultrasonography was done once daily from 2 days before CIDR insertion to 2 days after CIDR removal, and then twice-daily to ovulation. Although there was no difference among groups in the interval from oestradiol treatment to follicular wave emergence (4.2 +/- 0.3 days; P = 0.5), 5mg of E-17beta resulted in the least variable interval to wave emergence (P < 0.005), compared with the other treatment groups which were not different (P = 0.1). For the interval from CIDR removal to ovulation, there were no differences among groups for either means (P = 0.5) or variances (P = 0.1). In Experiment 3, beef heifers (n = 32) received a once-used CIDR on Day 0 (beginning of the experiment) plus 100mg progesterone i.m. and were assigned randomly to receive 5mg E-17beta or 1mg EB i.m. On Day 7, CIDR were removed and all heifers received PGF. On Day 8 (24h after CIDR removal), each group was subdivided randomly to receive 1mg of either E-17beta or EB i.m. There was no effect of oestradiol formulation on interval from treatment to follicular wave emergence (4.1 +/- 0.2 days; P = 0.7) or on the median interval (76.6h; P = 0.7) or range (72-120 h; P = 0.08) from CIDR removal to ovulation. In summary, oestradiol treatments suppressed FSH in ovariectomised cows, with the duration of suppression dependent on the oestradiol formulation. Both E-17beta and EB effectively synchronised ovarian follicular wave emergence and ovulation in CIDR-treated cattle, and the interval from CIDR removal to ovulation did not differ in heifers given either E-17beta or EB 24h after CIDR removal.

Effect of age and genetic group on characteristics of the scrotum, testes and testicular vascular cones, and on sperm production and semen quality in AI bulls in Brazil

The objectives were to determine the effects of age and genetic group on characteristics of the scrotum, testes and testicular vascular cones (TVC), and on sperm production and semen quality in 107 Bos indicus, B. taurus and cross-bred bulls at three artificial insemination (AI) centers in Brazil. In addition, predictors of sperm production and semen quality were identified. In general, scrotal circumference (SC), scrotal shape score, scrotal neck perimeter, and testicular size (length, width and volume) increased (P < 0.05) with age. Although there were no significant differences among genetic groups for SC or testicular size, B. indicus bulls had the least pendulous scrotal shape, the shortest scrotal neck length, and the greatest scrotal neck perimeter (P < 0.05). Fat covering the TVC was thinner (P < 0.05) in bulls < or = 36 months of age and in B. taurus bulls than in older bulls and B. indicus bulls, respectively. Age and genetic group did not affect testicular ultrasonic echotexture. B. indicus bulls tended (P < 0.1) to have the lowest average scrotal surface temperature (SST). In general, ejaculate volume, total number of spermatozoa and number of viable spermatozoa increased (P < 0.05) with age. However, there was no significant effect of age on sperm concentration, motility, major and total defects. The proportion of spermatozoa with minor defects was highest (P < 0.05) in bulls 37-60 months of age. B. indicus bulls had higher (P < 0.01) sperm concentration, total number of spermatozoa and number of viable spermatozoa than B. taurus bulls, with intermediate values for cross-bred bulls. Increased sperm production was associated with increased testicular volume, SC, TVC fat cover, and SST top-to-bottom gradient. Decreased semen quality was associated with increased SC and bottom SST, and decreased scrotal shape, scrotal neck perimeter and vascular cone diameter. In summary, age and genetic group affected the characteristics of the scrotum, testes, and TVC, sperm production and semen quality. In addition, characteristics of the scrotum, testes and TVC were associated with sperm production and semen quality in bulls and could be assessed for breeding soundness evaluation.

Prevalence of non-aureus staphylococci species causing intramammary infections in Canadian dairy herds

Non-aureus staphylococci (NAS), the microorganisms most frequently isolated from bovine milk worldwide, are a heterogeneous group of numerous species. To establish their importance as a group, the distribution of individual species needs to be determined. In the present study, NAS intramammary infection (IMI) was defined as a milk sample containing ≥1,000 cfu/mL in pure or mixed culture that was obtained from a cohort of cows assembled by the Canadian Bovine Mastitis Research Network. Overall, 6,213 (6.3%) of 98,233 quarter-milk samples from 5,149 cows and 20,305 udder quarters were associated with an NAS IMI. Of the 6,213 phenotypically identified NAS isolates, 5,509 (89%) were stored by the Canadian Bovine Mastitis Research Network Mastitis Pathogen Collection and characterized using partial sequencing of the rpoB housekeeping gene, confirming 5,434 isolates as NAS. Prevalence of each NAS species IMI was estimated using Bayesian models, with presence of a specific NAS species as the outcome. Overall quarter-level NAS IMI prevalence was 26%. The most prevalent species causing IMI were Staphylococcus chromogenes (13%), Staphylococcus simulans (4%), Staphylococcus haemolyticus (3%), Staphylococcus xylosus (2%), and Staphylococcus epidermidis (1%). The prevalence of NAS IMI as a group was highest in first-parity heifers and was evenly distributed throughout cows in parities ≥2. The IMI prevalence of some species such as S. chromogenes, S. simulans, and S. epidermidis differed among parities. Overall prevalence of NAS IMI was 35% at calving, decreased over the next 10 d, and then gradually increased until the end of lactation. The prevalence of S. chromogenes, Staphylococcus gallinarum, Staphylococcus cohnii, and Staphylococcus capitis was highest at calving, whereas the prevalence of S. chromogenes, S. haemolyticus, S. xylosus, and S. cohnii increased during lactation. Although the overall prevalence of NAS IMI was similar across barn types, the prevalence of S. simulans, S. xylosus, S. cohnii, Staphylococcus saprophyticus, S. capitis, and Staphylococcus arlettae IMI was higher in tiestall barns; the prevalence of S. epidermidis IMI was lowest; and the prevalence of S. chromogenes and Staphylococcus sciuri IMI was highest in bedded-pack barns. Staphylococcus simulans, S. epidermidis, S. xylosus, and S. cohnii IMI were more prevalent in herds with intermediate to high bulk milk somatic cell count (BMSCC) and S. haemolyticus IMI was more prevalent in herds with high BMSCC, whereas other common NAS species IMI were equally prevalent in all 3 BMSCC categories. Distribution of NAS species IMI differed among the 4 regions of Canada. In conclusion, distribution differed considerably among NAS species IMI; therefore, accurate identification (species level) is essential for studying NAS epidemiology.

Effects of plasma progesterone concentrations on LH release and ovulation in beef cattle given GnRH

The effects of plasma progesterone concentrations on LH release and ovulation in beef cattle given 100 microg of GnRH im were determined in three experiments. In Experiment 1, heifers were given GnRH 3, 6 or 9 days after ovulation; 8/9, 5/9 and 2/9 ovulated (P<0.02). Mean plasma concentrations of progesterone were lowest (P<0.01) and of LH were highest (P<0.03) in heifers treated 3 days after ovulation. In Experiment 2, heifers received no treatment (Control) or one or two previously used CIDR inserts (Low-P4 and High-P4 groups, respectively) on Day 4 (estrus=Day 0). On Day 5, the Low-P4 group received prostaglandin F(2alpha) (PGF) twice, 12 h apart and on Day 6, all heifers received GnRH. Compared to heifers in the Control and Low-P4 groups, heifers in the High-P4 group had higher (P<0.01) plasma progesterone concentrations on Day 6 (3.0+/-0.3, 3.0+/-0.3 and 5.7+/-0.4 ng/ml, respectively; mean+/-S.E.M.) and a lower (P<0.01) incidence of GnRH-induced ovulation (10/10, 9/10 and 3/10). In Experiment 3, 4-6 days after ovulation, 20 beef heifers and 20 suckled beef cows were given a once-used CIDR, the two largest follicles were ablated, and the cattle were allocated to receive either PGF (repeated 12h later) or no additional treatment (Low-P4 and High-P4, respectively). All cattle received GnRH 6-8 days after follicular ablation. There was no difference between heifers and cows for ovulatory response (77.7 and 78.9%, P<0.9) or the GnRH-induced LH surge (P<0.3). However, the Low-P4 group had a higher (P<0.01) ovulatory response (94.7% versus 61.1%) and a greater LH surge of longer duration (P<0.001). In conclusion, although high plasma progesterone concentrations reduced both GnRH-induced increases in plasma LH concentrations and ovulatory responses in beef cattle, the hypothesis that heifers were more sensitive than cows to the suppressive effects of progesterone was not supported.

Effects of environmental factors, age and genotype on sperm production and semen quality in Bos indicus and Bos taurus AI bulls in Brazil

The effects of ambient temperature and humidity, month, age and genotype on sperm production and semen quality in AI bulls in Brazil were evaluated. Data from two consecutive years were analyzed separately. Seven Bos indicus and 11 Bos taurus bulls from one artificial insemination (AI) center were evaluated in Year 1 and 24 B. indicus and 16 B. taurus bulls from three AI centers were evaluated in Year 2. Ambient temperature and humidity did not significantly affect sperm production and semen quality, probably because there was little variation in these variables. Month accounted for less than 2% of the variation in sperm production and semen quality. Increased bull age was associated with decreased sperm motility (P<0.10) and increased minor sperm defects (P<0.001) in Year 1. B. indicus bulls had greater (P<0.005) sperm concentration than B. taurus bulls in both years (1.7 x 10(9)/ml versus 1.2 x 10(9)/ml in Year 1 and 1.6 x 10(9)/ml versus 1.2 x 10(9)/ml in Year 2, respectively). Ejaculate volume was not significantly affected by genotype in Year 1 (6.6 ml versus 6.9 ml in B. indicus and B. taurus bulls, respectively), but B. indicus bulls had greater (P<0.05) total (11.4x10(9) versus 8.2 x 10(9)) and viable (6.7 x 10(9) versus 4.9 x 10(9)) numbers of spermatozoa in the ejaculate than B. taurus bulls. In Year 2, B. taurus bulls had greater (P<0.05) ejaculate volume than B. indicus bulls (8.2ml versus 6.7 ml, respectively) and total and viable number of spermatozoa in the ejaculate were not significantly different between genotypes (10.3 x 10(9) versus 9.1 x 10(9) and 6.1 x 10(9) versus 5.4 x 10(9) in B. indicus and B. taurus bulls, respectively). Sperm motility was not significantly affected by genotype (mean, 59%). In Year 1, B. indicus bulls tended (P<0.10) to have more major sperm defects and had more (P<0.05) total sperm defects than B. taurus bulls (11.8% versus 8.7% and 13.6% versus 10.0%, respectively). In Year 2, B. indicus bulls tended (P<0.10) to have more total sperm defects than B. taurus bulls (16.2% versus 13.3%, respectively). In conclusion, neither ambient temperature and humidity nor month (season) significantly affected sperm production and semen quality. B. indicus bulls had significantly greater sperm concentration and B. taurus bulls had significantly fewer morphologically defective spermatozoa.

Sexual development in early- and late-maturing Bos indicus and Bos indicus × Bos taurus crossbred bulls in Brazil

Two experiments were conducted to evaluate sexual development in early- and late-maturing Nelore (Bos indicus) and Canchim (3/8 Bos indicus x 5/8 Bos taurus crossbred) bulls and to determine predictors of sexual precocity, and pubertal and maturity status. In Experiment 1, 12 Nelore bulls where examined from 300 to 900 days of age. Puberty was characterized by an ejaculate containing > or =50 million sperm with > or =10% motile sperm, and maturity by an ejaculate containing > or =70% morphologically normal sperm. In Experiment 2, 28 Canchim bulls where examined from 295 to 488 days of age and puberty was characterized by an ejaculate containing > or =30% motile sperm. In both experiments, bulls were classified as early- or late-maturing based on age at puberty. Early-maturing bulls were younger (P < 0.05) than late-maturing bulls at puberty (527 days versus 673 days in Experiment 1 and 360 days versus 461 days in Experiment 2) and at maturity (660 days versus 768 days in Experiment 1). In general, early-maturing bulls were heavier and had greater scrotal circumference (SC), testes, and testicular vascular cone diameter than late-maturing bulls during the experimental period. Scrotal circumference adjusted for 365 days of age was a good predictor of sexual precocity; minimum yearling SC of 19 and 24 cm for Nelore and Canchim bulls, respectively, had the best predictive values. Early-maturing bulls were lighter and had smaller SC at puberty than late-maturing bulls; therefore, sexual precocity was not related to the attainment of a threshold body weight or testicular size earlier, but to lower thresholds in early-maturing bulls. When predictors of pubertal status were evaluated, SC had the best sensitivity/specificity relationship in Nelore bulls, and high sensitivity and specificity in Canchim bulls. When predictors of sexual maturity were evaluated in Nelore bulls, age, weight, and SC had similar sensitivity, specificity, and predictive values. At puberty, approximately 60% of the sperm present in the ejaculate were morphologically defective. Changes in semen quality after puberty in Nelore bulls were characterized by increased motility and proportion of morphologically normal sperm, with a decrease in the proportion of major sperm defects. In conclusion, early-maturing bulls were more developed in the pre-pubertal period and attained puberty at earlier stages of body and testicular development than late-maturing bulls. Yearling SC could be used to select bulls for sexual precocity and SC was the best predictor of pubertal status. Age, weight, and SC were equally good predictors of sexual maturity in B. indicus bulls.