Estrus and ovulation in beef cows following use of progesterone-releasing devices, progesterone and estradiol valerate.

Two hundred nonsuckling beef cows were treated with either 1) a progesterone-releasing intravaginal device (PRID) for 12 days; 2) PRID plus an IM injection of 200 mg progesterone (PRID-P); 3) PRID plus 5-mg IM injection of estradiol valerate (PRID-EV); or 4) PRID-EV-P. Cows were started on treatment on one of the first eight days of the estrous cycle. The number of cows which had P levels above 1 ng/ml one day after PRID removal was 12 to 50% lower in PRID-EV and PRID-EV-P groups than in PRID and PRID-P groups (P < 0.05). The proportion of cows showing estrus by 96 hours after PRID removal was 38, 36, 77, and 88% (P < 0.05) for the PRID, PRID-P, PRID-EV and PRID-EV-P groups, respectively. Thirty-one percent fewer cows treated with PRID on days 5 through 8 of the estrous cycle showed estrus by four days after PRID removal than those treated on days 1 through 4. In addition, 18 to 22% more cows had P levels above 1 ng/ml among cows treated with PRID or PRID-P on days 5 through 8 than among cows treated similarly on days 1 through 4. It was concluded that effective synchronization of estrus is achieved only when estrogen is used in conjunction with PRID in cows treated for twelve days during the first eight days of an estrous cycle.

Reproductive performance of synchronized beef cows as affected by inhibition of suckling with nose tags or temporary calf removal.

A study was conducted to determine whether presence of the calf during suckling inhibition influences the response to estrus synchronization in beef cows. Angus or Hereford cows (n=89) were administered Syncro-Mate-B (SMB), which consisted of a 6-mg norgestomet ear implant (in situ 9 d) in conjunction with 5 mg of estradiol valerate and 3 mg (im) of norgestomet. Cows were allotted by breed, body condition, stage of the estrous cycle, parity and date of parturition to 1 of 3 treatments: 48-h calf removal; ad libitum suckling; or inhibition of suckling with a nose tag for 48 h. Calves were weighed at time of SMB implant removal, 48 h later and at weaning. Cows were mated via AI approximately 12 h after detection of estrus during a 30-d period after implant removal followed by a natural service period of 35 d. At 48 h after implant removal, calf removal and nose tag calves had lost an average of 3.6 and 0.9 kg, respectively, while the suckled calves gained 1.8 kg (P < 0.01). Mean calf weight at weaning did not differ among treatments. Synchronized estrous response (within 5 d of implant removal) was not different among treatments. Pregnancy rate for cows exhibiting a synchronized estrus (5 d AI) for calf removal, nose tag and suckled cows was 76, 48 and 48%, respectively (P>0.10). Treatment did not affect the 30-d AI or overall 65-d pregnancy rate. In this study, there were no differences observed in the percentage of synchronized or pregnant cows following suckling inhibition by either a nose tag or calf removal. Transient reductions of calf body weight during the 48-h calf removal period did occur in both the nose tag and calf removal groups.

Correlation of in vivo testicle and seminal vesicle size with post mortem dimensions in bulls.

This study was conducted to quantify the relationships between in vivo measurements of testicular and seminal vesicle size and post mortem size of these organs in 30 Santa Gertrudis bulls. The in vivo measurements of testicles were obtained by transrectal ultrasonography and palpation per rectum, while scrotal circumference was measured by scrotal tape. Linear post mortem dimensions were obtained by direct measurements of the excised organs. Volume was assessed by water displacement while the testicles were weighed. Seminal vesicle length, determined by palpation, had the highest correlation with post mortem measurements (r = 0.70; P = 0.0001). Accurate estimation of the thickness of the vesicles (1.47 vs 1.55 cm for in vivo and post mortem, respectively) was performed by ultrasonograph. Of all seminal vesicle linear measurements, width had the highest correlations with volume measured by water displacement (r = 0.67; P = 0.0001 and r = 0.38; P = 0.04 for post mortem and in vivo, respectively). Testicular diameter was accurately measured by ultrasonography (5.54 vs 4.58 cm in vivo and post mortem, respectively) and was highly correlated (range r = 0.84 to 0.89; P = 0.0001) with post mortem measurements of testicular volume, weight and circumference. The correlation between scrotal circumference and diameter of the testicle was 0.75 (P = 0.0001). The correlations of testicular diameter measured by ultrasound with the post mortem measurements of testicular weight and circumference were similar to the correlations between scrotal circumference and those 2 post mortem measurements. We conclude that palpation of vesicle length is highly correlated with volume of the seminal vesicle in situ. Individual linear measurements do not seem to be an accurate predictor of the relativ size of the seminal vesicle. Furthermore, ultrasonography does not seem to be a more accurate measure of testicular size than scrotal circumference for evaluation of breeding soundness.

Relationships between seminal vesicle size and copulatory activity in bulls.

Two experiments were designed to investigate the hypothesis that dimensions of the seminal vesicle are positively correlated with copulatory behavior in bulls. In Experiment 1, thirty Santa Gertrudis bulls (16.5 mo old) were used to study the relationship between copulatory activity and seminal vesicle length and width (palpation per rectum), seminal vesicle thickness (ultrasonography), and volume. The bulls showed a low level of copulatory activity (6.0+/-1.5, 0.8+/-0.3 and 0.3+/-0.1 for mean number of mounts, intromissions and ejaculations, respectively) in 2 tests. The mean number of mounts but not the mean number of intromissions or ejaculations differed (P<0.01) among bulls. No significant correlations were found between seminal vesicle size and any of the variables of sexual behavior. In Experiment 2, 16 beef bulls (18 mo old) were used to study the relationship between copulatory activity and seminal vesicle length (palpation) or dorso-ventral thickness (ultrasonography). Differences were detected (P<0.01) among bulls in mean number of mounts, intromissions and ejaculations achieved in 2 serving capacity tests. No significant correlations were found between copulatory activity and seminal vesicle length or thickness. These data do not support the hypothesis of a positive relationship between seminal vesicle length or thickness with copulatory activity, even for bulls with marked diffences in intensity of sexual behavior.

Effects of ionophores on cow herd production: a review.

Feeding ionophores to beef cows or replacement heifers fed harvested forages increases weight gain and improves feed efficiency. These responses are influenced by diet quality and body condition of the animal. These compounds may reduce postpartum interval to estrus, but this effect appears to be diminished if nutritional status is poor. Although ionophores do not alter fertility, they decrease age at puberty in the female. These changes in reproductive performance appear to be related to a hormonal response to an increased propionate:acetate ratio in the rumen characteristic of ionophore feeding. Responses to ionophores in milk yield and weight gain improvements in calves of ionophore-fed cows are variable. Length of gestation, incidence of dystocia, calf birth weights and percent calf crop are not altered by ionophore feeding. The potential to improve cow herd production through the use of ionophores depends primarily on forage quality and availability.

Pregnancy rate in beef heifers after synchronization to either random or programmed estrous cycles.

We hypothesized that heifers in diestrus at the beginning of a Syncro-Mate-B (SMB) regimen would have higher pregnancy rates to AI than heifers not in diestrus and that administration of a PGF2alpha analogue 11 d before a SMB regimen would increase pregnancy rates to AI. In both replicate years of Exp. 1, heifers (n = 150) were classified by stage of the estrous cycle at the beginning of a SMB regimen (d 0). Following implant removal (d 9), heifers were artificially inseminated 12 h after the onset of estrus (95.5% in estrus by 72 h). Blood samples were collected for progesterone (P4) analysis on d 0, 9, and 20. Pregnancy rates did not differ between yr 1 and 2. Pregnancy rate for heifers classified in diestrus (53.6%; n = 69) was higher (P = 0.06) than for heifers in metestrus (43.7%; n = 48). Pregnancy rate for proestrus (44.4%; n = 18) heifers was not different from that for heifers in the metestrus or diestrus groups. Mean plasma P4 concentration was affected by both treatment and day. Pregnancy rate was higher (P < 0.01) for heifers with P4 > 1 ng/mL plasma (51.6%; n = 120) than for heifers with P4 < or = 1 ng/mL plasma (23.3%; n = 30) on d 0. In Exp. 2, beef heifers (Santa Cruz; n = 195) were allotted to two treatments. Heifers (n = 98) in the control group were administered a conventional SMB treatment. Heifers (n = 97) in the PGF group were injected with PGF2alpha 11 d (d -11) before a SMB regimen. Progesterone concentration was determined from blood samples collected on d -11, -2, 0, and 9. All heifers were artificially inseminated 48 to 50 h after implant removal. At the beginning of the SMB regimen (d 0), a greater (P < 0.05) percentage of PGF (74.2%) than of control heifers (59.2%) were in diestrus (P4 > 1 ng/mL). Mean P4 concentration was not affected by treatment or day x treatment but differed (P < 0.05) among days. Pregnancy rate of cycling heifers was similar for PGF (36%) and control heifers (35.9%). Pregnancy rate was higher (P < 0.01) for heifers with P4 > 1 ng/mL plasma (37.6%) than for heifers with P4 < or = 1 ng/mL plasma (18.5%) on d 0. These results support the hypothesis that fertility is enhanced when a progestin synchrony regimen is initiated during diestrus, but methods to program estrous cycles to increase fertility warrant investigation.

Performance of Bos indicus-influenced bulls in serving capacity tests and multiple-sire breeding groups.

Three experiments were conducted with Santa Gertrudis (SG) or F1 (Gelbvieh x SG or Red Angus x SG) bulls to assess factors that influence copulatory activity and fertility of Bos indicus-influenced genotypes. In Exp. 1, 3-yr-old SG bulls (n = 20) with sexual experience and 20-mo-old virgin SG bulls (n = 34) were allotted in a split-plot design (age, bull within age group, test day, and heifer treatment). Number of mounts (Mt), intromissions (I), and ejaculations (E) were measured 14 d apart during two 30-min serving capacity (SC) tests. Estrus was either induced via progesterone+estradiol cypionate (PE) injections or synchronized with Syncro-Mate B (SMB). There were more (P less than .05) I and E on Test d 2 than on Test d 1. Heifers treated with SMB received more (P less than .001) Mt, I, and E than did heifers treated with PE. Sixteen 20-mo-old bulls from Exp. 1 were allotted to breeding pastures at a bull:heifer ratio of 4:119 +/- 3 for 50 d in Exp. 2. Breeding pasture treatments either included or excluded low-SC bulls. Neither pregnancy rate nor least squares mean day of conception differed between treatments. Experiment 3 evaluated copulatory activity with a 2 x 2 factorial arrangement (breed and test day) in 14- to 16-mo-old SG (n = 45) and F1 (n = 16) bulls. The F1 bulls had more Mt, I, and E than did the SG bulls (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Artificial insemination outcomes in beef females using bovine sperm with a detectable fertility-associated antigen.

In this study, semen samples from 25 bulls that had passed a breeding soundness evaluation were analyzed for the presence or absence of a 31-kDa protein, known as fertility-associated antigen (FAA), on spermatozoal membranes. Eighteen bulls had FAA on sperm (FAA-positive) and seven were devoid of FAA on sperm (FAA-negative). A single ejaculate from each bull was extended and frozen with 25 to 30 x 10(6) sperm in .5-mL straws. Crossbred replacement heifers (n = 865) were estrus-synchronized and artificially inseminated either at timed AI or 12 h after they were detected in estrus. Mature cows (n = 285) were inseminated 12 h after they were detected in estrus during a 45-d AI period. Pregnancy rates (pooled) to first AI service for females (n = 764) inseminated with FAA-positive sperm were 65.6% and were 49.7% for females (n = 386) inseminated with FAA-negative sperm (P < .005). Among the estrus-synchronized replacement heifers, pregnancy rates to synchronized AI service for heifers (n = 550) inseminated with FAA-positive sperm were 62% and were 45.7% for heifers (n = 315) inseminated with FAA-negative sperm (P < .005). These data indicate that pregnancy rates to first AI service at spontaneous and synchronized estrus are higher when using semen from bulls with detectable FAA on spermatozoal membranes compared to semen from bulls devoid of FAA on membranes. Fertility-associated antigen is an important determinant for fertility potential of sperm from bulls to be used in AI breeding programs.

Sire marbling score expected progeny difference and weaning weight maternal expected progeny difference associations with age at first calving and calving interval in Angus beef cattle.

Field records from the American Angus Association were used to study the associations of sire marbling score EPD and sire weaning weight maternal (milk) EPD with age at first calving (AFC) and calving interval (CI). Cows were selected based on the accuracy of their sire's milk (> or =.7) or marbling (> or =.6) EPD. The data were screened using biological constraints, and regression models were used to identify records that were greater than 5 SD from the mean. The AFC was modeled for both milk and marbling data sets to account for effects of year, sire EPD, and their interaction. The CI was subdivided into first, second, and mature calving interval traits and modeled to account for state, year, calf sex, calf birth weight (BW), calf weaning weight (WW), sire EPD, and interactions of EPD with year and state. Derivative-free REML was used to estimate heritability and genetic correlations for AFC and CI. Sire milk EPD and marbling EPD were predictors of AFC (P < .001); however, pooled estimates were unreliable because of state x EPD interactions (P < .001). Increases in sire milk EPD resulted in reductions in AFC; however, there was no consistent pattern to effects of marbling EPD increases. Models accounted for < 8% of variation in AFC. Sire milk EPD was not a predictor of first, second, or mature CI (P > .1). Sire marbling score EPD was not a predictor of second, or mature CI (P > .1); however, it was associated (P = .059) with first CI, although regression estimates varied across states and prevented pooling. The BW, sex, and WW were predictors of CI (P < .001). Increases in BW resulted in longer mature CI, and mature CI decreased as WW increased. The AFC was heritable (.22), and CI traits had heritabilities ranging from .01 to .03. The AFC was genetically correlated with first CI (-.6) and mature CI (-.93). Genetic correlations between CI traits were uninterpretable because of low additive genetic variances. In conclusion, sire marbling score and milk EPD do not seem to be reliable predictors of AFC or CI. The BW and WW have significant but small effects on AFC and CI. Selection for AFC is possible, but earlier calving heifers may have longer calving intervals.

Fertility-associated antigen on bull sperm indicates fertility potential.

A 30-kDa heparin-binding protein named fertility-associated antigen (FAA) was identified in sperm membranes of beef bulls with greater fertility potential. In a survey of 2,191 beef bulls, 88% had FAA present in sperm membranes (FAA-positive), and 12% were FAA-negative. In the first study, 54 Santa Gertrudis and 51 Santa Cruz bulls were grouped (1 to 14 bulls per group) according to FAA profiles and were bred to 2,403 cows at ratios of 1 bull: 25 cows. Fertility for 14 groups of FAA-positive bulls averaged 88%, whereas three groups of FAA-negative bulls impregnated 79% of the cows. Thus, FAA-positive bulls were nine percentage points more (P < .01) fertile than FAA-negative bulls. In the second study, 2-yr-old Santa Cruz bulls (n = 26) were grouped according to FAA profiles and serving capacity. The fertility of the group of 12 high-serving-capacity, FAA-positive bulls was 87% of 270 cows. The group of six FAA-negative bulls with high serving capacity impregnated 78% of 143 cows. Among the groups of bulls with high serving capacity, FAA-positive bulls were nine percentage points more (P < .05) fertile than FAA-negative bulls. The group of eight FAA-positive bulls with low serving capacity impregnated the least (P < .01) percentage (69%) of 238 cows. Serving capacity of bulls should be considered when optimizing fertility potential. Among bulls with acceptable physical characteristics and serving capacity, determination of FAA profiles in sperm can be used as a tool to identify subfertile bulls.