Comparison of ovulation, fertilization and embryonic survival in low-fertility beef cows compared to fertile females.

The objective was to determine physiological causes of low fertility in beef cows. Fertility was compared between low-fertility cows (34 British cows and 64 Brahman crossbred cows; cows that did not get pregnant when mated to fertile bulls in one or two previous breeding seasons); fertile cows (16 Brahman crossbreds; cows having a calf in several of the preceding breeding seasons), and virgin heifers (45 Brahman crossbreds, 2 yr of age). Females were mated to fertile bulls and killed 3 or 34 d after breeding to obtain reproductive tracts. There were no significant differences among groups in rates of ovulation or fertilization. Overall, 14% of females failed to ovulate and 24% that ovulated failed to undergo fertilization. The proportion of cows that were not detected in estrus before Day 34 of pregnancy was lower (P<0.01) for low-fertility British cows (5 of 16 cows, 31%) than for other groups, including low-fertility Brahman crossbred cows (23/32, 72%), fertile cows (8/9, 89%), and heifers (21/24, 88%). All cows that did not return to estrus by Day 34 had an identifiable conceptus. The proportion of conceptuses recovered at Day 34 that were classified as normal (weight and length) was lower (P<0.05) for cows with low fertility (British: 2/5, 40%; Brahman crossbred: 9/23, 39%) than for fertile cows (8/8, 100%) or heifers (18/21; 86%). Similarly, the proportion of cows in which a normal embryo was recovered (cows with normal embryos/number of cows mated) was lower (P<0.001) for low-fertility British cows (2/16, 13%) and low-fertility Brahman crossbred cows (9/32, 28%) than for fertile cows (8/9, 89%) and heifers (18/24, 75%). In conclusion, cows that were infertile in previous breeding seasons did not experience reduced ovulation or fertilization rates, but had greater embryonic mortality. These data highlighted the importance of ovulation and fertilization failure and embryonic mortality as important determinants of pregnancy success. Moreover, increased embryonic loss after Day 34 contributed to infertility in low-fertility cows.

Criteria to evaluate bone mineralization in cattle: II. Noninvasive techniques.

An experiment was conducted to evaluate the capabilities of dual photon absorptiometry (PA), radiographic photometry (RP), and ultrasound (U) to estimate bone mineral content (BMC) and bone strength of a group of bovine third metacarpals (McIII). Metacarpals were chosen for evaluating BMC and bone strength because of their accessibility and susceptibility to biomechanical stress. The right and left McIII of 14 Angus heifers (24 to 32 mo of age) were collected at slaughter and all soft tissues (including periosteum) were removed. The BMC was estimated at both the midpoint and 3 cm proximal to the midpoint on the McIII diaphysis. Metacarpals then were tested by three-point bending to determine breaking load (BL) and breaking strength (BS). Bones were reassembled and two 2-cm sections were removed, one at the midpoint and one 1 cm proximal to the midpoint section. Sections then were ashed and ash content was expressed as grams per 2-cm slice and defined as BMC. Correlation coefficients (r) between BMC vs PA, RP, and U were .908 (P less than .0001), .967 (P less than .0001), and .565 (P less than .0001), respectively; r values between BS vs PA, RP, and U were .406 (P less than .05), .429 (P less than .05), and .499 (P less than .01), respectively, and r values between BL vs PA, RP, and U were .870 (P less than .0001), .865 (P less than .0001), and .588 (P less than .001), respectively. These data indicate that noninvasive techniques are useful in predicting BMC and BL in the bovine.

Criteria to evaluate bone mineralization in cattle: I. Effect of dietary phosphorus on chemical, physical, and mechanical properties.

Fourteen Angus heifers (210 +/- 6 kg initial BW) were allotted randomly to either a low P (LP: .12% P, DM basis) or an adequate P (AP: .20% P, DM basis) diet fed for 14 to 16 mo under drylot conditions on concrete floors to determine the influence of dietary P on chemical, physical, and mechanical properties of bone. Three weeks postpartum, after 14 to 16 mo on their diets, heifers were slaughtered and the right and left third metacarpals (McIII) were excised; soft tissue was removed and metacarpals were frozen in .9% saline. Metacarpals were subjected to a three-point flexure test using an Instron Testing Machine with a crossload speed of 50 mm/min to determine mechanical properties. Broken McIII were reassembled and a 2-cm section was removed at point of loading for determination of chemical and physical properties. Breaking load (BL) was greater (P less than .05) for McIII from the AP than for those from LP heifers (1,348 vs 1,179 kg). Breaking strength (BS) was greater (P less than .05) for AP than for LP heifers (202.5 vs 189.2 MPa). Animals receiving AP diets had greater (P less than .01) bone mineral content (12.6 vs 11.2 g/2-cm slice) and percentage of bone ash (68.0 vs 67.2%) than did LP animals. No differences (P greater than .10) were observed between treatment groups in Ca, P, or Mg percentage in bone ash. Circular, elliptical, radiographic, and planimeter area indices all were greater (P less than .05) in AP than in LP animals (1,048, 729, 1,069, and 570 vs 932, 660, 957, and 523 mm2, respectively). These data indicate that mechanical properties of bovine third metacarpals are sensitive to dietary P and reflect P status in the bovine. Mineral content of bone was highly correlated with its mechanical and physical properties.

Bull influences on conception percentage and calving date in Angus Hereford, Brahman and Senepol single-sire herds.

Bull breeding soundness parameters, semen characteristics and sexual behavior were evaluated for effects on reproductive performance in single-sire beef herds. A total of 155 cow herds (Angus, 50 herds; Hereford, 40 herds; Brahman, 46 herds; and Senepol, 19 herds) bred to bulls of the same breed were observed for 8 yr. All bulls produced adequate quality semen and had scrotal circumference (SC)>or=30 cm. Reproductive performance was evaluated by the conception rate (CON), conception rate during the first 21 d of the breeding season (21dCON), mean calving date (MCD), and mean calving date of the first half of the herd to calve (HHCD). Correlations were determined between breeding soundness parameters and reproductive performance for all bulls combined, by breed, and by age. The Cp statistic was used to select models for the effects of parameters on CON, 21dCON, MCD and HHCD. Breeding season length and breed had significant effects. The percentages of normal cells, proximal droplets, detached heads and the semen score (motility plus percentage of normal cells) had a significant effect on CON when all bulls were considered. After the effect of season was deleted, the most significant parameter affecting CON in the Brahman was the percentage of detached sperm heads. In the Angus, motility was significantly correlated with all reproductive performance indices. In the Hereford, breeding soundness examination score (BSE) was positively correlated with 21dCON.

Dietary phosphorus concentrations related to breaking load and chemical bone properties in heifers.

Effects of dietary P on breaking load and chemical properties of bone were evaluated in growing beef heifers. Initially, 14 weaned Angus heifers received ad libitum a low P diet (.10% P dry basis) for 270 d. Heifers were subsequently randomly allotted into two groups (7 heifers/group) and received ad libitum either .12 or .20% P (dry basis). The experimental endpoint was 245 d of the treatment phase for nonpregnant and 3 wk postpartum for pregnant heifers. Results indicate that chemical and physical properties of bovine bones are sensitive to dietary P. Mineralization of rib bones was less at .12% P (dry basis). Rib bone density (g/cm3) and mineral content expressed on a per unit volume basis (mg/cm3) were the most sensitive parameters measured. Breaking load results of 12th ribs also indicated a greater amount of mineral present in heifers receiving .20% P (153.8 vs. 114.3 kg). Vertebral bone density and mineral concentrations on a per unit volume basis were also sensitive to dietary P and clearly ranked the two dietary P amounts, whereas percentage of bone ash or mineral concentration expressed on an ash basis did not.

Fertility of Bos indicus and Bos indicus x Bos taurus crossbreed cattle after estrus synchronization.

Ninety-five cows (79 Boran and 16 Boran-Brahman crossbreeds) and 107 heifers (55 Boran and 52 Boran x Friesian F1 crossbreeds) were used to determine estrus response, estrus response interval and pregnancy rate following synchronization with prostaglandin (PGF(2)alpha), a progesterone-releasing intravaginal device (PRID) and Synchro-mate B (SMB). The proportion of cattle responding to synchronization treatment was 62.5, 43.5 and 57.7% for cows and 85.7, 68.0 and 81.5% for heifers using PGF(2)alpha, PRID and SMB, respectively. The overall mean response was 59 and 81.8% for cows and heifers, respectively. The estrus response of the control animals over a 45-d breeding period was 72.7 and 90% for cows and heifers, respectively. The estrus response interval for cows was 31.8, 22.1 and 18.0 h and it was 51.1, 38.0 and 21.6 h for heifers with PGF(2)alpha, PRID and SMB treatment, respectively. Mean pregnancy rate for cows was 50.0, 34.8, 46.2 and 68.8% and for heifers it was 60.7, 40.0, 55.6 and 77.8% in the PGF(2)alpha, PRID, SMB and control groups, respectively. Based on these findings, it was concluded that both PGF(2)alpha and SMB produce a satisfactory estrus response and pregnancy rate in the cattle studied.

Reproduction in Brahman cows calving for the first time at two or three years of age.

A comparison of the subsequent reproduction of heifers that calved for the first time at 2 vs. 3 yr of age was conducted on a purebred Brahman herd from 1971 to 1978 in central Florida. Pregnancy rate, birth rate and weaning rate were obtained on 1,612 animals. Sire of the cow had a significant effect on all three reproduction traits, indicating possible genetic differences in these important traits. Age at first calving (either 2 or 3 yr) had no significant effect on overall reproduction rates; however, subsequent pregnancy and weaning rate was 4% higher in females calving first at 2 yr of age. Thirty-eight percent of the females that became pregnant at 15 to 17 mo of age, weighed 650 to 700 lbs. These heifers had been born early in the previous calving season. It is suggested that Brahmans can be selected to calve at 2 yr of age if good nutrition and management are provided.

Artificial insemination of subtropical commercial beef cattle following synchronization with cloprostenol (ICI 80996): I. Fertility.

Two trials were conducted over a two-year period with 519 cycling Bos taurus x Bos indicus heifers and cows. The objectives of these trials were: 1) To compare fertility of artificial insemination at the cloprostenol-induced estrus and the naturally occurring estrus, 2) To evaluate the fertility of artificial insemination at a predetermined time (Timed AI) following an estrous synchronization regime with cloprostenol (CLP) and 3) To define the optimum interval from a second CLP treatment for Timed AI. In Trial I, 128 animals were assigned to four treatments: 1) Controls, which were inseminated at the natural occurring estrus; 2) timed AI at 72 hr and again at 96 hr post-second CLP; 3) Timed AI at 72 hr post-second CLP and 4) AI at the CLP-induced estrus. Trial II included 391 heifers distributed among six treatments; 1) Timed AI between 70 and 90 hr post-second CLP; 2) Sham AI between 70 and 90 hr post-second CLP, 3) Chute Stress between 70 and 90 hr post-second CLP; 4) AI at the CLP-induced estrus; 5) Control-AI at the naturally occurring estrus and 6) Non-treated and exposed to fertile bulls. The fertility of the animals artificially inseminated at the CLP-induced estrus was similar to that of insemination at the naturally occurring estrus in Trial I and Trial II (30 vs 46%; 37 vs 38%, respectively). The first service pregnancy rates of the animals bred at a predetermined time were similar to those bred at the CLP-induced estrus in Trial I, but lower in Trial II (P<.01).

Artificial insemination of subtropical commercial beef cattle following synchronization with cloprostenol (ICI 80996): II. Estrous response.

Data collected from two controlled breeding field trials involving 561 Bos indicusxBos taurus cows and heifers were analyzed for estrous and fertility response following a cloprostenol ICI-80, 996 (CLP) synchronization regime. Fertility data were discussed in a companion paper (1). In Trial 1, 128 animals were assigned to four treatments: 1) controls which were inseminated at the naturally occurring estrus; 2) Animals artificially inseminated at approximately 72 hr and 96 hr following a second CLP; 3) Animals artificially inseminated at approximately 72 hr following a second CLP; and 4) Animals artificially inseminated approximately 12 hr after detection of estrus post-second CLP. Trial II included 391 heifers distributed among six treatments: 1) Artificially inseminated between 70 and 90 hr post-second CLP; 2) Sham inseminated between 70 and 90 hr post-second CLP; 3) Processed with no manipulation of the genital tract between 70 and 90 hr post-second CLP; 4) Artificially inseminated approximately 12 hr after the detection of estrus following a second CLP; 5) Artificially inseminated at the naturally occurring estrus and 6) Non-treated heifers exposed to fertile bulls. Cloprostenol ICI-80996 was effective (P<.01) in synchronizing estrus in comparisons of treated vs non-treated controls in Trials I and II (82 vs 29%; 57 vs 19%, respectively). However, a significant reduction in the expression of estrus was observed following Timed AI when compared to heifers bred 12 hr after detection of CLP-induced estrus in Trial II (37 vs 54%, P<.05). The authors conclude that a single timed insemination of Brahman crossbred heifers suppresses the behavioral expression of estrus. Other evidence (1) indicates that the fertility during this period is similarly reduced.