Estrus synchronization of cattle in Kansas

In 22 field trials involving 1,692 cattle, we evaluated Lutalyse as an estrus-synchronization agent for both natural mating and artificial insemination. Only 52.7% of the females in all 22 trials were cycling at the start of the breeding season. Both body condition and days postpartum at the start of the breeding season influenced the response to Lutalyse. First-service pregnancy rate in the 2 or 3 days of synchronization was 38.4% for all 453 females bred artificially in 12 trials in northwestern Kansas. The rate was 59%, however, if only females observed to be in heat were counted; but only 24.5% if only those in which no heat was observed were counted

Luteinizing hormone release and plasma metabolites in mature, ovariectomized beef cows fed various lipid diets

Feeding rumen-escape lipid or soybean oil in a range supplement to beef cow resulted in elevated blood cholesterol and enhanced luteinizing hormone (LH) release compared to a control (milo and soybean meal) supplement. Cholesterol was elevated (P<.01) within 14 d of lipid feeding. The amplitude of each LH pulse and maximal pulse height were greater (P<.05) when cows were fed high-lipid diets. The positive influence of high-lipid diets on reproductive function may be explained in part by enhanced LH release

Effect of various levels of Ralgro on reproductive performance of yearling heifers

Implanting heifers at weaning time with 12, 24, or 36 mg of Ralgro did not affect reproductive performance of the heifers when bred as yearlings

Effect of heifer source on reproductive performance, culling, marketing and profitability for a commercial heifer development program

A commercial heifer development operation purchased 483 weanling Angus × Hereford heifers from 11 sources. Heifers were fed a common silage-based diet through an initial developmental period and retained or culled based on average daily gain, pelvic area, and disposition . The percentage of heifers culled from each source ranged from 18.1% to 94.7% and were either sold directly through a local sale barn or sent to a feedlot with retained ownership . Estrus was synchronized, and heifers were artificially inseminated (AI) for 30 days followed by 15 days of natural mating. First service conception rates for each source ranged from 0% to 92.3%, whereas overall pregnancy rates for the 45-day breeding season ranged from 81.3% to 100%. When expressed as a percentage of the original heifers purchased from each source, overall pregnancy rates ranged from 5.3% to 80%. Heifers that lost their fetuses were sold for a net loss of $213 per head. Heifers sold as first service AI bred, second service AI bred, and naturally mated netted$160, $129, and$89 per head, respectively. With accurate records, stringent culling practices, and evaluation of cost and performance, producers can optimize profit potential of replacement heifers. Early culling and pregnancy diagnosis also will decrease costs while increasing opportunities to minimize the financial risks

A three-year economic evaluation of a commercial heifer development program

In 1994, 1995, and 1996, a commercial heifer development operation purchased a total of 1542 potential replacement heifers. Heifers were purchased in the fall proceeding the spring breeding season and fed a silage-based diet during the developmental period. Before the breeding season began, heifers that failed to meet minimum requirements for pelvic area, average daily gain, body weight, disposition, or structural soundness were culled. During the first year, 42% of 483 heifers were culled, 17% of 468 heifers were culled in the second year, and 14% of 591 heifers in the third year. Estrus was synchronized and heifers were inseminated artificially (AI) for 30 days followed by 30 days of natural mating by cleanup bulls. First-service AI conception rates averaged 68% and overall pregnancy rates (AI + natural mating) averaged 95.1% over the 3-year period. Heifers culled prior to the breeding season realized a net profit of $9 per head, whereas heifers diagnosed nonpregnant after the breeding season lost$86, and heifers that aborted lost $133. Profits for pregnant heifers sold were$163 for first-service AI, $138 for second-service AI, and$83 for bull bred

Influence of source and amount of dietary protein on the performance and reproductive function of first-calf heifers

Increasing the amount of dietary protein above the NRC requirement increased weight gain of nursing first-calf heifers. Feeding a protein source with higher ruminal escape potential and increasing protein in the diet both improved calf gains. No significant changes in reproductive function or milk production were observed from either source or amount of dietary protein

Effect of monensin on weight gain, growth traits, and semen characteristics in yearling beef bulls

Feeding the ionophore monensin to yearling beef bulls improved (P\u3c.05) weight gain by 4.2%. Final hip height was similar between treatments, but bulls fed monensin had almost 1 cm greater (P\u3c.01) scrotal circumference and more than 10 cm 2 larger (P\u3c.01) pelvic area. Semen characteristics generally were unaffected by treatment. However, bulls fed monensin had less (P\u3c.01) semen motility than controls. Approximately 30 sperm morphology traits were evaluated; values were similar between treatments except for those traits listed. Collection date tended to influence (P\u3c.15) volume, concentration, motility, and postfreeze characteristics

A novel estrus-synchronization program for anestrous and cycling, suckled, beef cows

We used four herds at three Kansas ranches to evaluate the potential of two new estrus synchronization strategies to increase estrus expression and fertility of 911 crossbred suckled beef cows. The treatments included: 1) 100 μg of GnRH and a 6-mg norgestomet ear implant on day -7 and 25 mg of PG F2" and implant removal on day 0 (GnRH+NORG+PG F2"); 2) 100 μg of GnRH on day - 7 and 25 mg of PGF 2" on day 0 (GnRH+PG F2"); and 3 ) (control) 25- mg injections of PG F2" on days -14 and 0; (2×PGF2" control) . The GnRH+NORG+ PGF 2" and GnRH+PGF treatments increased (P<.01) 2" the overall percentages of cows detected in estrus by 49% and 27% and pregnancy rates by 46% and 37%, respectively, over the control group, without altering conception rate. Both treatments increase d the estrus, conception, and pregnancy rates of noncycling cows, compared to controls

Ralgro-implanted bulls: Performance, carcass characteristics, longissimus palatability and carcass electrical stimulation

Twenty of 40 Angus bulls were implanted (I) five times with 36 mg of Ralgro| at average intervals of 106 d, beginning near birth. All bulls and their dams were on bluestem pasture initially and, at an average age of 320 d bulls were fed a concentrate diet until they were slaughtered, weighing either 454 or 499 kg. One side of each carcass was electrically stimulated. Average daily gain and feed efficiency of I bulls improved 6.5 to 10.4% and 7.9 to 8.1%, respectively, depending upon the end point comparison with nonimplanted (NI) bulls. Implanted bulls attained their slaughter weights 42 d sooner than did NI bulls. Implantation decreased (P<.05) penis weight and length, testicle weight, volume and density, but did not affect (P>.05) seminal vesicle and pituitary weights. Carcasses from I bulls had more (P<.05) skeletal ossification and were fatter than carcasses from NI bulls. Marbling scores, quality grades and longissimus cooking losses and juiciness scores were not affected (P>.05) by implantation. Taste panel flavor intensity and detectable connective tissue scores were higher (P<.05) for steaks from I bulls than from NI bulls. Longissimus steak tenderness evaluations were higher (P<.05) for both I slaughter groups than for the NI light-weight group and were higher (P<.05) for the I lightweight group than for the NI heavy-weight group. Longissimus tenderness tended (P = .11) to be higher for steaks from the I heavy-weight group than those from the NI heavy-weight group. Electrical stimulation produced (P<.05) a softer, coarser textured lean, but it did not affect lean color, marbling or quality grade. Steaks from electrically stimulated sides tended to have higher (P = .09) myofibrillar tenderness scores and lower (P = .06) flavor scores than steaks from nonstimulated sides

Effects of dietary energy on reproductive function and production in suckled beef cows

Twenty-eight Hereford x Angus cows were utilized to determine the effects of dietary energy level before and after calving on reproductive function and production in suckled beef cows. Low levels of dietary energy before calving resulted in losses of body composition prior to calving, reduced calf birth weight, lengthened intervals from calving to ovulation, and decreased milk production and calf weight at 70 d of age (P\u3c.05). Low levels of dietary energy after calving decreased measures of body composition after calving, reduced the percentage of cows that ovulated following calving, and decreased cow milk production and calf weight at 70 d of age (P\u3c .05). We conclude that dietary energy before and after calving impacts the reproductive function and production of suckled beef cows