Insemination timing affects pregnancy rates in beef cows treated with CO-Synch protocol including an intravaginal progesterone insert.

Our objective was to determine the optimal time to artificially inseminate lactating beef cows (Bos taurus typicus) after using the standard CO-Synch protocol that also included a progesterone-releasing, intravaginal controlled internal drug release (CIDR) insert. Cows (N=605) at three locations were inseminated at four different times after CIDR insert removal and the prostaglandin F(2alpha) administration of the CO-Synch+CIDR protocol: 48, 56, 64, or 72h. Blood samples were collected 9 to 10 d before and on the day of CIDR insertion. Based on elevated (>1 ng/mL) serum progesterone concentrations, 60% of 605 cows had previously ovulated (were cycling) at the initiation of the study, with a range of 39.6% to 67.9% among locations (P<0.05). Age of cow, body condition score, and days postpartum affected (P< or =0.05) cycling status before ovulation was synchronized. Averaged across treatments, pregnancy rate to artificial insemination (AI) at Day 32 was affected (P< or =0.05) by pretreatment cycling status and body condition. Younger cows (< or =3 yr) tended to have greater AI pregnancy rates when inseminated at 56h, whereas older cows had similar pregnancy rates when inseminated at 56h or later (timing of AI by age interaction; P=0.085). Pregnancy loss between Days 32 and 63 was greatest (quadratic effect; P<0.05) when cows were inseminated at 48 and 72h. In summary, insemination times at or after 56h improved AI pregnancy rates when using the CO-Synch+CIDR program. Further work is warranted to examine age effects on timing of AI in the CO-Synch+CIDR program.

Effects of implanting and feeding zilpaterol hydrochloride on performance, carcass characteristics, and subprimal beef yields of fed cows.

Sixty crossbred cull cows were used to determine the combined effects of a trenbolone acetate-estradiol implant and feeding zilpaterol hydrochloride on performance, carcass characteristics, and subprimal yields of mature cows fed for 70 d. Cows were assigned to 1 of 5 treatments: 1) grazing native grass pasture (G); 2) concentrate-fed (C) a grain sorghum-sorghum silage diet; 3) concentrate-fed and implanted (CI) with Revalor-200 (trenbolone acetate-estradiol); 4) concentrate-fed and fed Zilmax (zilpaterol hydrochloride) beginning on d 38 of the feeding period (CZ); and 5) concentrate-fed, implanted, and fed Zilmax beginning on d 38 (CIZ). The concentrate diet consisted primarily of ground grain sorghum and sorghum silage. During the last 34 d of the feeding trial, concentrate-fed (C, CI, CZ, and CIZ) cows had greater (P < 0.05) gains than G cows. Hot carcass weights and dressing percentages were greater (P < 0.05) for the concentrate-fed cows than for G cows. Longissimus muscle area was largest (P < 0.05) for CIZ cows, whereas subprimal weights from the chuck were heavier (P < 0.05) from CIZ cows than C and G cows, and carcasses from CI and CZ cows had heavier (P < 0.05) chuck subprimal weights than G cows. Rib and round subprimal weights were heavier (P < 0.05) for concentrate-fed cows compared with G cows. In addition, carcasses from CIZ cows had heavier (P < 0.05) total subprimal weights, and total subprimals were a greater percentage of their initial BW than C cows. Rib cut-out and total soft tissue weights from the 9-10-11th rib were less (P < 0.05) for G cows than concentrate-fed cows. Feeding cull cows a concentrate diet increased carcass weight, dressing percentage, and subprimal yields compared with feeding cows a grass-based pasture diet, and the combination of a trenbolone acetate-estradiol implant and feeding zilpaterol hydrochloride can maximize trimmed beef yields from cull cows fed a high-concentrate diet.

Concentrations of fecal bacteria and nutrients in soil surrounding round-bale feeding sites.

An experiment was conducted over 7 mo (January to July 2003) to evaluate fecal bacteria and nutrient concentrations in soil surrounding round-bale feeders at 10 winter feeding sites. Soil samples 15 cm in depth were taken monthly from each site at distances of 3, 12, 21, and 30 m from the feeder. Soil samples were taken before livestock access to the sites (January), during the feeding period (February, March, and April), and after cattle removal from the sites (May, June, and July). Results indicated that fecal bacteria concentrations increased over the feeding period and were greatest at close proximity to round-bale feeders. Fecal Escherichia coli concentrations were greater in April (P < 0.03) at 3 and 12 m than in all other months, except March. At 21 and 30 m from the feeders, fecal E. coli concentrations were greater in April (P < 0.01) than in other months. At 3 m from the feeder, fecal Streptococci concentrations were greater in March and April (P < 0.01) than in other months. Although fecal E. coli concentrations in July had returned to levels similar to those in the prefeeding period, fecal Streptococci remained at higher concentrations (P < 0.05) than at the prefeeding period. The concentration of soil P at 3 m was greater in April (P < 0.02) than in January, February, and May. After cattle access to the sites, soil DM content was consistently less for samples taken at 3 m from the feeder compared with the other distances, with quadratic decreases (P < 0.02) noted in March, April, and July, and linear decreases (P < 0.01) in May and June, as distance from the feeder decreased.

Luteinizing hormone, growth hormone, insulin-like growth factor-I, insulin and metabolites before puberty in heifers fed to gain at two rates.

Fall born Angus x Hereford heifers were allotted to treatments at 9 mo of age to achieve the following growth rates: 1) fed to gain 1.36 kg/d (n = 10; HGAIN); and 2) fed to gain 0.23 kg/d for 16 wk, then fed to gain 1.36 kg/d (n = 9; LHGAIN). Growth hormone (GH), insulin-like growth factor-I (IGF-I0, insulin, glucose, nonesterified fatty acids (NEFA), and progesterone were quantified in twice weekly blood samples until onset of puberty. Body weight, hip height, and pelvic area were recorded every 28 d. Frequent blood samples (n = 8 heifers/treatment) were collected every 14 d, commencing on day 29 of treatment until onset of puberty to evaluate secretion of luteinizing hormone (LH) and GH. The HGAIN heifers were younger (369 d; P < 0.001), were shorter at the hip (115 cm; P < 0.05) and had smaller pelvic area (140 cm2; P < 0.10), but body weight (321 kg) did not differ at puberty compared with LHGAIN heifers (460 d; 119 cm; 155 cm2; 347 kg, respectively). The HGAIN heifers had greater (P < 0.05) concentrations of LH, IGF-I, and insulin in serum and glucose in plasma during the first 84 d of treatment than LHGAIN heifers, whereas LHGAIN heifers had greater (P < 0.05) concentrations of GH in serum and NEFA in plasma than HGAIN heifers. On day 68 of treatment, HGAIN heifers had less mean GH (P < 0.01) and greater (P < 0.05) LH pulse frequency than LHGAIN heifers, whereas LH pulse amplitude and mean LH did not differ (P < 0.10) between treatments. Treatment did not influence secretion of LH and GH at 1 and 3 wk before puberty. Mean GH concentrations in serum and GH pulse amplitude in all heifers were greater (P < 0.05) 2 to 9 d (12.9 and 40.7 ng/ml, respectively) than 16 to 23 d (10.4 and 20.0 ng/ml, respectively) before puberty. Nutrient restriction decreased LH pulse frequency and delayed puberty in beef heifers. Furthermore, dramatic changes in mean concentration and amplitude of GH pulses just before puberty in beef heifers may have a role in pubertal development.

Effects of energy or protein supplements and stage of production on intake and digestibility of hay by beef cows.

In two consecutive years, primi- and multiparous, spring-calving Hereford and Hereford x Angus cows (n = 32, yr 1; n = 42, yr 2) were used to determine the effects of supplements and lactational status on forage intake, digestibility, and energy intake. Cows were randomly alloted to treatments after being blocked by age, breed, and weight. Supplements fed during gestation provided .55 kg/d of CP from a 40% CP, soybean meal-based supplement (PROTEIN) or a 20% CP, soybean hull-based supplement (ENERGY). After calving, cows remained on the same supplement or were switched. In yr 2, a 40% CP supplement was also fed postpartum at nearly the same rate as ENERGY to provide twice the supplemental CP and energy as PROTEIN. Prairie hay (< 5% CP) DMI was measured directly and DM digestibility estimated for two 7-d periods during late gestation and early lactation. Gestating cows fed PROTEIN consumed 1 kg/d more hay DM and hay DM digestibility was greater (P < .001) than for cows fed ENERGY. Lactating cows also consumed more hay when fed PROTEIN than when fed ENERGY or HI PROT, but hay DMI was not affected. Total ME intake was similar for cows fed PROTEIN and ENERGY in late gestation or early lactation. Results indicated that ENERGY will decrease low-quality forage digestibility for prepartum cows and can decrease forage intake for both pre- and post-partum cows. Increasing the total energy intake of grazing cattle by feeding supplements is difficult after protein requirements are met.

Effects of feeding energy or protein supplements before or after calving on performance of spring-calving cows grazing native range.

In three consecutive years, spring-calving Hereford and Hereford x Angus cows (n = 348) were used to determine effects of level of supplemental energy or protein before and after calving on cowherd performance. Beginning on November 1, cows were individually fed 1.22 kg/d of a 40% CP (PROTEIN) or 2.44 kg/d of a 20% CP supplement (ENERGY) until calving. After calving, cows remained on the same supplement, were switched to the other supplement, or were fed 2.44 kg/d of a 40% CP supplement (HI PROT). Supplementation ended on April 20, the start of a 65-d breeding season. Cows fed ENERGY during gestation had greater BW gains (9 kg) at calving than PROTEIN-fed cows (P < .01). Calf weaning weight was not affected by supplementation. Cows fed ENERGY before calving had an 11% greater pregnancy rate than the cows fed PROTEIN (P < .002). Cows fed PROTEIN or ENERGY after calving had similar BW gains but cows fed HI PROT after calving lost less BW during supplementation (P < .002). Pregnancy rates were not influenced by treatments fed for a short period after calving. In conclusion, conception rates were significantly improved by feeding greater levels of supplemental energy prepartum but not postpartum. Energy supplements can affect reproduction with minimal effects on BW or condition.

Effects of postweaning diet on age and weight at puberty and mild production of heifers.

One hundred 7-mo-old spring-born beef heifers (215 kg) were used to evaluate effects of level of supplementation and short-term concentrate feeding on age and weight at puberty and milk production. In each of two winters, heifers were individually fed .9 kg/d of a 40% CP supplement (SBM) or 1.8 or 2.7 kg/d of a 20% CP supplement (LOW-20 or HIGH-20, respectively) while grazing dormant native pastures or .9 kg/d of SBM until February, and then fed a high-concentrate diet (NEg = 1.31 Mcal/kg) in drylot to weight the same as HIGH-20 heifers on May 1, the beginning of the breeding season. Weights on May 1 were similar for HIGH-20 and DRYLOT heifers (320 and 314 kg, respectively) and were heavier (P < .01) than those of LOW-20 heifers (289 kg), which were heavier (P < .01) than SBM-fed heifers (278 kg). Pubertal weight was similar for SBM, LOW-20, and DRYLOT (290, 296, and 297 kg, respectively) and heaviest for HIGH-20 heifers (P < .01, 325 kg). DRYLOT heifers reached puberty at 29 d younger (P < .05) than heifers on the other treatments. Percentage of heifers puberal on May 1 were 0, 9, 13, and 72 for SBM, LOW-20, HIGH-20, and DRYLOT heifers, respectively. Pregnancy rates were significantly lower for SBM (67%) than for LOW-20, HIGH-20, and DRYLOT (94, 94, and 86%, respectively). Milk production after first parturition was similar for all treatments. Age and weight at puberty may be altered by short-term feeding of high-concentrate diets.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship of milk production, milk expected progeny difference, and calf weaning weight in angus and simmental cow-calf pairs.

Milk EPD, used to predict the milk production potential of a parent's daughters, have been reported by all major cattle breed associations. Our objectives were to determine the relationship of milk EPD of a dam to actual milk production (both fluid and components) and offspring weaning weight. Angus (AN; n = 114) and Simmental (SM; n = 82) cows were machine-milked at approximately 60, 104, and 196 d postpartum after overnight calf removal. In addition, one herd of AN was also milked at approximately 35 and 145 d postpartum. A lactation curve was fitted to these measurements to estimate total milk production during lactation. Simple correlations between 205-d total milk yields (TMY) and adjusted 205-d calf weaning weight (WW) were .30 (P < .001) and .47 (P < .001) for AN and SM, respectively. Furthermore, milk EPD was positively correlated to adjusted WW (r = .38 P < .001; r = .39, P < .001) and TMY (r = .32, P < .001; r = .44, P < .001) for AN and SM cows, respectively. A 1-kg change in TMY changed WW by .014 +/- .006 kg (P < .001) in AN and by .032 +/- .009 kg (P < .001) in SM. A 1-kg change in milk EPD resulted in a 4.85 +/- 1.14 kg change in WW (P < .001) in AN and a 3.74 +/- 1.73 kg (P < .05) change in SM. Corresponding changes in TMY were 42.1 +/- 16.6 kg (P < .01) and 69.3 +/- 16.0 kg (P < .001) for AN and SM, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)