Evaluation of five resynchronization methods using different combinations of PGF2α, GnRH, estradiol and an intravaginal progesterone device for insemination in Holstein cows

This study was conducted to determine the use of repeated transvaginal ultrasound-guided cumulus oocyte complex (COC) aspiration on COC recovery rate, in vitro embryo production (IVP) and subsequent pregnancy rates in Holstein Friesian (HF) and Aberdeen Angus (AA) cows (Experiment 1), and in pregnant and non-pregnant Holstein Friesian cows (Experiment 2). Cycling, non-pregnant HF (n=17) and AA (n=32) cows with 40-70 days postpartum, between 3 and 5 years of age were used in the Experiment 1. All cows were submitted to repeated transvaginal ultrasound-guided COC aspiration twice a week for 5-7 weeks. Cumulus ooctye complexes (COC) were in vitro matured, fertilized and cultured for 8 days. An overall of 100 and 350 embryos from HF and AA cows respectively were cryopreserved using a conventional slow freezing (Experiment 1). A total of 81 and 285 frozen-thawed embryos from HF and AA cows respectively were transferred to recipient cows. Pregnancy diagnosis was performed at 60 and 150 days of gestation using transrectal ultrasonography. In Experiment 2, cycling non-pregnant (n=9) and pregnant (n=8) HF cows were submitted to repeated ultrasound-guided COC aspiration and COC were in vitro matured, fertilized and cultured as in Experiment 1, except that embryos were cryopreserved but not thawed and transferred as described for Experiment 1. The results of this study indicate that COC recovery rate and blastocyts production are affected by the breed of the donor cow. The quality of blastocyts produced from both breed did not differ in terms of pregnancy and calving rates (Experiment 1). The physiologic state of pregnancy did not affect COC recovery rate and blastocysts production per donor/session (Experiment 2). The use of ultrasound-guided COC aspiration and IVP could be a powerful technique to improve the genetic of beef and dairy cattle managed under pasture-based conditions management in the southern Chile.     

Effect of Feeding Selenium-Fertilized Alfalfa Hay on Performance of Weaned Beef Calves

Selenium (Se) is an essential micronutrient in cattle, and Se-deficiency can affect morbidity and mortality. Calves may have greater Se requirements during periods of stress, such as during the transitional period between weaning and movement to a feedlot. Previously, we showed that feeding Se-fertilized forage increases whole-blood (WB) Se concentrations in mature beef cows. Our current objective was to test whether feeding Se-fertilized forage increases WB-Se concentrations and performance in weaned beef calves. Recently weaned beef calves (n = 60) were blocked by body weight, randomly assigned to 4 groups, and fed an alfalfa hay based diet for 7 wk, which was harvested from fields fertilized with sodium-selenate at a rate of 0, 22.5, 45.0, or 89.9 g Se/ha. Blood samples were collected weekly and analyzed for WB-Se concentrations. Body weight and health status of calves were monitored during the 7-wk feeding trial. Increasing application rates of Se fertilizer resulted in increased alfalfa hay Se content for that cutting of alfalfa (0.07, 0.95, 1.55, 3.26 mg Se/kg dry matter for Se application rates of 0, 22.5, 45.0, or 89.9 g Se/ha, respectively). Feeding Se-fertilized alfalfa hay during the 7-wk preconditioning period increased WB-Se concentrations (P _Linear<0.001) and body weights (P _Linear = 0.002) depending upon the Se-application rate. Based upon our results we suggest that soil-Se fertilization is a potential management tool to improve Se-status and performance in weaned calves in areas with low soil-Se concentrations.     

Effects of bull exposure on the cyclic activity of beef cows

In Experiment I, 38 crossbred suckled beef cows grazing fescue pastures and 34 crossbred beef cows grazing bluestem pastures were randomly allocated at the time of calving into a group with 4 teaser bulls or no bulls. Two blood samples were collected 7 d apart from the cows to determine cyclic activity 67 and 76 d after calving in the fescue and bluestem pastures, respectively. Progesterone greater than 1.0 ng/ml in one or both samples indicated cyclic activity. There was no difference in the percentage of cows cyclic among the different groups. The number of cyclic cows in the fescue pasture with bulls was 16/19 (84%); in the fescue pasture with no bulls, 14/19 (74%); in the bluestem pasture with bulls, 17/17 (100%); and in the bluestem pasture with no bulls, 16/17 (94%). Overall cyclic activity among all cows for teaser bull-exposed and no bull was similar, 33/36 (91%) and 30/36 (83%). Overall cyclic activity was greater (P < 0.05) in cows grazing bluestem (33/34), 97% than fescue pastures (30/38), 80%. Measurements of cyclic activity were initiated too late in the postcalving period to quantify differences in estrous activity between the bull and no bull treatment groups. Another trial was planned for the following year with a modified protocol. In Experiment II, blood samples were collected for progesterone concentrations soon after calving and were repeated at intervals to characterize both the occurrence and duration of estrous cycles. In this experiment, 29 crossbred suckled beef cows grazing fescue pastures were randomly allocated 12 d after calving (Day 0) into 1 of 2 groups with teaser bulls or without bulls. Nineteen crossbred beef cows grazing bluestem pastures were allocated similarly 10 d after calving (Day 0). Bulls were added to the groups with bulls in fescue and bluestem pastures on day 6 after the initial allocations. Blood samples were collected from all cows on Day 0 and every 3 d until Day 46. Means (+/- SEM) of the cumulative progesterone concentrations (ng/ml) per cow for the 16 samples from cows grazing fescue were 12.5 +/- 3.5 for cows exposed to bulls, 2.5 +/- 0.16 for cows not exposed to bulls, 27.6 +/- 4.42 for cows grazing bluestem pastures and exposed to bulls, and 16.0 +/- 2.75 for cows without exposure to bulls. Progesterone concentrations were higher in cows exposed to bulls (P < 0.01). The percentages of both short and normal cycles increased (P < 0.01) in groups exposed to bulls (88%, 21/24 and 63%, 15/24) when compared with the no bull groups (29%, 7/24 and 21%, 5/24), respectively. Cows exposed to bulls also showed increased cyclic activity.     

Bovine pregnancy and nonreturn rates following artificial insemination using a covered sheath

Contamination transferred into the uterus from external genitalia during artificial insemination (AI) has been hypothesized to cause lowered bovine pregnancy rates (PR). Using aseptic techniques, there is still a possibility of uterine contamination during routine AI. Two experiments were conducted to evaluate the effect of two types of sheath covers (CS) placed over the conventional French Medium Syringe assembly (FMS) used for AI. Their use entailed passing the assembly to the external os of the cervix, pushing the FMS through the CS and manipulating the FMS to the cervical uterine junction in the normal manner. Fifty-six day non-return rate (NRR) in dairy and actual PR in beef cattle were evaluated. In Experiment 1, 30 professional technicians were employed to inseminate 7, 387 dairy cows, while in Experiment 2, six technicians with varying levels of experience inseminated 416 beef cows. Least-squares means for NRR in dairy cattle were 78% using a CS and 79% without. Means for PR in beef cattle were 57% using a CS and 62% without. In Experiment 2, the overall PR was lower in Trial l than in other trials (P<0.05). Since some technicians improved with time, the difference due to trial was attributed to technician variation in gaining experience with a CS. Results indicate that general use of a CS in routine AI of apparently healthy cows will not increase PR.     

Potential use of ovum pick-up for embryo production and breeding in cattle

The efficacy of transvaginal ultrasound-guided puncturing of ovarian follicles for collecting immature oocytes in cattle was studied. Three experiments were conducted to examine the effects of puncturing on follicle recruitment and on the number of oocytes collected. Puncture sessions were executed twice weekly at regular intervals of 3 and 4 d respectively. The oocytes were matured, fertilized and allowed to develop in vitro and the number of transferable embryos was recorded. The health of the cows was checked daily. In Experiment 1, dairy cows (n=10) were punctured over a period of 5 mo, and the collected oocytes were fertilized with the semen of 1 bull. In Experiment 2, oocytes were collected from one 12 year old high pedigree dairy cow and an one month pregnant cow were punctured. The oocytes of the old cow were fertilized with semen of 8 different bulls. In Experiment 3, beef cows (n=6) were punctured over a 2 mo period and the semen of 2 different bulls of the same breed was used to fertilize the oocytes from 3 of these cows. In Experiment 1, 14.5 +/- 0.4 (mean +/- SEM) follicles were punctured per session, and 8.0 +/- 0.3 (mean +/- SEM) oocytes were recovered. A mean of 16% of the oocytes developed into transferable embryos with a pregnancy rate of 40%. The results did not differ between the months of the experiments, indicating that the transvaginal puncturing method can be used successfully over a 5 mo period. No detrimental effects were observed after clinical and post mortem examinations, nor did breed, age or reproductive status appear to affect the results. However, large differences were observed between individual cows and between cow/bull combinations.     

Fertilization rates in superovulating cows after deposition of semen on the infundibulum, near the uterotubal junction or after insemination with high numbers of sperm

Three experiments were conducted with 105 superovulating Holstein dairy cows in attempts to improve the fertilization rate. Cows were superovulated with follicle-stimulating hormone (FSH) and time of estrus was regulated with prostaglandin F(2)alpha (PGF(2)alpha). Semen was deposited on each infundibulum through a laparoscope inserted through the flank (Experiment 1) or near the uterotubal junctions through flexible tubing passed through the cervix and uterine horns (Experiment 2). In the third experiment, high numbers of sperm in fresh semen were deposited in the uterus. Cows were necropsied and ova were recovered and examined about 3.5 d after the beginning of estrus. Deposition of 0.5 ml of frozen-thawed semen on each infundibulum (Experiment 1) reduced both ovum recovery and fertilization. In ten cows inseminated on the infundibulum, ova representing 43% of ovulation points were recovered and 9% of these recovered ova were fertilized. In ten control cows, ova representing 80% of ovulation points were recovered and 62% of them were fertilized. In a 2 x 2 experiment with 36 superovulating cows (Experiment 2), 1 ml of diluted fresh or frozen semen was deposited either near the uterotubal junction or in the uterine body. The overall fertilization rate was 61%, with no significant effect of site of semen deposition or type of semen used. In Experiment 3, 2 or 3 ml of neat semen (average of 4.4 billion sperm) was deposited in the uterus of 12 cows; 183 of 197 intact ova (93%) were fertilized. In 56 control cows inseminated with 0.5 to 1.5 ml of frozen diluted semen (average of 70 million sperm), 502 of 947 intact ova were fertilized (53%, P<0.001). Insemination with high numbers of fresh sperm overcame problems of sperm loss or sperm transport and improved the fertilization rate.     

Superstimulation of ovarian follicular development in beef cattle with a single intramuscular injection of Folltropin-V

The need to inject FSH twice daily for superstimulation of ovarian follicular development in cattle necessitates frequent attention by farm-personnel and increases the possibility of failures due to mishandling and errors in administration of treatments. A series of three experiments were designed to evaluate the feasibility of superstimulation in beef cattle with a single intramuscular (IM) injection of Folltropin-V diluted in a hyaluronan-based slow-release formulation (SRF). In Experiment 1, cows were assigned to one of three treatment groups to compare two methods of injection as compared to the twice daily IM injection protocol. Superovulatory response of cows (n=6) treated with twice daily IM injections over 4 days (Control) was greater than of cows treated with a single subcutaneous (SC) injection in SRF (n=6), while superovulatory response of cows treated with a single IM injection in SRF (n=6) was intermediate. Experiment 2 was designed to compare two concentrations of SRF (20mg/mL hyaluronan, 100% compared to 10mg/mL hyaluronan, 50%) in a single IM injection protocol. The mean number of corpora lutea (CL) were not significantly different (P≥0.05), but the numbers of total ova/embryos (P<0.05), fertilized ova (P<0.01) and transferable embryos (P<0.001) were greater in cows treated with FSH in 100% SRF (n=20) than cows treated with FSH in 50% SRF (n=20). Experiment 3 was designed to compare superovulatory response in Red Angus donor cows treated with a single IM injection of Folltropin-V diluted in 100% solution of SRF with those treated with the traditional twice-daily IM injection protocol over 4 days. Mean (±SEM) numbers of CL (13.7±1.2 compared to 13.8±1.2), total ova/embryos (12.3±1.5 compared to 13.7±2.1), fertilized ova (7.2±1.1 compared to 8.4±1.4) and transferable embryos (4.9±0.8 compared to 6.4±1.3) were not significantly different between Control (n=29) and Single injection (n=29) groups, respectively. In summary, superstimulation of beef donor cows with a single IM injection of Folltropin-V diluted in 100% solution of SRF resulted in a comparable superovulatory response to the traditional twice-daily IM administration of Folltropin-V diluted in saline over 4 days.     

Mycotoxin-contaminated diets and an adsorbent affect the performance of Nellore bulls finished in feedlots

Mycotoxins are present in almost all feedstuffs used in animal nutrition but are often ignored in beef cattle systems, even though they can affect animal performance. The objective of this study was to evaluate the effects of mycotoxins and a mycotoxin adsorbent (ADS) on performance of Nellore cattle finished in a feedlot. One hundred Nellore cattle (430 ± 13 kg) were used in a randomized complete block design with a 2 × 2 factorial arrangement of treatments. The factors consisted of two diets with either natural contamination (NC) or exogenous contamination (EC) and the presence (1 g/kg of DM; ADS) or absence of a mycotoxin adsorbent. The NC and EC diets had the following contaminations, respectively: 0.00 and 10.0 µg/kg aflatoxins, 5114 and 5754 µg/kg fumonisins, 0.00 and 42.1 µg/kg trichothecenes B, 0.00 and 22.1 µg/kg trichothecenes A and 42.9 and 42.9 µg/kg fusaric acid. At the beginning of the experiment, all animals were weighed, and four randomly selected animals were slaughtered to evaluate the initial carcass weight. After 97 days of treatment, all animals were weighed and slaughtered. There was no interaction among factors for the DM intake (DMI; P = 0.92); however, there was a tendency for the EC diets to decrease the DMI by 650 g/day compared to animals fed NC diets (P = 0.09). There was a trend for interaction among factors (P = 0.08) for the average daily gain (ADG), where the greatest ADG was observed for cattle fed the NC diet (1.77 kg), and the lowest was observed for those fed the EC diet (1.51 kg). The NC + ADS and EC + ADS treatments presented intermediate values for ADG. The animals fed the NC diet had a greater final BW (596 kg) than animals fed the EC treatment (582 kg; P = 0.04). There was a tendency for interaction among factors for carcass gain (P = 0.08). Similarly to ADG, the highest carcass gain was observed for animals fed the NC diet (1.20 kg), and the lowest was observed for those fed the EC diet (1.05 kg). The NC + ADS and EC + ADS treatments presented intermediate values. The natural contamination groups had greater carcass gain than that of the EC groups, and the use of the ADS recovered part of the weight gain in animals fed the EC diet. In conclusion, mycotoxins at the levels evaluated affected the performance of beef cattle, and adsorbents may mitigate their impact.     

Wagyu–Angus cross improves meat tenderness compared to Angus cattle but unaffected by mild protein restriction during late gestation

For the spring-calving beef herds, late gestation coincides with winter and early spring, when cows are dependent on feed supplements with low quality hay, which is hard to meet their nutrient requirements. However, the effects of deficiencies of metabolizable protein intake during late gestation on offspring beef quality are unclear. Wagyu cattle have excellent marbling, and insemination with Wagyu vs Angus semen is a practical option for beef producers to improve beef quality. To test, Angus cows (621 ± 73 kg) were selected and randomly separated into two groups. Each group was inseminated with either Angus or Wagyu semen. During the last 90 days of gestation, cows in each group were further separated and received either a low protein diet (85% of the NRC metabolizable protein requirement), which was a low quality hay-based diet common in northwestern region of the U.S., or an adequate protein diet (108% NRC requirement). All progeny was managed together and harvested at a final BW of 576.5 ± 16.6 kg. Wagyu-sired offspring had higher marbling scores and quality grades than Angus (P < 0.01). Protein supplementation did not affect Slice Shear Force (SSF) in either breeds (P = 0.60). However, Wagyu-sired cattle had lower SSF than Angus-sired (P < 0.01). In addition, Wagyu-sired cattle had higher intramuscular fat (P < 0.05) and total collagen content (P < 0.05), but Angus-sired had greater mature collagen cross-links, as shown by higher contents of Pyridinoline (P < 0.01) and Ehrlich Chromogen (P < 0.01). Consistently, the mRNA expression of enzymes catalyzing collagen cross-linking was higher in Angus-sired offspring, including Plod 1 (P < 0.05), Plod 2 (P = 0.08), and P4Hα 2 (P < 0.01). In conclusion, Wagyu-sired cattle had greater tenderness and marbling score compared to Angus-sired, which was associated with lower collagen cross-links. Feeding mature grass hay-based diet with relatively low protein content during late gestation had no major effect on beef quality of subsequent cattle.     

Effect of the metabolic environment at key stages of follicle development in cattle: focus on steroid biosynthesis

Cellular mechanisms that contribute to low estradiol concentrations produced by the preovulatory ovarian follicle in cattle with a compromised metabolic status are largely unknown. To gain insight into the main metabolic mechanisms affecting preovulatory follicle function, two different animal models were used. Experiment 1 compared Holstein-Friesian nonlactating heifers (n = 17) and lactating cows (n = 16) at three stages of preovulatory follicle development: 1) newly selected dominant follicle in the luteal phase (Selection), 2) follicular phase before the LH surge (Differentiation), and 3) preovulatory phase after the LH surge (Luteinization). Experiment 2 compared newly selected dominant follicles in the luteal phase in beef heifers fed a diet of 1.2 times maintenance (M, n = 8) or 0.4 M (n = 11). Lactating cows and 0.4 M beef heifers had higher concentrations of β-hydroxybutyrate, and lower concentrations of glucose, insulin, and IGF-I compared with dairy heifers and 1.2 M beef heifers, respectively. In lactating cows this altered metabolic environment was associated with reduced dominant follicle estradiol and progesterone synthesis during Differentiation and Luteinization, respectively, and in 0.4 M beef heifers with reduced dominant follicle estradiol synthesis. Using a combination of RNA sequencing, Ingenuity Pathway Analysis, and qRT-PCR validation, we identified several important molecular markers involved in steroid biosynthesis, such as the expression of steroidogenic acute regulatory protein (STAR) within developing dominant follicles, to be downregulated by the catabolic state. Based on this, we propose that the adverse metabolic environment caused by lactation or nutritional restriction decreases preovulatory follicle function mainly by affecting cholesterol transport into the mitochondria to initiate steroidogenesis.     

Induction of ovarian follicular wave emergence and ovulation in progestin-based timed artificial insemination protocols for Bos indicus cattle

The present study aimed to evaluate the efficacy of different inducers of new follicular wave emergence (FWE) and ovulation in fixed-time artificial insemination (FTAI) synchronization protocols using norgestomet ear implants (NORG) in Bos indicus cattle. In Experiment 1, the synchronization of FWE was evaluated when two different estradiol esters in different doses [2mg estradiol benzoate (EB), 2.5mg EV or 5mg estradiol valerate (EV)] were administered with NORG implant insertion in B. indicus cattle (estrous cyclic heifers and cows with suckling calves; n=10 per treatment). After estradiol treatment, ovarian ultrasonic exams were performed once daily to detect the interval between treatment and FWE. There were significant treatment-by-animal category interaction (P=0.05) on the interval from the estradiol treatment to FWE. An earlier (P<0.0001) and less variable (P=0.02) interval from estradiol treatment to FWE was observed in heifers treated with EB (2.5±0.2; mean±SE) than in those treated with 2.5mg EV (4.2±0.3) or 5mg EV (6.1±0.6). Cows treated with 5mg EV (4.0±0.5) had longer (P=0.05) interval than cows receiving EB (2.5±0.2), however, there was an intermediate interval in those cows treated with 2.5mg EV (3.1±0.4). In Experiment 2, the number of uses of the NORG implant (new; n=305 or previously used once; n=314) and three different ovulation induction hormones [0.5mg estradiol cypionate (EC) at implant removal (n=205), 1mg EB given 24h after implant removal (n=219), or 100μg gonadorelin (GnRH) given at FTAI (n=195)] were evaluated in Nelore heifers (2×3 factorial design). Similar pregnancy per AI (P/AI; 30 days after FTAI; P>0.05) were achieved using each of the three ovulation induction hormones (EB=40.6%; EC=48.3%, or GnRH=48.7%) and with a new (47.2%) or once-used NORG implant (44.3%). In Experiment 3, the effect of different ovulation induction hormones for FTAI [1mg EC at NORG implant removal (n=228), 10μg buserelin acetate at FTAI (GnRH; n=212) or both treatments (EC+GnRH; n=215)] on P/AI was evaluated in suckled beef cows treated with a once-used NORG implant and EB to synchronize the FWE. Similar P/AI (P=0.71) were obtained using GnRH (50.9%), EC (51.8%) or both treatments (54.9%) as ovulation induction hormones. Therefore, both doses of EV (2.5 or 5.0mg) with NORG implant delayed and increased the variation of the day of new FWE compared with EB in B. indicus cattle. These effects were more pronounced in B. indicus heifers than cows. Synchronization protocols for FTAI with either a new or once-used NORG implant with EB at insertion to induce a new FWE and either the use of EB, EC or GnRH as ovulation induction hormones may be successful in B. indicus heifers. Also, when a once-used NORG implant was used, either the administration of EC, GnRH or both as ovulation inducers resulted in similar P/AI in suckled B. indicus cows, showing no additive effect of the combination of both ovulation induction hormones.     

Persistence of Clostridium botulinum type B on a cattle farm after an outbreak of botulism.

On farms involved in botulism outbreaks, cycles of Clostridium botulinum have occurred. The cycles were initiated by feeding brewers' grains contaminated with proteolytic C. botulinum type B to the cows. Spreading of manure containing feces of these cows increased the contamination of the pastures. In grass silages prepared with wilted grass from these pastures the number of C. botulinum type B organisms increased, and toxin type B was produced. Feeding cows with the contaminated silage fodder completed the cycle. Besides contamination of human foodstuffs (milk and meat), further contamination of the environment occurred. It was demonstrated that fowl may be important vectors in spreading C. botulinum.     

Superovulatory response to a single subcutaneous injection of Folltropin-V in beef cattle

A series of 4 experiments were designed to evaluate the feasibility of superstimulation in beef cattle with a single sc injection of the porcine pituitary extract, Folltropin-V. In the preliminary study (Experiment 1), superovulatory response of cows (n=7) treated with a single sc injection of 400 mg NIH-FSH-P1 Folltropin-V was not different than that of cows (n=8) superstimulated with twice daily im injections over 4 d, or a single sc injection plus an injection of eCG (n=12). Experiments 2 and 3 were designed to determine the optimal site of a single sc injection. In Experiment 2, cows (n=25) with body condition scores (BCS) of 1 to 2 were used. The mean number of CL counted and ova/embryos collected was lower (P<0.05) in cows treated with the single sc injection in the neck region than in cows treated with a single sc injection behind the shoulder, or with the twice daily im injection treatment. In Experiment 3, cows (n=49) with BCS of 3 to 5 were used. There were no differences in the number of CL, total ova/embrvos collected, fertilized ova and transferable embryos whether treatments were given in the neck region or behind the shoulder, or whether the cows were implanted or not implanted with Syncro-Mate-B. Experiment 4 was designed to determine the optimal superstimulatory dosage of Folltropin-V administered by a single sc injection. Superovulatory response of cows treated with the higher doses (400 mg, 600 mg or 800 mg NIH-FSH-P1) was higher (P<0.05) than those treated with 200 mg NIH-FSH-P1. The number of unovulated (>/=10 mm) follicles at the time of ova/embryo collection was higher (P<0.05) in the 600 and 800 mg groups, and progesterone concentration at estrus was higher (P<0.05) in cows treated with 800 mg than with 400 or 200 mg. It was concluded that a single, bolus sc injection of 400 mg NIH-FSH-P1 of Folltropin-V is as efficacious as the 4-d, twice daily im treatment protocol for inducing superovulation in beef cows. The amount of subcutaneous fat and site of injection appeared to affect the efficacy of a single sc injection; a single bolus sc injection of Folltropin-V behind the shoulder resulted in the most predictable superovulatory response.     

Flaxseed supplementation decreases methanogenic gene abundance in the rumen of dairy cows

The objective of this study was to investigate the effects of a flaxseed-supplemented diet on archaeal abundance and gene expression of methanogens in the rumen of dairy cows. In all, 11 non-lactating dairy cows were randomly divided into two groups: group A (five cows) and B (six cows). The two diets fed were: (1) the control diet, a conventional dry cow ration; and (2) the flaxseed-supplemented diet, the conventional dry cow ration adjusted with 12.16% ground flaxseed incorporated into the total mixed ration. A cross-over experiment was performed with the two groups of cows fed the two different diets for five 21-day periods, which included the first adaptation period followed by two treatment and two wash out periods. At the end of each feeding period, rumen fluid samples were collected via rumenocentesis and DNA was extracted. Quantitative PCR was utilized to analyze the gene abundance of 16S ribosomal RNA (16S rRNA) targeting the ruminal archaea population and the mcrA gene coding for methyl coenzyme-M reductase subunit A, a terminal enzyme in the methanogenesis pathway. Results demonstrated a 49% reduction of 16S rRNA and 50% reduction of mcrA gene abundances in the rumen of dairy cows fed the flaxseed-supplemented diet in comparison with those fed the control diet. This shows flaxseed supplementation effectively decreases the methanogenic population in the rumen. Future studies will focus on the mechanisms for such reduction in the rumen of dairy cattle, as well as the relationship between methanogenic gene expression and methane production.     

Origin of contamination and genetic diversity of Escherichia coli in beef cattle

The possible origin of beef contamination and genetic diversity of Escherichia coli populations in beef cattle, on carcasses and ground beef, was examined by using random amplification of polymorphic DNA (RAPD) and PCR-restriction fragment length polymorphism (PCR-RFLP) analysis of the fliC gene. E. coli was recovered from the feces of 10 beef cattle during pasture grazing and feedlot finishing and from hides, carcasses, and ground beef after slaughter. The 1,403 E. coli isolates (855 fecal, 320 hide, 153 carcass, and 75 ground beef) were grouped into 121 genetic subtypes by using the RAPD method. Some of the genetic subtypes in cattle feces were also recovered from hides, prechilled carcasses, chilled carcasses, and ground beef. E. coli genetic subtypes were shared among cattle at all sample times, but a number of transient types were unique to individual animals. The genetic diversity of the E. coli population changed over time within individual animals grazing on pasture and in the feedlot. Isolates from one animal (59 fecal, 30 hide, 19 carcass, and 12 ground beef) were characterized by the PCR-RFLP analysis of the fliC gene and were grouped into eight genotypes. There was good agreement between the results obtained with the RAPD and PCR-RFLP techniques. In conclusion, the E. coli contaminating meat can originate from cattle feces, and the E. coli population in beef cattle was highly diverse. Also, genetic subtypes can be shared among animals or can be unique to an animal, and they are constantly changing.     

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.     

Allelopathy Among Prairie Grasses and its Possible Ecological Significance

The phytotoxic effect of four kinds of litter and three kindsof fresh material extracts of blue grama and western wheatgrasson seed germination of blue grama, western wheatgrass and buffalograss was tested. The four kinds of litter were collected fromthe Ecosystem Stress Area at the native shortgrass prairie site.These included litter from control, fertilized, irrigated, andfertilized plus irrigated plots. The three kinds of fresh materialswere harvested from blue grama and western wheatgrass growingunder growth chamber conditions at three distinct phenologicalstages. Results indicated that the fresh material extracts weremore phytotoxic than the litter extracts and among the formerthe fresh material harvested at the earlier phenological stagewas more phytotoxic than those collected at the advanced phenologicalstage. Chemical composition of litter and fresh material indicatedthat the fresh materials contained comparatively more phenolicsubstances than that of litter materials.     

Grazing behaviour and performance of lactating suckler cows, ewes and goats on partially improved heathlands

The foraging behaviour (grazing time and diet composition), live-weight (LW) changes and parasitic infection (faecal egg counts of gastrointestinal nematodes) of 12 beef cows, 84 ewes and 84 goats suckling their offspring, managed in mixed grazing on heathlands with 24% of improved pasture of perennial ryegrass-white clover, were studied during the years 2003 and 2006. The results showed that goats tended to graze for a longer time, and utilised significantly more heathland vegetation than cattle and sheep, including in their diet in an average of 0.39 herbaceous plants, 0.11 gorse and 0.51 heather over the grazing season, comparing with respective mean values of 0.85, 0.02 and 0.13 in cattle and sheep. Dietary overlap was higher between cattle and sheep (0.76) than between sheep and goats (0.53) or between cattle and goats (0.47). Despite the high performance of autumn-calving cows in spring, sheep had the best LW changes per livestock unit (LU) during the whole grazing season. Goats' performance per LU was lower than in sheep but higher than in spring-calving cows. Regarding offspring production, lambs had higher LW gains per LU than calves and kids. Mean nematode eggs/g fresh faeces (epg) during the grazing season were higher in goats (91 epg) compared with sheep (34 epg) and cattle (14 epg), particularly from September to December. In conclusion, sheep performed best on these heathlands with improved pasture areas if the entire grazing season was considered, despite the good level of production in spring from autumn-calving cows. The results suggested the complementary use of goats in order to increase the effective utilisation of the available vegetation, achieving production levels similar to those from spring-calving cows. Therefore, mixed flocks of sheep and goats would be the most appropriate sustainable systems from the animal production and vegetation use points of view.     

Effects of Feeding Selenium-Enriched Alfalfa Hay on Immunity and Health of Weaned Beef Calves

Previously, we reported that feeding selenium (Se)-enriched forage improves antibody titers in mature beef cows, and whole-blood Se concentrations and growth rates in weaned beef calves. Our current objective was to test whether beef calves fed Se-enriched alfalfa hay during the transition period between weaning and movement to a feedlot also have improved immune responses and slaughter weights. Recently weaned beef calves (n?=?60) were fed an alfalfa-hay-based diet for 7 weeks, which was harvested from fields fertilized with sodium selenate at 0, 22.5, 45.0, or 89.9 g Se/ha. All calves were immunized with J-5 Escherichia coli bacterin. Serum was collected for antibody titers 2 weeks after the third immunization. Whole-blood neutrophils collected at 6 or 7 weeks were evaluated for total antioxidant potential, bacterial killing activity, and expression of genes associated with selenoproteins and innate immunity. Calves fed the highest versus the lowest level of Se-enriched alfalfa hay had higher antibody titers (P?=?0.02), thioredoxin reductase-2 mRNA levels (P?=?0.07), and a greater neutrophil total antioxidant potential (P?=?0.10), whereas mRNA levels of interleukin-8 receptor (P?=?0.02), l-selectin (P?=?0.07), and thioredoxin reductase-1 (P?=?0.07) were lower. In the feedlot, calves previously fed the highest-Se forage had lower mortality (P?=?0.04) and greater slaughter weights (P?=?0.02). Our results suggest that, in areas with low-forage Se concentrations, feeding beef calves Se-enriched alfalfa hay during the weaning transition period improves vaccination responses and subsequent growth and survival in the feedlot.     

Performance of fattening cattle and lactating beef cows on diets high in chemically treated wheat straw and poultry litter

Three experiments were carried out to study the effect of chemical treatment on the nutritive value of wheat straw (WS) and the effect of diets containing such treated straw and poultry litter (PL) on the performance of fattening cattle and lactating beef cows. The chemical treatment consisted of treating half of the wheat straw with 60 kg sodium hydroxide/t and the other with 60 kg sulphuric acid/t, and then mixing the two to give “Celephos”. The digestibility coefficient of organic matter was 68.0 and 41.7 for “Celephos” and untreated straw, respectively.For a long term feeding trial, two mixtures were formulated: (a) including 23% WS and 19% PL; (b) including 30% chemically treated WS and 16% PL. A conventional high grain fattening diet (c) served as control. The metabolizable energy concentrations in the above diets were 2.37, 2.38 and 2.78 Mcal/kg DM. Protein content of the diets was regulated by PL or soya bean meal. Liveweight gain was 1059, 1137 and 1180 g/day, metabolizable energy conversion ratio to liveweight was 22.8, 20.7 and 20.0 Mcal/kg, and carcass gain was 565, 606 and 656 g/day for treatment groups (a), (b) and (c), respectively.In a third trial, lactating beef cows were fed on long straw or Celephos, PL and 1.5 kg grain per head per day. Intake of Celephos was 28% higher than that of untreated straw and milk output was 3 kg/day higher. This was reflected in an increase of 67 g/day in gain of suckled calves.