Milk production traits of beef cows as affected by horn fly count and sire breed type.

Horn fly infestations negatively impact economic traits of beef cattle. Our objective was to determine the impact of horn flies on beef cattle milk yield and quality. Cows (n = 53) were derived from Brangus dams and sired by Bonsmara (n = 7), Brangus (n = 13), Charolais (n = 8), Gelbvieh (n = 5), Hereford (n = 12), and Romosinuano (n = 8) bulls. Horn fly counts and estimates of milk yield and quality were recorded monthly from May through October on individual cows. Data for milk yield and quality and horn fly count were analyzed by mixed model least squares using a linear model including sire breed, cow in sire breed, month, and month × sire breed. Effects of horn fly count on milk yield and quality were estimated by analysis of covariance using log horn fly count and log horn fly count × sire breed. Horn fly counts varied by month (P < 0.0001), with lowest population recorded in May (99 flies) and peaked in August (520 flies). Bonsmara and Gelbvieh sired cows had greater (P < 0.05) milk yield compared to Hereford sired cows (8.75 and 8.62 vs. 6.02 kg/d, respectively). Milk yield from Charolais, Romosinuano, and Brangus sired cows was intermediate (7.28, 7.00, and 7.06 kg/d, respectively). Regression of milk yield on fly count differed (P < 0.05) among sire breeds. Milk yield was reduced (P < 0.05) by 0.99 and 0.64 kg/d per unit increase in log horn fly count in Gelbvieh and Bonsmara sired cows. Regression coefficient for milk yield on log horn fly count was reduced (P < 0.01) in Gelbvieh sired cows when compared with Brangus, Charolais, Hereford, and Romosinuano sired cows, and coefficients for Bonsmara sired cows were reduced (P < 0.05) in comparison to Brangus sired cows. Increases in log fly count were associated with decreases (P < 0.05) in milk fat, solids-not-fat, and milk urea nitrogen. Milk yield was reduced (P < 0.05) by increased fly numbers depending on month of lactation and interaction with log horn fly count. In May, June, and July milk yield was reduced 0.72, 0.68, and 0.71 kg/d per unit increase in log horn fly count. Our results indicate that horn fly infestations reduce milk yield and quality of spring-calving beef cows depending on sire breed and month of lactation. Development of sustainable beef production systems may include selecting breed types whose milk yield and quality is less influenced by horn flies, allowing for better expression of genetic potential for milk yield in nutritionally challenging environments.

Effects of forage type, body condition and single-nucleotide polymorphisms in the bovine cytochrome P450 regulatory region on cow productivity.

Single-nucleotide polymorphisms (SNP) in the coding sequence of cytochrome p450 (CYP3A28) have been associated with milk yield and composition, and calving traits in cows. In this study, we aimed to determine whether (i) the CYP3A28 regulatory region was polymorphic and (ii) SNP genotype, forage type, body condition and their interactions affect cow productivity. Primers for CYP3A28 promoter were designed to amplify a 483-bp segment by PCR. Amplicon sequences revealed seven SNP (T-318C, T-113A, C-189T, T-78G, A6G, G17A and T21C) in Brahman (38 cows), Brahman x Angus reciprocal crosses (47 cows) and crossbreds (98 cows). Angus cows (n = 41) appeared to be fixed at those SNP locations. Genotype and forage {endophyte-infected tall fescue [KY+; Lolium arundinaceum (Schreb.) S. J. Darbyshire] vs. bermudagrass [Cynodon dactylon (L.) Pers.]} effects on lifetime (8-years) calving rate, and calf weaning weights and heights were determined in Herd 1 (126 cows); genotype and BC (low vs. moderate) effects on calving date and calving percent were determined in Herd 2 (98 cows). Four SNP (T-318C, T-113A, A06G and T21C) appeared to be related to cattle productivity, CC cows at T-318C having a lower (p < 0.05) lifetime calving rate than TC or TT cows (65%, 85% and 81% respectively). Cows that grazed KY+ and were TT at T-318C produced calves that tended (p < 0.07) to weigh less than their contemporaries. Moreover, calves of TT cows were shorter (p < 0.05) at weaning than calves of CC or TC cows. In Herd 2, moderate-BC cows that were TT or AA at T-318C, T-113A, T-78G, A6G and T21C had greater (p < 0.05) calving rates (74-80%) than heterozygous cows (46-60%), and low-BC cows that were AA at G17A calved at least 6 days earlier (p < 0.05) than heterozygous cows. Our findings suggest that SNP in the CYP3A28 regulatory region of Brahman-influenced cows are associated with cattle productivity.

Performance by spring and fall-calving cows grazing with full, limited, or no access to toxic Neotyphodium coenophialum-infected tall fescue.

Replacing toxic, wild-type Neotyphodium coenophialum-infected tall fescue (E+) with nontoxic, N. coenophialum-infected tall fescue (NE+) has improved cow performance, but producer acceptance of NE+ has been slow. The objective was to compare performance by spring- and fall-calving cows grazing either E+ or NE+ at different percentages of the total pasture area. Gelbvieh×Angus crossbred cows (n=178) were stratified by BW and age within calving season and allocated randomly to 1 of 14 groups representing 5 treatments for a 3-yr study: i) Fall-calving on 100% E+ (F100); ii) Spring-calving on 100% E+ (S100); iii) Fall-calving on 75% E+ and 25% NE+ (F75); iv) Spring-calving on 75% E+ and 25% NE+ (S75); and v) Spring-calving on 100% NE+ (SNE100). Groups allocated to F75 and S75 grazed E+ until approximately 28 d before breeding and weaning, then were then moved to their respective NE+ pasture area for 4 to 6 wk; those allocated to F100, S100, and SNE100 grazed their pastures throughout the entire year. Samples of tall fescue were gathered from specific cells within each pasture at the time cows were moved into that particular cell (∼1 sample/mo). Blood samples were collected from the cows at the start and end of the breeding season. Stocking rate for each treatment was 1 cow/ha. Forage IVDMD, CP, and total ergot alkaloid concentrations were affected (P<0.05) by the treatment×sampling date interaction. Hay offered, cow BW, and BCS at breeding, end of breeding, and at weaning were greater (P<0.05) from fall-calving vs. spring-calving. Cow BW at weaning was greater (P<0.05) from F75 and S75 vs. F100 and S100. The calving season×NE+ % interaction affected (P<0.05) calving rates. Preweaning calf BW gain, actual and adjusted weaning BW, ADG, sale price, and calf value at weaning were greater (P<0.05) from fall-calving vs. spring-calving and from SNE100 vs. S75 except for sale price which was greater (P<0.05) from S75 vs. SNE100. Cow concentrations of serum prolactin at breeding and serum NEFA at the end of breeding were affected (P<0.05) by the calving season×NE+ % interaction. Serum Zn and Cu concentrations from cows were affected (P<0.05) by calving season. A fall-calving season may be more desirable for cows grazing E+, resulting in greater calving rates, cow performance, and calf BW at weaning, whereas limited access to NE+ may increase calving rates, serum prolactin, and NEFA concentrations during certain times in the production cycle, particularly in spring-calving cows.

Effects of bovine cytochrome P450 single-nucleotide polymorphism, forage type and body condition on production traits in cattle.

Relating single-nucleotide polymorphisms (SNP) to cows with acceptable productivity could benefit cattle breeders in areas where tall fescue is the predominant forage. This study aimed to (i) identify SNPs in bovine cytochrome P450 3A28 (CYP3A28) and (ii) determine the associations between SNP genotype, forage and cow body condition (BC). Genotype (CC, CG or GG) and forage [Kentucky-31 wild-type endophyte-infected tall fescue (KY+) vs. bermudagrass] effects on milk volume and quality were determined in Herd 1 cows (123 cows); in Herd 2 (99 cows), genotype and BC (low vs. moderate) effects on ovarian follicle size, calving date and calving per cent were determined; and in Herd 3 (114 cows), effects of genotype and fescue cultivar [KY+ vs. non-toxic endophyte-infected tall fescue (HiMag4)] were related to calving per cent, calving date and weaning weights of both cow and her calf. A cytosine (C) to guanine (G) transversion at base 994 (C994G) in CYP3A28 was identified. There was a genotype × forage type interaction (p < 0.05) on milk protein in Herd 1 cows; CC cows grazing bermudagrass had greater milk protein percentage in relation to other cows in the herd. In Herd 2, BC and genotype × BC tended (p < 0.10) to influence follicle size and Julian calving date respectively. Diameter of the largest follicle tended to be larger in moderate BC than in low-BC cows; whereas, CC and CG cows in moderate BC and homozygous (CC and GG) cows in low BC tended to calve 14 days earlier in relation to CG cows in low BC. In Herd 3, there was a genotype × forage type interaction (p < 0.05) on calving per cent, Julian calving date and calf weaning weight. In this study, genetic alterations (G allele at C994G) coupled with nutritional factors (low BC and toxic tall fescue) resulted in overall lower productivity in cows.

Board-invited review: St. Anthony's Fire in livestock: causes, mechanisms, and potential solutions.

After a brief history of ergot alkaloids and ergotism, this review focuses on the metabolism and mechanisms of action of the ergot alkaloids. The authors provide models of how these alkaloids afflict grazing livestock under complex animal-plant/endophyte-environmental interactions. Alkaloid chemistry is presented to orient the reader to the structure-function relationships that are known to exist. Where appropriate, the medical literature is used to aid interpretation of livestock research and to provide insight into potential modes of action and alkaloid metabolism where these are not known for livestock. In closing the paper, we discuss management of ergot alkaloid intoxication in livestock and future research needs for this field of study.

Effects of body condition on measures of intramuscular and rump fat, endocrine factors, and calving rate of beef cows grazing common bermudagrass or endophyte-infected tall fescue.

Multiparous beef cows were managed to achieve marginal (BCS = 4.7 ± 0.07; n = 106) or good (BCS = 6.6 ± 0.06; n = 121) body condition (BC) to determine the influence of forage environment on BW and BC changes, intramuscular fat percentage (IMF), rump fat (RF), and serum hormones during 2 yr. Cows within each BC were randomly assigned to graze either common bermudagrass (CB; n = 3 pastures/yr) or toxic endophyte-infected tall fescue (EI; n = 3 pastures/yr) during a 60-d breeding season. Blood samples were collected at d 0, 30, and 60 of the breeding season, and serum concentrations of prolactin (PRL), IGF-I, and cortisol (CORT) were quantified; PRL and progesterone (P(4)) also were quantified 10 d before the breeding season (d -10). Body weight and BCS were recorded during the breeding season (d 0, 30, and 60). Cow IMF and RF were measured via ultrasonography at the start and end of the breeding season. Cows with increased (>1 ng/mL) P(4) at the beginning of the breeding season (cyclic) had greater (P < 0.02) concentrations of PRL on d 30 and 60 compared with anestrous cows. A forage environment × BC interaction tended (P = 0.07) to influence PRL. Cows grazing CB independent of BC had increased PRL compared with cows grazing EI. Prolactin was decreased in good-BC cows grazing EI compared with cows grazing CB, and cows in marginal BC grazing EI had the least concentrations of PRL. Concentrations of IGF-I were similar (P > 0.10) among good- and marginal-BC cows grazing CB, as well as good-BC cows grazing EI; however, marginal-BC cows grazing EI had reduced (P < 0.04) concentrations of IGF-I compared with all other groups. Cows in marginal BC grazing CB gained (P = 0.02) the most BW during the breeding season, whereas good-BC cows grazing EI gained the least amount of BW. Marginal-BC cows grazing CB tended (P = 0.06) to increase BC during the breeding season, whereas good-BC cows grazing either CB or EI lost BC. Rump fat tended (P = 0.07) to increase during the breeding season in marginal-BC cows compared with cows in good BC. Calving rates were similar (P > 0.10) among good- (82%) and marginal- (84%) BC cows grazing CB, and good-BC cows grazing EI (79%); however, marginal-BC cows grazing EI had a reduced (P = 0.04) calving rate (61%). Cattle grazing EI during the breeding season lost BC. That reduction in BC may be communicated to the pituitary via hormones that include IGF-I or PRL or both, resulting in decreased calving rates.

Influence of body condition and forage type on prevalence of Escherichia coli O157:H7 and Salmonella in grazing beef cows.

AIM: To determine the influence of body condition (BC) and forage type on the prevalence of faecal shedding of Escherichia coli O157:H7 and Salmonella from beef cows. METHODS AND RESULTS: Thin or moderately conditioned cows (n = 115) were randomly assigned to graze either common bermudagrass (n = 3 pastures) or toxic endophyte-infected tall fescue (n = 3 pastures) for 62 days. Faecal samples were collected on day 0, 30 and 62. Overall percentage of faecal samples positive for E. coli O157:H7 was 2.6% and 2.0% for Salmonella. Percentage of cows positive for both E. coli O157:H7 and Salmonella on at least one occasion was 6.1%. BC, forage type or the interaction did not influence the prevalence of E. coli O157:H7 or Salmonella in the faeces of cows. CONCLUSIONS: BC at initiation of the grazing period or loss of BC in moderate conditioned cows during the grazing period did not influence faecal shedding of E. coli O157:H7 or Salmonella. Consumption of either forage type did not influence faecal shedding of either E. coli O157:H7 or Salmonella in beef cows of thin or moderate BC. SIGNIFICANCE AND IMPACT OF THE STUDY: Change in BC that typically occurs during the normal production cycle in grazing cows did not influence faecal shedding of pathogenic bacteria regardless of forage type.

Fate of Escherichia coli O157:H7 and Salmonella from contaminated manure slurry applied to soil surrounding tall fescue.

AIM: To investigate the potential transfer of Escherichia coli O157:H7 and Salmonella from contaminated manure slurry into the tissue of tall fescue plants. METHODS AND RESULTS: Tall fescue plants (n = 50) were fertilized with a manure slurry inoculated with E. coli O157:H7 and Salmonella. Soil was collected and tall fescue plants (n = 10 per day) harvested on day 1, 2, 4, 8, and 14 after manure slurry fertilization. Soil samples were positive for E. coli O157:H7 on all days and on day 1, 2, 8, and 14 for Salmonella. None of the plant tissue samples were positive for E. coli O157:H7 on day 1 or 2; however, 20%, 30% and 40% of plant tissue samples were positive for E. coli O157:H7 on day 4, 8, and 14, respectively. CONCLUSIONS: It may be possible that E. coli O157:H7 can become transmitted and internalized into tall fescue plant tissue within 4 days after exposure to an E. coli O157:H7-contaminated manure slurry. Salmonella did not appear to be transferred to tall fescue plant tissue. SIGNIFICANCE AND IMPACT OF THE STUDY: Faeces contaminated with E. coli O157:11H7 may be one means by which grazing ruminants spread bacterial pathogens to additional animals.

Influence of toxic endophyte-infected fescue on sperm characteristics and endocrine factors of yearling Brahman-influenced bulls.

Sixteen (mean age = 1.1 +/- 0.1 yr; mean BW = 478 +/- 34 kg) Brahman-influenced bulls were used to determine the influence of fescue type on sperm characteristics and serum concentrations of prolactin, cortisol, and testosterone. Bulls were blocked by BW, scrotal circumference (SC), and pregrazing sperm characteristics and randomly assigned to graze toxic endophyte-infected (EI; 4 bulls/pasture; 2 pastures) or novel endophyte-infected (NE; 4 bulls/pasture; 2 pastures) tall fescue for 121 d. Semen was collected by electroejaculation, and SC was measured and blood samples collected monthly. Sperm were evaluated for motility and morphology with an integrated visual optical system. Overall mean concentration of prolactin was decreased more (P < 0.01) in EI bulls than NE bulls from May to August. Scrotal circumference was not affected by fescue type (P = 0.58); overall SC averaged 36.7 +/- 2.3 cm. Percentage of live sperm was not different (P = 0.24) between NE bulls (80%) than EI bulls (67%) in July and August. Bulls grazing NE fescue had more (P < 0.06) motile sperm than EI bulls in July and August. Percentages of progressive (57 vs. 38%, NE and EI, respectively; P < 0.06) and rapid (67 vs. 46%, NE and EI, respectively; P = 0.04) sperm were greater from bulls grazing NE than EI bulls in July and August. Average velocity of the smoothed sperm path and progressive velocity in a straight line from the beginning to the end of the sperm track were slower (P < 0.09) in EI bulls than NE bulls and were slower (P = 0.04) in August compared with July. Mean width of head oscillation as the sperm swims was less (P < 0.06) in August than July. Concentrations of cortisol and testosterone were not (P > 0.10) influenced by fescue type. Semen from bulls grazing EI had reduced motility and morphology than bulls grazing NE. Detrimental effects of toxic fescue may not be mediated by cortisol, testosterone, or both. Semen quality of bulls grazing toxic EI tall fescue was decreased with increased maximum ambient temperatures.

Effects of the ergot alkaloids dihydroergotamine, ergonovine, and ergotamine on growth of Escherichia coli O157:H7 in vitro.

A series of experiments were conducted to evaluate the effects of ergot alkaloids (dihydroergotamine, ergonovine, and ergotamine) on E. coli O157:H7 in both pure and mixed ruminal fluid culture. Alkaloids were added to solutions of E. coli O157:H7 strains 933 (pure and ruminal cultures) and 6058 (ruminal culture only), and growth rates and colony-forming units (CFU) of E. coli O157:H7 were measured. Two mixtures of all three alkaloids at either 2 or 500 microM for each alkaloid decreased (p < 0.001) the growth rate of E. coli O157:H7 in pure culture compared to the individual alkaloids. Dihydroergotamine tended (p = 0.07) to reduce growth rate of E. coli O157:H7 in pure culture compared with ergonovine or ergotamine alone. Increased concentrations of dihydroergotamine and ergotamine decreased (p < 0.003) growth rate of E. coli O157:H7 but increasing concentrations of ergonovine did not influence (p > 0.10) E. coli O157:H7 growth rate. Similar to results in pure culture, a mixture of all three alkaloids at various concentrations for each alkaloid decreased (p < 0.001) the CFU of E. coli O157:H7 strain 6058 in mixed ruminal culture compared to the individual ergot alkaloids. Dihydroergotamine decreased (p = 0.04) CFU of E. coli O157:H7 strain 6058 when compared to ergonovine but CFU were similar (p > 0.10) between dihydroergotamine and ergotamine. Ruminal and (or) intestinal populations of E. coli O157:H7 may be influenced in livestock consuming endophyte-infected tall fescue, and these alterations could be due to the presence of ergot alkaloids in fescue plants.

Effects of fescue type and sampling date on the nitrogen disappearance kinetics of autumn-stockpiled tall fescue.

Two tall fescue [Lolium arundinaceum (Schreb.) Darbysh] forages, one an experimental host plant/endophyte association containing a novel endophyte that produces low or nil concentrations of ergot alkaloids (HM4) and the other a typical association of Kentucky 31 tall fescue and the wild-type endophyte (Neotyphodium coenophialum; E+), were autumn-stockpiled following late-summer clipping and fertilization with 56 kg/ha of N to assess N partitioning and ruminal disappearance kinetics of N for these autumn-stockpiled tall fescue forages. Beginning on December 4, 2003, sixteen 361 +/- 56.4-kg replacement dairy heifers were stratified by weight and breeding, and assigned to one of four 1.6-ha pastures (2 each of E+ and HM4) that were strip-grazed throughout the winter. Pastures were sampled before grazing was initiated (December 4), each time heifers were allowed access to a fresh pasture strip (December 26, January 15, and February 4), and when the study was terminated (February 26). Generally, fescue type and the fescue type x sampling date interaction exhibited only minor effects on total forage N, or partitioning of N within the cell solubles or the cell wall. For pregrazed forages, concentrations of N and N partitioned within the cell solubles both declined in a strongly linear relationship with sampling dates. In contrast, concentrations of cell-wall-associated N changed in erratic and often higher-ordered relationships with time, but the magnitude of these responses generally was limited. Unlike the partitioning of N within cell-wall and cell-soluble fractions, kinetic characteristics of ruminal N disappearance frequently exhibited interactions of fescue type and sampling date. For pregrazed forages, these included interactions for all response variables, and for postgrazed forages, fractions B and C, as well as rumen degradable protein. Ruminal disappearance rate for pregrazed E+ and HM4 exhibited quadratic (range = 0.057 to 0.082/h) and cubic (range = 0.057 to 0.075/h) relationships with time, respectively. For postgrazed E+ and HM4 forages, ruminal disappearance rate was unaffected (mean = 0.066/h) or only tended to be affected by sampling date (mean = 0.065/h), respectively. Concentrations of rumen degradable protein exhibited various curvilinear relationships with sampling dates, but disappearance was consistently extensive, and the overall range was relatively narrow (71.3 to 78.9% of N). These findings suggest that ruminal disappearance of N for autumn-stockpiled tall fescue forages remains extensive throughout the winter months and is only affected minimally by fescue type, sampling date, and grazing status.

Endocrine factors and ovarian follicles are influenced by body condition and somatotropin in postpartum beef cows.

Multiparous beef (1/4 to 3/8 Bos indicus; n = 99) cows were managed to achieve low (BCS = 4.3 +/- 0.1; n = 50) or moderate (BCS = 6.1 +/- 0.1; n = 49) body condition (BC) to determine the influence of bovine (b) ST on the number of follicles, diameter of largest follicle, and serum concentrations of IGF-I, triiodothy-ronine (T3), thyroxine (T4), and prolactin. Beginning 32 d postpartum, cows within each BC were assigned randomly to treatment with or without bST. Non-bST-treated cows received no treatment, and treated cows were administered bST (Posilac, 500 mg, s.c.) on d 32, 46, and 60 postpartum. On d 60, all cows received a controlled internal drug-releasing (CIDR) device for 7 d and PGF(2alpha) at CIDR removal (CIDR-PGF(2alpha)). Blood samples (7 mL) were collected at each bST treatment and d 39 and 67 postpartum. Ultrasound was performed 1 d after CIDR-PGF(2alpha) to determine the number of small (2 to 9 mm) and large (>/=10 mm) follicles and the diameter of largest follicle. Cows treated with bST in low BC had increased (P < 0.05) IGF-I vs. low-BC non-bST-treated cows on d 39, 46, 60, and 67 postpartum. Prolactin and T3 were greater (P < 0.05) in moderate-BC than in low-BC cows on all sample dates. Thyroxine was greater (P < 0.001) in moderate-BC cows on d 46, 60, and 67 compared with low-BC cows. On d 67, bST-treated cows had greater (P < 0.05) T4 compared with non-bST-treated cows. Diameter of the largest follicle 1 d after CIDR-PGF(2alpha) was greater (P < 0.01) in anestrous cows treated with bST than for non-bST-treated anestrous cows. Diameter of the largest follicle was correlated with concentrations of IGF-I (r >/= 0.18; P /= 0.17; P /= 0.20; P

Effects of fescue type and sampling date on the ruminal disappearance kinetics of autumn-stockpiled tall fescue.

Two tall fescue (Festuca arundinacea Schreb.) forages, one an experimental host plant/endophyte association containing a novel endophyte (HM4) that produces low or nil concentrations of ergot alkaloids, and the other a typical association of Kentucky 31 tall fescue and the wild-type endophyte (Neotyphodium coenophialum; E+), were autumn-stockpiled following late-summer clipping and fertilization with 56 kg/ha of N to assess the nutritive value and ruminal disappearance kinetics of autumn-stockpiled tall fescue forages. Beginning on December 4, 2003, sixteen 361 +/- 56.4-kg replacement dairy heifers were stratified by weight and breeding and assigned to one of four 1.6-ha pastures (2 each of E+ and HM4) that were strip-grazed throughout the winter. Pastures were sampled before grazing was initiated (December 4), each time heifers were allowed access to a fresh strip (December 26, January 15, and February 4), and when the study was terminated (February 26). For fiber components, there were no interactions between fescue type and sampling date for either pregrazed or postgrazed forages. Over sampling dates, neutral detergent fiber (NDF; 56.5 to 67.8%), acid detergent fiber (27.7 to 34.9%), hemicellulose (28.8 to 34.0%), cellulose (25.0 to 28.1%), and lignin (3.61 to 10.05%) varied with sampling date, but patterns were almost exclusively curvilinear with time. Ruminal disappearance rate of dry matter (DM) was not affected by any treatment factor (overall mean for both pregrazed and postgrazed forages = 0.050 h(- 1)); similar responses were observed for NDF disappearance (overall mean = 0.048 h(- 1)). Interactions of fescue type and sampling date were observed for both pregrazed and postgrazed forages with respect to effective ruminal disappearance of DM; however, estimates were relatively high for all forages (overall mean = 64.0%). Effective disappearance of NDF was relatively extensive for all forages (overall mean = 55.4% of NDF). Based on the results of this trial, the endophyte status of stockpiled tall fescue forages had little practical effect on forage nutritive value and kinetics of ruminal DM or NDF disappearance. Overall, autumn-stockpiled tall fescue forages would appear to be a legitimate and lower cost alternative to harvested forages, and appear to possess suitable nutritional characteristics for developing dairy heifers in the Ozark Highlands.

Influence of body condition and bovine somatotropin on estrous behavior, reproductive performance, and concentrations of serum somatotropin and plasma fatty acids in postpartum Brahman-influenced cows.

Ninety-nine multiparous Brahman-influenced (1/4 to 3/8 Brahman) cows were managed to achieve low (BCS = 4.3 +/- 0.1; n = 50) or moderate (BCS = 6.1 +/- 0.1; n = 49) body condition (BC) to determine the influence of bovine somatotropin (bST) on estrous characteristics, reproductive performance, and concentrations of serum GH and plasma NEFA. Beginning 32 d postpartum, cows within each BC were assigned randomly to treatment with or without bST. Non-bST-treated cows received no treatment, and treated cows were administered bST (Posilac, 500 mg s.c.) on d -35, -21, and -7 before initiation of the breeding season. On d -7, all cows received an intravaginal, controlled internal drug-releasing (CIDR) device. On d 0 (initiation of the 70-d breeding season), the CIDR were removed and cows received prostaglandin F2alpha (PGF2alpha). Blood samples were collected from the median caudal vein of the cows at each bST treatment and at d -28 and 0. Estrous behavior was monitored by radiotelemetry during the first 30 d of the breeding season. Growth hormone was increased (P < 0.05) in low and moderate BC cows treated with bST. The percentage of cows detected in estrus during the first 30 d of the breeding season was decreased (P = 0.05) for low BC (64%) compared with moderate BC (82%) cows. The interval to first estrus tended (P = 0.07) to be shorter in low BC-bST-treated cows (3.7 +/- 1.9 d) than in moderate BC-bST-treated cows (9.6 +/- 1.8 d). During the first 30 d of the breeding season, cows in low BC had a decreased (P = 0.02) number of mounts received and increased (P = 0.001) quiescence between mounts compared with cows in moderate BC. The number of mounts received was reduced (P = 0.04) in bST-treated cows. More (P = 0.02) cows treated with bST became pregnant during the first 3 d of the breeding season compared with non-bST-treated cows. The cumulative first-service conception rate tended (P = 0.07) to be greater for bST-low BC cows than non-bST-treated cows in low or moderate BC. On d 0, NEFA were greater (P < 0.05) in bST-treated vs. non-bST-treated cows. Low BC and bST reduced the intensity of behavioral estrus in postpartum Brahman-influenced cows. However, bST increased the first-service conception rate during the first 30 d of breeding and pregnancy rates during the first 3 d of breeding in postpartum Brahman-influenced cows.

Influence of dietary endophyte (Neotyphodium coenophialum)-infected tall fescue (Festuca arundinacea) seed on fecal shedding of antibiotic resistance-selected Escherichia coli O157:H7 in ewes.

The objectives were to determine the effects of short-term feeding of a toxic endophyte (Neotyphodium coenophialum)-infected tall fescue seed (Festuca arundinacea, cultivar 'Kentucky 31') on fecal shedding and intestinal concentrations of Escherichia coli O157:H7 and the concentrations of prolactin, cortisol, and NEFA in experimentally inoculated ewes. Twelve ewes (mean BW = 46 +/- 2 kg) were fed a diet containing either high endophyte-infected (HI-E) or low endophyte-infected (LO-E) tall fescue seed for 7 d. Each diet consisted of 50% (as-fed basis) tall fescue seed. Ewes were experimentally inoculated with antibiotic resistance-selected E. coli O157:H7 on d 1 of the feeding treatment, and fecal shedding of inoculated pathogens was monitored daily on d 2 to 6. On d 7, ewes were weighed and euthanized, and tissues and contents were sampled from the ileum, cecum, and rectum for quantitative enumeration of E. coli O157:H7. Urine was collected at euthanization to determine total ergot alkaloid concentrations. Ewes fed HI-E had lower (P < 0.001) DMI than did ewes fed LO-E (0.8 and 1.6 +/- 0.1 kg/d of DMI for HI-E and LO-E ewes, respectively); consequently, there was a tendency (P = 0.06) for HI-E ewes to lose 0.3 +/- 0.4 kg of BW/d and LO-E ewes to gain 0.2 +/- 0.4 kg of BW/d during the 7 d. Urinary ergot alkaloids were increased (P < 0.001) in ewes fed HI-E (47.8 +/- 9.4 ng/mg of creatinine) compared with those fed LO-E (6.2 +/- 9.4 ng/mg of creatinine). Prolactin tended (P = 0.06) to be decreased in ewes fed HI-E (7.2 +/- 7.0 ng/mL) compared with those fed LO-E (27.7 +/- 7.0 ng/mL). Fecal shedding of E. coli O157:H7 tended (P = 0.06) to be increased in HI-E ewes [5.4 cfu (log10)/g of feces] compared with LO-E ewes [4.5 cfu (log10)/g of feces]. The population of E. coli O157:H7 in luminal contents from the ileum, cecum, and rectum did not differ (P > 0.36) between treatments. Treatment did not influence (P = 0.30) the occurrence of E. coli O157:H7 in cecal or rectal tissues; however, ileal tissues from HI-E ewes tended (P = 0.12) to have an increased incidence of E. coli O157:H7. Concentrations of NEFA tended (P = 0.12) to be greater in HI-E ewes than in LO-E ewes, whereas cortisol was similar (P = 0.49) for HI-E and LO-E ewes. We conclude that short-term feeding of HI-E tall fescue seed may alter the concentrations of prolactin and NEFA, and may increase fecal shedding of E. coli O157:H7 in experimentally inoculated ewes.

Escherichia coli O157:H7 and Salmonella in water and soil from tall fescue paddocks.

Six 1-ha paddocks of tall fescue (Festuca arundinacea) grazed by Gelbvieh x Angus heifers from 1 March to 21 June 2005 were used to determine the prevalence of Escherichia coli O157:H7 and Salmonella in water tanks, and standing water and surface soil surrounding water tanks in tall fescue paddocks grazed by cattle. Paddocks included two each of Kentucky-31 endophyte-infected tall fescue (E+), Jesup tall fescue with the AR542 endophyte strain (MaxQ), and HiMag tall fescue with strain 4 endophyte (HiMag4). Samples were collected weekly (6 June to 5 July) from water tanks (n = 30), and standing water (n = 18) and surface soil (n = 30) surrounding the water tanks in each paddock commencing 3 weeks prior to termination of grazing until 2 weeks after cattle removal. Prevalence of E. coli O157:H7 tended (p = 0.07) to be increased in standing water and surface soil surrounding water tanks when cattle were present. Presence of cattle resulted in muddy conditions surrounding water tanks. Consumption of E+ tall fescue did not influence (p > 0.10) the prevalence of E. coli O157:H7 or Salmonella in or around water tanks. Neither E. coli O157:H7 or Salmonella were detected in water tanks. Total percentage of standing water samples positive for E. coli O157:H7 was 27.8% and 5.6% for Salmonella. Escherichia coli O157:H7 (6.7%) and Salmonella (10%) also were detected in the surface soil surrounding the water tanks. We conclude that areas surrounding water tanks in tall fescue paddocks can be reservoirs of pathogenic bacteria.

Estrous behavior and initiation of estrous cycles in postpartum Brahman-influenced cows after treatment with progesterone and prostaglandin F2alpha.

Spring-calving, crossbred (1/4 to 3/8 Brahman) primiparous (n = 56) and multiparous (n = 102) beef cows were used to evaluate the effects of progesterone, delivered via a controlled internal drug-releasing (CIDR) device, and prostaglandin F(2alpha) (PGF(2alpha)) on estrous behavior, synchronization rate, initiation of estrous cycles, and pregnancy rate during a 2-yr period. To determine luteal activity, weekly blood samples were collected 3 wk before initiation of a 75-d breeding season. Treated cows received a CIDR for 7 d beginning on d -7 of the breeding season. On d 0, CIDR were removed, and cows receiving CIDR were administered PGF(2alpha); control cows received no treatment. Cows were exposed to bulls, and estrous activity was monitored using a radiotelemetry system for the first 30 d of the breeding season. Treatment with CIDR-PGF(2alpha) increased (P < 0.05) the number of mounts received (22.5 +/- 3.0 vs. 13.7 +/- 3.9 for CIDR-PGF(2alpha) vs. untreated control cows, respectively) but did not influence duration of estrus or quiescence between mounts. Number of mounts received and duration of estrus were greater (P < 0.05) in multiparous compared with primiparous cows. Synchronization of estrus was greater (P < 0.05) in cows treated with CIDR-PGF(2alpha) (56%) compared with control cows (13%) during the first 3 d of the breeding season. More (P < 0.05) anestrous cows treated with CIDR-PGF(2alpha) than anestrous control cows were in estrus during the first 3 d (59 vs. 12%) and 30 d (82 vs. 63%) of the breeding season. Treatment with CIDR-PGF(2alpha) decreased (P < 0.05) the interval to first estrus after treatment during the first 30 d of the breeding season compared with control cows (5.5 +/- 1.1 vs. 9.0 +/- 1.4 d). First service conception rate was greater (P < 0.05) in CIDR-PGF(2alpha)-treated cows compared with control cows. Cyclic cows at initiation of the breeding season had an increased (P < 0.05) 75-d pregnancy rate compared with anestrous cows, and the pregnancy rate tended (P = 0.10) to be greater in multiparous compared with primiparous cows. We conclude that treatment of Brahman-influenced cows with progesterone via a CIDR for 7 d, along with administration of PGF(2alpha) at CIDR removal, increases the number of mounts received, improves synchronization and first service conception rates, decreases the interval to first estrus after treatment, and may be effective at inducing estrous cycles in anestrous cows.

Prevalence of Escherichia coli O157:H7 and Salmonella in beef steers consuming different forage diets.

AIMS: To compare the prevalence of faecal shedding of Escherichia coli O157:H7 and Salmonella in growing beef cattle consuming various forages. METHODS AND RESULTS: In Experiment I, faecal samples were collected from steers grazing either endophyte-infected (E+) tall fescue or common bermudagrass (CB). Steers grazing E+ tall fescue were confined to a dry-lot pen and fed CB hay ad libitum for 10 days. In Exp. II, faecal samples were collected from steers grazing either E+ or novel endophyte-infected (NE) tall fescue and treated with one of two anthelmintics: ivermectin (I) or fenbendazole (F). In Exp. I, prevalence of E. coli O157:H7 was less in E+ tall fescue steers fed CB hay than steers grazing CB. More I-treated steers shed Salmonella than F-treated steers at 42-day postanthelmintic treatment but shedding of Salmonella was similar between anthelmintics at day 63 in Exp. II. CONCLUSIONS: Faecal shedding of pathogenic bacteria was not affected by grazing E+ tall fescue. Alterations of forage diets may influence the prevalence of E. coli O157:H7, and anthelmintic treatment could affect faecal shedding of Salmonella. SIGNIFICANCE AND IMPACT OF THE STUDY: Knowledge of factors that influence shedding of pathogenic bacteria in cattle is necessary to develop on-farm intervention strategies aimed at reducing pathogen shedding.

Effect of rotation frequency and weaning date on forage measurements and growth performance by cows and calves grazing endophyte-infected tall fescue pastures overseeded with crabgrass and legumes.

A grazing study was initiated in April 2000 and continued through three calving and weaning cycles (ending July 2003) to investigate the effects of rotational grazing management (twice monthly [2M] vs. twice weekly [2W]) and weaning date (mid-April [EARLY] vs. early June [LATE]) on production of fall-calving cow-calf pairs (495 +/- 9.6 kg initial BW) grazing Neotyphodium coenophialum-infected tall fescue (Festuca arundinacea Schreb.) overseeded with legumes and crabgrass. Secondary objectives of the experiment were to monitor differences in quantity and quality of available forage and to evaluate changes in forage species composition. Pastures were dominated by tall fescue throughout the study, and the proportion of basal cover was greater (P < 0.05) in 2M than in 2W pastures. The percentage of legumes was very low across all treatment combinations, but the percentage of crabgrass continued to increase (P < 0.05) linearly and quadratically across years for both summer and fall sampling periods, regardless of rotation or weaning program. In vitro DM disappearance and mineral concentrations varied minimally because of rotation frequency or weaning date. Rotation frequency did not substantially affect (P = 0.11 to 0.97) cow BW, hay offered, milk production, calving interval, calf birth weight, or actual or adjusted weaning weights; however, 2M cows had 0.3 units higher (P < 0.05) BCS at the time of breeding than 2W cows. Calves weaned late had greater (P < 0.05) actual weaning weight and weighed more (P < 0.05) on the LATE weaning date than on the EARLY weaning date, but 205-d adjusted weaning weights did not differ (P = 0.74) across weaning dates. Therefore, rotation frequency and/or weaning date had little effect on forage species composition or forage quality. In addition, the rapid rotation program offered little advantage with respect to animal performance, and weaning fall-born calves grazing endophyte-infected tall fescue pastures at approximately 189 d of age seemed to be detrimental to calf performance compared with delaying weaning until 243 d of age.

Aerobic stability of wheat and orchardgrass round-bale silages during winter.

Using recently developed technology, balage is often stored in large (1.2 x 1.2 m) round bales that are wrapped in plastic film with an in-line wrapper. The aerobic stability of this fermented forage is important, particularly during winter months when it is fed to livestock or sold as a cash crop. Two types of forage, orchardgrass [Dactylis glomerata L.; 54.4% dry matter (DM)] and wheat (Triticum aestivum L.; 62.4% DM), were packaged in large round bales and wrapped with an in-line wrapper during May 2002. Twenty-one bales of each balage type were unwrapped and exposed to air on Dec. 10, 2002 for 0, 2, 4, 8, 16, 24, or 32 d (ambient temperature range = 0.6 to 19.4 degrees C) to evaluate aerobic stability. For both orchardgrass and wheat balage, final bale weight, concentration of DM, and pH were not affected by exposure time. Across both balage types, DM recoveries were > or = 97% for all bales, indicating that both balage types were very stable when exposed to air. For orchardgrass balage, exposure time had no effect on concentrations of NDF, ADF, hemicellulose, cellulose, or lignin, thereby indicating that little deterioration occurred. Similarly, no contrast relating any fiber component with exposure time was significant for wheat balage. Concentrations of crude protein (CP) were not affected by exposure time for wheat balage, but there was a tendency for exposed orchardgrass bales to have greater concentrations of CP than bales sampled on d 0. Exposure time had no effect on 48-h in situ digestibility of DM for wheat balage, but there was a tendency for a linear increase with exposure time for orchardgrass balage. However, the overall range (78.2 to 80.5%) over the 32-d exposure period was very narrow, and this response is probably of limited biological significance. Generally, concentrations of fermentation acids were low, primarily because of the high concentration of DM within these balages, and only minimal changes in these acids were observed over the exposure interval. These results suggest that the balage evaluated in this trial during winter conditions was very stable after exposure to air for up to 32 d. This should allow for considerable flexibility with respect to feeding, transport, and marketing of balage during winter months without significant aerobic deterioration.