Weaning and post-weaning performance by fall-born beef calves weaned on different dates in the spring from Neotyphodium coenophialum-infected tall fescue pastures

Fall-born calves grazing Neotyphodium coenophialum-infected tall fescue [E+; Lolium arundinaceum (Schreb.) Darbysh.] pastures should benefit from early weaning because of reduced exposure to fungal toxins. However, fall-born calves that grazed E+ and were weaned in mid-April had reduced post-weaning performance compared with calves managed similarly but weaned in early June. Gelbvieh × Angus calves (n = 238) were used in a 3-year study to determine the optimal time to wean fall-born calves grazing E+. Cow/calf pairs were allocated randomly to one of four weaning date treatments: 1) March 16 (177 ± 4.7 days of age; MarW), 2) April 13 (204 ± 4.7 days of age; AprW), 3) May 11 (236 ± 4.7 days of age; MayW), and 4) June 8 (264 ± 4.8 days of age; JuneW). On their assigned weaning date, calves were weighed, vaccinated, blood samples were collected, and calves were moved to 3.2-ha pastures adjacent to their dams for 14 days. After the weaning period, calves were weighed, blood samples were collected, and then calves were moved to pastures containing non-toxic forages. Birth weight and calf weights on MarW, AprW, and MayW weaning dates did not differ (P ≥ 0.21) across weaning date treatments. However, calf weaning weights on their respective weaning dates, weight on JuneW and on June 22 (14 days following the JuneW), daily gain between birth and June 22, and weight change between MarW and JuneW increased linearly (P < 0.05) across weaning dates. Linear decreases (P < 0.05) across weaning dates were noted for antibody titers to bovine virus diarrhea (BVD) and infectious bovine rhinotracheitis (IBR), serum Cu, and platelets at the time of actual weaning. Linear increases (P < 0.05) across weaning dates were noted for: i) total antioxidant potential and eosinophils at weaning; ii) changes in antibody titers to BVD and IBR, total antioxidant potential, and serum Zn during the 14-day post-weaning period; and iii) and changes in BVD and BRSV titers and serum Cu between actual weaning date and June 22. Heifer weight at breeding increased (P < 0.05) and steer weight at shipping, hot carcass weight and backfat thickness tended (P ≤ 0.10) to increase linearly across weaning dates. Final feedlot weight and gain did not differ (P ≥ 0.18) among weaning dates. Therefore, delaying weaning of fall-born calves grazing E+ pastures until early June may be beneficial for calf weight and immune function at weaning, and heifer weight at breeding, but those benefits in steers may be mitigated through the feedlot period.     

Ruminal in situ disappearance kinetics of nitrogen and neutral detergent insoluble nitrogen from common crabgrass forages sampled on seven dates in northern Arkansas

Southern crabgrass (Digitaria ciliaris [Retz.] Koel.) is often an undesirable species in field and forage crops, but visual observations suggest that livestock prefer it to many other summer forages. The objectives of this study were to assess the nutritive value of crabgrass sampled weekly between July 11 and August 22, 2001 and then to determine ruminal in situ disappearance kinetics of N and neutral detergent insoluble N (NDIN) for these forages. A secondary objective was to compare these kinetic estimates for crabgrass with those of alfalfa (Medicago sativa L.), bermudagrass (Cynodon dactylon [L.] Pers.), and or-chardgrass (Dactylis glomerata L.) as control hays. All kinetic evaluations were conducted with 5 ruminally cannulated Gelbvieh x Angus x Brangus steers (383 +/- 22.7 kg). Concentrations of N for crabgrass decreased linearly (P < or = 0.002) across sampling dates for leaf, stem, and whole-plant tissues. Conversely, percentages of the total N pool within NDIN and ADIN fractions generally increased over sampling dates in mostly linear patterns. For crabgrass, the immediately soluble portion of the total N pool (fraction A; overall mean = 54.6% of N) was greater (P < 0.001) than for all control hays. Crabgrass exhibited a more rapid N disappearance rate (overall mean = 0.093/h; expressed as a proportion disappearing/h) than that of bermudagrass (0.046/h; P < 0.001), but the disappearance rate for alfalfa N (0.223/h) was considerably faster (P < 0.001) than for crabgrass. The effective ruminal disappearance of N was greater (P < 0.001) for crabgrass (overall mean = 85.4%) than for the alfalfa (83.3%), bermudagrass (72.3%), or orchardgrass (76.0%) control hays. For alfalfa, the ruminal disappearance rate of NDIN (0.150/h) was more rapid (P < 0.001) than for crabgrass (overall mean = 0.110/h); however, the disappearance rate for crabgrass was faster than that for bermudagrass (0.072/h; P < 0.001) or for orchardgrass (0.098/h; P = 0.010). Effective ruminal disappearance of NDIN was greater (P < 0.001) for crabgrass (overall mean = 72.0%) than for the bermudagrass (69.0%) or alfalfa hays (50.5%), but there was no difference (P = 0.865) between crabgrass and orchardgrass (72.1%). Although crabgrass forages exhibited concentrations of total N that were comparable with those of alfalfa and rates of ruminal N disappearance that were < 50% of those for the alfalfa hay control, improvements in N use efficiency relative to alfalfa are questionable because of the excessively large Fraction A for crabgrass.     

Isolation and pathogenicity of Australian strains of Eimeria praecox and Eimeria mitis

Objective To determine the presence of E praecox and E mitis in Australia, to isolate representative strains of these species from chickens and determine their pathogenicity.
Design Morphological, physiological and cross protection studies were undertaken to confirm the identity of Australian isolates of E praecox and E mitis.
Procedure Oocysts were isolated from a backyard flock at Jimboomba, southeastern Queensland and numbers of E praecox and E mitis enriched by passage in chickens immune to five other species of poultry Eimeria . Oocysts of mean conformation and size of the two species were purified by single oocyst passage. Two isolates that closely matched recorded parameters for E praecox and E mitis were selected and designated JP and JM respectively. The cross protection between the isolates and E acervulina was determined by infection and challenge experiments. The virulence of the two isolates was determined by comparing weight gains of groups of birds inoculated with JP isolate or JM isolate with untreated groups.
Results Isolates JP and JM most closely matched recorded parameters of E praecox and E mitis respectively. Groups of chickens, previously infected with JP and JM isolates, showed no significant protection against infection with E acervulina . In a separate trial, groups of susceptible chickens inoculated with 10⁵ oocysts of JP and JM isolates showed significantly reduced weight gains compared with untreated controls.
Conclusion Isolates JP and JM are E praecox and E mitis respectively, confirming the presence of these species in Australia. These isolates were found capable of causing significant reductions in weight gains in susceptible chickens.     

Impact of heating-degree-day accumulation during bermudagrass hay storage on nutrient utilization by lambs.

Spontaneous heating in stored alfalfa (Medicago sativa) has reduced forage quality and DM and N digestibility through microbial respiration and Maillard polymer formation. The impact of heating-degree-day (HDD) accumulation in stored bermudagrass (Cynodon dactylon [L.] Pers.) was evaluated for its effect on nutrient utilization by lambs. Twenty Rambouillet wether lambs (53.1 +/- 0.74 kg) were used in a completely randomized total collection experiment. The hays selected for this study had previously undergone spontaneous heating, producing either 5, 119, 201, 273, or 401 HDD (> 35 degrees C) during a 60-d storage period. Lambs were offered diets of these hays at 1.5% of BW. Dry matter intake did not differ (P = 0.59) among hays. Linear relationships were detected between HDD and apparent digestibilities of DM (y = 59.1 - 0.016x; P < 0.01; R2 = 0.37), OM (y = 59.3 - 0.017x; P < 0.01; R2 = 0.43), NDF (y = 66.4 - 0.012x; P = 0.01; R2 = 0.30), and hemicellulose (y = 74.0 - 0.012x; P = 0.02; R2 = 0.27). Similarly, significant regressions were observed for fecal N excretion (g/d; y = 4.70 + 0.004x; P < 0.01; R2 = 0.68), apparent N absorbed (g/d; y = 7.4 - 0.005x; P < 0.01; R2 = 0.50), apparent N absorption (%; y = 61.2 - 0.038x; P < 0.01; R2 = 0.71), apparent neutral detergent insoluble nitrogen digestibility (%; y = 85.8 - 0.026x; P = 0.01; R2 = 0.73), and apparent acid detergent insoluble nitrogen digestibility (%; y = 1.5 + 0.101x; P < 0.01; R2 = 0.62). Therefore, spontaneous heating during the storage of bermudagrass hay has a negative effect on dry matter and fiber digestion and nitrogen absorption by lambs.