Barriers to natural regeneration in temperate forests across the USA

New Forests - For millennia, natural disturbance regimes, including anthropogenic fire and hunting practices, have led to forest regeneration patterns that created a diversity of forest lands...     

Gaseous and leaching nitrogen losses from no-tillage and conventional tillage systems following surface application of cattle manure

Previous studies have demonstrated inconsistent results on the impact of tillage systems on nitrogen (N) losses from field-applied manure. This study assessed the impact of no-tillage (NT) and conventional tillage (CT) systems on gaseous N losses, N₂O:N₂O + N₂ ratios and NO₃⁻-N leaching following surface application of cattle manure. The study was undertaken during the 2003/2004 and 2004/2005 seasons at two field sites in Nova Scotia namely, Streets Ridge (SR) in Cumberland County and the Bio-environmental Engineering Centre (BEEC) in Truro. Results showed that the NT system had higher (p < 0.05) NH₃ losses than CT. Over the two seasons, manure incorporation in CT reduced NH₃ losses on average by 86% at SR and 78% at BEEC relative to NT. At both sites and during both seasons, denitrification rates and N₂O fluxes in NT were generally higher than in CT plots, presumably due to higher soil water and organic matter content in NT. Over the two seasons, mean denitrification rates at SR were 239 and 119 g N ha⁻¹ d⁻¹, while N₂O fluxes were 120 and 64 g N ha⁻¹ d⁻¹ under NT and CT, respectively. At BEEC mean denitrification rates were 114 and 71 g N ha⁻¹ d⁻¹, while N₂O fluxes were 52 and 27 g N ha⁻¹ d⁻¹ under NT and CT, respectively. Conversely, N₂O:N₂O + N₂ ratios were lower in NT than CT suggesting more complete reduction of N₂O to N₂ under NT. When averaged across all soil depths, NO₃⁻-N was higher (p < 0.05) in CT than NT. Nitrate-N decreased with depth at both sites regardless of tillage. In most cases, NO₃⁻-N was higher under CT than NT at all soil depths. Similarly, flow-weighted average NO₃⁻-N concentrations in drainage water were generally higher under CT. This may be partly attributed to higher denitrification rates under NT. Therefore, NT may be a viable strategy to remove NO₃⁻-N from the soil, and thus, reduce NO₃⁻-N contamination of groundwater. However, it should be noted that while the use of NT reduces NO₃⁻-N leaching it may come with unintended environmental tradeoffs, including increased NH₃ and N₂O emissions.     

Prevalence and risk factors for Cryptosporidium spp. infection in young calves

A cross-sectional study was designed to investigate the prevalence and risk factors for Cryptosporidium infection in young calves. Forty-one farms in a discrete, densely farmed 100 km2 area of North West England were visited over a 3-week period and 215 faecal samples were collected from young calves. Farms were not selected on the basis of existing scour problems. At the time of sampling, several investigator-observed variables were recorded at the pen, animal and stool levels. Samples were screened and 60/215 were confirmed as positive by PCR of the 18S rRNA gene. Risk factors for infection were explored using multilevel multivariable logistic regression with farm as a random effect. Age was significant in the final model, with a higher risk of infection in calves aged 8-21 days, when compared to those aged 0-7 days. The depth of the bedding was also significant in the final model, with calves housed in bedding 11-15 cm deep being at lower risk of infection than those on beds 0-5 cm deep. Consistency of the faeces was highly correlated with age and colour of the faeces and was not significantly associated with infection when these variables, and clustering at farm-level, were accounted for. This is interesting as Cryptosporidium is considered to be a primary enteropathogen. The results suggest that intervention strategies should be targeted at calves under 21 days old. These animals represent a significant reservoir of infection on the farm and may also pose a risk to public health, assuming that the species and genotypes shed are zoonotic pathogens.     

A study of feline upper respiratory tract disease with reference to prevalence and risk factors for infection with feline calicivirus and feline herpesvirus.

A cross-sectional survey of a convenience sample of cats was carried out to determine the prevalence of and risk factors for respiratory tract disease, feline calicivirus (FCV) infection and feline herpesvirus (FHV) infection. Seven hundred and forty cats were studied; samples for isolation of FCV and FHV were obtained from 622 (84%). Data on individual cat and household variables were obtained by questionnaire for each cat and analysed using univariable and logistic regression analysis. Thirty-eight percent (282/740) of cats surveyed had respiratory tract disease. Eighteen of 24 predictor variables were found to be significantly (P<0.05) associated with the presence of respiratory tract disease in a cat on univariable analysis. Following logistic regression, several factors retained significance including isolation of FCV and FHV, younger cats (4-11 months of age) and multiple cat households. A negative association was found with breeding catteries and other types of household in comparison with rescue catteries. Overall, feline calicivirus was isolated from 162/622 (26%) of cats sampled; 33% of the cats with respiratory tract disease were FCV positive compared to 21% of healthy cats. Variables significantly associated with FCV isolation on logistic regression were the presence of respiratory tract disease and contact with dogs with and without respiratory tract disease. Feline herpesvirus was isolated from 30/622 (5%) of all cats sampled; 11% of cats with respiratory tract disease were FHV positive compared to 1% of healthy cats. Variables significantly associated with FHV isolation on univariable analysis included age, gender, and the presence of respiratory tract disease. Vaccination showed a negative association. Logistic regression analysis of the data for FHV was limited by the sample size and the low prevalence of FHV.     

Effects of bovine somatotropin and ruminally undegraded protein on feed intake, live weight gain, and mohair production by yearling Angora wethers.

Yearling Angora wethers (n = 24; 24+/-1.0 kg BW) were used in an experiment with a 2 x 2 factorial arrangement of treatments to investigate effects of bovine somatotropin (bST) treatment and dietary level of ruminally undegraded protein on DMI, ADG, and mohair production. Untreated casein (UC) or casein treated with formaldehyde (TC) was included at 7% DM of a diet containing 11% CP and 46% concentrate. A slow-release bST form was administered weekly to deliver 0 (Control) or 100 microg/ (kg BW.d) of bST. Plasma concentrations of bST and IGF-I were increased (P < .05) during the 7-d period following bST injection. Ruminal fluid ammonia N concentration was lower (P < .01) for TC than for UC before feeding (6.6 vs 7.5 mg/dL) and 4 h later (8.2 vs 12.2 mg/dL), and total VFA concentration was lower (P < .01) for TC than for UC. Treatment with bST decreased (P = .08) DMI with UC (1.15 vs .91 kg/d) and increased (P = .08) DMI with TC (.95 vs 1.06 kg/d). Formaldehyde treatment of casein increased ADG (65, 74, 55, and 91 g/d; P = .03) and clean fleece production (P < .01; 14.1, 17.3, 15.0, and 18.4 g/d for UC-Control, TC-Control, UC-bST, and TC-bST, respectively), with no effect of bST during the 8-wk period of treatment or for the 8 wk thereafter (P > .10). In conclusion, with yearling Angora wethers, bST does not seem useful to enhance mohair production and may not alter effects of dietary level of ruminally undegradable protein on mohair production.     

An investigation of carbohydrate and protein degradation ratios,nitrogen to energy synchronization and hourly effective rumen digestion of barley: effect of variety and growth year

The objective of this study was to investigate rumen available soluble, insoluble and total protein (CP), estimated structural (SC) and non‐structural carbohydrate (starch: ST), degradation characteristic ratios and hourly effective degradation of six barley varieties during three consecutive growth years (2003, 2004, 2005). The magnitude of the differences was determined between the varieties and growth years. Measured degradation kinetics included soluble fraction (S), undegradable fraction (U), lag time (T₀) and rate of degradation (K_d) of the insoluble but degradable fraction (D). Rumen available soluble, insoluble, and total N, SC and ST and the rumen degradation characteristic ratios were determined using the Tamminga rumen degradation ratio system. Characteristics of the hourly effective degradation between N and carbohydrate (CHO) among the six barley varieties for 3 years were also studied. The degradation ratios included were total rumen available N and carbohydrate ratio (FN/FCHO), rumen available soluble N and carbohydrate ratio (SN/SCHO), and rumen available insoluble N and carbohydrate ratio (EN/ECHO). Results show that both the barley variety and growth year had a significant effect on degradation kinetics (S, D, U, T₀ and/or K_d). Differences in the ratio of FN/FCHO among varieties ranged from 16.6 to 19.0 g/kg (p < 0.01). There was no difference in SN/SCHO (p > 0.05) with an average of 4.9 g/kg. The difference in the EN/ECHO ratio tended to be significant among the varieties (p = 0.069) ranging from 18.4 to 21.3 g/kg. Differences in the hourly effective degradation between N and CHO were relatively small at shorter incubation times (2–4 h) However, as the length of rumen incubation increased (12–24 h), much larger differences in the rate of effective hourly degradation were observed. In conclusion, both barley variety and growth year had significant effects on rumen degradation kinetics. The mean FN/FCHO ratio of 17.2 (16.6–19.0) was observed for the six barley varieties in this experiment. All barley varieties exhibited a less optimal rumen fermentation ratio (17.2 < optimum: FN/FCHO = 25 to 33 g N per kg CHO). The large differences in the degradation kinetics, characteristics ratios and hourly effective degradation among barley varieties and growth years may help to explain some of the large variations that are seen in cattle performance.