. 2006. Effect of pasture type (alfalfa vs. grass) on methane and carbon dioxide production by yearling beef heifers. Can. J. Anim. Sci. 86: [409][410][411][412][413][414][415][416][417][418]. The objective of this study was to determine effect of pasture type on methane and carbon dioxide production by heifers grazing alfalfa or grass pastures at three sites across western Canada. All pastures were intensively managed so that heifers had ad libitum access to new forage material each day, and pastures were back-fenced to prevent the heifers accessing previously grazed areas. As measured using the sulfur hexafluoride (SF 6 ) tracer technique, total methane production at the Brandon, MB, and Swift Current, SK, sites was unaffected by pasture type (averaging 157.4 g CH 4 head -1 d -1 ), whereas at Lethbridge, AB, heifers grazing alfalfa produced more methane than did those on the grass pasture (162.8 vs. 113.5 g CH 4 head -1 d -1 ; P < 0.05). Calculated with dry matter intake (DMI) estimated by alkane analysis, methane production per unit DMI was 39% lower from heifers consuming grass compared with alfalfa (P < 0.001). When intakes were estimated by the Cornell Net Carbohydrate and Protein System (CNCPS) model, CH 4 production kg -1 DMI did not differ (P > 0.05) between pasture types. Loss of gross energy intake (GEI) to methane, as estimated by alkane analysis, was 6.9% for heifers grazing grass, and 9.6% for heifers grazing alfalfa (P < 0.001). Calculated using CNCPS, losses were similar (P > 0.05) between grass and alfalfa (5.8 vs. 6.2% of GEI, respectively). Carbon dioxide production per unit DMI did not differ between pasture types, irrespective of method used to estimate intake (alkanes or CNCPS). The method used to predict intake can have a major influence on calculated values when methane emissions are expressed as a percentage of GEI in grazing ruminants. At each site, CH 4 emissions and in vitro digestibility of the forage were influenced by the composition of the stand and the maturity of the forage at the time of harvest.
Background:Epidemiological studies suggest that increased ozone exposure during gestation may compromise fetal growth. In particular, the implantation stage of pregnancy is considered a key window of susceptibility for this outcome.Objectives:The main goals of this study were to investigate the effects of short-term ozone inhalation during implantation on fetal growth outcomes and to explore the potential for alterations in uterine arterial flow as a contributing mechanism.Methods:Pregnant Long-Evans rats were exposed to filtered air, 0.4 ppm ozone, or 0.8 ppm ozone for 4 h/d during implantation, on gestation days (GD) 5 and 6. Tail cuff blood pressure and uterine artery Doppler ultrasound were measured on GD 15, 19, and 21. To assess whether peri-implantation ozone exposure resulted in sustained pulmonary or systemic health effects, bronchoalveolar lavage fluid, serum metabolic and inflammatory end points, and kidney histopathology were evaluated in dams at GD 21. Growth parameters assessed in GD 21 offspring included fetal weight, length, and body composition.Results:Measures of maternal uterine arterial flow, including resistance index and mean velocity, indicated that resistance increased between GD 15 and GD 21 in 0.8 ppm dams but decreased in controls, although absolute values were similar in both groups on GD 21. Ozone-exposed dams also had lower serum glucose and higher free fatty acid concentrations than controls on GD 21. On GD 21, both male and female offspring had lower body weight than controls, and pooled subsets of 3 male and 3 female fetuses from litters exposed to 0.8 ppm ozone had lower lean mass and fat mass than pooled control offspring.Conclusions:Findings from our experimental model suggest that the offspring of dams exposed to ozone during implantation had reduced growth compared with controls, possibly as a consequence of ozone-induced vascular dysfunction. https://doi.org/10.1289/EHP2019
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