The aim of this study was to measure methane emissions (CH4) and herbage intake, and, on the basis of these results, obtain the methane yield (MY, methane yield as g CH4/kg dry matter intake (DMI) and Ym, methane yield as a percentage of Gross Energy intake), from beef cows grazing on native grasslands. We used forty pregnant heifers, with two treatments of herbage allowance (HA) adjusted seasonally (8 and 5 kg dry matter (DM)/kg cattle live weight (LW), on average), during autumn, winter and spring. Methane emissions (207 g CH4/d), organic matter intake (OMI, 7.7 kg organic matter (OM)/d), MY (23.6 g CH4/kg DMI) and Ym (7.4%), were similar between treatments. On the other hand, all variables had a marked increase in spring (10.8 kg OM/d and 312 g CH4/d), except for Ym. The methane emission factor from Intergovernmental Panel on Climate Change (IPCC) Tier 2 estimated with these results was 78 kg CH4/head/year. The results show that methane emissions and intake were influenced by the season, but not by the HA analyzed in this study. This information for cow–calf systems in native grasslands in Uruguay can be used in National greenhouse gases (GHG) inventories, representing a relevant contribution to global GHG inventories.
A grazing experiment was undertaken to assess the effects of two levels of herbage mass (HM) on herbage DM intake (DMI), fat and protein corrected milk yield (FPCM), grazing behaviour, energy expenditure (HP), and methane emissions (CH 4 ) of grazing dairy cows in spring. Treatments were a low HM (1447 kg DM/ha; LHM) or a high HM (1859 kg DM/ha; HHM). Pasture was composed mainly of cocksfoot (Dactylis glomerata) and lucerne (Medicago sativa), offered at a daily herbage allowance of 30 kg DM/cow, above 5 cm. Eight multiparous Holstein cows were used in a 2 × 2 Latin Square design in two 10-day periods. Despite the differences in pre-grazing HM between treatments, OM digestibility was not different (P = 0.28). Herbage mass did not affect DMI or FPCM. Grazing time was not different between treatments, but cows had a greater bite rate when grazing on LHM swards. However, HP did not differ between treatments. Daily methane emission (per cow), methane emission intensity (per kg FPCM) and methane yield (as percentage of gross energy intake) were not different. The lack of effect of the amount of pre-grazing HM on energy intake, confirms that the difference between HM treatments was beyond the limits that impose extra energy expenditure during grazing.
En ovejas nulíparas pastoreando campo natural que parieron al inicio o al final del invierno se comparó el estatus metabólico durante la gestación avanzada, parto y posparto temprano, el comportamiento maternal, la mortalidad de corderos, la producción y calidad de la leche, el peso (PV) de los corderos durante los primeros 60 días, la presentación de celos de las corderas en su primer otoño y el comportamiento reproductivo de las madres en el siguiente servicio. Se utilizaron 64 ovejas Corriedale nulíparas; 39 parieron a inicio (Grupo J) y las restantes 25 a final del invierno (Grupo S). Ni la mortalidad de corderos nacidos de parto simple durante los primeros 7 días de vida, ni el comportamiento maternal, ni la producción de leche fue diferente entre grupos. El estatus metabólico al parto fue mejor en el Grupo J que en el Grupo S (mayor PV, condición corporal, concentración plasmática de glucosa, colesterol, y proteína total, y menor de urea; P<0,05). Sin embargo, esta situación se revirtió durante el pos parto temprano. La calidad de leche fue mejor en el Grupo J que en el S (mayor contenido de proteína y grasa; P<0.0001). El PV de los corderos al nacer (PNAC) no fue diferente, pero la media global fue mayor en el Grupo S que en el J (Grupo S: 9.51 ± 0.21 kg vs Grupo J: 8.87 ± 0.21 kg; P = 0.05). No se observaron consecuencias en el comportamiento reproductivo en las ovejas al segundo servicio. Tampoco se observó mayor proporción de corderas en celo en su primer otoño. Los resultados permiten concluir que adelantar el mes de parto al inicio del invierno aumenta el estatus metabólico de la oveja al parto sin efectos sobre el PNAC, mortalidad de los corderos, o el comportamiento maternal.
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