Intake, Energy Expenditure and Methane Emissions of Grazing Dairy Cows at Two Pre-Grazing Herbage Masses

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 (CH4) 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.

Hepatic Expression of Insulin-Like Growth Factor-1 inUnderfed Pregnant Ewes

The liver is one of the most important visceral organs, which represents a large contribution to whole animal energyexpenditure and the major synthetic site of insulin-like growth factor-I （IGF-1） peptide. Decreased plane of nutrition acts byreducing the metabolic rate and mass of metabolic tissues, such as liver. Also, undernutrition results in the reduced circulating IGF-1concentrations, due to the uncoupled growth hormone-IGF （GH-IGF） axis. This study investigated whether a 22-day period ofundernutrition （half maintenance） could affect liver mass and IGF-1 protein and gene expression. Sixteen pregnant ewes fed all （n =9） or half （n = 7） of their maintenance energy requirements were slaughtered on day 7 of pregnancy （oestrus = day 0）. Body and livermass, IGF-1 plasmatic concentrations and liver IGF-1 mRNA and protein expression were determined. Liver mass and the proportionof liver mass to empty body weight were lower in underfed animals. While IGF-1 plasmatic concentrations were lower inundernourished ewes, no differences in liver mRNA expression were found. This is the first time that differences inimmunohistochemistry intensity and total content are reported in sheep. In summary, the decreased plasma IGF-I concentrationsinduced by undernutrition in ewes was not associated with its reduced hepatic mRNA or protein expression, but to a decrease in livermass.