In vitro and in situ Ruminal Degradability of Oak Leaves (Quercus persica) as Affected by Growth Stage during Spring Season and Polyethylene Glycol Application

This study was conducted to identify the nutritive and anti-nutritive composition, in situ rumen degradabil-ity, and the kinetics of in vitro gas production of Persian oak (Quercus persica) leaves harvested at three growth stages during the spring season. A tannin bioassay was also performed using polyethylene glycol (PEG 6000) as a tannin-complexing agent in a gas production test. Leaves were harvested in monthly inter-vals in spring, starting on April when leaves were at the early vegetative stage, and then May and June. As the leaf maturity progressed, crude protein decreased but total phenols, total tannins, and hydrolysable tan-nins increased. Condensed tannin concentration was not affected by maturity stage (Average=13.0 mg leu-cocyanidin equivalent/g dry matter (DM)). As leaf maturity increased, the rapidly degradable A fraction of DM increased. In vitro gas production, metabolizable energy, in vitro DM degradability, ruminal NH3-N, and short-chain fatty acid concentrations were greatest in leaves harvested at the early vegetative stage (April) compared with other months. Application of PEG increased in vitro gas production, metabolizable energy, in vitro DM degradability, and NH3-N and short-chain fatty acid production in the rumen fluid compared with no addition of PEG. Overall, oak leaves harvested at the early vegetative stage appeared to be a good source of forage for ruminants. However, as leaf maturity increased, ruminal fermentability de-creased, which was improved with PEG addition

Effect of dietary starch source on milk production and composition of lactating Holstein cows

The objective of this study was to evaluate the effects of four sources of starch on milk production and composition, nutrient digestion and blood metabolites of lactating Holstein cows. Four multiparous Holstein cows (708 ± 70 kg of body weight; 83 ± 9 days in milk) were used in a 4 × 4 Latin square design with 21-d periods. The concentrate portion of the diet contained wheat, barley, maize or potato as the primary source of starch. Intake of dry matter (DM) ranged from 18.7 kg/d to 19 kg/d, and was similar among treatments. Milk production was higher in cows fed the wheat-based diet compared with other diets while the milk fat concentration of the cows fed the maize-based diet was the highest. Milk protein concentration was unaffected by the source of dietary starch. Cows fed the potato-based diet had a lower milk protein, lactose and solid-non-fat yield. Milk yield/kg of DM intake and net energy for lactation (NEL)/NEL intake were higher in cows fed wheat-, barley- or maize-based diets compared with those fed the potato-based diet. Feed nitrogen efficiency was higher in cows fed the maize-based diet compared with the other experimental diets. Total tract apparent digestibility of organic matter, crude protein and ether extract were higher in cows fed the wheat- or maize-based diets compared with those fed barley- or potato-based diets; however, total tract apparent digestibility of neutral detergent fibre and acid detergent fibre were higher in cows fed the wheatbased diet compared with those fed the potato-based diet. These results showed that improved production performance in cows fed the wheat-based diet appeared to be because of greater nutrient digestibility and greater nutrient utilization efficiency. Furthermore, potato starch is not superior to grain starch as a readily available energy source for lactating dairy cows.Keywords: Nutrient digestibility, nutrient efficiency, plasma metabolites, wheat, barley, potato, maiz