The effects of synchronizing the rate of dietary energy and nitrogen supply to the rumen on milk production and metabolism of ewes offered grass silage based diets

Twenty-four multiparous ewes were used to test the hypothesis that synchron izing the hourly rate of release of energy and nitrogen in the rumen would optimize milk production. Three diets were formulated using the in situ deg radability of the food ingredients, to differ in their rate of organic matt er (OM) and nitrogen (N) release in the rumen. All diets contained 400 g gr ass silage per kg dry matter (DM) and were predicted to have a similar cont ent of metabolizable energy (11.8 MJ/kg DM), metabolizable protein (102 g/k g DM), neutral-detergent fibre (365 g/kg DM) and daily untie of N : OM supp ly to the rumen but differ in their hourly pattern of nutrient release to b e either synchronous (S), asynchronous (A) or intermediate (I). The diets w ere offered ad libitum as a complete feed in a 3 X 3 Latin-square design co nsisting of three periods each of 28 days duration. Synchronizing the hourl y supply of energy and N to the rumen did not significantly alter milk or m ilkfat yield (g/d), milk protein content (g/kg), DM intake (kg/day), total time spent eating or the number of meals per day. However, compared with ew es offered diets I or A, those offered diet S had a lower milkfat content ( g/kg; P < 0.05) whilst protein yield (g/day) tended to be increased (P = 0. 05). Animals offered the synchronous diet (S) had lower plasma urea concent rations throughout the day and significantly higher beta-hydroxybutyrate co ncentrations at 14:00 and 18:00 h than those offered diets I or A. In concl usion, synchronizing dietary energy and N supply to the rumen did not have a major effect on milk production in ewes.