Fishmeal supplementation to grazing dairy cows in early lactation.

Our objectives were to determine if grazing dairy cows would respond to fishmeal supplementation and to determine if responses could be explained by stimulation of adipose tissue lipolysis. Thirty-four multiparous Holstein cows (25+/-11 DIM) were supplemented with isonitrogenous concentrates containing either fishmeal or pelleted sunflower meal. On a dry matter (DM) basis, concentrates contained fishmeal (14.5%) or sunflower meal (24.2%), corn grain (55.6% and 50.6%), wheat bran (26.7% and 22%), a mineral-vitamin complex (2.9%) and a flavoring agent (0.3%). Concentrates were consumed at a rate of 5 kg/cow per day. Herbage allowance averaged 49.8+/-6.1 kg of DM/cow per d. Milk (26.8 vs. 25.2 kg/d), fat-corrected milk (23.9 vs. 22.2 kg/d) and milk protein yields (0.90 vs. 0.81 kg/d) were increased by fishmeal. Milk protein percentage was similar among treatments. Milk fat yield and milk and plasma urea nitrogen tended to be higher in cows fed fishmeal. Plasma glucose and nonesterified fatty acids concentrations and differences in concentrations between jugular and mammary veins were increased by fishmeal. The in vivo lipolytic response to a beta-adrenergic agent or the antilipolytic + hypoglycemic action of insulin were not affected. The higher milk production observed with fishmeal can be explained by the quantity and quality of the absorbed protein, higher glucose availability to the mammary gland, and increased lipid mobilization without change in responsiveness of the adipose tissue to lipolytic stimuli.