Open PRAIRIE: Open Public Research Access Institutional Repository and Information Exchange
Abstract
An extruded blend of 44% crude protein soybean meal (50%), sunflower seeds (45%), and premix (5%) was evaluated as a protein and energy source for dairy cows in early lactation. Thirty Holstein cows (24 multiparos and 6 primiparous) were assigned to either a corn-oats-soybean meal concentrate (SBM) or a concentrate where soy-sunflower blend replaced all soybean meal and portions of corn and oats (SSF). Dry matter of total mixed diets was 36% corn silage, 21% alfalfa haylage, and 43% concentrate. Yields of milk (33.6 and 33.8 kg/day) and 4% fat-corrected milk (30.9 and 30.5 kg/day) were similar for cows fed SBM or SSF, while percentages of total solids (11.92 and 11.38), fat (3.55 and 3.30), protein (2.91 and 2.74), and solids-not-fat (8.38 and 8.09) were lower in milk from cows fed SSF. Milk from cows fed SSF contained fewer short and medium chain fatty acids, more 18-carbon fatty acids, and was more unsaturated than from cows fed SBM. Intakes of dry matter and changes in body weight were not different between diets. Ruminal fluid pH and molar ratio of acetate to propionate were higher in cows fed SSF, while concentrations of total volatile fatty acids and ammonia were lower in cows fed SSF. Concentrations of essential amino acids in arterial serum and calculated uptakes of amino acids by the mammary gland were similar between diets. Transfer efficiencies of phenylalanine, valine, isoleucine, leucine, and tyrosine were lower in cows fed SSF. In cows fed either diet, methionine appeared to be most limiting, while tryptophan and arginine were least limiting
