Protein preservation and ruminal degradation of ensiled forage treated with heat, formic acid, ammonia, or microbial inoculant.

The objectives of this study were to determine whether treatment of forage with heat would reduce proteolysis during subsequent fermentation. In Experiment 1, direct-cut barley forage and alfalfa were untreated, microwaved, or steamed and then ensiled in laboratory silos as wilted forages. Silages of microwaved or steamed forage showed a marked increase in N bound to neutral detergent fiber and in the recovery of protein; however, alfalfa silages also had high pH values and concentrations of butyric acid. In Experiment 2, steam heating was compared with formic acid and NH3 treatments for the prevention of proteolysis in alfalfa silages. Silage of steamed alfalfa had a greater amount of N bound to neutral detergent fiber and greater recovery of protein than did control silage or silages of forage treated with formic acid or NH3. Silage of steamed forage had lower pH values than did silages of wilted, direct-cut, or control forage. Microbial innoculant added to steamed forage increased the recovery of protein. Silage of steamed forage had less aerobic stability than did silage of direct-cut forage. Ruminal degradability of crude protein (CP) and organic matter of silage from both experiments was evaluated. Degradability of CP was 8 to 26 percentage units lower in silages of microwaved or steamed forage in Experiment 1 than in silage of unheated forage because of slower degradation rates, but all had similar undegraded CP after incubation for 72 h. In Experiment 2, wilting, steam, formic acid, and NH3 treatments affected CP degradability similarly, but CP degradability was decreased when compared with silage of direct-cut forage without treatment.

Assessment of lipoprotein activators of skim milk lipoprotein lipase and the relationship between lipoprotein lipase activity and milk fat synthesis.

Bovine plasma and lipoproteins isolated by gel filtration chromatography were examined for their ability to activate skim milk lipoprotein lipase. Addition of equal amounts of protein from either triglyceride-rich lipoprotein, low density lipoprotein, high density lipoprotein or plasma to a lipoprotein lipase assay resulted in 6.0, 2.2, 2.5, or 1.1% hydrolysis of radiolabelled triglyceride emulsion. Lipoprotein lipase activity in skim milk was evaluated as an indicator of mammary lipid secretory capacity. Skim milk lipoprotein lipase activity was significantly lower immediately prepartum as compared with activity immediately postpartum (.2 vs. 5.4% of substrate hydrolyzed). Skim milk lipoprotein lipase was significantly higher during the final 12 d of lactation than in samples obtained 12 d after machine milking was terminated (5.6 vs. less than 1% of substrate hydrolyzed). Although skim milk lipoprotein lipase activity appeared positively related to mammary lipid secretory capacity during the time immediately surrounding initiation and cessation of copious milk production, activity between those periods was not correlated to milk fat percentage, milk fat yield, or stage of lactation.