The influence of formic acid and formaldehyde additives and type of harvesting machine on the utilization of nitrogen in lucerne silages: 1. The voluntary intake and nitrogen rerention of young sheep consuming the silages with and without intraperitoneal supplements of DL-methionine
Authors: Barry T. N. , Cook J. E. , Wilkins R. J. 
Published: March 2009

Silages were made from lucerne using either a flail or a precision-chop harvester without additive, with 8 1 formaldehyde (35% w/w/)/t or with 1·5, 3·0 or 6·01 formic acid (85% w/w)/t. The silages were deep frozen and later offered to young sheep with and without intraperitoneal injections of DL-methionine. Fresh lucerne, cut with both machines from the same crop, was deep frozen and offered to sheep with and without methionine injections in a separate experiment.

The untreated silages were characterized by extensive protein degradation, high contents of ammonia and acetic acid and low contents of lactic acid. Formaldehyde markedly reduced protein degradation and carbohydrate fermentation in the silo and caused a large reduction in nitrogen digestibility; these effects were of greater magnitude with precision-chopped than with flail-harvested silage. Voluntary intake and nitrogen retention were increased by formaldehyde application.

Increased rate of addition of formic acid reduced the overall extent of carbohydrate fermentation, decreased the proportion of fermentation products Which could be attributed to clostridial activity, and decreased protein degradation, though not by the same extent as did formaldehyde. With the precision-chop harvester, formic acid addition increased both voluntary intake and nitrogen retention. Intakes were low on the three flail-harvested silages made with formic acid, as these were heavily contaminated with soil. However, the additive improved nitrogen utilization and within this group of treatments intake increased with increasing rate of formic acid application. The increases in nitrogen retention with additive treatment resulted from increases in the quantity of nitrogen truly retained per unit of nitrogen intake as well as from increases in intake.

Methionine supplementation had no effect on voluntary intake, but caused a small and consistent improvement in nitrogen utilization except with the soil-contaminated silages. There was no effect of methionine supplementation on utilization of nitrogen in the fresh lucerne.

Voluntary intake, apparent biological value and nitrogen retention all decreased linearly with increasing protein degradation and formation of acetic acid and ammonia. Separate regression equations were calculated for the prediction of organic-matter intake for silages made with the two types of harvester. These were parallel, but with intakes from the precision-chopped silages higher by ca. 20 g D.M./kg W0·75 per day. Precision chopping produced a similar advantage with the fresh lucerne. Data from silages made by the two harvesting methods fitted the same regressions for nitrogen retention, which decreased by 0·3 g/day for each 1% increase in ammonia-N (% total N). It was deduced that to produce silage with high nutritive value it is particularly important that the degradation of amino acids by proteolytic clostridia is prevented; restriction of the degradation in the silo of true protein to amino acids is apparently less important.