Replacing alfalfa silage with tannin-containing birdsfoot trefoil silage in total mixed rations for lactating dairy cows

Authors: BRODERICK, GLEN - Retired ARS Employee; Grabber, John; MUCK, RICHARD - Retired ARS Employee; HYMES-FECHT, URSULA - Former ARS Employee

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/10/2017
Publication Date: 3/3/2017
Publication URL: http://handle.nal.usda.gov/10113/5650880
Citation: Broderick, G.A., Grabber, J.H., Muck, R.E., Hymes-Fecht, U.C. 2017. Replacing alfalfa silage with tannin-containing birdsfoot trefoil silage in total mixed rations for lactating dairy cows. Journal of Dairy Science. doi: 10.3168/jds.2016-12073.

Interpretive Summary: Low concentrations of condensed tannin in forage legumes fed to cows can improve protein utilization and milk production while reducing excretion of urinary nitrogen that is susceptible to loss in the environment. However, the optimal amount of tannin for maximizing cow performance is not known. In this study, we compared cow responses to silages made from: 1) several harvests of alfalfa (contains no tannins naturally), and; 2) three populations of birdsfoot trefoil with varying amounts of tannin. Diets formulated with birdsfoot trefoil silages containing 0.5% tannin had the greatest feed intake and yields of both energy-corrected milk and milk protein. Compared to alfalfa silage diets, all diets containing birdsfoot trefoil had reduced excretion of urea in milk and less nitrogen excreted in urine, but this was accompanied by little or no improvement in protein-use efficiency in terms of feed protein conversion to milk protein. In a previous study, we found that feeding birdsfoot trefoil silages containing 1.6% tannin in place of alfalfa silage had no effect on feed intake, but caused much larger gains in energy-corrected milk yield, milk protein yield, and protein use-efficiency and more modest reductions in urea excretion in milk and nitrogen excretion in urine. Silage analyses indicated the inconsistent responses among trials may in part be related to crop growth environment or ensiling effects that altered the extent and type of tannin-protein interactions in birdsfoot trefoil silage. Differences in diet formulation among trials may have also influenced cow responses to tannin. The results from the previous and current trials suggest further work is needed to identify optimum tannin levels in forages and to reveal how forage growth environment, forage conservation methods, and diet formulation influence the milk production and protein-use efficiency of dairy cattle fed tannin-containing forages. This work will also help to optimize the production and feeding of alfalfa that is being bioengineered to produce tannin in its herbage.

Technical Abstract: Two lactation trials were conducted to assess the feeding value of silage made from populations of birdsfoot trefoil (BFT, Lotus corniculatus L.) that had been selected for low (BFTL), medium (BFTM), and high (BFTH) levels of condensed tannins (CT). These silages were compared to an alfalfa silage (AS) control when fed as the principal forage in diets offered to lactating dairy cows. In Trial 1, CT concentrations in BFT silages were 5.6 (BFTL), 11.7 (BFTM) and 16.6 (BFTH) g/kg DM. Thirty-two lactating Holstein cows were blocked by DIM and, within block, randomly assigned to treatment sequences in 8 balanced 4x4 Latin squares. Cows were fed total mixed rations (TMRs) containing (DM basis) 51% AS or one of the 3 BFT, plus corn silage, high moisture corn, soybean meal, minerals and vitamins. Although diets were formulated to contain 17.5% CP, AS contained 26% CP (DM basis) and that diet had 2 percentage units more CP than the BFT diets. Periods were 4-wk long (16 wks total); data were collected over the last 2-wk of each period. Results were analyzed using the mixed procedures of SAS. Intake ranged from 1.3 kg/d (BFTH) to 2.8 kg DM/d (BFTM) more on BFT than on AS; cows gained 0.5 kg BW/d on BFT while losing 0.14 kg BW/d on AS. There was a trend for a diet effect on ECM yield with greatest production on BFTM. Milk true protein yield was greater on BFTL and BFTM (average 1.33 kg/d) than on AS and BFTH (average 1.27 kg/d) and apparent N-efficiency was greater on all 3 BFT silages (average 27%) than on AS (25%). In Trial 2, CT concentrations in BFT silages were 5.1 (BFTL), 8.4 (BFTM) and 14.8 (BFTH) g/kg DM. Fifty lactating Holstein cows, including 10 fitted with ruminal cannulae, were fed a covariate diet for 2 wk and then blocked by parity, DIM, and cannulation status into 10 blocks and randomly assigned within blocks to 1 of 5 dietary treatments that were fed continuously for a total of 12 wk. Diets were fed as TMR and contained (DM basis) 48% AS (covariate and AS control), 16% AS plus 32% of 1 of the 3 BFT silages, or 48% of a mixture of equal DM from each BFT silages. The balance of the diets were corn silage, high moisture shelled corn, soy hulls, solvent soybean meal, supplemental fat, plus minerals and vitamins. As fed in the trial, diets averaged 16.5% CP and 30% NDF (DM basis). Intake of DM was greatest on BFTL and BFTM, intermediate on AS and the BFT mix, and lowest on BFTH but there were no differences in BW change, which averaged about 0.6 kg gain/d. The DMI responses were reflected in differences in milk yield; actual milk secretion was greatest on BFTL and BFTM, intermediate on BFT mix, and lowest on AS and BFTH. Mean differences in ECM yields followed a similar pattern with the ranking BFTL > BFTM > AS > BFTH; ECM yield on the BFT mix was not different from any other treatment. Yields of true protein, lactose and SNF were greatest on BFTL, next highest on BFTM, intermediate on AS and the BFT mix, and lowest on BFTH. Relative to AS in both trials, MUN was reduced and excretory N shifted from urine to feces on diets containing BFT silage. These results confirm our earlier findings showing improved milk and true protein yields and enhanced N-efficiency on diets containing BFT.