|Hymes Fecht, Ursula|
Submitted to: International Silage Conference
Publication Type: Abstract Only
Publication Acceptance Date: 5/6/2012
Publication Date: N/A
Technical Abstract: Extensive degradation of crude protein (CP) in ensiled legumes impairs N utilization when these silages are fed to dairy cattle. Previously, we reported that feeding birdsfoot trefoil (BFT; Lotus corniculatus) with elevated levels of condensed tannin (CT) reduced silage nonprotein N and was associated with improved yield of milk and milk components (Hymes-Fecht et al., 2005). In this abstract, we report on results of a follow-up trial comparing milk production on silages prepared from subsequent harvests of the same BFT germplasm to that on lucerne silage (LS; Medicago sativa). Forages from BFT selected for low (LTBFT), medium (MTBFT) and high (HTBFT) concentrations of CT and lucerne were field-wilted to 35 to 40% dry matter (DM) and ensiled in plastic silos. Twenty-eight lactating Holstein cows were blocked by days-in-milk and, within block, randomly assigned to treatment sequences in 7 balanced 4x4 Latin squares. Cows were fed total mixed rations containing (DM basis) 50% LS or one of the 3 BFT, plus corn silage, high-moisture corn, soybean meal, minerals and vitamins. All diets contained about 17% CP and 27% neutral detergent fiber (NDF). Periods were 4 weeks long (16 weeks total); data were collected over the last 2 weeks of each period. Results were analyzed using the mixed procedures of SAS. Silages were similar in CP and NDF content. Intake of DM was lowest on LS and greatest on MTBFT; low dry matter intake (DMI) resulted in substantial body weight loss on LS relative to the 3 BFT diets. There were no differences in yield of milk or energy-corrected milk (ECM). The mean range in weight change of 0.67 kg/d between cows fed LS and BFT confounded results, but likely explained the greater efficiencies (milk/DMI and ECM/DMI) observed on LS. Greater yield of true protein on BFT silages with low and medium CT, along with reduced milk urea nitrogen (MUN) on all BFT diets, indicated improved N utilization relative to LS. However, our findings were confounded by lower DMI on LS. Improved true protein yield and reduced MUN indicated that N utilization was improved when BFT replaced LS in the diet of lactating cows. Higher true protein yield and numerically higher milk and ECM yield suggested that MTBFT was the optimal forage.