Intake, digestibility, rumen fermentation, and nitrogen balance in sheep offered alfalfa and tall fescue-mixtures harvested and ensiled after a frost

Authors: NIYIGENA, VALENS - University Of Arkansas; COFFEY, KENNETH - University Of Arkansas; Coblentz, Wayne; PHILIPP, DIRK - University Of Arkansas; ALTHABER, D. - University Of Arkansas; DIAZ GOMEZ, JOSE - University Of Arkansas; RHEIN, ROBERT - University Of Arkansas; PRUDEN, M. - University Of Arkansas

Submitted to: Animal Feed Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2022
Publication Date: 3/15/2022
Citation: Niyigena, V., Coffey, K.P., Coblentz, W.K., Philipp, D., Althaber, D., Diaz Gomez, J., Rhein, R.T., Pruden, M.C. 2022. Intake, digestibility, rumen fermentation, and nitrogen balance in sheep offered alfalfa and tall fescue-mixtures harvested and ensiled after a frost. Animal Feed Science and Technology. 286:115268. https://doi.org/10.1016/j.anifeedsci.2022.115268.
DOI: https://doi.org/10.1016/j.anifeedsci.2022.115268

Interpretive Summary: Harvesting forages after frost is advantageous because under freezing conditions, forages reduce plant respiration, thereby increasing the retention of non-structural carbohydrates. However, the negative impacts on the plant that follow frost can include plant leaf loss, and a decline in forage yield. Additionally, harvesting forage to conserve as dry hay in the fall season is very challenging due to shorter days and lower intensities of solar radiation. The objective of this study was to investigate the effects of blending different proportions of alfalfa and tall fescue harvested after frost on silage fermentation characteristics, and the subsequent effects on silage intake, digestibility and nitrogen balance by sheep. Harvesting alfalfa and tall fescue after frost and mixing both forages improved silage fermentation characteristics, especially the production of lactic acid, which is critical in preserving silage. However, intake, digestibility, and N utilization improved with mixing alfalfa and tall fescue, rather than feeding tall fescue alone. Rumen fermentation characteristics also were affected by the proportion of fescue in the diet, with a greater acetate production from animals offered the higher-fiber diet. Harvesting and ensiling alfalfa and tall fescue after frost may be an alternative approach to hay making, and may improve silage fermentation characteristics compared to alfalfa ensiled alone, but this approach can have significant negative impacts on forage utilization by ruminants.

Technical Abstract: The objective of this study was to determine the effects of ensiling mixtures of alfalfa (Medicago sativa L.) and tall fescue [Schedonorus arundinaceus (Schreb.) Dumort] forages that were harvested after frost events on the subsequent silage fermentation characteristics, as well as intake, digestibility and ruminal fermentation of these silages determined with ewe lambs. Forages were harvested in October of 2017, wilted, and blended as either alfalfa alone, 67% alfalfa + 33% novel endophyte-infected tall fescue, 33% alfalfa + 67% fescue, or 100% fescue. Twenty bins were lined with 2 plastic bags, packed (n = 5/trt) with the respective forages, stored for 3 months, and then assigned randomly to Dorper ewe lambs (n = 20; mean BW = 34.7 ± 6.65 kg) and offered for ad libitum consumption. Lambs were allowed 14 d of adaptation followed by 5 d of total feces and urine collection. Data were analyzed using PROC-MIXED of SAS and orthogonal polynomial trends were used to identify trends associated with different proportions of fescue to alfalfa. Silage total acids, lactate, and acetate concentrations increased linearly (P < 0.01), while silage ammonia decreased linearly and quadratically (P < 0.01) with increasing proportions of fescue in the silage. The proportions of lactate to total acids (g/kg total acids) increased linearly (P < 0.01) and quadratically (P < 0.05) with increasing fescue-to-alfalfa ratio. Dry matter (DM) and organic matter (OM) intake (g/kg BW), digestibility, and intake of digestible DM and OM (g/kg BW) decreased linearly (P < 0.01) as fescue proportion increased in the silages. Total volatile fatty acids (VFA), as well as concentrations of isovalerate and total branched-chain VFA decreased (P < 0.05) linearly and quadratically, butyrate and valerate decreased linearly (P < 0.01), and ruminal acetate concentrations increased (P < 0.01) linearly with increasing fescue concentration in the silage. All N utilization measurements (intake, absorption and retention) decreased with increasing fescue concentration in the silage (P < 0.01). Ensiling alfalfa with fescue that was harvested after a killing frost may improve forage fermentation characteristics, but may reduce intake and digestibility by sheep compared to feeding undiluted alfalfa silage.