Nitrogen balance and blood urea nitrogen by gestating sheep offered alfalfa silage wrapped with or without an enhanced oxygen barrier plastic after time delays up to three days

Authors: NIYIGENA, V. - University Of Arkansas; COFFEY, K. - University Of Arkansas; Coblentz, Wayne; PHILIPP, D. - University Of Arkansas; RHEIN, R. - University Of Arkansas; CALDWELL, J. - Delacon Usa, Inc; SHANKS, B. - Lincoln University Of Missouri

Submitted to: Small Ruminant Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/18/2021
Publication Date: 2/17/2021
Citation: Niyigena, V., Coffey, K., Coblentz, W.K., Philipp, D., Rhein, R., Caldwell, J., Shanks, B. 2021. Nitrogen balance and blood urea nitrogen by gestating sheep offered alfalfa silage wrapped with or without an enhanced oxygen barrier plastic after time delays up to three days. Small Ruminant Research. https://doi.org/10.1016/j.smallrumres.2021.106355.
DOI: https://doi.org/10.1016/j.smallrumres.2021.106355

Interpretive Summary: In normal farming operations, there are multiple situations that can result in unnecessary exposure of forages to oxygen prior to fermentation into silage. Many studies have been conducted to address the impact of the consequences of this type of exposure, such as the number of layers of plastic used to wrap silage bales, or silage packing density. Another scenario that occurs routinely is an unexpected time delay between baling and wrapping silages that also can increase exposure to oxygen. However, there is limited information regarding how pre-ensiling conditions affect subsequent forage protein utilization by ruminants. Therefore, the objective of this study was to investigate the effects of wrapping alfalfa round bales after 1, 2, or 3-day time delays with plastic embedded with (or without) an enhanced oxygen-limiting barrier on the subsequent N utilization by gestating sheep. Wrapping silage with an enhanced oxygen limiting barrier improved N retention by sheep without impacting concentrations of different nitrogenous components or apparent N absorption. Extending time delay between baling and wrapping was associated with heat damage, which increased insoluble N, and decreased N absorption. However, the reduction of N absorption due to heat damage did not impact overall N retention by sheep. However, heating alone was not responsible for these observations, because there are other confounding factors that occur when silages undergo spontaneous heating. Therefore, the nitrogen utilization results should be interpreted carefully while evaluating the impact of heat damage.

Technical Abstract: Exposing ensiling forage to oxygen can result in dry matter deterioration and reduce silage intake by animals. This study was conducted to investigate the effects of two different wrapping sources and time intervals between baling and wrapping on nitrogen utilization in gestating sheep offered alfalfa silage. Alfalfa silage was baled in large round bales (moisture concentration = 591 ± 43.0 g/kg), then wrapped with plastic using either an enhanced oxygen-limiting barrier (EOB) or no additional barrier (conventional wrap; CW) on the day of baling or 1, 2 or 3 d after baling. After 5 months of storage, silages were chopped, then offered randomly for ad libitum consumption to 16 gestating ewes [63.5 ± 1.71 kg body weight] to provide 2 observations per treatment for each of 3 experimental periods. Each period consisted of a 10-d dietary adaptation period followed by 7 d of total fecal and urine collection. Blood was collected immediately prior to feeding and four hours after feeding on the last day of each period. Data were analyzed using PROC MIXED of SAS for a 2 × 4 factorial treatment arrangement, while blood data were treated as repeated measures. When expressed as a portion of total N, neutral detergent insoluble N (NDIN) content of silage increased (P = 0.02) linearly and quadratically, and acid detergent insoluble N (ADIN) concentrations increased (P < 0.01) linearly with longer wrapping delays. Nitrogen apparent absorption (g/d and g/kg N intake) and urinary N (g/d) decreased (P = 0.04) linearly with extended time delays between baling and wrapping. Retained N (g/kg of N intake and of absorbed N) was greater (P = 0.04) from silage wrapped with EOB. Blood urea N concentrations (mg/dL) decreased (P = 0.02) quadratically with extended delay between baling and wrapping. Apparent absorption of NDIN (g/kg NDIN intake) increased (P = 0.03) linearly with extending time delay when silage was wrapped with EOB and linearly and quadratically (P < 0.01) when wrapped with CW. Apparent absorption of ADIN increased (P = 0.02) quadratically with increasing delay between baling and wrapping averaged across wrap types. Therefore, management practices to limit oxygen exposure during packaging and ensiling can prevent a decline in protein utilization by ruminants.