Effects of Dairy Slurry on the Nutritive Value and Fermentation Characteristics of Alfalfa Silages
Dairy producers frequently ask questions about the risks associated with applying dairy slurry onto growing alfalfa. Our objectives were to determine the effects of dairy-slurry application on the subsequent nutritive value and fermentation characteristics of alfalfa silages. Dairy slurry was applied to 0.17-ha plots of alfalfa; applications were made to the second and third cuttings during 2012 at mean rates of 42,437 ± 5505.6 L/ha and 41,729 ± 2503.5 L/ha, respectively. Four application strategies were evaluated. These included: i) no slurry; ii) slurry applied directly to stubble immediately after the preceding harvest; iii) slurry applied after 1 week of regrowth; or iv) slurry applied after 2 weeks of regrowth. All harvested forage was packaged in (0.9 x 0.9 x 1.8-m) large-rectangular bales that were ensiled as wrapped balage. Each bale was sampled on both a pre-ensiled (June or August 2012) and post-ensiled basis (May 2013). Yields of DM harvested from the second (2477 ± 175.8 kg/ha) and third (781 ± 73.9 kg/ha) cuttings were not affected (P ≥ 0.19) by slurry application treatment. By May 2013, all silages appeared to be well-fermented, with no indication of undesirable odor. Only minor differences across manure application treatments were observed for post-storage nutritive value, as well as final pH, unfermented water-soluble carbohydrates, and starch. Clostridium tyrobutyricum, which is known to negatively affect cheese production, was not detected in any forage on either a pre- or post-ensiled basis. On a pre-ensiled basis, counts (log10 genomic copies/g) for Clostridium Cluster 1 were greater for slurry-applied plots than for those not receiving slurry, and this response was consistent across the second (4.44 vs. 3.29; P < 0.01) and third cuttings (4.99 vs. 3.88; P < 0.01). Similar (P < 0.01) responses were observed on a post-ensiled basis; however, post-ensiled counts also were greater for delayed applications onto growing alfalfa compared with applications onto stubble for both the second (5.51 vs. 5.17; P = 0.02) and third (5.84 vs. 5.28; P < 0.01) cuttings. For the third cutting, counts also were greater following a 2-week application delay compared to a 1-week application delay (6.23 vs. 5.45; P < 0.01). These results suggest that the risk of secondary clostridial fermentations in alfalfa silages is greater following manure applications to alfalfa, and that applications to stubble are preferred (and less risky) compared to delayed applications onto growing alfalfa.
Keywords: alfalfa silage, clostridial fermentations, dairy slurry