The effect of red clover (Trifolium pretense L.) accessions and ploidy on in vitro utilisable crude protein in red clover silage: A two-year comparative study

Sammanfattning

Variations in protein concentration and the ruminal nitrogen utilisation in diploid and tetraploid red clover (Trifolium pretense L.) silage across two years (2022 and 2023) were studied by using in vitro utilisable crude protein (uCP) method. A total of 45 in 2022 and 44 accessions in 2023 were assessed including four control varieties. Plant materials were harvested with a haldrup plot harvester, which was then allowed to wilt until they reached a dry matter (DM) concentration of 25% to 30%. After the determination of DM content, wilted forage was chopped and treated with a formic acid-based silage additive at a rate of 6 mL/kg fresh matter. Herbage was then vacuum-packed and placed to ensile for 100 days, after which the samples of the ensiled silage were taken for analysis and the rest was freeze-dried. The ammonia-N concentrations were determined during an in vitro incubation at 4, 9, 20 and 30h, used to determine the uCP at 16 h rumen retention time (uCP16). In both years all silage samples exhibited good fermentation characteristics. Low pH values (lower than 4.06 in 2023) and high concentration of lactic acid (35.15 g/kg DM in 2022 and 81.22 g/kg DM in 2023) compared to other volatile fatty acids indicative of well-preserved silage. Diploid red clover (RC) was higher in crude protein (CP) and lower in neutral detergent fibre (NDF) content than tetraploid RCs in both years. A strong positive correlation (R2 = 0.78) was indicated between uCP16 and CP content in the silage across the two years. A negative linear correlation between NDF and both uCP16 and CP indicates that higher content of fibre levels may compromise the ruminal protein utilisation. The uCP16 values of silages were significantly affected only by the year factor and not by ploidy. Three RC accessions had 5 to 9 g/kg DM lower uCP16 concentration than predicted by the model based on silage CP concentration, whereas 6 accessions had observed uCP16 values between 4 to 7 g/kg DM higher than predicted values. Those results indicate that selecting accessions with higher CP utilisation potential might be possible and that the CP concentration alone is not enough for selection for better CP efficiency in the rumen. Furthermore, numerical variations were observed in protein utilisation between tetraploids and diploids of RC accessions and significant differences between the years. Further research is warranted to evaluate the efficiency of protein utilisation in the rumen with red clover ploidies, and it is essential to further study, other parameters associated with protein utilisation in red clover.