Broderick G A, Abrams S M, Rotz C A
Agricultural Research Service, USDA US Dairy Forage Research Center, Madison, WI 53706.
J Dairy Sci. 1992 Sep;75(9):2440-6. doi: 10.3168/jds.S0022-0302(92)78005-9.
Eighty-nine samples, 45 of standing forage and 44 of baled hay, were collected from alfalfa harvested at various maturities over three cuttings each during 2 yr. Alfalfa was cut and conditioned mechanically; samples of standing forage were collected by removing bunches of forage from windrows and freeze-drying them. Forage was allowed to field cure and was harvested at an average 80% DM as small rectangular bales; samples of baled hay were collected by coring bales after storing for 3 to 6 mo. Samples were analyzed for DM, ADF, total N, fractions of total N present as ADIN, N degraded at 0 h, and potentially degradable protein N. Ruminal protein degradation rates and escapes were estimated using an inhibitor in vitro system, assuming that ADIN was unavailable and that ruminal passage rate was .06/h. Standing forage contained smaller fractions of ADIN and N degraded at 0 h, contained a larger fraction of potentially degradable N, and had more rapid degradation rates and lower estimated protein escapes than baled hay. Mean degradation rates and estimated escapes were .171/h and 24% for standing forage and .075/h and 40% for baled hay. There were no differences in degradation rate or estimated escape because of harvest year, and neither was significantly related to maturity or to ADF concentration. Results indicate a significant advantage in ruminal protein escape, compared with grazed alfalfa, for alfalfa harvested and stored as hay.
在两年时间里，从三次刈割的不同成熟度的苜蓿中采集了89个样本，其中45个是直立牧草样本，44个是打捆干草样本。苜蓿采用机械切割和调制；直立牧草样本是从草条中取出一束束牧草后进行冷冻干燥采集的。牧草在田间晾晒，以平均80%的干物质含量作为小长方形草捆收获；打捆干草样本是在储存3至6个月后通过取芯草捆采集的。对样本进行了干物质、酸性洗涤纤维、总氮、酸性洗涤不溶性氮占总氮的比例、0小时降解的氮以及潜在可降解蛋白氮的分析。使用体外抑制剂系统估计瘤胃蛋白质降解率和逃逸率，假设酸性洗涤不溶性氮不可利用，瘤胃通过率为0.06/小时。直立牧草中酸性洗涤不溶性氮和0小时降解的氮比例较小，潜在可降解氮的比例较大，降解速度更快，估计的蛋白质逃逸率比打捆干草低。直立牧草的平均降解率和估计逃逸率分别为0.171/小时和24%，打捆干草分别为0.075/小时和40%。由于收获年份不同，降解率或估计逃逸率没有差异，且两者均与成熟度或酸性洗涤纤维浓度无显著相关。结果表明，与放牧苜蓿相比，收获并储存为干草的苜蓿在瘤胃蛋白质逃逸方面具有显著优势。
