Modeling degradation ratios and nutrient availability of anthocyanidin-accumulating Lc-alfalfa populations in dairy cows

摘要

Dairy cattle eating fresh or ensiled alfalfa as the main portion of their diet often have low protein efficiency because of the rapid initial rate of ruminal protein degradation of fresh and ensiled alfalfa. Ruminal protein degradation of alfalfa might be reduced by introducing a gene that stimulates the accumulation of mono- or polymeric anthocyanidins in alfalfa. The objectives of this study were to fractionate protein and carbohydrates by in situ and chemical approaches, to evaluate in situ ruminal degradation characteristics and synchronization ratios, to determine protein availability to dairy cattle using the 2007 digestible intestinal protein/ rumen-degraded protein balance (DVE/OEB) protein system, and to determine net energy for lactation using the Dutch net energy for lactation (VEM) system for 3 newly developed transgenic winter hardy anthocyanidin-accumulating T_1 Lc-alfalfa populations. These T_1 Lc-alfalfa populations, called ~(T1)Beav Lcl, ~(T11)RambLc3, and ~(T1)RangLc4, had an average anthocyanidin accumulation of 163.4 μg/g of DM, whereas AC Grazeland (selected for a low initial rate of degradation) did not accumulate anthocyanidin. The basic chemical composition of the original samples, soluble and potentially degradable fractions, and degradation characteristics of crude protein and carbohydrates were similar in T_1 Lc-alfalfa and AC Grazeland. The undegradable in situ crude protein and neutral detergent fiber fraction had 1.3% lower CP and 4.8% lower CHO, respectively, in T_1 Lc-alfalfa compared with the amounts in AC Grazeland. The T_1 Lc-alfalfa had a 0.34 MJ/kg of DM higher calculated net energy for lactation and 1.9% of CP higher buffer soluble protein compared with that in AC Grazeland. By the protein evaluation model, it was predicted that T_1 Lc-alfalfa tended to have 11.9, 6.9, and 8.4 g/kg of DM higher rumen degradable protein, OEB, and intestinal available protein, respectively, compared with the amounts in AC Grazeland. The hourly OEB included an initial and substantial peak (oversupply) of protein relative to energy, which was highest in ~(T1)RangLc4 and lowest in ~(T1)RambLc3. The hourly OEB between 4 and 24 h was similar and more balanced for all 4 alfalfa populations. In conclusion, T_1 Lc-alfalfa accumulated anthocyanidin, tended to have higher predicted intestinal protein availability, and had higher predicted net energy of lactation availability for dairy cattle than did AC Grazeland.