Impact of heating-degree-day accumulation during bermudagrass hay storage on nutrient utilization by lambs

Spontaneous heating in stored alfalfa (Medicago sativa) has reduced forage quality and DM and N digestibility through microbial respiration and Mailla rd polymer formation. The impact of heating-degree-day (HDD) accumulation i n stored bermudagrass (Cynodon dactylon [L.] Pers.) was evaluated for its e ffect on nutrient utilization by lambs. Twenty Rambouillet wether lambs (53 .1 +/- 0.74 kg) were used in a completely randomized total collection exper iment. The hays selected for this study had previously undergone spontaneou s heating, producing either 5, 119, 201, 273, or 401 HDD (> 35 degreesC) du ring a 60-d storage period. Lambs were offered diets of these hays at 1.5% of BW. Dry matter intake did not differ (P = 0.59) among hays. Linear relat ionships were detected between HDD and apparent digestibilities of DM (y = 59.1 - 0.016x; P < 0.01; R-2 = 0.37), OM (y = 59.3 - 0.017x; P < 0.01; R-2 = 0.43), NDF (y = 66.4 - 0.012x; P = 0.01; R-2 = 0.30), and hemicellulose ( y = 74.0 - 0.012x; P = 0.02; R-2 = 0.27). Similarly, significant regression s were observed for fecal N excretion (g/d; y = 4.70 + 0.004x; P < 0.01; R- 2 = 0.68), apparent N absorbed (g/d; y = 7.4 - 0.005x; P < 0.01; R = 0.50), apparent N absorption (11'e;; y = 61.2 0.038x; P < 0.01; R-2 = 0.71), appa rent neutral detergent insoluble nitrogen digestibility (%; y = 85.8 - 0.02 6x; P = 0.01; R-2 = 0.73), and apparent acid detergent insoluble nitrogen d igestibility (%; y = 1.5 + 0.101x; P < 0.01; R-2 = 0.62). Therefore, sponta neous heating during the storage of bermudagrass hay has a negative effect on dry matter and fiber digestion and nitrogen absorption by lambs.