Sorghum forage as an alternative to corn silage in dairy cows feeding

Aim of the study was to study the possibility of substituting corn silage with low lignin (brown midrib, BMR)-sorghum silage in the diet of lactating cows. Two TMRs containing BMR333 single harvest sorghum forage silage (SF) or corn silage (CS) were fed to 60 Holstein dairy cows in a change-over design. Diets included (dry basis) 26.3% CS or 17.3% SF, 6.0% alfalfa hay, 11.0% Italian ryegrass hay and 56.6% or 65.7% concentrate for CS or SF diet, respectively. Diets had 15.5% CP, 31.5% aNDFom and 24.2% starch, on DM. Due to the low SF starch content (2.8% on DM), a higher amount of corn meal was included in the SF diet (5.7 vs 8.0 kg/d). Forages were also incubated in situ to determine rumen degradability and degradation rate (kd) of NDF. All data were statistically analyzed by SAS-GLM procedure. DMI was not affected by diet (24.4 vs 25.4 kg/d for CS and SF fed cows). Milk yield (32.6 and 33.1 kg/d for CS and SF diets), milk fat (4.16% for both diets) and milk protein (3.42 and 3.40% for CS and SF diets) were not affected by dietary treatment (NS). MUN was lower in the diet CS (9.2 vs9.9 mg/dl; P<0.001); this was probably due to the higher starch fermentability of corn silage as compared to corn meal, included at a higher proportion in the SF diet, resulting in a better N utilization for CS diet. The rate of aNDFom degradability (kd) was higher for SF, although only a trend was detected. On the other hand potentially degradable aNDFom (a+b) was higher for CS; thus, effective degradability was not different between the two forages (table 1), confirming the results obtained in vivo. BMR sorghum silage can be effectively used in dairy cow feeding, provided starch content of the diet is balanced. Table 1. In situ rumen DM and aNDFom degradability DM aNDFom CS SF SE P CS SF SE P a1 (%) 33.1 23.7 0.44 *** 3.63 3.27 1.08 NS b2 (%) 46.3 48.7 0.23 ** 67.3 63.3 1.55 NS kd (%/ h) 3.3 3.3 0.19 NS 2.5 3.10 0.17 0.07 a+b3 (%) 79.4 72.4 0.39 *** 70.9 66.6 0.71 * Effective deg4 49.5 40.8 0.73 ** 21.5 21.8 1.11 NS *P<0.05; ** P<0.01; *** P<0.001. 1soluble fraction; 2degradable fraction; 3 potentially degradable fraction; 4effective degradability with a passage rate of 6%/h