Effect of crabgrass (Digitaria ciliaris) hay harvest interval on forage quality and performance of growing calves fed mixed diets

¹ University of Arkansas, Division of Agriculture, Southwest Research and Extension Center, Hope 71801

^* To whom correspondence should be addressed. E-mail: pbeck{at}uaex.edu.

	Abstract

Twelve 0.81-ha crabgrass (Digitaria ciliaris [Retz.] Koel.) hay fields were harvested at 21, 35, and 49 d of regrowth (average phenologic growth stage of 30, 51, and 56, respectively). Increased harvest interval linearly decreased (P < 0.01) CP (14.1, 13.7, and 10.6% of DM, respectively) and increased (P < 0.01) NDF (65.3, 70.6, and 70.2% of DM, respectively) and ADF (35.7, 38.9, and 42.7% of DM, respectively). Hays were incorporated into 3 diets which contained 20% (DM basis) crabgrass hay, ground corn (33%), and soybean hulls (32%). Diets contained 14.4, 14.4, and 13.6% CP; 1.83, 1.72, 1.81 Mcal NEm/kg; and 1.21, 1.10, 1.17 Mcal NEg/kg; respectively. Diets were fed to beef calves in 12 pens at a rate of 2.3% (DM basis) of BW in one experiment (n = 120, initial BW 210 ± 4.4 kg) and ad libitum in another experiment (n = 60, initial BW 207 ± 4.4 kg). To measure passage rate of the hay and concentrate portions of the diets, 12 heifer calves (BW = 145 ± 4.5 kg) were individually fed 2.3% of BW for 14 d and dosed with Dy labeled soybean hulls and Yb labeled hay. In situ DMD of the hays and diets were determined using three ruminally cannulated steers (BW = 584 ± 10.4 kg). Data were analyzed as a completely random design using the mixed procedure of SAS. Least-square means were separated using orthogonal contrasts for linear and quadratic effects of hay harvest interval. Harvest interval did not affect (P 0.11) ADG of limit-fed calves during diet acclimation or growing phase (average 0.32 and 0.80 kg, respectively) or calves fed ad libitum (average 1.21 kg). Dry matter intake of calves fed ad libitum averaged 7.9 kg/d (3.28% of BW) and was not affected (P 0.22) by harvest interval. Gain:feed was not affected (P 0.20) by harvest interval (0.13 and 0.15 for limit fed and ad libitum fed calves, respectively). Increased hay harvest interval linearly increased (P < 0.01) ruminal retention time of the hay and tended (P = 0.06) to linearly increase ruminal retention time of concentrate portions of the diet. In situ analysis indicated harvest interval of hay linearly decreased (P 0.05) extent of degradability and effective degradability of DM and NDF of hays, but DM disappearance of the total diet did not differ (P 0.35). In the conditions of this study, increasing harvest interval of crabgrass hay from 21 to 49 d had no deleterious impact on animal performance or feed efficiency when fed to growing calves in high-concentrate mixture.

Key Words: cattle, digitaria ciliaris, growth, hay quality

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