198 Improving the nutritional value of wheat, canola, and flax straw to beef cattle with calcium hydroxide treatment.

Abstract Beef cattle can utilize byproduct and high fiber feeds, such as straw, that are not suitable for use in human and non-ruminant diets. However, straw has a low digestibility, limiting its inclusion in cattle diets. The objective of this study was to determine if calcium hydroxide [Ca(OH)2] treatment of straws improve nutrient digestibility. Six ruminally canulated heifers were used in a 6 × 6 Latin square to determine the effect of calcium hydroxide treatment of wheat (WS), canola (CS), and flax (FS) straw on dry matter intake (DMI), ruminal pH, the concentration of ruminal short-chain fatty acids (SCFA), and dry matter digestibility. Straw was included at 40% of the dietary dry matter (DM) and was hydrated to 50% moisture before being combined with either calcium hydroxide (CH) or limestone (CTL) at 5% of forage DM. Experimental periods lasted 24 d, with 14 d of dietary adaptation and 10 d of data and sample collection. Sample collection included feed and refusals, total fecal output, and ruminal fluid. Data were analyzed using the MIXED procedure of SAS 9.4 with fixed effects of calcium treatment, straw type, and the treatment × straw type interaction, with random effects of heifer and period. No interactions between straw type and calcium treatment were observed (P ≥ 0.20). Heifers consuming CH treated straw had a 10.8% greater DMI than those consuming CTL treated straw (P < 0.01), with the greatest intake observed for WS and FS (P < 0.01). Calcium treatment did not affect ADG (P = 0.35), but ADG was greatest for WS and least for CS (1.03 vs. -0.10 kg/d; P < 0.01). No effect of CH treatment was observed for ruminal pH (P ≥ 0.33), but heifers fed CS had the greatest mean ruminal pH and those fed FS had the least (P < 0.01). The total ruminal SCFA concentration was greater for heifers fed CH treated straw over CTL (124.8 vs. 110.2 mM; P < 0.01), and was less for heifers fed CS compared to WS and FS (P < 0.01). The molar proportion of acetate was greater for CH over CTL (P < 0.01). Dry matter digestibility was increased by 3.9% for CH compared to CTL (58.3 vs. 56.1%; P = 0.03) and was greatest for WS compared to FS and CS (P < 0.01). Calcium hydroxide treatment improved dry matter intake, digestibility, and total SCFA concentration, regardless of straw type, suggesting it may be an effective strategy to enhance the nutritional value of straw.