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1297
Effect of lactose inclusion in calf starters on rumen fermentation of weaned calves
The objective of this study was to evaluate the effects of lactose inclusion in calf starters on ruminal pH and VFA profile. Sixty Holstein bull calves were raised on an intensified nursing program using milk replacer containing 28% CP and 15% fat, until 56 days of age. Calves were fed texturized calf starters containing lactose at 0 % (Control), 5.0 % (LAC5), or 10.0 % (LAC10; n = 20 for each treatment) on a DM basis. All calf starters were formulated for 23.1% CP. All calves were fed treatment calf starters ad libitum from d 7 and their hay (Klein grass) intake was limited to 150 g/d (as fed). Ruminal pH was measured every 2 min using small ruminant rumen pH loggers (Dascor, CA, USA) immediately after weaning (d 55 to 62) for 15 calves (5 calves per treatment), and 3 weeks after weaning (d 77 to 80) for the other 45 calves (15 calves per treatment). Daily mean, minimum, maximum ruminal pH, and duration and area under rumen pH 5.8 were not affected by treatment for both periods (d 55 to 62 and d 77 to 80). However, Spearman's correlation coefficient (rs) was 0.306 (P < 0.05) between lactose intake and minimum ruminal pH for d 77 to 80, indicating that actual lactose consumption may affect ruminal pH. In addition, hay intake was not affected by treatment, but it was positively correlated with daily mean (rs = 0.338, P < 0.05) and maximum ruminal pH (rs = 0.408, P < 0.01), and the variation in hay intake might have masked treatment effects on ruminal pH. Ruminal molar ratio of acetate (mean ± SE) was 40.6 ± 1.26 (Control), 42.8 ± 1.26 (LAC5), and 45.3 ± 1.26 % (LAC10), molar ratio of propionate was 40.2 ± 0.98 (Control), 38.1 ± 0.98 (LAC5), 35.3 ± 0.98 % (LAC10), and acetate / propionate ratio was 1.01 ± 0.06 (Control), 1.15 ± 0.06 (LAC5), 1.29 ± 0.06 % (LAC10) on d 80, and the differences were significant between Control and LAC10 (P < 0.05) for ruminal fluid samples collected on d 80. However, molar ratio of butyrate was not affected by treatment. These results indicate that inclusion of lactose in calf starter affects ruminal VFA profile, but its effects on rumen pH warrants further investigation.
Keywords: calf, lactose, rumen