The effect of feeding level on intake and digestibility of Rhodes grass (Chloris gayana, cv Kunth) by dairy cows

The effects of feeding level (FL) on intake and digestibility was studied using eight lactating dairy cows fed on primary and secondary growths of 6, 8, 10 and 12 week old Rhodes grass. For each growth, eight feeding levels were used and the cows were randomly assigned to two blocks of treatments, each containing four levels of feeding and four plant ages in a double 4 × 4 Latin square arrangement. All forages were fed green and unchopped and levels of organic matter (OM) fed per day varied from 1.7 to 4.8 and from 2.8 to 5.4 kg per 100 kg BW for 1st and 2nd growth forages, respectively. ws consumed more leaves than stems. Refusals had lower crude protein (CP) and true in vitro organic matter digestibility and were higher in neutral detergent fibre (NDF) than the feed on offer. Selection against stems increased with age of the forage. The level of feeding had no significant effect on OM, CP and NDF digestibility in vivo. Intake of OM, digestible OM, leaves and stems increased significantly with increasing FL and decreased with age of the 1st cut forages (P < 0.001). In the 2nd cut age was significant for all parameters except intake of NDF and FL for all parameters except stems (P < 0.05). Cows fed 1st cut forages did not reach maximum intake within the range of FL used. At the maximum refusal level of about 25%, intake was still increasing. The curves for 2nd cut approached maximum intake at about 40% refusals. Calculations of optimal FL for the best compromise between excess feed and intake above maintenance (VAP-max: maximum value for animal production) showed increasing FL and decreasing VAP-max with age in the 1st cut but no trend for the 2nd cut.