Publications

The definition of a sward height that allows maximizing the herbage and nutrient intake rate has been implemented as a sustainable grazing management strategy in forage-based dairy production systems. The aim of this thesis was to determine the sward height of the kikuyu grass (Cenchrus clandestinus - Hochst. ex Chiov) that allows dairy heifers to maximize the herbage and total digestible nutrients intake rate. Additionally, assess the effect of sward height from herbage samples of top stratum (stratum potentially grazed by cattle) on the chemical composition, in vitro organic matter digestibility (IVOMD), and the main in vitro ruminal fermentation parameters, including CH4 production. A grazing experiment was carried out whose treatments consisted of five sward heights of kikuyu grass (10, 15, 20, 25 and 30 cm). Short-term intake rate (STIR) of herbage was measured with the double weighing technique and for the determination of bite mass (BM), bite rate (BR) and the eating time the IGER Behaviour recorder was used. It was found that the sward height of kikuyu grass that maximizes the herbage and nutrient intake per unit of eating time was approximately 20 cm. Define very low (10 cm) or very tall (30 cm) sward heights of kikuyu grass as a grazing management target would constraint the BM, and thus, the STIR. The chemical composition and IVOMD of the herbage samples from the top stratum did not differ in sward heights ranged between 10 to 25 cm, in addition, these sward heights tended to have a higher IVOMD than 30 cm. The in vitro gas production and the IVDMD displayed a negative and linear fit to increasing sward height. The CH4 (ml /g IVDMD) showed a broken line response being similar between 10 to 20 cm sward height, and then, increased with increases in sward height above to 21 cm. The acetate molar proportion (mol/100 mol) had a similar response to CH4 (mL/g IVDMD). The propionate molar proportion (mol/100 mol) also displayed a broken line response but opposite to CH4 (ml /g IVDMD), increasing until sward heights close to 20 cm and then decreasing. In conclusion, to optimize the STIR and TDN-STIR of dairy heifers, kikuyu grass should be managed at 20 cm of sward height. Additionally, at this sward height the in vitro CH4 production (mL/g IVDMD) would be also reduced.