Comparison of methods for estimating herbage intake in grazing dairy cows

Estimation of herbage intake is a challenge both under practical and experimental conditions. The aim of this study was to estimate herbage intake with different methods for cows grazing 7 h daily on either spring or autumn pastures. In order to generate variation between cows, the 20 cows per season were either allocated to low or high stocking rate. At low stocking rate, there were 6.7 and 3.5 cows per hectare during spring and autumn, respectively, and at high stocking rate, there were 8.8 and 4.6 cows per hectare during spring and autumn, respectively. The experiment lasted 16 days in each season, and the herbage intake was estimated twice during each season. Cows were on pasture from 8:00 until 15:00, and were subsequently housed inside and fed a mixed ration (MR) based on maize silage ad libitum. Herbage intake was estimated with nine different methods: (1) animal performance (2) intake capacity, (3) content of C-13 in faeces and diet, (4) C-13 in faeces and diet, and with assumption of C-13 discrimination in the digestive tract, (5) C-13 in faeces and diet, with assumption of C-13 discrimination and in combination with in vitro organic matter digestibility (IVOM), (6) simultaneous use of two internal markers (ingestible neutral detergent fibre (INDF) and acid detergent lignin (ADL)), (7) titanium oxide in combination with IVOM, (8) titanium oxide in combination with INDF and (9) titanium oxide in combination with ADL. Furthermore, grazing time of the individual cows was recorded. The estimated average herbage dry matter intake (DMI) varied from 2.2 kg for the method using the INDF:ADL ratio to 7.6 for the methods using C-13 and intake capacity. There was a low correlation between the different methods. Dry matter intake of herbage was not affected by stocking rate except for the method using titanium oxide and ADL as markers. Milk yield was not affected by stocking rate either. It was concluded that methods based on animal performance, C-13 including discrimination factor or in combination with IVOM as well as methods based on titanium oxide gave similar estimates of the average herbage DMI intake during grazing in systems with indoor concentrate and forage feeding during night. (C) 2015 Elsevier B.V. All rights reserved.