Feed Intake: Appendix B Alkane Feed intake technique Piacenza, Italy

Estimation of individual feed intake is carried out utilising all cows in a group (maximum 50 cows). Cows are fed a Total Mixed Ration, fed ad libitum, with about 3-5 % refusals.

Feed intake is estimated adopting the alkane technique. A fixed amount of C32 Dotriacontane dispersed in 50 g of corn meal is included in a bolus and gun dosed to dairy cows at feeding time. The first day, a double dose of the marker is dosed. After 7 days of administration of the marker, faeces are collected in the morning at feeding time for 5 consecutive days (day 8 to day 12), continuing with marker dosing. Faeces are homogenized and a 200 g sample is oven dried.

Representative samples of TMR are collected from the day before the collecting period to the day before ending collection of faeces. Feed refusals are sampled daily in combination with collection of faeces.

Amounts of TMR offered and refused are weighed each day during the period of sampling (day 7 to 11 for TMR, day 8 to 12 for refusals).

At the end of the faeces collecting period, dried faecal samples are pooled by animal, milled and analyzed for alkanes by GC. TMR samples are similarly processed. Refusals are oven dried to measure dry matter content.

Individual intakes are preliminary predicted for each cow, assuming the same recovery values for the alkanes C31, C32 and C33, according to the equation:

y = (F_i/F_j * D_j) / [ H_i – (F_i/F_j) * H_j]

where: y is predicted dry matter intake (kg of DM/ d); Fi and Hi are the respective concentrations (mg/kg of DM) of natural odd-chain n-alkane in diet and faeces; Fj and Hj the respective concentrations (mg/kg of DM) of even chain n-alkane in diet and faeces; Dj is the dose rate of even chain n-alkane (mg/d).

Feed intake is calculated by correcting the preliminary data based on the ratio between average predicted intake of the whole group of cows and the dry matter intake calculated as difference between feed offered and refused.