Energy and protein requirements of crossbred Holstein x Gyr calves fed milk with milk replacer containing increasing dry-matter concentrations

Context There is a lack of studies concerning the nutrient requirements of dairy calves, mainly, evaluating different genetic groups. Aims. The objective was to quantify energy and protein requirements of dairy calves up to 60 days, testing the influence of genetic composition (Holstein or crossbred Holstein x Gyr) on these requirements. Methods. The study involved 42 bull calves (3 days of age), including animals with less than 15/16 Holstein composition (considered crossbred) and animals with more than 15/16 Holstein pedigree (considered purebred). Six calves were slaughtered at the start of the experiment to estimate the initial body composition of the animals. Of the remaining animals, four formed the maintenance group (fed 3 L/day of raw milk), and the other 32 were distributed into four treatments, which consisted of 6 L/day of raw milk, with increasing DM contents of 13.5%, 16.1%, 18.2% and 20.4% respectively. The DM contents were corrected for adding milk replacer to the raw milk. All animals had free access to starter feed and water. Digestibility trials were conducted at 28 and 56 days of life, with total faeces collection being performed for 5 days and urine collection for a period of 24 h. At 60 days of life, the animals were slaughtered to determine their body composition. Key results. Net energy requirements for maintenance and metabolisable energy requirements for maintenance were 57.6 and 86.8 kcal/(empty bodyweight, EBW)(0.75).day respectively. The efficiency of utilisation of metabolisable energy for maintenance was 66%. Net energy requirements for gain (NEg, Mcal/day) can be estimated by the following equation: NEg = 0.7098(+/- 0.)(2345) x EBW0.2521 +/- 0.068 x EBG" where EBG is empty body gain (kg/day) and EBW is in kilograms. The efficiency of utilisation of metabolisable energy for gain was 27%. The metabolisable-protein requirement for maintenance was 3.22 g/EBW0.75.day. Net protein requirement for gain (NPg, g/day) can be estimated by the following equation: NPg = -27.43 + 104.53 x EBG + 46.81 x RE, where RE is retained energy (Mcal/day). The efficiency of utilisation of metabolisable protein for gain was 59.1%. Conclusions. Genetic group does not affect energy or protein requirements of pre-weaned calves. The estimates presented here can be used to calculate nutrient requirements of pre-weaned calves aged up to 60 days.