Animals and feeding

The study was conducted in the Experimental Shed at the School of Veterinary Medicine and Animal Science of the Federal University of Goias (UFG), Campus Samambaia, between February and March 2015. We used 21 mixed-breed Holstein × Jersey calves, aged between 3 and 15 d and an average weight of 36.8 kg, identified and housed in individual bays, and provided with milk and water buckets and troughs for hay and concentrate (Table 1). Hay and concentrate were provided ad libitum for all treatments. The animals were donated by dairy farmers from different properties in the region within 50 km of Goiânia. The animals had an adaptation period of 7 d to both the diet and the facilities. Animals were distributed in a completely randomized design with three treatments and seven repetitions. Treatments consisted of 1) Control: 6 liters of milk/day in the first period (P1) and 6 liters of milk/day in the second period (P2); 2) RES (milk restriction): 3 liters in P1 and 6 liters of milk/day in P2; 3) RES + HMTBa: 3 liters in P1 and 6 liters of milk/day in P2 with 3.3 g of HMTBa/day (MintrexZn feed supplement with 83% HMTBa and 2.4% Zinc; Novus International Inc., St. Charles, MO). Milk was provided over 42 d in buckets and divided into the first and second periods of 21 d each. The daily amount of milk and HMTBa supplement treatment was divided into two portions at 8:00 a.m. and 4:00 p.m. In P1, the Control group received two meals of 3 liters of milk, whereas the RES and RES + HMTBa groups received two meals of 1.5 liters each. In P2, the animals of all groups received two meals of 3 liters each. The nutritional composition of milk supplied to calves as a percentage of dry matter (% DM) was as follows: 13.24 DM, 3.67 crude protein (CP), 4.69 lactose, and 4.31 fat. MintrexZn (Novus International Inc., St. Charles, MO) is a compound that has in its chemical structure calcium ionically bound to two molecules of HMTBa calcium bis(2-hydroxy-4-(methylthio)) butyrate and Zn chelated to two molecules of HMTBa (chelated Zn). MintrexZn is a powder with density of 0.65 to 0.75 g/cm³ and is supplied in milk.

Chemical composition, g kg⁻¹ DM, of concentrate and hay used in the experiment

¹Proportion of ingredients in concentrate: ground corn and cornmeal (70.0%), soybean meal (29.0%), and mineral premix without additive (1.0%).