Discipline: calf rearing; Keywords: calf, lactose, fat, milk replacer.
Compared with Holstein milk, some conventional milk replacer (MR) formulations provide high amounts of lactose, low concentrations of fat, and comparable crude protein levels. Consequently, MR provides a lower dietary energy density than whole milk. Fat inclusion in MR compositions should raise the energy content, but the literature shows both positive and negative results. In the study by Dr Juanita Echeverry-Munera and colleagues, the objective was to measure responses when partially replacing lactose with fat in MR on voluntary feed intake, growth and feeding behaviour. They hypothesized that the partial replacement of lactose by fat as a source of energy in MR will decrease voluntary milk intake without compromising calf growth performance. The study was published in the Journal of Dairy Science, Volume 104 of 2021, page 5432 to 5444, the title being: Effect of partial exchange of lactose with fat in milk replacer on ad libitum feed intake and performance in dairy calves.
Thirty-two male Holstein calves (2.1 ± 0.16 d of age, 46.4 ± 0.77 kg of body weight; BW) were assigned to 16 blocks of two calves per block based on arrival date and serum immunoglobulin (IgG). Within each block, the calves were randomly assigned to two treatments: a high-lactose MR (HL: 17% fat; 44% lactose), or a high-fat MR (HF: 23% fat; 37% lactose) treatment. Lactose was exchanged by fat on a weight per weight basis, resulting in a 6% difference in metabolizable energy density per kg of MR. The experiment was divided into three phases: pre-weaning (P1: 0–35 days), weaning (P2: 36–56 days), and post-weaning (P3: 57–84 days). For the first two weeks of P1, the calves were individually housed, fed their respective MR ad libitum through teat buckets, and provided access to water. At 14.2 ± 0.5 days of age, the calves were group-housed (4 blocks/pen, 8 calves) and housed in group pens for the remainder of the study. In the group pens, the calves were fed ad libitum MR, starter feed, chopped wheat straw, and water via automated feeders. During P2, the calves were gradually weaned until complete milk withdrawal by 57 days and then monitored until 84 days (P3). Measurements included daily intakes and feeding behaviour (rewarded and unrewarded visits), weekly BW and body measurements, and biweekly blood samples.
The results showed that increasing fat content at the expense of lactose decreased MR intake during P1 by 15% (HL = 1.32 ± 0.04; HF = 1.17 ± 0.04 kg of dry matter per day), whereas the total starter intake was not affected by MR composition. Once MR was restricted during P2, HL calves had more unrewarded visits to the automatic milk feeder than HF calves (11.9 ± 0.95 vs. 8.4 ± 1.03 visits per day, respectively). Crude protein intake was higher for HL calves during P1 (352.1 ± 11.2 vs. 319.6 ± 11.6 g per day), which was attributed to the higher intake of MR during that period, and metabolizable energy intake and the protein-to-energy ratio remained comparable between treatments. Plasma cholesterol and non-esterified fatty acids levels were higher in HF calves as a consequence of the diet. Nevertheless, the final BW at 84 days did not differ between treatments.
Overall, the calves fed ad libitum seemed to regulate their intake of MR based on energy density, without significant effects on solid feed intake, overall growth and reduced hunger-related behaviour during weaning. Furthermore, the calves seemed to regulate MR intake according to its caloric density. Moreover, plasma cholesterol in the pre-ruminant phase increased with fat intake, which has been linked to improved calf health and lower early mortality.