Growth performance, efficiency and composition of Holstein heifers fed two levels of nutrient intake from 44 kg to 350 kg body weight

No published data sets describe the effects of differences in nutrient intake, initiated shortly after birth and continued beyond puberty, on the growth characteristics of Holstein heifers. The objective of this study was to evaluate the effects of 2 levels of nutrient intake on growth characteristics and composition of Holstein heifers at stages ranging from early life up to one-half of mature BW. Starting at 44 kg, heifers (n = 78) were assigned to either an elevated (E) or restricted (R) level of nutrient intake formulated to support an ADG of 950 g and 650 g, respectively. Six heifers were harvested at approximately 46 kg to serve as a baseline for body composition. From the remaining animals, 6 heifers per treatment were harvested at 50 kg increments from 100 to 350 kg. Elevated nutrient intake resulted in increased daily gains of hip height and empty body weight (EBW) and the expected reduction in age at a common BW relative to cohorts raised on a lower level of nutrient intake. The lifetime BW gains observed closely matched the intended ADG for both groups while E-heifers converted feed into gain more efficiently than R-heifers until 250 kg. The E-heifers attained puberty 107 d earlier and, from that point onward, were consistently shorter than R-heifers. The proportion of gut fill in the BW was not constant during growth and was affected by level of nutrient intake after 250 kg being lower in E- than in R-heifers. A greater proportion of the blood and organs fraction and total fat mass reduced the contributions from the other body fractions to the EBW, in E- compared R-heifers. The content of fat increased and that of water decreased in both the EBW and the gain as growth progressed. These changes in fat and water content were accentuated by the E-level of nutrient intake after 200 kg, decreasing as a result the proportion of the fat-free mass (FFM) gain in the EBW gain. The mass of final and retained protein was unaffected by level of nutrient intake. Although the protein content of the EBW and gain was reduced in E-heifers, that of the FFM gain was similar between feeding groups. The ash content of the FFM gain was reduced in E- compared with R-heifers. Changes in fat gain and deposition resulted in equivalent variations in energy retention. The elevated intake of both protein and energy improved growth and feed efficiency without impacting lean growth or increasing adiposity up to approximately 30% of the heifer's mature BW. Taking into consideration the evolving contribution of gastrointestinal fill and fat to the BW gain during development due to level of nutrient intake, these data could be used to refine current descriptions of nutrient requirements and expected growth of Holstein heifers up to 350 kg.