Effects of Feeding Prepubertal Heifers a High-Energy Diet for Three, Six, or Twelve Weeks on Feed Intake, Body Growth, and Fat Deposition

The objective was to determine the effects of feeding prepubertal dairy heifers a high-energy diet for a duration of 0, 3, 6, or 12 wk on feed intake, growth, and fat deposition. We also used feed composition, daily intake, and body growth data to evaluate the nutritional model of the 2001 National Research Council (NRC) Nutrient Requirements of Dairy Cattle. Holstein heifers (age = 11 wk; body weight = 107 ± 1 kg) were assigned to 1 of 4 treatments (n = 16/treatment) designated H0, H3, H6, and H12 and fed a low-energy diet for 12, 9, 6, or 0 wk, followed by a high-energy diet for 0, 3, 6, or 12 wk, respectively. Four heifers were killed initially (11 wk of age) and 64 heifers were killed at the end of the treatment period (23 wk of age). The low-energy diet was formulated to achieve 0.6 kg of average daily gain and contained 16% crude protein, and 45% neutral detergent fiber. The high-energy diet was formulated to achieve an average daily gain of 1.2 kg and contained 18% crude protein and 23% neutral detergent fiber. Actual daily gains averaged over the 12-wk treatment period were 0.64, 0.65, 0.83, and 1.09 kg for the H0, H3, H6, and H12 groups, respectively. Body weight, withers height, hip width, carcass weight, liver weight, and perirenal fat increased in heifers fed a high-energy diet for a longer duration. In addition, percentage of fat increased and percentage of protein decreased in rib sections with a longer duration on the high-energy diet. Uterine and ovarian weights adjusted for body weight decreased when heifers were fed the high-energy diet for a longer duration. The 2001 NRC underestimated dry matter intake of the high-energy diet and overestimated dry matter intake of the low-energy diet. On the basis of actual intakes of each diet, the NRC slightly underestimated gain for the low-energy diet and overestimated gain by 40% for the high-energy diet. The likely explanation for this is that the NRC underestimated the proportion of gain that was fat in the heifers fed the high-energy diet and therefore predicted more body gain per unit of energy intake. We concluded that feeding a high-energy diet for a short duration altered body growth and fat deposition in a time-dependent, linear manner consistent with feeding a high-energy diet for a long duration.