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Abstract Traditional heifer feeding strategies typically involve modest rates of body weight (BW) gain and include a relatively low proportion of concentrate feeds. In situations of limited forage or high feed costs, additional concentrates may be included in the diets and fed at a limited rate. High-concentrate diets can enhance the efficiency of nutrient utilization, alter characteristics of the gastrointestinal tract (GIT), and influence the composition of gain. The objective of this study was to evaluate the strategy of limit-feeding high-concentrate diets on feeding behavior, carcass characteristics, and GIT morphometrics in replacement beef heifers. Crossbred beef heifers (n = 20) began receiving either a high forage (75% forage:25% concentrate; HF, n =10) or high concentrate (25% forage:75% concentrate; HC, n =10) diet 74 ± 4 d before breeding. Heifers were inseminated with sexed male semen from a single bull. Individual intake and feeding behavior data were recorded using the Insentec Roughage Intake Control system, and heifers were weighed, and diet deliveries were adjusted every 2 wk to target a BW gain of 0.45 kg/d for both groups. Heifers were harvested at 180 d of gestation, where the viscera were removed, and weights of the full gastrointestinal tract, including the stomach complex, and small and large intestines were recorded. After removing digesta, weights of the empty gastrointestinal tract, rumen-reticulum, omasum, abomasum, small and large intestine, and mesenteric fat were recorded. Carcass characteristics were assessed 24 h after slaughter. Data were analyzed using the MIXED procedure of SAS, with heifer as the experimental unit. No differences were observed in final BW, average daily gain, or body condition score (P ≥ 0.18) between treatments (Table 1). Reflecting that HC heifers were limit-fed to a greater extent than HF heifers, therefore, dry matter intake, number of meals, visits to the feed bunk, time spent eating, and time per meal were less in HC heifers than in the HF group (P ≤ 0.001). In contrast, HC heifers had greater (P ≤ 0.001) eating rates of DM per minute, per visit and per meal compared with HF heifers. Though no differences were observed in back (P = 0.31) or rib fat (P = 0.37), HC heifers had greater (P = 0.04) marbling score and tended to have greater carcass weight (P = 0.06) and ribeye area (P = 0.07) as compared with HF heifers (Table 2). Greater (P 0.001) full weights of GIT and stomach complex, empty weight of rumen-reticulum, weight of total digesta, and digesta as a proportion of BW (i.e., fill) were observed in HF heifers. In contrast, HC heifers had greater (P 0.001) weights of full small intestine and mesenteric fat than HF heifers. These findings demonstrate that, despite similar rates of gain, limit-feeding high-concentrate diets can alter the composition of weight gain, favoring fat, muscle, and GIT development, potentially altering dam efficiency throughout her productive life.
Carlis et al. (Sun,) studied this question.