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Effect of post-weaning heifer development system on average daily gain, pregnancy rates, and subsequent feed efficiency as a pregnant heifer
A 4-yr study was conducted using Angus-based, spring born heifers. In Yr 1, weaned heifers grazed corn residue (CR, n = 50) or were fed in a drylot (DLHI, n = 50). In Yr 2, 3, and 4, heifers grazed CR (n = 75), upland range (RANGE, n = 75), or were fed diets differing in energy, high (DLHI, n = 75) or low (DLLO, n = 75), in a drylot. Percent of mature BW prior to the breeding season was greater (P = 0.01) for DLHI (67%) compared with Range (59%), CR (60%), and DLLO (63%). Pregnancy rates to AI were similar (P = 0.39) among treatments (67, 63, 61, 49 ± 7.2%; RANGE, CR, DLHI, DLLO), and final pregnancy rates were also similar (84, 90, 91, 91 ± 5.4%; Range, CR, DLHI, DLLO; P = 0.59). A subset of AI pregnant heifers from each treatment was placed in a Calan gate system. Heifers were allowed a 20 d acclimation period before beginning the 90 d trial at approximately gestational d 170. Heifers were offered ad libitum hay; amount offered was recorded daily and orts collected weekly. Initial BW was not different (P = 0.35) among treatments (451, 457, 472, 464 ± 10 kg; RANGE, CR, DLHI, DLLO). Body weight at the end of the trial was also similar (P = 0.24; 488, 497, 511, 502 ± 14 kg; RANGE, CR, DLHI, DLLO). Intake was similar, either as DMI (P = 0.27; 9.74, 9.97, 10.18, 10.00 ± 0.76 kg; RANGE, CR, DLHI, DLLO) or residual feed intake (P = 0.61; 0.094, 0.091, -0.056, -0.0743 ± 0.160 kg; RANGE, CR, DLHI, DLLO). There was no difference in ADG (P = 0.36; 0.38, 0.45, 0.43, 0.41 ± 0.17 kg/d; RANGE, CR, DLHI, DLLO) among treatments. Although the development cost was not different among treatments (P = 0.41; $166, 141, 160, 171 ± 12, RANGE, CR, DLHI, DLLO), there was a $30 numerical difference between the most (DLHI) and least (CR) expensive treatment. Developing heifers to a greater pre-breeding BW did not influence subsequent AI or overall pregnancy rates or feed efficiency as a pregnant heifer.
Keywords: beef heifers, feed conversion, heifer development