Effect of development system on growth and reproductive performance of beef heifers.
Reproductive performance was evaluated in beef heifers born over a 2-yr period to determine the effects of target breeding weight (TBW) and development system (SYS) on growth and subsequent reproductive efficiency. Spring-born Angus heifers (253 ± 0.7 kg) were randomly allocated over 2 consecutive yr (yr 1, n = 80; yr 2, n = 96) to be developed to either 55% (350 kg) of mature BW (moderate gain, MG) or 62% (395 kg) of mature BW (high gain, HG). Each MG and HG group was further assigned to 1 of 2 replicated systems: (1) bale graze bromegrass-alfalfa round bales in field paddocks (BG) or (2) fed bromegrass-alfalfa round bales in drylot pens (DL). Heifers were fed a diet of bromegrass-alfalfa hay (56.9% TDN; 9.8% CP) and barley grain supplement (85.1% TDN; 12.3% CP). After the 202-d development period, heifers were exposed to bulls for a 63-d breeding season. Target BW × SYS interactions were not detected for any measured parameters. During the winter development period, MG heifers had lower (P = 0.01) ADG than HG heifers and MG heifers had lighter (P = 0.01) BW at breeding. The proportion of heifers attaining puberty by 14.5 mo of age was less (P = 0.05) in MG (20 ± 4%) than HG heifers (52 ± 3%). From the end of the 202-d development period to pregnancy diagnosis, ADG was greater (P = 0.04) in MG heifers than HG heifers (0.83 vs. 0.71 kg/d). First-calf pregnancy rates were 86 and 88% for MG and HG heifers, respectively (P = 0.41). Second- and third-calf pregnancy rates of cows, developed in either a MG or HG system as heifers, were not different (P = 0.74; 94.7 vs. 95.9% and 93.8 vs. 93.9%, respectively). Economic analysis revealed a $58 reduced development cost for heifers developed to 55% compared with 62% of mature BW without a loss in reproductive performance.
Western Beef Development Centre, Humboldt, SK S0K 2A0, Canada Department of Animal and Poultry Science, University of Saskatchewan, Saskatoon, SK S7N 5B5, Canada blardner.wbdc@pami.ca.
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Lardner
Western Beef Development Centre, Humboldt, SK S0K 2A0, Canada Department of Animal and Poultry Science, University of Saskatchewan, Saskatoon, SK S7N 5B5, Canada.
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Damiran
Department of Large Animal Clinical Sciences, Western College of Veterinary Medicine, Saskatoon, SK S7N 5B4, Canada.
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Hendrick
Western Beef Development Centre, Humboldt, SK S0K 2A0, Canada.
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Larson
West Central Research and Extension Center, University of Nebraska-Lincoln, North Platte 69101.
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Funston
D000821:Animal Feed; D000822:Animal Husbandry / Q000379:methods; D000818:Animals; D001947:Breeding / Q000379:methods; D002417:Cattle / Q000254:growth & development* / Q000502:physiology; D004032:Diet / Q000662:veterinary; D004435:Eating; D005260:Female; D011247:Pregnancy; D012098:Reproduction / Q000502:physiology*; D012621:Seasons
bale grazing; heifer development; reproduction; system cost; target breeding weight