Lardner H A, Damiran D, Hendrick S, Larson K, Funston R
Western Beef Development Centre, Humboldt, SK S0K 2A0, Canada Department of Animal and Poultry Science, University of Saskatchewan, Saskatoon, SK S7N 5B5, Canada
Western Beef Development Centre, Humboldt, SK S0K 2A0, Canada Department of Animal and Poultry Science, University of Saskatchewan, Saskatoon, SK S7N 5B5, Canada.
J Anim Sci. 2014 Jul;92(7):3116-26. doi: 10.2527/jas.2013-7410. Epub 2014 Apr 28.
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.
对2年内出生的肉用小母牛的繁殖性能进行了评估，以确定目标繁殖体重（TBW）和发育系统（SYS）对生长及后续繁殖效率的影响。春季出生的安格斯小母牛（253±0.7千克）在连续2年（第1年，n = 80；第2年，n = 96）中被随机分配，分别发育至成熟体重的55%（350千克）（中等增重，MG）或62%（395千克）（高增重，HG）。每个MG组和HG组又进一步被分配到2个重复系统中的1个：（1）在牧场围场中放牧苜蓿-黑麦草圆捆（BG），或（2）在干栏式畜舍中饲喂苜蓿-黑麦草圆捆（DL）。给小母牛饲喂苜蓿-黑麦草干草（总可消化养分56.9%；粗蛋白9.8%）和大麦谷物补充料（总可消化养分85.1%；粗蛋白12.3%）。在202天的发育期结束后，让小母牛在63天的繁殖季节接触公牛。未检测到目标体重×系统之间在任何测量参数上的相互作用。在冬季发育期间，MG小母牛的平均日增重（ADG）低于HG小母牛（P = 0.01），且在配种时MG小母牛的体重较轻（P = 0.01）。14.5月龄达到青春期的小母牛比例，MG组（20±4%）低于HG组小母牛（52±3%）（P = 0.05）。从202天发育期末到妊娠诊断期间，MG小母牛的ADG高于HG小母牛（P = 0.04）（分别为0.83千克/天和0.71千克/天）。MG和HG小母牛的头胎妊娠率分别为86%和88%（P = 0.41）。作为小母牛时在MG或HG系统中发育的母牛，其二胎和三胎妊娠率没有差异（P = 0.
