Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/22/2007
Publication Date: 8/1/2007
Citation: Grings, E.E., Geary, T.W., Short, R.E., MacNeil, M.D. 2007. Beef Heifer Development Within Three Calving Systems. Journal of Animal Science 85:2048-2058. Interpretive Summary: Development of heifers is a critical component of a beef production enterprise. Altering dates of calving and weaning to match cow nutritional requirements with forage quality dynamics impacts calf weight at weaning. This may affect subsequent management needs of heifer calves in anticipation of their entry into the breeding herd. Altering harvested feed inputs into replacement heifer programs can impact cost of raising a heifer from weaning to breeding. Other researchers have suggested that allowing heifers to make rapid rates of gain during the last three months before breeding could decrease feed costs through maintenance of a lighter weight heifer in the early post-weaning period. Our objective was to evaluate the impact of differing nutrient patterns from birth until first breeding on weight gain and evidence of luteal activity before first breeding for heifers born in three different seasons. We concluded that either constant gain or alternate gain management strategies can be used to develop heifers from weaning to breeding. This suggests there are a wide variety of options available for rearing heifers. Heifers from varied calving, pre- and post-weaning management strategies performed similarly in initial reproductive performance and subsequent calf production. Heifers were a minimum of 58% of mature weight at first breeding and our conclusions regarding calving season and post-weaning management programs should not be extended to heifers reaching less than this level of maturity.
Technical Abstract: A 3-yr study was conducted to evaluate impacts of calving system, weaning age, and post-weaning management on growth and reproduction in beef heifers. Heifer calves (n=676) born in late winter (LW; avg birth date = Feb 7 ± 9 d) or early spring (ES; avg birth date Apr 3 ± 10 d) were weaned at 190- or 240-d of age and heifers born in late spring (LS; avg birth date May 29 ± 10 d) were weaned at 140- or 190-d of age. Heifers were managed to be first exposed for breeding at approximately 14-mo of age. After weaning calves were placed in drylots or on pasture. Heifers in drylot were fed a corn silage and hay-based diet (CSH). Heifers on forage treatments (FOR) were placed on pasture but were fed grass hay and/or a supplement depending on forage conditions. Three months before their respective breeding seasons, heifers on forage were moved to drylot and fed a corn silage and barley-based diet (LW or ES) or moved to high quality spring pasture (LS). Data were analyzed using mixed model procedures with calving system, weaning age, and post-weaning management options creating 12 treatments. Year was considered a random effect. Non-orthogonal contrasts were used to make logical treatment comparisons. Average daily gain was 0.36 ± 0.05 kg/d less (P < 0.01) for FOR heifers during the first post-weaning phase, whereas these heifers gained 0.44 ± 0.03 kg/d faster (P < 0.01) than CSH heifers during the last 90-d before breeding. Weights at the beginning of the breeding season did not differ between CSH and FOR heifers, but were affected (P < 0.01) by calving system and weaning age, reflecting some of the differences in initial weights. Pre-breeding weights for heifers weaned at 190-d were 36 ± 6.4 kg heavier for heifers born in LW and ES compared with LS and were 388, 372, and 330 kg for heifers weaned in Oct at 240-, 190-, or 140-d of age. Proportion of heifers exhibiting luteal activity at the beginning of the breeding season was not affected by treatment. In conclusion, heifers from varied calving systems and weaning strategies can be raised to breeding using either constant or variable gain strategies without affecting percentage of heifers cycling at the beginning of the breeding season. These results suggest that producers have multiple options for management of heifer calves from differing calving systems.