Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/1/2002
Publication Date: 6/1/2002
Citation: GRINGS, E.E., SHORT, R.E., GEARY, T.W., MACNEIL, M.D. HEIFER DEVELOPMENT WITHIN THREE SEASONS OF CALVING. WESTERN SECTION OF ANIMAL SCIENCE PROCEEDINGS. 2002. v. 53. p. 261-264. Interpretive Summary: Development of heifers is a critical component of a beef production enterprise. Altering seasons of calving and weaning to impact the match-up of cow nutrient requirements with forage quality dynamics affects calf weight at weaning and subsequent management of heifer calves in anticipation of their entry into the breeding herd. Altering harvested feed inputs into the replacement heifer program will impact cost of raising a heifer from weaning to breeding. Time of calving, age at weaning, pasture quality, and environmental conditions could all impact this response. The objective of this study was to evaluate growth and reproductive potential of heifers born in different seasons and exposed to varied nutrient patterns from birth until first breeding. Crossbred beef heifers were from herds that had been managed separately to calve in late winter (Feb), early spring (Apr), or late spring (Jun) based on a 32-d synchronized breeding season. Heifers were weaned at 4- (Jun), 6- (Feb, Apr, Jun), or 8-mo-(Feb, Apr) of-age. Approximately 2 wk after weaning, heifers were assigned to one of two post-weaning treatments. One treatment was intended to allow heifers to grow at a constant rate from weaning to breeding. The second treatment was intended to minimize harvested feed inputs. Season of calving and weaning age effects on initial weight carried through to weight at breeding but did not affect cyclicity of beef heifers. Post-weaning management affected proportion of heifers puberal by breeding even when weights at breeding were similar within a calving season.
Technical Abstract: A 2-yr study was conducted to evaluate the impact of season of calving (SOC), weaning age (W), and post-weaning management (PWM) on growth and reproduction of beef heifers (n=483). Heifer calves born in Feb were weaned in Aug (6-mo) or Oct (8-mo) and heifers born in Apr or Jun were weaned in Oct (6- or 4-mo) or Dec (8- or 6-mo). Heifers were managed to enter breeding herds associated with their SOC. After weaning, calves were placed in drylot or on pasture. Heifers in drylot were fed a corn silage and hay-based diet. Heifers on forage treatments were placed on pasture but were fed grass hay and/or a supplement depending on forage conditions. Heifers on forage were moved to drylot 3 mo before their respective breeding seasons and fed a corn silage and barley-based diet (Feb or Apr) or moved to high quality spring pasture (Jun). Data were analyzed as a completely random design with treatment (n=12), year, and treatment by year included in the model. Rates of gain during drylot and forage phases differed with SOC, W, and PWM. For heifers weaned at 6-mo of age, gains were greatest for Feb followed by Apr and then Jun (0.73 vs 0.65 vs 0.62 kg/d). Overall gains were 0.77, 0.65, and 0.55 kg/d for 8, 6, and 4 mo W in Oct. Overall gains were less for heifers on forage than drylot treatments (0.66 vs 0.69 kg/d). Weights at the beginning of the breeding season did not differ with PWM but were affected by SOC and W, reflecting differences in initial weights. Proportion of heifers cycling at the beginning of the breeding season was greater for heifers in drylot (0.98) than forage treatments (0.92). Thus, SOC and W effects on initial weight carried through to weight at breeding, whereas post-weaning management affected cyclicity of beef heifers.