HEIFER DEVELOPMENT WITHIN THREE SEASONS OF CALVING

Authors: Grings, Elaine; SHORT, ROBERT - RETIRED 5434-05-00; Geary, Thomas; Macneil, Michael

Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
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. JOURNAL OF ANIMAL SCIENCE SUPPLEMENT. 2002. v. 80(Suppl. 2). p. 120.

Interpretive Summary: 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.

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.