Effect of dietary energy intake on nutrient utilization, performance, and maintenance requirements in late gestation cows and their calves.
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Sixty multiparous, late-gestation beef cows (462 kg initial BW) were limit-fed, high-concentrate diets. Cows were blocked by BW and individually fed one of four treatments (70, 85, 100, and 115% of NRC-predicted maintenance energy) in Calan gates for an average of 71 d prior to calving. Diets consisted of 2.00 kg of wheat straw (2.5% CP; 79% NDF) and one of four levels of a mixture of corn (45%), distillers grain (42%) and premix (13%) fed 2.70, 3.41, 4.12, and 5.84 kg/d to correspond with the 70, 85, 100, and 115% treatments. Digestible energy intake increased linearly (5.92, 6.78, 7.77 and 8.86 Mcal/d for 70, 85, 100, and 115%; P < 0.01) per design. No effects (P > 0.05) for diet digestion were observed; DM digestion averaged 62%. Cow retained energy during the limit-feeding period (d 0 to 52) increased linearly (P < 0.01) from 46.6 Mcal for 70% to 50.7, 106.3, and 123.8 Mcal for 85, 100, and 115%. Body weight gain increased linearly over the same time period (P < 0.01) from 0.7 kg for 70% to 3.6, 17.7, and 24.2 kg for 85, 100, and 115%. Calf birth weight increased linearly (P = 0.01) from 32.5 kg for 70% to 35.5, 35.2, and 36.8 kg for 85, 100, and 115%. Brix (%) values for colostrum at parturition and 24 h post parturition did not differ (P > 0.05). Immunoglobulin G levels in calf serum collected at birth, 24 h and 7 d did not differ (P > 0.05) and averaged 0, 4,749, and 4,464 mg/dL, respectively. Cow body weights remained greater (linear, P < 0.05) in cows fed increasing levels of energy at days 60 and 90 post parturition; however, treatments no longer differed (P > 0.05) at 120 or 160 days post parturition or at weaning their calves (d 270). Level of energy intake during gestation did not result in significant differences (P > 0.05) in calf weights at 60, 90, 120 or 160 days post parturition or at weaning (averaged 206 kg). Cow 30 and 60 d conception rates were 82% and 98%, respectively.
