Influence of prepartum body in multiparous beef cows condition score change on reproduction calving in moderate body condition

Multiparous, spring-calving beef cows (n = 250) were used to determine whet her large changes in body energy reserves during mid- to late gestation inf luenced subsequent reproductive performance of cows calving in moderate bod y condition, In three states, cows were blocked by BW and body condition sc ore (BCS; 1 = emaciated to 9 = obese) then allotted to receive either a hig h or low plane of nutrition from late summer to early winter over a 3-yr pe riod. This generated an array of BCS by the beginning of the last trimester of pregnancy when cows were grouped by BCS as follows: Group 1, BCS less t han or equal to 4; Group 2, BCS of 5 or 6; and Group 3, BCS greater than or equal to 7. Each group was managed so that individual cows would calve wit h a BCS of 5 to 6. At the time of group assignment, mean BW and BCS differe d (P < .01) among groups and were 480 kg and 3.6, 541 kg and 5,5, and 594 k g and 7.1 for Groups 1 to 3, respectively. Within 28 d before calving, BW a nd BCS were similar (P > .20) among groups averaging 555 kg and 5.1. Prepar tum BCS changes averaged 1.4, -.4, and -2.0 units for Groups 1 to 3, respec tively (P < .01). Cows were managed as a single group after calving in each state,location effect war;significant for the prepartum and postpartum-BW and BCS changes but not for postpartum reproductive performance. Significan t location x BCS group interactions were found for the 90-d prepartum BW, B CS at calving, and prepartum changes in BW, but were caused by differences in magnitude among locations. The percentage of cows with luteal activity a t the start of a subsequent breeding season was not affected (P > .20) by e ither location or BCS group, and averaged 66%, Mean pregnancy rates at 20, 40, and 60 d of a subsequent breeding season were 55, 76, and 89% for Group 1; 51, 67, and 82% for Group 2; and 64, 79, and 89% for Group 3 (P > .30). Mean days to conception were 89, 87, and 85 for Groups 1 to 3, respectivel y (P = .70). Neither calf birth weight ((x) over bar = 38.6 kg) nor adjuste d 205-d weight ((x) over bar = 223.6 kg) were affected by prepartum BW and BCS changes. We conclude that reproductive performance of cows calving in m oderate body condition is not influenced by large changes in body energy re serves during the last trimester of pregnancy.