Author
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Roberts, Andrew |
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Submitted to: Meeting Proceedings
Publication Type: Proceedings Publication Acceptance Date: 4/2/2008 Publication Date: 6/23/2008 Citation: Roberts, A.J. 2008. Assessment of insulin-like growth factor-1 as an indicator of competence for rebreeding in first calf heifers. Proceedings, Western Section, American Society of Animal Science 59:257-260. Interpretive Summary: Failure of cows to rebreed after calving is a major factor influencing economic viability beef cattle operations. This is especially true for young cows after their first and second calf due to the fact that these cows are still growing which adds to their nutritional requirements. Industry has adapted the use of BCS as a tool for producers to evaluate competency of their cows to resume cycling after calving. Results from the present research indicate that circulating concentrations of IGF-1 during the peripartum period were better indicators of rebreeding performance of first calf heifers than either BCS or BW. Results from the present study also indicate that associations of IGF-1 and rebreeding were stronger when IGF-1 was measured prior to calving, rather than after calving. Technical Abstract: Objective of this research was to evaluate whether concentrations of IGF-1 in circulation, BW and BCS measured before calving, after calving and immediately before breeding could be used as indicators of nutritional competency for time of rebreeding in first calf heifers. Heifers were artificially inseminated at about 14 mo of age and then exposed to bulls for the remainder of a 53-d breeding season. This breeding season resulted in a 71-d calving period that began on March 8. Blood samples, BW and BCS were obtained at 3 time points from 74 cows: February 25, which was 12-d prior to beginning of the calving period, 0 to 14 d after calving (date varied in relation to calving), and again on May 27 (before a 52-d breeding season). Separate regression analyses were run for each time point, using a model that included concentration of IGF-1, cow BW, cow BCS and day of calving as independent variables, with day of second calving as the dependant variable. For precalving data, birthday of second calf was influenced (P = 0.01; R*2 = 0.17) by birthday of previous calf (P =0.01; b = 0.31 ± 0.12) and circulating concentration of IGF-1 (P =0.001; b = -0.20 ± 0.06), but not by BW (P =0.4) or BCS (P =0.9). Regression analyses with postcalving (P = 0.14; R*2 = 0.10) and prebreeding (P = 0.25; R*2 = 0.07) data accounted for less variation in birthday of second calf than precalving measurements of IGF-1. However, similar trends toward a negative relationship between IGF-1 and second calving day were observed with postcalving (P = 0.06; b = -0.08 ± 0.04) or prebreeding (P=0.09; b = -0.07 ± 0.04) measures of IGF-1. Results indicate precalving concentrations of IGF-1 may be a useful indicator of nutritional competency for rebreeding in first calf heifers. In contrast, measures of BW and BCS at the 3 time points evaluated in this study did not appear to be indicative of time to rebreeding. |
