Administration of pig relaxin to beef heifers 4 or 7 days pre partum

Abstract

Summary. Crossbred beef heifers (N = 36) were assigned to one of three treatment groups: untreated controls (C; N = 15); Group R4, treated with pig relaxin (1\m=.\0mg i.m.) 4 days pre partum (N = 11); or Group R7, treated with pig relaxin ( 1 \ m=. \ 0 mg i.m.) 7 days pre partum (N = 10). Bioactivity of the pig relaxin (UMC-R-P8) was determined by the mouse interpubic ligament assay to be \ m=ge\ 3000 U/mg, both before and after the experiment was conducted. Peripheral serum immunoreactive relaxin values were 7\ m=. \ 5, 3\m=.\4,2\m=.\5, and 1\m=.\5, ng/ml at 2, 4, 6 and 8 h after injection of relaxin, respectively. Gestation lengths were 282\m=.\9\m=+-\1 \ m= . \ 1 285\m=.\5\ m=+-\1\m=.\3 and 285\m=.\6\ m=+-\1\ m=. \ 5days for Groups C, R4 and R7 (C vs R4 + R7; P \ m=si meq\ 0\m=.\08).Calving difficulty score (1 to 4) tended to be greater (P \ m=si meq\ 0\m=.\08) for Group R4 and R7 heifers (C vs R4 + R7; 1\m=.\3 \ m=+-\ 0\m=.\24vs 1\m=.\75 \ m=+-\ 0\m=.\28 + 2\m=.\04\m=+-\ 0\m=.\32), but the incidences of dystocia and retained placentae were not influenced by treatment (P \m=ge\ 0\m=.\10). The mean concentration and concentration profile of daily serum progesterone, oestradiol-17\g=b\,dihydroprostaglandin F-2\g=a\and relaxin were not affected by treatment from 6 days pre partum through 2 days post partum. Cervical diameter, cervical softness score, pelvic measurements, and vulva opening length during the periparturient period were not affected (P \m=ge\ 0\m=.\10)by treatment, but all of these characteristics changed over time (P \m=l e\ 0\m=.\01), relative to calving. We conclude that i.m. administration of pig relaxin (\m=ge\3000 U) does not effectively alter periparturient characteristics of beef heifers. Discrepancies between these results and those reported for intracervical administration cannot be readily explained.