Growth Hormone Level in the Blood of Dwarf and Normal Hereford Cattle

The GH serum level of 152 head of cattle was determined by means of an immunological assay technique using the complement fixation test as an indicator between GH and its antiserum. Dwarfs, carriers of the dwarf gene, and normal individuals did not differ significantly in the GH content of their blood serum. The results indicate that there is no severe lack of GH release from the anterior pituitary gland into the blood stream of the snorter dwarf. It seems more likely that dwarfism may be due to a failure of the target cells and organs to respond to this hormone or the hormone is not active. The mean GH level in the blood of beef cattle in this study was 41±19 mcg./100 ml. of blood, but a large individual variation was observed. The heritability estimate for GH content of the blood was 0.56±.25 for 132 bull calves from 14 different sires. No significant correlation was found between growth hormone level and preweaning gains, 210-day weights, 392-day weights, feedlot gains and conformation scores. Low but significant positive coefficients of correlation of 0.22 (P<.05) and 0.27 (P<.02), respectively, for GH and cholesterol in the blood and GH and globulin in the blood were observed. No significant coefficients of correlation were found between GH level and other blood constituents. A low nonsignificant (P<.10) coefficient of correlation of −.20 was found for age and GH level in normal individuals. These results agree with those of other workers that increasing age does not result in the failure of the anterior pituitary gland to secrete GH and release it into the blood stream.