Genetic and physiological relationships of growth hormone and growth in goats Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/05741v220

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  • An F₁ population resulting from mating pygmy and normal goats (local commercial breeds) was crossed to give an F₂ population. Analysis of wither height and body weight indicated that the F₂ population was intermediate between the parental types (pygmy and normal) with little overlap of phenotypic values for body size between the F₂ population and parental types. Thus, it was concluded that a full segregation for size determining genes was not being exhibited in the small F₂ population indicating that the pygmy trait in these goats is polygenic in inheritance. Serum growth hormone (GH) levels were measured in three genetic groups (6 normal males, and 21 pygmy and 30 F₂ animals of both sexes) of goats at monthly intervals from one to six months of age. Growth hormone levels were quantified using a bovine GH double-antibody radioimmunoassay. Serum GH levels in male normal goats decreased significantly (P < .005) while serum GH levels in the male pygmy goats increased significantly (P < 005) during the six month period. Over the entire six month period there were no significant differences in serum GH levels between male normal and male pygmy goats although significant differences were observed at one and six months of age. Serum GH levels in the male F₂ population were relatively intermediate between parental types during the six month study; however, they increased significantly (P < . 005) with increasing age similar to the changes observed in the pygmy males. Male pygmy and F₂ goats had significantly higher (P < . 005) serum GH levels than their female contemporaries while normal females were unavailable for comparison with normal males in this age group. Serum GH levels in pygmy females remained relatively constant while increasing GH levels in the F₂ females during the six month period approached significance (P = . 06). Serum GH levels were also measured in three genetic groups (6 normals, 14 pygmy and 18 F₁) of mature female goats. Serum GH levels in the adult F₁ females were similar to GH levels in the adult pygmy females although both had significantly higher (P < . 005) serum GH levels than adult normal females. Pituitary GH concentration in normal and pygmy male goats at six months of age was essentially equal while total pituitary GH content was higher in the normal goats as a result of significantly (P < . 005) larger anterior pituitaries. Pituitary GH per kg of body weight was relatively equal in normal and pygmy male goats while pituitary GH per kg body weight in both sexes in the F₂ goats was significantly (P < . 01) lower than in the pygmy goats. No differences between sexes within genetic groups were observed in pituitary GH levels. Analysis of pituitary GH in adult female goats indicated that pituitary GH concentration and content per kg body weight were significantly higher (P < .005) in mature female pygmy goats as compared to mature female normal and F₁ goats. Neither serum GH levels nor measures of pituitary GH status (pituitary GH concentration, total GH content and GH content per kg body weight) showed consistent relationships with body size measurements in any of the genetic groups in young or adult animals. Serum GH levels were not significantly related to any measure of pituitary GH status used in this study. Additional experiments were designed to determine the effect of blood collection stress on serum GH levels. Repeated blood sample collection via jugular venipuncture failed to alter serum GH levels while GH levels in blood samples collected by jugular cannula were slightly higher and more variable than GH levels in blood samples collected by jugular venipuncture. Restraining goats by tying had no effect on serum GH levels, Serum GH in pygmy goats was observed to fluctuate at irregular intervals as determined by collecting blood samples by jugular cannula and without the goats' knowledge.
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