Exogenous administration of GRF or somatotropin in poultry and pigs : effects on performance, meat quality and reproductive function

Abstract

In ad libitum-fed pigs administered with porcine somatotropin (pST) during the finishing period, daily feed intake is reduced (2-22%), growth is generally accelerated (up to 47%) and feed efficiency is dramatically improved (3-38%), in connection with a sharp reduction in fat deposition (7-44%). Lean content of the carcass is augmented (2-23%). Due to the increased weight of some organs (liver, heart, etc.), dressing percentage is reduced (1-4%). Administration of GRF or of a GRF analog has qualitatively the same effects as pST. The main factors of variation of pST effect on performance and carcass characteristics of pigs include : 1) Dose of pST. Daily feed intake and fat deposition decline linearly with increasing pST doses while the response of feed efficiency, growth rate and lean deposition is quadratic. 2) Mode of administration. Sustained release of pST seems to be less efficient than daily injection. 3) Age and weight. The effects of pST are similar, both qualitatively and quantitatively, during the growing period or in heavy pigs than during the finishing period. 4) Genotype, sex and castration. The effects of pST are negatively related to the animal’s potential for lean tissue growth. The effect of pST on the percentage of the various muscle fiber types is unclear. However, an increase in their size is most often noticed. PST effects on muscular characteristics may vary widely according to muscles. Physical and sensory properties of meat are generally unaffected or only slightly altered by pST treatment. Besides the pST effects on muscle and fat composition, the most consistent changes concern elevated ultimate pH measurements, increased shear force values and decreased tenderness. Consumer acceptance of fresh pork or processed products does not seem to be impaired by pST treatment. The impact of pST treatment on the onset of puberty is not clear. However, there is convincing evidence that any possible adverse reproductive change associated with chronic administration of pST to prepubertal gilts is transient. Administration of pST during gestation has no effect on litter. The impact of pST treatment on milk production by lactating sows is still controversial. Although somatotropin seems to be involved to some extent in the regulation of growth in birds, exogenous administration of GRF or somatotropin has only a transient effect (or, most often, no effect at all) on growth performance and carcass characteristics of chickens..