IMPACTS OF CONTEMPORARYBIOTECHNOLOGY-ANIMAL SCIENCE 65

 1937). This effect was intensively studied in Britain as a way of increasing
 milk supply during World War II (Young, 1947). Subsequently, the active
 component within the pituitary extracts was shown to be bovine growth
 hormone (Brumby and Hancock, 1955). This observation remained only a
 curiosity until the gene was cloned and the hormone was produced in
 quantity by microorganisms. A recent publication by Bauman et al. (1985)
 demonstrated that methionyl bovine growth hormone, made by E. coli,
 increased milk production over a 188 day period by 23 to 41 percent,
 depending on the daily dose. Just as importantly, the efficiency with which
 feed was converted to milk improved up to a maximum of about 10 per-
 cent. These data indicate that bovine growth hormone could enable the
 dairy industry to satisfy the current demand for milk with an estimated 30
 percent fewer cattle and at a considerably reduced cost in feed (Animal
 Pharm, November 14, 1985, p. 15).
 It should be noted that the increases in milk production induced by
 growth hormone did not lead to net losses of body weight. Indeed the
 cattle gained weight while being treated with growth hormone and the
 gains were comparable to those of untreated cattle during the same period.
 This observation should put to rest concerns that growth hormone will
 strain dairy cattle by causing them to produce excessive milk (Biotechnol-
 ogy News, April 18, 1986, p. 1).
 A very novel alternative use of bovine growth hormone to stimulate milk
production was recently patented by Bauman and Sejrsen (U.S. Patent No.
4,521,409). These inventors discovered that treatment of dairy cattle dur-
ing adolescence stimulates mammary development and increases milk out-
put after their first calf. Whether treating with additional growth hor-
mone during lactation will further enhance milk production remains to be
determined (Genetic Technology News, July 1985, p.3).
 The role of growth hormones in regulating growth has been recognized
for years and for most species reductions in circulating growth hormone
levels have been unambiguously associated with reduced growth. How-
ever, until very recently it was questionable whether giving additional
growth hormone to "normally" growing animals would improve either
their growth or utilization of feed. The answers for the important stock
animals have been mixed. Increasing growth hormone levels in chickens
three- to ten-fold did not affect growth rate (Souza et al., 1984). When
growth hormone purified from ovine pituitaries was given to growing
wether lambs, growth was improved slightly but not significantly and effi-
ciency was improved significantly by about five percent (Muir et al.,
1983). In a more recent experiment (Johnsson and Hart, 1985), treatment
of growing female lambs with growth hormone from bovine pituitaries