Ml. Green et al., Serum concentrations of melatonin during scotophase and photophase in 3, 4, 5 and 6 month old gilts and barrows, ANIM REPROD, 57(1-2), 1999, pp. 99-110
One-hundred-twenty prepubertal crossbred gilts (Hampshire x Duroc) x (Yorks
hire x Landrace) were removed from the nursery at 68.7 +/- 0.4 days of age
and 23.6 +/- 0.9 kg body weight and relocated to a conventional grower-fini
sher unit. In addition, 60 barrows of similar genetics were relocated from
the nursery at 71.0 +/- 0.5 days of age and 27.4 +/- 0.5 kg body weight to
the same building. Twelve mature anestrous ewes that weighed 77.0 +/- 2.4 k
g were assigned randomly to one of four pens of equal dimensions among the
pens containing pigs. Ewes were included in this study to serve as positive
controls since their secretory profiles of melatonin are well characterize
d. All pigs were bled by jugular venipuncture at approximately 3, 4, 5 and
6 months of age. At each age in the pigs and the mature ewes, a single samp
le was obtained during photophase and scotophase. Illumination intensity du
ring the period of incandescent lighting averaged 220 1x. Blood collection
was initiated approximately 4 h after sunrise and 3.5-4 h after sunset. The
proportion of animals that exhibited a nocturnal rise in melatonin (MEL) w
as similar (P > 0.05) between gilts and barrows, but was higher (P < 0.002)
in ewes than in pigs at each age examined. A greater proportion (P = 0.007
) of 3 month old barrows had a nocturnal rise of MEL than any other age of
barrow. Similarly, there was a tendency (P = 0.06) for more 3 month old gil
ts to exhibit a nocturnal increase in serum MEL than 4, 5 or 6 month old gi
lts. (C) 1999 Elsevier Science B.V. All rights reserved.