Nutritional skewing of conceptus sex in sheep: effects of a maternal diet enriched in rumen-protected polyunsaturated fatty acids (PUFA).
BACKGROUND
Evolutionary theory suggests that in polygynous mammalian species females in better body condition should produce more sons than daughters. Few controlled studies have however tested this hypothesis and controversy exists as to whether body condition score or maternal diet is in fact the determining factor of offspring sex. Here, we examined whether maternal diet, specifically increased n-6 polyunsaturated fatty acid (PUFA) intake, of ewes with a constant body condition score around the time of conception influenced sex ratio.


METHODS
Ewes (n = 44) maintained in similar body condition throughout the study were assigned either a control (C) diet or one (F) enriched in rumen-protected PUFA, but otherwise essentially equivalent, from four weeks prior to breeding until d13 post-estrus. On d13, conceptuses were recovered, measured, cultured to assess their capacity for interferon-tau (IFNT) production and their sex determined. The experiment was repeated with all ewes being fed the F diet to remove any effects of parity order on sex ratio. Maternal body condition score (BCS), plasma hormone and metabolite concentrations were also assessed throughout the study and related to diet.


RESULTS
In total 129 conceptuses were recovered. Ewes on the F diet produced significantly more male than female conceptuses (proportion male = 0.69; deviation from expected ratio of 0.5, P < 0.001). Conceptus IFNT production was unaffected by diet (P > 0.1), but positively correlated with maternal body condition score (P < 0.05), and was higher (P < 0.05) in female than male conceptuses after 4 h culture. Maternal plasma hormone and metabolite concentrations, especially progesterone and fatty acid, were also modulated by diet.


CONCLUSIONS
These results provide evidence that maternal diet, in the form of increased amounts of rumen-protected PUFA fed around conception, rather than maternal body condition, can skew the sex ratio towards males. These observations may have implications to the livestock industry and animal management policies when offspring of one sex may be preferred over the other.
Green
Mark P
MP
Division of Animal Sciences, University of Missouri, Columbia MO 65211, USA. mark.green@agresearch.co.nz
Spate
Lee D
LD
Parks
Tina E
TE
Kimura
Koji
K
Murphy
Clifton N
CN
Williams
Jim E
JE
Kerley
Monty S
MS
Green
Jonathan A
JA
Keisler
Duane H
DH
Roberts
R Michael
RM
D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D004041:Dietary Fats / Q000494:pharmacology*; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology*; D005260:Female; D005333:Fetus / Q000378:metabolism; D007370:Interferon Type I / Q000096:biosynthesis; D011247:Pregnancy; D011257:Pregnancy Proteins / Q000096:biosynthesis; D011270:Pregnancy, Animal / Q000502:physiology*; D011374:Progesterone / Q000097:blood; D012417:Rumen / Q000378:metabolism; D012744:Sex Ratio; D012756:Sheep / Q000502:physiology*
D004041:Dietary Fats; D005231:Fatty Acids, Unsaturated; D007370:Interferon Type I; D011257:Pregnancy Proteins; C020947:interferon tau; D011374:Progesterone