Two experimental flocks of Romney sheep selected for increased hogget fleece weight show high selection responses (30-40% of their controls) and evidence for altered seasonal patterns of annual wool growth, in line with published evidence from other flocks. While a preliminary experiment was unable to detect consistently significant line differences in plasma prolactin concentration at set time periods, there were indications of altered seasonal patterns in prolactin concentration and line differences in its association with wool growth. Both selection and control lines showed low prolactin concentrations in June and July (16 ng/ml). Concentrations rose in August, September and October, approximately doubling each month to an average level of 111 ng/ml in early November. Early results from this longitudinal study, still in progress, suggest that animals from the selected lines tended to maintain their low prolactin concentrations longer into the winter and early spring, and that this tendency is associated with a higher hogget fleece weight. By contrast, in the unselected control lines, high hogget fleece weight tended to be positively associated with increasing prolactin levels over the winter/early spring period.
Proceedings of the New Zealand Society of Animal Production, Volume 53, , 319-322, 1993
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