@conference {40705,
	title = {Grazing behaviour of alpaca and sheep},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {55},
	year = {1995},
	month = {Jan},
	pages = {183-185},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	abstract = {Differences between breeds in seasonal breeding activity have been  linked to seasonal shifts in both LH levels and the magnitude of oestradiol  negative feedback. Studies were undertaken to determine the endocrine  differences in ewes of the same breed with high or low breeding values  (BVs) for date of lambing.   Forty-eight ewes (24BV- early lambing and 24BV + later lambing) were  selected from the flocks and 16 ewes (8 of each BV class) were  ovariectomized (ovx) and implanted with silastic implants containing  oestradiol- 17Beta. All ewes were bled 2 x week for a 12 month period  commencing in November to provide data on basal LB. The ovx ewes were  subjected to rapid sampling (every 20 min for 24 h) using automated  sampling equipment, on 5 occasions approximately 1 month after each  equinox and solstice in that year and samples were analysed for LH pulse  frequency.   Basal LH levels showed a seasonal shift with the ovx ewes having a greater  amplitude of change than the entire ewes. LH levels in the ovx ewes were  lower in November to January, and higher in March, April, May and June;  and lower again in August, September, October than in entire ewes. There  was no evidence of a major difference in pattern due to BV. In the ovx ewes  the values for the BV- animals tended to be lower than those for the BV+  ewes during March through July.   At the initial rapid bleed no animals showed pulse activity. In April the BV-  group had more pulses per 24 h (6.0 v 2.8). In July there was no difference  in proportion having pulses (8/8) nor in the pulse frequency (5.3 v 5.6/24 h).   In October the BV- animals had a higher pulse frequency (2.8 v 1.0), while  the proportion of animals (3/8) exhibiting pulses was the same. More BV-  ewes had pulses in January (6 v 3) and of those with pulses the BV- group  had higher frequency (7.7 v 4.7).   These data confirm the seasonal shifts in basal LH levels and in LH pulse  frequency. Selection for earlier lambing had no effect on the pattern of basal  levels. In the ovariectomized ewe the differences in LH pulse frequency due  to BV detected in October and final bleed in January were not as marked as  expected for the differences in the breeding activity of the two flocks but  they confirm that differences in sensitivity to oestradiol 17Beta negative  feedback are associated with differences in the onset of breeding season of  ewes selected for earlier lambing within one breed. It would appear that  selection for earlier lambing has disturbed the association between day length  and LH pulse activity and the sensitivity of the pituitary to GnRH.  },
	issn = {1176-5283},
	author = {Sharp P and Knight TW and Hodgson J}
}
