Metabolic changes in ewes shorn during mid-pregnancy
R.G. SHERLOCK, P.R. KENYON, S.T. MORRIS AND T.J. PARKINSON
Institute of Veterinary, Animal and Biomedical Sciences, Massey
University, Palmerston North, New Zealand.
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NZSAP 2003 Abstract No. 35
Proceedings of the New Zealand Society of Animal Production
63: 144-148
Previous work has shown that, under appropriate circumstances,
mid-pregnancy shearing results in an increase of both the birth and
weaning weights of multiple-born lambs. However, the physiological
mechanisms for this response are poorly understood. This paper attempts
to clarify the link between mid-pregnancy shearing and heavier lamb
weights by investigating the metabolic changes that occur in ewes that
are shorn in mid-pregnancy. Twenty-four twin-bearing ewes were assigned
to one of two treatment groups; mid-pregnancy shorn (70 days after the
mid-point of mating: P70) or unshorn. Groups were balanced for ewe age
and weight. Blood samples were collected from all animals on days P53,
P69, P81, P84, P90, P109 and P130, for measurement of concentrations of
triiodothyronine (T3), thyroxine (T4), cortisol, glucose, non-esterified
fatty acids (NEFA) and beta-hydroxybutyrate. Lamb birth weight, girth
and crown-rump length (CRL) measurements were collected within 24 hrs of
birth. Lambs were weighed at weaning. Mid-pregnancy shearing increased
lamb birth weights and girths by 0.43 kg (P<0.05) and 2.18 cm
(P<0.05) respectively although these differences were not significant
once adjusted for date of birth. There was no effect on CRL. Plasma
concentrations of T3 and T4 were significantly higher in
mid-pregnancy-shorn ewes relative to unshorn ewes at both P81
(P<0.01) and P84 (P<0.01 and P<0.05 respectively) and T4
concentrations tended to be higher at P90 (P<0.10). There was a
significant effect of shearing treatment at P81 on plasma NEFA
concentrations (P<0.05). There were no significant post-shearing
differences in mean cortisol, glucose or beta-hydroxybutyrate
concentrations. The study proposes that the most likely mechanism by
which mid-pregnancy results in higher lamb birth weights is by
increasing maternal thyroid hormone concentrations, resulting in an
increase in fat mobilisation causing increased NEFA concentrations in
the maternal blood supply, which in turn improves placental nutrition
and, thus, lamb birth weight.
Keywords: NZSAPAB;
mid-pregnancy shearing; birth weight; thyroxine; cortisol; NEFA;
metabolism
Last Updated 8/07/2004
