Death in lambs during the prenatal

Supplementation of Merino ewes with cholecalciferol in late
pregnancy improves the vitamin D status of ewes and lambs
at birth but is not correlated with an improvement in immune
function in lambs
A. LockwoodA,D, A. Currie A
, S. HancockA, S. BroomfieldA, S. Liu B
, V. ScanlanA,
G. A. KearneyC and A. N. ThompsonA
ASchool of Veterinary and Life Sciences, Murdoch University, Murdoch, WA 6150, Australia.
B
School of Animal Biology, University of Western Australia, Crawley, WA 6009, Australia.
C36 Payne Road, Hamilton, Vic. 3300, Australia.
DCorresponding author. Email: [email protected]
Abstract. Functional deficiencies of the immune system are known to predispose human and animal neonates to death.
Thus, immune competency may be a significant factor influencing the mortality of lambs. Vitamin D has been recognised to
improve immune function and is transferred across the placenta. This study tested the hypotheses that (1) supplementation of
Merino ewes with cholecalciferol during late pregnancy will increase the concentrations of vitamin D in the ewe and lamb
at birth and (2) supplementation of Merino ewes with cholecalciferol during late pregnancy is correlated with an increase in
innate phagocytic and adaptive antibody immune responses in the lamb. Merino ewes (n = 53) were injected intramuscularly
with 1 · 106 IU cholecalciferol at Days 113 and 141 of pregnancy. A control group (n = 58) consisted of ewes receiving no
additional nutritional treatments. The vitamin D status of ewes and lambs was assessed up until 1 month post-lambing.
Lamb immune function was assessed by analysing the functional capacity of phagocytes, and the plasma IgG and antitetanus-toxoid antibody concentrations between birth and weaning. Maternal supplementation with cholecalciferol
increased the plasma 25(OH)D concentrations of both ewes (137 vs 79 nmol/L; P < 0.001) and lambs (49 vs 24 nmol/
L; P < 0.001) at birth compared with the controls. Supplementation with cholecalciferol had no significant effect on the
phagocytic capacity of monocytes or polymorphonuclear leukocytes, the concentration of IgG in the colostrum or plasma
of lambs, or the vaccine-specific antibody response against tetanus toxoid. Overall, the results support our first hypothesis,
but suggest that maternal supplementation with 1 · 106 IU cholecalciferol does not improve innate, passive or adaptive
immune function in lambs.
Additional keywords: lamb survival, immunity.
Received 12 February 2015, accepted 22 October 2015, published online 18 February 2016
Introduction
Lamb mortality represents a major production loss for the
Australian sheep industry. On average, 30% of all lambs born
will die before weaning, and ~80% of lamb deaths occur in the
first 48–72 h of life (Miller et al. 2010; Oldham et al. 2011;
Hawken et al. 2012; Hinch and Brien 2014; Paganoni et al. 2014).
Lamb birthweight is the greatest contributor to lamb survival
and is strongly influenced by ewe nutrition during pregnancy
(Oldham et al. 2011; Paganoni et al. 2014). However, even at
the optimal birthweight of 4.5–5.5 kg (Oldham et al. 2011; Hinch
and Brien 2014), lamb survival to weaning rarely exceeds 90%
for singles, 75% for multiples and 60% for triplets (Paganoni
et al. 2014), suggesting that factors independent of birthweight
must also influence lamb survival. Functional innate and
adaptive immune deficiencies in neonatal mammals are known
to predispose them to infections, and the associated inflammation
may cause tissue damage and/or dysfunction and death,
particularly in the perinatal period (Firth et al. 2005; Futata
et al. 2012). However, the role of immune competency in the
survival of lambs is poorly understood. The incidence of
infection directly causing death in lambs during the prenatal
and neonatal periods ranges from 0.2% to 30% (Hughes et al.
1971; Dennis 1974; Dwyer 2008; Rad et al. 2011), and while
active infections have been previously identified in lambs,
primarily via postmortem examination, the abilities of lambs
to mount immune responses in early life have not been widely
investigated.
Neonatal lambs are reliant on passive transfer of antibodies
from the ewe’s colostrum for protection in early life, and failure
of passive transfer of immunity is well recognised as a cause
of postnatal infection and death in lambs during the first
week of life (Gokce and Erdogan 2009; Gokce et al. 2014).

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