Animal Production Science Question

Immunoglobulin-G (IgG) is the predominant immunoglobulin
found in ewe colostrum and measurement of serum IgG
concentration in neonatal lambs can be used as an indicator of
immune status (Bernadina et al. 1991; Hashemi et al. 2008).
Passively acquired IgG molecules have several functions that
promote neonatal innate immune responses, including activation
of complement, prevention of microorganism attachment to
mucosal membranes and the opsonisation of bacteria for
phagocytosis and killing (Parkin and Cohen 2001). Phagocytosis
is an essential innate immune defence, whereby phagocytes
identify, engulf and destroy invading pathogens through an
array of cellular mechanisms (Tosi 2005). Phagocytosis is also
essential in linking innate to adaptive immune responses, by
promoting the induction of T-cell responses and, hence, humoral
immunity (Prosser et al. 2013). Impaired phagocytosis in the
newborn can lead to inadequate control of pathogen replication,
resulting in higher microbial loads and greater induction of
pathogen-driven inflammatory responses in affected tissues
and organs (Garvy 2004). Hence, poor adaptive immune
competency in ewes, and poor passive immunity in the lamb,
along with immature phagocyte function in newborns, may be
associated with adverse infection outcomes in lambs, and,
therefore, could contribute to lamb mortality.
Vitamin D has been recognised to have several roles in
the regulation of immune function and can enhance innate
antimicrobial immune responses, while dampening excessive
adaptive responses and inflammation to maintain self-tolerance
and prevent auto-immunity (Lang et al. 2013). During
pregnancy, vitamin D is thought to enhance innate antimicrobial and anti-inflammatory responses within the
placenta and reproductive tissues, which may protect the
fetus from intrauterine infection and subsequent inflammation
(Grayson and Hewison 2011). Maternal transfer of vitamin D to
the lamb may occur in utero, or, to a lesser degree, postnatally
via intake of milk (Lapillonne 2010). Thus, any vitamin D
deficiency in pregnant ewes could have negative impacts on
the immune system of the ewe and/or lamb. Increasing the
vitamin D concentrations in neonatal lambs at birth may
confer a greater ability to control infection and/or limit
infection-driven inflammation, and, thus, may contribute
to improved lamb survival. Supplementation of ewes with
vitamin D during pregnancy could provide an effective
means to increase the concentrations of vitamin D in the ewe
and her lamb/s in utero, thereby improving innate and/or
adaptive immunity in the ewe, and innate and/or passive
immunity in the lamb. The present study, therefore, 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.
Materials and methods
All procedures described were performed according to the
guidelines of the Australian Code of Practice for the Use of
Animals for Scientific Purposes 2013 and received approval
from the Murdoch University Animal Ethics Committee.
Research site, animals and experimental design
The research was performed at the University of Western
Australia Future Farm near Pingelly in Western Australia
(32
300
2300S, 116
590
3100E) between November 2013 and
August 2014. Two hundred Merino ewes aged between 4 and
7 years were sourced from the ‘Maternal Efficiency Flock’
(Rosales Nieto et al. 2013). All ewes had full pedigree
records. Ewes were artificially inseminated with semen from
four Merino sires, and those identified to be pregnant were
allocated into three replicates of each of the two treatment
groups, namely, control or vitamin D supplementation during
late pregnancy. The ewes were shorn in November 2013 before
artificial insemination. Lambing occurred during late April–early
May 2014 and lambs were weaned in early August 2014.
Animal management and treatments
Ewes were managed to achieve a body condition score greater
than three for joining. Oestrus was synchronised in ewes via
controlled internal drug releases (Eazi-Breed CIDR® Sheep
and Goat Device, Zoetis, Sydney, NSW, Australia) that were
inserted into the vagina of all ewes 14 days before artificial
insemination and were withdrawn 48 h before artificial
insemination. One day before artificial insemination, the ewes
were weighed and body condition was scored (Jefferies 1961).
Ewes were artificially inseminated laproscopically in November
2013. Semen from the four sires was allocated to the ewes
according to their age and liveweight and condition score
before insemination. The ewes were managed as a single flock
and grazed the same paddocks until Day 113 of pregnancy.
Ewes were pregnancy scanned via trans-abdominal
ultrasonography on Day 55 of pregnancy to identify singleand twin-bearing ewes (Fowler and Wilkins 1984). After
confirmation of pregnancy status, ewes were weighed and
condition scored every 1–2 weeks and nutrition was managed
accordingly, so as to achieve a body condition score of 2.5 at
lambing. The ewes grazed paddocks with very low levels of dry
annual pastures and, on average, were supplemented with
700 g/day of supplementary feed (52% lupins (13.9 MJ ME/kg
DM and 31.2% CP), 31% oats (12.8 MJ ME/kg DM and 12.2%
CP) and 17% oaten chaff (9.3 MJ ME/kg DM and 7.6% CP))
between pregnancy scanning and lambing.
On Day 111 of pregnancy, ewes were administered a
clostridial 6-in-1 booster vaccine (Glanvac® 6, Zoetis). Ewes
were then allocated into three replicates for each of the two
treatment groups, namely, control or vitamin D supplementation,
according to ewe age, sire of the lamb, pregnancy status, and
liveweight and condition score at insemination (n = 17–20 ewes
per treatment per replicate). The control group (n = 58) consisted
of ewes receiving no additional nutritional treatments. Ewes
supplemented with vitamin D (n = 53) received an injection of
cholecalciferol (vitamin D3; Bova Compounding, Sydney, NSW,
Australia) at Days 113 and 141 of pregnancy. On each occasion,
1.0 · 106 IU cholecalciferol, in oil, was injected intramuscularly
into the hind-limb. Each replicate of the two treatments was
combined after the first injection of cholecalciferol and the three
flocks of 37 control and vitamin D ewes grazed separate prelambing plots until Day 141 of pregnancy. At this time, the ewes
within each replicate were reallocated to a lambing plot according

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