BSc- MSc (Integrated)

A study was conducted to evaluate the differences in the meat production characteristics
of three indigenous goat breeds (Osmanabadi, Malabari and Salem Black) to heat stress
challenges. The primary objective of the study was to compare the meat production potential
of two indigenous goat breeds (Malabari and Salem Black) when they were shifted from their
native tract to a new agro-ecological zone with the local breed (Osmanabadi) during heat stress
exposure. The impact of heat stress on meat production were assessed based on the changes in
their carcass characteristics, primal cuts, carcass dimensions, physico-chemical attributes,
proximate analysis, organoleptic variables, plasma leptin level and skeletal muscle myostatin
and heat shock protein 70 (HSP70) gene expression patterns. The study was conducted for a
period of 45 days in thirty six 10 months to one year old female goats (12 animals in each
breed). The goats were randomly allocated into six groups: OSC (n=6; Osmanabadi control),
OSHS (n=6; Osmanabadi Heat stress), MC (n=6; Malabari Control), MHS (n=6; Malabari Heat
stress), SBC (n=6; Salem Black Control) and SBHS (n=6; Salem Black Heat Stress). Goats
were stall-fed with a diet composed of 60% roughage and 40% concentrate. All animals had
access to ad-libitum feed and water and they were fed and watered individually. The OSC, MC
and SBC goats were placed in the shaded pens while OSHS, MHS and SBHS goats were
exposed to heat stress in outside environment between 10.00 h to 16.00 h. The animals were
slaughtered at the end of the study and their meat characteristics were assessed. The findings
from the study revealed that heat stress caused significant reduction in live weight (P<0.01),
pre-slaughter weight (PSW) (P<0.01), loin eye area (LEA) (P<0.01), and fat score (P<0.01) in
all three breeds but with different magnitude. However, heat stress reduced (P<0.01) only the
hot carcass weight and separable fat in SBHS and OSHS goats respectively. Further, heat stress
significantly influenced only the fore saddle (P<0.01), hind saddle (P<0.05), rack (P<0.05),
and breast (P<0.01), weights of the primal cuts. Among the linear carcass dimensions, heat
stress significantly (P<0.05) reduced only the chest depth and leg length in the goats. Further
among the offals, heat stress significantly reduced the liver (P<0.01) weight while significantly
(P<0.01) increased the lung with trachea (P<0.01) weights in only SBHS group. In addition,
heat stress increased (P<0.01) the ultimate meat pH in both OSHS and MHS groups. Among
the sensory characteristics, appearance reduced significantly (P<0.01) in both OSHS and MHS
groups and flavour reduced (P<0.01) in both MHS and SBHS groups. Further, texture was
found to be significantly (P<0.05) lower in OSHS while the overall acceptability was
significantly (P<0.01) lower in SBHS group. Heat stress also was found to significantly
(P<0.01) increase the plasma leptin level both in MHS and SBHS goats. In addition, heat stress
reduced (P<0.05) the skeletal muscle myostatin mRNA expression both in OSHS and MHS
goats. Furthermore, heat stress increased (P<0.05) the HSP70 mRNA expression in all the
stress groups. However, the magnitude of difference pertaining to increased HSP70 expression
was significantly (P<0.05) higher in OSHS while significantly (P<0.05) lower in SBHS group.
Thus, it was concluded that heat stress induced deteriorating changes in the meat characteristics
of all the three breeds. However, the magnitude of these changes was comparatively less severe
in Salem Black breed. Further, the study also revealed the scope of using plasma leptin,
myostatin and HSP70 genes as biomarkers to assess the impact of heat stress on meat
production characteristics in indigenous goats.
Keywords: Carcass traits; Climate change; Goats; Heat stress; HSP70; Leptin; Myostatin