SEMEN QUALITY AND HAEMATOLOGICAL CHARACTERISTICS OF EXOTIC AND CROSSBRED BOARS EXPOSED TO DIFFERENT DURATIONS OF THERMAL STRESS IN THE HUMID TROPICS

ABSTRACT

This study was conducted to investigate the effect of 45 and 60 minutes of exposure of crossbred (LW x Local) and exotic (LW) boars to tropical solar radiation on their body temperature pattern, libido, semen quality and haematological profile. 12 LW x Local and 12 LW boars of 10 months old were used for the experiment. The experiment was carried out in the Piggery Unit of the Department of Animal Science Farm, University of Nigeria, Nsukka for a period of eight weeks (4 weeks for the exposure and, another 4 weeks for the  boars  to  recover).  The  results  showed  that,  in  the  exposure  period,  the  rectal temperature of the boars exposed to solar radiation significantly (P<0.05) increased from 36.80 ± 0.360C to 41.88 ± 0.470C in LW x Local and 37.23 ± 0.360C to 42.04 ± 0.240C in LW boars and these changes varied significantly (P<0.05) between the durations of the exposure.  The  hyperthermic  state  of the exposed  boars  adversely  affected  the  libido, semen  quality  and  haematological  characteristics.  Specifically,  the  values  for  sperm progressive  motility,  sperm  concentrations,  sperm  abnormalities,  reaction  time,  and ejaculation  time were significantly  (P<0.05)  affected  between  genotypes  and between durations  of exposure  to thermal treatments.  The  interactions  effects of genotype  and duration of exposure (G x D) were highly significant (P<0.01) in all these parameters. Total volume  of ejaculate  was  significantly  (P<0.01) higher in LW boars than LW x Local,  while  volume  of   gel-fraction,   strained  ejaculate   and  semen  pH  were  not significantly (P>0.05) different between genotypes and between durations of exposure. G x D interaction also had no significant effect on these parameters. Total ejaculate volume was not significantly (P<0.05) affected by durations of exposure and G x D interaction. Erythrocyte count, PCV, Hb concentration, MCV, MCH and MCHC were significantly different  (P<  0.05)  between  genotype  and  between  durations  of  exposure  to thermal stress.  G x D interaction  significantly  (P<  0.05)  influenced  these  parameters.  In the recovery phase, the two genotypes were reared under  average ambient temperature  of 26.100C. They returned to their normal body temperature of 37.00 ± 0.190C and 36.97

±0.200C  for LW x Local and LW boars respectively  within  period of one hour  after withdrawal of heat stress. The LW x Local boars recovered much more rapidly (30-40 minutes) than LW (45 -60 minutes). The LW x Local boars recovered much faster than the LW in most of the semen quality and haematological traits under both durations of exposure. The crossbred pigs retuned to their post exposure values from the 2nd week for

boars under 45 minutes exposure and 3rd week for boars exposed for 60 minutes.  The

LW boars recovered from the 3rd week and 4th week respectively for boars exposed for

45  minutes  and  60  minutes.  Based  on the  results  recorded,  The  LW  x  Local  boars appeared to have resisted the thermal stress better than the LW boars and may be suitable for the out-door system of production in this climate than the LW.

CHAPTER ONE

1.1 Background of the Study

INTRODUCTION

In some parts of Nigeria, especially the southern parts, farmers keep indigenous and exotic pigs outdoors during the day to search for food. These pig farmers have a target which is to save money (Bull, 1997; McGlone, 1998). However, in these areas which have humid tropical climate, pigs are mostly exposed to ambient temperatures above their thermo-neutral zone during the day (Curtis 1992; McGlone, 1998) while at night they are kept indoors when the  ambient temperatures  are somewhat  near their thermo-neutral  zone. Despite  this  diurnal  variation  in ambient  temperatures,  pigs in these areas still survive and reproduce, but the temperature variation to which they are exposed constantly tend to significantly affect their reproductive performance (Ayo et al.,  1996),  semen  quality  (McNitt  and  First,  1970;  Wettemann  et  al.,  1976),  and haematological status (Schalm et al., 1975; Coles 1986).

Generally,  reproductive  performance  of boars is reduced during the hot  season (Ayo  et al., 1996;  Hahn,  1999;  Ugwu  and Nwakalor,  2007).  Exposure  of  boars  to increased  ambient  temperatures  results  in the reduction  of semen  quality  (Setchell,

1998). This decrease in semen quality of boars during heat stress may be  associated with  reduced  pregnancy  rates  (Setchell,  1998;  Walters  et  al.,  2005)  and  increased embryonic mortality (Zhu and Setchell, 2004; Zhu et al., 2004). Exposure of boars to increased  ambient  temperature  for 3 days caused  a  reduction  in semen  quality  that persisted  for 6 to 8 weeks  after  treatment  (Setcell,  1998;  Zhang,  2006).  Similarly, fertility  was reduced  in rams after  short-term  exposure  of whole  body to increased ambient  temperatures  (Hafez  1993).  Also,  exposure  to  high  ambient  temperatures influences the erythrocytes  and hemoglobin concentrations  (Coles, 1986; Connor and

Orzechowski, 2001) as well as packed cell volume (Schakm et al., 1975). The effects of exposing boars to tropical solar radiation as is the case in the humid tropical climate have not been substantially studied.

Therefore,  the  present  research  is undertaken  to determine  the semen  quality, haematological  characteristics,  libido  and  body  temperature  regimes  of  exotic  and crossbred boars exposed to tropical solar radiation for 45 and 60 minutes.

1.2      Objectives of the Study

The general objectives  of this study is to determine  the effect of 45 and  60 minutes exposure of Large White x Local (LW x Local) crossbreds and Large White (LW)  boars  to  tropical  solar  radiation  on  their  body  temperature  regimes,  libido, ejaculate characteristics and hematological parameters.

The specific objectives of the study are:

i.         to  determine the effect of exposing LW x Local and LW boars to different durations of solar radiation on their normal body temperature pattern;

ii.        to determine the effect of the exposure on ejaculation reaction time of the two genotypes;

iii.       to  compare  the  characteristics   of  the  ejaculates   of  the  two   exposed genotypes;

iv.       to compare the effect of the exposure on haematological profile of the two boar genotypes; and

v.        to  find  out  the  time  of  full  recovery  to  normal  semen  quality   and haematology in the two genotypes after exposure to tropical solar radiation.

1.3      Justification of the Study

The reproductive  efficiency of pigs in tropical countries like Nigeria tends  to fluctuate.  This  may  be  because  of  the  seasonal  and  diurnal  variation  in  prevailing temperatures which causes adverse changes in the growth and reproductive pattern of pigs (Samisoni and  Blankshaw, 1971; Hafez, 1993) and haematology (Schalm, 1975; Coles, 1986). These changes are accompanied by poor quality semen and low fertility rate. The consequences of this problem are obviously grave in southern parts of Nigeria where ambient temperatures,  coupled  with high humidity, occur throughout the year and more so with the present adverse global climate change.

The  management  of  boars  to ensure  good  sperm  production  under  different environmental conditions is a major concern for swine keepers in tropical countries and countries where there are extreme environmental changes.  Such changes create stress in boars and negatively influence the production of spermatozoa (Egbunike and Dede,

1980; Matswki et al., 2003). High temperature during dry season may result in lower feed consumption and create stress that may result in the alteration of spermatogenesis (Steinbach,  1971; Ayo et al., 1996). However,  management  strategies  such as good housing,  proper  mating  conditions  and normal  mating  frequency,  may be useful  in facilitating  production  of  good  quality  semen   and   sustaining  good  reproductive efficiency in hot climates.

Also, high temperature as obtained during dry season may adversely influence haematological    traits   such   as   erythrocyte    count   (Coles,   1986);    hemoglobin concentration  (Hb)  (Schalm,  1975;  Coles,  1986;  Santoro  and  Faucitano,  1996)  and packed cell volume (PCV) (Schakm, 1975; Cheesbrough,  1991).    Other factors that affect  the  blood  picture  of  pigs  are  diet  (Edwards  1985),  water  intake  and  feed restriction (Hill and Powell, 1975; Graf, 1984; Esonu, 2000).

In general, thermal stress during hot seasons is an unwholesome development in swine  industry  of  the  tropics.    There  is,  therefore,  the  need  to conduct  studies  to determine the effects of daily stress due to persistent solar radiation on two genotypes of boars mainly reared in this part of the humid tropics.

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