|Livestock Research for Rural Development 27 (2) 2015||Guide for preparation of papers||LRRD Newsletter||
Citation of this paper
An evaluation of one hundred and eight ewes and eighteen rams was made to determine the effect of coat colour on the reproductive performance of sheep. Mating was carried out for three consecutive lambings and reproductive traits of 36 ewes in each coat colour group (black, white and brown) were monitored. Traits measured were lambing interval, prolificacy, fecundity, litter weights, litter size at weaning and pre-weaning mortality. Data were analyzed using General Linear Model procedure of SAS (2007).
Black ewes had the shortest lambing interval of 7.61 months followed by brown ewes with 7.99 months while the white ewes had the longest lambing interval of 8.25 months. Prolificacy of the different coat colour types ranged between 1.58 and 1.18; black coat colour ewes had the highest prolificacy. The black ewe also had the greatest fecundity (2.50). Brown ewes produced the heaviest litters (3.43 kg). However, there was no significant difference in the litter weight of lambs produced by black ewes (2.82 kg) and that produced by white ewes (2.77 kg). Black ewes had the largest litter size (1.31) at weaning followed by brown ewes (1.15). White ewes had the least number of litters at weaning (1.03). Parity of the ewes as well as season of lambing also had significant effect on some of the traits measured. Black ewes were superior to other coat colour types with regards to the reproductive traits.
Key words: coat colour, reproductive performance, West African Dwarf Ewe
Reproductive performance is an important economic trait of interest for increasing the number of animals in a flock (Osinowo 2006). The reproductive rate of the flock is one of the most important factors affecting productivity and economic success. The reproductive efficiency of sheep is the net biological accomplishment of all reproductive activities i.e. puberty, oestrus, ovulation, fertilization, implantation, gestation and successful lambing. It reflects the fecundity, fertility and prolificacy of an adult animal (Khan et al 2000). An effective breeding plan can only be devised after a thorough knowledge has been obtained about the inheritance of economically important traits (Thiruvenkadan et al 2008).
The West African Dwarf sheep are the predominant breed of sheep in the humid zone, where other Nigerian breeds of sheep are susceptible to trypanosome infection. They have a range of coat colours that vary from white, brown, black to combinations of these colours in various proportions (Ozoje 1998). The colouration of hair and wool is due to the pigment melanin. The different shades and colours are therefore brought about by variations in the size, density and the distribution of the pigment granules (Adalsteinsson 1994). In the sheep, as in other mammals, there are two types of pigment. Eumelanin responsible for black or a brown colour and the phaeomelanin, which results in a tan or yellow colour (Lundie 2011).
The effect of coat colour has been reported on certain growth traits in the West African Dwarf goats (Odubote1994 ,Ozoje and Mgbere 2002). Some authors have reported the effects of coat colour of sheep on adaptive traits like tolerance to heat stress and tolerance to helminth infestation (Mc Manus et al2011; Sanusi et al 2011).
There is a need to examine the influence of coat colour on reproductive performance which is an important economic trait of interest in sheep as this will help in developing breeding plans for the improvement of West African Dwarf sheep. This study is therefore carried out to evaluate the reproductive performance of pure black, white and brown West African Dwarf sheep which are the prominent colours of this breed of sheep.
The experiment was carried out at the sheep unit of the Teaching and Research Farm, University of Agriculture, Alabata road, Abeokuta, Ogun State, Nigeria. The University Teaching and Research Farm is located in Odeda Local Government Area of Ogun State, Nigeria. The area which lies in the South Western part of Nigeria has a prevailing tropical climate with a mean annual rainfall of about 1037 mm. The mean ambient temperature ranges from 28°C in December to 36°C in February with a yearly average humidity of about 82%. The vegetation represents an interphase between the tropical rainforest and the derived savannah.
One hundred and eight ewes and eighteen rams (36 white ewes, 36 black ewes, 36 brown ewes, 6 black rams, 6 white rams, and 6 brown rams) and their progeny were used for this study. Semi-intensive management system was practiced. The animals were housed in slated floor pens and were allowed to graze in the morning but were restricted from grazing during the mating period. Concentrate feed which was composed of maize (15%), wheat offal (45%), PKC (30%), oyster shell (3.5%), bone meal (5%), salt (1%), premix (0.5%) was supplied to the animals on their arrival from grazing in the afternoon. Ecto- and endo-parasites medications (Ivomec) were periodically given to the animals during the period of the experiment. The health status of all the animals was also properly monitored and immediate adequate treatment was given to sick animals. Peniciling-streptomycin and oxytetraciline injection were used as broad spectrum antibiotics. A mating ratio of one ram to six ewes was use throughout in the study. Mating was carried out for three consecutive lambing periods.
|Photo 1. Brown ram x Brown Ewes||Photo 2. Black ram x Black ewes||Photo 3. White ram x White ewes|
Reproductive traits of the 36 ewes of each group were monitored within the 3 lambing seasons. The study was carried out for a period of two years.
The parameters evaluated included:
Lambing interval (LI): This is the period between one parturition (lambing)
and the next one in months.
Prolificacy / Litter size at birth (PFC): The number of offspring produced by a ewe at the time of parturition.
Fecundity (FD): This was estimated as the average number of offspring produced by each dam per year. It was based on the total number of offspring produced by each dam during the entire period of study.
Litter weights (LWT): The average weight of the litter at birth in kg.
Litter size at weaning (LSW): The number of offspring at weaning per ewe.
Pre-weaning mortality: The percentage of lamb mortality to the litter size at birth was estimated.
Data were analyzed using General Linear Model procedure of SAS (2007). The model was:
Yijkl = µ + Ci + Pj +Sk + (CP)ij + (PS)jk + (CS)ik + (CPS)ijk+ eijkl
Yijkl = the parameter of interest
µ = overall mean for the parameter of interest
Ci = fixed effect of ith coat colour type (i=1-3)
Pj = fixed effect of jth parity group (j=1-3)
Sk = fixed effect of kth season (k=1-2)
(CP)ij= interaction effect of coat colour and parity group
(PS)jk= interaction effect of parity group and season
(CS)ik = interaction effect of coat colour and season
(CPS)ijk= interaction effect of coat colour, parity and season
eijkl= random error associated with each record (normally, independently and identically distributed with zero mean and variance σ²e).
Means were compared using Duncan multiple range test procedure of the same statistical software.
Black ewes had the shortest lambing interval followed by brown ewes, while the white ewes had the longest lambing interval (Table 1). Prolificacy of the different coat colour types ranged between 1.58 and 1.18. Black coat colour ewes had the highest prolificacy. There was no significant difference in prolificacy between brown and white ewes. Litter size was affected by coat colour of ewes in this study. Black ewe had the largest litter size at birth. This is in line with the study of Ebozoje and Ikeobi (1998) on West Africa Dwarf goat who reported that litter size increased with increase in pigmentation intensity. However Odubote (1994) reported that coat pigmentation had no significant effect on the litter size of West Africa Dwarf goats under an intensive management system.
The least square means of fecundity rate as affected by coat colour of ewes followed similar pattern as that of prolificacy. The difference in fecundity rate between brown (1.89) and white ewe (1.71) was not significant. Nevertheless, the black ewe had the largest fecundity (2.50) as shown on Table 1. Brown ewes produced the heaviest litter (3.43 kg). However, there was no significant difference in the litter weight of lambs produced by black ewes (2.82 kg) and that produced by white ewes (2.77 kg). The significant effect of coat colour of West Africa Dwarf sheep on prolificacy and fecundity in this study agreed with the result of the study Ebozoje and Ikeobi (1998) who reported that prolificacy and fecundity rates were highly affected by coat colour among West Africa Dwarf (WAD) goats. Lower fecundity was recorded for white sheep in this study. This result also corresponds with that of Drymundsson and Adalsteinsson (1980) who reported that ewes with the Awh allele (white coat colour) had 15% lower fecundity on the average than those without the alleles. Similarly Adalsteinsson (1994) also observed that dominant allele Awt which produce white coat colour depressed ewe fertility in Icelandic sheep.
Black ewes had the largest litter size (1.31) at weaning followed by brown ewes (1.15). White ewes had the least number of litters at weaning (1.03). In the present study, it was observed that brown ewes produced the lambs which recorded the heaviest weaning weight while lambs with the lightest weaning weight were produced by white ewes in this study. Ebozoje and Ikeobi (1998) also reported that kids from the black does were about 1 kg heavier than kids from the white / tan does, 0.4 kg heavier than those from the brown does and 0.6 kg heavier than kids from does with white spots or patches on pigmented background at weaning. However, Odubote (1994) reported contrary results among West Africa Dwarf goats, claiming that weaning weights decreased with increase in coat colour intensity. In this study, lambing interval was significantly affected by variation in the coat colour of ewe as black coloured ewe had the shortest interval. The lambing interval reduced with the pigmentation intensity. Ebozoje and Ikeobi (1998) however reported that kidding interval was not affected significantly by coat colour among West Africa Dwarf goats.
The least square means shown in Table 1 showed that the highest pre-weaning mortality (29.6 %) was recorded among lambs produced by white ewes followed by lambs from brown ewes (21.3 %). Black ewes produced lambs with the least percentage pre-weaning mortality (15.3 %).
|Table 1. Least square means of reproductive traits as affected by coat colour|
|Lambing interval , months||7.61c||7.99b||8.23a||0.041||0.035|
|Litter weight at birth, kg||2.82b||3.43a||2.77b||0.231||0.038|
|Litter size at weaning||1.31a||1.15b||1.03c||0.132||0.045|
|Pre-weaning mortality, %||15.2c||21.3b||29. 6a||1.97||0.024|
|abcmeans in the same row for each parameter with different superscripts are significantly different (p <0.05)|
The significant effect of coat colour of ewe on the percentage pre- weaning mortality of West Africa Dwarf lambs observed in this study corroborated the finding of Ebozoje and Ikeobi (1998) who reported that mortality rate was affected by coat colour as percentage mortality decreased with increase in pigmentation intensity among West Africa Dwarf kids raised extensively. The authors termed coat colour as an adaptive feature favoring the less obvious ones. Odubote (1994) though reported a non- significant effect of coat colour on percent mortality of kids under an intensive management system, it was stated that coat colour is an adaptive feature necessary for survival.
Black ewes had the highest over-all reproductive performance while the least performance was recorded for the white ewes. Adalsteinsson (1970) as cited by Ebozoje and Ikeobi (1998) reported that the top dominant allele at the agouti locus (Awh) which produces white coat colour depressed ewe fertility in Icelandic sheep by about 0.15 lambs per ewe mated. Similar suppressive action of this allele could have been responsible for the differences observed in this study.
From the results, it is evident that parity of ewe significantly affected prolificacy and fecundity. In fact, prolificacy advanced with parity. Ewes in their first and second parity had the least prolificacy rate (1.19). However, there was no significant difference in prolificacy rate between ewes in third and fourth parity as well as those in fifth and sixth parities. The least square means of fecundity rate followed the same pattern with that of prolificacy. Young ewes in their first and second parity had the least fecundity rate (1.81). The difference in the least square means of the fecundity of ewes in the third and fourth parity (2.13) and that in fifth and sixth parity (2.15) was not significant. The lowest litter weight at birth was obtained for lambs produce by primiparous ewes and those in the second parity. The multiparous ewes in the fifth and sixth parity had the highest litter weight at birth (3.57 kg). In this study, the number of times at which an ewe had lambed (parity) was significant on prolificacy (litter size at birth) of West Africa Dwarf sheep. This is similar to the report of Baiden (2007) on the performance of West African Dwarf goats that litter size of first parity of doe was significantly smaller than those of subsequent parities. The result of the study of Notter (2000) on United State Targhee Suffolk and Polypay sheep also showed a positive relationship between parity and litter size. Ali et al (2009) reported a significant increase in litter size with advanced parity. Koycegiz et al (2009) reported that the peak litter size was achieved at fourth parity of ewes. However, Bemji et al (2001) reported sixth parity for Yankasa sheep. The features required for successful litter bearing are not fully developed in young ewes while these have been attained in multiparous ewes and this may be responsible for the increase in prolificacy as parity advanced.
Primiparous ewes and those in the second parity had the smallest litter size at weaning (1.05) followed by those in the third and fourth parities (1.29) while the ewes in their fifth and sixth parity had the largest number (1.35) of litter (Table 3). Contrary to the observation of Koycegizet al (2009) that parity was a significant source of variation for litter size at birth but not at weaning, parity had significant effect on both litter size at birth and at weaning in this study.
Percentage pre-weaning mortality of lambs reduced with increase in parity. Ewes in the first two parities had the highest percentage (23.75%) pre-weaning mortality followed by those in the third and fourth parity (21.50% ). The multiparous ewes in the fifth and sixth parity had the least pre-weaning mortality rate of 20.92 percent.
|Table 2. Least square means of reproductive traits as affected by parity of ewe|
- 6th parity
|Lambing interval, months||7.94||7.87||7.99||0.072||0.088|
|Litter weight at birth, kg||2.17b||3.28a||3.57a||0.213||0.047|
|Litter size atweaning||1.05b||1.29ab||1.35a||0.171||0.048|
|Pre-weaning mortality, %||23.8a||21.5ab||20.9b||1.02||0.045|
|abmeans in the same row for each parameter with different superscripts are significantly different (p <0.05)|
The reduction of pre-weaning lamb mortality for ewes as their parity advanced in this study agreed with the findings made by Atta and El Khidir (2005) on the reproductive performance of multiparous and primiparous Nilotic ewes of Sudan.Abegaz et al (2000) also reported that lambs born by primiparous ewes had lower survival rates compared to those born by multiparous Horro ewes of Ethiopia. The observed reduction in pre-weaning lamb mortality for ewes in their 5th and 6th parities in this study could be as a result of improved maternal behaviour related to the increase in number of birth experiences for the ewes in these parities.
Lambing interval was however, not significantly affected by parity. This was in line with the report of Bemjiet al (2001) who observed that parity had no significant effect on lambing interval among the Yankasa breed of sheep.
The analysis of variance on reproductive traits revealed that season of birth was a significant source of variation for lambing interval. The West African Dwarf ewes lambing in the wet season had shorter interval of 7.84 months compared to their counterparts lambing in the dry season with interval of 8.04 months as shown on Table 3. Prolificacy, fecundity as well as litter size at weaning were not significantly affected by season. Season was however a significant source of variation for the litter weight of lambs produced. Heavier litter weight (3.25 kg) was recorded for the lambs parturated during the dry season than their counterparts in the wet season with average litter weight of 2.76 ± 0.16kg at birth.
The significant effect of season on the lambing interval corroborates the findings of Bemji et al (2001) who reported that season had significant effect on the lambing interval as Yankasa ewes lambing in the wet season had shorter lambing interval than ewes lambing in the dry season. High estimates of lambing interval observed for ewes lambing in the dry season during this study could be associated with slow growth rate of lambs during the dry season. Lamb growth rate was retarded under nutritional stress of ewes due to low availability of quality forage in the dry season. Lambs are therefore weaned at a later age than rainy season born lambs and this consequently had effect on the next conception and lambing interval.
In this study the effect of season was not significant on litter size at birth and at weaning. This agreed with the findings of Koycegiz et al (2009) in their study on the fat tailed sheep of Turkey reported that lambing season did not affect litter size either at birth or at weaning. Ali et al (2009) also reported that the effect of season was not significant on the fertility of Farafra ewes. The report of Baiden (2007) on the performance of West African Dwarf goat raised in Accra region of Ghana showed that does that kidded in the dry season had a significantly higher litter size than those that kidded in wet season. The influence of season on litter size was also observed by Bemji et al (2001). It was reported that ewes lambing in the late wet season had lower litter sizes with a trend towards improvement from early dry to late dry and to early wet seasons.
Ewes lambing in the wet season suffered higher percentage (24.67%) pre-weaning mortality of their lambs than those lambing during dry season with an average pre-weaning mortality of 19.44 %.
|Table 3. Least square means of reproductive traits as affected by season.|
|Traits||Wet Season||Dry Season||SEM||p|
|Lambing interval, months||7.84b||8.04a||0.031||0.047|
|Litter weight at birth, kg||2.76b||3.25a||0.172||0.039|
|Litter size at weaning||1.25||1.21||0.041||0.058|
|Pre-weaning mortality, %||24.7a||19.4b||1.86||0.042|
|abmeans in the same row for each parameter with different superscripts are significantly different (p <0.05)|
The seasonal variation in the pre-weaning mortality of West Africa Dwarf lambs in this study is in line with the findings of Ebozoje and Ngere (1995) who showed that pre-weaning mortality rate among West African Dwarf kids was significantly affected by season. According to the authors, the highest number of death was observed among kids reared in rainy season. The highest percentage of pre-weaning mortality for lambs born during rainy season in this study could be attributed to the prevalence of environmental conditions that predisposes the lambs to diseases during this season. Diarrhoea, pneumonia, peste-de petite ruminate (PPR) and mycoplasmosis occurred mostly in the wet season (Ebozoje and Ngere, 1995).
The interaction between coat colour and parity, coat colour and season as well as parity and season were not significant on any of the reproductive traits measured.
Black ewes were superior to other coat colour types with regards to reproductive traits such as prolificacy, fecundity and litter size at weaning. Lambing interval reduced with increasing coat colour intensity. Black ewes had the shortest interval. There was a positive relationship between parity and litter size of lamb at birth. Litter size at weaning also increased as parity of the ewe advanced. Pre-weaning mortality was affected by coat colour. White ewes are less favoured with respect to pre-weaning mortality of their lambs. There was a reduction in the pre-weaning mortality for the lambs of the ewes with advanced parity. There was a seasonal variation in the pre-weaning mortality of West African Dwarf lambs. Lambs born during the wet season had higher pre-weaning mortality than those born in dry season.
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Received 12 June 2014; Accepted 20 December 2014; Published 4 February 2015
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