Milk yield and milk composition of West African dwarf, Yankasa and crossbred sheep in southwest of Nigeria

O O Adewumi and O A Olorunnisomo* 

Department of Animal Production and Health Sciences, University of Ado-Ekiti, PMB 5363, Ado –Ekiti, Nigeria, and
Department of Animal Production and Health, Federal University of Technology, PMB 704 Akure, Nigeria
badewumi2003@yahoo.com

^*Department of Animal Science, University of Ibadan, Ibadan, Nigeria
sholanisomo@yahoo.com

Abstract 

Increasing demand for milk and its products in Nigeria has made it imperative to look for other sources of milk apart from cattle. The West African dwarf (WAD) and Yankasa are common sheep breeds in Nigeria that could be milked for household consumption. Milk yield and milk composition of WAD, Yankasa and WAD x Yankasa crosses at different ages were evaluated in two lactations.

Milk production was significantly higher (P < 0.05) in crossbred sheep than either of the pure breeds. Yankasa ewes produced more milk than WAD ewes, however, when body weight (BW) was taken into consideration, WAD sheep produced more milk per kilogramme of body weight than Yankasa. Average daily milk production (two lactations) was 239.8, 307.7 and 378.6 ml day^-1 while mean body weight was 20.8, 29.4 and 25.1 kg for WAD, Yankasa and crossbred sheep respectively. On body weight basis, milk yield was 11.5, 10.5 and 15.1 ml kg^-1BW day^-1 body weight for WAD, Yankasa and crossbred sheep respectively. Fat and lactose were higher in milk of Yankasa ewes than that of WAD or crossbred ewes. Fat content was 7.10, 7.50 and 7.17 % while lactose content was 4.37, 5.52 and 4.86 % for milk of WAD, Yankasa and crossbred sheep respectively.

Since milk yield is related to body size, selection for increased body size in WAD sheep could also lead to higher milk production in this breed of sheep.

Keywords: milk composition, milk yield, West African dwarf, Yankasa, sheep

Introduction

In Nigeria, cattle are the primary source of milk for human consumption. Indigenous cattle breeds continue to dominate the traditional dairy subsector in spite of their low potential for milk production (RIM 1992). Over the years, local milk production has consistently fallen short of demand, especially in urban centres, leading to massive importation of milk and milk products. Continuous dependence on imported milk has discouraged local milk production and led to increase in cost of milk. Although there is an affinity for milk products in the country, the high cost of milk has put these products beyond the reach of the average Nigerian, hence it is necessary to look for alternative sources of milk for local consumption.

Local sheep breeds in Nigeria have the potential to supply a significant portion of the milk deficit in the country because sheep numbers far exceed cattle numbers in both rural and urban communities (RIM 1992, Adewumi 2005). They are also more affordable to resource-poor families and produce more milk in relation to body size than cattle (Nuru 1985). Sheep milk has been found to be richer in critical nutrients, except lactose, than milk of humans, cattle and goats (Buffano et al 1996). The high content of vitamin D and calcium helps in fighting against osteoporosis. Sheep milk showed less susceptibility to mastitis than other ruminants (Anyam and Adekeye 1985) and produce a higher yield of cheese per litre of milk with a higher retail price than cow’s milk (Chamberlain 1989, Adewumi et al 2001). It is very useful in the treatment of neurotic indigestion, insomnia, dyspepsia, peptic ulcer, pyloric stenosis, and rheumatism. It is also perceived by some consumers in Nigeria to have a better and more natural taste than cow’s milk (Adewumi et al 2001). In spite of this potential, sheep have largely been neglected by researchers in the quest for increased milk production.

It is therefore the objective of this study to evaluate the milk yield and milk composition of WAD sheep, Yankasa and their crossbreds as affected by age at first lambing. 

Materials and methods 

This study was conducted at the Teaching and Research Farm of the Federal University of Technology Akure, Nigeria. This location falls within the rainforest region with a typical hot and humid climate.

A total of 36 ewe lambs, comprising of 12 WAD, 12 Yankasa and 12 crossbred sheep were used in this study. Animals within each breed were divided into 3 groups according to their age at first mating (12, 16 and 20 months). Body weight ranged from 16-37 kg and age at first lambing ranged from 17-25 months. The experimental design used was the randomized complete block design. All ewes were synchronized for oestrous using Prostaglandin 2F alpha administered intramuscularly. Proven WAD rams were introduced once signs of heat were detected. Milk production during the first and second lactation periods were recorded for each genotype.

Milking commenced 4 days post-partum to give lambs access to sufficient colostrums. A 100-day lactation length and a total of two lactations were observed in this study. Animals were hand milked once daily between 7 and 9am, and grazed together with their lambs between 9am and 4pm. Lambs were separated from their dams after grazing and a concentrate diet was offered to the ewes. Daily concentrate allowance ranged from 160-365g per head, representing about 1% of animal body weight. Milk yield was measured daily using a measuring cylinder and total milk yield in 100days determined. Milk samples were taken from each breed during the second, eighth and fourteenth week of lactation to determine milk composition. Samples were kept in a freezer at -10^oC daily until required for analysis. Total solids were determined by drying 10g of sample to constant weight at 105^oC for 24 hours. Fat content was determined by the Gerber method while protein (N x 3.68) was determined with Markham’s semi-micro Kjeldahl apparatus (AOAC 1995). Total ash was determined by evaporating 10g of sample to dryness and ashed in a muffle furnace at 600^oC for 3hours. Other components of milk were determined as follows:
 

Solids-not-fat (SNF) = Total solids ­­­- Fat

Lactose = SNF – (% Protein + % Ash)
 

Data obtained were analysed using analysis of variance and covariate analysis. Significant means were separated by Duncan’s multiple range tests using SAS (1995) statistical package. The model used was:

Y_ijk    =     U + B_i + C_j + BC_ij + E_ijk

where,

Y_ijk = observation of dependent variable k of the i^th genotype, of the j^th age

U = overall mean of all observations

B_i = effect of the i^th genotype

C_j = effect of the j^th age  

BC_ij = effect of interaction between i^th genotype and j^th age

E_ijk = random error

Results 

The composition of concentrate diet fed to the experimental animals is given in Table1.

Milk yield

Milk yield was analysed using body weight and age as covariates. Results showed that there was a significant (P< 0.05) linear relationship between milk yield and bodyweight of sheep while age of sheep had little relationship with milk yield. Daily milk yield and total milk yield of three breeds of sheep (as affected by age at lambing) in 100-day lactation during the first and second lactation periods are summarized in Table 2.

Cross bred ewes (WAD x YAN) had the highest milk production followed by Yankasa ewes while WAD ewes had the lowest milk production. Daily milk production of WAD sheep ranged from 146 – 217 ml day^-1; Yankasa, 210 – 327 ml day^-1; and crossbred sheep, 273 – 385 ml day^-1 during the first lactation. Total lactation yield at this period was 18, 27 and 32 litres for WAD, Yankasa and WAD x Yankasa crosses respectively. Age of ewes at first lambing ranged from 17 – 25 months. Milk yield declined as age of ewes at first lambing increased. This trend was observed across the three genotypes. Milk yield was higher for the three breeds during the second lactation and followed a similar trend as the first lactation with crossbred sheep showing superior milk yield to WAD and Yankasa breeds. Milk production also declined with increasing age of ewes although this effect is not as pronounced as in first lactation period. Average daily milk production (two lactations) was 239.8, 307.7 and 378.6 ml day^-1 for West African dwarf, Yankasa and crossbred sheep respectively.

Mean lactation yield of sheep (body weight basis) in two lactations for the three breeds and body weight of ewes at different ages are presented in Table 3.

The mean body weight of Yankasa ewes was higher than either the WAD sheep or the crossbreds. Crossbred ewes had the highest milk yield per kilogramme of body weight while Yankasa ewes had the lowest.

Milk composition

The average composition of milk from three sheep genotypes (WAD, Yankasa and crossbreds) raised in the southwest of Nigeria is presented in Table 4.

There were no significant differences in protein and ash content of milk among the different breeds during the first lactation period. However, fat and lactose content varied significantly between the breeds, with Yankasa ewes having the highest values for fat and lactose, while the WAD ewes had the lowest values. Total solids in milk were highest in Yankasa and lowest in WAD sheep. This is largely a reflection of the fat and sugar content of the milk.

During the second lactation period, there was no significant difference in the composition of milk between the different genotypes, except for lactose, where Yankasa and crossbred sheep had significantly higher sugar content in their milk. Average protein content over the two lactation periods was 5.80, 5.94 and 5.84 % for WAD, Yankasa and crossbred sheep respectively. Fat content was 7.10, 7.50 and 7.17 % while sugar content was 4.37, 5.52 and 4.86 % for WAD, Yankasa and crossbred sheep respectively.

Discussion

This study was carried out in a humid tropical environment which is the natural habitat for the WAD sheep. Over the years this sheep which is characterized by a small body size, has adapted to the hot and humid climate of southwest Nigeria (Adu and Ngere 1979). The Yankasa sheep however, originates from the drier parts of northern Nigeria where they are sometimes milked for household consumption.

From the results above, crossbred sheep showed the highest milk production in two lactations followed by Yankasa sheep. In spite of the ecological advantage that the WAD sheep has over the Yankasa in southwest Nigeria, its milk production was lower during the first and second lactation. This is probably due to the small size of the dwarf sheep compared to the Yankasa.  Low milk production has been linked to small body size in Muturu cows (Ezekwe and Machebe 2005). Yankasa sheep also seem to be adapted to occasional milking by farmers than the WAD which is not milked at all. The average body weight of WAD sheep used in this study varied between 15.8 and 25.8 kg while Yankasa varied between 22.8 and 37.4 kg. However, when milk yield of these two breeds are compared on body weight basis (Table 3), WAD sheep produced more milk per kilogramme of body weight than Yankasa. This suggests that the dwarf sheep could produce more milk than Yankasa if body size is improved upon. This position is supported by the superior milk production of the WAD x Yankasa ewes which had a higher body size than the pure WAD sheep but lower body size than the Yankasa. The higher milk yield in WAD x Yankasa crosses agree with the principle of heterosis in animal breeding where offspring of crosses between two breeds are expected to perform above the average of the two parents (Legates and Warwick 1990, Bryant et al 2005). Milk production generally increased during the second lactation. Contrary to expectations, delaying the age at first mating of ewes did not have any advantage on milk production for the three breeds studied. Milk production actually decreased as age of animals increased. The reason for this observation is difficult to explain.

Fat content in milk of Yankasa ewes was higher than WAD and crossbred ewes during the first lactation; however during the second lactation fat content was similar for the three breeds. Sugar content of Yankasa milk was higher than that of WAD and crossbred sheep during the first and second lactations. Fat content of sheep’s milk obtained in this study ranged between 6.77 and 7.54 %. This is much higher than the fat content reported by Ezekwe and Machebe (2005) for Muturu cow’s milk which varied from 4.14 – 5.34 %. The implication of this is that sheep milk will yield more products per litre of milk during cheese and butter production.

Conclusions 

• In terms of total milk production, Yankasa ewes produced more milk than WAD ewes. However, when body weight is taken into consideration, WAD sheep produced more milk per kilogramme of body weight than Yankasa. 

  
  

• Body size of WAD and Yankasa crosses was higher than that of pure WAD sheep but intermediate between the two breeds.

  
  

• Milk production was significantly higher in crossbred sheep than either of the pure breeds, showing that these crosses were able to combine the advantage of large body size in Yankasa with the adaptability of the dwarf sheep to the hot and humid climate of southwest Nigeria.

  
  

• It is expected that selection for larger body size in WAD sheep will lead to increased milk production in this breed.

  
  

• Results from this study shows that there is no advantage in delaying the age at first mating beyond 12 months as milk produced tended to reduce with increasing age of the animals.

References 

Adewumi O O 2005 Sheep milk: The most important but neglected source of protein. Proceedings of the 10th Annual Conference of Animal Science Association of Nigeria, University of Ado-Ekiti, Nigeria September 12-15, 2005, pp237-239.

Adewumi O O, Ologun A G and Alokan J A 2001 Sensory evaluation and marketability of sheep milk in Nigeria. Journal of Agriculture, Forestry and Fisheries 2: 5-7

Adu I F and Ngere L O 1979 The indigenous sheep of Nigeria. World Review of Animal Production 15(3): 51-62

Anyam A A and Adekeye J O 1985 Bacteria flora associated with mastitis in sheep and goat in Zaria (Nigeria) area. Bulletin of Animal Production in Africa 43: 163-165

AOAC 1995 Official Methods of Analysis. 16th Edition. Association of Official Analytical Chemists, Washington DC.

Bryant M, Galina C and Carles A 2005 Breeding strategies for sustainable improvement. In: Livestock and Wealth Creation- Improving the husbandry of animals kept by resource-poor people in developing countries. E Owen, A Kitalyi, N Jayasuriya and T Smith (Editors), Nottingham University Press, United Kingdom, pp 215- 232

Buffano G, Dario C and Laudadio V 1996 International Symposium on somatic cell milk of small ruminants. R Rubino (Editor), Bella, Italy September 25-27, Wageningen Pers, EAAP, Publication Number 77: 301-304

Chamberlain A 1989 Milk Production in the Tropics. Intermediate Tropical Agriculture Series (W J A Payne, Editor). Longman Group UK Limited, pp 210-219

Ezekwe A G and Machebe N 2005 Milk composition of Muturu cattle under the semi-intensive system of management. Nigerian Journal of Animal Production 32(2): 287-292

Legates J E and Warwick E J 1990 Breeding and improvement of farm animals. 8th Edition. McGraw Hill Publishing Company, pp 241-273

Nuru S 1985 Trends in small ruminants production in Nigeria. In: Proceedings of National Conference on small ruminants production, NAPRI, Shika, Nigeria, 6-10 March, pp 36-48

RIM 1992 Resources Inventory Management Limited. Nigerian Livestock Survey. Volume 2. National Synthesis. Federal Department of Livestock and Pest Control Services, Abuja, Nigeria. 289 pp.

SAS Institute 1995 SAS/STAT User’s Guide. Version 6, 4th Edition. Volume 1 and 2. SAS Institute Inc., Cary, NC.

Received 26 June 2008; Accepted 18 December 2008; Published 10 March 2009

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