Evaluation of some factors affecting milk composition of indigenous goats in Nigeria

D Zahraddeen, I S R Butswat and S T Mbap

Animal Production Programme, School of Agriculture and Agricultural Technology,
Abubakar Tafawa Balewa University, P.M.B.0248, Bauchi, Nigeria
zdtabra2003@yahoo.com

Abstract

This study was carried out at the Research Farm of Abubakar Tafawa Balewa University, Bauchi, Nigeria (October 2003 – May 2006) to evaluate some factors (breed, season, stage of lactation and parity) affecting goat milk composition.

The results showed that per cent crude protein, fat, lactose and total solid contents were significantly (P<0.05) affected by breed; with pH and ash contents differed non-significantly in the three breeds. The percentages of crude protein, fat and lactose contents were significantly (P<0.001) different in the four stages of lactation (colostrum, early, mid and late), while the differences in the total solid, pH and ash contents were not affected by the lactation stages. There were seasonal (P<0.001) variations in the per cent fat and lactose contents; with crude protein, total solid, pH and ash contents being not influenced by the two seasons (dry and wet). Similarly, fat and lactose contents showed significant (P<0.001) parity effects; with the crude protein, total solid, pH and ash values differed non-significantly in the three parities (first, second and third).

It is therefore concluded that the goat milk composition studied is comparable to the levels obtained in improved goats reported elsewhere. It is therefore suggested that improvement in the goat milk composition of the local breeds can be made through improved management and cross-breeding with higher-yielding local or exotic goats.

Key words: Breed, lactation stage, parity, season

Introduction

In Nigeria, the indigenous cattle have been the major source of domestic meat and milk supply. Milk supply from other animals such as sheep, goats and camels is negligible (Ibeawuchi and Dalyop 1995). The dairy industry still remains rural and traditional with Fulani pastoralists controlling more than 95 per cent of the national herd. Anon (1990) reported that the annual collectable milk from the national herd was approximately 555,000 tonnes and this might not have changed much.

Goats in the country are kept mainly for meat production; their milk is rarely used for human consumption (Butswat et al 2002). However, there is a growing awareness of the importance of goats as a source of milk for man (Malau-Aduli et al 2001). In some tropical and temperate countries, the Anglo-nubian, Jamnapari, Saanen, Toggenburg, La Mancha, Alpine, Oberhasli and few other breeds are used for milk production (Mc Donald and Low 1985).

Goat milk is more widely produced than sheep milk, and globally goat production yields 60 per cent of its value as milk, 35 per cent as meat and 5 per cent as skin ( Devendra and Mcleroy 1988; Malau-Aduli et al 2001). Webster (1989) reported that countries like Iraq and Libya obtain half their total milk requirements from goats. Although there is similarity between cattle, goats, sheep and buffaloes in the genetics of milk production, there is evidence that on live weight basis the goat is a much more efficient milk producer than the other species (Malau-Aduli et al 2001). The goat also has higher feed conversion efficiency to meat and milk than the cow, sheep and buffaloes (Okello and Obwolo 1985).

Milk composition and quality are important attributes that determine the nutritive value and consumer acceptability. Malau-Aduli et al (2001) reported goat milk yield and  composition are affected by breed, age, stage of lactation, season and plane of nutrition. Barnet and Frederick (2000) showed that goat milk contains more fat and ash than cow milk. However, as infant food it is nearly as high in vitamin B₆ and twice in vitamin B₁₂ as human milk. They also reported that vitamin A in goat milk exists exclusively in its true form and not as carotenoid pigments.

Evaluation of goat milk composition with respect to differences in breed, stage of lactation, season and parity is practically non-existent in literature in the study area. Therefore, this study was designed to investigate the effects of these factors on goat milk composition in Bauchi, a part of northern guinea savannah ecological zone of Nigeria.
 

Materials and methods

Location and climate

Bauchi metropolis, the study area, apart from being the State capital and headquarters of Bauchi Local Government, is also the main urban centre in the State. It is situated on latitude 10⁰ 17^I north, longitude 8⁰ 49^I east and at an altitude of 690.2 metres above sea level in the northern guinea savannah ecological zone of Nigeria (Kowal and Knabe 1972). The annual rainfall is about 1016-1270mm. The mean monthly hours of sunshine is highest in December (300.3h) and lowest in August (150.1h). April is the hottest month with mean maximum and minimum temperatures of 30.1 and 13.7 ^oc respectively. The mean relative humidity is highest in August (74.0%) and lowest in February (16.5%) (Butswat et al 2000).

Soil and vegetation

The soils and vegetation of Bauchi have been previously described by Butswat et al (2000). Ferruginous (Haplustalf) soils on sandy parent material are common. They are generally considered to be of high fertility. However, their susceptibility to erosion and drought has limited their maximum utilization for crop production. The vegetation is open savannah woodland with trees up to 6m or more. The trees normally occur singly or in clusters, while the spaces between are occupied by non-woody species up to 3m high. The effect of cultivation and burning has reduced the vegetation in many places to Acacia shrubs. Grasses in such areas normally reach a height of 3.5m or more. These grasses are generally brown and have low nutritive value during the dry season. With the onset of the rainy season, however, there is lush pasture which has higher nutritive value.

Experimental goats

The breeds of goat used for the study were the Red Sokoto (RS), Sahel (SG) and West African Dwarf (WAD). A total of 43 goats including two bucks per breed constituted the initial stock. The bucks were used for within-breed natural mating on the nulliparous does aged one-year. The composition of does at the beginning of the fertility trial was 15 RS, 12 SG and 10 WAD. The detailed descriptions of these breeds have been reported by Osinowo (1990). 

Goat management

The animals were managed semi-intensively. In the night, they were kept in cross-ventilated pens within the animal house but allowed to graze during the day within the University premises. They were supplemented with mineral licks and concentrate; a mixture of poultry litter, maize offal and rice bran in 1:2:1 ratio, which gave 89.9% dry matter, 8.4% ash, 18% crude protein, 1.1% ether extract and 13% crude fibre. At times they were also fed groundnut haulms. Routine health care practices such as vaccination/medication, ectoparasite control and deworming were also regularly carried out. Fresh drinking water was provided ad libitum.

Collection of milk samples and analysis

Goat milk samples were collected from the Research Farm of Abubakar Tafawa Balewa University, Bauchi, Nigeria (October 2003 to May 2006) and were quickly transported to the laboratory, and stored in a deep-freeze cabinet at –5^oC till required for analysis. Before analysis, each sample was thawed at 40^oC to melt the fat and then cooled to 20^oC. The entire content was then thoroughly mixed without any preservatives and evaluated for gross composition (total solids, fat, crude protein, lactose, pH and ash).

The total solids were determined by drying 5g of milk at 100^oC for 3 hours to constant weight (AOAC 1995). Fat was estimated by the Gerber method (AOAC 1995). Solid not fat (SNF) content was calculated as the difference between the total solids and fat content, protein (N ´ 6.38) was determined by Kjeldahl methods IDF standard 20A (IDF 1986) and  lactose content  was assessed by the method of Barnet and Tawab (1957). Ash content was determined by igniting the dried samples at 500^oC (AOAC 1995), the protein-fat (P/F) and fat-solid-not-fat (F/SNF) ratios were also calculated (Gupta and Rao 1972). Measurements were classified based on breed, season, stage of lactation and parity.

Data analysis

The data generated were subjected to analysis of variance using the General Linear Model (GLM) of SPSS (2001). Means were subsequently separated using DMRT method described by Humburg (1977).

Results

Goat milk composition as influenced by genotype, stage of lactation, season and parity is presented in Table1.

Crude protein was significantly (P<0.001) affected by breed and stage of lactation. The crude protein was highest in RS (3.84 + 0.03%) followed by SG (3.45 + 0.03%) and lowest in WAD (3.27 + 0.04%) does. On the other hand, the crude protein content decreased with advancing lactations. The crude protein values during colostrum period, early, mid and end of lactation were 3.85 + 0.04, 3.66 + 0.04, 3.38 + 0.04 and 3.20 + 0.04% respectively. Season and parity however had no effect on milk crude protein content.

The fat content was significantly (P<0.001) affected by all the factors (breed, stage of lactation, season and parity) investigated. Fat content was highest in SG (5.16 + 0.02%) and lowest in RS (4.38 + 0.02%). Like crude protein fat content decreased as lactation progressed. The fat contents during the colostrum period, early, mid and end of lactation were 5.35 + 0.03, 4.97 + 0.03, 4.62 + 0.03 and 4.13 + 0.03% respectively. Fat content was highest in the third parity (5.54 + 0.03%) followed by the second parity (4.73 + 0.03%) and least in the first parity (4.39 + 0.02%). Wet season had higher fat content (5.04 + 0.02%) than the dry season (4.49 + 0.12%).

There was significant breed effect (P<0.05) on the total solids. The effects of lactation stage, season and parity however were not significant. Similarly, ash and pH of milk were not significantly influenced by breed, lactation stage, season and parity as shown in Table 1.

The results of lactose content revealed breed differences (P<0.001) being highest in RS (4.90 + 0.03%) followed by SG (4.46 + 0.04%) goats. There was also significant (P<0.001) decrease in lactose as lactation progressed.  The values of lactose content during colostrum period, early, mid and end of lactation were 5.02 + 0.04, 4.72 + 0.04, 4.40 +0.04 and 4.07 +0.04% respectively. Conversely, lactose content increased significantly (P<0.001) with increase in the parity number.  In addition, there  was significant (P<0.001) seasonal effect on lactose content; the values being 4.25 + 0.03 and 4.85 + 0.03% for dry and wet seasons respectively (P<0.001) (Table 1). There were similarly significant (P<0.01) interaction effects between breed x lactation stage, breed x season, breed x parity, lactation stage x season and lactation stage x parity interactions with respect to lactose, fat and crude protein.

Table 2 shows the overall correlation matrix of goat milk components.

There were significant positive and negative (P<0.05-0.01) correlations between a lot of the milk constituents. For instance, the correlations between crude protein vs total solid, crude protein vs fat, crude protein vs lactose, total solid vs lactose and fat vs lactose were -0.25, 0.35, 0.63, -0.21 and 0.60 respectively (P<0.05).
 

Discussion

The mean percentage of crude protein observed in goat milk in this study was influenced by breed, and was lower than the value (4.89 + 1.03%) reported by Agbede et al (1997) in WAD does. The breed differences may be attributable to genetics. There was significant effect of stage of lactation on crude protein content of goat milk in this study. A similar report was made by Beyene and Seifu (2005) in Borana goat milk in Ethiopia. Protein content showed a downward trend until mid-lactation before significant increase towards the end of lactation. Egbowon (2004) reported that milk protein percentage is inversely related to milk yield. This parameter started at a moderate level, decreased to the lowest level during peak lactation and gradually increased towards the end of lactation in accordance with the inverse relationship with milk production.

This study observed non-significant effects of season and parity on protein content in milk. This may probably be attributable to the uniform nutrition and other management practices the animals were subjected to over the period of the study which overrode the expected effect of seasonal variation on protein. Egbowon (2004) also stated that under- feeding causes lower proportion of milk components.

The mean percentage fat content of RS, SG and WAD goats in this study were higher than the value reported by Agbede et al (1997) in WAD does and lower than the value reported by Beyene and Seifu (2005) in Borana goats.  Egbowon (2004) observed that milk fat is higher in dual purpose breeds such as RS, WAD and East African Dwarf goats than those selected for milk production alone such as the Finish, Saanen, Alpine or Anglo Nubian breeds. This, she mainly attributed to the negative correlation between milk fat and milk yield. This implies that selection for milk yield will invariably reduce the concentrations of milk fat.

The percentage fat content in the present study decreased significantly with advances in stage of lactation. This contrasts with earlier report by Beyene and Seifu (2005) who observed significant increase in the fat content of Borana goat with stage of lactation. Similar observations had been made by Egbowon (2004) that fat content of milk decreased from the beginning of lactation to a minimum in mid-lactation and continuously increased until the end of lactaton; an inverse relationship with milk production similar to the case of protein content .

The milk fat of goat milk observed in the wet season was significantly higher than in the dry season. This low fat content of milk during this season may be attributed to excessively high ambient temperature especially in the late dry season, which reflected in the decreased feed intake and body heat production. Brown et al (1983) however reported that increase in temperature depressed milk yield, solids, fat and nitrogen yields more in Alpines than in Nubian goats.

Milk fat in this study was significantly affected by parity. This parameter increased with increase in the parity. This might have been influenced by the fact that doe mammary gland needs to fully develop according to genetic limit before milk secretion. Egbowon (2004) reported that at any stage of lactation the first quantity of milk removed from the udder is lowest in fat percentage while the milk removed last is highest in fat percentage, i.e. residual milk is higher in fat content.

The total solid observed in the goat milk studied was significantly influenced by breeds, being higher in SG and WAD than RS goats. Agbede et al (1997) however observed non-significant difference in total solid of WAD and Yankasa ewes in humid environment. Non-significant difference was also observed in the total solid content of goat milk with stage of lactation, which contradicts the result reported by Beyene and Seifu (2005) in Borana breed of goats. These workers observed that the total solid increased to a maximum at mid-lactation and declined by end of lactation. Conversely, Boros (1986) reported a minimum at mid-lactation with higher values during the rest of lactation.

The present study observed non-significant breed, stage of lactation, season and parity effects on the total ash content of goat milk. This disagrees with the results obtained by Agbede et al (1997) that there were significant species and breed effects on ash content of WAD goats and Yankasa ewes. However, the observations made in this study contradict the reports by Brendehaug and Abrahamsen (1986) that ash content progressively increased as lactation advanced. Similarly, Beyene and Seifu (2005) reported significant changes in ash content as lactation advanced. The pH content of goat milk remains unchanged, irrespective of breed, stage of lactation, season or parity. Beyene and Seifu (2005) similarly observed that the pH content of Borana goats differed non-significantly with advances in lactation, with similar values obtained in this study.

The lactose content of RS, SG and WAD goat milk in this study differed significantly. However, the lactose contents were lower than the values reported by Agbede et al (1997) in WAD does. The lactose content was initially high (in the colostrum) but decreased significantly during the remainder of lactation. Similarly, Brendehaug and Abrahamsen (1986) found that lactose content decreased throughout lactation. Boros (1986) however observed that lactose was fairly constant over the lactation period showing no substantial changes.

Lactose content was significantly lower in the dry than wet season. This low value in the dry season may be linked to lower nutrition during the season. For instance, Egbowon (2004) highlighted that under-feeding reduces total milk production and milk components. The late dry season (January to March) is characterized by low quality feed supply in Bauchi thus inflicting some stress on the animals. There was very high and significant increase in the lactose content of goat milk as parity increased. This may be associated with the differences in nutrients utilization with increase in age.

The observed significant interactions between some factors in this study are valuable for making management decisions in order to get the best milk composition when two factors are jointly considered at a time. For instance, the lactose or fat content  of goat milk can be improved appreciably by combining breed x season or parity and also when stage of lactation x season or parity are considered in an experiment. 

Significant correlations existed between several goat milk constituents. Therefore, the easily measurable traits could be used for development of selection criteria for improvement of milk yield and composition in this species.

Conclusion

• The goat milk composition observed in the present investigation is comparable to the levels obtained in improved goats reported elsewhere. Therefore, substantial improvement in the milk composition of the local goats can be made through improved management practices and cross- breeding with higher-yielding local or exotic goats.

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Received 21 June 2007; Accepted 12 August 2007; Published 1 November 2007

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