A note on factors influencing milk yield of local goats under semi-intensive system in Sudan savannah ecological zone of Nigeria

A study was conducted at the Research Farm of Abubakar Tafawa Balewa University, Bauchi, Nigeria to investigate the milk yield of local goats of Nigeria under semi-intensive management as influenced by genetic and non-genetic factors.

The results showed that all the factors investigated had significant (P<0.001) influence on the partial milk yield (PDM). For instance, the Sahel does had the largest average PDM followed by the Red Sokoto and lowest in West African Dwarf goats. PDM significantly (P<0.001) increased with increase in the body condition score (BCS) of does. Does with BCS 4 produced the highest PDM followed by those with score 3 and least in score 2. Similarly, PDM was significantly (P<0.001) highest in the third parity and lowest in the first parity. Does milked in the dry season had significantly (P<0.001) higher PDM than their counterparts milked in the wet season. Does with single kids at birth had lower (P<0.001) PDM than those with twins. There was also significant (P<0.001) week of lactation effect on PDM. However, PDM increased from first week, reaching peak in the third week and then declined subsequently up to fourteenth week. The results also revealed many significant interactions between many of the traits investigated.

Introduction

In Nigeria, the distribution of goats is not uniform through out the country. More than 60 per cent of the goat population is found in the sudan savannah ecological zone of Nigeria, which also includes part of Bauchi (Adalemo and Baba 1993). A survey in Kaduna State showed that over 90 per cent of traditional house-holds kept goats or sheep (Otchere et al 1987).

Indigenous goats in Nigeria belong to three distinct breeds. The long-legged Sahel found in the arid and Sahel regions, the relatively small body-sized Red Sokoto found in the savannah zone and the hardy, short-legged West African Dwarf restricted to high altitude areas and humid forest of the south (Adu et al 1979; Osinowo1992). Virtually all these breeds are found in Bauchi State, the study area. The Red Sokoto had the highest population followed by the West African Dwarf and Sahel with least population (Zahraddeen 2006). The State being located in the savannah zone the ecological niche of Red Sokoto.

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 2004). Goat milk is a very useful product for subsistence peasant farmers; it is an important source of animal protein.

However, evaluation of lactation performance of goats with respect to breed, season, litter size, body condition score, parity and week of lactation is practically non- existent in literature. This study was therefore undertaken to investigate the effect of these factors under the semi-intensive management.

Materials and methods

Location and climate

The research was carried out on-station at the Research Farm of Abubakar Tafawa Balewa University, Bauchi, Nigeria. Bauchi metropolis, 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' north, longitude 8⁰ 49' east and at an altitude of 690.2 metres above sea level in the sudan savannah ecological zone of Nigeria (Kowal and Knabe 1972). The annual rainfall is between 1016-1270 mm. 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 34.7 and 29.2 ^oc respectively. The mean relative humidity is highest in August (70.9 per cent) and lowest in December (31.5 per cent) as reported by Butswat et al (2000) and FME/ ZERI (2006).

Soil and vegetation

The soil and vegetation of Bauchi have been previously described by Butswat et al (2000). Ferruginous (Haplustalf) soils on sandy parent materials 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 6 metres or more. The trees normally occur singly or in clusters, while the spaces between are occupied by non-woody species up to 3 metres 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 3.5 metres 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). The detailed descriptions of these breeds have been reported by Osinowo (1990). A total of 43 goats including two bucks per breed constituted the initial stock. The composition of does at the beginning of fertility trial was 27 RS, 20 SG and 15 WAD. These does were used to produce the offspring on which records were taken.

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 (between 10am and 5pm) 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 (18% crude protein). At times they were also fed groundnut haulms. Routine healthcare practices such as vaccination/medication, ecto-parasite control and de-worming were also regularly carried out. Fresh drinking water was provided ad libitum. The animals were also kept for a period of three weeks to acclimatize before the commencement of the study.

Data collection

The data for this study were collected from October 2003 to May 2006. The age of the goats was determined by dentition method. Body condition score was also determined as per the procedures laid down by Jefferies (1961). Breeding was monitored up to third parity using within breed mating. All does were hand-mated.

At kidding, the does with their kid(s) were separated into individual pens and measurements commenced immediately post-partum. Dams were separated from their kids at 18:00hr till after milk collection the next morning (6:00hr). The does were hand-milked weekly for 14 weeks. Milk yields were measured using a 100 ml measuring cylinder immediately after collection. The milk thus harvested was defined as the partial daily milk yield (PDM), which is a combination of milk off-take and 12-hour milk yield (James and Osinowo 2004).

Data analysis

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

Results

There were significant (P<0.001) effects of breed, body condition score, parity, season and litter size on partial daily milk yield (Table 1).

Table 1. Mean (± S.E) partial daily milk yield (PDM/ml) in goats as influenced by breed, body condition score, parity, season and litter size
	n	Partial daily milk yield
Overall	820	188.22±1.09
Breed		*******
Red Sokoto	376	188.27±1.28^b
Sahel	247	207.74±1.45^a
West African Dwarf	197	168.63±1.27^c
Body condition score		*******
2	460	184.53±1.39^c
3	263	186.31±1.56^b
4	97	193.81±1.56^a
Parity		*******
1	442	173.63±1.20^c
2	308	182.92±1.20^b
3	70	208.11±1.91^a
Season		*******
Dry	486	194.79±1.15^a
Wet	334	181.64±1.27^b
Litter size		*******
1	764	174.07±0.97^b
2	56	202.37±2.15^a
***; P<0.001; ^a,b,c Means in the same column within a subset having different superscripts are significantly different (P≥0.05)

The SG does had the highest (207.74 ±1.45 ml ) average partial daily milk yield (PDM) followed by RS (188.27 ±1.28 ml ) and lowest in WAD (168.63 ±1.27 ml ) does. PDM significantly (P<0.001) increased with increase in the body condition score. PDM also increased with increase in the parity number and the PDM was highest in the third parity. Does milked in the dry season had significantly higher PDM than those milked in the wet season. Similarly, does with single birth had lower PDM than does that kidded twins. There were significant (P<0.001) week of lactation effect on average PDM. The PDM increased from the first week, reached a peak in the third week and then declined subsequently up to the fourteenth week (Table 2).

Table 2. Mean (± S.E) partial daily milk yield (PDM/ml) in goats as influenced by week of lactation
	n	Partial daily milk yield
Overall	820	188.22±1.09
Week of lactation		*******
1	62	237.46±2.08^c
2	62	250.17±2.08^b
3	62	260.74±2.10^a
4	61	249.95±2.09^b
5	59	233.18±2.11^c
6	59	217.25±2.11^d
7	59	209.89±2.11^c
8	58	196.46±2.12^f
9	58	183.03±2.12^g
10	56	156.80±2.16^h
11	56	137.07±2.15ⁱ
12	56	114.83±2.15^j
13	56	99.30±2.16^k
14	56	88.89±2.16^l
***; P<0.001; ^a,b,c Means in the same column within a subset having different superscripts are significantly different (P≥0.05)

The results also showed that there were many significant interaction effects on PDM. The significant interactions included body condition score x parity (P<0.05), breed x week of lactation, breed x parity, week of lactation x parity, week of lactation x season, week of lactation x litter size, parity x season and season x litter size (P<0.001). Breed x body condition score, breed x season, body condition score x week of lactation, body condition score x season and body condition score x litter size interactions, however, were not significant.

Discussion

The difference in PDM among the three breeds might have been due to the difference in genetic potentials of these animals. A similar report has been made by James (2000) using the same breeds in humid parts of Nigeria. The PDM values in the present investigation were higher than150.9±2.04ml, 142.5±2.04ml and 118.7±1.12ml for SG, RS and WAD does, reported by James and Osinowo (2004). The two breeds (SG and RS) used in the former study were reared in the rain forest, an environment markedly different from their natural habitat. This might have accounted for the shortfall in their milk yield. However, the WAD does though a forest breed showed increased lactation performance when tested in the savannah zone. Osinowo (1992) stated that the WAD goats in their natural habitat are about 50 cm in height and 20 kg in weight, but tend to be larger as the savannah zone is approached. This might have accounted for the increase in milk yield in the savannah. Malik et al (1980) stated that the weight of does at kidding influence their milk yield positively.

Does’ body condition scores significantly influenced milk yield. This parameter increased with increase in the doe’s body condition score. Morand-Fehr et al (1982) stated that within genetic limits, nutrition during lactation is the primary factor that influences milk yield.

Milk yield was significantly influenced by parity. The parameter increased progressively with advance in parity. This confirms the observations made by Butswat et al (2002) that milk yield of SG and RS goats increased significantly up to the third parity and declined subsequently. Garcia et al (1976) also found that the milk yield of Anglo-Nubian, Alpine, Toggenburg and Saanen goats peaked in the third lactation.

Milk yield of goats in this study was higher during the dry season than the wet season. This is in close agreement with the reports of Iloeje et al (1981) who reported that in Nigeria WAD does that kidded from January to March had more milk than those kidded from April to July.

There was significant litter size effect on milk yield in goats in this study. Does with twins had more milk yield as compared to those that had singles. This confirms earlier study by Zygoyiannis (1994). The difference in milk yield due to litter size could probably be attributed to the extra pressure or stimulation on the mammary gland as a result of the additional suckling of the second kid. Rai and Chorey (1965) stated that the increase in milk yield arising from multiple births depends on the number of kids suckled and not on the number born.

Peak milk yield was observed in the third week of lactation. Variable peaks of lactation have been obtained in various studies. For instance, Butswat et al (2002) reported peak milk yield in the fourth week in RS and SG goats in Bauchi, a part of Sudan savannah ecological zone of Nigeria. James and Osinowo (2004) reported that the WAD does in humid environment attained peak milk yield in the third week of lactation with SG and RS in the second week.

The significant two-factor interactions indicate that factors have to be suitably combined to ensure high PDM. For instance, peak PDM will be obtained by choosing a good breed at a particular week of lactation or parity. Similarly, more PDM will be obtained by selecting does with good body condition scores at higher parities.

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