The Boer Goat  Growth, Nutrient Requirements, Carcass and Meat Quality II

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By: N. H. Casey and W. A. Van Niekerk
Department of Livestock Science, Faculty of Agriculture, University of Pretoria.
0002 Pretoria, South Africa (21 May 1988 )

ABSTRACT
Van Niekerk, W. A. and Casey, N. H., 1988. The Boer Goat. II. Growth, nutrient
requirements, carcass and meat quality. Small Rumin. Res., 1: 355-368.

Growth rates of Boer goats were generally lower than sheep and, under favorable nutritional conditions, weight gains of more than 200 g/day were obtained, against values of up to 176 g/day under extensive subtropical conditions. Lactation and pregnancy had a marked effect on ME intake, and the latter had an improved feed conversion ratio (6.06 kg/kg) in comparison to that of virgin does (10.96 kg/kg). Below 6% crude protein in the diet, feed intake is reduced and has negative effects on birth weights, growth and milk production. Little information is available on mineral requirements of goats. The carcass of Boer goats is generally leaner, less compact and has different carcass proportions than sheep. The relatively high collagen contents with lower solubility of Boer goat meat, has meant that the
eating quality has been regarded as inferior to that of lamb and mutton. Breeding holds the key to improving tenderness of goat meat; different slaughtering techniques can be used as well. Boer goats have high potential as meat animals when yielding three kid crops in 2 years and when fed to gain more than 200 g/day.

INTRODUCTION

The value of meat animals lies in the acceptability of the carcass on the market. According to Devendra and Owen (1983) the demand for goat meat exceeds supplies in many parts of the world, notably in the tropics and subtropics, where 74% of the world's goat meat is produced. Consequently, goat meat is sold at premium prices, and is increasingly substituted by "cheaper" mutton. In Southern Africa the situation is reversed, and lamb and mutton enjoy premium prices while goat meat is a secondary product. Price of lamb on wholesale auction markets in metropolitan areas is approximately 30% more than that of kids and mutton is on the average 18% more expensive than goat meat.

Consumer preference for goat meat or mutton is dictated by cultural and traditional
background and the socio-economic status of the community. Generally, goat meat is consumed (1) by those who culturally do not eat beef and find goat an acceptable substitute for lamb and mutton; and (2) by rural Africans for whom goats are traditionally part of their livestock, but these are of lower status value than beef (Schapera, 1959). Discrimination against goat meat arises when sheep and cattle are the dominant sources of red meat. These then set standards for growth, feed conversion, carcass evaluation and palatability of meat against which goats are evaluated. These standards are some of the adversities that have to be overcome before the full potential of goat meat and that of the Boer goat can be realized
on the more profitable metropolitan markets in Southern Africa.

GROWTH

Goats do not generally have a high growth rate, compared with lambs. Under favorable nutritional conditions, Boer goats may gain weight at more than 200 g/day. Naude and Hofmeyr (1981) reported average preweaning growth rates by 54 kids of 227 g/day. These were born of 30 does, kept under intensive conditions in a barn with free access to a complete ration (60% digestible DM, 14% crude protein). The kids had free access to a creep ration (70% digestible DM, 14% crude protein) and were weaned at 35 days.  A post-weaning growth rate of 200 g/day was obtained on an ad libitum feeding regime (65% digestible DM, 14% crude protein) over a 12 week period.

In a subsequent comparative trial involving 20 male offspring of each of four sheep breeds, the South African Mutton Merino (SAMM), Merino, Dorper and Pedi (a fat-tailed breed) and Boer goats, the goats had the lowest growth rate (N.H. Casey and R.T. Naude, 1982, unpublished data) (Table 1). Lambs and kids were born of synchronized dams, separated from their mothers at 24 hrs and reared artificially according to Hofmeyr (1971) in single pens. Weaning was at 42 days and lambs and kids were castrated but not docked. All obtained the creep ration previously described ad libitum until each had attained a randomly pre-allotted slaughter weight of 10, 23, 32 or 41 kg. Birth weights and average daily gains (ADG) are in Table 1.

TABLE 1

Average birth weight (kg) and average daily gains (ADG) (g/day) of four sheep breeds and
Boer goats (N. H. Casey and R. T. Naude, 1982, unpublished data)

SAMM = South African Mutton Merino
MERI = Merino Sheep
DORP = Dorper Sheep
PEDI = Pedi (fat-tailed) Sheep
BOER = Boat Goat
SD = Standard Deviation

Over the entire period the Boer goat kids grew at 124 g/day, whereas, from birth to 10 kg weight, the rate was 62 g/day; 10-23 kg, 139 g/day; 23-32 kg, 182 g/day; and, 32-41 kg, 194 g/day. The relatively poor growth results were ascribed to kids having adapted poorly to pens. These poor growth results did not deter kids from fattening, however, which may place a different perspective on poor growth results. Their total body fat content was greater than that of the SAMM, Merino and Dorper at all slaughter weights with the exception of the Dorper at 41 kg (N.H. Casey and R.T. Naude, 1982, unpublished data).

Growth rates were 136 g/day for each of two groups of 12 Boer goat male kids kept in (a)   individual crates, and (b) in a paddock of 50 square meters in size (Dreyer, 1975). A group of 10 doe kids in crates grew at 108 g/day and 10 in a paddock at 64 g/day. Their ration consisted of 60% milled alfalfa and 40% maize meal, fed ad libitum for 96 days over the weight interval of 22.5 kg-35.6 kg for males, 20.8-31.3 kg for crated females, and 27.0 kg for penned females. In contrast, growth of highly selected Boer goat kids left with their dams until weaning at 100 days and then given free access to a concentrate ration while kept on good mixed shrub savannah grazing, grew at rates often in excess of 150 g/day (Table 2) (Q.P. Campbell, 1977, unpublished data; Naude and Hofmeyr, 1981).

TABLE 2

Body weight and growth rate in highly selected Boer goat kids (Q. P. Campbell, 1977,
unpublished data)

(?)-Denotes possible typographical errors in original manuscript.

Perhaps the most realistic results have been recorded under extensive conditions in a subtropical grass-bush community. Average daily gain of the entire kid crop was 169 g/day in 1976/1977 and 176 g/day in 1977/1978 (Aucamp and du Toit, 1980). Results of the following season, in the same range, are in Tables 3 and 4 (Aucamp and Venter, 1981).

TABLE 3

Average reproductive performance of Boer goats (Aucamp and Venter, 1981 )

TABLE 4

Average growth performance of Boer goats (Aucamp and Venter, 1981)

The range in average daily gains illustrates existing possibilities for higher growth rates through a combination of nutritional management and selection. However, attempts to improve growth rates must not have adverse effects on the economically important prolificacy of Boer goats.

FEED CONVERSION AND NUTRIENT REQUIREMENTS

Efficiency of feed conversion which is a function of feed composition and level of feed intake relative to maintenance and production needs, has a marked influence on efficiency of a meat production system. Productivity of a herd will depend on amount and availability of energy in the daily diet. Sachdeva et al. (1973) reported that energy shortages resulted in lower fertility, less milk production, delayed puberty and retarded growth of kids. Besides normal physiological requirements for growth, pregnancy, lactation and body maintenance, environmental stress adds to energy requirements. Topography, climate and grazing material density are considered in tables of nutrient requirements, since goats' grazing patterns are
more active and so they will cover a greater area per day than sheep or cattle (NRC,
1981).

Goats seem to have a higher fasting metabolism than sheep (Roy-Smith, 1980; Holmes and Moore, 1981), but a lower heat increment which compensates for the former. The lower heat increment is advantageous to goats in their adaptation to hot and tropical environments.

Research on feed energy exchanges of Boer goat does during growth, pregnancy and
lactation has been reported by Viljoen (1985). Six Boer goat does were fed ad libitum on a diet containing 18.3% crude protein and 11.5 MJ ME/kg DM. Two does were bred at 40 weeks of age and hand milked for 23 weeks post-partum. ME intake was measured daily and live weight weekly. Heat production by indirect calorimetry and body composition by tritiated water space were determined every third week. Five distinct growth phases were identified by plotting the natural logarithm (ln) of cumulative ME intake against the ln of body weight. The beginning of the second growth phase was linked to the stage of first ovulation, and the onset of the other growth phases was linked to the seasonal sexual behavior of the does. In a specific growth phase, good relationships were obtained between protein and water deposition (g/day). Rates of deposition of protein and water decreased while fat
deposition increased with higher live weight and age in growing animals. A change in partial efficiency of protein synthesis with age was observed. No distinct patterns could be established, for partial efficiency of fat synthesis.

Pregnancy had marked effects on ME intake, rates at which energy was deposited as
protein and fat, and rate of heat production, which increased as pregnancy progressed. Positive effects of pregnancy were an improved feed conversion ratio (6.06 kg/kg) of pregnant does in comparison to virgin does (10.96 kg/kg). Lactation also had a marked stimulating effect on ME intake and heat production, which tended to decrease as lactation progressed. Rate of energy deposited as protein and fat in the lactating doe decreased relative to virgin does as lactation progressed (Viljoen, 1985).

Apart from energy, protein is the most important nutrient in animal production (Satter and Roffler, 1975). Below 6% crude protein in the diet, feed intake is reduced, which leads to combined deficiency of energy and protein. Protein deficiencies per se have a negative effect on kid birth weights and on growth and milk production of the doe (Sengar, 1980; NRC, 1981).

Although goats supplement their grazing diet with shrubs and edible tree parts, which are often higher in mineral and vitamin content than forages commonly used by sheep and cattle, little information is available on the mineral requirements of goats (Haenlein, 1980, 1987). Extrapolations from mineral and vitamin requirements of other species to goats (NRC, 1981) may be incorrect, because cattle, sheep and goats differ in milk, blood and tissue contents (Haenlein, 1980). In order to provide proper supplies and balanced minerals and vitamins, a knowledge of bioavailability is more important than actual levels in the diet (Miller, 1981).

Castrated Boer goat male kids in crates had an average feed conversion of 8.99 kg/kg and in pens 9.10 kg/kg (Dreyer, 1975). Crated Boer goat female kids averaged 9.54, but in pens, 15.13, with a low growth rate of 64 g/day. Ueckermann (1969) fed Boer goat kids three diets: a 60% concentrate, a 60% roughage and a total roughage diet. Animals were slaughtered at 31.8 or 45.4 kg body weight. Respective feed conversion ratios on the three diets were 8.6, 8.1 and 10.3 for the 31.8 kg slaughter group and 9.5, 9.5 and 13.2 for the 45.4 kg slaughter group. Hofmeyr and Lategan (1964 ) reported no significant differences between 30 month old Boer goat and Dorper sheep castrates. Naude and Hofmeyr (1981) concluded that, for a given growth rate or feed intake, Boer goat kids are as efficient as lambs. The fact that Boer goats have an apparently higher total body fat content than some sheep breeds could be related to poorer feed conversion in goats than sheep (Naude and
Hofmeyr,1981; N.H. Casey and R.T. Naude, 1982, unpublished data).

Growth rate of Boer goat bucks was greater than that of a number of other breeds
evaluated in Tunesia for weaning weight and weaning weight per doe per annum (Steinbach, 1987). However, when weaning weight efficiency is expressed in terms of weaning weight per doe metabolic weight (W^0.75) per annum Boer goats were not as efficient as local Tunesian goats. Steinbach (1987) also reported a larger sexual dimorphism in mature weight than in Alpine, Saanen or local Tunesian goats. This may be important in crossbreeding programmes. Angwenyi and Cartwright (1987) concluded from cross breeding studies with East African, Galla and Boer goats, that the Boer was a logical sire breed, contributing significant directly additive effects to body weights at 4 to 12 months of age, and to preweaning absolute growth rates. Boer goat maternal additive effects were mostly negative, however.

CARCASS AND MEAT CHARACTERISTICS

Boer goats offer a carcass that is generally lean in appearance, less compact than sheep and of differing carcass proportions with less total tissue distributed to the hind leg than in sheep (Naude and Hofmeyr, 1981; Casey, 1982).

Dressing percentage (DP) is an important criterion describing carcass yield. However, since it expresses a ratio of live weight to carcass weight and many factors influence weighting of these fractions (for example, fleece or hide weight, alimentary tract size and fill, slaughtering procedures and the partitioning of body fat) dressing percentage must be interpreted carefully and comparisons should be made within species and within breed types. The DP of goats varies between 44% and 55% (Naude and Hofmeyr, 1981), and that of Boer goats between 40.3% at 10 kg live weight and 52.4% at 41 kg live weight (Casey, 1982). It may even reach 56.2% in entire male goats (Owen and Norman, 1977).

In a comparative trial, mean DP of Boer goats was remarkably high (48.3%) compared to woolled SAMM (46.6%) and Merino (41.0%), but was almost the same as that of non-woolled Dorper (48.5%) sheep. This compares well with mean values of 52.2% and 53.0% for milk-, 2-,4- and 6-tooth, indigenous African castrate goats and sheep, respectively (Owen and Norman, 1977). In these studies, total body fat (TBF) in Boer goats was considerably higher (18.31%) than in SAMM (11.8%), Merino (15.0%) or Dorper sheep (16.7%), but less than in the very early developing Pedi sheep (24.5%). In terms of total carcass fat (TCF), Boer goats were leaner (18.2%) than Dorper (19.3%) and Pedi (24.8%), but fatter than SAMM (14.1%) and Merino (17.9%). Partitioning of TBF (Table 5) shows why this occurred. Boer goats yielded 51.8% TCF and 48.2% total non-carcass fat (TNCF) but the Dorper sheep 60.6% TCF and 37.6% TNCF. Furthermore, a partitioning between subcutaneous fat (SCF) and intermuscular fat (IMF) showed that, despite a TCF of 24.1% at 41 kg live weight, which compares favorably with 23.8% of the SAMM sheep at 41 kg and 24% of the Dorper at 32 kg live weight, the Boer goat partitioned only 6.7% to the SCF depot.

TABLE 5

Two-way analysis of variance for % bone, % muscle, % TCF, % SCF, % IMF, % tail &
kidney fat, % whole tail, and % TBF in four sheep breeds and Boer goats (N. H. Casey
and R. T. Naude, 1982, unpublished data)

*P<0.01, NS=statistically not significant
Breeds: SAMM = South African Mutton Merino sheep; MER = Merino sheep; DORP = Dorper sheep; PEDI = Pedi sheep; and BOER = Boer goat.

Comparatively poor fat covering of the kid carcass means that the criterion of subcutaneous fatness, which is a reliable predictor of yield in lamb and mutton carcasses (Bruwer, 1984), as it is currently applied in classifying and grading of such carcasses, is not suitable for classifying and grading goat carcasses in South Africa. In the study of Owen and Norman (1977), the thickness of the SCF was measured at a point of 20 mm from the medial plane along the caudal edge of the 13th rib. These measurements on Boer goat carcasses of the 23, 32 and 41 kg slaughter groups were, respectively, 1.2 ±0.45, 1.8 ±0.84 and 3.4 ±1.14 mm, which were less than those measured on any of the sheep carcasses (Table 6). Reliability of these measurements as a predictor of percent TCF was low (R^2=0.32) compared to lamb carcasses (R^2=0.73). Combined with cold carcass weight in a multiple regression model, predictability for Boer goats improved (R^2=0.47) but was not as high as for all four lamb breeds (SAMM, R^2=0.89; Merino, R^2=0.89; Dorper, R^2=0.80; Pedi, R^2=0.90) (N.H. Casey and R.T. Naude, 1982, unpublished data). Note: R^2 is
designation for "R squared", & shown this way since most web browsers cannot depict superscripts.

TABLE 6

Subcutaneous fat thickness over the 13th rib, 20 mm from the medial plane for 23, 32 and 41 kg slaughter groups (N. H. Casey and R. T. Naude, 1982, unpublished data)

*P<0.01, NS=statistically not significant
Breeds: SAMM = South African Mutton Merino sheep; MER = Merino sheep; DORP = Dorper sheep; PEDI = Pedi sheep; and BOER = Boer goat.

Boer goats had a high muscle and low bone content, resulting in a high mean muscle to bone ratio of 4.7:1 compared with 4.4:1 for SAMM, 4.3:1 for Merino and 4.8:1 for Dorper. The Boer goat ratio was considerably higher than reported by Owen et al. (1978) for milk-, 2-, 4- and 6-tooth indigenous male castrates, which ranged from 2.6 to 3.0. Full mouth goats had a ratio of 3.1. Differences may be ascribed to nutrition. A greater carcass and leg length of Boer goats results in the carcass being less compact than sheep, which is a trait that traditionally, but erroneously, is discriminated against in the market place as being associated with poor muscling (Naude and Hofmeyr, 1981).

TISSUE COMPOSITION

Differences in gross tissue composition were explained by analysis of allometric growth coefficients (Casey and Naude, 1984). Growth coefficients for muscle in relation to empty body weight ranged between 0.96 (Merino) and 0.83 (Pedi) in sheep, but were 1.08 in Boer goats. Growth coefficients for TBF were 2.03 (SAMM), 2.02 (Merino), 2.12 (Dorper), 1.87 (Pedi) and l.72 (Boer goat). These illustrate again that a straight comparison between the two species is incorrect. Low growth coefficients of muscle in sheep, seen against higher growth coefficients for TBF in SAMM, Merino and Dorper and low rate in the Pedi may be interpreted as meaning that these breeds had passed out of a predominantly muscle growth phase into fattening. In Boer goats, muscle was still in a cumulative phase, the growth coefficient being > 1.0, while TBF deposition was in a lag phase. Differential growth rate of TCF in Boer goats exceeded that of muscle after an empty body weight of 49.7 kg, in SAMM 42.4 kg, in Merino 27.8 kg, in Dorper 27.2 kg and in Pedi 22.3 kg. Likewise, TCF exceeded TNCF at 12.5 kg empty body weight in Boer goats, 8.1 kg in SAMM, 15.6 kg in Merino, 8.3 kg in Dorper and 10.3 kg in Pedi.

Carcasses were separated into five anatomically definable parts: fore limb,
neck, ventral trunk, dorsal trunk and hind limb. Boer goats had less total tissue (Table 7) in the hind limb (28.4%) than sheep with a range of 31.6%-34.1%; but Boer goats had greater mean distribution of tissue to fore limb, neck and ventral trunk regions (N.H. Casey and R.T. Naude, 1982, unpublished data).

TABLE 7

Mean weight distributions (%) (N. H. Casey and R. T. Naude, 1982 unpublished data)

MEAT TENDERNESS AND FLAVOR

Eating quality of Boer goat meat, as judged for toughness and flavor, has been regarded as inferior to lamb and mutton. Toughness or lack of tenderness has been ascribed to marketing maturer animals (Van Tonder, 1980). Study of collagen contents and solubility of seven selected muscles from four sheep breeds and Boer goats revealed that they had a relatively higher collagen content with lower solubility (Table 8), which may yield tougher meat than in sheep (Heinze et al., 1986). Evaluation of collagen alone was apparently insufficient for conclusions that goat meat was tougher than lamb. Other factors may also play a role in tenderness of meat, especially the type of matrix formed by collagen, muscle fibres and state of muscle contraction (Heinze et al., 1986).

TABLE 8

Mean values for collagen content (Hypro N/Total N X 10^3), solubility (%)
and index value of different breeds (Heinze et al, 1986)