Materials and Methods

A summary of the experimental work done is given. The conditions of experimentation, some basic equipment used and methods of data analysis are also briefly mentioned.

Origin of the sheep used in the experiments: The sheep used for the various experiments are based on a herd of the Cameroon sheep and various breeds of German sheep. The Cameroon sheep are originally from Cameroon, West Africa. They have a small body size (males, 60 - 70 cm at the withers and weighing 40 -50 kg; females, 58 - 65 cm at the withers and weighing 30 - 40 kg), hardy, less demanding and suitable for paddock rearing. They have a hairy coat, brown in colour with a black belly, head and legs. Their head is long with small ears slanting forward. Ewes have no horns but the males have snail-like horns and a mane on the neck and breast. Unlike the German breeds of sheep, they are short-tailed (ANONYMOUS, 1992, Deutsche Kamerunschafzucht). Although all the Cameroon lambs used in the experiments were born and reared at the Animal Production Research Station in Dahlem, Berlin, the original herd at the station was bought from the Zoo in Berlin and from Büren and was genetically similar to those found in Cameroon.

In numerical terms, the German breeds of sheep were made up of 46% Texel and some Blauköpfiges Fleischschaf, Rauwolliges Pommersches Landschaf, Coburger Fuchsschaf, Braunes Bergschaf, Merino Landschaf and the German Milk Sheep. These and others were also reared at the Animal Production Research Station in Dahlem, Berlin. Whereas all C1 and C2 lambs used in the experiments were born and reared in Dahlem, their parents were either also born in Dahlem, or bought in from other breeding stations.

The C1 crosses were produced by mating between the rams of the Cameroon and ewes of German breeds of sheep mentioned above and more especially the Texel. The C2 crosses were obtained by mating C1 rams with C1 females. Numerically, forty-seven (47) percent of the C2 crossbreds were produced by mating Cameroon X German Milk Sheep C1 males and females.

In order to compare the pre-weaning and post-weaning growth performance of pure Cameroon and crossbred (C1 and C2) lambs reared on the ewe, and when subjected to different feeding levels and to high ambient temperature during the day with alternating feeding levels, respectively, and in order to compare the milk yield performance of pure Cameroon and C1 (Cameroon x Mutton) ewes, the following experiments were conducted:

List of experiments

1. Pre-weaning growth

Duration: 12 weeks i. e. from birth to about 80 days of age

Animals used:

Cameroon:

9

C1 (Cameroon x German):

31

C2 (Cameroon x German):

27

Duration: 12 weeks i. e. from birth to about 80 days of age.

Animals used:

Cameroon:

11

C1 (Cameroon x German):

21

C2 (Cameroon x German):

28

2. Milk yield of ewes

Duration: 9 weeks

Animals used:

C1 ewes:

5

The ewes were about 1 year old.

Duration: 11 weeks

Animals used:

Cameroon ewes:

8

C1 (Cameroon x Mutton) ewes

9

The ewes were aged 2 about years.

3. Post-weaning growth

Reaction to different feeding levels

Duration: 12 weeks

Animal material:

Cameroon lambs:

10

C1 (Cameroon x Mutton) lambs:

10

C2 (Cameroon x Milk) lambs:

10

The lambs were aged about 80 days.

Duration: 12 weeks
Reaction to high ambient temperature and alternating feeding levels

Animals used:

Cameroon lambs:

5

C2 (Cameroon x Mutton) lambs:

5

The lambs were aged about 70 days.

4. Carcass evaluation

All lambs in the post-weaning growth experiments.

Comparative pre-weaning growth performance of lambs of different genotypes

The experiment compared the pre-weaning growth performance of the crossbred lambs reared on the ewe with those of the pure Cameroon lambs reared under similar conditions. In this way, the growth performance of the crosses could be studied at an early stage. Only lambs born in February and March were included in the analysis. Estimated live body weight and Average Daily Gain (ADG) was done for 30, 60 and 90 days of age and from 0 - 30, 30 - 60 and 60 - 90 days, respectively.

Animals used

A total of 127 lambs were made available for this experiment from birth to weaning at about 80 days. A total of 67 lambs were available in 1994 and 60 in 1995. Three (3) genotypes were represented namely, 19 Cameroon lambs, 52 C1 (Cameroon x Mutton) and 55 C2 (Cameroon x German) crossbred lambs. “German” breeds included both mutton and milk types.

Feeding

Lambs were introduced to ad libitum feeding with hay from ten (10) days of age and to concentrated feed (Type 047, Ströh, Hobbersdorf) at the rate of 200g per animal per day from fourteen (14) days of age. The energy content of the concentrated feed was at the level of 5.9 MJ ME/kg. All animals had free access to water.

Housing of animals

Lambs were housed in pens together with their mothers after birth and later reared outside on pasture during warmer months from May to July.

Management of experimental animals

The parameter measured was pre-weaning live weight. Weights were taken from birth to 80 days once every two weeks in 1994; and once per week in 1995. (Interpolation of missing values was made for the 1994 weights).

Milk yield performance of Cameroon and C1 ewes rearing lambs using the suckling method

The milk yield performance of the C1 (Cameroon x Mutton) ewes using the suckling method was compared with that of the pure Cameroon ewes during 11 weeks of lactation of which only the first 9 were considered in the analysis.

Animals used

Five (5) Cameroon ewes aged about 1 year in their first parity were available in 1994 for this experiment over a period of 9 weeks from about lactation week 3. In 1995 there were eight (8) Cameroon ewes aged about 4 years and in parity 1 - 3 and nine (9) C1 (Cameroon x Mutton) ewes aged 2- 3 years in parity 2 - 3 available over a period of eleven (11) weeks from about lactation week 1. In the analysis, only data on milk performance in 1995 was considered up to 9 weeks of lactation.

Feeding

Ewes were fed on group basis at the rate of 200g of concentrated feed (Type 047, Ströh, Hobbersdorf) per animal per day and hay, ad libitum. Of the 200g concentrated feed fed per ewe per day, 100g including hay (ad libitum) was fed at 7⁰⁰ hrs and the rest with hay at 14⁰⁰hrs on group basis. The energy content of concentrated feed was at the level of 5.9 MJ ME/kg. Lambs used in the suckling method were introduced to hay from ten (10) days of age and to concentrated feed from fourteen (14) days of age. All animals had free access to water.

Housing of animals

Lambs were housed in pens or kept on pasture together with their mothers except during separation prior to milk recording.

Management of experimental animals

Milk performance was recorded indirectly using the suckling method, i.e. weight of the lamb after suckling minus weight of the lamb before suckling (WALLACE, 1948; OWEN, 1957; COOMBE et al., 1960; METZ, 1990).

The time of suckling was 7⁰⁰ hrs in the morning, 13⁰⁰ hrs in the afternoon and 19⁰⁰ hrs in the evening. The evening before the day when milk yield was determined using the suckling method, the lambs were allowed to suckle after being separated from the ewes for six (6) hours, and then separated again until the next day. This was to maintain equilibrium in the udder (METZ, 1990). Any ewe refusing to be suckled was restrained and made to do. The ewes were weighed at the beginning of the experiment and every four (4) weeks thereafter in 1994; in 1995 ewes were weighed every 14 days: twenty-four (24) hours before the day of suckling and on the day of suckling itself.

Suckling time was five (5) minutes (METZ, ibid.). In 1994, suckling was done at the rate of one ewe at a time. In 1995, suckling was done on group basis after individual weighing of the lambs before and after. This is based upon the behaviour of the animals and the experience of the previous year: no loss of weight by defecating or urinating (except for one case) and the nervous behaviour of the Cameroon ewes which made it necessary to leave them in peace during the time of suckling.

The following parameters were measured:

Milk yield performance: Weekly measurements were made in 1994. In 1995, each genotype was recorded for milk yield every 14 days: the C1 ewes were weighed in the first week and the Cameroon ewes in the following week. Measurements started and ended a week later in the Cameroon ewes than in the C1 (Cameroon X Mutton) ewes because of the relatively younger age of their lambs at the time of starting the experiment.

Live weight: The live weight of the ewes was recorded every month in 1994; every 14 days in 1995 and once before the day of milk recording and once on the day of milk recording.

Comparative post-weaning growth performance of lambs of different genotypes Influence of different feeding levels
This experiment compared the post-weaning performance of pure Cameroon lambs subjected to High-Low and Low-High levels of feeding with that of the C1 (Cameroon x Mutton) and C2: (Cameroon x Milk) X (Cameroon x Milk) crossbreds. In a practical situation where feed availability is seasonal, and lamming aseasonal, it reflects the effects of limited access to feed at weaning followed by a period of plenty and vice versa.
Animals used
Thirty lambs i.e. 10 Cameroon, 10 C1 (Cameroon x Mutton) and 10 C2 (Cameroon x Milk) weaned at about 80 days of age were assigned to two equal treatment groups of fifteen (15) each. Both the Weißes Ostfriesiches Milchschaf and Braunes Ostfriesisches Milchschaf were used as ewes to produce the C1 with the Cameroon. All crosses were twins with one twin being assigned to treatment group 1 and the other to treatment group 2 in order to balance genetic composition.
Feeding
Feeding was done twice per day at 7⁰⁰ hrs in the morning and at 15⁰⁰ hrs in the afternoon using concentrated feed (Type 046, Ströh, Hobbersdorf) with an energy level of 11.85 MJ ME/kg (SCHAFFT, 1993) and wheat straw with a level of energy estimated at 5 MJ ME/kg.

Conditioning lasted for one week. One group (1) of lambs was subjected to High-Low feeding with concentrated feed i. e. ad libitum feeding during the first 6 weeks followed by feed restriction (1.5 x maintenance) during the last 6 weeks of the experiment. The other group (2) was subjected to Low-High feeding by reversing the conditions of feeding in group 1, i. e. feed restriction (1.5 x maintenance) during the first 6 weeks followed by ad libitum feeding with concentrated feed during the last 6 weeks. Maintenance was calculated on the basis of 0.45 MJ ME/kg^0.75 (ARC, 1980) supplied by the concentrated feed.

Wheat straw was supplied at a fixed rate of 200g per day per lamb for both groups. Feeding of both concentrated feed and straw was done twice daily in two equal portions at 7⁰⁰ hrs in the morning and at 15⁰⁰ in the afternoon. Water was made available at all times for ad libitum consumption.
Housing of animals
The first group on High-Low feeding treatment was reared individually in cages of about 1.18m² area at stall ambient temperature conditions. The second group on Low-High feeding treatment was reared separately in individual cages of about 1.57m² area at stall ambient temperature conditions.

An element of confounded effects owing to the separate housing of the lambs of both groups might have set in.
Management of experimental animals
Animals not being subjected to restriction of concentrated feed plus a fixed (200g per animal per day) amount of wheat straw, were supplied with the same at an incremental rate of 50g per animal if the amount of feed (concentrated or wheat straw) at a given level were completely eaten up over a period of two days (SCHAFFT, 1993).

A sample of the straw fed to the lambs was taken daily and stored in plastic bags for the determination of dry matter as mixed 14 day samples. Leftover straw was collected for each lamb for the same purpose. Pre-drying of straw was done in an oven for twenty-four hours at a temperature of 60°C and then for a further twenty-four hours at 105°C.

Parameters measured were as follows:

Live weight: Live weight was recorded twice per week before the morning feeding at 7 ⁰⁰hrs.

Feed and water intake: Feed intake and refusals were recorded every day; and water intake every week for group 2.
Reaction to high ambient temperature during the day and of alternating feeding levels
This experiment studied the influence of high (31°C /50%RH) ambient temperature during the day and low (15°C /70%RH) at night with alternating feeding levels (High-Low-High) on the post-weaning productive performance and physiological reaction of C2 (Cameroon X Mutton) crossbred lambs compared with that of the pure Cameroon. This is a reflection of high ambient temperature combined with seasonal feed restriction which is a common feature of the tropical environment.

The level of temperature and relative humidity used in this experiment is an approximation of that in the geographical area of The Republic of Zambia and is thus practically representative of a specific tropical ambient temperature. It is based on the mean maximum and mean minimum temperature for day and night, respectively, and the corresponding level of relative humidity during the months of August to November. The means were calculated from weather data from thirty-six (36) meteorological stations over a period of six (6) years from 1989 to 1994, inclusive. They represent the means of extremes of high and low ambient temperature in this geographical area in the months of August to November, inclusive.

The period August to November is the hot dry period characterised by high ambient temperature during the day and cool nights. It is the period after the harvest, and then the winter period; the period of scarcity of feed and water, the period before the rainy season which starts in mid November to December. It is also the major period of lamming, kidding and calving. And with whirlwinds and frequent fires, it can be seen as a critical period for animal production during the course of the year.
Animals used
Ten (10) lambs weaned at about 70 days comprising five (5) Cameroon lambs and five (5) C2 (Cameroon x Mutton) crossbred male and female lambs reared in individual cages (1.18m²) in the climate chamber were used for this experiment.
Feeding
During the period of conditioning and throughout the experiment, feeding was done every day at 7⁰⁰ hrs in the morning and at 15⁰⁰ hrs in the afternoon.

The lambs were fed ad libitum with concentrated feed for a period of four (4) weeks, then restricted at a level of 1.5 times above maintenance for the next four (4) weeks and then finally realimented (ad libitum) in the last four weeks of the experiment. Feeding was done using concentrated feed (Type 046, Ströh, Hobbersdorf) with an energy level of 11.85 MJ ME/kg (SCHAFFT, 1993) and wheat straw with a level of energy estimated at 5 MJ ME/kg. Feeding of wheat straw was fixed at 200g per day per lamb. Water was made available at all times for ad libitum consumption. One week before the start of the experiment, the lambs were separated and fed at a rate of 200g concentrated feed and wheat straw ad libitum supplied as a bundle. Conditioning then followed for one week.

During the High phases of feeding of concentrated feed an incremental rate of 50g per animal was given if the feed was completely eaten up over a period of two days (SCHAFFT, 1993).
Housing of animals
Rearing was done in the climate chamber under controlled temperature and relative humidity: 31°C/50% RH during the day and 15°C/70% RH at night. The technical specifications (size and operational data) of the climate chamber as given by BBC York were as follows:

Area:

68.75m².

Guarantied technical performance:

- Temperature:

15 - 35 ±1°C

- Relative humidity:

30 - 80 ±5%

- Fresh air throughput:

≤ 1000m³/h

- Lighting:

16 lamps at 65 Watt each

Management of experimental animals
Animals were subjected to 12 hours of light and 12 of darkness. Light and 31°C/50%RH ambient temperature was administered from 6⁰⁰ hrs to 18⁰⁰ hrs. From 18⁰⁰ hrs to 6⁰⁰ hrs light was switched off and the climate chamber was set at 15°C/70%RH. To avoid any drastic change of ambient temperature, the lambs entered the climate chamber at 20°C/50% RH day temperature which increased to 25°C/50% RH on the second day and finally to 31°C/50% RH on the third day of the conditioning phase. The night temperature remained unchanged for the rest of the duration of the experiment. However, during Week 3 and the first day of Week 4, all measurements were done at 29°C/88% RH due to problems with the climate chamber.

A sample of the straw fed to the lambs was taken daily and stored in plastic bags for the determination of dry matter as mixed 14 day samples. Leftover straw was collected for each lamb for the same purpose. Pre-drying of straw was done in an oven for twenty-four hours at a temperature of 60°C and then for a further twenty-four hours at 105°C.

The following parameters were measured:

Live weight: Live weight was recorded twice per week before the morning feeding at 7⁰⁰hrs.

Feed and water intake: Feed intake and refusals were recorded every day; and water intake once per week.

Rectal temperature and breathing rate: Measurement of rectal temperature and breathing rate was done at 12⁰⁰ hrs on each day of measuring i. e. after six (6) hours of high (31°C/50%RH) ambient temperature and five (5) hours after the morning feeding period and then at 20⁰⁰ i. e. after two (2) hours of low (15°C/70%RH) ambient temperature and five (5) hours after the afternoon feeding period in both cases in order to avoid heat released due to increased metabolic activity immediately after feeding. Measurement of rectal temperature and breathing rate was done both on daily basis and once per week. A digital thermometer (Hartmann) was used to measure rectal temperature and a timer to measure breathing rate per minute by counting the number of movements of the flanks. A total of 90 measurements of rectal temperature and 88 of breathing rate were taken per lamb during the day at 12⁰⁰ hrs and at night at 20⁰⁰ hrs.

Carcass evaluation
Each lamb used in the experiment was assigned to an individual cage at random and fed and watered individually. From the end of each feeding experiment to slaughter, each lamb was fed at the same rate per day as per the last day of each experiment. A carcass evaluation involving all lambs used in the experiments was done at the end of each experiment in order to compare carcass values between treatments and genotypes.

Objective of carcass evaluation: The objective of evaluating the carcass of slaughtered lambs in terms of the weight of muscle, fat and bones aimed to quantify the edible and therefore economically important parts of the carcass. It was also aimed at comparing the effects of specific treatments on the weight of edible parts and of some physiologically important organs of digestion and thermoregulation and to make a comparison in the performance of the pure Cameroon and the C1 and C2 crossbred lambs. Important carcass parts were cut using the system recommended by the Deutsche Landwirtschaftliche Gemeinschaft (DLG). Aspects of quality were also considered within the same context.

Animal material: All lambs subjected to the post-weaning growth experiments: 30 in 1995 and 10 in 1996.

Parameters of carcass evaluation: Lambs to be slaughtered were fasted twenty-four (24) hours before slaughter and only allowed water (ad libitum) during this time.

Weights of carcass, valuable cuts and organs; length measurements; and measurements of quality were done for each slaughtered lamb. One and half hours after slaughter, pH-measurement of the musculus longismus dorsi (MLD) and musculus semimembranosis (MSM) was done using a pH-meter (pH-STAR, Rudolf Matthaeus, Poettmes) and then repeated after twenty-four (24) hours. Each such measurement was done twice in 1995 and 1996. Body organs were weighed upon slaughter except for the entrails which were emptied, cleaned and washed, drained and preserved in the cold room and weighed the following day. The cold room was maintained at about 0 ±5°C.

The femur, hindleg bone and the foreleg bone of the Right Half were weighed and their lengths and circumferences measured using a tape measure at the end of the day of slaughter.

The weight of the warm dressed carcass was taken on the day of slaughter and that of the cold dressed carcass on the following day. Measurements of the lengths of the hindleg, the rump (round the rump region with the tape measure passing below the tail), back and chest were done using a tape measure on the cold dressed carcass. Subjective qualitative measurements (points between 1 and 10) based on the shape and fat distribution of the carcass was done for subcutaneous fat distribution, arm, back and hindleg by the Institute’s meat technologist. The Right Half of the cold dressed carcass was then cut into seven (7) valuable parts as follows: hindleg, breast, foreleg, thinning, back, middle, and neck. Using a transparency, the eye muscle area on the back (13th rib) was marked and a little piece of muscle cut off for determination of fluid content by pressing for five minutes on absorbent paper ( No. 332 077, Schleicher & Shuell). The areas of the eye muscle (one drawing per animal) and that for fluid content (two samples per animal) were estimated using a planimeter (Type 34051, A. Ott, Kempton). Two measurements of the reflection score (Goefo) of the eye muscle area (13th rib) were then done though limited to the year 1995. The seven (7) valuable parts were dissected to determine the weights of muscles, fat and bones.

Analysis of data
The analysis of data was done using the General Linear Model of the SAS software package Version 6.11 (SAS Institute 1990). Analysis of variance, means of the main effects with standard errors were calculated. The following basic models were used to analyse the experimental data:

Basic models of the experiments

Comparative pre-weaning growth performance of lambs of different genotypes

:

= Estimated live body weight, kg / Estimated ADG, g

= mean

= effect of genotype, _i

= effect of year, j

= effect of sex, k

= interaction effect of genotype and year, ij

= error

Milk yield performance of Cameroon and C1 ewes rearing lambs using the suckling method

:

= Milk yield of the ewe, g

= mean

= effect of genotype, _i

= error

Comparative post-weaning growth performance of lambs of different genotypes

Influence of different feeding levels

= Live body weight of the lamb, kg

= mean

= effect of treatment, _i

= effect of genotype, j

= interaction effect of treatment and genotype, ij

= effect of sex, k

= error

Reaction to high ambient temperature during the day and alternating feeding levels

= Live body weight of the lamb, kg

= mean

= effect of genotype, _i

= effect of sex, j

= error

Physiological reaction to high ambient temperature

= Rectal temperature (°C) / Breathing rate (No./minute) of lamb

= mean

= effect of genotype, _i

=effect of sex, j

= error

Carcass evaluation

Influence of different feeding levels

= Weight (g) of organs or carcass parts of lamb / Measure of carcass quality of lamb

= mean

= effect of treatment, _i

= effect of genotype, j

= effect of sex, k

= error

Reaction to high ambient temperature during the day and alternating feeding levels

= Weight (g) of organs or carcass parts of lamb/ Relative weight (%)/Carcass quality of lamb

= mean

= effect of genotype, _i

= effect of sex, j

= error