Fernando Grasso » 11.Sheep

Italian sheep breeds

The major advantage of sheep in agricultural systems is their ability to utilise pasture to produce saleable milk, meat and wool. In hill and upland areas, they use land that would otherwise be of little value for agricultural purposes.

The principal role of sheep is therefore as a grazing animal, and the aim of efficient sheep production is to maximize output from pasture, with some help from conserved fodder and forage crops.

Sheep breeds are classified according to their prevalent purpose (milk, meat and wool). The main sheep breeds farmed in Italy can be grouped as following:

• breeds specialised for milk production: Sarda, Comisana, Massese, Delle Langhe, Leccese, Altamurana;
• breeds specialised for meat production: Bergamasca, Merinizzata Italiana, Appenninica, Laticauda;
• dual purpose breeds (wool and meat): Gentile di Puglia, Sopravissana.

Dairy sheep management

Most dairy sheep producers should have a barn or shed that can accommodate all their ewes. It is necessary to provide adequate space for ewes and lambs.
The barn should have a porous floor (dirt, gravel, etc.) to allow moisture to move away from the sheep. The barn also should have good ventilation but be draught-free to prevent chilling of newborn lambs. Such a barn is a necessity for flocks which lamb in the winter.
Dairy breeds will lactate for 120 to 240 days, thereby increasing milk yield per ewe per year.
In general, producers can expect to milk 85 to 90% of ewes that were bred. Some ewes will not be able to be milked due to problems with breeding, lambing or mastitis.
On some farms, ewes are not milked until their lambs have been weaned at 30 to 60 days of age.
Another system allows lambs to suckle their lambs for 8 to 12 hours per day, after which time they are separated for the night and the ewes are milked the following morning. After the lambs are weaned at 28 to 30 days, the ewes are milked twice per day.
Maximum milk yield is obtained when the lambs are removed from their dams within 24 hours of birth and raised on artificial milk replacer.

Reproductive characteristics

Main reproductive traits of sheep

Breeding activity varies among breeds and even between individuals within a breed. Many types have a restricted season based on day length, temperature, and the age of the ewe.

Polyestral seasonal species.

Puberty: by 6 to 7 months of age.

Beginning of sexual activity: males 13-15 months; females 10-12 months.

length of oestrus cycle: 16-18 days

• proestrus 2 – 2.5 days
• estrus 24 – 36 hours
• metaestrus 2 days
• diestrus 11 days

Optimal time for insemination: last 18 hours after onset of oestrus

Optimal ram/ewes ratio: 1/40

Breeding seasons: April – June and September – November

Gestation length: 144 – 153 days (~ 5 months)

Reproductive characteristics

Oestrous Cycle
Sheep are short-light breeders, that is, they usually cycle in the fall of the year as the light phase of the photoperiod decreases. The ewe is polyestrous and will cycle several times during one breeding season if not bred; the average cycle for the ewe is 16 days (range, 14-20). The actual period of oestrous receptivity is 30 to 36 hours in the ewe. The duration of oestrus in lambs and in the first oestrus of the season, is shorter than that of the normal oestrus. Puberty is dependent on the time of birth (6-7 months).
Reproductive activity of domestic sheep raised in the tropics and subtropics occurs all year. Therefore, sheep raised at higher latitudes show a shorter breeding season than tropical ones.
In Italy, there are two mating seasons: april-june to produce lambs in Christmas time and september-november to produce lambs in Easter time.

Ram effect
Most sheep breeding is still done naturally, with the rams pastured with the ewes all year or introduced in the late summer. The introduction of the ram tends to synchronize oestrus in a high proportion of the ewes 15 to 17 days later. Continuous exposure to a ram tends to increase the incidence of oestrus in the normally anoestrous period. The presence of a ram also shortens the duration of oestrus, but this depends on direct physical contact with the ram and probably on mounting of the ewe by the ram, rather than on pheromones.

Lambing

Most ewes produce single or twin lambs. During or soon after labor, ewes and lambs may be confined to small pens designed to aid both careful observation of ewes and to cement the bond between them and their lambs.
The first sign of lambing comes when the ewe leaves the rest of the flock and finds a quiet location in which to lamb. Within an hour or so, labour will start.
When the ewe is in labour she may stand and paw the ground searching for a lamb in the hope that her efforts have been productive.
Lambs are normally born head first with the front feet tucked up under the chin.
Sheep generally lamb freely without intervention, but periodically a lamb may be breached in the womb or otherwise displaced and the ewe may require assistance from the shepherd.
Once the head and shoulders are through the rest of the lamb is pushed out very quickly.
At birth lambs are often born with mucus membranes covering their faces. The ewe will instinctively clear this by licking the newborn lamb. If the shepherd is nearby he will assist by removing the membranes and placing the lamb in front of the ewe.
Licking will continue for some minutes and during this time the lamb will be gaining strength and starting to think about milk. After the first lamb, the second quickly follows. Some breeds of sheep have only one lamb.
In just fifteen minutes both lambs have been born. After birth the “after birth” will follow. This is the mucal membrane that contained the lambs within the womb. Part of this can be seen trailing from the rear of the ewe. Sometimes the ewe will eat her own afterbirth.
The urge to suck is very strong in the new born lamb and within 20 minutes the lamb will be looking for milk. Most lambs will begin standing within an hour of birth. In normal situations, lambs nurse after standing, receiving vital colostrum milk. The shepherd may assist the lamb if it is struggling to find the ewe’s teat.

Lambing

The first few hours of life are critical for the newborn lamb. As soon as the lamb is completely dropped, it is recommended to rub it briskly with clean towels or other cloths to get its circulation going. Lambs can also be immersed in warm water to get their bodies functioning. The cord can be cut about six inches from the lamb’s body and the area disinfected with iodine. The cord itself will dry up and fall in a week’s time.
It is very important that the lamb nurse as soon as possible after birth. The suckling is encouraged by placing the finger in the mouth and, when it begins to suck, transferring it to the mother’s udder.
Lambs that either fail to nurse or that are rejected by the ewe require aid to live, such as bottle-feeding or fostering by another ewe.
After one week to ten days it is time to dock the lamb. At birth, it has a long tail resembling a dog’s tail. To prevent feces build-up, the tail is clipped with a special docking instrument. It is cut about two inches from the rump. Lambs will frequently be traumatized by the pain, but they will resume normal activity in a few hours.
Lambs will begin feeding about two weeks after birth. Creep feeder is used, fashioned to allow only small-headed animal’s access to the feed. The ewe and lamb should be fed separately for the first few days after birth, or until the lamb is strong enough to ward off the jealous advances of other mothers.

Lambs management

Raising lambs artificially
It is important that newborn lambs consume adequate amounts of colostrum during their first 24 hours of life. If colostrum is not available from the dam or another ewe, cow colostrum can be used. When cow colostrum is used, 30% more should be fed to lambs. When artificially rearing lambs, it is recommended that they be fed milk replacer that has been specifically formulated for lambs. Calf milk replacer is generally unacceptable. Ewe’s milk contains more fat, protein and minerals than cow’s milk. In addition, the fat globules in lamb’s milk are homogenized, and cow’s milk contains excessive amounts of lactose that may cause bloat or digestive upset in lambs. Goat’s milk contains more fat soluble vitamins and vitamin C than either ewe or cow milk. On the other hand, it is acceptable to rear lambs on fresh goat’s milk. Milk replacer should be mixed according to the manufacturer’s instructions. Small numbers of lambs can be fed using individual bottles fitted with rubber teats. For the first few days of life, lambs should be fed frequently.
For larger numbers of lambs, an automatic feeding system (self feeder or lamb bar) can be set up. Lambs will drink cold milk from a lamb bar at frequent intervals, much like they would if they were nursing a ewe.
In order to wean lambs at an early age, it is important to get them consuming dry feed as soon as possible. By the time the lambs are ten days of age, they should have access to a starter feed which is palatable and contains 18 to 20 percent crude protein.

Young lambs will consume more feed if it is coarsely ground, though a pelleted ration may also be fed. Green, leafy hay and a source of fresh water should also be provided.

Lambs management

Lambs should be vaccinated for overeating disease and tetanus at six weeks of age, followed by a booster two to four weeks later. They should be vaccinated at three weeks of age, if they did not receive adequate protection through the colostrum. Because milk replacer is expensive, lambs should be weaned at an early age, such as 6 weeks.Weaning should be abrupt and lambs should be left in familiar surroundings at the time of weaning to minimize stress. If orphan lambs are properly fed and managed, they should gain nearly as well as lambs being raised on their dams.There are three management systems for weaning lambs from ewes:

1. Lambs are removed from their mother 24 to 36 hours after lambing. The ewes are milked twice a day and the lambs are raised on milk replacer. All of the milk produced is sold, but milk replacer costs will be high. This system is the most labor intensive.
2. Ewes nurse their lambs for 30 days after which the lambs are completely weaned and the ewes are milked twice a day. While this method is the least labor intensive, the total amount of milk sold per ewe will be less. Lambs will consume nearly 25% of the ewe’s total lactation milk production. In high-producing ewes, the lambs may not be able to consume all of the milk produced, and the potential for mastitis is greater.
3. Ewes nurse their lambs for 30 days. One week after lambing, lambs are separated from ewes in the evening, ewes are milked only in the morning, and ewes are returned to their lambs for the day. Lambs adapt quickly to this system, and lamb growth is reduced only slightly. However, the fat content of the milk collected during the nursing period is lower, which decreases the value of the milk for cheese production.

Milking parlors

The sheep farmer frequently requires specialised equipment in order to simplify the general running of the farm and to increase its efficiency.
Producers with 150 or more ewes should consider constructing a “pit” parlor where the ewes enter at ground level and the milker stands in a pit.
Minimum milking equipment in the parlor will include a vacuum pump and line, one set of milking claws, and a milking bucket. Milking time is reduced with more milking claws and buckets. Use of buckets requires carrying of milk from the parlor to the milk room. Labor is reduced, but capital and maintenance costs increased if a pipeline is installed which transports the milk from the sheep to the milk room. In the milk room, the milk is deposited into a bulk tank for cooling. After the milk is cooled, it can be transported to the processing plant.

Milk composition

Sheep’s milk contains almost twice as much solids as cow’s milk. In sheep’s milk, casein counts for 80% of the total proteins. The percentage of α_s1 and α_s2 casein is higher in sheep’s milk than in goat’s milk but significantly lower than in cow’s milk. Casein β, however, represent 50% of the total casein in sheep’s milk for 2/3 in goat’s milk and 1/3 in cow’s milk. Because of a higher casein content, sheep’s milk has better coagulation properties and better cheese making potential than cow’s milk. Sheep’s milk yields 18-25 % cheese; that is, it takes only 4 to 5 kg of sheep’s milk to produce 1 kg of cheese (it takes 10 kg of cow’s milk to produce the same amount). Moreover, the higher casein content makes the rennet coagulation time for sheep’s milk shorter and the curd firmer.
Sheep’s milk is highly nutritious, richer in vitamins A, B, and E, calcium, phosphorus, potassium, and magnesium than cow’s milk. It contains a higher proportion of short- and medium-chain fatty acids, which have recognized health benefits.
The higher proportion of short-chain fatty acids such as caproic, caprylic and capric in sheep’s milk than in cow’s milk (but less than in goat’s milk) gives sheep’s milk its special taste and aroma, although some other compounds such as phospholipids and phenols have an important role.
Lipases attack the ester linkages of the short-chain fatty acids more rapidly, so these differences may contribute to more rapid digestion of goat and sheep’s milk.
The amount of cholesterol in sheep’s milk increases with the amount of fat and has been found to be between 150 and 300 mg/liter.
Sheep’s milk has more conjugated linoleic acid (CLA) than the milk of other species.
The color of fat in sheep’s milk is very white because of a total absence of β-caroten.

Milk composition

Differences between sheep and bovine milk.

Milk composition

Factors affecting milk composition

Breed of ewes – The breed of sheep can affect the composition of the milk mostly because there is a negative correlation between milk yield and concentration of milk components. Therefore, breeds highly selected for dairy production tend to have a lower concentration of fat, protein and total solids. As a consequence, with high milk production, the total amount of cheese produced from the milk will be higher but the relative yield of cheese from each liter of milk will be lower.

Somatic cell count – In sheep’s milk, only 10% of the somatic cells are mammary glands cells (eosinophils, epithelial cells), normally secreted together with the milk as a result of cellular turnover in the mammary gland. The remaining 90% of the somatic cells are blood cells (macrophages, leucocytes, lymphocytes). These normally contribute to the immune defense of the mammary gland, but their number increases considerably in the case of inflammatory or pathological processes within the mammary gland. A high somatic cell count results in changes in the composition of milk with a higher pH, a reduction in fat, casein, total solids, soluble calcium, and an increase in total nitrogen, non-protein nitrogen and whey proteins.

Milk composition

Factors affecting milk composition

Stage of lactation – The amount of fat, protein, total solids, and somatic cells is high at the beginning and at the end of lactation and low at the peak of lactation. The processing performance of the milk tends to decrease as the lactation proceeds, with an increase in renneting time and rate of curd formation and a decrease in the consistency of the curd.

Season of milking – Many researchers have shown that sheep’s milk produced in summer has poor cheese making performance due to long renneting time, poor consistency of the curd, and high proteolytic and lipolytic activities.

Nutrition – Nutrition affects the total milk production as well as the quality of the milk. The concentration of fat in the milk is correlated with the concentration of fiber in the diet.

Meat production

In sheep meat production comes from culled animals and from animals slaughtered at different live weight, as following:

• light sucking lamb (abbacchio): age = 30-35 d live weight = 8-12 kg
• heavy sucking lamb: age = 50-60 d live weight = 12-20 kg
• light lamb: age = 100-130 d live weight = 25-35 kg
• heavy lamb: age = 180-200 d live weight = > 35 kg
• wether (castrated male): age = > 240 d live weight = > 45 kg

Older animals have a stronger flavour than lamb because they contain a higher concentration of species-characteristic fatty acids.
Meat from younger animals can be expected to be more tender than those of older lambs. Young lambs tend to contain more cartilage than older lambs because cartilage turns to bone as the lamb matures. In addition, young lambs will have break joints in their shanks. This is a good indication of maturity. Furthermore, the color of the meat becomes a much darker red as the lamb matures.
Lamb is often sorted into three kinds of meat: forequarter, loin, and hindquarter.

Meat production

Carcass dissection and available cuts.

Lamb meat quality

Meat quality is defined by the compositional quality (lean to fat ratio) and palatability (appearance, juiciness, tenderness, and flavour).
Tenderness can be attributed to a person’s perception of meat such as ease of chewing, softness, etc. Tenderness is a result of the lamb’s age and sex as well as the location of the muscle from which the cut of meat was taken.
Meat flavour can be described as salty, sweet, bitter, etc. Meat flavour can be affected by age, water retention during cooking, and fat within the muscle.